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+
+*** START OF THE PROJECT GUTENBERG EBOOK 75683 ***
+
+
+
+
+
+Transcriber’s Note: Italics are enclosed in _underscores_. Additional
+notes will be found near the end of this ebook.
+
+
+
+
+                                  THE
+                  TELEPHONE, MICROPHONE, & PHONOGRAPH
+
+
+
+
+                             THE TELEPHONE
+                    THE MICROPHONE & THE PHONOGRAPH
+
+                                   BY
+                            COUNT DU MONCEL
+
+                          MEMBRE DE L’INSTITUT
+
+
+                        _AUTHORISED TRANSLATION
+             WITH ADDITIONS AND CORRECTIONS BY THE AUTHOR_
+
+
+                     WITH 70 ILLUSTRATIONS ON WOOD
+
+
+                            _FOURTH EDITION_
+
+
+                                 LONDON
+                KEGAN PAUL, TRENCH, TRÜBNER, & CO. LTD.
+                 PATERNOSTER HOUSE, CHARING CROSS ROAD
+                                  1892
+
+
+
+
+(_The rights of translation and of reproduction are reserved_)
+
+
+
+
+_CONTENTS._
+
+
+                                                                    PAGE
+
+  History of the telephone                                             1
+
+
+                         _MUSICAL TELEPHONES._
+
+  Reiss’s telephone                                                   11
+
+  Wray’s telephone                                                    15
+
+  Electric harmonica                                                  18
+
+  Gray’s telephone                                                    21
+
+  Pollard and Garnier’s singing condenser                             26
+
+
+                        _SPEAKING TELEPHONES._
+
+  String telephones                                                   31
+
+  Bell’s electric telephone                                           35
+
+  Gray’s share in invention of telephone                              62
+
+
+              _FUNDAMENTAL PRINCIPLES OF BELL TELEPHONE._
+
+  Explanation of principles                                           67
+
+
+               _ORDINARY ARRANGEMENT OF BELL TELEPHONE._
+
+  Description and illustrations                                       71
+
+
+                         _BATTERY TELEPHONES._
+
+  Edison’s telephone                                                  83
+
+  Edison’s chemical telephone                                         90
+
+  Navez’ telephone                                                    93
+
+  Pollard and Garnier’s telephone                                     97
+
+  Hellesen’s telephone                                               100
+
+  Thomson and Houston’s telephone                                    101
+
+  Telephones with liquid senders                                     103
+
+  Telephones with voltaic arcs                                       107
+
+  Mercury telephones                                                 110
+
+  Friction telephones                                                113
+
+
+                  _MODIFICATION OF BELL TELEPHONES._
+
+  Telephones with several diaphragms                                 114
+
+  Gray’s system                                                      118
+
+  Phelps’s system                                                    118
+
+  Cox Walker’s system                                                121
+
+  Trouvé’s system                                                    121
+
+  Demoget’s system                                                   124
+
+  Mac Tighe’s system                                                 125
+
+  Modifications of telephonic organs                                 125
+
+  Righi’s system                                                     126
+
+  Ader’s system                                                      129
+
+  Jorgenson’s system                                                 131
+
+
+                   _EXPERIMENTS WITH THE TELEPHONE._
+
+  On the effects of voltaic and induced currents                     132
+
+  On the effects of different telephonic organs                      139
+
+  Edison’s experiments                                               140
+
+  Canestrelli’s experiments                                          142
+
+  Hughes’s and Roy’s experiments                                     143
+
+  Bréguet’s experiments                                              149
+
+  Luvini’s experiments                                               149
+
+  Warwick’s experiments                                              151
+
+  Experiments on the effects of mechanical shocks                    154
+
+  Des Portes’ experiments                                            154
+
+  Thompson’s experiments                                             158
+
+  Theory of telephone                                                159
+
+  Nature of vibrations                                               160
+
+  Action of diaphragm                                                163
+
+  Action of magnet                                                   167
+
+  Action of currents                                                 169
+
+  Wiesendanger’s thermophone                                         171
+
+
+                _OTHER EXPERIMENTS WITH THE TELEPHONE._
+
+  D’Arsonval’s experiments                                           173
+
+  Eick’s experiments                                                 175
+
+  Demoget’s experiments                                              176
+
+  Sensitiveness of telephone                                         179
+
+  Hellesen’s experiments                                             180
+
+  Zetsche’s experiments                                              181
+
+
+                           _THE MICROPHONE._
+
+  History of microphone                                              182
+
+  Different systems                                                  187
+
+  Hughes’s microphone                                                188
+
+  Gaiffe’s system                                                    190
+
+  Carette’s system                                                   191
+
+  Ducretet’s system                                                  192
+
+  Ducretet’s speaker                                                 193
+
+  Boudet’s speaker                                                   195
+
+  Gaiffe’s thermoscope                                               197
+
+  Blyth’s system                                                     199
+
+  Microphone as a speaking instrument                                200
+
+  Hughes’s system                                                    203
+
+  Other arrangements of microphones                                  205
+
+  Varcy’s and Trouvé’s microphones                                   207
+
+  Lippens’s microphone                                               209
+
+  Hughes’s experiments                                               211
+
+  Hughes’s theory                                                    215
+
+  Microphone used as thermoscope                                     217
+
+  Edison’s thermoscope                                               219
+
+  Experiments in London                                              220
+
+  Experiment at Bellinzona                                           223
+
+
+                     _APPLICATIONS OF MICROPHONE._
+
+  Its application to scientific research                             226
+
+  Application to telephonic relays                                   229
+
+  Application to surgery                                             232
+
+  Various applications                                               236
+
+
+           _EXTERNAL INFLUENCE ON TELEPHONIC TRANSMISSIONS._
+
+  Disturbing influences                                              239
+
+  Confusion of circuits                                              241
+
+  Induced reactions                                                  243
+
+  Mr. Preece’s suggestions                                           245
+
+  Effects of heat and moisture                                       249
+
+
+                 _ESTABLISHMENT OF TELEPHONE STATION._
+
+  Pollard and Garnier’s system                                       252
+
+  Bréguet and Roosevelt’s system                                     254
+
+  Edison’s system                                                    257
+
+
+                       _CALL-BELLS AND ALARUMS._
+
+  Weinhold’s system                                                  262
+
+  Dutertre and Gouault’s system                                      264
+
+  Puluj’s system                                                     266
+
+  Chiddey’s system                                                   267
+
+
+                     _APPLICATIONS OF TELEPHONE._
+
+  Its application to simultaneous transmissions                      270
+
+  Bell’s system                                                      273
+
+  Lacour’s system                                                    276
+
+  Gray’s system                                                      282
+
+
+                   _VARIOUS USES OF THE TELEPHONE._
+
+  Its use in offices                                                 293
+
+  Its use in telegraphic service                                     294
+
+  Its application to military purposes                               297
+
+  Its application to industry                                        302
+
+  Its application to scientific research                             303
+
+
+                           _THE PHONOGRAPH._
+
+  Edison’s patent                                                    309
+
+  Description of phonograph                                          313
+
+  Several systems                                                    322
+
+  Theory of phonograph                                               327
+
+
+                         _USES OF PHONOGRAPH._
+
+  Account by Edison                                                  333
+
+  Lainbrigot’s system                                                339
+
+
+  _FABER’S SPEAKING MACHINE_                                         341
+
+
+                              _APPENDIX._
+
+  Perrodon’s system of telephonic alarum                             351
+
+  Varey’s microphone speaker                                         352
+
+  Fitch’s microphone speaker                                         353
+
+  Theory of telephone                                                353
+
+  Pollard’s microphone                                               356
+
+  Ader’s electrophone                                                357
+
+  Gower’s new telephone                                              358
+
+  Transmission of speech by telephones without diaphragm             360
+
+
+
+
+THE TELEPHONE,
+
+_&c._
+
+
+
+
+_HISTORY OF THE TELEPHONE._
+
+
+Strictly speaking, the telephone is merely an instrument adapted for
+the transmission of sound to a distance, and this idea of transmitting
+sound is as old as the world itself. The Greeks made use of means which
+might effect it, and there is no doubt that these means were sometimes
+used for the pagan oracles. But such transmission of sound was within
+somewhat narrow limits, and certainly did not exceed those of a
+speaking-tube. Mr. Preece considers that the earliest document in which
+this transmission of sound to a distance is distinctly formulated,
+dates from 1667: he refers to a paper by one Robert Hooke, who writes
+to this effect: ‘It is not impossible to hear a whisper at a furlong’s
+distance, it having been already done; and perhaps the nature of the
+thing would not make it more impossible, though that furlong should
+be ten times multiply’d. And though some famous authors have affirm’d
+it impossible to hear through the thinnest plate of Muscovy glass; yet
+I know a way, by which ’tis easie enough to hear one speak through a
+wall a yard thick. It has not yet been thoroughly examin’d how far
+otacousticons may be improv’d, nor what other wayes there may be of
+quickning our hearing, or conveying sound through other bodies than
+the air; for that is not the only medium I can assure the reader, that
+I have, by the help of a distended wire, propagated the sound to a
+very considerable distance in an instant, or with as seemingly quick a
+motion as that of light, at least incomparably quicker than that which
+at the same time was propagated through the air; and this not only in a
+straight line or direct, but in one bended in many angles.’
+
+This plan for the transmission of sound is the principle of the
+string telephones which have attracted attention for some years, and
+it remained in the stage of simple experiment until 1819, when Sir
+Charles Wheatstone applied it to his magic lyre. In this instrument,
+sounds were transmitted through a long strip of deal, with one end
+in connection with a sounding board: one step more led to the use of
+the membrane employed in string telephones. It would be difficult
+to say with whom this idea originated, since it is claimed, as if
+beyond dispute, by several telephone-makers. If we may believe some
+travellers, it has long been used in Spain for the correspondence
+of lovers. However this may be, it was not to be found among the
+scientific appliances of some years ago, and it was even supposed by
+many persons that the cord consisted of an acoustic tube of slender
+diameter. Although the instrument has become a child’s toy, it has
+great scientific importance, for it proves that vibrations capable
+of reproducing speech may be extremely minute, since they can be
+mechanically transmitted more than a hundred yards.
+
+From the telegraphic point of view, however, the problem of
+transmitting sounds to a distance was far from being solved in this
+way, and the idea of applying electricity to this mode of transmission
+naturally arose as soon as the wonderful effects of electric telegraphy
+were observed, that is, in the years subsequent to 1839. A surprising
+discovery made in America by Mr. Page, in 1837, and afterwards
+investigated by MM. Wertheim, De la Rive, and others, must also have
+led up to it: for it was observed that a magnetic bar could emit sounds
+when rapidly magnetised and demagnetised, and these sounds corresponded
+with the number of currents which produced them. Again, the electric
+vibrators devised by MM. Macaulay, Wagner, Neef, etc., and adapted
+to produce musical sounds, between 1847–1852, by MM. Froment and
+Pétrina, showed that the problem of transmitting sounds to a distance
+was not insoluble. Yet, up to 1854, no one had ventured to admit the
+possibility of transmitting speech by electricity, and when M. Charles
+Bourseul published in that year a paper on the electric transmission
+of speech, the idea was regarded as a fanciful dream. I confess that
+I myself thought it incredible, and when I produced the paper in
+the first edition of my account of the applications of electricity,
+published in 1854, I felt bound to add that the scheme seemed more
+than doubtful. Yet, as the paper was thoughtfully written, I had no
+hesitation in publishing it, affixing the signature of CH. B. Events
+justified this daring idea, and although it did not include the only
+principle which could lead to the reproduction of articulate sounds,
+yet it was the germ of the fertile invention which has made the names
+of Graham Bell and Elisha Gray famous. For this reason I will again
+quote M. Charles Bourseul’s paper.
+
+‘After the telegraphic marvels which can reproduce at a distance
+hand-writings, or even more or less complicated drawings, it may appear
+impossible to penetrate further into the region of the marvellous. Yet
+we will try to advance a few steps further. I have, for example, asked
+myself whether speech itself may not be transmitted by electricity--in
+a word, if what is spoken in Vienna may not be heard in Paris. The
+thing is practicable in this way:--
+
+‘We know that sounds are made by vibrations, and are adapted to the
+ear by the same vibrations which are reproduced by the intervening
+medium. But the intensity of the vibrations diminishes very rapidly
+with the distance: so that it is, even with the aid of speaking-tubes
+and trumpets, impossible to exceed somewhat narrow limits. Suppose that
+a man speaks near a moveable disk, sufficiently flexible to lose none
+of the vibrations of the voice, that this disk alternately makes and
+breaks the currents from a battery: you may have at a distance another
+disk, which will simultaneously execute the same vibrations.
+
+‘It is true that the intensity of the sounds produced will be variable
+at the point of departure, at which the disk vibrates by means of the
+voice, and constant at the point of arrival, where it vibrates by means
+of electricity; but it has been shown that this does not change the
+sounds. It is, moreover, evident that the sounds will be reproduced at
+the same pitch.
+
+‘The present state of acoustic science does not permit us to declare _à
+priori_ if this will be precisely the case with syllables uttered by
+the human voice. The mode in which these syllables are produced has not
+yet been sufficiently investigated. It is true that we know that some
+are uttered by the teeth, others by the lips, and so on; but this is
+all.
+
+‘However this may be, observe that the syllables can only reproduce
+upon the sense of hearing the vibrations of the intervening medium:
+reproduce precisely these vibrations, and you will reproduce precisely
+these syllables.
+
+‘It is, at all events, impossible in the present condition of science
+to prove the impossibility of transmitting sound by electricity.
+Everything tends to show, on the contrary, that there is such a
+possibility. When the application of electro-magnetism to the
+transmission of messages was first discussed, a man of great scientific
+attainments treated the idea as utopian, and yet there is now direct
+communication between London and Vienna by means of a simple wire. Men
+declared it to be impossible, but so it is.
+
+‘It need not be said that numerous applications of the highest
+importance will immediately arise from the transmission of speech by
+electricity. Any one who is not deaf and dumb may use this mode of
+transmission, which would require no apparatus, except an electric
+battery, two vibrating disks, and a wire. In many cases, as for
+example in large establishments, orders might be transmitted in this
+way, although transmission by electricity will not be used while
+it is necessary to go from letter to letter, and to make use of
+telegraphs which require use and apprenticeship. However this may
+be, it is certain that in a more or less distant future, speech will
+be transmitted by electricity. _I have made some experiments in this
+direction_: they are delicate, and demand time and patience, but _the
+approximations obtained_ promise a favourable result.’
+
+This description is certainly not full enough to enable us to
+discern from it the arrangement which would lead to the solution
+of the problem, and if the vibrations of the disk at the receiving
+station were to follow from making and breaking the current at the
+sending-station, under the influence of vibrations caused by the voice,
+they would only produce musical, and not articulate sounds. Yet the
+idea was magnificent, as Mr. Preece said, even when he thought it
+impossible to realise it. Besides, it is easy to see that M. Bourseul
+himself was not deceived as to the difficulties of the problem, as
+far as articulate sounds are concerned, for he points out, as we
+have seen, the difference existing between the simple vibrations
+which produce musical sounds, and the complex vibrations which cause
+articulate sounds; but, as he justly said: ‘Reproduce at the one end
+of the line the vibrations of air caused at the other, and speech
+will be transmitted, however complex the mechanism may be by which it
+is effected.’ We shall presently see how the problem was solved, and
+it is probable that some attempts had already enabled M. Bourseul to
+anticipate the solution of the question; but there is nothing in his
+paper to show what were the means he proposed, so that the discovery of
+the electric transmission of speech cannot reasonably be ascribed to
+him, and we do not understand why we should be reproached for having
+at that time failed to appreciate the importance of a discovery which
+seemed to be then only within the range of fancy.
+
+It was not until 1876 that the problem of the electric transmission of
+speech was finally solved, and the discovery has lately given rise to
+an interesting controversy as to priority between Mr. Elisha Gray, of
+Chicago, and Mr. Graham Bell, on which we must say a few words.
+
+As early as 1874 Mr. Elisha Gray was occupied with a system of
+musical telephone, which he wished to apply to manifold telegraphic
+transmissions, and the investigations which he made, in order to
+establish this system under the best possible conditions, gave him
+a glimpse of the possibility of transmitting articulate words by
+electricity. While carrying on his experiments on the telegraphic
+system, he arranged in fact, about the 15th January, 1876, a system of
+_speaking telephone_, and he deposited the specification and drawings
+in the American Patent Office, in the form of a _caveat_ or provisional
+specification. The deposit was made on the 14th February, 1876: on the
+very same day, Mr. Graham Bell also deposited, in the American Patent
+Office, a request for a patent in which he spoke of an instrument of
+the same kind, but with special application to simultaneous telegraphic
+transmissions by means of a telephonic apparatus; and the few words
+which could, in this specification, refer to a telephone with
+articulate sounds, applied to an instrument which, by Mr. Bell’s own
+admission, had not produced any satisfactory results. In Mr. Gray’s
+_caveat_, on the contrary, the application of the instrument to the
+electric transmission of speech alone is indicated, the description
+of the system is complete, and the drawings which accompany it are so
+exact, that a telephone made from them would work perfectly: this was
+proved by Mr. Gray himself, when, some time afterwards, he finished
+his instruments, which differed in no respect from the one described
+in Mr. Bell’s statement as worked by a battery. On these grounds Mr.
+Elisha Gray would certainly have obtained the patent, if the expiration
+of his _caveat_ had not been the result of an omission of form in the
+Patent Office, which, as we know, decides the priority of inventions
+in America. An action on the ground of this omission has lately been
+brought against Mr. Bell, in the Supreme Court of the American Patent
+Office, to set aside the patent granted to him. If Mr. Gray did
+not appeal before, it was because he was then wholly occupied with
+experiments on the system of harmonic telephone, applied to telegraphic
+communication, and he had no time to attend to the matter.
+
+However this may be, Mr. Bell did not begin to give serious attention
+to the speaking telephone until he had obtained his patent, and his
+efforts were soon crowned with success: a few months later, he
+exhibited his speaking telephone at Philadelphia, which has from that
+time attracted so much public attention, and which, when perfected in a
+practical point of view, reached Europe in the autumn of 1877 under the
+form we know.
+
+To complete this summary account of the telephone, we ought to say
+that since its success a good many claims of priority have arisen,
+as if by enchantment. Mr. John Camack, of English origin, has among
+others claimed the invention of the telephone, not merely relying on
+the description he gave of the instrument in 1865, but on the drawings
+he executed; he even adds, that if he had not lacked means for its
+construction, this would have been the date of the discovery of the
+telephone. A similar pretension has been put forward by Mr. Dolbear, a
+fellow countryman of Mr. Bell, of whose claim we shall speak presently.
+
+Signor Manzetti, of Aosta, says the same thing, asserting that his
+telephonic invention was described in several newspapers of 1865, among
+others in ‘Le Petit Journal,’ of Paris, on the 22nd November, 1865;
+‘Il Diritto’ at Rome, 16th July, 1865; ‘L’Echo d’Italia,’ New York,
+9th August, 1865; ‘L’Italia,’ Florence, 10th August, 1865; ‘La Comuna
+d’Italia,’ Genoa, 1st December, 1865; ‘La Verità,’ Novara, 4th January,
+1866; ‘Il Commercio,’ Genoa, 6th January, 1866. It is true that no
+description of the system was given, and that the journals in question
+only asserted that experiments had been made, which proved that the
+practical solution of the problem of transmitting speech by electricity
+became possible by this system. At any rate M. Charles Bourseul must
+still have the credit of the priority of the idea, and, in our opinion,
+all claims made after the fact only merit slight consideration.
+
+Before considering Bell’s telephone, and the different modifications
+which have been applied to it, it seems worth while, in order to make
+the reader perfectly familiar with these kinds of instruments, to study
+the electro-musical telephones which preceded it, and especially that
+of M. Reiss, which was made in 1860, and became the starting point
+of all the others. We shall find that these instruments have very
+important applications, and that telegraphy will probably be one day
+much advanced by their use.
+
+
+
+
+MUSICAL TELEPHONES.
+
+
+_Telephone of M. Reiss._--This telephone is, as far as the reproduction
+of sound is concerned, based upon Mr. Page’s discoveries in 1837,
+and, as regards electric transmission, it is based on the vibrating
+membrane of which Mr. L. Scott made use in his phonautograph, in 1855.
+This instrument is composed, like telegraphic systems, of two distinct
+parts, a sender and a receiver, as represented in fig. 1.
+
+[Illustration: FIG. 1.]
+
+The sender was virtually composed of a sounding box K, having on its
+upper surface a large circular opening, across which a membrane was
+stretched, and in its centre there was fitted a thin disk of platinum
+_o_, above which a metallic point _c_ was fixed, and this, together
+with the disk, constituted the contact-breaker. On one face of the
+sounding-box K, there was a sort of speaking-tube, for the purpose of
+collecting the sound, and directing it to the interior of the box, in
+order that it might then react upon the membrane. Part of the box K is
+broken away in the plate, in order that the different parts of which it
+is made may be seen.
+
+The rods _a_, _c_, which support the platinum point _b_, are in
+metallic contact with a Morse key _t_, placed on the side of the box K,
+and with an electro-magnet A, which belongs to a telegraphic system,
+intended to exchange the signals required to start the action of the
+two instruments at their respective stations.
+
+The receiver consists of a sounding-box B, on which rest two supports
+_d_, _d_, bearing an iron rod of the thickness of a knitting needle. An
+induction coil of insulated wire _g_ is wound round this rod, and the
+whole is enclosed by the lid D, which concentrates the sound already
+increased by the sounding-box: for this purpose the box is provided
+with two openings below the coil.
+
+The circuit is completed through the primary of this coil by the two
+terminals 3 and 4, and a Morse key _t_ is placed at the side of box B,
+in order to exchange signals.
+
+In order to work this system, the speaking instrument should be placed
+before the opening T, and this instrument may be a flute, a violin,
+or even the human voice. The vibrations of air occasioned by these
+instruments cause the telephonic membrane to vibrate in unison, and the
+latter, rapidly moving the platinum disk _o_ to and from the point
+_b_, causes a series of breaks in the current, which are repeated in
+the iron wire _d d_, and transformed into metallic vibrations, of which
+the number is equal to that of the sounds successively produced.
+
+According to this mode of action, the possibility of transmitting
+sounds with their relative value becomes intelligible: but it is
+equally clear that sounds thus transmitted will not have the _timbre_
+of those which produce them, since the _timbre_ is independent of the
+number of vibrations, and it must be added that the sounds produced
+by M. Reiss’s instrument were as shrill as those of a child’s penny
+trumpet, and by no means attractive. The problem of transmitting
+musical sounds by electricity was, however, really solved, and it can
+be said with truth that an air or a melody could be heard at any given
+distance.
+
+The invention of this telephone dates, as we have seen, from 1860, and
+Professor Heisler speaks of it in his treatise of technical physics,
+published at Vienna in 1866; he even asserts, in the article which he
+devotes to the subject, that although the instrument was still in its
+infancy, it was capable of transmitting vocal melodies, and not merely
+musical sounds. The system was afterwards perfected by M. Van der
+Weyde, who, after reading the account published by M. Heisler, sought
+to make the box of the sender more sonorous, and to strengthen the
+sounds produced by the receiver. He writes as follows in the ‘American
+Scientific Journal:’
+
+‘In 1868, I caused two telephones to be made, similar to those I have
+described, and I exhibited them at a meeting of the Polytechnic Club
+of the American Institute. The transmitted sounds were produced at the
+farthest extremity of the Cooper Institute, quite outside the hall
+in which the audience sat: the receiver was placed on a table in the
+hall itself. The vocal airs were faithfully reproduced, but the sound
+was rather weak and nasal. I then tried to improve the instrument,
+and I first obtained stronger vibrations in the box K by causing
+reverberation from the sides of the box, by means of hollow partitions.
+I next intensified the sounds produced by the receiver, by introducing
+several iron wires into the coil, instead of one. These improvements
+were submitted to the meeting of the American Association for the
+Advancement of Science, which was held in 1869, and it was considered
+that the invention contained the germ of a new method of telegraphic
+transmission which might lead to important results.’ This opinion was
+soon afterwards justified by the discoveries of Bell and Elisha Gray.
+
+
+_Messrs. Cecil and Leonard Wray’s Telephone._--This system, represented
+in figs. 2 and 3, is simply an improvement on that of M. Reiss, with
+the object of intensifying the effects produced. The sender is provided
+with two membranes, instead of one; and its receiver, instead of
+being formed of a single iron wire covered with a magnetising coil,
+is composed of two distinct coils H, H′ (fig. 2), placed in the
+same straight line, and within which are two iron rods. These rods
+are fastened by one of their ends to two copper disks A, B; these
+disks are maintained in a fixed position by screws I, I′, and the
+two other extremities of the rods, between the coils, are opposite
+each other, not touching, but divided by a very small interval. The
+instrument is set upon a sounding-box, in which there is a hole T in
+the space corresponding to the interval between the coils: these coils
+communicate with four terminals, which are connected with the electric
+current in such a way that the adjacent poles of the two rods are of
+opposite polarity, thus forming a single magnet, divided in the centre.
+It seems that by this arrangement the sound produced becomes much more
+distinct.
+
+[Illustration: FIG. 2.]
+
+[Illustration: FIG. 3.]
+
+The form of the sender also is somewhat different from the one
+we have previously described: the upper part, instead of being
+horizontal, is rather inclined, as it appears in fig. 3, and the
+opening E through which the sound has to communicate with the vibrating
+membrane, occupies a great part of the upper surface of the box, which
+consequently appears to be somewhat oblique. The second membrane G,
+which is of caoutchouc, forms a sort of partition which divides the
+box in two, starting from the upper end of the opening: the inventor
+states that this will protect the outer membrane D from the breath and
+other injurious effects, while increasing the force of the vibrations
+produced on the first membrane, as in a drum. The contact-breaker
+itself also differs from the one in M. Reiss’s instrument. The platinum
+disk _b_ is only placed in circuit by means of two slender wires of
+platinum or steel, which are immersed in two small cups, filled with
+mercury, and connected with the circuit. In this way, the movements of
+the membrane D are free, and its vibration is rendered more easy.
+
+The circuit is also broken by a little platinum point resting on a
+lever with a spring-joint, K H, which is above the disk: one end of the
+lever, which is fixed below a kind of Morse key M I, makes it possible
+to close the circuit with the hand, so as to give the signal for
+setting the apparatus to work.
+
+
+_Electric Harmonica._--Long before M. Reiss’s invention, and
+consequently still longer before that of Mr. Elisha Gray, I mentioned
+a sort of electric harmonica, and described it as follows in the first
+edition of my ‘Exposé des applications de l’Electricité,’ published in
+1853:--
+
+‘The power possessed by electricity to set metallic plates in motion
+and cause their vibration has been used for the production of distinct
+sounds, which can be combined and harmonised; but in addition to this
+purely physical application, electro-magnetism has come to the aid
+of certain instruments, such as pianos, organs, &c., rendering them
+capable of being played at a distance. So that this extraordinary
+force may be turned to account in arts which are apparently the least
+susceptible of any application of electricity.
+
+‘We have already spoken of M. de la Rive’s contact-breaker. It is, as
+we know, an iron disk, soldered to a steel spring, and maintained in
+a fixed position opposite to an electro-magnet by another spring in
+connection with one branch of the current. As the other branch, after
+passing into the wire of the electro-magnet, terminates in the iron
+disk itself, the electro-magnet is only active at the moment when the
+disk touches the terminal spring; at the moment of leaving it, the
+magnetism ceases, and the iron disk returns to its normal position,
+and then leaves it again. In this way a vibration is produced, rapid
+in proportion to the small size of the vibrating disk, and to the
+greatness of the force produced by the approach of the disk to the
+electro-magnet.
+
+‘In order to increase the acuteness of the sounds, one or other of
+these expedients must be employed. The simplest way is to use a screw
+which can be tightened or relaxed at pleasure, and which in this manner
+removes the vibrating disk to a greater or less distance from the
+electro-magnet. This is the case in M. Froment’s instrument, and by
+this means he has obtained sounds of extraordinary acuteness, although
+not unpleasant to the ear.
+
+‘M. Froment has not applied the apparatus to a musical instrument,
+but it is evident that it would be easy to do so; it would only be
+necessary to make the notes of a key-board act on metallic levers, of
+a length corresponding to the position required by the disk for the
+vibration of different tones. These different levers, resting on the
+disk, would act as a point of contact, but the point would vary in
+position, according to the touch.
+
+‘If the current were constant, such an instrument would certainly have
+many advantages over the pipe instruments which are in use, since the
+vibration might be prolonged at will in the case of each note, and
+the sounds would be softer; unfortunately the irregular action of the
+battery makes it difficult in practice. These kinds of instruments are
+therefore only used as a means of regulating by ear the force of the
+battery, a much more convenient regulator than the rheometers, since it
+is possible to estimate by them the variations of the battery during an
+experiment without any distraction of the mind.’
+
+In 1856 M. Pétrina, of Prague, invented an analogous arrangement,
+to which he gave the name of electric harmonica, although, strictly
+speaking, he had not thought of it as a musical instrument. This is
+what I have said on the subject in vol. iv. of the second edition of my
+‘Exposé des applications de l’Electricité,’ published in 1859:--
+
+‘The principle of this instrument is similar to that of Neef’s
+rheotome, in which the hammer is replaced by slender rods, whose
+vibrations produce a sound. Four of these rods are placed side by
+side, and when moved by keys, and arrested by levers, produce combined
+sounds of which the origin may be easily shown.’
+
+It is true that nothing is said in this passage of the capability
+possessed by these instruments of being played at a distance; but
+this idea was quite legitimate, and German periodicals assert that it
+was accomplished by M. Pétrina even before 1856. It was the result of
+what I said at the outset: ‘that electro-magnetism may come to the
+aid of certain instruments, such as pianos, organs, &c., _in order
+to enable them to be played at a distance_,’ and I also pointed out
+the expedients employed for the purpose, and even for setting them at
+work, under the influence of a small musical box. I did not, however,
+ascribe importance to the matter, and it is only by way of historical
+illustration that I speak of these systems.
+
+
+_Telephone by Mr. Elisha Gray, of Chicago._--This system, invented in
+1874, is in reality only an instrument of the nature of those which
+preceded it, but with important modifications, which made it possible
+to apply it usefully to telegraphy. In an early model, he made use
+of an induction coil, with two helices, one over the other: the
+contact-breaker, which was vibrating, was multiple, and so arranged as
+to produce vibrations numerous enough to emit sounds. These sounds may,
+as we have seen, be modified by this arrangement, according to the
+mode in which the instrument is adjusted, and if there are a certain
+number of such contact-breakers side by side, with vibrating disks
+so ordered as to produce the different notes of the scale on several
+octaves, it becomes possible, by a combination of certain notes, to
+execute on this new kind of instrument a piece of music such as may be
+produced by an harmonium, an accordion, or any other instrument with
+blowers. The contact-breakers are set in motion by means of the primary
+current of the induction coil, as it circulates through one or other of
+the electro-magnets of these contact-breakers, actuated by the lowering
+of the notes of a key-board connected with them, and the secondary
+currents which arise in the coil, in consequence of the interruptions
+in the primary currents, transmit the corresponding vibrations to a
+remote receiver. There is an analogy between this instrument and the
+telephones of which we have already spoken by Reiss and Wray, but the
+effect is increased by Mr. Gray’s modifications.
+
+We represent in fig. 4 the arrangement of the first system. The
+vibrators are A and A′, the key-board M and M′, the induction coil B,
+and the receiver C. This receiver consists, as we see, of a simple
+electro-magnet N N′: above its poles there is a metal cylindrical
+case C, of which the bottom is made of iron, to serve as an armature.
+This box, like a violin, is pierced with two holes in the form S,
+to serve as a sounding-board; and Mr. Elisha Gray has ascertained
+that the molecular motion which takes place in the magnetic core and
+its armature, under the influence of alternate magnetisation and
+demagnetisation, sufficed to produce vibrations corresponding to the
+velocity of these alternations, and to emit sounds which became audible
+when they were magnified by the sounding-board.
+
+[Illustration: FIG. 4.]
+
+It is quite intelligible that the effect obtained in this system might
+be reproduced, if, instead of contact-breakers or electric rheotomes,
+mechanical contact-breakers were used at the sending station, so
+arranged as to furnish the requisite number of breaks in the current
+which communicates the vibrations of the different notes of the scale.
+In this way also it would be possible to dispense with the induction
+coil, by causing the current which has been broken by the mechanical
+contact-breaker to react upon the receiver. Mr. Elisha Gray has
+moreover made a different arrangement of this telephonic system, which
+he has applied to telegraphy for simultaneous electric transmissions,
+of which we shall speak presently.
+
+If we may believe Mr. Elisha Gray, the vibrations transmitted by
+the secondary currents would be capable, by the intervention of the
+human body, of causing the sounds to be reproduced at a distance
+by conducting disks, which vibrate readily, and are placed on a
+sounding-box. In this way musical sounds may be evoked from copper
+cylinders placed upon a table, from a metallic disk fastened to a kind
+of violin, from a membrane stretched on a drum, or from any other
+resonant substance, by touching any of these objects with one hand,
+while holding the end of the line with the other. These sounds, of
+which the quality must vary with the substance touched, would reproduce
+the transmitted note with the precise number of vibrations which belong
+to it.[1]
+
+_Mr. Varley’s Telephone._--This is, strictly speaking, merely a musical
+telephone of the same kind as that of Mr. Gray, but the arrangement of
+the receiver is original and interesting. This part of the instrument
+essentially consists of a drum of large size (three or four feet
+in diameter), within which is a condenser formed of four sheets of
+tinfoil, divided by sheets of some insulating material, and with a
+surface of about half the size of the drum. The plates of the condenser
+are placed parallel to the membranes of the drum, and very little
+removed from its surface.
+
+If an electric charge is communicated to one of the series of
+conducting plates of the condenser, those which correspond to it are
+attracted, and if they were movable they might communicate to the
+intervening strata of air a movement which, on reaching the membranes
+of the drum, might, by a series of charges in rapid succession, cause
+the membranes to vibrate, and thus produce sounds: these sounds
+would correspond to the number of charges and discharges which had
+occurred. Since these charges and discharges are determined by the
+contact of the two plates of the condenser, at the extremities of the
+secondary circuit of an induction coil, of which the primary circuit
+has been duly broken, it becomes evident that, in order to cause the
+drum to emit any given sound, it will be enough to produce the number
+of vibrations in the contact-breaker of the induction coil which are
+required for this sound.
+
+The means employed by Mr. Varley to produce these interruptions are
+the same which are in use in several electrical instruments, and
+especially in chronographs--an electro-magnetic tuning-fork, regulated
+so as to emit the sound required. This tuning-fork may, by acting as
+contact-breaker, react on the primary current of the induction coil;
+if the number of the tuning-forks equals that of the musical notes
+which are to be transmitted, and if the electro-magnets which set them
+in motion are connected with the key-board of a piano, it would be
+possible to transmit a melody to a distance by this system, as well as
+by that of Mr. Elisha Gray.
+
+The peculiarity of this system consists in the reproduction of sounds
+by the action of a condenser, and we shall presently see that this
+idea, adopted by Messrs. Pollard and Gamier, led to interesting results.
+
+
+_Singing Condenser of MM. Pollard and Garnier._--This instrument, which
+astonishes all who hear it, attracted public attention in London some
+time ago. It is difficult to say why its fame was not greater, since
+much attention has been bestowed on less curious instruments. It is
+a fact that we have been able, thanks to MM. Pollard and Garnier, to
+hear songs issue from a sort of copy-book, so as to become audible
+throughout the room. The songs thus reproduced are certainly not
+always perfectly true; yet when the person who sings into the sender
+is a musician, and understands how to make use of it, the condenser in
+question will emit sounds somewhat resembling those of the violoncello
+or the hautbois.
+
+The singing instrument consists of a condenser K, formed of thirty
+sheets of paper, laid one over the other, from nine to thirteen
+centimètres in thickness: between these, twenty-eight sheets of
+tinfoil, from six to twelve centimètres thick, are intercalated, so
+joined as to form the two plates of the condenser. For this purpose
+the pair sheets are joined together at one end of the copy-book, and
+the odd sheets at the other end. This system is fastened to a stiff
+_carton_, after taking care to bind it with a strip of paper, and the
+sheets of tinfoil are joined to the two ends of the condenser by two
+copper rims D, D, which are provided with terminals for the circuit
+wire, and in this way the singing instrument is constructed. A somewhat
+heavy weight, placed upon the condenser to compress the sheets, does
+not in any way prevent it from working; and this vitiates the theory
+first put forward to explain its effects, that the sheets were moved by
+attraction.
+
+[Illustration: FIG. 5.]
+
+The sending instrument consists of a sort of telephone without a
+handle, E, of which the vibrating disk is formed of a very thin plate
+of tin. A cylindrical piece of carbon C is fastened to its centre, and
+is supported by another cylinder of the same material H. This rests
+on a transverse piece of wood A B, jointed on the side A, on the edge
+opposite to the box, by means of a regulating screw V. An arched spring
+R (the end of a watch spring) placed across this piece of wood gives
+it a certain elasticity beneath the pressure, and this elasticity is
+necessary in order that the instrument may act properly, and it thus
+becomes a sort of microphone with a diaphragm.
+
+The tin plate is put into communication with one pole of a battery P,
+of six Leclanché cells, and the lower carbon cylinder H corresponds to
+the primary helix of an induction coil M, previously connected with
+the second pole of the battery: Finally, the two extremities of the
+secondary helix of the coil, _a_ and _b_, are in immediate connection
+with the two plates D, D, of the condenser.
+
+This secondary helix should consist of twenty strands of wire No. 32,
+covered with silk, and the primary helix is made of five strands of
+wire No. 16. The length of the coil should not exceed seven centimètres
+and the diameter of the core of fine iron wire ought to be about one
+centimètre.
+
+In order to produce song on the condenser, the sender must be so
+regulated that the two carbons C and H do not touch each other in
+their normal condition, but they should be so close that in singing
+the vibrations of the disk L L may effect the needful contacts. The
+adjustment can be easily made by the touch, and by uttering the same
+note until it is repeated by the condenser. If three notes, given in
+succession, are faithfully reproduced, the instrument may be assumed to
+be properly regulated, and, in order to make it work, it is enough to
+apply the mouth to the mouthpiece as it is applied to a reed pipe.
+
+In order to obtain a satisfactory result, the disk of the instrument
+must be heard to vibrate, as in a _flûte à l’oignon_. Instead of
+carbons, contacts of platinum may be used; but when arranged as we
+have described, the instrument may be employed for several purposes,
+as we shall see presently. This instrument is made by MM. Chardin and
+Prayer. M. Janssens has made the system more portable by fastening the
+sender, represented in fig. 5, to a handle in which the induction coil
+is placed: the instrument then resembles an ordinary telephone, and
+the vibration of the diaphragm is made more easy by piercing two holes
+in it. On the side of the sending-box, above and below the diaphragm,
+there are binding screws in connection with the end of the handle,
+since the instrument may be used as an ordinary telephonic sender, and
+even as a telephonic receiver.
+
+
+
+
+SPEAKING TELEPHONES.
+
+
+We have seen that the telephones just described can only transmit
+musical sounds, since they can merely repeat simple vibrations,
+in greater or less number, it is true, but not in simultaneous
+combinations like those which reproduce articulate sounds. Up to the
+time of Mr. Bell’s invention, the transmission of speech could only
+take place with the aid of acoustic tubes, or of the string telephones
+of which we have spoken. Although these instruments have no connection
+with the object of our study in this work, we have thought it necessary
+to say a few words about them, since they may sometimes be combined
+with electric telephones, and also represent the first stage of the
+invention.
+
+
+_String Telephones._--These instruments, which have flooded the cities
+of Europe for several years, since the date of the invention was 1867,
+are interesting in themselves, and we are surprised that they have not
+hitherto taken a place in the collections of physical science. They
+are made of two metal or cardboard tubes, in the form of a cylindrical
+cone: one end is closed by a tightly stretched membrane of parchment,
+in the centre of which the cord or string intended to connect the two
+cylinders is fastened by a knot. When two such tubes are connected
+in this way, and the cord is tightly stretched, as in fig. 6, it is
+only necessary to apply one tube to the ear, while another speaks into
+the opening of the other tube: the words spoken by the latter are
+instantly transmitted, and it is even possible to converse in quite
+an undertone. Under these conditions the vibrations of the membrane
+affected by the voice are mechanically transmitted to the other
+membrane by the string, which, as Robert Hooke declared in 1667, is a
+better transmitter of sound than the air. In this way it is possible to
+communicate at a distance of 170 yards, and the size and nature of the
+cord have some influence. The sellers of these instruments say that the
+best results are obtained from silken cords, and the worst from those
+made of hemp. Cords of plaited cotton are usually employed for the sake
+of cheapness.
+
+[Illustration: FIG. 6.]
+
+In some patterns, the tubes are so arranged as to present, between
+the membrane and the mouth, a diaphragm pierced with a hole, and the
+instrument somewhat resembles a bell with its base bored and closed
+again a little above the parchment membrane; but I have not observed
+that this pattern is decidedly superior to the others.
+
+It has also been asserted that horn-shaped tubes of nickel silver are
+to be preferred, of which I am equally doubtful. At any rate, these
+instruments have produced unexpected results; and although their
+practical use is very limited, they are interesting from a scientific
+point of view, and are instructive toys for children.
+
+Mr. Millar, of Glasgow, declares that the effect produced by these
+telephones depends very much on the nature of the string, the way in
+which it is attached, and the way in which the membrane is fastened to
+the mouthpiece.
+
+
+_Improvements made in the String Telephone._--The amazing effects
+of the Bell telephones have lately brought the string telephones,
+which were only regarded as children’s toys, again into fashion.
+Since they have made it possible to transmit to several persons the
+words reproduced by an electric telephone, means have been sought for
+combining them usefully with the latter, and the best mode of making
+them speak on a string presenting several angles has been sought for:
+it has been shown that, under the usual conditions, these instruments
+only speak distinctly when the string is stretched in a right line.
+To solve this problem, it occurred to M. A. Bréguet to make use of a
+sort of tambourine for the supports, with the string passed through
+their centre; the sound conveyed by that part of the string which is in
+connection with the speaking-horn causes the membrane of the tambourine
+to vibrate, which again communicates the vibration to the next portion
+of string. In this way the angles may be multiplied at will, and the
+string may be supported throughout the length compatible with this kind
+of telephone, which does not exceed 112 yards.
+
+M. A. Bréguet has also invented a system of relays to accomplish the
+same object. He makes the strings terminate in two membranes which
+close the two openings of a brass cylinder. The sounds reproduced on
+one of these membranes react upon the other, which vibrates under its
+influence, as if it were affected by the voice. The cylinder then acts
+as an ordinary acoustic tube, and its form may be varied at pleasure.
+
+M. A. Badet, on February 1, 1878, succeeded in making string telephones
+in an analogous way, and he used parchment stretched upon frames which
+acted as resonant boards. The string was fixed in the centre of the
+membrane, and made with it the angle desired.
+
+Several scientific men, among others Messrs. Wheatstone, Cornu, and
+Mercadier, have long been occupied about these ways of transmission
+by wire, and Messrs. Millar, Heaviside, and Nixon have lately made
+some interesting experiments, on which we must say a few words. Mr.
+Millar ascertained that by means of a telegraphic wire, stretched
+and connected by two copper wires with two vibrating disks, musical
+sounds might be conveyed to a distance exceeding 160 yards, and that
+by stretching these wires through a house, and connecting them with
+mouth-and-ear holes in different rooms, communication between them
+became perfectly easy.
+
+For the vibrating disks he employed wood, metal, or gutta-percha, in
+the form of a drum, with wires fixed in the centre. The sound seems to
+become more intense in proportion to the thickness of the wire.
+
+Messrs. Heaviside and Nixon, in their experiments at Newcastle-on-Tyne,
+have ascertained that the most effective wire was No. 4 of the English
+gauge. They employed wooden disks ⅛ inch in thickness, and these may
+be placed in any part of the length of the wire. When the wire was
+well stretched and motionless, it was possible to hear what was said
+at a distance of 230 yards, and it seems that Mr. Huntley, by using
+very thin iron diaphragms, and by insulating the line wire on glass
+supports, was able to transmit speech for 2,450 feet, in spite of the
+zigzags made by the line on its supports.
+
+
+_Mr. Graham Bell’s Electric Telephone._--Telephonic instruments were
+at this stage when Bell’s telephone was shown at the Philadelphia
+Exhibition of 1876. Sir William Thompson did not hesitate to call
+it ‘the wonder of wonders,’ and it instantly attracted universal
+attention, although there was at first much incredulity as to its
+genuineness. This telephone, in fact, reproduced articulate words, a
+result which surpassed all the conceptions of physicists. In this case
+it was no longer a conception, to be treated as visionary until there
+was proof to the contrary: the instrument spoke, and even spoke so
+loudly that it was not necessary to apply the ear. Sir William Thompson
+spoke to this effect on the subject at the meeting of the British
+Association at Glasgow in September 1876:--
+
+‘In the department of telegraphs in the United States I saw and heard
+Mr. Elisha Gray’s electric telephone, of wonderful construction, which
+can repeat four despatches at the same time in the Morse code, and,
+with some improvements in detail, this instrument is evidently capable
+of a fourfold delivery. In the Canadian department I heard “To be or
+not to be? There’s the rub,” uttered through a telegraphic wire, and
+its pronunciation by electricity only made the rallying tone of the
+monosyllables more emphatic. The wire also repeated some extracts
+from New York papers. With my own ears I heard all this, distinctly
+articulated through the slender circular disk formed by the armature
+of an electro-magnet. It was my fellow-juryman, Professor Watson, who,
+at the other extremity of the line, uttered these words in a loud
+and distinct voice, while applying his mouth to a tightly stretched
+membrane provided with a small piece of soft iron, which executed
+movements corresponding to the sound vibrations of the air close to an
+electro-magnet introduced into the circuit. This discovery, the wonder
+of wonders in electric telegraphy, is due to a young fellow-countryman
+of our own, Mr. Graham Bell, a native of Edinburgh and now naturalised
+in New York.
+
+‘It is impossible not to admire the daring invention by which we have
+been able to realise with these simple expedients the complex problem
+of reproducing by electricity the tones and delicate articulations of
+voice and speech; and it was necessary, in order to obtain this result,
+to find out the means of varying the intensity of the current in the
+same proportion as the inflections of the sound emitted by the voice.’
+
+If we are to believe Mr. Graham Bell, the invention of the telephone
+was not due to a spontaneous and fortunate conception: it was the
+result of his long and patient studies in acoustic science, and of
+the labours of the physicists who preceded him.[2] His father, Mr.
+Alexander Melville Bell, of Edinburgh, had studied this science
+deeply, and had even succeeded in representing with great ingenuity
+the adaptation of the vocal organs for the emission of sound. It was
+natural that he should instil a taste for his favourite studies into
+his son’s mind, and they made together numerous researches in order to
+discover the relations which exist between the different elements of
+speech in different languages, and the musical relations of vowels. It
+is true that several of these researches had been made by M. Helmholtz,
+and under more favourable conditions; but these studies were of great
+use to Mr. Bell when he was afterwards occupied with the telephone, and
+Helmholtz’s experiments, which he repeated with one of his friends,
+Mr. Hellis of London, concerning the artificial reproduction of vowels
+by means of electric tuning-forks, launched him into the study of the
+application of electricity to acoustic instruments. He first invented
+a system of an electric harmonica with a key-board, in which the
+different sounds of the scale were reproduced by electric diapasons of
+different forms, adapted to different notes, and which, when set in
+motion by the successive lowering of the keys, could reproduce sounds
+corresponding to the notes touched, just as in an ordinary piano.
+
+He next, as he tells us, turned his attention to telegraphy, and
+thought of making the Morse telegraphs audible by causing the
+electro-magnetic organ to react on sounding contacts. It is true
+that this result had already been obtained in the sounders used
+in telegraphy, but he thought that by applying this system to his
+electric harmonica, and by employing such an intensifying instrument as
+Helmholtz’s resonator at the receiving station, it would be possible to
+obtain through a single wire simultaneous transmissions which should be
+due to the action of the voice. We shall see presently that this idea
+was realised almost at the same time by several inventors, among others
+by M. Paul Lacour, of Copenhagen, Mr. Elisha Gray, of Chicago, and
+Messrs. Edison and Varley.
+
+Mr. Bell’s study of electric telephones really dates from this time,
+and he passed from complex to simple instruments, making a careful
+study of the different modes of vibration which arise from different
+modes of electric action. The following is an abstract, with the
+omission of more technical details, of the paper read by Mr. Bell to
+the Society of Telegraphic Engineers, London, October 31, 1877.
+
+If the intensity of an electric current is represented by the ordinates
+of a curve, and the duration of breaks in the current by the abscissæ,
+the given curve may represent the waves of the positive or negative
+current respectively, above and below the line of X, and these waves
+will be more or less accentuated, just as the transmitted currents are
+more or less instantaneous.
+
+If the currents which are interrupted to produce a sound are quite
+instantaneous in their manifestation, the curve represents a series of
+isolated indentations, as we see in fig. 7; and if the interruptions
+are so made as only to produce differences of intensity, the curve
+is presented under the form of fig. 8. Finally, if the emissions of
+current are so ordered that their intensity alternately increases
+and diminishes, the curve takes the form represented in fig. 9. In
+the first case, the currents are _intermittent_; in the second,
+_pulsatory_; in the third case, they are _undulatory_.
+
+[Illustration: FIG. 7.]
+
+[Illustration: FIG. 8.]
+
+[Illustration: FIG. 9.]
+
+These currents are necessarily positive or negative, according to their
+position above or below the line _x_, and if they are alternately
+reversed, the curves present the form given in fig. 10, curves which
+essentially differ from the first, not merely in the different form
+of the indentations, but especially in the suppression of the extra
+current, which is always found in the pulsatory and undulatory
+currents.
+
+[Illustration: FIG. 10.]
+
+The two former systems of currents have long been in use for the
+electric transmission of musical sounds, of which we have an
+interesting example in Reiss’s telephone already described. But Mr.
+Bell claims to have been the first to employ the undulatory currents,
+which made it possible to solve the problem of transmitting speech.[3]
+In order to estimate the importance of this discovery, it will be
+enough to analyse the effects produced with these different systems of
+currents when several notes of varying pitch are to be combined.
+
+Fig. 7 shows a combination in which the styles _a_, _a′_, of two
+sending instruments cause the interruption of the current from the same
+battery B, so that the given vibrations should be between them in the
+relation of a tierce major, that is in the relation of four to five.
+Under such conditions, the currents are intermittent, and four contacts
+of _a_ are produced in the same space of time as the five contacts of
+_a′_, and the corresponding electric intensities will be represented
+by the indentations we see in A^2 and in B^2: the combination of
+these intensities A^2 + B^2 will produce the indentations at unequal
+intervals which may be observed on the third line. It is evident that
+although the current maintains a uniform intensity, there is less time
+for the breaks when the interrupting styles act together than when they
+act separately, so that when there are a number of contacts effected
+simultaneously by styles working at different degrees of velocity, the
+effects produced will have the effect of a continuous current. The
+maximum number of distinct effects which can be produced in this way
+will, however, greatly depend on the relation which exists between
+the durations of the make and break of the current. The shorter the
+contacts are, and the longer the breaks, the more numerous will be the
+effects transmitted without confusion, and _vice versâ_.
+
+By the aid of pulsatory currents the transmission of musical sounds is
+effected in the way indicated in fig. 8, and it is seen that when they
+are produced simultaneously, the result A^2 + B^2 is analogous to that
+which would be produced by a continuous current of minimum intensity.
+
+In the case of undulatory currents the result is different, but in
+order to produce them it is necessary to have recourse to inductive
+effects, and fig. 9 indicates the manner in which the experiment should
+be made. In this case, ‘the current from the battery B is thrown into
+waves by the inductive action of iron or steel reeds M, M, vibrated in
+front of electro-magnets _e_, _e_, placed in circuit with the battery:
+A^2 and B^2 represent the undulations caused in the current by the
+vibration of the magnetised bodies, and it will be seen that there are
+four undulations of B^2 in the same time as five undulations of A^2.
+The resultant effect upon the main line is expressed by the curve A^2
++ B^2, which is the algebraical sum of the sinusoidal curves A^2 and
+B^2. A similar effect is produced when reversed undulatory currents are
+employed, as in fig. 10, where the current is produced by the vibration
+of permanent magnets united upon a circuit, without a voltaic battery.
+
+‘It will be understood from figs. 9 and 10 that the effect of
+transmitting musical signals of different pitches simultaneously along
+a single wire is not to obliterate the vibratory character of the
+current, as in the case of intermittent and pulsatory currents, but to
+change the shapes of the electrical undulations. In fact, the effect
+produced upon the current is precisely analogous to the effect produced
+in the air by the vibration of the inducing bodies M, M′. Hence it
+should be possible to transmit as many musical tones simultaneously
+through a telegraph wire as through the air.’
+
+[Illustration: FIG. 11.]
+
+After applying these principles to the construction of a telegraphic
+system for multiple transmissions, Mr. Bell lost no time in making use
+of his researches to improve the vocal training of deaf mutes. ‘It is
+well known,’ he said, ‘that deaf mutes are dumb merely because they are
+deaf, and that there is no defect in their vocal organs to incapacitate
+them from utterance. Hence it was thought that my father’s system of
+pictorial symbols, popularly known as visible speech, might prove a
+means whereby we could teach the deaf and dumb to use their vocal
+organs and to speak. The great success of these experiments urged upon
+me the advisability of devising methods of exhibiting the vibrations
+of sound optically, for use in teaching the deaf and dumb. For some
+time I carried on experiments with the manometric capsule of Koenig,
+and with the phonautograph of Léon Scott. The scientific apparatus in
+the Institute of Technology in Boston was freely placed at my disposal
+for these experiments, and it happened that at that time a student of
+the Institute of Technology, Mr. Maurey, had invented an improvement
+upon the phonautograph. He had succeeded in vibrating by the voice
+a stylus of wood about a foot in length which was attached to the
+membrane of the phonautograph, and in this way he had been enabled to
+obtain enlarged tracings upon a plane surface of smoked glass. With
+this apparatus I succeeded in producing very beautiful tracings of
+the vibrations of the air for vowel sounds. Some of these tracings
+are shown in fig. 11. I was much struck with this improved form of
+apparatus, and it occurred to me that there was a remarkable likeness
+between the manner in which this piece of wood was vibrated by the
+membrane of the phonautograph and the manner in which the _ossiculæ_
+of the human ear were moved by the tympanic membrane. I determined
+therefore to construct a phonautograph modelled still more closely
+upon the mechanism of the human ear, and for this purpose I sought
+the assistance of a distinguished aurist in Boston, Dr. Clarence J.
+Blake. He suggested the use of the human ear itself as a phonautograph,
+instead of making an artificial imitation of it. The idea was novel,
+and struck me accordingly, and I requested my friend to prepare a
+specimen for me, which he did. The apparatus, as finally constructed,
+is shown in fig. 12. The _stapes_ was removed, and a stylus of hay
+about an inch in length was attached to the end of the _incus_. Upon
+moistening the _membrana tympani_ and the _ossiculæ_ with a mixture of
+glycerine and water, the necessary mobility of the parts was obtained;
+and upon singing into the external artificial ear the stylus of hay
+was thrown into vibration, and tracings were obtained upon a plane
+surface of smoked glass passed rapidly underneath. While engaged in
+these experiments I was struck with the remarkable disproportion in
+weight between the membrane and the bones that were vibrated by it. It
+occurred to me that if a membrane as thin as tissue paper could control
+the vibration of bones that were, compared to it, of immense size
+and weight, why should not a larger and thicker membrane be able to
+vibrate a piece of iron in front of an electro-magnet, in which case the
+complication of steel rods shown in my first form of telephone, could
+be done away with, and a simple piece of iron attached to a membrane be
+placed at either end of the telegraphic circuit?
+
+[Illustration: FIG. 12.]
+
+‘For this purpose I attached the reed A (fig. 13) loosely by one
+extremity to the uncovered pole _h_ of the magnet, and fastened the
+other extremity to the centre of a stretched membrane of goldbeaters’
+skin _n_. I presumed that upon speaking in the neighbourhood of the
+membrane _n_, it would be thrown into vibration and cause the steel
+reed A to move in a similar manner, occasioning undulations in the
+electrical current that would correspond to the changes in the density
+of the air during the production of the sound; and I further thought
+that the change of the intensity of the current at the receiving end
+would cause the magnet there to attract the reed A′ in such a manner
+that it should copy the motion of the reed A, in which case its
+movements would occasion a sound from the membrane _n′_ similar in
+_timbre_ to that which had occasioned the original vibration.
+
+[Illustration: FIG. 13.]
+
+[Illustration: FIG. 14.]
+
+‘The results, however, were unsatisfactory and discouraging. My friend
+Mr. Thomas A. Watson, who assisted me in this first experiment,
+declared that he heard a faint sound proceed from the telephone at
+his end of the circuit, but I was unable to verify his assertion.
+After many experiments attended by the same only partially successful
+results, I determined to reduce the size and weight of the spring as
+much as possible. For this purpose I fastened a piece of clock spring,
+about the size and shape of my thumbnail, firmly to the centre of the
+diaphragm, and had a similar instrument at the other end (fig. 14);
+we were then enabled to obtain distinctly audible effects. I remember
+an experiment made with this telephone, which at the time gave me
+great satisfaction and delight. One of the telephones was placed in my
+lecture-room in the Boston University, and the other in the basement
+of the adjoining building. One of my students repaired to the distant
+telephone to observe the effects of articulate speech, while I uttered
+the sentence, “Do you understand what I say?” into the telephone
+placed in the lecture-hall. To my delight an answer was returned
+through the instrument itself, articulate sounds proceeded from the
+steel spring attached to the membrane, and I heard the sentence, “Yes,
+I understand you perfectly.” It is a mistake, however, to suppose
+that the articulation was by any means perfect, and expectancy no
+doubt had a great deal to do with my recognition of the sentence;
+still, the articulation was there, and I recognised the fact that the
+indistinctness was entirely due to the imperfection of the instrument.
+I will not trouble you by detailing the various stages through which
+the apparatus passed, but shall merely say that after a time I produced
+the form of instrument shown in fig. 15, which served very well as
+a receiving telephone. In this condition my invention was exhibited
+at the Centennial Exhibition in Philadelphia. The telephone shown in
+fig. 14 was used as a transmitting instrument, and that in fig. 15 as
+a receiver, so that vocal communication was only established in one
+direction.
+
+[Illustration: FIG. 15.]
+
+‘The articulation produced from the instrument shown in fig. 15 was
+remarkably distinct, but its great defect consisted in the fact that it
+could not be used as a transmitting instrument, and thus two telephones
+were required at each station, one for transmitting and one for
+receiving spoken messages.
+
+‘It was determined to vary the construction of the telephone, and I
+sought by changing the size and tension of the membrane, the diameter
+and thickness of the steel spring, the size and power of the magnet,
+and the coils of insulated wire around their poles, to discover
+empirically the exact effect of each element of the combination, and
+thus to deduce a more perfect form of apparatus. It was found that a
+marked increase in the loudness of the sounds resulted from shortening
+the length of the coils of wire, and by enlarging the iron diaphragm
+which was glued to the membrane. In the latter case, also, the
+distinctness of the articulation was improved. Finally, the membrane
+of goldbeaters’ skin was discarded entirely, and a simple iron plate
+was used instead, and at once intelligible articulation was obtained.
+The new form of instrument is that shown in fig. 16, and, as had been
+long anticipated, it was proved that the only use of the battery was to
+magnetise the iron core of the magnet, for the effects were equally
+audible when the battery was omitted and a rod of magnetised steel
+substituted for the iron core of the magnet.
+
+‘It was my original intention, and it was always claimed by me, that
+the final form of telephone would be operated by permanent magnets in
+place of batteries, and numerous experiments had been carried on by Mr.
+Watson and myself privately for the purpose of producing this effect.
+
+[Illustration: FIG. 16.]
+
+‘At the time the instruments were first exhibited in public the results
+obtained with permanent magnets were not nearly so striking as when a
+voltaic battery was employed, wherefore we thought it best to exhibit
+only the latter form of instrument.
+
+‘The interest excited by the first published accounts of the operation
+of the telephone led many persons to investigate the subject, and I
+doubt not that numbers of experimenters have independently discovered
+that permanent magnets might be employed instead of voltaic batteries.
+Indeed one gentleman, Professor Dolbear, of Tufts College, not only
+claims to have discovered the magneto-electric telephone, but I
+understand charges me with having obtained the idea from him through
+the medium of a mutual friend.
+
+[Illustration: FIG. 17.]
+
+‘A still more powerful form of apparatus was constructed by using a
+powerful compound horseshoe magnet in place of the straight rod which
+had been previously used (see fig. 17). Indeed the sounds produced by
+means of this instrument were of sufficient loudness to be faintly
+audible to a large audience, and in this condition the instrument was
+exhibited in the Essex Institute, in Salem, Massachusetts, on February
+12, 1877, on which occasion a short speech shouted into a similar
+telephone in Boston, sixteen miles away, was heard by the audience in
+Salem. The tones of the speaker’s voice were distinctly audible to an
+audience of 600 people, but the articulation was only distinct at a
+distance of about 6 feet. On the same occasion, also, a report of the
+lecture was transmitted by word of mouth from Salem to Boston, and
+published in the papers the next morning.
+
+[Illustration: FIG. 18.]
+
+‘From the form of telephone shown in fig. 16 to the present form of
+the instrument (fig. 18) is but a step. It is in fact the arrangement
+of fig. 16 in a portable form, the magnet N S being placed inside the
+handle, and a more convenient form of mouthpiece provided.
+
+‘And here I wish to express my indebtedness to several scientific
+friends in America for their co-operation and assistance. I would
+specially mention Professor Peirce and Professor Blake, of Brown
+University, Dr. Channing, Mr. Clarke, and Mr. Jones. It was always my
+belief that a certain ratio would be found between the several parts of
+a telephone, and that the size of the instrument was immaterial; but
+Professor Peirce was the first to demonstrate the extreme smallness of
+the magnets which might be employed. The convenient form of mouthpiece
+shown in fig. 17, now adopted by me, was invented solely by my friend
+Professor Peirce.’
+
+[Illustration: FIG. 19.]
+
+Another form of transmitting telephone exhibited in Philadelphia,
+intended for use with the receiving telephone (fig. 15), is represented
+by fig. 19.
+
+A platinum wire attached to a stretched membrane completed a voltaic
+circuit by dipping into water. Upon speaking to the membrane,
+articulate sounds proceeded from the telephone in the distant room.
+The sounds produced by the telephone became louder when dilute
+sulphuric acid, or a saturated solution of salt, was substituted for
+the water. Audible effects were also produced by the vibration of
+plumbago in mercury, in a solution of bichromate of potash, in salt and
+water, in dilute sulphuric acid, and in pure water.
+
+Mr. Bell goes on to say:
+
+‘I have found also that a musical tone proceeds from a piece of
+plumbago or retort carbon when an intermittent current of electricity
+is passed through it, and I have observed the most curious audible
+effects produced by the passage of reversed intermittent currents
+through the human body. A rheotome was placed in circuit with the
+primary wires of an induction coil, and the fine wires were connected
+with two strips of brass. One of these strips was held closely against
+the ear, and a loud sound proceeded from it whenever the other slip was
+touched with the other hand. The strips of brass were next held one in
+each hand. The induced currents occasioned a muscular tremor in the
+fingers. Upon placing my forefinger to my ear a loud crackling noise
+was audible, seemingly proceeding from the finger itself. A friend who
+was present placed my finger to his ear, but heard nothing. I requested
+him to hold the strips himself. He was then distinctly conscious of a
+noise (which I was unable to perceive) proceeding from his finger. In
+this case a portion of the induced currents passed through the head of
+the observer when he placed his ear against his own finger; and it is
+possible that the sound was occasioned by a vibration of the surfaces
+of the ear and finger in contact.
+
+‘When two persons receive a shock from a Ruhmkorff’s coil by clasping
+hands, each taking hold of one wire of the coil with the free hand, a
+sound proceeds from the clasped hands. The effect is not produced when
+the hands are moist. When either of the two touches the body of the
+other, a loud sound comes from the parts in contact. When the arm of
+one is placed against the arm of the other, the noise produced can be
+heard at a distance of several feet. In all these cases a slight shock
+is experienced so long as the contact is preserved. The introduction
+of a piece of paper between the parts in contact does not materially
+interfere with the production of the sounds, but the unpleasant effects
+of the shock are avoided.
+
+‘When an intermittent current from a Ruhmkorff’s coil is passed through
+the arms, a musical note can be perceived when the ear is closely
+applied to the arm of the person experimented upon. The sound seems to
+proceed from the muscles of the fore-arm and from the biceps muscle.
+Mr. Elisha Gray[4] has also produced audible effects by the passage of
+electricity through the human body.
+
+‘An extremely loud musical note is occasioned by the spark of a
+Ruhmkorff’s coil when the primary circuit is made and broken with
+sufficient rapidity; when two rheotomes of different pitch are caused
+simultaneously to open and close the primary circuit, a double tone
+proceeds from the spark.
+
+‘A curious discovery, which may be of interest to you, has been made
+by Professor Blake. He constructed a telephone in which a rod of
+soft iron, about six feet in length, was used instead of a permanent
+magnet. A friend sang a continuous musical tone into the mouthpiece of
+a telephone, like that shown in fig. 17, which was connected with the
+soft iron instrument alluded to above. It was found that the loudness
+of the sound produced in this telephone varied with the direction in
+which the iron rod was held, and that the maximum effect was produced
+when the rod was in the position of the dipping-needle. This curious
+discovery of Professor Blake has been verified by myself.
+
+‘When a telephone is placed in circuit with a telegraph line, the
+telephone is found seemingly to emit sounds on its own account. The
+most extraordinary noises are often produced, the causes of which
+are at present very obscure. One class of sounds is produced by the
+inductive influence of neighbouring wires and by leakage from them, the
+signals of the Morse alphabet passing over neighbouring wires being
+audible in the telephone, and another class can be traced to earth
+currents upon the wire, a curious modification of this sound revealing
+the presence of defective joints in the wire.
+
+‘Professor Blake informs me that he has been able to use the railroad
+track for conversational purposes in place of a telegraph-wire, and
+he further states that when only one telephone was connected with the
+track the sounds of Morse operating were distinctly audible in the
+telephone, although the nearest telegraph-wires were at least forty
+feet distant; and Professor Peirce has observed the most curious sounds
+produced from a telephone in connection with a telegraph-wire during
+the aurora borealis.’
+
+Mr. Bell went on to describe instances in which airs sung or played
+upon a musical instrument are transmitted by a telephone, when
+it is not known whence they come; but the strongest proof of the
+extraordinary sensibility of this instrument consists in its becoming
+possible by its means to transmit speech through bodies which might
+be supposed to be non-conductors. Thus communication with the earth
+through the human body can be made in spite of the intervention of
+shoes and stockings; and it may even be effected if, instead of
+standing on the ground, the person stands on a brick wall. Only hewn
+stone and wood are a sufficient hindrance to communication, and if the
+foot touches the adjoining ground, or even a blade of grass, it is
+enough to produce electric manifestations.
+
+Mr. Bell says in conclusion:
+
+‘The question will naturally arise, Through what length of wire can the
+telephone be used? In reply to this, I may say that the maximum amount
+of resistance through which the undulatory current will pass, and yet
+retain sufficient force to produce an audible sound at the distant end,
+has yet to be determined; no difficulty has, however, been experienced
+in laboratory experiments in conversing through a resistance of 60,000
+ohms, which has been the maximum at my disposal. On one occasion, not
+having a rheostat at hand, I may mention having passed the current
+through the bodies of sixteen persons, who stood hand in hand. The
+longest length of real telegraph line through which I have attempted
+to converse has been about 250 miles. On this occasion no difficulty
+was experienced so long as parallel lines were not in operation. Sunday
+was chosen as the day on which it was probable other circuits would
+be at rest. Conversation was carried on between myself in New York,
+and Mr. Thomas A. Watson in Boston, until the opening of business upon
+the other wires. When this happened the vocal sounds were very much
+diminished, but still audible. It seemed, indeed, like talking through
+a storm. Conversation, though possible, could be carried on with
+difficulty, owing to the distracting nature of the interfering currents.
+
+‘I am informed by my friend Mr. Preece that conversation has been
+successfully carried on through a submarine cable, sixty miles in
+length, extending from Dartmouth to the Island of Guernsey, by means of
+hand telephones.’
+
+[Illustration: FIG. 20.]
+
+
+_Mr. Elisha Gray’s Share in the Invention of the Telephone._--We
+have seen that if Mr. Bell was the first to construct the speaking
+telephone in a practical form, Mr. Gray had at the same time conceived
+the idea of an instrument also capable of reproducing speech, and the
+description given of it in his _caveat_ was so precise that if it had
+been made from his design, it would have acted perfectly. This was, in
+fact, afterwards proved by him. In order that our readers may judge
+from their own knowledge of the share which should be ascribed to Mr.
+Elisha Gray in the invention of the telephone, we reproduce in fig. 20
+the drawing which accompanied the _caveat_ in question.
+
+The sender, as we see, is composed of a sort of tube, closed at its
+lower end by a membrane to which a platinum wire is fixed; this wire
+dips into a liquid of moderate conducting power, and an electrode made
+of platinum, in communication with a battery, is fixed at the bottom
+of the vessel containing the liquid. The receiver is composed of an
+electro-magnet, of which the armature is fixed to the centre of a
+membrane, stretched on a kind of resonator or ear-trumpet which is held
+to the ear, and the two instruments are united by the line wire as we
+see in the plate.
+
+Under these conditions, the undulatory currents necessary for the
+reproduction of speech were obtained in a mode analogous to that
+pointed out by Mr. Bell in his specification, that is, by the
+variations of resistance in the liquid layer interposed between the
+platinum wires of the transmitter; and their action, exerted on an
+electro-magnet, of which the armature was fixed on the diaphragm of the
+resonator, was produced under more favourable conditions than in Mr.
+Bell’s specification (see fig. 13), since that gentleman regards this
+arrangement (represented in fig. 14) as an important improvement on his
+first conception.
+
+The whole importance of the invention rests on the intervention of
+undulatory currents, which, as we have seen, are indispensable for the
+reproduction of speech, and it concerns us to know whether it was Mr.
+Bell or Mr. Gray who first declared their importance; for in both the
+specifications deposited on February 14, 1876, the use of undulatory
+currents was declared to be indispensable. Mr. Gray asserts that he had
+recognised their importance for the transmission of combined sounds
+as early as 1874; but Mr. Bell believes that the undulatory currents
+mentioned by Mr. Gray at that time were only currents analogous to
+those he had designated under the name of pulsatory currents, which
+we have represented in fig. 8. We have seen that since these currents
+only represent the abrupt elevations and depressions of intensity, they
+are unfit for the reproduction of articulate sounds, which, on the
+contrary, demand that the variations of intensity should result from
+successive efforts, in exact correspondence with all the inflections
+of the sonorous vibrations effected by the voice. Mr. Bell’s claim to
+priority on this question has been recognised by the American Patent
+Office, since he has been placed in possession of the patent. However
+this may be, Mr. Gray’s telephonic system was complete, and we see in
+it, as we have already said, the origin of the battery telephones,
+which have recently produced such important results. Let us now
+consider the relation which this system bears to Mr. Bell’s.
+
+The Bell system, as we have seen, although making use of a battery
+in the first instance, only obtained the diminution and increase of
+electric force necessary for the articulation of words by means of
+induction currents produced by the movements of an armature of soft
+iron, currents of which the intensity was consequently due to the
+range and inflections of these movements. The battery only intervened
+in order to communicate magnetic force to the inducer. This use of
+induced currents in telephonic transmissions was already of great
+importance, since various experiments subsequently made have proved
+their superiority to voltaic currents for this purpose. But experience
+soon convinced Mr. Bell that a powerful inductive apparatus worked by a
+battery was not only unnecessary for the action of this apparatus, but
+that a permanent magnet, very small and weak, would provide sufficient
+currents. This discovery, in which, as we have seen, Mr. Peirce had
+some share, was of great importance, since it became possible to
+reduce the size of the instrument considerably, so as to make it
+portable and adapted for sending and receiving; and it was shown that
+the telephone was the most sensitive of all instruments in revealing
+the action of currents. If, therefore, Mr. Bell was not the first to
+employ the successful mode of transmitting articulate words, it must
+be said that he sought, like Mr. Gray, to solve the problem by means
+of undulatory currents, and that he obtained these currents by the
+effect of induction, a system which, as soon as it was perfected, led
+to the important results with which we are all acquainted. If he had
+only given to the astonished world an instrument capable of reproducing
+speech telegraphically, his fame would be great; for this problem had
+hitherto been regarded as insoluble.
+
+Mr. Gray’s claims to the invention of the telephone are given in the
+following summary from a very interesting work, entitled ‘Experimental
+Researches on Electro-harmonic Telegraphy and Telephony:’
+
+‘1. I was the first to discover the means of transmitting compound
+sounds and variable inflections through a closed circuit by means of
+two or more electric waves.
+
+‘2. I assert that I was the first to discover and utilise the mode
+of reproducing vibrations by the use of a magnet receiver constantly
+supplied with electric action.
+
+‘3. I also assert that I was the first to construct an instrument
+consisting of a magnet with a circular diaphragm of magnetic substance,
+supported by its edge at a little distance from the poles of a magnet,
+and capable of being applied to the transmission and reception of
+articulate sounds.’
+
+It is a curious fact, worth recording here, that Mr. Yates, of Dublin,
+in 1865, when trying to improve Reiss’s telephone, realised to a
+certain extent Mr. Gray’s conception of the liquid transmitter; for he
+introduced into the platinum contacts of Mr. Reiss’s instrument a drop
+of water which adapted it for the reproduction of articulate sounds.
+However, no notice was then taken of this result.
+
+
+
+
+EXAMINATION INTO THE FUNDAMENTAL PRINCIPLES ON WHICH BELL’S TELEPHONE
+IS BASED.
+
+
+Although the preceding account would suffice to make the principle
+of Bell’s telephone intelligible to persons acquainted with electric
+science, this would not be the case with the majority of our readers,
+and we therefore think it necessary to enter into some details as to
+the source of the electric currents which are employed in telephonic
+transmissions. These details seem to us the more necessary, since
+many persons still believe that Bell’s telephones are not electric,
+because they do not require a battery, and they are often confounded
+with string telephones, so that the difference of price between Bell’s
+instruments and those hawked in the streets seems astonishing.
+
+Without defining what is meant by an electric current, which would
+be too elementary, we may say that electric currents can be produced
+by different causes, and that, in addition to those which are due to
+batteries, strong currents are also produced by the force exerted by
+magnets on a conducting circuit properly arranged. Such currents are
+called induction currents, and are used in Bell’s telephone. In order
+to understand how they are developed under these conditions, it will
+be enough to examine what takes place when the pole of a magnet is
+brought near to, and withdrawn from, a closed circuit. To do this, let
+us suppose a copper wire attached to a galvanometer in the form of a
+circle, and that one pole of a permanent magnet is directed towards the
+centre of the circle. Now observe what happens:
+
+1. At the moment when the magnet approaches an electric current arises,
+causing the galvanometer to deviate to one side. This deviation will
+be great in proportion to the extent of the movement, and the tension
+of the current will be great in proportion to the abruptness of the
+movement. The current will however be only instantaneous.
+
+2. At the moment when the magnet is withdrawn, a fresh current of the
+same nature will arise, but it will appear in an opposite direction
+from the former. It will be what is called a direct current, because it
+is in the same direction as the magnetic current of the magnet which
+produces it, while the other current is called _inverse_.
+
+3. If, instead of advancing or withdrawing the magnet by means of a
+single movement, it is advanced in jerks, a succession of currents
+in the same direction is produced, of which the existence can be
+ascertained by the galvanometer when there is a sufficient interval
+between the movements, but when the intervals are very slight the
+currents are interfused; and since inverse effects take place when the
+magnet is moved in a contrary direction, the needle of the galvanometer
+follows the movements of the magnet, and to a certain extent
+stereotypes them.
+
+4. If, instead of reacting on a simple closed circuit, the magnet
+exerts its force on a considerable number of circumvolutions of this
+circuit, that is, on a bobbin of coiled wire, the effects will be
+considerably increased, and they will be still greater if there be a
+magnetic core within the bobbin, since the inducing action will then
+be more effectually exerted throughout the bobbin. As the magnetic
+core, when it is magnetised and demagnetised under the influence of its
+approach to or withdrawal from the inducing magnet, is subject to the
+reaction from all the fluctuations which occur in the movements of the
+magnet, the induced currents which ensue are perfectly defined.
+
+5. If, instead of a movable magnet, we suppose it to be fixed in the
+centre of the coil, the induced currents of which we have spoken may
+then be determined by modifying its force. In order to do so, it is
+enough that an iron armature should react upon its poles. When this
+armature is brought close to one of the poles, or to both at once, it
+acquires force, and produces an inverse current, that is, a current
+in the direction which would have corresponded to an approach of the
+magnet to the closed circuit. On its withdrawal the inverse effect is
+produced; but in both cases the induced currents correspond with the
+extent and direction of the movements accomplished by the armature,
+and consequently they may reproduce its movements by their effects.
+If this armature is an iron plate, which vibrates under the influence
+of any sound in this disposition of the electro-magnetic system, the
+alternate movements of the plate will be transformed into the induced
+currents, and these will be stronger or weaker, more or less definite,
+according to the range and complexity of the vibrations: they will,
+however, be undulatory, since they will always result from successive
+and continuous movements, and will consequently be in the conditions
+which, as we have seen, are required for the transmission of speech.
+
+As for the action produced upon the receiver, that is, on the
+instrument for reproducing speech, it is somewhat complex, and we
+shall have occasion to speak of it presently; but we can get a general
+impression of it, if we consider that the effects produced by the
+induced currents of variable intensity, which traverse the coil of the
+electro-magnetic system, must determine, by the magnetisations and
+demagnetisations which ensue, the vibrations of the armature disk;
+these vibrations, more or less amplified and defined, exactly represent
+those of the disk before which the speaker stands, and can only be
+obtained from them. The effects are, however, in reality more complex,
+although they are produced under analogous conditions, and we shall
+have more to say about them when we come to speak of the experiments
+made with the telephone. It must meanwhile be observed that, for the
+reproduction of speech, it is not necessary that the magnetic core
+should be of soft iron, since the vibratory effects may follow from
+differential as well as from direct magnetisation.
+
+
+
+
+ORDINARY ARRANGEMENT OF THE BELL TELEPHONE.
+
+
+The arrangement most generally adopted for the telephone is the one
+represented in fig. 21. It consists of a kind of circular wooden
+box, fitted to the extremity of a handle M, which is also of wood,
+and contains the magnetic bar N S. This bar is fixed by means of a
+screw _t_, and is so arranged as to be moved forward and backward by
+tightening or loosening the screw, a condition necessary in order to
+regulate the instrument. At the free extremity of the bar the magnetic
+coil B is fixed; this must, according to MM. Pollard and Garnier, be
+made of wire No. 42, so as to present a considerable number of spirals.
+The ends of this coil generally terminate at the lower end of the
+handle in two copper rods _f_, _f_, which traverse its length, and are
+fastened to two binding-screws I, I′, where the line wires C, C are
+fixed. In the instruments made by M. Bréguet there are, however, no
+binding-screws, but a little twist, made of two flexible wires covered
+with gutta-percha and silk, is fastened to the two rods. A wooden cap
+is screwed to the end of the handle, and the twist passes through a
+hole made in this cap, so that there is no inconvenience in working the
+instrument. By laying hold of the ends of the wire twist with pliers it
+is possible to join them to the circuit. This instrument is represented
+in fig. 22.
+
+[Illustration: FIG. 21.]
+
+By another arrangement, the wires of the coil end immediately in
+the binding-screws which are placed below the wooden box, but this
+arrangement is inconvenient.
+
+Above the pole of the magnetic bar is placed the iron vibrating plate
+L L, which is coated either with black or yellow varnish, with tin
+or blue oxide, but which must always be very thin. This plate is in
+the form of a disk, and by its rim, resting on a caoutchouc ring, it
+is firmly fixed to the circular edges of the wooden box, which is for
+this purpose made in two pieces. These pieces are adjusted to each
+other, either by screws or by spirals cut in half the thickness of the
+wood. This disk ought to be as near as possible to the polar end of
+the magnet, yet not so near as to produce contact between the two by
+the vibrations of the voice. Finally, the mouthpiece R R′ (fig. 21),
+which is in form of a wide funnel, terminates the upper part of the
+box, and should be so arranged as to leave a certain space between the
+disk and the edges of the hole V, which is open in its centre. The
+size of the box should be so calculated as to permit of its acting as
+a sounding-box, without however provoking echoes and a confusion of
+sounds.
+
+[Illustration: FIG. 22.]
+
+When the instrument is properly made, it will produce very marked
+effects; and M. Pollard, one of the first Frenchmen to take up the
+study of telephones, has written as follows on the subject:
+
+‘The instrument which I have prepared gives results which are truly
+astonishing. In the first place, when considering the resistance, the
+introduction into the circuit of five or six persons does not sensibly
+diminish the intensity of sounds. On putting an instrument to each
+ear, the sensation is precisely the same as if the correspondent were
+speaking some yards behind. The intensity, the clearness, the purity of
+tone are irreproachable.
+
+‘I can speak to my colleague in quite an undertone, scarcely breathing
+as I may say, and persons placed within two yards of me will be unable
+to catch a single word of our conversation.
+
+‘On the part of the receiver, if anyone raises his voice to call me, I
+hear the call in all parts of my office, at least when silence prevails
+there; at any rate, when I am seated at my table with the instrument
+some yards off, I can always hear the call. In order to increase the
+intensity of sound, I fitted the mouthpiece with a copper horn of
+conical shape, and under these conditions words spoken in my bureau two
+or three yards from the mouthpiece can be heard at the other end of the
+line; from my station, a little more than a yard from the tube, I can
+hear and speak to my colleague without effort.’
+
+In using the ordinary Bell telephone, it is necessary to speak
+distinctly before the mouthpiece of the telephone which is handled,
+while the listener placed at the corresponding station keeps the
+mouthpiece of the receiver to his ear. These two instruments form
+a closed circuit with the two wires which connect them, but one is
+enough to make the transmission perfect, if care is taken to place
+both instruments in connection with the earth, which thus takes the
+place of the second wire. M. Bourbouze asserts that the intensity of
+sound in the telephone is much increased by employing this expedient,
+but we believe that this increase depends upon the conditions of the
+circuit, although he asserts that the fact can be proved in a circuit
+not exceeding eighty yards.
+
+For practical purposes it is necessary to have two telephones at each
+station, so as to hold one to the ear while speaking through the other,
+as in fig. 23. It is also much more easy to hear with a telephone
+applied to each ear, in which case they are held as in fig. 24. In
+order not to fatigue the arms, an arrangement has been made by which
+they are held before the ears by a strap and spring which goes round
+the head.
+
+[Illustration: FIG. 23.]
+
+The sending power of the telephone varies with different voices.
+Mr. Preece asserts that shouting has no effect, and that, in order
+to obtain a favourable result, the intonation must be clear, the
+articulation distinct, and the sounds emitted must resemble musical
+sounds as much as possible.
+
+Mr. Wilmot, one of the electricians employed by the Post Office,
+says that he has been able to make himself heard on circuits through
+which no other voices were audible. The vowel sounds are most readily
+transmitted, and among other letters _e_, _g_, _j_, _k_, and _q_ are
+always repeated more imperfectly. The ear requires practice, and
+the faculty of hearing varies in a surprising degree in different
+people. Singing is very distinctly heard, as well as wind instruments,
+especially the cornet-à-piston, which, when played in London, was heard
+by thousands of people in the Corn Exchange at Basingstoke.
+
+[Illustration: FIG. 24.]
+
+According to Mr. Rollo Russell, it is not necessary to isolate the
+circuit of a telephone when the distance is relatively slight; thus,
+with a circuit of about 430 yards, it is possible to use a simple
+copper wire, laid on the grass, without destroying the telephonic
+transmission from a small musical box, as long as the two wires do not
+touch each other. Transmission took place, even when the circuit was
+buried in moist earth for a length of thirty-five yards, or immersed in
+a well for a length of forty-eight yards. The words transmitted under
+such conditions did not differ from those transmitted by an isolated
+circuit.
+
+The telephone may be heard at the same moment by several listeners,
+either by connecting the wires which unite the telephones in
+correspondence (near the receiving telephone) with branch wires of
+other telephones, which may be done up to the number of five or six,
+in short circuits; or by means of a little sounding-box closed by two
+thin membranes, one of which is fixed on the vibrating disk. When a
+certain number of acoustic tubes are connected with the membrane, Mr.
+M’Kendrick asserts that several people can hear distinctly.
+
+Telephones may also transmit speech to different stations
+simultaneously, by inserting them on the same circuit, and experiments
+made at New York showed that five instruments placed in different parts
+of the same telegraphic line could be made to speak in this way. In
+the telephonic experiments made on the canal lines in the department
+of the Yonne, it was ascertained that on a wire seven miles and a
+half in length, on which several telephones were placed at varying
+distances, three or four persons were able to converse with each other
+through the telephones, and each could hear what the other was saying.
+The questions and answers could be understood, even in crossing. It
+was also possible, by placing a telephone on a second wire, a little
+over five miles in length, and half a yard distant from the other, to
+hear the conversation exchanged on the first wire by following it to a
+distance not exceeding a mile and a quarter. Even the different voices
+of the two speakers could be distinguished.
+
+Since the telephone made its appearance in Europe, several inventors
+have asserted that they are able to make a telephone speak so as to be
+audible in all parts of a large hall. It has been shown that this was
+accomplished by Mr. Bell, and in this respect we do not see that those
+who have attempted to improve the telephone have attained results of
+greater importance. It is certain that the ordinary telephone can emit
+musical sounds which become perfectly audible in a tolerably large
+room, while the instrument is still attached to the wall. We should
+also remember the results obtained by MM. Pollard and Garnier in the
+experiments made at Cherbourg to connect the mole with the _Préfecture
+Maritime_.
+
+The mole at Cherbourg is, as we know, a kind of artificial island
+thrown up before the town in order to make an anchorage. The forts
+which have been constructed on the mole are connected by submarine
+cables with the military port and with the _Préfecture Maritime_. On
+one occasion, after making experiments in the Préfet’s study on one
+of the cables applied to a telephone, several persons were talking
+together in the room, and were much surprised to hear the bugle sound
+the retreat, the sound appearing to come from one part of the room.
+It was found, on examination, that the telephone hung to the wall was
+occupied with this performance. On enquiry, it appeared that one of
+the manipulators on the mole station had amused himself by sounding
+the bugle before the telephone on that station. The mole is more than
+three miles from Cherbourg, and the _Préfecture Maritime_ is in the
+centre of the town. Yet these telephones had been roughly made in the
+dockyard workshops; and we have here another proof of the small amount
+of accuracy required for the successful working of these instruments.
+
+[Illustration: FIG. 25.]
+
+Telephones of various construction on the Bell model are to be seen at
+M. C. Roosevelt’s, Mr. Bell’s agent in Paris, 1, Rue de la Bourse. They
+are, for the most part, constructed by M. Bréguet, and the model in the
+greatest request, exclusive of the one we have described, is the great
+square model, with a horseshoe magnet enclosed in a flat box, and a
+horn on its upper side, which serves as a mouthpiece. This system is
+represented in fig. 25, and it has been neatly constructed at Boston
+under the best conditions. In this new model, made by Mr. Gower, the
+magnet is composed of several plates terminated by magnetic cores of
+iron, to which the coils are fixed, and the whole is covered with a
+thick layer of paraffin. The sounds thus reproduced are much stronger
+and more distinct. Mr. Gower, who is now Mr. Roosevelt’s partner, has
+made considerable improvements in the different forms of Mr. Bell’s
+instrument. There is one model in the form of a snuff-box, in which
+the magnet is twisted into a spiral, so as to maintain its length in
+a circular form. The pole, which is in the centre of the spiral, is
+furnished with an iron core, to which the induction coil is fastened,
+and the cover of the snuff-box supports the vibrating disk as well
+as the mouthpiece: this model is represented in fig. 26. In another
+model, called the mirror telephone, the preceding arrangement is fitted
+on to a handle like the glass of a portable mirror, and there is a
+mouthpiece on one of the lateral faces, so that the speaker uses the
+instrument as if he were speaking before a chimney screen.
+
+[Illustration: FIG. 26.]
+
+Mr. Bailey has different models of telephones worked by a battery or by
+the Edison carbon of which we shall speak presently, and these, as well
+as the telephones by Messrs. Gray and Phelps, are more successful in
+conveying sound on a long line of wire.
+
+
+DIFFERENT ARRANGEMENTS OF TELEPHONES.
+
+The prodigious results attained with the Bell telephones, which were
+at first discredited by many scientific men, necessarily provoked,
+as soon as their authenticity was proved, innumerable researches on
+the part of inventors, and even of those who were originally the most
+incredulous. A host of improvements and modifications have consequently
+been suggested, which are evidently not without interest, and must now
+be considered by us.
+
+
+
+
+BATTERY TELEPHONES.
+
+
+_The Edison Telephone._--One of the earliest and most interesting
+improvements made in the Bell telephone is that introduced by Mr.
+Edison in the early part of the year 1876. This system is indeed more
+complicated than the one we have just considered, since it requires
+a battery, and the sending instrument differs from the receiving
+instrument; but it is less apt to be affected by external causes, and
+transmits sound to a greater distance.
+
+The Edison telephone, like Mr. Gray’s, which we have already had
+occasion to mention, is based upon the action of undulatory currents,
+determined by the variations in the resistance of a conductor of
+moderate conducting power, which is inserted in the circuit, and the
+vibrations of a diaphragm before which the speaker stands react upon
+it. Only, instead of employing a liquid conductor, which is practically
+useless, Mr. Edison has attempted to use semi-conducting solid
+bodies. Those which were most suitable from this point of view were
+graphite and carbon, especially the carbon extracted from compressed
+lamp-black. When these substances are introduced into a circuit between
+two conducting plates, one of which is moveable, they are capable of
+modifying the resistance of the circuit almost in the same proportion
+as the pressure exerted upon them by the moveable plate,[5] and it
+was seen that, in order to obtain the undulatory currents necessary
+for the production of articulate sounds, it was enough to introduce
+a disk of plumbago or of lamp-black between the vibrating plate of a
+telephone and a platinum plate placed in connection with the battery.
+When the telephone disk is placed in circuit, its vibrations before
+the disk of carbon produce a series of increasing and decreasing
+pressures, thus causing corresponding effects in the intensity of the
+transmitted current, and these effects react in an analogous manner on
+the undulatory currents determined by induction in the Bell system. In
+order to obtain good results, however, several accessory arrangements
+were necessary, and we represent in fig. 27 one of the arrangements
+made in this part of Mr. Edison’s telephonic system.
+
+[Illustration: FIG. 27.]
+
+In this figure a section of the instrument is given, and its form
+greatly resembles that of Bell. L L is the vibrating disk; O′ O, the
+mouthpiece; M, the opening to the mouthpiece; N N N, the case for the
+instrument, which is, like the mouthpiece, made of ebonite, and below
+the disk it presents a rather large cavity, and a tubular hole which
+is scooped in the handle. In its upper part this tube terminates in a
+cylindrical rim, furnished with a worm on which is screwed a little
+rod with a ridge on its inner side, and the rheostatic system is
+placed within this tube. The system consists, first, of a piston E,
+fitted to the end of a long screw E F, and the turning of the button
+will move the piston up or down within a certain limit. Above this
+piston there is fitted a very thin platinum plate A, connected by a
+flexible chain and a wire with a binding-screw P′. Another plate B,
+exactly similar, is connected with the binding-screw P, and the carbon
+disk C is placed between these two plates. This disk is composed of
+compressed lamp-black and petroleum, and its resistance is one _ohm_,
+or 110 yards, of telegraphic wire. Finally, an ebonite disk is fastened
+to the upper platinum plate, and an elastic pad, composed of a piece
+of caoutchouc tube G, and of a cork disk H, is interposed between the
+vibrating plate L L and the disk B, in order that the vibrations of
+the plate may not be checked by the rigid obstacle formed by the whole
+rheostatic system. When these different parts are in position, the
+instrument is regulated by the screw F, and this is easily done by
+screwing or unscrewing it until the receiving telephone gives out its
+maximum of sound.
+
+[Illustration: FIG. 28.]
+
+In another model, represented in fig. 28, which has produced the best
+results in the distinctness with which sounds are transmitted, the
+vibrating plate L L is supported on the disks of the secondary carbon
+conductor C by means of a little iron cylinder A, instead of the
+caoutchouc pad, and the pressure is regulated by a screw placed below
+_e_. The mouthpiece E of the instrument is more prominent, and its
+opening is larger. Finally, the instrument, which is cased in nickel
+silver, is without a handle. The rigid disk _b_, resting on the first
+platinum plate _p_, is of aluminium instead of ebonite.
+
+[Illustration: FIG. 29.]
+
+The receiving telephone somewhat resembles that of Mr. Bell, yet it
+presents some differences which can be understood from the examination
+of fig. 29. The magnet N S is horseshoe in form, and the magnetising
+coil E only covers one of the poles, N: this pole is precisely in
+the centre of the vibrating plate L L, while the second pole is near
+the edge of this plate. The size of the plate itself is considerably
+reduced: its superficies is about the same as that of a five-franc
+piece, and it is enclosed in a kind of circular groove, which keeps
+it in a definite position. In consequence of this arrangement the
+handle of the instrument is of solid wood, and the vacant space for
+the electro-magnetic system is somewhat larger than in the Bell model;
+but an arrangement is made for subduing the echo, and there is a kind
+of sounding-box to magnify the sound. It is evident that the relation
+which the electro-magnetic system bears to the vibrating disk must
+increase the sensitiveness of the instrument; for as the pole S is in
+close contact with the disk L L, the latter is polarised, and becomes
+more susceptible to the magnetic influence of the second pole N, which
+is separated from it by an interval not exceeding the thickness of a
+sheet of coarse paper. In Mr. Edison’s two instruments, the receiver
+and sender, the upper part C C, corresponding to the vibrating disk,
+instead of being fixed by screws to the handle, is screwed on to the
+handle itself, which makes it much more easy to dismount the instrument.
+
+Mr. Edison has varied the form of his instruments in many ways, and
+their cases have of late been made of metal with a funnel-shaped
+mouthpiece of ebonite.
+
+When Mr. Edison had ascertained, as indeed Mr. Elisha Gray had done
+before him, that induced currents are more favourable to telephonic
+transmissions than voltaic currents, he transformed the currents from
+the battery which passed through his sender into induced currents by
+making them pass through the primary circuit of a carefully insulated
+induction coil; the line wire was then put into communication with
+the secondary wire of the coil. We shall afterwards describe some
+experiments which show the advantages of this combination: for the
+present we can only point out the fact, for it is now an integral
+quality of almost all the systems of battery telephones.
+
+
+_Edison’s Chemical Telephone._--The curious and really useful effects
+produced by Mr. Edison with his _electro-motograph_ prompted, about the
+beginning of the year 1877, his idea of applying the principle of this
+instrument to the telephone for the reproduction of transmitted sounds;
+and he obtained such interesting results that the author of an article
+on telephones, published in the ‘Telegraphic Journal,’ August 15, 1877,
+put forward this invention as one of the finest of the nineteenth
+century. It certainly appears to have given birth to the phonograph,
+which has lately become famous, and has so much astonished men of
+science.
+
+To understand the principle of this telephone, we must give some
+account of Mr. Edison’s electro-motograph, discovered in 1872. This
+instrument is based upon the principle that if a sheet of paper,
+prepared with a solution of hydrate of potash, is fastened on a
+metallic plate which is united to the positive pole of a battery, and
+if a point of lead or platinum connected with the negative pole is
+moved about the paper, the friction which this point encounters ceases
+after the passage of the current, and it is then able to slide as if
+upon a mirror until the current is interrupted. Now, as this reaction
+may be effected instantaneously under the influence of extremely weak
+currents, the mechanical effects produced by these alternations of
+arrest and motion may, by a suitable arrangement of the instrument,
+determine vibrations in correspondence with the interruptions of
+current produced by the transmitter.
+
+In this system the telephonic receiver consists of a resonator and a
+drum mounted on an axis and turned by a winch. A paper band, wound
+upon a reel, passes over the drum, of which the surface is rough, and
+a point tipped with platinum, and fitted to the end of a spring which
+is fixed in the centre of the resonator, presses strongly on the paper.
+The current from the battery, first directed on the spring, passes
+by the platinum point through the chemical paper, and returns by the
+drum to the battery. On turning the winch, the paper moves forward,
+and the normal friction which is produced between the paper and the
+platinum point pushes the point forward, while producing by means
+of the spring a tension on one side of the resonator; but since the
+friction ceases at each passage of the current through the paper, the
+spring is no longer drawn out, and the resonator returns to its normal
+position. Since this double effect is produced by each vibration made
+in the sender, a series of vibrations takes place in the resonator,
+repeating those of the sender, and consequently the musical sounds
+which affected the sender are reproduced to a certain extent. According
+to the American journals, the results produced by this instrument
+are astonishing: the weakest currents, which would have no effect
+on an electro-magnet, become perfectly efficacious in this way. The
+instrument can even reproduce with great intensity the highest notes of
+the human voice, notes which can hardly be distinguished by the use of
+electro-magnets.
+
+The sender nearly resembles the one we have previously described,
+except that, when it is used for musical sounds, a platinum point
+is employed instead of the disk of carbon, and it ought not to be
+in constant contact with the vibrating plate. According to the
+‘Telegraphic Journal,’ it consists simply of a long tube, two inches
+in diameter, having one end covered with a diaphragm formed of a thin
+sheet of copper, and kept in its place by an elastic ring. A small
+platinum disk is riveted to the centre of the copper diaphragm, and a
+point of the same metal, fitted with a firm support, is adjusted before
+the disk. When the singer stands before the diaphragm, its vibration
+causes it to touch the platinum point, and produces the number of
+breaks in the current which corresponds to the vibration of the notes
+uttered.
+
+The experiments lately made in America, in order to decide on the
+merits of various telephonic systems, show that Mr. Edison’s telephone
+gives the best results. The ‘Telegraphic Journal,’ May 1, 1878, states
+that on April 2 Mr. Edison’s carbon telephone was tested between New
+York and Philadelphia on one of the numerous lines of the West Union.
+The length of the line was 106 miles, and ran parallel to other wires
+almost throughout its length. The effects of induction caused by
+telegraphic transmissions through the adjacent wires were enough to
+make speech inaudible through the other telephones, but they had no
+influence on Edison’s telephone, which was worked with a battery of two
+cells and a small induction coil, and Messrs. Batchelor, Phelps, and
+Edison were able to converse with ease. Mr. Phelps’ magnetic telephone,
+which is considered to be the most powerful of its kind, did not afford
+such good results.
+
+In the experiments made between the Paris Exhibition building and
+Versailles, the jury commission was able to ascertain that the results
+were equally favourable.
+
+
+_Telephones by Colonel Navez._--Colonel Navez of the Belgian Artillery,
+inventor of the well-known balistic chronograph, has endeavoured to
+improve the Edison telephone by employing several disks of carbon
+instead of one. He considers that the variations of electric resistance
+produced by carbon disks under the influence of unequal pressure
+depend chiefly on their surface of contact, and he consequently
+believes that the more these surfaces are multiplied, the greater
+the differences in question will be, just as it happens when light
+is polarised through ice. He adds that these disks act well by their
+surfaces of contact, since, if they are separated by copper disks, the
+speech reproduced ceases to be articulate.[6]
+
+I am not surprised to learn that Colonel Navez has found a limit to the
+number of carbon disks, for the reproduction of speech in this system
+is due both to the greatness of the differences of resistance in the
+circuit, and to the intensity of the transmitted current. If therefore
+the instrument’s sensitiveness to articulate sounds is increased
+by increasing the number of imperfect contacts in the circuit, the
+intensity of the transmitted sounds is diminished, and thus sounds lose
+their power. There is consequently a limit to be observed in the number
+of carbon disks placed upon each other; and it depends on the nature of
+the imperfect contacts which are employed, and on the tension of the
+electric generator.
+
+In order to stop the unpleasant musical vibrations which accompany
+telephonic transmissions, Colonel Navez employs for the vibrating plate
+of the sender a silver-plated copper disk, and for the vibrating plate
+of the receiver an iron disk lined with brass and soldered together. He
+also employs caoutchouc tubes with mouthpieces and ear-tubes for the
+transmission and reception of sound, and these instruments are placed
+level on a table. For this purpose the magnetised bar of the receiving
+telephone is replaced by two horizontal magnets, acting through a pole
+of the same nature on a little iron core which carries the coil, and
+which is placed vertically between the two magnets. He necessarily
+makes use of a small Ruhmkorff coil to transform the electricity of the
+battery into induced electricity.
+
+[Illustration: FIG. 30.]
+
+[Illustration: FIG. 31.]
+
+Figs. 30 and 31 represent the two parts of this telephonic system. The
+carbon battery is in C (fig. 30), the vibrating disk in L L, and the
+mouthpiece E, fitted to a caoutchouc tube T E, corresponds at the lower
+end to the vibrating disk. The carbon battery is placed in metallic
+contact with the circuit by a platinum rod E C, and the vibrating disk
+also communicates with the circuit through a binding-screw. In the
+receiving telephone (fig. 31) the upper part is arranged much as in
+the ordinary telephones, except that, instead of a mouthpiece, the
+instrument is fitted with an ear-tube T O. The two horseshoe magnets,
+A, A, which communicate a uniform polarity to the iron core N, support
+the induction coil B. The two terminals of this receiver are connected
+with the supplementary wire of the induction coil, and the two
+terminals of the sender are connected with the two ends of the primary
+of this coil, and with the battery which is inserted in the circuit
+near this instrument.
+
+
+_The Pollard and Garnier Telephones._--The battery telephone made
+by MM. Pollard and Garnier differs from the foregoing in this
+particular: it simply employs two points of graphite, mounted in
+metallic porte-crayons, and these points are directly applied against
+the vibrating plate with a pressure which must be regulated. Fig. 32
+represents the arrangement adopted, which, however, may be infinitely
+varied.
+
+L L is the vibrating tin plate, above which is the mouthpiece E, and
+P, P′ are the two graphite points with their porte-crayons. There is a
+screw on the lower part of the porte-crayons which is fixed in a hole
+pierced in a metallic plate C C, and by this means the pressure of the
+pencils against the disk L L can be regulated. The metallic plate C C
+is made in two pieces, placed side by side, but insulated from each
+other, so that they may be placed in communication with a cylindrical
+commutator, and by its means the circuit can be arranged in different
+ways. Since the commutator consists of five sheets, the transition from
+one combination to another is instantaneous, and these combinations are
+as follows:
+
+1. The current enters by the pencil P, passes into the plate, and so to
+line.
+
+2. The current enters by the pencil P′, passes into the plate, and so
+to line.
+
+3. The current comes simultaneously by the two pencils P and P′, goes
+into the plate, and thence to line.
+
+4. The current comes by the pencil P, goes thence to the plate, then
+into the pencil P′, and so to line.
+
+[Illustration: FIG. 32.]
+
+By this means there are two elements of combination, which may be
+employed separately, or by coupling them for tension or quantity.
+
+When the pencils are properly regulated and give a regular transmission
+of equal intensity, the effects produced in the transition from
+one combination to another may be easily studied, and it has been
+ascertained: first, that in a short circuit there is no appreciable
+change, whatever be the combination employed; secondly, that when the
+circuit is long, or of great resistance, the tension arrangement is the
+best, and this in proportion to the length of the line.
+
+This telephonic system, like the two preceding ones, requires an
+inducing machine to transform voltaic into induced currents: we shall
+presently speak of this important accessory of these instruments.
+
+Besides this arrangement, MM. Pollard and Garnier have employed the one
+we have represented in fig. 5, which has given better results. We shall
+see presently that it can be used as the receiving organ of sounds. In
+each case the two carbons must be placed in contact, and subjected to a
+certain initial pressure, which should be regulated by the screw fitted
+to the support of the lower carbon.
+
+As for the receiving telephone, the arrangement adopted by MM. Pollard
+and Garnier is the same as Bell’s, except that they employ tin plates
+and helices of greater resistance. This resistance ranges in fact
+from 100 to 125 miles. ‘We have always held,’ these gentlemen say,
+‘that whatever may be the resistance of the outer circuit, there is an
+advantage in increasing the number of spirals, even when using wire
+No. 42, which is the one we prefer.’
+
+[Illustration: FIG. 33.]
+
+
+_M. Hellesen’s Reaction Telephone._--M. Hellesen believed that the
+vibrations produced by the voice on the carbon of a telephonic sender
+would be magnified if the moveable part of the rheotome were subjected
+to an electro-magnetic action resulting from the vibrations themselves,
+and he has contrived a sender, which is based on the principle shown
+in fig. 33, and which has the merit of forming in itself the inducing
+apparatus intended to transform the voltaic currents employed. This
+instrument is composed of a vertical iron tube, supported on a
+magnetic bar N S, and surrounded by a magnetising coil B B, above
+which is fixed an inducing helix of fine wire I I, communicating with
+the circuit. Within the tube there is a lead pencil C, held by a
+porte-crayon which can be raised or lowered by means of a screw V fixed
+below the magnetic bar. Finally, above this pencil, there is an iron
+vibrating plate L L, with a platinum point in communication with the
+battery in its centre; the local circuit communicates with the pencil
+by means of the magnetising helix B, and for this purpose one end is
+soldered to the iron tube.
+
+From this arrangement it follows that the vibrations of the plate L
+L, at the moment when it comes nearest to the pencil, tend to become
+greater in consequence of the attractive force exerted on the plate,
+and as the pressure of the lead pencil is increased, it increases the
+differences of resistance which result from it, and consequently causes
+greater variations in the intensity of the transmitted currents.
+
+
+_Reaction Telephone of Messrs. Thomson and Houston._--The telephonic
+arrangement we have described has lately been adopted by Mr. Elihu
+Thomson and Mr. Edwin J. Houston, who, on June 21, 1878, two months
+after M. Hellesen explained his system to me,[7] published an article
+in ‘The English Mechanic and World of Science’ about an instrument
+very similar to that of M. Hellesen.
+
+In their instrument, the current, which passes through a body of
+moderately conducting capacity, acts on an electro-magnet provided with
+an induction coil, and this electro-magnet reacts on the diaphragm,
+in order to increase the range of its vibrations, and to create at
+the same moment two electric actions in the same direction: the only
+difference lies in the arrangement of the contact of this indifferent
+conductor with the vibrating plate. Instead of a simple contact
+effected by pressure between this plate and a carbon pencil, a fragment
+of the same substance with a sharpened point is fixed on the vibrating
+plate, and it dips into a drop of mercury which has been poured into
+the receptacle made for it at the upper end of the electro-magnet.
+In other respects, the arrangement of the instrument is that of an
+ordinary telephone, and the iron rod of the electro-magnet represents
+the magnetised bar of the Bell telephone. The inventors assert that
+this instrument can be used both as a sender and receiver, and it is in
+the following manner that it is worked in each case.
+
+When the instrument is transmitting, the morsel of carbon dips more or
+less into the mercury, and consequently differences are produced in the
+surfaces of contact, according to the range of vibrations made by the
+plate; the current varies in intensity in proportion to this range, and
+induced currents in the induction coil result from these variations;
+the induced currents react on the receiving telephone, as in Bell’s
+instrument, and are further strengthened by those which are produced
+electrically by the movement of the diaphragm before the induction
+coil, and the iron of the electro-magnet.
+
+When the instrument is used as a receiver, the usual effects are
+displayed, for since the iron of the electro-magnet is magnetised by
+the current, its conditions are precisely those of the ordinary Bell
+telephone, and the induced currents reach it in the same manner, only
+with greater intensity. Messrs. Thomson and Houston assert that their
+system has produced excellent results, and that by it the sound of the
+voice is much less altered than in other telephones.
+
+
+_Telephones with batteries and liquid senders._--We have seen that in
+1867 Mr. Gray conceived the idea of a telephonic system based on the
+differences of resistance effected in a circuit completed by a liquid,
+when the layer of liquid interposed between the electrodes varies in
+thickness under the influence of the vibrations of the telephonic plate
+which is in communication with one of these electrodes. This system
+has since been the subject of study by several inventors, among others
+by MM. Richemond and Salet; and I give some of the accounts which have
+been published respecting their researches.
+
+Another telephone for the reproduction of articulate sounds, which
+M. Richemond terms the _electro-hydro telephone_, has been recently
+patented in the United States. It resembles that of Mr. Edison in
+some respects, but instead of making use of carbon disks to modify
+the resistance of the circuit, water is employed, and this water is
+placed in communication with the circuit and battery by means of two
+platinum points, one of which is fixed on the metallic diaphragm which
+vibrates under the influence of the voice. As the vibrations of the
+diaphragm transport the point which is attached to it to different
+parts of the interpolar layer of liquid, they diminish or increase the
+electric resistance of this layer, and cause corresponding variations
+in the intensity of the current traversing the circuit. The receiving
+telephone is of the usual kind. (See ‘Telegraphic Journal,’ September
+15, 1877.)
+
+M. Salet writes: ‘I thought it would be interesting to construct a
+telephone in which there should be absolute solidarity in the movements
+of the two membranes, and for this purpose I have availed myself of the
+great resistance of liquids. Mr. Bell had already obtained some results
+by attaching to the vibrating membrane a platinum wire communicating
+with a battery, and dipping more or less into a metallic vessel, itself
+connected by the line with the receiving telephone and containing some
+acidulated water. I have substituted for the platinum wire a small
+aluminium lever supporting a disk of platinum, and at a very slight
+distance from it there is a second disk in connection with the line.
+The vibrations of the membrane, tripled or quadrupled in their range,
+are not altered in form, thanks to the small size and light weight of
+the lever: they cause variations in the thickness of the liquid layer
+traversed by the current, and consequently in its intensity, and these
+variations cause corresponding differences in the attractive force
+of the receiving electro-magnet. Under its influence the receiving
+membrane executes movements which are identical with those of the
+sending membrane. The sound transmitted is very distinct, and its
+_timbre_ is perfectly maintained, a result which might have been
+anticipated. The consonants, however, are not so clearly pronounced
+as those transmitted by Mr. Bell’s instrument. This inconvenience is
+most apparent when the lever is heavy, and might easily be obviated.
+The electrolysis also produces a continual murmur, but this does not
+interfere with the distinctness of the sound.
+
+‘Since on this system the voice is not required to _produce_, but only
+to _direct_ the electric current generated by a battery, the intensity
+of the sound received might in theory be increased at pleasure. I have
+in fact been able to make the receiver emit very powerful sounds, and
+I think that this advantage greatly counterbalances the necessity of
+employing a battery, and a somewhat delicate sending instrument.
+Unfortunately it can only be used for moderate distances. Assuming that
+any displacement of the transmitting membrane increases the resistance
+to a degree equivalent to five or six hundred yards of wire: if the
+line is five hundred yards long, the intensity of the current will be
+reduced by one half, and the receiving membrane will take up a fresh
+position, considerably differing from the first; but if the line is
+three hundred miles in length, the intensity of the current will only
+be modified by a thousandth part. An immense battery must therefore be
+employed in order that this variation may be translated by a sensible
+change in the position of the receiving membrane.’ (See ‘Comptes Rendus
+de l’Académie des Sciences,’ February 18, 1878.)
+
+M. J. Luvini, in an article inserted in ‘Les Mondes,’ March 7,
+1878, has suggested a system of rheotome by means of a current, for
+battery telephones, which, although complicated, possibly offers some
+advantages, since it produces currents alternately reversed. In this
+system, the vibrating disk of the sender, which should be in a vertical
+position, reacts on a moveable horizontal wire, turned back at a right
+angle, and supporting on each of its branches two platinum points
+which dip into two bulbs, filled with a liquid of moderate conducting
+capacity. The two branches of this wire, insulated from each other, are
+placed in communication with the two poles of the battery, and the
+four cups into which the platinum wire dips communicate inversely with
+the line and the earth by means of platinum wires immoveably fixed in
+the cups. It follows from this arrangement, that when the distances
+are duly regulated between the fixed and moveable wires, two equal
+currents will be opposed to each other across the line circuit when the
+diaphragm is motionless; but as soon as it vibrates, the respective
+distances of the wires will vary, and it follows from this that there
+will be a differential current, of which the intensity will correspond
+with the extent of the displacement of the system, or with the range
+of vibrations, and the direction will vary with the movements above or
+below the line of the nodes of vibration. In this way the advantage of
+the induced currents is obtained.
+
+
+_Telephones with a battery and voltaic arcs._--In order to obtain
+variations of resistance of still greater sensitiveness than is the
+case with liquids or pulverised substances, the idea has been suggested
+of employing conductors of heated gas, and several arrangements of
+battery telephones have been made in which the circuit was completed
+by a stratum of air, separating the vibrating disk from a platinum
+point, which serves to excite an electric discharge of high tension.
+Under these conditions, the stratum of air becomes the conductor, and
+the intensity of the current which traverses it corresponds to its
+thickness. This problem has been solved, either by means of voltaic
+currents of high tension, or by a Ruhmkorff coil.
+
+The former system was arranged by M. Trouvé, and he writes as follows
+on the subject in the journal ‘La Nature’ of April 6, 1878: ‘A metallic
+vibrating membrane forms one of the poles of a high tension battery;
+the other pole is fastened before the disk by a micrometer screw which
+can be adjusted so as to vary the distance from the disk according to
+the tension of the battery, but without ever coming in contact with it.
+The distance must not in any case exceed that to which the discharge
+of the battery can extend. Under these conditions, the membrane which
+vibrates under the influence of the waves of sound has the effect of
+constantly modifying the distance between the two poles, and thus
+of continually varying the intensity of the current: consequently
+the receiving instrument (a Bell telephone, or telephone with an
+electro-magnet) is subjected to magnetic variations, corresponding to
+the variations of the current which affect it, and this has the effect
+of making the receiving instrument vibrate at the same moment. This
+kind of telephonic instrument relies, therefore, on the possibility of
+varying within wide limits the resistance of the outer circuit of a
+high-tension battery, in which the poles are not in contact. In order
+to vary the conditions of this resistance, it is also possible to
+interpose some vapour or other medium, such as air, or gas of greater
+or less rarity.’
+
+M. Trouvé thinks that he was successful with his battery of small
+disks, moistened with sulphate of copper and sulphate of zinc,
+arranging these elements, to the number of five or six hundred, in
+glass tubes of small diameter. It is well known that it is unnecessary
+for the elements to be of large size in order to obtain tension
+currents.
+
+M. de Lalagade has suggested an analogous mode by employing for the
+formation of the arc a current of which the tension is increased by
+inserting a strong electro-magnet into the circuit. This electro-magnet
+acts on a Hughes magnet in order to produce induction currents capable
+of making the receiving instrument act. M. de Lalagade says that a
+Bunsen battery, or one of six cells with bichromate of potash, will
+be enough to produce a continuous voltaic arc between the vibrating
+plate of a telephone and a platinum point which is sufficiently remote
+to avoid contact. It is necessary, however, to begin with a contact,
+in order to produce the formation of this arc. In M. de Lalagade’s
+system, the vibrating plate should have in its centre a small platinum
+plate, in order to obviate the oxidising effects of the spark. The
+inventor asserts that sounds transmitted in this way, and reproduced
+in a telephone of which the electro-magnetic system is set upon a
+sounding-box, will have greater intensity than the sounds transmitted
+by an ordinary telephone, and the speaker will appear to be close to
+the ear.
+
+
+_Mercury Telephones._--These systems are based on the physical
+principle discovered by M. Lippmann, that if a layer of acidulated
+water is placed above mercury, and connected with it by an electrode
+and wire, every mechanical action which exerts pressure on the surface
+of the mercury, and alters the form of its meniscus, will cause an
+electric reaction, capable of producing a current with a force which
+corresponds to the mechanical action exerted. Conversely, every
+electric action produced on the circuit of such a system will occasion
+a displacement of the meniscus, and consequently its movement, which
+will be more marked in proportion to the smallness of the tube in which
+the mercury is placed, and to the greatness of the electric action.
+This electric action may result from a difference of potential in
+the electric condition of the two extremities of the circuit, which
+communicate with the electric source employed, or with some electric
+generator.[8]
+
+[Illustration: FIG. 34.]
+
+In accordance with these effects, it is intelligible that if two tubes
+T T, pointed at the end, and containing mercury, are plunged into
+two vessels V V (fig. 34) containing acidulated water and mercury,
+and metallic wires, P P, Q Q, are used, first to connect the columns
+of mercury in the tubes, and secondly the layers of mercury at the
+bottom of the two vessels, the tubes being a little removed from
+the surface of the mercury in the vessels, we shall then have a
+metallic circuit, completed by two electrolytes, one of which will
+be subjected to the mechanical or electrical effects produced in the
+other. If two vibratory plates B B are placed above the tubes, and
+one of these is caused to vibrate, the other will reproduce these
+vibrations, influenced by the vibratory movements communicated by the
+corresponding column of mercury. The vibrations themselves will be in
+connection with the electrical discharges resulting from the movements
+of the column of mercury in the first tube, which are mechanically
+produced. If an electric generator is introduced into the circuit, the
+effect which we have just analysed will be caused by modifications in
+the potential of this generator, in consequence of electro-capillary
+effects. But if no generator is employed, the action will result from
+electric currents determined by the electro-capillary attraction
+itself. In the latter case, however, the instrument must be more
+delicately made, in order to obtain more sensitive electric reaction,
+and M. A. Bréguet describes his instrument as follows.
+
+‘The instrument consists of a tube of thin glass, a few centimètres in
+length, containing alternate drops of mercury and acidulated water,
+so as to constitute so many electro-capillary elements, connected in
+tension. The two ends of the tube are fused together, yet so as to
+allow a platinum wire to touch the nearest drop of mercury on each
+side. A small circle of thin deal is fixed at right angles to the tube
+by its centre, thus providing a surface of some extent, which can be
+applied to the ear when the instrument is a receiver, and to make the
+tube more mobile under the influence of the voice when the instrument
+is a sender. The following are the advantages offered by instruments of
+this construction:--
+
+‘1. They do not involve the use of a battery.
+
+‘2. The disturbing influence of the resistance of a long line is almost
+destroyed in these instruments, although it is still appreciable in the
+Bell telephone.
+
+‘3. Two mercury telephones, coupled together as we described above, are
+absolutely correlative, in this sense, that even different positions
+in the equilibrium of the mercury in one of them produce different
+positions of equilibrium in the opposite instrument. It is therefore
+possible to reproduce at a distance, without a battery, not merely
+faithful indications of oscillatory movements, which is done by the
+Bell telephone, but also the exact image of the most general movements.’
+
+
+_Friction Telephones._--Mr. E. Gray has quite recently applied the
+principle of producing sounds by the friction of animal tissues to the
+construction of a speaking telephone which may be heard through a whole
+room, like the singing condenser. He obtains this result by means of
+clockwork, which causes the rotation of the metallic disk of which we
+have spoken (p. 23), and on which a piece of skin is so arranged as to
+produce friction. A carbon or liquid telephone is placed at the sending
+station, in such a way as to react on an induction coil, as in the
+systems of Edison, Navez, or Pollard, and speech is reproduced on the
+rotating disk, and is audible, as we have said, without the necessity
+of approaching the ear to the instrument.
+
+The best arrangement of the metallic disk on which the animal tissue
+rubs is that of a cylindrical box, of which the outer lid is made of a
+thin sheet of zinc with a highly polished, slightly oxidised surface;
+for the agent of friction, glove-leather slightly moistened with
+acidulated water may be used, or a sinew of an ox, or skin taken from
+the ear or tail of a pig.
+
+
+
+
+MODIFICATIONS INTRODUCED IN THE CONSTRUCTION OF THE BELL TELEPHONES.
+
+
+The modifications which we have been considering relate to the
+principle of the instrument; those which we have now to consider are
+only modifications in the form and arrangement of the different organs
+which form the Bell telephone itself, and which have been designed with
+the object of increasing the intensity and distinctness of the sounds
+produced.
+
+
+_Telephones with several diaphragms._--When we remember that the
+induced currents caused in a magnet result from the vibratory movements
+of the diaphragm, and that these are produced by the vibrations of
+the stratum of air interposed between this diaphragm and the vocal
+organ, it necessarily follows that if these vibrations of the air react
+on several diaphragms, each attached to its electro-magnetic organ,
+several induced currents might be caused simultaneously, and if these
+were properly connected, their effects on the receiver would be so
+much the more intense, since the sounds produced would result from the
+combination of several sources of sound. Several inventors, starting
+from this argument, have planned instruments of varying ingenuity,
+which we will now describe, but without being able to declare who
+was the first to realise this idea. It is in fact so simple, that it
+probably suggested itself to the minds of several inventors at the
+same time, and we see that while M. Trouvé proposed this improvement
+in France in November 1877, it was tried in America and discussed in
+England, where indeed it was not expected to produce very favourable
+results. Mr. Preece wrote on the subject in a paper entitled ‘On some
+Physical Points connected with the Telephone,’ which was published
+in April 1878. He observes that all the attempts to improve the
+telephone have ended in disappointment and failure. One of the first
+attempts of the kind was made by Mr. Wilmot, who expected to obtain
+favourable results by augmenting the number of diaphragms, helices,
+and magnets, connecting the helices in a series, and causing them
+to act simultaneously, so as to increase the energy of the currents
+developed by the influence of the voice; but experience showed that
+when the instrument acted directly, the vibratory effect of each of the
+diaphragms decreased in proportion to their number, and the general
+effect remained the same as with a single diaphragm. Mr. Wilmot’s
+instrument was made in the beginning of October 1877, and that of M.
+Trouvé was only an imitation of it.
+
+On the other hand, we see that if the telephones with several membranes
+were not successful in England, this was not the case in America, for
+the telephones which experience has shown to give the best results in
+that country are those of Mr. Elisha Gray and Mr. Phelps, and these
+have several diaphragms. It is evident that there are details of
+construction in these instruments which may appear insignificant in
+theory, and which are notwithstanding very important from a practical
+point of view, and we believe that it is to this circumstance that
+instruments of this kind owe their success or failure. Thus, for
+example, it seems that the vibrations of air caused in the mouthpiece
+ought to be immediately directed on the surface of the diaphragms by
+means of distinct channels; it is necessary that the empty space round
+each diaphragm should be sufficiently limited to prevent echoes and
+interruptions, unless the case is so large that there is no danger of
+such effects. Above all, it is necessary that the organs should be
+fixed in some material unsusceptible of reverberation, and for this
+reason a preference is given to iron or ebonite. It is certain that
+when the instrument is properly made, its effects are superior to
+those of the Bell telephones, and it is asserted in the ‘Telegraphic
+Journal’ that experiments were made with one of these instruments
+before the Royal Society, in London, May 1, 1878, and that the
+intensity of sound was in proportion to the number of diaphragms. This
+instrument was designed by Mr. Cox Walker, of York, and possessed eight
+diaphragms. He considers that this is the arrangement which gives the
+best results.
+
+[Illustration: FIG. 35.]
+
+
+_Mr. Elisha Gray’s System._--Mr. Elisha Gray’s last system, which
+we represent in fig. 35, is one of those which have given the best
+effects. It is made, as we see, of two telephones, side by side, to
+which correspond two tubes, issuing from a common mouthpiece E. One
+of these telephones is seen in section in the plate, the other in
+elevation, and they correspond to the two branches of a nickel-plated
+horseshoe magnet N U S, which may serve as a suspension ring. In that
+part of the plate which represents the section, the induction coil is
+shown in B, and the magnetic core, of soft iron, in A, which is screwed
+to the polar end of the magnet S; the vibrating plate is in L L, and,
+as we see, the tube of the mouthpiece terminates on its surface.
+
+In another model there are four telephones side by side, instead of
+two, and the effects produced are still more marked.
+
+
+_Mr. Phelps’s System._--This system is only deduced from the last, but
+there are two models of it. In the larger one, which makes it possible
+to hear as distinctly as if the person with whom conversation is held
+were speaking in a loud voice in the same room, the two telephones are
+placed parallel to each other, and so as to present their diaphragms
+vertically; the space between these two diaphragms is occupied by
+a vertical tube, terminating at its lower end in a horizontal tube
+corresponding to the centres of the two diaphragms, and on this tube
+the mouthpiece is fitted, which projects outside the box in which
+the instrument is enclosed. The induction coils, and the magnetic
+cores which traverse them, follow the axis of the system, and seem
+to constitute the axis of a wheel which is polarised by the poles
+of a horseshoe magnet, of which the position with reference to the
+surface of the diaphragms can be regulated by moveable screws. The
+appearance of the instrument somewhat resembles a gyroscope, resting by
+a horizontal axis on two shafts which issue from a flattened horseshoe
+magnet.
+
+Above this system there is the electro-magnetic apparatus of the
+call-bell, in which there is nothing peculiar, and which is like the
+German alarums of which we shall speak at the end of this account.
+This instrument is remarkable for strength and clearness of sound, and
+especially for its freedom from the Punch and Judy voice so displeasing
+in other telephones.
+
+Mr. Phelps’s small model is in the form of an oblong or elliptical
+snuff-box, of which the two centres are occupied by two telephonic
+systems, influenced by the same magnet. This magnet is placed in a
+horizontal position below the snuff-box, and its poles correspond to
+the magnetic cores of the coils. These cores are made of iron tubes,
+split longitudinally in order to destroy irregular induction reactions,
+and the iron diaphragms rest on five spiral springs, which raise them
+above the magnetic system. On their other surface the diaphragms are
+provided with rings of some semi-elastic substance, which prevent the
+central vibrations of the disks from becoming complicated by those of
+their edges. The lid, hollowed out in very shallow cavities, is next
+placed upon the disks, and there are channels of communication in it
+to serve as a sounding-box. The mouthpiece corresponds to one of these
+cavities, and the other is closed by a small metallic stopper, which
+can be withdrawn to regulate the instrument when necessary. Since the
+vibrations of air are transmitted by the channels to both cavities, the
+two telephones act together, although at first sight only one of them
+seems to be required to produce the effect.
+
+Mr. Phelps praises the simultaneous effects produced on the two
+instruments, which he ascribes, first, to the semi-elastic ring
+surrounding the rim of each disk, and acting as the hammer of the ear,
+that is, as a damper; then, to the longitudinal splits of the magnetic
+core, and lastly to the small size of the cavities left above the
+vibrating disks. The instrument is made of ebonite, grooved on the
+surface in order to give a better grasp to the hand.
+
+Mr. Phelps has a new model, called _the crown telephone_, which is now
+in use in America, together with Mr. Edison’s carbon sender. In it
+each of the two systems of the large model we have described is worked
+by six horseshoe magnets radiating round the magnetic core, and so
+arranged that the north poles correspond to this core, and the other
+poles to the circular rim of the diaphragm. In this way the magnetic
+field is considerably enlarged, and the sound much intensified.
+
+In experiments recently made at Dr. Wells’s church, New York, an
+assembly of three hundred people were able to hear speech and vocal or
+instrumental music distinctly in different parts of the hall.
+
+
+_Mr. Cox Walker’s System._--This system, on which we have already said
+a few words, has exactly the arrangement of that by Mr. Elisha Gray.
+The magnets which act upon the diaphragms are horseshoe, and separate
+pipes, issuing from a common mouthpiece, direct the vibrations of
+air on the diaphragms. These, indeed, are only defined parts of one
+diaphragm, bounded in a circle by mouthpieces corresponding to the
+air-pipes, and sufficiently restricted on their edges to limit the
+field of vibration.
+
+
+_M. Trouvé’s System._--M. Trouvé has simplified the arrangement of
+telephones with a double diaphragm, by designing the instrument so
+as to make Bell’s bar magnet react by both poles at once on several
+disks. For this purpose, he employs a tubular magnet, and winds a
+helix throughout its whole length, as we see in fig. 36. This magnet
+is maintained in a fixed position in the centre of a small cylindrical
+box, of which the base is slightly funnel-shaped, thus acting as a
+mouthpiece and acoustic tube. It is consequently pierced in the centre
+with a hole larger at _a_, the station for speaking, than on the
+opposite side _b_. Between the base and the poles of the magnet there
+are two vibrating iron plates, M, M′, one of which, M, is pierced with
+a hole _a_ of the same diameter as the hollow part of the magnet, and
+consequently smaller than that of the mouthpiece. Finally, several
+other plates _n_, _n_, _n_, are ranged in parallel lines between these
+two plates, so that the magnet and its helix may pass through them.
+
+[Illustration: FIG. 36.]
+
+When anything is said before the mouthpiece _a_, the waves of sound
+encountering the edges of the plate M place it in vibration, and,
+continuing their passage inside the tubular magnet, they cause the
+plate M′ to vibrate at the same time as M. A double inducing action
+therefore takes place on the tubular magnet, and this is translated by
+the induced currents developed in the helix, which have greater energy
+since each of the plates intensifies the magnetic effects produced at
+the pole opposite to the one they influence, which is always the case
+with bar magnets when the inactive pole is provided with an armature.
+This advantage may even be obtained in the case of ordinary telephones,
+if the screw which holds the magnet is placed in contact with a mass of
+soft iron.
+
+In M. Trouvé’s arrangement, the induced currents therefore possess
+greater energy; but he adds that the sounds reproduced will also be
+strengthened by the multiplicity of vibratory effects, and by the
+enlargement of the magnetic effects, which results from a better
+arrangement of the magnets.
+
+‘When the ear is placed at _a_,’ M. Trouvé writes, ‘it perceives
+immediately the sounds produced by the first plate M, and those of
+the second plate reach the ear through the interior of the magnet.
+This new arrangement is well adapted for an experimental comparison
+of the results produced by a telephone with a single membrane (a Bell
+telephone), and those produced by a telephone with several membranes.
+It is in fact enough to listen at the two faces of the telephone
+alternately, in order to perceive at once the difference of intensity
+in the sounds produced. Those collected at _a_, on the side of the
+pierced iron plate, appear manifestly doubled in intensity compared
+with those collected at _b_ on the side of the simple membrane which
+forms the ordinary telephone.
+
+‘The difference is still more striking if, in transmitting or receiving
+a sound of invariable intensity through a multiple telephone, the
+unbroken membrane M′ is repeatedly prevented from vibrating.’
+
+Before making this arrangement M. Trouvé had planned another, which he
+presented to the Académie des Sciences, November 26, 1877, and which we
+have glanced at in the beginning of this chapter. He describes it in
+these terms:--
+
+‘In order to increase the intensity of the effects produced in the Bell
+telephone, I have substituted for the single membrane a cubic chamber,
+of which each face is, with one exception, formed of a vibrating
+membrane. Each of these membranes, put in vibration by the same sound,
+influences a fixed magnet, which is also provided with an electric
+circuit. In this way, by connecting all the currents generated by the
+magnets, a single intensity is obtained, which increases in proportion
+to the number of magnets influenced. The cube might be replaced by a
+polyhedron, of which the faces might be formed of an indefinite number
+of vibrating membranes, so as to obtain the desired intensity.’
+
+
+_M. Demoget’s System._--Several other systems of telephones with
+multiple membranes have been proposed. One of them, planned by M.
+Demoget, consists in placing before the vibrating disk of the ordinary
+Bell telephone, separated by the space of a millimètre, one or two
+similar vibrating disks, taking care to pierce in the centre of the
+first a circular hole of the same diameter as that of the bar magnet,
+and to pierce a larger hole in the second membrane. The inventor
+asserts that the distinctness as well as the intensity of sounds is
+increased in this way.
+
+‘By this arrangement,’ says M. Demoget, ‘since the vibrating magnetic
+mass is larger in proportion to the magnet, the electro-motive force of
+the currents generated is increased, and consequently the vibrations of
+the disks of the second telephone are more perceptible.’
+
+
+_Mr. McTighe’s Telephone._--In this telephone, which has several
+diaphragms, there is a horseshoe magnet, and instead of placing the
+coils upon the poles, there is a single coil fastened to an iron core,
+which is inserted between wide polar appendices fitted to the two poles
+of the magnet. These appendices consist of thin plates, which act as
+vibrating plates.
+
+
+_Modifications in the arrangement of Telephonic Organs._--We see that
+the forms given to the Bell telephone are very varied, and this is
+still more the case with its constituent organs, without, however,
+producing any remarkable improvements. Mr. Preece observes that little
+has been gained by varying the size and strength of the magnets, and
+the best effects have been obtained by using the horseshoe magnets
+directed by Mr. Bell himself. The telephone was certainly introduced
+into Europe with the arrangement which is theoretically the best,
+although Mr. Bell is still occupied in improving it. This is also the
+opinion of M. Hellesen, who, like Mr. Preece, has made many experiments
+on this point; but this has not deterred several people from declaring
+that they have discovered the way of making a telephone speak so as to
+be audible to an assembly of people.
+
+Of the different instruments made with this object, that of M. Righi
+seems to be the most important. It was lately tried with success at the
+Académie des Sciences, the Conservatoire des Arts et Métiers, and the
+Press pavilion of the Exhibition.
+
+[Illustration: FIG. 37.]
+
+The receiver is only a Bell telephone of large size, with a diaphragm
+of parchment L L (fig. 37), in the centre of which there is a
+sheet-iron disk F. This membrane is stretched on a large funnel E,
+which is fixed on a box C C, containing the electro-magnetic coil B:
+and the magnet N S, much larger than in the ordinary instruments,
+issues from the box, and serves as its support.
+
+[Illustration: FIG. 38.]
+
+The sender resembles the one represented in fig. 19, except that,
+instead of liquid, M. Righi employs plumbago mixed with powdered
+silver, and the platinum needle is replaced by a metallic disk D (fig.
+38). The receiver I, which contains the powder, is supported on a
+spring R, which can be pushed up and down by a regulating screw V,
+and the whole is fitted into a box C C, and supported on a foot P.
+The speaker places himself above the mouthpiece E, and the vibrations
+transmitted to the membrane L L cause the variations of resistance in
+I which are necessary for the transmission of speech, as in the Edison
+system. Two Bunsen cells are enough to set the instrument at work, and
+it will make the sound of a trumpet or flute audible throughout a room.
+Vocal music, which is less intense, is necessarily transmitted to a
+rather less distance, and words spoken in the natural voice are heard
+by those standing about two yards and a half from the instrument.
+
+The maximum distance at which the instrument has been worked with the
+battery only is twenty-eight miles, the distance between Bologna and
+Ferrara, and for greater distances it is necessary to have recourse to
+induction coils.
+
+In this case, an induction coil is introduced into the circuit at each
+station, and its primary wire is traversed by a current from the local
+battery, and so also is the sender, which is elsewhere connected with
+the receiver by a commutator. The secondary circuit of these coils
+is completed through the earth and line wire. From this arrangement
+it follows that the induced current which influences the receiver in
+correspondence, only produces its effect after a second induction,
+produced on the primary wire of the local coil, and it appears that
+this is a sufficient effect; but the advantage of this arrangement is,
+that it is possible to receive and transmit sounds without the aid of
+anything but the commutator.
+
+Among other arrangements which have been suggested, we may mention one
+in which, instead of the bar magnet, a horseshoe magnet is used, with
+a vibrating plate placed between its poles. For this purpose the poles
+are tipped with iron, and one of them is pierced with a hole which
+corresponds to the mouthpiece of the instrument. The two branches of
+the magnet are also furnished with magnetising helices. When anything
+is spoken before the hole, the vibrating plate causes induced currents
+in the two helices: these currents would be of opposite direction if
+the poles were of like nature, but, since the magnetic poles are of
+contrary nature, they are in the same direction. The vibrating plate
+then acts like the two plates of M. Trouvé’s instrument, which we have
+described above.
+
+In another arrangement, lately made by Ader, the receiver is only an
+ordinary two-branched magnet, of which the armature is supported, at
+about two millimètres from its poles, by a glass plate to which it is
+glued, and the plate itself is fastened to two rigid supports. In order
+to hear it is only necessary to apply the ear to the plate. The sender
+is a moveable rod of iron or carbon, which rests on a fixed piece
+of carbon, with no pressure except its own weight, and it supports a
+concave disk, to which the speaker applies his mouth. These two parts
+are so arranged as to move horizontally, so that, when the instrument
+is suspended, the circuit is forcibly disconnected by the fact of its
+position, and is therefore closed until anyone takes it up to speak.
+Speech is well reproduced by this system, and may be transmitted to
+some distance if it is made on a larger scale.
+
+Again, an anonymous inventor, in a little note inserted in ‘Les
+Mondes,’ February 7, 1878, writes as follows: ‘Since the intensity of
+the currents produced in the telephone is in proportion to the mass of
+soft iron which vibrates before the pole of the magnet, and since, on
+the other hand, the plate is sensitive in proportion to its tenuity, I
+employ, instead of the ordinary plate, one reduced by nitric acid to
+the least possible thickness, and I fix it to a circle of soft iron,
+which keeps it stretched and forms part of the same substance. This
+circle is placed in a circular opening made inside the compartment. The
+intensity of a telephone is much increased when such a system replaces
+the ordinary plate, even at one end of the line.’
+
+In order to obtain vibrating plates of extreme tenuity, M. E. Duchemin
+thought of employing very thin plates of mica, sprinkled with
+pulverised iron fixed to the plate by a layer of silicate of potash.
+The inventor asserts that it is possible to correspond in a low voice
+with the aid of this system; but it has this inconvenience, that the
+plate will be broken by speaking too loud.
+
+Professor Jorgenson, of Copenhagen, has also made a Bell telephone
+which produces very intense sounds, and which has permitted him to
+observe some curious effects. In this instrument, the magnet is made
+in a mode analogous to Nicklès’ tubular magnets. There is first a
+cylindrical magnet with a core of soft iron at its upper end, to which
+the coil is fitted; next, a magnetised tube, formed of a steel ring,
+which encloses the first magnetic system, and is connected with it by
+an iron tube. Finally, above the polar extremities of this system,
+there is the vibrating disk, with the same arrangement as that of
+ordinary telephones, and of which the superficies is large. If this
+plate is only a millimètre in thickness, the words spoken can be heard
+throughout a room; but the sounds lose their clearness when the ear
+is approached to the vibrating plate, the words are confused, and
+there is the reverberation which is observed on speaking in a place
+apt to produce echoes: the listener is, in fact, stunned by the sounds
+produced. On using a thicker plate--one, for example, of three or four
+millimètres--the telephone only produces the effect of the ordinary
+instruments, and it is necessary to apply the ear to it.
+
+M. Marin Maillet, of Lyons, has suggested that the sounds reproduced by
+the telephone might be increased by reflecting them through a certain
+number of reflectors, which, by concentrating them in a focus on a
+resonator, would considerably enlarge them. Since this idea was not
+accompanied by experiments, it can hardly be regarded as serious.
+
+
+
+
+TELEPHONIC EXPERIMENTS.
+
+
+Since Mr. Bell’s experiments of which an account has been given in the
+early part of this work, much study has been given by men of science
+and inventors to the effects produced in this curious instrument, so as
+to ascertain its theory and deduce improvements in its construction. We
+will take a glance at these researches in succession.
+
+
+_Experiments on the Effects produced by Voltaic and Induced
+Currents._--The comparative study of the effects produced in the
+telephone by voltaic and induced currents was one of the first and
+most important. In 1873, as we have seen, Mr. Elisha Gray converted
+the voltaic currents, which he employed to cause the vibrations of his
+transmitting plate, into induced currents by means of an induction
+coil, such as Ruhmkorff’s. The voltaic currents then traversed the
+primary helix of the coil, and the induced currents reacted on the
+receiving instrument, producing on its electro-magnetic system the
+vibrations excited at the sending station. When Mr. Edison designed
+his battery telephone, he had recourse to the same means to work his
+receiving telephone, since he had ascertained that induced currents
+were superior to voltaic currents. But this peculiarity of Mr. Edison’s
+arrangement was not clearly understood from the descriptions which
+reached Europe, so that several persons believed that they had invented
+this arrangement--among others, Colonel Navez and MM. Pollard and
+Garnier.
+
+Colonel Navez, in an interesting paper on the new telephonic system,
+presented to the Belgian Royal Academy, February 2, 1878, only suggests
+this arrangement as a mode of reproducing speech at a great distance;
+but he quotes no experiment which distinctly shows the advantages
+of this combination. Twenty days later, MM. Pollard and Garnier,
+unacquainted with Colonel Navez’s researches, sent to me the results
+they had obtained by similar means, and these results appeared to me
+so interesting that I communicated them to the Académie des Sciences,
+February 25, 1878. In order that the importance of these results may
+be clearly understood, I will repeat the text of M. Pollard’s letter,
+addressed to me on February 20, 1878:
+
+‘With the object of increasing the variations of electric intensity
+in the Edison system, we induce a current in the circuit of a small
+Ruhmkorff coil, and we fix the receiving telephone to the extremities
+of the induced wire. The current received has the same intensity as
+that of the inducing current, and consequently the variations produced
+in the current which works the telephone have a much wider range. The
+intensity of the transmitted sounds is strongly increased, and the
+value of this increase depends upon the relative number of spirals in
+the inducing and induced circuits. Our attempts to determine the best
+proportions have been laborious, since it is necessary to make a coil
+for each experiment; we have hitherto obtained excellent results with
+a small Ruhmkorff coil reduced to its simplest form, that is, without
+condenser or contact-breaker. The inducing wire is No. 16, and is wound
+in five layers; the induced wire is No. 32, and in twenty layers. The
+length of the coil is seven centimètres.
+
+‘The following is the most remarkable and instructive experiment: When
+setting the sender to work with a single Daniell cell, there is no
+appreciable effect at the receiving station, at least in the telephone
+which I have made, when it is in immediate connection with the circuit;
+after inserting the small induction coil, sounds become distinctly
+audible, and their intensity equals that of good ordinary telephones.
+Since the battery current is only moderately intense, the points of
+plumbago are not worn down, and the regulating apparatus lasts for a
+long while. When a stronger battery is used, consisting of six cells
+of bichromate of potash (in tension) or twelve Leclanché cells,
+sufficient intensity is obtained by the direct action to make sounds
+nearly as audible as in ordinary telephones; but when the induction
+coil is inserted, the sounds become much more intense, and may be heard
+at a distance of from fifty to sixty centimètres from the mouthpiece.
+Songs may, under such circumstances, be heard at a distance of several
+yards; but the relative increase does not appear to be so great as in
+the case of the single Daniell cell.’
+
+On the other hand, ‘Les Mondes,’ March 7, 1878, contains an account of
+a series of experiments made by Signor Luvini, Professor of Physics
+at the Military Academy of Turin, which proved that the introduction
+of electro-magnets into the circuit which connects the two telephones
+sensibly increases the intensity of sound. The maximum effect is
+produced by placing one close to the transmitting, and the other close
+to the receiving telephone, and the introduction of other magnets is
+of no use. The inducing wire of a Ruhmkorff coil, when introduced into
+such a circuit, excited no sensible effects of induction in the induced
+circuit, and consequently could not set the telephone in connection
+with this circuit at work. But the current of a Clarke machine produces
+sounds resembling the beats of a drum, which are deafening when the ear
+is applied to the instrument: they become very faint, however, at the
+distance of a mètre. The currents of a Ruhmkorff machine are still
+more energetic, and the sound fills a whole room. By modifying the
+position of the lever of the coil, the sound passes through different
+tones, which are always in unison with the breaks of the current, at
+least up to a certain pitch.
+
+This property of currents induced by the Ruhmkorff coil has enabled
+M. Gaiffe to obtain by their means a very simple mode of regulating
+telephones, so as to produce in them the maximum amount of sensibility.
+For this purpose he places the telephone he proposes to regulate in the
+circuit of an induction instrument with moveable helices and graduated
+intensities. The sounds which result from the vibrator are then
+reverberated from the telephone, and are audible at a distance from the
+instrument; by using a screw-driver, it is possible to adjust the screw
+to which the free end of the bar magnet of the instrument is fixed. It
+can be tightened or loosened, so as to advance or withdraw the other
+end of the magnet from the vibrating plate of the telephone, and the
+process is repeated until the maximum intensity of sound is obtained.
+
+On the other hand, as the sounds given out by the two telephones in
+correspondence are intense in proportion to the degree of unison in
+the vibrations produced by them, it is necessary to select those which
+emit the same sounds for the same given note; and the mode we have just
+described may be employed with advantage, since it will be enough to
+observe what instruments give the same note in the condition of maximum
+sensibility, when regulated in the same way by the induction machine.
+
+It is very important that the telephones in correspondence should
+be well matched, not only to ensure clear transmissions, but also
+with reference to the tone of voice of those who are to use it. The
+sound becomes more audible when the tone of voice corresponds to the
+telephonic tone; and for this reason some telephones repeat the voices
+of women and children better than those of men, and with others the
+reverse takes place.
+
+The telephonic vibrations vary in different instruments, and these
+variations may be noted in the way we have indicated.
+
+The advantages of induced currents in telephonic transmissions may be
+easily understood, if we consider that the variations of resistance
+in the circuit, resulting from the greater or less range in the
+vibrations of the transmitting plate, are of constant value, and can
+only manifest their effects distinctly in short circuits; consequently
+the articulate sounds which result from them can only be really
+appreciable in circuits of great resistance. According to Mr. Warren
+de la Rue’s experiments (reported in the ‘Telegraphic Journal,’ March
+1, 1878), the currents produced by the vibrations of the voice in an
+ordinary telephone represent in intensity those of a Daniell cell
+traversing 100 megohms of resistance (or 10,000,000 kilomètres); and
+it is plain that the simple question of greater or less intensity in
+the currents acting on the receiving telephone is not the only thing we
+have to consider. With an energetic battery, it is evident, in fact,
+that the differential currents will always be more intense than the
+induced currents produced by the action of the instrument. I myself
+am inclined to believe that induced currents owe the advantages they
+possess to the succession of inverse currents and their brief duration.
+These currents, of which M. Blaserna considers that the duration does
+not exceed 1/200 of a second, are much more susceptible than voltaic
+currents of the multiplied vibrations which are characteristic of
+phonetic vibrations, and especially since the succession of inverse
+currents which take place discharge the line, reverse the magnetic
+effects, and contribute to make the action more distinct and rapid.
+We cannot therefore be surprised that the induced currents of the
+induction coil, which can be produced under excellent conditions at the
+sending station, since the circuit of the voltaic current is then very
+short, are able to furnish results, not only more effective than the
+voltaic currents from which they take their origin, but even than the
+induced currents resulting from the action of the Bell telephone, since
+they are infinitely more energetic.
+
+As for the effects produced by the currents of Bell telephones, which
+are relatively great when we consider their size, they are easily
+explained from the fact that they are produced under the influence of
+the vibrations of the telephone plate, so that their variations of
+intensity always maintain the same proportion, whatever may be the
+resistance of the circuit, and consequently they are not effaced by the
+distance which divides the two telephones.
+
+
+_Experiments on the part taken by the different telephonic organs
+in the transmission of speech._--In order to introduce all the
+improvements of which a telephone is capable, it is important to be
+quite decided as to the effects produced in the several parts of which
+it is composed, and as to the part taken by the several organs which
+are at work. To attain this object several men of science and engineers
+have undertaken a series of experiments which have produced very
+interesting results.
+
+One of the points on which it was most important to throw light
+was that of ascertaining whether the vibrating plate used in their
+telephone receivers by Messrs. Bell and Gray is the only cause of the
+complex vibrations which reproduce speech, or if the different parts
+of the electro-magnetic system of the instrument all conduce to this
+effect. The experiments made by Mr. Page in 1837 on the sounds produced
+by the resonant electro-magnetic rods, and the researches pursued in
+1846 by Messrs. de la Rive, Wertheim, Matteucci, &c., on this curious
+phenomenon, allow us to state the question, which is certainly more
+complex than it at first appears.
+
+In order to start from a fixed point, it must first be ascertained
+whether a telephone can transmit speech without a vibrating plate.
+Experiments made by Mr. Edison[9] in November 1877, with telephones
+provided with copper diaphragms, which produced sounds, make the
+hypothesis credible; and it received greater weight from the
+experiments made by Mr. Preece and Mr. Blyth. The fact was placed
+beyond a doubt by Mr. Spottiswoode (see the ‘Telegraphic Journal’
+of March 1, 1878), who assures us that the vibrating plate of
+the telephone may be entirely suppressed without preventing the
+transmission of speech, provided that the polar extremity of the
+magnet be placed quite close to the ear; and it was after this that
+I presented to the Académie des Sciences my paper on the theory of
+the telephone, which led to an interesting discussion of which I
+shall speak presently. At first the authenticity of these results was
+denied, and then an attempt was made to explain the sounds heard by Mr.
+Spottiswoode as a mechanical transmission of the vibrations, effected
+after the manner of string telephones; but the numerous experiments
+which have subsequently been made by Messrs. Warwick, Rossetti, Hughes,
+Millar, Lloyd, Buchin, Canestrelli, Wiesendanger, Varley, and many
+others, show that this is not the case, and that a telephone without a
+diaphragm can transmit speech electrically.
+
+Colonel Navez himself, who had first denied the fact, now admits that a
+telephone without a diaphragm can emit sounds, and even, under certain
+exceptional conditions, can reproduce the human voice; but he still
+believes that it is impossible to distinguish articulate words.
+
+This uncertainty as to the results obtained by the different physicists
+who have studied the matter shows that at any rate the sounds thus
+reproduced are not clearly defined, and that in physical phenomena,
+only appreciable to our senses, the appreciation of an effect so
+undefined must depend on the perfection of our organs. We shall
+presently see that this very slight effect can be largely increased
+by the arrangement adopted by Messrs. Bell and Gray, and we shall
+also see that, by a certain mode of magnifying the vibrations, it
+has been decisively proved that a telephone without a diaphragm can
+readily reproduce speech. I proceed to give the description of such a
+telephone, which was shown by Mr. Millar at the meeting of the British
+Association at Dublin in August 1878.
+
+This instrument consists of a small bar magnet, three inches in length
+and 5/16 of an inch in width and thickness, and a copper helix (No. 30)
+of about six mètres in length is wound round the bar. It is fixed in a
+box of rather thick pasteboard, fitted above and below with two zinc
+plates, which render it very portable. With a telephonic battery sender
+and a single Leclanché cell, speech can be perfectly transmitted; the
+whistling of an air, a song, and even the act of respiration become
+audible. It seems also that the instrument can act without a magnet,
+merely with a piece of iron surrounded by the helix; but the sounds are
+then much fainter.
+
+Signor Ignace Canestrelli obtained the same results by making one of
+the carbon telephonic senders react on a telephone without a diaphragm,
+by means of an induction coil influenced by two Bunsen cells. He writes
+as follows on the subject:
+
+‘With this arrangement I was able to hear the sound of any musical
+instrument on a telephone without a diaphragm: singing, speaking, and
+whistling were perfectly audible. Whistling could be heard, even when
+the telephone without a diaphragm was placed at some distance from
+the ear. In some cases, depending on the pitch of the voice, on the
+distance of the sending station, and on the joint pressure exerted by
+the carbons, I could even distinguish words.
+
+‘I finally discharged the currents of the transmitter into the coils
+of insulated copper wire with which the two poles of a magnet were
+provided. This magnet was placed on a musical box, made of very thin
+slips of wood, and on placing the ear at the opening of the box I
+obtained the same results as with the ordinary telephones without a
+diaphragm.’
+
+M. Buchin, after repeating experiments of the same kind as the above,
+intimates that it is easy to hear the sounds produced by a telephone
+without a diaphragm, by introducing into the ear the end of an iron
+rod, of which the other end is applied to the active pole of the bar
+magnet of the telephone. (See ‘Le Journal d’Electricité,’ October 5,
+1878.)
+
+I repeat finally the account of some experiments made by Mr. Hughes and
+M. Paul Roy which are interesting from our present point of view.
+
+1. If an armature of soft iron is applied to the poles of an
+electro-magnet, with its two branches firmly fixed on a board, and if
+pieces of paper are inserted between this armature and the magnetic
+poles, so as to obviate the effects of condensed magnetism; if,
+finally, this electro-magnet is connected with a speaking microphone,
+of the form given in fig. 39, it is possible to hear the words spoken
+in the microphone on the board which supports the electro-magnet.
+
+2. If two electro-magnets are placed in communication with a
+microphone, with their poles of contrary signs opposite to each other,
+and if their poles are separated by pieces of paper, speech will be
+distinctly reproduced, without employing armature or diaphragm. These
+experiments are, however, delicate, and demand a practised ear.
+
+3. If, instead of causing the current produced by a microphone to pass
+through the helix of a receiving telephone, it is sent directly into
+the bar magnet of this telephone in the direction of its axis--that
+is, from one pole to another--the words pronounced in the microphone
+may be distinctly heard. This experiment by M. Paul Roy indicates,
+if it is exact, that the electric pulsations which traverse a magnet
+longitudinally will modify its magnetic intensity. The experiment,
+however, demands verification.
+
+Another point was obscure. It was important to know whether the
+diaphragm of a telephone really vibrates, or at least if its vibrations
+could involve its displacement, such as occurs in an electric vibrator,
+or in wind instruments which vibrate with a current of air. M.
+Antoine Bréguet has made some interesting experiments on the subject,
+which show that such a movement cannot take place, since speech was
+reproduced with great distinctness from telephones with vibrating
+plates of various degrees of thickness, and he carried the experiment
+so far as to employ plates fifteen centimètres in thickness.[10]
+When pieces of wood, caoutchouc, and other substances were laid upon
+these thick plates, the results were the same. In this case it cannot
+be supposed that the plates were moved to and fro. I have moreover
+ascertained, by placing a layer of water or of mercury on these plates,
+and even on thin diaphragms, that no sensible movement took place, at
+least when the induced currents produced by the action of speaking
+were used as the electric source. No ripples could be seen on the
+surface of the liquid, even when luminous reflectors were employed
+to detect them. And indeed it can hardly be admitted that a current
+not more intense than that of a Daniell element, which has traversed
+10,000,000 kilomètres of telegraphic wire--a current which can only
+show deviation on a Thomson galvanometer--should be powerful enough to
+make an iron plate as tightly stretched as that of a telephone vibrate
+by attraction, even if we grant that the current was produced by laying
+a finger on the diaphragm.
+
+Very nice photographic experiments do, however, show that vibrations
+are produced on the diaphragm of the receiving telephone; they are
+indeed excessively slight, but Mr. Blake asserts that they are enough
+to cause a very light index, resting on the diaphragm, to make slight
+inflections on a line which it describes on a register. Yet this small
+vibration of the diaphragm does not show that it is due to the effect
+of attraction, for it may result from the act of magnetisation itself
+in the centre of the diaphragm.[11] An interesting experiment by Mr.
+Hughes, repeated under different conditions by Mr. Millar, confirms
+this opinion.
+
+If the magnet of a receiving telephone consists of two magnetised bars,
+perfectly equal, separated from each other by a magnetic insulator, and
+they are so placed in the coil as to bring alternately the poles of
+the same and of contrary signs opposite to the diaphragm, it is known
+that the telephone will reproduce speech better in the latter case than
+in the former. Now, if the effects were due to attraction, this would
+not be the case; for the actions are in disagreement when the poles of
+contrary signs are subjected to the same electric influence, while they
+are in agreement when these poles are of like signs.
+
+On the other hand, it is known that if several iron plates are
+put together in order to form the diaphragm of the receiver, the
+transmission of sounds is much stronger than with a simple diaphragm;
+and yet the attraction, if it has anything to do with it, could only be
+exerted on one of the diaphragms.
+
+It further appears that it is not merely the magnetic core which emits
+sounds, but that they are also produced with some distinctness by the
+helices. Signor Rossetti had already ascertained this fact, and had
+even remarked that they could be animated by a slight oscillatory
+movement along the bar magnet, when they were not fixed upon it.
+Several observers, among others M. Paul Roy, Herr Wiesendanger, and
+Signor Canestrelli, have since mentioned similar facts, which are
+really interesting.
+
+‘If,’ writes M. Paul Roy, ‘a coil of fine wire, which is at the
+extremity of the bar magnet of a Bell telephone, receives the pulsatory
+currents transmitted by a carbon telephone, it is only necessary to
+bring the coil close to the ear in order to hear the sounds.
+
+‘The sounds received in this way are very faint, but become much
+stronger if a piece of iron is introduced into the circuit coil. A
+magnet acts with still greater force, even when it consists of a simple
+magnetised needle. Finally, the sound assumes its maximum intensity
+when an iron disk is inserted between the ear and the coil.
+
+‘By placing the end of the coil to the ear, and sending a current
+through it from the bar magnet, it is ascertained that the sound is
+at its minimum when the neutral line of the magnet is enclosed by the
+coil, and that it increases until attaining its maximum, when the
+magnet is moved until one of its poles corresponds to the coil.
+
+‘This fact of the reproduction of sounds by a helix is universal. Every
+induction coil and every electro-magnet are capable of reproducing
+sound when the currents of the sender are of sufficient intensity.’
+
+Signor Canestrelli writes as follows: ‘With the combination of a
+carbon telephone and one without diaphragm or magnet--that is, with
+only a simple coil--I was able to hear whistling through the coil,
+placed close to the ear. This coil was of very fine copper wire, and
+the currents were produced through an induction coil by two Bunsen
+elements. The contacts of the telephone were in carbon, and it was
+inserted in the primary circuit.
+
+‘I fastened the coil to the middle of a tightly stretched membrane
+which served as the base of a short metal cylinder. When a magnet was
+placed near this part of the coil, the sounds were intensified, and
+when I fixed the magnet in this position, I could hear what was said.
+
+‘I afterwards substituted for the magnet a second coil, fastened to
+a wooden bar, and on causing the induced currents to pass into both
+coils at once I was able to hear articulate speech, although not
+without difficulty.
+
+‘Under these latter conditions I found it possible to construct a
+telephone without a magnet, but it required a strong current, and it
+was necessary to speak into the sender in a special manner, so as to
+produce strong and concentrated sounds.’
+
+Another very interesting experiment by M. A. Bréguet shows that all
+the constituent parts of the telephone--the handle, the copper rims,
+and the case, as well as the diaphragm and the electro-magnet--can
+transmit sounds. M. Bréguet ascertained this fact by the use of string
+telephones, which he attached to different parts of the telephone on
+which the experiment was made. In this way he was not only able to
+establish a correspondence between the person who worked the electric
+telephone and the one who was listening through the string telephone,
+but he also made several string telephones act, which were attached to
+different parts of the electric telephone.
+
+These two series of experiments show that sounds may be obtained
+from different parts of the telephone without any very appreciable
+vibratory movements. But Signor Luvini wished for a further assurance
+of the fact, by ascertaining whether the magnetisation of any magnetic
+substance, followed by its demagnetisation, would involve a variation
+in the form and dimensions of this substance. He consequently caused
+a large tubular electro-magnet to be made, which he filled with a
+quantity of water, so that, when its two ends were corked, the liquid
+should rise in a capillary tube fitted to one of the corks. In this
+way the slightest variations in the capacity of the hollow part of
+the electro-magnet were revealed by the ascent or descent of the
+liquid column. He next sent an electric current of varying intensity
+through the electro-magnet, but he was never able to detect any change
+in the level of the water in the tube; although by this arrangement
+he could measure a change of volume of 1/30 of a cubic millimètre.
+It appears from this experiment that the vibrations produced in a
+magnetic substance under the influence of successive magnetisations and
+demagnetisations, are wholly molecular. Yet other experiments made by
+M. Canestrelli seem to show that these vibrations are so far sensible
+as to produce sounds which can be detected by the microphone. He writes
+as follows on the subject:
+
+‘When the broken currents of an induction coil are discharged into
+a coil placed on a sounding-box, it is possible to hear at a little
+distance the sounds produced by the induced currents thus generated.
+On approaching the magnet to the opening of the coil, these sounds are
+intensified, and the vibrations of the magnet become sensible to the
+touch; this vibration might even be made visible by suspending the
+magnet inserted into the coil to a metallic wire, which is fitted to
+a membrane stretched on a drum, and the latter will then reproduce
+sounds. When the same magnet is suspended to a microphone, it is
+possible, with the aid of a telephone, to ascertain the same effects,
+which are then increased.’
+
+We shall presently consider how these different deductions are to
+be interpreted, so as to render the true theory of the telephone
+intelligible; but, before doing so, we will mention some other
+experiments which are not without interest.
+
+We have seen that the experiments of Messrs. Edison, Blyth, and Preece,
+show that sounds may be reproduced by a telephone with a diaphragm
+made of some unmagnetic substance, and they also show, which is still
+more curious, that these sounds may be transmitted under the influence
+of induced currents produced by these diaphragms when they are placed
+in vibration before the magnet. Messrs. Edison and Blyth had already
+adduced this fact, which was received with incredulity, but it has
+been confirmed by Mr. Warwick in an article published in the ‘English
+Mechanic.’ He writes that in order to act upon the magnet, so as to
+produce induced currents, something possessed of greater energy than
+gas must first be made to vibrate. It is not, however, necessary that
+this substance should be magnetic, for diamagnetic substances act
+perfectly.[12] Mr. Preece sought for the cause in the induced currents
+developed in any conducting body when a magnet is moved before it,
+currents which give rise to the phenomenon discovered by Arago and
+known by the name of magnetism by rotation. Yet these facts do not
+appear to us to be sufficiently well established to make the theory
+worthy of serious consideration, and it is possible that the effects
+observed resulted from simple mechanical transmissions.
+
+To conclude the account of these experiments, we will add that
+Mr. W. F. Barrett thinks it somewhat difficult to define the mode
+of vibration of the diaphragm, since, while a certain amount of
+compression exerted on the iron destroys the sounds resulting from the
+peculiar effects of magnetisation, a still stronger compression causes
+them to reappear. It is certain that the question is full of obscurity,
+and demands great research: it is enough to have shown that the theory
+hitherto held is insufficient.
+
+On the other hand, Colonel Navez considers that the intensity of sound
+reproduced in a telephone depends not only on the range of vibrations,
+but also on the vibrating surface and the effect it produces on the
+stratum of air which transmits the sound. (See paper by Colonel Navez
+in the ‘Bulletin de l’Académie de Belgique,’ July 7, 1878.)
+
+
+_Experiments on the Effects which result from Mechanical Shocks
+communicated to different parts of a Telephone._--If a piece of iron is
+applied to the screw which holds the magnet of the ordinary telephone,
+it is observed that the transmitted sounds are more distinct, owing to
+the force supplied to the active pole of the magnet; but at the moment
+when the piece of iron is applied to the screw a distinct noise is
+heard, which seems to be due to the mechanical vibrations caused in
+the magnet at the moment of the shock. M. des Portes, a lieutenant in
+the French navy, has lately made some interesting experiments on this
+class of phenomena. He has observed that if, in a telephonic circuit
+of 90 yards completed by the earth, the sending telephone is reduced
+to a simple magnet, provided with the coil which constitutes its
+electro-magnetic organ, and if this magnet is suspended vertically by a
+silken thread, with the coil above it, a blow struck upon the magnet,
+either by a copper rod or a piece of wood, will cause distinct sounds
+to be produced in the receiving telephone--sounds which will increase
+in intensity when the blow is struck close to the coil, and which will
+become still stronger, but less clear, if a vibrating plate of soft
+iron is placed in contact with the upper pole of the magnet.
+
+When the striking instrument is made of iron, the sounds in question
+are more strongly marked than if it is of wood, and when the magnet has
+a vibrating disk applied to its active pole, a vibration of the disk
+takes place at the moment when the shock is heard.
+
+If the striking body is a magnet, the sounds produced resemble those
+obtained when it is of iron, if the effect is produced between poles
+of the same nature; but if the poles are of contrary natures, a second
+noise is heard after each blow, which is produced by drawing away the
+magnet, and which appears to be a blow struck with much less force.
+The sound is of course increased if the magnet is provided with its
+vibrating disk.
+
+If words are uttered on the vibrating disk of the sending telephone,
+when it is applied to the pole of the magnet, various sounds are
+heard on the receiving telephone, somewhat similar to those produced
+by vibrating one of the strings of a violin, and the sound made in
+withdrawing the disk from contact with the magnet is distinctly heard
+in the receiver.
+
+The person who applies his ear to the vibrating disk of the sender when
+it is arranged as above, may hear the voice of anyone who speaks into
+the receiver, but cannot distinguish the words, owing, no doubt, to the
+condensed magnetism at the point of contact between the magnet and the
+vibrating disk, which slackens the magnetic variations and makes it
+more difficult for them to take place.
+
+A coil is not necessary in order to perceive the blows struck upon
+the magnet with a rod of soft iron. It is enough to wind three turns
+of naked conducting wire, which acts as line wire, round one end of
+the magnet, and the sounds perceived cease, as in other experiments,
+when the circuit is broken, plainly showing that they are not due to
+mechanical transmission. It is a still more curious fact that if the
+magnet is placed in the circuit, so as to form an integral part of it,
+and if the two ends of the conducting wire are wound round the ends of
+the magnet, the blows struck upon the latter with the soft iron rod
+are perceived in the telephone as soon as one pole of the magnet is
+provided with a vibrating disk.
+
+I have myself repeated M. des Portes’ experiments by simply striking
+on the screw which, in ordinary telephones, fastens the magnet to
+the instrument, and I have ascertained that, whenever the circuit was
+complete, the blows struck with an ivory knife were repeated by the
+telephone: they were, it is true, very faint when the vibrating disk
+was removed, but very marked when the disk was in its place. On the
+other hand, no sound was perceived when the circuit was broken. These
+sounds were louder when the blows were struck upon the screw than when
+they were struck on the pole of the magnet itself above the coil: for
+this reason, that in the first case the magnet could vibrate freely,
+while in the second the vibrations were stifled by the fixed position
+of the bar magnet.
+
+These effects may be to some extent explained by saying that the
+vibrations caused in the magnet by the shock produce undulatory
+displacements of the magnetised particles in the whole length of the
+bar, and that induced currents would, according to Lenz’s law, result
+in the helix from these displacements--currents of which the force
+would increase when the power of the magnet was further excited by the
+reaction of the diaphragm, which acts as an armature, and also by that
+of the striking instrument when it also is magnetic. Yet it is more
+difficult to explain M. des Portes’ later experiments, and the effect
+may be produced by something more than the ordinary induced currents.
+
+These are not the only experiments which show the effects produced
+under the influence of molecular disturbance of various kinds. Mr.
+Thompson, of Bristol, has observed that if a piece of iron and a tin
+rod placed perpendicularly on the iron are introduced into the circuit
+of an ordinary telephone, it is enough to strike the tin rod in order
+to produce a loud sound in the telephone. He has also shown that if
+the two ends of a bar magnet are enclosed by two induction coils which
+are placed in connection with the circuit of a telephone, and if the
+flame of a spirit lamp is moved below the magnet in the space dividing
+the two coils, a distinct sound is heard as soon as the flame exerts
+its influence on the bar magnet. This effect is undoubtedly due to the
+weakening of the magnetic force of the bar which is produced by the
+action of heat. I have myself observed that a scratching sound on one
+of the wires which connect the telephones is heard in both of them, at
+whatever point in the circuit the scratch is made. The sounds produced
+are indeed very faint, but they can be distinctly heard, and they
+become more intense when the scratch is made on the binding-screws of
+the telephone wires. These sounds cannot result from the mechanical
+transmission of vibrations, since they are imperceptible when the
+circuit is broken. From these experiments it appears that some sounds
+which have been observed in telephones tried on telegraph stations may
+arise from the friction of the wires on their supports--a friction
+which produces those very intense sounds which are sometimes heard on
+telegraphic wires.
+
+
+_Theory of the Telephone._--It appears from the several experiments
+of which we have spoken that the explanation generally given of the
+effects produced in the telephone is very imperfect, and that the
+transmission of speech, instead of resulting from the repetition by the
+membrane of the receiving telephone (influenced by electro-magnetism)
+of vibrations caused by the voice on the membrane of the transmitting
+membrane, is due to molecular vibrations produced in the whole
+electro-magnetic system, and especially on the magnetic core contained
+in the helix. These vibrations must be of the same nature as those
+which have been observed in resonant electro-magnetic rods by MM. Page,
+de la Rive, Wertheim, Matteucci, &c., and these have been employed in
+telephones by Reiss, by Cecil and Leonard Wray, and by Vanderweyde.
+
+According to this hypothesis, the principal office of the vibrating
+plate consists in its reaction, in order to produce the induced
+currents when the voice has placed it in vibration, and by this
+reaction on the polar extremity of the bar magnet it strengthens the
+magnetic effects caused in the centre of the bar when it vibrates under
+the electro-magnetic influence, or at least when it is affected by the
+magnet. Since the range of these vibrations for a single note is great
+in proportion to the flexibility of the note, and since, on the other
+hand, the variations in the magnetic condition of the plate are rapid
+in proportion to the smallness of its mass, the advantage of employing,
+as Mr. Edison has done, very thin and relatively small plates is
+readily understood. In the case of transmission, the wider range of
+vibration increases the intensity of the induced currents transmitted.
+In the case of reception the variations in the magnetising force which
+produces the sounds are rendered clearer and more distinct, both in
+the armature membrane and in the bar magnet: something is gained,
+therefore, in each case. This hypothesis by no means excludes the
+phonetic effects of the mechanical and physical vibrations which may
+be produced in the armature plate under the influence of magnetisation
+and demagnetisation to which it is subjected, and these join their
+influence to that of the magnetic core.
+
+What is the nature of the vibrations sent into the receiving telephone?
+This question is still obscure, and those who have studied it are far
+from being in agreement: as early as 1846 it was the subject of an
+interesting discussion between MM. Wertheim and de la Rive, and the new
+discoveries render it still more complex. M. Wertheim considers that
+these vibrations are at once longitudinal and transverse, and arise
+from attractions exchanged between the spirals of the magnetising helix
+and the magnetic particles of the core. M. de la Rive holds that in
+the case we are considering the vibrations are simply longitudinal,
+and result from molecular contractions and expansions produced by the
+different combinations assumed by the magnetic molecules under the
+influence of magnetisation and demagnetisation. This appears to us to
+be the most natural explanation, and it seems to be confirmed by the
+experiment made by M. Guillemin in 1846. M. Guillemin ascertained that
+if a flexible iron rod, surrounded by a magnetising helix, is kept in
+position by a vice at one end, and bent back by a weight at the other,
+it can be made to return instantly to its normal position by sending a
+current through the magnetising helix. This recovery can in such a case
+be due to nothing but the contraction caused by the magnetic molecules,
+which, under the influence of their magnetisation, tend to produce
+intermolecular attractions, and to modify the elastic conditions of the
+metal. It is known that when iron is thus magnetised it becomes as hard
+as steel, and a file makes no impression on its surface.
+
+It is at any rate impossible to dispute that sounds are produced in
+the magnetic core, as well as in the armature, under the influence
+of intermittent electric action. These sounds may be musical or
+articulate; for as soon as the sender has produced the electric action
+required, there is no reason why vibrations which are effected in a
+transverse or longitudinal direction should transmit the one more than
+the other. These vibrations may, as we have seen, be termed microscopic.
+
+Signor Luvini, who shares our opinion of the foregoing theory, does
+not, however, think it wholly satisfactory, unless account is taken
+of the reaction caused by the bar magnet on the helix which surrounds
+it. ‘There cannot,’ he says, ‘be _action_ without _reaction_, and
+consequently the molecular action produced in the magnet ought to cause
+corresponding variations in the helix, and these two effects ought to
+contribute to the production of sounds.’ He supports this remark by a
+reference to Professor Rossetti’s experiment, of which we have spoken
+above.
+
+We believe, however, that this double reaction of which Signor Luvini
+speaks is not indispensable, for we have seen that insulated helices
+can produce sounds; it is true that the spirals, reacting on each
+other, may be the cause of this.
+
+The difficulty of explaining the production of sounds in an
+electro-magnetic organ destitute of armature caused the authenticity
+of the experiments we have described to be at first denied, and
+Colonel Navez started a controversy with us which is not likely to be
+soon terminated; yet one result of this controversy is that Colonel
+Navez was obliged to admit _that the sound of the human voice may be
+reproduced by a telephonic receiver without a disk_. But he still
+believes that this reproduction is so faint that it is not possible
+to recognise articulate words, and he maintains that the transverse
+vibrations of the disk, which are due to effects of attraction, are
+the only ones to reproduce articulate speech with such intensity as to
+be of any use.
+
+It is certain that the articulation of speech requires a somewhat
+intense vibration which cannot easily be produced in a telephone
+without a diaphragm; for it must be remembered that in an instrument
+so arranged, the magnetic effects are reduced in a considerable ratio,
+which is that of the magnetic force developed in the magnet, multiplied
+by itself, and that so faint an action as that effected in a telephone
+becomes almost null when, in consequence of the suppression of the
+armature, it is only represented by the square root of the force which
+produced it. It is therefore possible that the sounds which are hardly
+perceptible in a telephone without a diaphragm become audible when
+the cause which provokes them is multiplied by itself, and when there
+are in addition the vibrations produced in the heart of the armature
+itself, influenced by the magnetisations and demagnetisations to which
+it is subjected.
+
+In order to show that the action of the diaphragm is less indispensable
+than Colonel Navez seems to imagine, and that its vibrations are not
+due to electro-magnetic attractions, it will be enough to refer to Mr.
+Hughes’s experiments, which we have mentioned above. It is certain
+that if this were the effect produced, we should hear better when the
+two bar magnets present their poles of the same nature before the
+diaphragm, than when they present the poles of contrary natures, since
+the whole action would then converge in the same direction. Again, the
+more marked effects obtained with multiple diaphragms in juxtaposition
+completely exclude this hypothesis. It is, however, possible that
+in electro-magnetic telephones the iron diaphragm, in virtue of the
+rapid variations of its magnetic condition, may contribute to render
+the sounds clearer and more distinct; it may react in the way the
+tongue does; but we believe that the greater or less distinctness of
+the articulate sounds must be chiefly due to the range of vibrations.
+Thus Mr. Hughes has shown that the carbons of metallised wood employed
+in his microphonic speakers were to be preferred to retort carbons
+for the transmission of speech, for the very reason that they had
+less conductivity, so that the differences of resistance which result
+from differences of pressure are more marked, and consequently it is
+easier to seize the different degrees of vocal sounds which constitute
+articulate speech.
+
+It must be clearly understood that what we have just said only applies
+to the Bell telephone, that is, to a telephone in which the electric
+currents have such a faint intensity that it cannot be supposed there
+is any external attractive effect. When these currents are so energetic
+as to produce such an effect, a transverse electro-magnetic vibration
+certainly takes place, which is added to the molecular vibration, and
+helps to increase the sounds produced. But it is no less true that this
+transverse vibration by attraction or by movement of the diaphragm
+is not necessary for the reproduction of sounds, whether musical or
+articulate.
+
+We are not now concerned with the discussion of magnetic effects;
+there has been an advance in science since Colonel Navez started the
+controversy, and we must ask how his theory of the movements of the
+telephone diaphragm by attraction will explain the reproduction of
+speech by a receiving microphone destitute of any electro-magnetic
+organ, and I can assert that my experiments show that there can be no
+mechanical transmission of vibrations, since no sound is heard when
+the circuit is broken or deprived of its battery. Colonel Navez must
+therefore accept the molecular vibrations. This certainly gives us a
+new field for study; but it is because European men of science persist
+in remaining bound by incomplete theories that we have allowed the
+Americans who despise them to reap the glory of the great discoveries
+by which we have lately been astonished.
+
+The experiments quoted above show that sounds may be reproduced not
+only by simple helices without an electro-magnetic organ, but also by
+the plates of a condenser, in spite of the pressure exerted upon them;
+and when we add to this the effects I have just pointed out, it may
+be supposed that vibrations of sound must result from every reaction
+between two bodies which has the effect of producing abruptly and at
+close intervals modifications in the condition of their electric or
+magnetic equilibrium. It is known that the presence of ponderable
+matter is necessary for the production of electric effects, and it
+is possible that the molecular vibrations of which I have spoken may
+be the result of molecular movements, due to the variations of the
+electric force which holds the molecules in a special condition of
+reciprocal equilibrium.
+
+In conclusion, the theory of the telephone and microphone, considered
+as reproductive organs of speech, is still far from being perfectly
+clear, and it would be imprudent to be too positive on questions of
+such recent origin.
+
+The theory of the electric transmission of sounds in electro-magnetic
+telephones is somewhat complex. It has been seen that they can be
+obtained from diaphragms of non-magnetic substance, and even from
+simple mechanical vibrations produced by shocks. Are we to ascribe
+them in the first case to the inductive reaction of the magnet on the
+vibrating plate, and in the second case to the movements of magnetic
+particles before the spirals of the helix? The matter is still very
+obscure; yet it is conceivable that the modifications of the inducing
+action of the magnet on the vibrating diaphragm may involve variations
+in the magnetic intensity, just as we can admit an effect of the same
+kind due to the approach and withdrawal of the magnetic particles of
+the spirals of the helix; M. Trève, however, believes that there is in
+the latter case a special action, which he has already had occasion
+to study under other circumstances, and he sees in the current thus
+caused the effect of the transformation of the mechanical labour
+produced amidst the magnetic molecules. The question is complicated by
+the fact that these effects are often produced by purely mechanical
+transmissions.
+
+There is another point to consider, on which Colonel Navez has made
+some interesting remarks; that is, whether the effects in the receiver
+are stronger with permanent than with temporary magnets. In the
+first model of the telephone, exhibited by Mr. Bell at Philadelphia,
+the receiver was, as I have said, made of a tubular electro-magnet,
+furnished with a vibrating disk at its cylindrical pole; but this
+arrangement was abandoned by Mr. Bell, with the object, as he states
+in his paper, of rendering his instrument both a receiver and a
+sender.[13] Yet Colonel Navez maintains that the magnet plays an
+important part, and is even indispensable under the present conditions
+of its form. ‘It is possible,’ he says, ‘under certain circumstances,
+and by making the instrument in a special way, to make a Bell receiver
+speak without a permanent magnet, yet with an instrument of the usual
+construction the sound ceases when the magnet is withdrawn and replaced
+by a cylinder of soft iron. In order to restore the voice of the
+telephone, it is enough to approach the pole of a permanent magnet to
+the cylinder of soft iron. It follows from these experiments that a
+Bell telephone cannot act properly unless the disk is subjected to an
+initial magnetic tension obtained by means of a permanent magnet. It is
+easy to deduce this assertion from a consideration of the theory.’
+
+The assertion may be true in the case of Bell telephones, which
+are worked by extremely weak currents, but when these currents are
+relatively strong, all electro-magnets will reproduce speech perfectly,
+and we have seen that M. Ader made a telephone with the ordinary
+electro-magnet which acted perfectly.
+
+The action of the currents sent through the helix of a telephone can be
+easily explained. Whatever may be the magnetic conditions of the bar,
+the induced currents of different intensity which act upon it produce
+modifications in its magnetic state, and hence the molecular vibrations
+follow from contraction and expansion. These vibrations are likewise
+produced in the armature under the influence of the magnetisations and
+demagnetisations which are produced by the magnetic action of the core,
+and they contribute to the vibrations of the core itself, while at the
+same time the modifications in the magnetic condition of the system are
+increased by the reaction of the two magnetic parts upon each other.
+
+When the bar is made of soft iron, the induced currents act by creating
+magnetisations of greater or less energy, followed by demagnetisations
+which are the more prompt since inverse currents always succeed to
+those which have been active, and this causes the alternations of
+magnetisation and demagnetisation to be more distinct and rapid. When
+the bar is magnetised, the action is differential, and may be exerted
+in either direction, according as the induced currents corresponding to
+the vibrations which are effected pass through the receiving coil in
+the same or opposite direction as the magnetic current of the bar. If
+these currents are in the same direction, the action is strengthening,
+and the modifications are effected as if a magnetisation had taken
+place. If these currents are of opposite direction, the inverse effect
+is produced; but, whatever the effects may be, the molecular vibrations
+maintain the same reciprocal relations and the same height in the scale
+of musical sounds. If the question is considered from the mathematical
+point of view, we find the presence of a constant, corresponding
+with the intensity of the current, which does not exist in mechanical
+vibrations, and which may possibly be the cause of the peculiar tone
+of speech reproduced by the telephone, a tone which has been compared
+to the voice of Punch. M. Dubois Raymond has published an interesting
+paper on this theory, which appeared in ‘Les Mondes,’ February 21,
+1878, but we do not reproduce it here, since his remarks are too
+scientific for the readers for whom this work is intended. We will only
+add that Mr. C. W. Cunningham asserts that the vibrations produced in
+a telephone cannot be manifested under precisely the same conditions
+as those which affect the tympanum of the ear, because the latter has
+a peculiar funnel-shaped form, which excludes every fundamental note,
+specially adapted to it, and this is not the case with the bars and
+magnetic plates which possess fundamental notes capable of greatly
+altering the half-tones of the voice. He considers the alteration
+of the voice observed in the telephone must be ascribed to these
+fundamental notes.
+
+
+_M. Wiesendanger’s Thermophone._--M. Wiesendanger, in an article
+inserted in the ‘English Mechanic and World of Science,’ September
+13, 1878, ascribes the reproduction of speech in certain telephones
+to vibratory movements resulting from molecular expansions and
+contractions produced by variations of temperature, and these
+variations would follow from the currents of varying intensity which
+are transmitted through the telephonic circuits. He was conscious of
+one objection to this theory, namely, that the movements of expansion
+and contraction due to heat are slowly produced, and consequently are
+not capable of substantial action, rapid enough to produce vibrations;
+but he considers that molecular effects need not take place under the
+same conditions as those which are displayed in the case of material
+substances.
+
+M. Wiesendanger believes that this hypothesis will explain the
+reproduction of speech in the receiving microphones of Mr. Hughes,
+and that it may even be applied to the theory of the electro-magnetic
+telephone, if we consider that a magnetising helix, as well as a
+magnetic core, round which an electric current circulates, is more
+or less heated, according to the intensity of the current which
+traverses it, especially when the wire of the helix and the core
+are bad conductors of electricity and of magnetism. Pursuing this
+idea, M. Wiesendanger has sought to construct telephones in which
+calorific effects are more fully developed, and with this object he
+used very fine wire of German silver and platinum to make the coils.
+He ascertained that these coils could produce sounds themselves, and,
+to increase their intensity, he put them between disks of iron, or on
+tin tubes, placed on resonant surfaces close to the disks. In this way
+he says that he was able to make a good receiving telephone without
+employing magnets. He afterwards arranged the instrument in different
+ways, of which the two following are the most noteworthy.
+
+In the first, the electro-magnetic system was simply formed by a
+magnetic disk with a helix wound round it, of which the wire was in
+connection with the circuit of a microphone, and which was fastened to
+the centre of the parchment membrane of an ordinary string telephone;
+the disk consisted of two iron plates separated by a carbon disk of
+smaller diameter, and the whole was so compressed as to form a solid
+mass.
+
+In the second, the helix was wound on a tin tube, six inches long and
+five-eighths of an inch in diameter, which was soldered by merely a
+point to the centre of the diaphragm of an ordinary telephone.
+
+The inventor asserts that the tube and diaphragm only act as
+resonators, and that the sounds produced by this instrument are nearly
+the same as those obtained from the ordinary string telephone: the
+tunes of a musical box were heard, and the reproduction of speech
+was perfect, both in intensity and in distinctness of sound; it even
+appeared that telephonic sounds were audible with the tin tube alone,
+surrounded by the helix. M. Wiesendanger says that ‘these different
+receiving telephones show clearly that the diaphragm and magnet are
+not essential, but merely accessory, parts of a telephone.’
+
+
+
+
+VARIOUS EXPERIMENTS MADE WITH THE TELEPHONE.
+
+
+We must now consider a series of experiments which demonstrate the
+wonderful properties of the telephone, and which may also give some
+indication of the importance of the influences by which it is liable to
+be affected.
+
+
+_Experiments by M. d’Arsonval._--We have seen that the telephone is an
+extremely sensitive instrument, but its sensitiveness could scarcely be
+appreciated by ordinary means. In order to gauge it, M. d’Arsonval has
+compared it to the nerve of a frog, which has hitherto been regarded
+as the most perfect of all galvanoscopes, and it appears from his
+experiments that the sensitiveness of the telephone is two hundred
+times greater than that of the frog’s nerve. M. d’Arsonval has given
+the following account of his researches in the records of the Académie
+des Sciences, April 1, 1878:
+
+‘I prepared a frog in Galvani’s manner. I took Siemens’ instrument of
+induction, used in physiology under the name of the chariot instrument.
+I excited with the ordinary pincers the sciatic nerve, and I withdrew
+the induced coil until the nerve no longer responded to the electric
+excitement. I then substituted the telephone for the nerve, and the
+induced current, which had ceased to excite the latter, made the
+instrument vibrate strongly. I withdrew the induced coil, and the
+telephone continued to vibrate.
+
+‘In the stillness of night I could hear the vibration of the telephone
+when the induced coil was at a distance fifteen times greater than the
+minimum at which the excitement of the nerve took place; consequently,
+if the same law of inverse squares applies to induction and to
+distance, it is evident that the sensitiveness of the telephone is two
+hundred times greater than that of the nerve.
+
+‘The sensitiveness of the telephone is indeed exquisite. We see how
+much it exceeds that of the galvanoscopic frog’s leg, and I have
+thought of employing it as a galvanoscope. It is very difficult to
+study the muscular and nervous currents with a galvanometer of 30,000
+turns, because the instrument is deficient in instantaneous action,
+and the needle, on account of its inertia, cannot display the rapid
+succession of electric variations, such as are effected, for example,
+in a muscle thrown into electric convulsion. The telephone is free
+from this inconvenience, and it responds by vibration to each electric
+change, however rapid it may be. The instrument is therefore well
+adapted for the study of electric tetanus in the muscle. It is certain
+that the muscular current will excite the telephone, since this current
+excites the nerve, which is less sensitive than the telephone. But for
+this purpose some special arrangement of the instrument is required.
+
+‘It is true that the telephone can only reveal the variations of an
+electric current, however faint they may be; but I have been able, by
+the use of a very simple expedient, to reveal by its means the presence
+of a continuous current, also of extreme faintness. I send the current
+in question into the telephone, and, to obtain its variations, I
+break this current mechanically with a tuning-fork. If no current is
+traversing the telephone, it remains silent. If, on the other hand,
+the faintest current exists, the telephone vibrates in unison with the
+tuning-fork.’
+
+Professor Eick, of Wurzburg, has also used the telephone for
+physiological researches, but in a direction precisely opposite to
+that explored by M. d’Arsonval. He ascertained that when the nerves of
+a frog were placed in connection with a telephone, they were forcibly
+contracted when anyone was speaking into the instrument, and the
+force of the contractions chiefly depended on the words pronounced.
+For instance, the vowels _a_, _e_, _i_ produced hardly any effect,
+while _o_ and especially _u_ caused a very strong contraction. The
+words _Liege still_, pronounced in a loud voice, only produced a faint
+movement, while the word _Tucker_, even when spoken in a low voice,
+strongly agitated the frog. These experiments, reminding us of those
+by Galvani, were necessarily based on the effects produced by the
+induced currents developed in the telephone, and they show that if this
+instrument is a more sensitive galvanoscope than the nerve of a frog,
+the latter is more susceptible than the most perfect galvanometer.
+
+
+_Experiments by M. Demoget._--In order that he might compare the
+intensity of the sounds transmitted by the telephone with the intensity
+of original sounds, M. Demoget placed two telephones in an open
+space. He held the first to his ear, while his assistant withdrew
+to a distance, constantly repeating the same syllable with the same
+intensity of tone in the second instrument. He first heard the sound
+transmitted by the telephone, and then the sound which reached him
+directly, so that comparison was easy, and he obtained the following
+results.
+
+At a distance of 93 yards the original and the transmitted sounds
+were received with equal intensity, while the vibrating disk was
+about 5 centimètres from the ear. At this moment, therefore, the
+relative intensity was as 25 to 81,000,000. In other words, the sound
+transmitted by the telephone was only 1/3000000 of the emitted sound.
+‘But,’ said M. Demoget, ‘since the stations at which we worked could
+not be regarded as two points freely vibrating in space, the ratio may
+be reduced by one half on account of the influence of the earth, and
+the sound transmitted by the telephone may be supposed to be 1,500,000
+times weaker than that emitted by the voice.
+
+‘Again, since we know that the intensity of the two sounds is in
+proportion to the square of the range of vibrations, it may be
+concluded that the vibrations of the two telephone disks were in
+direct proportion to the distance, that is, as 5 to 9,000, or that the
+vibrations of the sending telephone were eighteen hundred times greater
+than those of the receiving telephone. These latter may therefore be
+compared to molecular vibrations, since the range of those of the
+sending telephone was extremely small.
+
+‘Without in any degree detracting from the merit of Bell’s remarkable
+invention,’ continues M. Demoget, ‘it follows from what I have said
+above that the telephone, considered as a sending instrument, leaves
+much to be desired, since it only transmits the 18/100 part of the
+original power; and if it has produced such unexpected results, this
+is due to the perfection of the organ of hearing, rather than to the
+perfection of the instrument itself.’
+
+M. Demoget considers this loss of power which takes place in the
+telephone to be chiefly owing to the eight transformations in
+succession to which sound is subjected before reaching the ear, setting
+aside the loss due to the electric resistance of the line, which might
+in itself suffice to absorb the whole force.
+
+In order to estimate the force of the induced currents which act upon
+a telephone, M. Demoget has attempted to compare them with currents of
+which the intensity is known, and which produce vibrations of like
+nature and force: for this purpose he has made use of two telephones,
+A and B, communicating through a line 22 yards in length. He placed a
+small file in slight contact with the vibrating disk of the telephone
+A, and caused friction between the file and a metallic plate: the sound
+thus produced was necessarily transmitted by the telephone B, with
+an intensity which could be estimated. He then substituted a battery
+for the telephone A, and the file was introduced into the circuit by
+connecting it with one of the poles. The current could only be closed
+by the friction of the file with the plate, which had a spring, and was
+in communication with the other end of the circuit. In this way broken
+currents were obtained, which caused vibration in the telephone B, and
+produced a sound of which the intensity varied with the strength of
+the battery current. In this way M. Demoget endeavoured to find the
+electric intensity capable of producing a sound similar to that of the
+telephone A, and he ascertained that it corresponded in intensity to
+that produced in a small thermo-electric battery formed of an iron and
+a copper wire, two millimètres in diameter, flattened at the end, and
+soldered to the tin: the faint current produced by this battery only
+caused a short wire galvanometer to deviate two degrees.
+
+This estimate does not appear to us to unite so many conditions of
+accuracy as to enable us to deduce from it the degree of sensitiveness
+possessed by a telephone, a sensitiveness which the experiments of
+Messrs. Warren de la Rue, Brough, and Peirce show to be much greater.
+Mr. Warren de la Rue, as we have seen, used Thomson’s galvanometer,
+and compared the deviation produced on the scale of this galvanometer
+with that caused by a Daniell cell traversing a circle completed by a
+rheostat: he ascertained that the currents discharged by an ordinary
+Bell telephone are equivalent to those of a Daniell cell traversing
+100 megohms of resistance, that is, 6,200,000 miles of telegraphic
+wire. Mr. Brough, the Director of Indian Telegraphs, considers that the
+strongest current which at any given moment causes a Bell telephone
+to work does not exceed 1/1000000 of the unit of current, that is,
+one Weber, and the current transmitted to the stations on the Indian
+telegraphic line is 400,000 times as strong. Finally, Professor
+Peirce, of Boston, compares the effects of the telephonic current
+with those which would be produced by an electric source of which the
+electro-motive force should be 1/200000 part of a volt, or one Daniell
+cell. Mr. Peirce justly remarks that it is difficult to estimate the
+real value of these kinds of currents at any precise sum, since it
+essentially varies according to the intensity of the sounds produced
+on the transmitting telephone; but it may be affirmed that it is less
+than the 1/1000000 part of the current usually employed to work the
+instruments on telegraphic lines.
+
+Signor Galileo Ferraris, who has recently published an interesting
+treatise on this question in the ‘Atti della Reale Accademia delle
+Scienze di Torino’ (June 13, 1878), states that the intensity of the
+currents produced by the ordinary Bell telephone varies with the pitch
+of the sound emitted.
+
+
+_Experiments by M. Hellesen, of Copenhagen._--In order to estimate the
+reciprocal effects of different parts of a telephone, M. Hellesen has
+made telephones of the same size with three different arrangements
+which act inversely to each other. The first was of the ordinary form,
+the second like that of Bell’s first system, that is, with a membrane
+supporting a small iron armature on its centre, instead of a vibrating
+disk, and the third telephone consisted of a hollow cylindrical magnet,
+with the vibrating disk fixed to one of its poles, and the disk was
+adapted to move before a flat, snail-shaped spiral, of which the number
+of spirals equalled those of the two other helices. In this last
+arrangement, the induced currents resulting from the vibrations of the
+voice might be assimilated to those which follow from the approximation
+and withdrawal of the two parallel spirals, one of which should be
+traversed by a current. It is this last arrangement which Mr. Bell has
+adopted as producing the best effects, and it is rare in the history of
+discoveries that an inventor hits at once on the best arrangement of
+his instrument.
+
+
+_Experiments by M. Zetsche._--There are always a few perverse minds,
+impelled by a spirit of contradiction to deny evidence, and thus they
+attempt to depreciate a discovery of which the glory irritates them.
+The telephone and the phonograph have been the objects of such unworthy
+criticism. It has been said that electric action had nothing to do with
+the effects produced in the telephone, and that it only acted under the
+influence of mechanical vibrations transmitted by the conducting wire,
+just as in a string telephone. It was in vain to demonstrate to these
+obstinate minds that no sound is produced when the circuit is broken,
+and in order to convince them M. Zetsche has made some experiments to
+show, from the mode in which sound is propagated, that it is absurd
+to ascribe the sound produced in a telephone to mechanical vibration.
+He wrote to this effect in an article inserted in the ‘Journal
+Télégraphique,’ Berne, January 25, 1878:
+
+‘The correspondence by telephone between Leipzig and Dresden affords
+another proof that the sounds which reproduce words at the receiving
+station are due to electric currents, and not to mechanical vibrations.
+The velocity with which sound is transmitted by vibrations on the wire,
+in the case of longitudinal undulations, may be estimated at three
+miles one furlong a second, so that the sound ought to traverse the
+distance from Leipzig to Dresden in 25 seconds. The same time ought
+to elapse before receiving the answer. Consequently there should be
+an interval of more than three-quarters of a minute allowed for each
+exchange of communication, which is by no means the case.’
+
+
+_Experiments which may be made by anyone._--We will conclude this
+chapter, devoted to the account of the different experiments made
+with the telephone, by the mention of a singular experiment, which,
+although easily performed, has only been suggested a few months ago by
+a Pennsylvanian newspaper. It consists in the transmission of speech by
+a telephone simply laid on some part of the human body adjacent to the
+chest. It has been asserted that any part of the body will produce this
+effect, but according to my experience, I could only succeed when the
+telephone was firmly applied to my chest. Under such conditions, and
+even through my clothes, I could make myself heard when speaking in a
+very loud voice, from which it appears that the whole of the human body
+takes part in the vibrations produced by the voice. In this case, the
+vibrations are mechanically transmitted to the diaphragm of the sending
+telephone, not by the air, but by the body itself acting on the outside
+of the telephone.
+
+
+
+
+THE MICROPHONE.
+
+
+The microphone is in fact only the sender of a battery telephone,
+but with such distinctive characteristics that it may be regarded
+as an original invention which is entitled to a special name. The
+invention has lately given rise to an unfortunate controversy between
+its inventor, Mr. Hughes, and Mr. Edison, the inventor of the carbon
+telephone and the phonograph--a controversy which has been embittered
+by the newspapers, and for which there were no grounds. For although
+the scientific principle of the microphone may appear to be the same
+as that of Mr. Edison’s carbon sender, its arrangement is totally
+different, its mode of action is not the same, and the effect required
+of it is of quite another kind. Less than this is needed to constitute
+a new invention. Besides, a thorough examination of the very principle
+of the instrument must make us wonder at Mr. Edison’s claim to
+priority. He cannot in fact regard as his exclusive possession the
+discovery of the property possessed by some substances of moderate
+conductivity of having this power modified by pressure. In 1856, and
+often subsequently, as for example in 1864, 1872, 1874, and 1875, I
+made numerous experiments on this point, which are described in the
+first volume of the second edition of my ‘Exposé des applications de
+l’Electricité,’ and also in several papers presented to the Académie
+des Sciences, and inserted in their _Comptes rendus_. M. Clarac again,
+in 1865, employed a tube made of plumbago, and provided with a moveable
+electrode, to produce variable resistances in a telegraphic circuit.
+Besides, in Mr. Edison’s telephonic sender, the carbon disk, as we
+have seen, must be subjected to a certain initial pressure, in order
+that the current may not be broken by the vibrations of the plate on
+which it rests, and consequently the modifications of resistance in
+the circuit which produce articulate sounds are only caused by greater
+or less increase and diminution of pressure, that is, by differential
+actions. We shall presently see that this is not the case with the
+microphone. In the first place, the carbon contact is effected in
+the latter instrument on other carbons and not with platinum disks,
+and these contacts are multiple. In the second place, the pressure
+exerted on all the points of contact is excessively slight, so that the
+resistances can be varied in an infinitely greater ratio than in Mr.
+Edison’s system; and for this very reason it is possible to magnify
+the sounds. In the third place, a microphone can be made of other
+substances besides carbon. Finally, no vibrating disk is needed to make
+the microphone act; the simple medium of air is enough, so that it is
+possible to work the instrument from some little distance.
+
+We do not therefore see the grounds for Mr. Edison’s assertions,
+and especially for the way in which he has spoken of Messrs. Hughes
+and Preece, who are well known in science and are in all respects
+honourable men. I repeat my regret that Mr. Edison should have made
+this ill-judged attack on them, since it must injure himself, and
+is unworthy of an inventor of such distinction. If we look at the
+question from another point of view, we must ask Mr. Edison why, if
+he invented the microphone, he did not make us acquainted with its
+properties and results. These results are indeed startling, since the
+microphone has in so short a time attracted general attention; and it
+is evident that the clear-sighted genius of this celebrated American
+inventor would have made the most of the discovery if it were really
+his. The only justification for Mr. Edison’s claim consists in his
+ignorance of the purely scientific discoveries made in Europe, so that
+he supposed the invention of the microphone to be wholly involved in
+the principle which he regards as his peculiar discovery.
+
+In Mr. Hughes’s instrument which we are now considering, the sounds,
+instead of reaching the receiving stations much diminished, which is
+the case with ordinary telephones, and even with that of Mr. Edison,
+are often remarkably increased, and it is for this reason that Mr.
+Hughes has given to this telephonic system the name of Microphone,
+since it can be employed to discover very faint sounds. Yet we must add
+that this increase really takes place only when the sounds result from
+mechanical vibrations transmitted by solid substances to the sending
+instrument. The sounds propagated through the air are undoubtedly a
+little more intense than in the ordinary system, but they lose some
+of their force, and therefore it cannot be said that in this case the
+microphone has the same effect upon sounds as the microscope has on
+objects on which light is thrown. It is true that with this system it
+is possible to speak at a distance from the instrument, and I have
+even been able to transmit conversation in a loud voice, when standing
+at a distance of nine yards from the microphone. When close to the
+instrument, I was also perfectly able to make myself heard at the
+receiving station while speaking in a low voice, and even to send the
+sounds to a distance of ten or fifteen centimètres from the mouthpiece
+of the receiving telephone by raising the voice a little; but the
+increase of sound is not really very evident unless it is produced by a
+mechanical action transmitted to the standard of the instrument.
+
+Thus the steps of a fly walking on the stand are clearly heard, and
+give the sensation of a horse’s tread; and even a fly’s scream,
+especially at the moment of death, is said by Mr. Hughes to be audible.
+The rustling of a feather or of a piece of stuff on the board of the
+instrument, sounds completely inaudible in ordinary circumstances, are
+distinctly heard in the microphone. It is the same with the ticking of
+a watch placed upon the stand, which may be heard at ten or fifteen
+centimètres from the receiver. A small musical box placed upon the
+instrument gives out so much sound, in consequence of its vibratory
+movements, that it is impossible to distinguish the notes, and in order
+to do so it is necessary to place the box close to the instrument,
+without allowing it to come in contact with any of its constituent
+parts. It therefore appears that the instrument is affected by the
+vibrations of air, and the transmitted sounds are fainter than those
+heard close to the box. On the other hand, the vibrations produced
+by the pendulum of a clock, when placed in communication with the
+standard of the instrument by means of a metallic rod, are heard
+perfectly, and may even be distinguished when the connection is made by
+the intervention of a copper wire. A current of air projected on the
+system gives the sensation of a trickle of water heard in the distance.
+Finally, the rumbling of a carriage outside the house is transformed
+into a very intense crackling noise, which may combine with the ticking
+of a watch, and will often overpower it.
+
+
+_Different Systems of Microphones._--The microphone has been made in
+several ways, but the one represented in fig. 39 is the arrangement
+which renders it the most sensitive. In this system, two small carbon
+cubes, A, B, are placed one above the other on a vertical wooden
+prism; two holes are pierced in the cubes to serve as sockets for a
+spindle-shaped carbon pencil, that is, with the points fined off at
+the two ends, and about four centimètres long: if of a large size, the
+inertia will be too great. One end of this pencil is in the cavity of
+the lower carbon, and the other must move freely in the upper cavity
+which maintains it in a position approaching to that of instable
+equilibrium, that is, in a vertical position. Mr. Hughes states that
+the carbons become more effective if they are steeped in a bath of
+mercury at red heat, but they will act well without undergoing this
+process. The two carbon cubes are also provided with metallic contacts
+which admit of their being placed in connection with the circuit of
+an ordinary telephone in which a Leclanché battery has been placed,
+or one, two, or three Daniell cells, with an additional resistance
+introduced into the circuit.
+
+[Illustration: FIG. 39.]
+
+In order to use this instrument, it is placed on a table, with the
+board which serves to support it, taking care to deaden any extraneous
+vibrations by interposing between this board and the table several
+folds of stuff so arranged as to form a cushion, or, which is better,
+a belt of wadding, or two caoutchouc tubes: what is said by a person
+standing before this system is immediately reproduced in the telephone,
+and if a watch is placed on the stand, or a box with a fly enclosed in
+it, all its movements are heard. The instrument is so sensitive that
+words said in a low voice are most easily heard, and it is possible, as
+I have already said, to hear the speaker when he is standing nine yards
+from the microphone. Yet some precautions are necessary in order to
+obtain good results with this system, and besides the cushions placed
+beneath the instrument to guard it from the extraneous vibrations which
+might ensue from any movements communicated to the table, it is also
+necessary to regulate the position of the carbon pencil. It must always
+rest on some point of the rim of the upper cavity; but as the contact
+may be more or less satisfactory, experience alone will show when it
+is in the best position, and it is a good plan to make use of a watch
+to ascertain this. The ear is then applied to the telephone, and the
+pencil is placed in different positions until the maximum effect is
+obtained. To avoid the necessity of regulating the instrument in this
+way, which must be done repeatedly by this arrangement, MM. Chardin
+and Berjot, who are ingenious in the construction of telephones on this
+pattern, have added to it a small spring-plate, of which the pressure
+can be regulated, and which rests against the carbon pencil itself.
+This system works well.
+
+[Illustration: FIG. 40.]
+
+M. Gaiffe, by constructing it like a scientific instrument, has given
+the instrument a more elegant form. Fig. 40 represents one of his
+two models. In this case, the cubes or carbon dice are supported by
+metallic holders, and the upper one E is made to move up and down a
+copper column G, so as to be placed in the right position by tightening
+the screw V. In this way the carbon pencil can be made to incline
+more or less, and its pressure on the upper carbon can be altered at
+pleasure. When the pencil is in a vertical position, the instrument
+transmits articulate sounds with difficulty, on account of the
+instability of the points of contact, and rustling sounds are heard.
+When the inclination of the pencil is too great, the sounds are purer
+and more distinct, but the instrument is less sensitive. The exact
+degree of inclination should be ascertained, which is easily done by
+experiment. In another model M. Gaiffe substitutes for the carbon
+pencil a very thin square plate of the same material, bevelled on its
+lower and upper surfaces, and revolving in a groove cut in the lower
+carbon. This plate must be only slightly inclined in order to touch
+the upper carbon, and under these conditions it transmits speech more
+loudly and distinctly.
+
+I must also mention another arrangement, devised by Captain Carette
+of the French Engineers, which is very successful in transmitting
+inarticulate sounds. In this case the vertical carbon is pear-shaped,
+and its larger end rests in a hole made in the lower carbon; its upper
+and pointed end goes into a small hole made in the upper carbon, but so
+as hardly to touch it, and there is a screw to regulate the distance
+between the two carbons. Under such conditions, the contacts are so
+unstable that almost anything will put an end to them, and consequently
+the variations in the intensity of the transmitted current are so
+strong that the sounds produced by the telephone may be heard at the
+distance of several yards.
+
+[Illustration: FIG. 41.]
+
+Fig. 41 represents another arrangement, devised by M. Ducretet. The
+two carbon blocks are at D D′, the moveable carbon pencil is at C, the
+telephone at T, and the binding screws at B B′. An enlarged figure of
+the arrangement of the carbons is given on the left. The arm which
+holds the upper carbon D is fastened to a rod, bearing a plate P′,
+of which the surface is rough, and a little cage C′, made of wire
+netting, can be placed upon the plate, so as to enable us to study the
+movements of living insects.
+
+When speech is to be transmitted with a force which can make the
+telephone audible in a large room, the microphone must have a special
+arrangement, and fig. 42 represents the one which Mr. Hughes considers
+the most successful, to which he has given the name of _speaker_.
+
+[Illustration: FIG. 42.]
+
+In this new form, the moveable carbon which is required to produce
+the variable contacts is at C, at the end of a horizontal bar B A,
+properly balanced so as to move up and down on its central point. The
+support on which the bar oscillates is fastened to the end of a spring
+plate in order that it may vibrate more easily, and the lower carbon
+is placed at D below the first. It consists of two pieces laid upon
+each other, so as to increase the sensitiveness of the instrument, and
+we represent the upper piece at E, which is raised so as to show that
+when it is desired only one of these carbons need be used. For this
+purpose the carbon E is fastened to a morsel of paper, which is fixed
+to the little board and contributes to the articulation. A spring R, of
+which the tension can be regulated by the screw _t_, serves to regulate
+the pressure of the two carbons. Mr. Hughes recommends the use of
+metallised charcoal prepared from deal.[14] The whole is then enclosed
+in a semi-cylindrical case H I G, made of very thin pieces of deal, and
+the system is fixed, together with another similar system, in a flat
+box, M J L I, which, on the side M I, presents an opening before which
+the speaker stands, taking care to keep his lower lip at a distance of
+two centimètres from the bottom of the box. If the two telephones are
+connected for strength, and if the battery employed consists of two
+cells of bichromate of potash, it is possible to act so strongly on the
+current, that, after traversing an induction coil only six centimètres
+long, a telephone of Bell’s square model can be made to speak, so as
+to be heard from all parts of a room; a speaking tube, about a yard
+long, must indeed be applied to it. Mr. Hughes asserts that the sounds
+produced by it are nearly as loud as those of the phonograph, and this
+is confirmed by Mr. Thomson.
+
+M. Boudet de Paris has lately invented a microphone speaker of the same
+kind, with which it is possible to make a small telephone utter a loud
+sound. An induction coil, influenced by a single Leclanché cell, must
+be employed.
+
+Suppose that a very small carbon rod with pointed ends is placed at
+the bottom of a box, of about the size of a watch. One end of the rod
+rests against a morsel of carbon, which is fastened to a very thin
+steel diaphragm, placed before a mouthpiece which acts as a lid to
+the box, and is screwed above it. Next suppose that a small piece of
+paper, folded in two, in the shape of the letter V, is fixed above that
+part of the carbon in contact with the carbon of the diaphragm. This
+constitutes the instrument, and in order to work it, it must be held
+in a vertical position before the mouth, at a distance of about three
+centimètres, and it is necessary to speak in the ordinary tone. If the
+telephone is placed in direct communication with this instrument, it
+will send the voice to a distance. Without employing a Leclanché cell,
+the voice may be heard at the distance of ten yards, if one of the
+carbons used for the phonograph is placed before the mouthpiece of the
+telephone.
+
+In this system, the sensitiveness of the instrument is entirely due to
+the slightness of the contact between the two carbons, and the slight
+elasticity of the folded paper constitutes the contact. Perhaps the
+paper itself has some influence; at any rate the most delicate spiral
+spring is incapable of producing the same effect, and it is necessary
+to suspend the instrument vertically, in order that the weight of the
+moveable carbon may not affect it. It can be regulated by depressing or
+elevating that part of the paper which rests on the carbon rod.
+
+Although it is possible to work all telephones with this instrument,
+some are more effective than others. The mouthpiece must be concave,
+and the diaphragm must be close to its rim, and must be made of a
+particular kind of tin. The ordinary diaphragm does not act well, and
+M. Boudet de Paris has tried several, so as to obtain the maximum
+effect.
+
+It is certain that when the instruments are as well regulated as those
+which the inventor has deposited with me, their results are really
+surprising. It is even possible, by using several microphones at the
+sending station, to obtain the reproduction of duets, and even of
+trios, with remarkable effect.
+
+With this kind of microphone speaker M. Boudet de Paris is able to
+transmit speech into a snuff-box telephone, merely consisting of a
+flat helix of wire, placed before a slightly magnetised steel plate,
+and without insertion of a magnetic core. A single Leclanché cell was
+enough. An experiment of the same nature was tried in England, but it
+was found necessary to use six Leclanché cells.
+
+[Illustration: FIG. 43]
+
+[Illustration: FIG. 44.]
+
+The microphone may also be made of morsels of carbon pressed into a
+box between two metallic electrodes, or enclosed in a tube with two
+electrodes represented by two elongated fragments of carbon. In the
+latter case the carbons ought to be as cylindrical as possible, and
+those made by M. Carré for the Jablochkoff candles are very suitable.
+Fig. 43 represents an instrument of this kind which M. Gaiffe arranged
+for me, and which, as we shall see, serves as a thermoscope (fig.
+44). It is composed of a quill filled with morsels of carbon, and
+those at the two ends are tipped with metal. One of these metal tips
+ends in a large-headed screw which, by means of its supports A B, is
+able to press more or less on the morsels of carbon in the tube, and
+consequently to establish a more or less intimate contact between
+them. When the instrument is properly regulated, speech can be
+reproduced by speaking above the tube. It is therefore a microphone
+as well as a thermoscope. Mr. Hughes has remarked one curious fact,
+namely, that if the different letters of the alphabet are pronounced
+separately before this sort of microphone, some of them are much
+more distinctly heard than others, and it is precisely those which
+correspond to the breathings of the voice.
+
+A microphone of this kind may be made by substituting for the carbon
+powders of more or less conductivity, or even metal filings. I have
+shown in my paper on the action of substances of moderate conductivity,
+that such power varies considerably with the pressure and the
+temperature; and as the microphone is based on the differences of
+conducting power which result from differences of pressure, we can
+understand that these powders may be used as a means of telephonic
+transmission. In a recent arrangement of this system Mr. Hughes has
+made the powder adhere together with a sort of gum, and has thus made a
+cylindrical pencil which, when connected with two electrodes which are
+good conductors, can produce effects analogous to those we have just
+described. As I have said, it is possible to use metal filings, but Mr.
+Hughes prefers powdered charcoal.
+
+Mr. Blyth states that a flat box, about 15 inches by 9, filled with
+coke, and with two tin electrodes fixed to the two ends, is one of
+the best arrangements for a microphone. He says that three of these
+instruments, hung like pictures against the wall of a room, would
+suffice, when influenced by a single Leclanché cell, to make all the
+sounds produced in a telephone audible, and especially vocal airs. Mr.
+Blyth even asserts that a microphone capable of transmitting speech can
+be made with a simple piece of coke, connected with the circuit by its
+two ends, but it must be coke: a retort carbon, with electrodes, will
+not act.
+
+It is a remarkable property of these kinds of microphones that they can
+act without a battery, at least when they are so arranged as to form a
+voltaic element for themselves, and this can be done by throwing water
+on the carbons. Mr. Blyth, who was the first to speak of this system,
+does not distinctly indicate its arrangement, and we may assume that
+his instrument did not differ from the one we have already described,
+to which water must have been added. In this way, indeed, I have been
+able to transmit not only the ticking of a watch and the sounds of
+a musical box, but speech itself, which was often more distinctly
+expressed than in an ordinary microphone, since it was free from the
+sputtering sound which is apt to accompany the latter. Mr. Blyth also
+asserts that sounds may be transmitted without the addition of water,
+but in this case he considers that the result is due to the moisture of
+the breath. Certainly much moisture is not required to set a voltaic
+couple in action, especially when a telephone is the instrument of
+manifestation. The ordinary microphone may be used without a battery,
+if the circuit in which it is inserted is in communication with the
+earth by means of earthen cakes; the currents which then traverse the
+circuit will suffice to make the tickings of a watch placed upon the
+microphone perfectly audible. M. Cauderay, of Lausanne, in a paper sent
+to the Académie des Sciences, July 8, 1878, informs us that he made
+this experiment on a telegraphic wire which unites the Hôtel des Alpes
+at Montreux with a _châlet_ on the hill--a distance of about 550 yards.
+
+
+_The Microphone used as a Speaking Instrument._--The microphone can
+not only transmit speech, but it can also under certain conditions
+reproduce it, and consequently supply the place of the receiving
+telephone. This seems difficult to understand, since a cause for the
+vibratory motion produced in part of the circuit itself can only be
+sought in the variations in intensity of the current, and the effects
+of attraction and magnetisation have nothing to do with it. Can the
+action be referred to the repulsions reciprocally exerted by the
+contiguous elements of the same current? Or are we to consider it to
+be of the same nature as that which causes the emission of sounds from
+a wire when a broken current passes through it, so that an electric
+current is itself a vibratory current, as Mr. Hughes believes? It is
+difficult to reply to these questions in the present state of science;
+we can only state the fact, which has been published by Messrs.
+Hughes, Blyth, Robert Courtenay, and even by Mr. Edison himself.
+I have been able to verify the fact myself under the experimental
+conditions indicated by Mr. Hughes, but I was not so successful in
+the attempt to repeat Mr. Blyth’s experiments. This gentleman stated
+that in order to hear speech in a microphone it would be enough to
+use the model made from fragments of carbon, as we have described,
+to join to it a second microphone of the same kind, and to introduce
+into the circuit a battery consisting of two Grove elements. If anyone
+then speaks above the carbons of one of the microphones, what is said
+should be distinctly heard by the person who puts his ear to the
+other, and the importance of the sounds thus produced will correspond
+with the intensity of the electric source employed. As I have said,
+I was unable by following this method to hear any sound, still less
+articulate speech; and if other experiments had not convinced me, I
+should have doubted the correctness of the statement. But this negative
+experiment does not in fact prove anything, since it is possible that
+my conditions were wrong, and that the cinders which I employed were
+not subject to the same conditions as Mr. Blyth’s fragments of coke.
+
+[Illustration: FIG. 45.]
+
+With respect to Mr. Hughes’s experiments, I have repeated them with
+the microphone made by MM. Chardin and Berjot, using that by M. Gaiffe
+as the sender, and I ascertained that with a battery of only four
+Leclanché cells, a scratch made on the sender, and even the tremulous
+motion and the airs played in a little musical box placed on the
+sender, were reproduced--very faintly, it is true--in the second
+microphone; in order to perceive them, it was enough to apply the ear
+to the vertical board of the instrument. It is true that speech was not
+reproduced, but of this Mr. Hughes had warned me; it was evident that
+with this arrangement the instrument was not sufficiently sensitive.
+
+A different arrangement of the microphone is required for the
+transmission and the reproduction of speech by this system, and a
+section of the one which Mr. Hughes found most successful is given in
+fig. 45. It somewhat resembles Mr. Hughes’s microphone speaker, placed
+in a vertical position, and the fixed carbon is fastened to the centre
+of the stretched membrane of a string telephone. The ear or mouth tube
+is at A, the membrane at D D, the carbon just mentioned at C: this
+carbon is of metallised charcoal prepared from deal, and so also is the
+double carbon E, which is in contact with it and is fastened to the
+upper end of the little bar G I. The whole is enclosed in a small box,
+and the pressure exerted on the contact of the two carbons is regulated
+by a spring R and a screw H. The tube of the telephone serves as an
+acoustic tube for the listener, and Mr. Hughes’s speaker, described
+above, acts as sender. It is hardly necessary to say that the two
+instruments are placed at each end of the circuit, that the carbons
+are connected with the two poles of a battery of one or two cells of
+bichromate of potash, or two Bunsen or six Leclanché cells, and the
+two instruments are connected by the line wire. Under such conditions,
+conversation may be exchanged, but the sounds are always much less
+distinct than they are in a telephone.
+
+I was able to ascertain this fact with a roughly made instrument
+brought from England by Mr. Hughes. MM. Berjot, Chardin, and de
+Méritens, who were also present at the experiments, were able with me
+to hear speech perfectly, and I have since successfully repeated the
+experiment alone, but it does not always succeed, and under its present
+conditions the instrument has no importance in a scientific point of
+view. It is evident that the instrument can dispense with any support,
+and the little box then forms the handle of the instrument; in this
+case the two binding screws are placed at the end of this handle, as in
+a telephone. The microphone speaker with a disk, represented in fig.
+5, which acts as sender to the singing condenser, can be used, when
+properly regulated, as a receiving microphone. M. Berjot has obtained
+good results from a little instrument of the same kind as that in fig.
+45, but with a metal diaphragm, and the microphonic system consists
+of a cylindrical piece of carbon resting on a small disk of the same
+substance, which is galvanised and soldered to the diaphragm. The whole
+is enclosed in a small round box, with its upper part cut in the form
+of a mouthpiece.
+
+It seems that all microphone senders with disks can reproduce speech
+more or less perfectly; it is a question of adjusting and refining
+the carbon points of contact. A weak battery, consisting of a single
+Leclanché cell, is better for these instruments than a strong battery,
+precisely because of the effects of oxidation and polarisation, which
+are so energetically produced at these points of contact when the
+battery is strong.
+
+The effects of the microphone receiver explain the sounds, often very
+intense, produced by the Jablochkoff candles when they are influenced
+by electro-magnetic machines. These sounds always vibrate in unison
+with those emitted by the machine itself, and they result, as I have
+already shown, from the rapid magnetisations and demagnetisations which
+are effected by the machine. These effects, observed by M. Marcel
+Deprez, were particularly marked in M. de Méritens’ first machines.
+
+
+_Other Arrangements of Microphones._--An arrangement such as we have
+just described has been employed by M. Carette to form an extremely
+powerful microphone speaker. The only difference is that the stretched
+membrane is replaced by a thin metallic disk: he fastens one of the
+carbons to the centre of this disk, and applies to it the other carbon,
+which is pointed, and held by a _porte-carbon_ with a regulating
+screw, so that the pressure which takes place between the two carbons
+may be regulated at pleasure. By this arrangement speech may be heard
+at a distance from the telephone. In other respects it resembles the
+telephone sender represented in fig. 5.
+
+M. de Méritens has executed the system represented, fig. 45, on a large
+scale, forming the tube A B of a zinc funnel a yard in length, and in
+this way he has been able to magnify the sounds, so that a conversation
+held in a low voice, three or four yards from the instrument, has been
+produced in a telephone with more sonorous distinctness. The instrument
+was placed on the floor of the apartment, with the opening of the
+funnel above, and the telephone was in the cellars of the house.
+
+The form of the microphone has been varied in a thousand ways, to suit
+the purposes to which it was to be applied. In the ‘English Mechanic
+and World of Science,’ June 28, 1878, we see the drawings of several
+arrangements, one of which is specially adapted for hearing the steps
+of a fly. It is a box, with a sheet of straw paper stretched on its
+upper part; two carbons, separated by a morsel of wood, and connected
+with the two circuit wires, are fastened to it, and a carbon pencil,
+placed crosswise between the two, is kept in this position by a groove
+made in the latter. A very weak battery will be enough to set the
+instrument at work, and when the fly walks over the sheet of paper it
+produces vibrations strong enough to react energetically on an ordinary
+telephone. The instrument must be covered with a glass globe. When a
+watch is placed on the membrane, with its handle applied to the morsel
+of wood which divides the two carbons, the noise of its ticking may
+be heard through a whole room. Two carbon cubes placed side by side,
+and only divided by a playing-card, may also be used instead of the
+arrangement of carbons described above. A semicircular cavity, made
+in the upper part of the two carbons, in which are placed some little
+carbon balls, smaller than a pea and larger than a mustard seed, will
+make it possible to obtain multiple contacts which are very mobile and
+peculiarly fit for telephonic transmissions. This arrangement has been
+made by Mr. T. Cuttriss.
+
+Several other arrangements of microphones have been devised by
+different makers and inventors, such as those of Messrs. Varey, Trouvé,
+Vereker, de Combettes, Loiseau, Lippens, de Courtois, Pollard, Voisin,
+Dumont, Jackson, Paterson, Taylor, &c., and they are more or less
+satisfactory. The instruments of MM. Varey, Trouvé, Lippens, and de
+Courtois are the most interesting, and we will describe them.
+
+M. Varey’s microphone consists of a sounding box of deal, mounted in
+a vertical position on a stand, and two microphones are arranged on
+either side of it, with vertical carbons united for tension. A small
+Gaiffe cell of chloride of silver, without liquid, is applied to the
+standard of the instrument, and is enough to make it work perfectly.
+This system is extremely sensitive.
+
+M. Trouvé’s microphones, represented in figs. 46, 47, 48, are extremely
+simple, so that he is able to sell them at a very moderate price. They
+generally consist of a small vertical cylindrical box, as we see in
+the figure, with disks of carbon at its two ends, which are united by a
+carbon rod, or by a metallic tube tipped with carbon. This rod or tube
+turns freely in two cavities made in the carbons, and the box, while
+acting as a sounding box, becomes at the same time a prison for the
+insects whose movements and noises are the objects of study.
+
+[Illustration: FIG. 46.]
+
+These boxes may be suspended on a cross-bar (fig. 47) by the two
+communicating wires, so as to be completely insulated. In this case the
+ticking of a watch placed upon the board, friction, and external shocks
+are hardly heard, but on the other hand the sound vibrations of the air
+alone are transmitted, and they acquire great distinctness. We have
+often repeated these experiments, and have always found that the tones
+of the voice were perfectly preserved.
+
+The model represented fig. 48 is still more simple, and appears to
+be the latest development of this kind of instrument. It consists
+of a stand and a disk united by a central rod. The upper disk moves
+round the central rod, and permits the vertical carbon to assume any
+inclination which is desired. It is evident that the instrument will
+become less sensitive when the carbon is more oblique.
+
+[Illustration: FIG. 47.]
+
+We must also mention a very successful microphone devised by M.
+Lippens. It is a slightly made box, like that of M. Varey, and on its
+opposite faces there are applied, on two frames left empty for the
+purpose, two thin plates of hardened caoutchouc, in the centre of which
+inside the box, two carbons are fastened, and on their outer surface a
+half-sphere is hollowed.
+
+[Illustration: FIG. 48.]
+
+The interval between the two carbons hardly amounts to two millimètres,
+and a carbon ball is inserted into the two cavities which form its
+spherical case. This ball is supported by a spiral spring which can be
+extended more or less by means of a wire wound on a windlass which is
+fixed above the instrument, like the spring of an electric telegraph
+instrument. By means of this spring, the pressure of the carbon ball
+against the sides of the cavity which contains it can be regulated at
+pleasure, and the sensitiveness of the instrument and its capacity
+for transmitting speech can be adjusted. Under these conditions, the
+vibrations of the caoutchouc plates directly affect the microphone,
+and the currents of air have no influence on it, so that the effects
+are more distinct. It is so sensitive that it is best for the speaker
+to place himself at the distance of at least 50 centimètres from the
+instrument. M. Lippens’ instrument is a pretty one, mounted on a wooden
+stand, which is neatly turned.
+
+In order to put an end to the sputtering usual in microphones, it
+occurred to M. de Courtois to prevent any cessation of contact
+between the carbons by keeping them close together, and to effect the
+variations of resistance necessary for articulate sounds by making them
+slide over each other, so as to insert a shorter or longer portion
+of the carbon in the circuit. For this purpose a vibrating disk is
+placed in a vertical position in a rigid frame, and a small conducting
+rod, terminated by a pointed carbon, is applied to it, with this
+carbon point resting on another flat piece of carbon placed below it.
+Influenced by the vibrations of the disk, the carbon point moves to and
+fro, effecting more or less extensive contacts with the lower carbon,
+and thus producing variations of resistance which almost correspond to
+the range of vibrations on the disk.
+
+
+_Experiments made with the Microphone._--I must now mention the
+interesting experiments which led Mr. Hughes to the invention of
+the remarkable instrument of which we have spoken, as well as those
+undertaken by other scientific men, either from a scientific or a
+practical point of view.
+
+Believing that light and heat can modify the conductivity of bodies,
+Mr. Hughes went on to consider whether sound vibrations, transmitted
+to a conductor traversed by a current, would not also modify this
+conductivity by provoking the contraction and expansion of the
+conducting molecules, which would be equivalent to the shortening
+or lengthening of the conductor thus affected. If such a property
+existed, it would make it possible to transmit sounds to a distance,
+since variations in the conductivity would result from variations
+corresponding to the intensity of the current acting on the telephone.
+The experiment which he made on a stretched metal wire did not,
+however, fulfil his expectation, and it was only when the wire vibrated
+so strongly as to break, that he heard a sound at the moment of its
+fracture. When he again joined the two ends of the wire, another sound
+was produced, and he soon perceived that imperfect contact between the
+two broken ends of wire would enable him to obtain a sound. Mr. Hughes
+was then convinced that the effects he wished to produce could only be
+obtained with a divided conductor, and by means of imperfect contacts.
+
+He then sought to discover the degree of pressure which it was most
+expedient to exert between the two adjacent ends of the wire, and
+for this purpose he effected the pressure by means of weights. He
+ascertained that when the pressure did not exceed the weight of an
+ounce on the square inch at the point of connection, the sounds
+were reproduced with distinctness, but somewhat imperfectly. He next
+modified the conditions of the experiment, and satisfied himself that
+it was unnecessary to join the wires end to end in order to obtain this
+result. They might be placed side by side on a board, or even separated
+(with a conductor placed crosswise between them), provided that the
+conductors were of iron, and that they were kept in metallic connection
+by a slight and constant pressure. The experiment was made with three
+Paris points, and arranged as it appears in fig. 49, and it has since
+been repeated under very favourable conditions by Mr. Willoughby Smith
+with three of the so-called rat-tail files, which made it possible to
+transmit even the faint sound of the act of respiration.[15]
+
+[Illustration: FIG. 49.]
+
+He afterwards tried different combinations of the same nature, which
+offered several solutions of continuity, and a steel chain produced
+fairly good results, but slight inflections, like those caused by
+the _timbre_ of the voice, were not reproduced, and he tried other
+arrangements. He first sought to apply metallic powders to the points
+of contact; powdered zinc and tin, known in commerce under the name
+of white bronze, greatly increased the effects obtained; but they
+were unstable, on account of the oxidation of the contacts; and it
+was in seeking to solve this difficulty, as well as to discover the
+most simple means of obtaining a slight and constant pressure on the
+contacts, that Mr. Hughes was led to the arrangement, previously
+described, of carbons impregnated with mercury, and he thus obtained
+the maximum effect.[16]
+
+Mr. Hughes considers that the successful effects of the microphone
+depend on the number and perfection of the contacts, and this is
+doubtless the reason why some arrangements of the carbon pencil in the
+instrument described above were more favourable than others.
+
+In order to reconcile these experiments with his preconceived ideas,
+Mr. Hughes thought that, since the differences of resistance proceeding
+from the vibrations of the conductor were only produced when it
+was broken, the molecular movements were arrested by the lateral
+resistances which were equal and opposite, but that if one of these
+resistances were destroyed, the molecular movement could be freely
+developed. He considers that an imperfect contact is equivalent to
+the suppression of one of these resistances, and as soon as this
+movement can take place, the molecular expansions and contractions
+which result from the vibrations must correspond to the increase
+or diminution of resistance in the circuit. We need not pursue Mr.
+Hughes’s theory further, since it would take too long to develope it,
+and we must continue our examination of the different properties of the
+microphone.[17]
+
+Carbon, as we have said, is not the only substance which can be
+employed to form the sensitive organ of this system of transmission.
+Mr. Hughes has tried other substances, including those which are good
+conductors, such as metals. Iron afforded rather good results, and the
+effect produced by surfaces of platinum when it was greatly subdivided
+was equal, if not superior, to that furnished by the mercurised carbon.
+Yet since the difficulty of making instruments with this metal is
+greater, he prefers the carbon, which resembles it in being incapable
+of oxidation.
+
+We have already said that the microphone may be used as a thermoscope,
+in which case it must have the special arrangement represented in fig.
+43. Under these conditions, heat, reacting on the conductivity of these
+contacts, may cause such variations in the resistance of the circuit
+that the current of three Daniell cells will be annulled by approaching
+the hand to the tube. In order to estimate the relative intensity of
+the different sources of heat, it will be enough to introduce into
+the circuit of the two electrodes A and B, fig. 43, a battery P, of
+one or two Daniell cells, and a moderately sensitive galvanometer G.
+For this purpose one of 120 turns will suffice. When the deviation
+decreases, it shows that the source of heat is superior to the
+surrounding atmosphere; and conversely, that it is inferior when the
+deviation increases. Mr. Hughes says that the effects resulting from
+the intervention of sunshine and shadow are shown on the instrument by
+considerable variations in the deviations of the galvanometer. Indeed
+it is so sensitive to the slightest variations of temperature that it
+is impossible to maintain it in repose.
+
+I have repeated Mr. Hughes’s experiments with a single Leclanché cell,
+and for this purpose I employed a quill, filled with five fragments
+of carbon, taken from the cylindrical carbons of small diameter which
+are made by M. Carré for the electric light. I have obtained the
+results which are mentioned by Mr. Hughes, but I ought to say that the
+experiment is a delicate one. When the pressure of the fragments of
+carbon against each other is too great, the current traverses them with
+too much force to allow the calorific effects to vary the deviation
+of the galvanometer, and when the pressure is too slight, the current
+will not pass through them. A medium degree of pressure must therefore
+be effected to ensure the success of the experiment, and when it is
+obtained, it is observed that on the approach of the hand to the
+tube, a deviation of 90° will, after a few seconds, diminish, so that
+it seems to correspond with the approach or withdrawal of the hand.
+But breathing produces the most marked effects, and I am disposed to
+believe that the greater or less deviations produced by the emission
+of articulate sounds when the different letters of the alphabet are
+pronounced separately, are due to more or less direct emissions of
+heated gas from the chest. It is certain that the letters which require
+the most strongly marked sounds, such as A, F, H, I, K, L, M, N, O, P,
+R, S, W, Y, Z, produce the greatest deviations of the galvanometric
+needle.
+
+In my paper on the conductivity of such bodies as are moderately good
+conductors, I had already pointed out this effect of heat upon divided
+substances, and I also showed that after a retrograde movement, which
+is always produced at once, a movement takes place in an inverse
+direction to the index of the galvanometer when heat has been applied
+for some instants, and this deviation is much greater than the one
+which is first indicated.
+
+In a paper published in the ‘American Scientific Journal,’ June 28,
+1878, Mr. Edison gives some interesting details on the application of
+his system of a telephonic sender to measuring pressures, expansions,
+and other forces capable of varying the resistance of the carbon disk
+by means of greater or less compression. Since his experiments on
+this subject date from December 1877, he again claims priority in
+the invention of using the microphone as a thermoscope; but we must
+observe that according to Mr. Hughes’s arrangement of his instrument,
+the effect produced by heat is precisely the reverse of the effect
+described by Mr. Edison. In fact, in the arrangement adopted by the
+latter, heat acts by increasing the conductivity acquired by the
+carbon under the increased pressure produced by the expansion of a
+body sensitive to heat: in Mr. Hughes’s system, the effect produced
+by heat is precisely the contrary, since it then acts only on the
+contacts, and not by means of pressure. Therefore the resistance
+of the microphone-thermoscope is increased under the influence of
+heat, instead of being diminished. This contrary effect is due to
+the division of some substance which is only a moderate conductor,
+and I have shown that under such conditions these bodies, when only
+slightly heated, always diminish the intensity of the current which
+they transmit. I believe that Mr. Edison’s arrangement is the best for
+the thermoscopic instrument, and makes it possible to measure much less
+intense sources of heat. Indeed he asserts that by its aid the heat of
+the luminous rays of the stars, moon, and sun may be measured, and also
+the variations of moisture in the air, and barometric pressure.
+
+This instrument, which we give fig. 50, with its several details, and
+with the rheostatic arrangement employed for measuring, consists of
+a metallic piece A fixed on a small board C, and on one of its sides
+there is the system of platinum disks and carbons shown in fig. 28. A
+rigid piece G, furnished with a socket, serves as the external support
+of the system, and into this socket is introduced the tapering end
+of some substance which is readily affected by heat, moisture, or
+barometric pressure. The other extremity is supported by another socket
+I, fitted to a screw-nut H, which may be more or less tightened by a
+regulating screw. If this system is introduced into a galvanometric
+circuit _a, b, c, i, g_, provided with all the instruments of the
+electric scale of measure, the variations in length of the substance
+inserted are translated by greater or less deviations of the
+galvanometric needle, which follow from the differences of pressure
+resulting from the lengthening or shortening of the surface capable of
+expansion which is inserted in the circuit.
+
+[Illustration: FIG. 50.]
+
+The experiments on the microphone made in London at the meeting of the
+Society of Telegraphic Engineers on May 25, 1878, were wonderfully
+successful, and they were the subject of an interesting article in
+the ‘Engineer’ of May 31, which asserts that the whole assembly heard
+the microphone speak, and that its voice was very like that of the
+phonograph. When the meeting was informed that these words had been
+uttered at some distance from the microphone, the Duke of Argyll,
+who was present, while admiring the important discovery, could not
+help exclaiming that this invention might have terrible consequences,
+since, for instance, if one of Professor Hughes’s instruments were
+placed in the room in Downing Street, in which Her Majesty’s ministers
+hold their cabinet council, their secrets might be heard in the room
+in which the present meeting took place. He added that if one of these
+little instruments were in the pocket of Count Schouvaloff, or of Lord
+Salisbury, we should at once be in possession of the secrets for which
+all Europe was anxiously waiting. If these instruments were able to
+repeat all the conversations held in the room in which they stood, they
+might be really dangerous, and the Duke thought that Professor Hughes,
+who had invented such a splendid yet perilous instrument, ought next to
+seek an antidote for his discovery. Dr. Lyon Playfair, again, thought
+that the microphone ought to be applied to the aërophone, so that by
+placing these instruments in the two Houses of Parliament, the speeches
+of great orators might be heard by the whole population within five or
+six square miles.
+
+The experiments lately made with the microphone at Halifax show that
+the Duke of Argyll’s predictions were fully justified. It seems that
+a microphone was placed on a pulpit-desk in a church in Halifax, and
+connected by a wire about two miles long with a telephone placed close
+to the bed of a sick person, who was able to hear the prayers, the
+chanting, and the sermon. This fact was communicated to me by Mr.
+Hughes, who heard it from a trustworthy source, and it is said that
+seven patients have subscribed for the expense of an arrangement by
+which they may hear the church services at Halifax without fatigue.
+
+The microphone has also lately been applied to the transmission of a
+whole opera, as we learn from the following account in the ‘Journal
+Télégraphique,’ Berne, July 25, 1878:--
+
+‘A curious micro-telephonic experiment took place on June 19 at
+Bellinzona, Switzerland. A travelling company of Italian singers was to
+perform Donizetti’s opera, “Don Pasquale,” at the theatre of that town.
+M. Patocchi, a telegraphic engineer, took the opportunity of making
+experiments on the combined effects of Hughes’s carbon microphone as
+the sending instrument, and Bell’s telephone as the receiver. With
+this object he placed a Hughes microphone in a box on the first tier,
+close to the stage, and connected it by two wires, from one to half a
+millimètre in thickness, to four Bell receivers, which were placed in a
+billiard-room above the vestibule of the theatre, and inaccessible to
+sounds within the theatre itself. A small battery of two cells, of the
+ordinary type used in the Swiss telegraphic service, was inserted in
+the circuit, close to the Hughes microphone.
+
+‘The result was completely successful. The telephones exactly
+reproduced, with wonderful purity and distinctness, the instrumental
+music of the orchestra, as well as the voices of the singers. Several
+people declared that they did not lose a note of either, that the
+words were heard perfectly; the airs were reproduced in a natural key,
+with every variation, whether _piano_ or _forte_, and several amateurs
+assured M. Patocchi that by listening to the telephone they were able
+to estimate the musical beauty, the quality of the singers’ voices,
+and the general effect of the piece, as completely as if they had been
+among the audience within the theatre.
+
+‘The result was the same when resistances equivalent to 10 kilomètres
+were introduced into the circuit, without increasing the number of
+cells in the battery. We believe that this is the first experiment of
+the kind which has been made in Europe, at least in a theatre, and
+with a complete opera; and those who are acquainted with the delicacy
+and grace of the airs in “Don Pasquale” will be able to appreciate the
+sensitiveness of the combined instruments invented by Hughes and Bell,
+which do not suffer the most delicate touches of this music to be lost.’
+
+Although experiments with the microphone are of such recent date, they
+have been very various, and among other curious experiments we learn
+from the English newspapers that the attempt has been made to construct
+an instrument on the same principle as the telephone, which shall be
+sensitive to the variations of light. It is known that some substances,
+and particularly selenium, are electrically affected by light, that is,
+that their conductivity varies considerably with the greater or less
+amount of light which is shed upon them. If, therefore, a circuit in
+which a substance of this nature is inserted, is abruptly subjected to
+a somewhat intense light, the increase of resistance which results from
+it ought to produce a powerful sound in a telephone inserted in the
+circuit. This fact has been verified by experiment, and Mr. Willoughby
+Smith infers from it, as we have already suggested, that the effects
+produced in the microphone are due to variations of resistance in the
+circuit, which are produced by more or less close contacts between
+imperfect conductors.
+
+In order to obtain this effect under the most favourable conditions,
+Mr. Siemens employs two electrodes, consisting of network of very
+fine platinum wire, fitting into each other like two forks, of which
+the prongs are interlaced. These electrodes are inserted between two
+glass plates, and a drop of selenium, dropped in the centre of the two
+pieces of network, connects them on a circular surface large enough
+to establish sufficient conductivity in the circuit. It is on this
+flattened drop that the ray of light must be projected.
+
+
+
+
+APPLICATIONS OF THE MICROPHONE.
+
+
+The applications of the microphone increase in number every day, and
+in addition to those of which we have just spoken, there are others of
+really scientific and even of practical interest. Among the number is
+the use which can be made of it as a system of relays for telegraphy,
+in science for the study of vibrations imperceptible to our senses, in
+medicine and surgery, and even in manufactures.
+
+
+_Its application to Scientific Research._--We have seen that several
+physicists, including Messrs. Spottiswoode, Warwick, Rossetti,
+Canestrelli, Wiesendanger, Lloyd, Millar, Buchin, and Blyth, have been
+able to hear what is said in a telephone which has no iron diaphragm,
+but it was so difficult to establish the fact that it has been often
+disputed. More certain evidence was desirable, and the microphone is an
+opportune agent for affording it.
+
+The ‘Telegraphic Journal’ of September 1, 1878, observes that M.
+du Moncel, in order to claim the victory in his controversy with
+Colonel Navez, had still to show that the sounds which appeared
+to be inarticulate in telephones without a diaphragm might become
+intelligible if they were intensified. This has been done for him by
+the use of Mr. Hughes’s microphone, and the following experiments were
+made for the purpose.
+
+1. If a magnetising coil, surrounding a bar of soft iron, is inserted
+in the circuit of a microphone, with a battery of three cells, the
+ticking of a watch and other sounds of the same kind may be heard
+on approaching the ear to the electro-magnet which has been thus
+constituted. It is true that these sounds are very faint when they are
+not amplified, but if the electro-magnet is fastened to a board, and
+a second microphone is fixed to the same board, the sounds produced by
+the electro-magnet are magnified, and become distinctly audible in the
+telephone which is placed in connection with this second microphone.
+
+2. These sounds may be further amplified by resting one of the
+extremities of the core of the electro-magnet on one of the poles of
+a permanent magnet, which is fixed upon the board. Articulate speech
+may then be heard in the telephone which is placed in connection with
+the microphone resting on the board, and the point at issue between
+MM. Navez and Du Moncel is completely decided in this way: for the
+auxiliary microphone can only propagate and amplify the vibration of
+articulate sounds, which are communicated by the bar magnet of the coil
+to the board on which the two instruments are placed. In this way it
+would be possible to render articulate sounds perceptible to M. Navez,
+when transmitted by the bar magnet of a telephone without a diaphragm.
+
+3. When a second bar magnet rests on the free pole of the
+electro-magnet, so as to present to it a pole of the same nature as the
+one with which it is already in communication--in a word, if a bar is
+placed between the two poles of a horseshoe electro-magnet, the effects
+are still more marked, and hence it may be assumed that the bar reacts
+as an armature, by concentrating the lines of magnetic force in the
+vicinity of the helix.
+
+4. When the two poles of a horseshoe magnet are inserted together
+inside a coil, their effects are equally energetic, although by this
+arrangement one of the poles might be expected to neutralise the
+effect of the other: but the most important effects have been obtained
+by placing an armature of soft iron across the poles of the magnet
+which has been already inserted in the coil. Under these conditions
+articulate sounds are distinctly heard.
+
+These experiments were confirmed by Mr. F. Varley, in a letter
+published in the ‘Telegraphic Journal’ of September 15, 1878, and among
+the fresh experiments mentioned by him, we will quote those which he
+made with an iron tube inserted in a helix, in which the two opposite
+poles of two bar magnets are introduced. These poles are only separated
+from each other by the interval of an inch, so that the centre of the
+iron tube may be strongly magnetised.
+
+Mr. Varley says that this last arrangement reproduces the articulate
+sounds which issue from a sending microphone, and this experiment is
+more decisive than that of Professor Hughes, in which case it might
+be supposed that the bar magnet, resting on the polar end of an
+electro-magnetic bar, was only a modification of the disk in the Bell
+telephone, set in vibration by the alternate currents passing through
+the helix, and that these vibrations were communicated to the board,
+and became sensible when enlarged by the microphone. But such an
+objection cannot be alleged in the case of the arrangement described
+above, for since the sound is produced between the current passing
+into the helix and the magnetic current of the bar, it can only be
+the result of a vibration produced by a disturbance of the reciprocal
+relations subsisting between these two elements. Mr. Varley adds
+that these experiments confirm M. du Moncel’s researches, which have
+thrown considerable light upon the causes which are at work in the
+action of the speaking telephone, and with which we have hitherto been
+imperfectly acquainted.
+
+
+_Its application to Telephonic Relays._--In February 1878, I first
+began to consider the mode of forming telephonic relays, but I was
+checked by the discovery that there was no vibration in the receiving
+telephone, and I made the following communication on the subject to
+the Académie des Sciences on February 25:--‘If the vibrations of the
+disk in the receiving telephone were the same as those of the sending
+telephone, it is easy to see that if a telephone with a local battery,
+acting both as sender and receiver, were substituted for the receiving
+telephone, it might, by the intervention of the induction coil, act
+as a relay, and might therefore not only amplify the sound, but also
+transmit it to any distance. It is, however, doubtful whether the
+vibrations of the two corresponding disks are of the same nature, and
+if the sound be due to molecular contractions and expansions, the
+solution of the problem becomes much more difficult. Here is therefore
+a field for experiments.’ These experiments have been successfully made
+by Mr. Hughes, who acquainted me with them early in June 1878, and they
+led to the discovery of a most interesting system of microphonic relays.
+
+On a wooden board of moderate size, such as a drawing board, he placed
+a microphone with a carbon brought to a fine point at each end, and
+fixed in a vertical position. One or more telephones were placed in the
+circuit, with their membranes facing the board, and a continuous sound
+was heard, sometimes resembling a musical note, sometimes the singing
+of boiling water in an oven; and the sound, which could be heard at
+a distance, went on indefinitely, as long as the electric force was
+exerted. Mr. Hughes explains this phenomenon in the following way.
+
+The slightest shock which affects the microphone has the effect
+of sending currents, more or less broken, through the telephones,
+which transform them into sound vibrations, and since these are
+mechanically transmitted by the board to the microphone, they maintain
+and even amplify its action, and produce fresh vibrations on the
+telephones. Thus a fresh action is exerted on the microphone, and so
+on indefinitely. Again, if a second microphone, in connection with
+another telephonic circuit, be placed upon the same board, we have an
+instrument which acts as a telephonic relay, that is, it transmits
+to a distance the sounds communicated to the board, and these sounds
+may serve either as a call, or as the elements of a message in the
+Morse code, if a Morse manipulator is placed in the circuit of the
+first microphone. Mr. Hughes adds that he has made several very
+successful experiments with this system of instruments, although he
+only employed a Daniell battery of six cells without any induction
+coil. By fastening a pasteboard tube, 40 centimètres in length, to
+the receiving telephone, he was able to hear in all parts of a large
+room the continuous sound of the relay, the ticking of a watch, and
+the scratching of a pen upon paper. He did not try to transmit speech,
+since it would not have been reproduced with sufficient distinctness
+under such conditions.
+
+Since this first attempt, Mr. Hughes has arranged another and still
+more curious system of microphonic relays, for which two microphones
+with vertical carbons are required. He places two microphones
+of this description on a board, and connects one of them with a
+third microphone, which acts as a sender, while the second is in
+communication with a telephone and a second battery: in this way the
+words uttered before the sender are heard in the telephone, without
+employing any electro-magnetic organ for the telephonic relay.
+
+In August 1878, Messrs. Houston and Thomson likewise arranged a system
+of telephonic relays which only differs from that of Mr. Hughes in
+the particular of having the microphone fixed on the diaphragm of the
+telephone, and not on the board beside it. The system consists of three
+vertical microphones, which can be combined for tension or quantity,
+according to the conditions for which they are required. The model of
+this instrument was represented in the ‘Telegraphic Journal’ of August
+15, 1878, to which we must refer our readers, if they wish for further
+information on the subject.
+
+
+_Its application to Medicine and Surgery._--The extreme sensitiveness
+of the microphone suggested its use for the observation of sounds
+produced within the human body, so that it might serve as a stethoscope
+for listening to the action of the lungs and heart. Dr. Richardson and
+Mr. Hughes are now busy in the attempt to carry out this idea, but so
+far the result is not very satisfactory, although they still hope to
+succeed. Meanwhile, M. Ducretet has made a very sensitive stethoscopic
+microphone, which we represent in fig. 51. It consists of a carbon
+microphone C P, with a simple contact, of which the lower carbon P is
+fitted to one of M. Marais’ tambourines with a vibrating membrane T.
+This tambourine is connected with another T′, by a caoutchouc tube,
+which is to be applied to the different parts of the body which demand
+auscultation, and which is therefore termed the _tambour explorateur_.
+The sensitiveness of the instrument is regulated by means of a
+counterpoise P O, which is screwed upon the arm of a bent lever, and
+to this the second carbon C is fixed. The extreme sensitiveness of
+M. Marais’ tambourines in transmitting vibrations is well known, and
+since their sensitiveness is further increased by the microphone, the
+instrument becomes almost too impressionable, since it reveals all
+sorts of sounds, which it is difficult to distinguish from each other.
+Such an instrument can only be of use when entrusted to experienced
+hands, and a special education of the organ of hearing is needful, in
+order to turn it to account.
+
+[Illustration: FIG. 51.]
+
+In a work lately published by M. Giboux on the application of the
+microphone to medicine, this stethoscopic system is rather severely
+criticised, and not without reason if, as M. Giboux asserts, it is only
+sensitive to the movements which take place on the surface of the body,
+and those which are internal are either lost or altogether changed
+in character. But without pronouncing on the improvements which may
+ultimately be made in the instrument, M. Giboux thinks that its most
+important use in medical practice consists in its allowing a certain
+number of students to observe with the professor the different sounds
+of the body, to study them with him in their different phases, and thus
+to profit more readily by his teaching. A microphonic circuit might
+bifurcate between several telephones, so that each person might hear
+for himself what is heard by others.
+
+The most important application of the instrument to surgical purposes
+has lately been made by Sir Henry Thompson, aided by Mr. Hughes, for
+the examination of the bladder in cases of stone. It enables him to
+ascertain the presence and precise position of calculi, however small
+they may be. For the purpose of research, he uses a sound, made of a
+Maillechort rod, a little bent at the end, and placed in communication
+with a sensitive carbon microphone. When the sound is moved about in
+the bladder, the rod comes in contact with stony particles, even if
+they are no larger than a pin’s head, and friction ensues, producing
+in the telephone vibrations which can be easily distinguished from
+those caused by the simple friction of the rod on the soft tissues of
+the sides of the bladder. The arrangement of the instrument is shown
+in fig. 52. The microphone is placed in the handle which contains the
+sound, and is the same as that given in fig. 42, but of smaller size,
+and the two conducting wires _e_ which lead to the telephone, issue
+from the handle by the end _a_ opposite to that _bb_ to which the
+sound _dd_ is screwed. As this instrument is not intended to reproduce
+speech, retort carbons instead of wood carbons may be used.
+
+[Illustration: FIG. 52.]
+
+Some deaf people, whose sense of hearing is not completely destroyed,
+have been able to hear by an expedient based upon the principle of the
+microphone. For this purpose two telephones, connected by a metallic
+crown, which is placed on the temples, are applied to the ears of
+the deaf person, and the telephones are placed in communication with
+a battery microphone, which hangs to the end of a double conducting
+wire. The deaf man keeps the microphone in his pocket, and presents it
+as an acoustic tube to the person who wishes to converse with him. Mr.
+Hughes’s speaker, represented fig. 42, is the one used.
+
+
+_Various Applications._--The microphone may be used in many other ways,
+some of which are suggested in the ‘English Mechanic’ of June 21,
+1878. The article states that by means of this instrument, engineers
+will be able to estimate the effects of the vibrations caused on
+old and new buildings by the passage of heavy loads; a soldier will
+be able to discover the enemy’s approach when he is several miles
+off, and may even ascertain whether he has to do with artillery or
+cavalry; the approach of ships to the neighbourhood of torpedoes may be
+automatically heralded on the coast by this means, so that an explosion
+may be produced at the right moment.
+
+It has also been proposed to use the microphone to give notice of an
+escape of gas in coal-mines. The gas, in escaping from between the
+seams of coal, makes a whistling noise, which might, with the aid
+of the microphone and telephone, be heard at the top of the shaft.
+Again, it has been suggested that the microphone might be used as a
+seismograph to reveal the subterranean noises which generally precede
+earthquakes and volcanic eruptions, and which would be much intensified
+by this instrument. It might even be of use to Signor Palmieri for his
+observations in the Vesuvius Observatory.
+
+The microphone has also been used by Mr. Chandler Roberts to render the
+diffusion of gaseous molecules through a porous membrane sensible to
+the ear.
+
+As might have been expected, the acclamation with which Mr. Hughes’s
+invention was received led to the assertion of other claims to
+priority, and in addition to that of Mr. Edison, on which we have
+already given our opinion, there are several others, showing that if
+some microphonic effects were discovered at different times before the
+date of Mr. Hughes’s discovery, they could not have been considered
+important, since they were not even announced. Among the number was
+that of Mr. Wentworth Lascelles Scott, specified in the ‘Electrician’
+of May 25, 1878, and that of M. Weyher, presented to the Société de
+Physique, Paris, in June 1878. Another, made by M. Dutertre, is of
+somewhat greater importance, for his experiments were reported in
+the Rouen papers in February of the same year: yet there is no just
+ground for such claims, since the earliest date of his experiments is
+subsequent to the experiments first made by Mr. Hughes. These began
+early in December 1877, and in January 1878 they were exhibited to
+officials of the Submarine Telegraph Company, as Mr. Preece declared in
+a letter addressed to the several scientific men.
+
+
+
+
+EXTERNAL INFLUENCE ON TELEPHONIC TRANSMISSIONS.
+
+
+The obstacles which occur in telephonic transmissions proceed from
+three causes: 1. The intensity of sound is diminished by the loss of
+current in transmission--a loss which is much greater in the case of
+induced currents than in those received from a battery. 2. Confusion
+is caused by the influence of adjacent currents. 3. The induction
+from one wire to another. This last influence is much greater than is
+usually supposed. If two perfectly insulated wires are placed side
+by side, one in communication with the circuit of an electric bell,
+and the other with the circuit of a telephone, the latter will repeat
+the sounds of the bell with an intensity often great enough to act as
+a call without applying the instrument to the ear. MM. Pollard and
+Garnier, in their interesting experiments with the induced currents
+of the Ruhmkorff coil, have ascertained that in this way not merely
+sounds may be obtained which correspond with the induced currents
+resulting from the action of the primary current, but also those which
+result from the action of the secondary current on other helices, which
+are termed currents of the second order. These different reactions
+frequently cause the telephonic transmissions made on telegraphic
+lines to be disturbed by irregular sounds, arising from the electric
+transmissions on adjoining lines; but it does not appear that these
+influences altogether neutralise each other, so that conversation held
+in the ordinary way and a message sent in the Morse code may be heard
+simultaneously.
+
+At the Artillery School, Clermont, a telephonic communication has
+been established, for the sake of experiments, between the school
+and the butts, which are at a distance of about eight miles. Another
+communication of the same kind has been established between the
+Clermont Observatory and the one at Puy-de-Dôme, which is nearly nine
+miles from the former. These two lines are carried on the same posts
+for a course of six miles, together with an ordinary telegraphic wire,
+and for a distance of 330 yards there are seven other such wires.
+The two telephonic wires are separated from each other by a space of
+85 centimètres. The following facts have been observed under these
+conditions.
+
+1. The school telephone is perfectly able to read off from their sound
+the Morse messages which pass through the two adjacent telegraph wires,
+and the ticking of the instrument does not at all interfere with the
+vocal communication of the telephone, nor render it inaudible.
+
+2. The two adjacent telegraphic lines, although not in contact, confuse
+their messages together, and it has sometimes been possible to hear
+messages from Puy-de-Dôme at the school through the wire which runs to
+the butts, although the distance between the two lines is nowhere less
+than 85 centimètres.
+
+These inconveniences have been in some degree remedied by inserting
+strong resistances in the circuit, or by putting the current to earth
+at some distance from the telephonic stations.
+
+M. Izarn, Professor of Physics at the Lycée, Clermont, holds that
+telephonic electric currents may readily be turned aside by the earth,
+especially if in the course of their passage they encounter metallic
+conductors, such as gas or water pipes. He writes as follows on the
+subject, in a paper addressed to the Académie des Sciences, on May
+13, 1878:--‘I set up a telephone in the Clermont Lycée with a single
+wire, more than 50 yards in length, which crosses the court-yard of
+the Lycée, and goes from the laboratory, where it is suspended to a
+gas-burner, to a room near the porter’s lodge, where it is suspended
+to another gas-burner. When I applied my ear to the telephone, I could
+distinctly hear the telegraphic signals, Morse or otherwise, which came
+either from the telegraph office at Clermont, or from the telephone
+office which was at work between the School of Artillery and the butts
+below Puy-de-Dôme, a distance of eight miles. I could overhear words,
+and especially the military orders issued at the butts for the purpose
+of being heard at the school. Yet my wire is perfectly independent of
+those used for signalling, and is even very remote from them; but as
+the wires of the telegraph office and of the School of Artillery go to
+earth at a little distance from the gas-pipes, it is probable that this
+phenomenon is caused by a diversion of the current produced in my wire,
+by means of the earth and the network of metal pipes.’
+
+Mr. Preece made the same remark in his notice of ‘some physical points
+connected with the telephone.’ Again, we read in the ‘Telegraphic
+Journal’ of June 15, 1878, that in a telephonic concert transmitted
+from Buffalo to New York, the singers at Buffalo were heard in an
+office placed outside the telegraphic circuit in which the transmission
+was effected. On enquiry, it was ascertained that the wire through
+which the telephonic transmission took place, was at one point in its
+course close to the one which directly transmitted the musical sounds,
+but the distance between the two wires was not less than ten feet.
+
+When the circuits are altogether metallic, there is much less risk of
+confusion, and M. Zetzche declares that sounds proceeding from other
+wires are in this case little heard, and then only momentarily, so that
+it is much more easy to hear with this arrangement than with the one in
+ordinary use. ‘It is not,’ he says, ‘the resistances of the wire, but
+rather the diversions of the current near the posts, which interfere
+with telephonic correspondence on long lines above ground. This was
+proved by the following experiments:--I connected the telegraphic line
+from Dresden to Chemnitz with a line from Chemnitz to Leipzig (54
+miles), which made a circuit of 103 miles, going to earth at its two
+extremities. There was no communication between Dresden and Leipzig,
+but Leipzig and Dresden could communicate with ease, in spite of the
+greater extent of line. I broke the connection with earth, first at
+Leipzig, then simultaneously at Leipzig and Dresden, and I observed
+the following effects. When insulation took place at Leipzig only,
+the telephone could be heard at the stations of Dresden, Riesa, and
+Wurzen; when the line was insulated at both ends, the communication was
+good between the two latter stations, but it was observed that at the
+intermediate station the words spoken at Wurzen were more distinctly
+heard than the words spoken at Riesa were heard at Wurzen. Since the
+distance from Wurzen to Leipzig is little more than half that from
+Riesa to Dresden, there are consequently nearly twice as many posts
+on the latter line, which carry the currents to earth, and hence I
+conclude that these diversions of current explain the possibility
+of conversing on an insulated line, and also why sounds are more
+distinctly heard at the Riesa station in consequence of the greater
+intensity of current still remaining on the line.’
+
+Some vibrations also result from the action of currents of air on
+telegraphic wires, which produce the humming sound so well known on
+some lines, and these may also react on the telephone; but they are
+in this case generally mechanically transmitted, and they may be
+distinguished from the others, if the sounds which ensue are heard
+after the telephone is excluded from the circuit by a break with a
+short circuit and after the communication to earth established behind
+the telephone has been broken.
+
+The induced reactions caused by the line wires on each other are not
+the only ones which may be observed on a telephonic circuit: every
+manifestation of electricity near a telephone may produce sounds of
+greater or less force. Of this we have already given a proof in M.
+d’Arsonval’s experiments, and others by M. Demoget demonstrate the
+fact still more clearly. In fact, if a small bar magnet provided with
+a vibrator be placed before one of the telephones of a telephonic
+circuit, and the vibrating plate of the telephone be removed, in
+order to draw away the sound produced by the vibrator, its humming
+noise may be distinctly heard on the second telephone of the circuit;
+a noise which attains its maximum when the two extremities of the
+electro-magnet are at their nearest point to the telephone without
+a diaphragm, and it is at its minimum when this electro-magnet is
+presented to it along its neutral line. M. Demoget supposes that the
+action which is exerted in this instance is that of a magnet exerting
+two inducing actions which are opposite and symmetrical, with a field
+limited by a double paraboloid and with an axis, according to his
+experiments, which extended 55 centimètres beyond the magnetic core,
+and a vertical diameter of 60 centimètres. He believes that in this way
+it would be easy to telegraph on the Morse system, and that, in order
+to do so, it would only be necessary to apply a key to the inducing
+electro-magnet.
+
+Mr. Preece points out three ways of overcoming the difficulty presented
+by the induced reactions caused by the wires on each other.
+
+1. By increasing the intensity of the transmitted currents, so as to
+make them decidedly stronger than the induced currents, and to reduce
+the sensitiveness of the receiving telephone.
+
+2. To place the telephonic wire beyond the range of induction.
+
+3. To neutralise the effects of induction.
+
+The first mode may be effected by Edison’s battery system, and we have
+seen that it is very successful.
+
+In order to put the second mode in practice, Mr. Preece says that
+it would be necessary to study the two kinds of induction which are
+developed on telegraphic lines: electro-static induction, analogous
+to that produced on submarine cables, and electro-dynamic induction,
+resulting from electricity in motion. In the former case, Mr. Preece
+proposes to interpose between the telephone wire and the other wires a
+conducting body in communication with the earth, capable of becoming a
+screen to the induction by itself absorbing the electro-static effects.
+He says that this might be accomplished by surrounding the telegraphic
+wires adjacent to the telephonic wire with a metallic envelope, and
+then plunging them in water. He adds that the effects of static
+induction are not completely destroyed in this way, since the substance
+used is a bad conductor, but they are considerably reduced, as he
+has proved by experiments between Dublin, Holyhead, Manchester, and
+Liverpool. In the second case, Mr. Preece admits that an iron envelope
+might paralyse the electro-dynamic effects produced by absorbing them,
+so that if insulated wires were employed, covered with an iron case,
+and communicating with the earth, the two induced reactions would be
+annulled. We will not follow Mr. Preece in his theory as to these
+effects--a theory which seems to us open to question, but we content
+ourselves with pointing out his proposed mode of attenuation.
+
+In order to carry out the third expedient, it might be thought that it
+would be enough to employ a return wire instead of going to earth, for
+under such conditions the currents induced on one of the wires would be
+neutralised by those resulting from the same induction on the second
+wire, which would then act in an opposite direction; but this mode
+would only be successful when there is a very small interval between
+the two telephone wires, and they are at a considerable distance from
+the other wires. When this is not the case, and they are all close
+together, as in submarine or subterranean cables, consisting of several
+wires, this mode is quite inefficient. A small cable, including two
+conductors, insulated with gutta-percha, may be successfully carried
+through the air.
+
+The use of two conductors has the further advantage of avoiding the
+inconvenience of stray currents on the line and through the earth,
+which, when the communications to earth are imperfect, permit the line
+current to pass more or less easily into the telephonic line.
+
+In addition to the disturbing causes in telephonic transmission we have
+just mentioned, there are others which are also very appreciable, and
+among them are the accidental currents which are continually produced
+on telegraphic lines. These currents may proceed from several causes,
+at one time from atmospheric electricity, at another from terrestrial
+magnetism, at another from thermo-electric effects produced upon the
+lines, at another from the hydro-electric reactions produced on the
+wires and disks in communication with the earth. These currents are
+always very unstable, and consequently they are likely, by reacting
+on the transmitted currents, to modify them so as to produce sounds
+upon the telephone. Mr. Preece asserts that the sound proceeding
+from earth currents somewhat resembles that of falling water. The
+discharges of atmospheric electricity, even when the storm is remote,
+produce a sound which varies with the nature of the discharge. When
+it is diffused and the clap takes place near at hand, Dr. Channing,
+of Providence, U.S., says that the sound resembles that produced by a
+drop of fused metal when it falls into water, or, still more, that of
+a rocket discharged at a distance: in this case it might seem that the
+sound would be heard before the appearance of the flash, which clearly
+shows that the electric discharges of the atmosphere only take place in
+consequence of an electric disturbance in the air. Mr. Preece adds that
+a wailing sound is sometimes heard, which has been compared to that of
+a young bird, and which must proceed from the induced currents which
+terrestrial magnetism produces in the metallic wires when placed in
+vibration by currents of air.
+
+M. Gressier, in a communication made to the Académie des Sciences on
+May 6, 1878, has spoken of some of these sounds, but he is totally
+mistaken in the source to which he ascribes them.
+
+‘In addition to the crackling sound caused by the working of telegraph
+instruments on the adjacent lines, a confused murmur takes place in the
+telephone, a friction so intense that it might sometimes be thought
+that the vibrating disk was splitting. This murmur is heard more by
+night than by day, and is sometimes intolerable, since it becomes
+impossible to understand the telephone, although nothing is going on
+in the office to disturb the sound. The same noise is heard when only
+one telephone is used. A good galvanometer inserted in the circuit
+reveals the presence of sensible currents, sometimes in one direction,
+sometimes in another.’
+
+I studied these currents for a long time with the galvanometer, and
+made them the subject of four papers which were laid before the
+Académie des Sciences in 1872, and I am convinced that they have in
+general nothing to do with atmospheric electricity, but result either
+from thermo-electric or hydro-electric influence. They take place
+constantly and in all weathers on telegraph lines, whether these lines
+are insulated at one end, or in contact with the earth at both ends.
+In the first case, the polar electrodes of the couple are formed by
+the telegraph wire and the earth plate, generally of the same nature,
+and the intermediate conducting medium is represented by the posts
+which support the wire and the earth which completes the circuit. In
+the second case, the couple is formed in almost the same way, but
+the difference in the chemical composition of the ground at the two
+points where the earth plates are buried, and sometimes their different
+temperature, exert a strong influence. If only the first case be
+considered, it generally happens that on fine summer days the currents
+produced during the day are inverse to those which are produced by
+night, and vary with the surrounding temperature in one or the other
+direction. The presence or absence of the sun, the passage of clouds,
+the currents of air involve abrupt and strongly marked variations,
+which may be easily followed on the galvanometer, and which cause more
+or less distinct sounds in the telephone.
+
+During the day, the currents are directed from the telegraph line to
+the earth plate, because the heat of the wire is greater than that of
+the plate, and these currents are then thermo-electric. During the
+night, on the other hand, the wire is cooled by the dew, which causes a
+greater oxidation on the wire than that which takes place on the plate,
+and the currents then become hydro-electric.
+
+I say more about these currents because, in consequence of a mistaken
+belief as to their origin, it has been supposed that the telephone
+might serve for the study of the variations of the atmospheric
+electricity generally diffused through the air. Such an application of
+the telephone would, under these conditions, be not only useless, but
+also misleading, by inducing the study of very complex phenomena, which
+could lead to nothing more than I have already stated in my different
+papers on the subject.
+
+Certain local influences will also produce sounds in the telephone.
+Thus the distension of the diaphragm by the moist heat of the breath,
+when the instrument is held before the mouth in speaking, causes a
+perceptible murmur.
+
+From the electro-static reactions, so strongly produced on the
+submarine cables, in consequence of electric transmissions, it might be
+supposed that it would not be easy to hold telephonic correspondence
+through this kind of conductor, and, to ascertain the fact, an
+experiment was made on the cable between Guernsey and Dartmouth, a
+distance of sixty miles. Articulate speech, only a little indistinct,
+was, however, perfectly transmitted. Other experiments, made by
+Messrs. Preece and Wilmot, on an artificial submarine cable, placed
+in conditions analogous to those of the Atlantic cable, showed that a
+telephonic correspondence might be kept up at a distance of a hundred
+miles, although the effects of induction were apparent. At the distance
+of 150 miles, it was somewhat difficult to hear, and the sounds were
+very faint, as if some one were speaking through a thick partition. The
+sound diminished rapidly until the distance of 200 miles was reached,
+and after that it became perfectly indistinct, although singing could
+still be heard. It was even possible to hear through the whole length
+of the cable, that is, for 3,000 miles, but Mr. Preece believed this to
+be due to the induction of the condenser on itself: he holds, however,
+that singing may be heard at a much greater distance than speech,
+owing to the more regular succession of electric waves.
+
+Mr. Preece also made experiments on the subterranean telegraphs
+between Manchester and Liverpool, a distance of 30 miles, and found
+no difficulty in exchanging correspondence; and it was the same with
+the cable from Dublin to Holyhead, a distance of 67 miles. This cable
+had seven conducting wires, and when the telephone was connected with
+one of them, the sound was repeated through all the others, but in a
+fainter degree. When the currents of the telegraphic instruments passed
+through the wires, the induction was apparent, but not so great as to
+prevent telephonic communication.
+
+
+
+
+ESTABLISHMENT OF A TELEPHONIC STATION.
+
+
+Although the telephonic system of telegraphy is very simple, yet
+certain accessory arrangements are indispensable for its use. Thus,
+for example, an alarum call is necessary, in order to know when the
+exchange of correspondence is to take place, and information that
+the call has been heard is likewise necessary. An electric bell is
+therefore an indispensable addition to the telephone, and since the
+same circuit may be employed for both systems, if a commutator is
+used, it was necessary to find a mode of making the commutator act
+automatically, so as to maintain the simple action of the system which
+constitutes its principal merit.
+
+
+_MM. Pollard and Garnier’s System._--With this object, MM. Pollard and
+Garnier devised a very successful arrangement last March, which employs
+the weight of the instrument to act upon the commutator.
+
+For this purpose, they suspended the instrument to the end of a spring
+plate, fastened between the two contacts of the commutator. The circuit
+wire corresponds with this plate, and the two contacts correspond, the
+one with the telephone, the other with the bell. When the telephone
+hangs below the spring-support, that is, when it is not at work,
+its weight lowers the spring plate on the lower contact, and the
+communication of the line with the bell is established: when, on the
+other hand, the telephone is raised for use, the spring plate touches
+the higher contact, and communication is established between the line
+and telephone. In order to make the bell sound, it is only necessary to
+establish, on the wire which connects the line with the bell contact of
+the commutator, a breaker which can both join and break the current,
+and which communicates on one side with the contact of the bell, and
+on the other with its battery. The ordinary push of an electric bell
+will be sufficient, if it is supplied with a second contact, but MM.
+Pollard and Garnier wished to make this action also automatic, and
+consequently they devised the arrangement represented in fig. 53.
+
+[Illustration: FIG. 53.]
+
+In this system, as well as in those which have since been devised, two
+telephones are employed, one of which is constantly applied to the ear,
+and the other to the mouth, so as to make it possible to speak while
+listening. The telephones are supported by three wires, two of which
+contain flexible conductors, while the third only acts as a support.
+
+Two of the four wires of the two telephones are connected with each
+other, and the other two are connected with the two binding screws of
+the commutator _t_, _t′_: the wires without conductors are suspended to
+the extremities of the two flexible plates _l_, _l′_, which correspond
+with earth and line.
+
+When at rest, the weight of the telephones presses the two plates _l_,
+_l′_, on the lower contacts S, S′, but when the instruments are taken
+up these plates press against the higher contacts.
+
+The two bell wires terminate on the lower contacts, those of the
+telephones on the higher contacts, and one of the poles of the battery
+is connected with the lower contact on the left S′, the other with the
+higher contact on the right T.
+
+When at rest, the system is applied to the electric bell, and the
+current sent from the opposite station will follow the circuit L _l_
+S S′ S′ _l′_ T, so that the call will be made. On taking up the two
+telephones, the circuit of the bell system is broken, and that of the
+telephones is established, so that the current follows the course L
+_l_ T _t t′_ T′ _l′_ T. If only one telephone is held at a time, the
+current is sent into the bell system of the opposite station, and
+follows the route + P S _l_ L T _l′_ T′ _t_ P --. In this way the
+three actions necessary for calling, corresponding, and enabling the
+corresponding instrument to give a call, are almost involuntarily made.
+
+
+_System by MM. Bréguet and Roosevelt._--In the system established by
+the Paris agents of the Bell company, the arrangement resembles the
+one just described, except that there is only one spring commutator,
+and the call is made with the push of an ordinary electric bell. A
+mahogany board is suspended from the wall, and on it are arranged,
+first, the ordinary electric bell system, with a sending push fixed
+below it; second, two forks supporting two telephones, one of which is
+fastened to the bar of a commutator, arranged as a Morse key. The two
+telephones are connected by two conducting wires, so arranged as to
+be capable of extension, and two of their four binding screws are in
+immediate connection with each other, and the other two with the earth,
+line, and battery, by means of the commutator, the sending push, and
+the bell system. The arrangement is shown in fig. 54.
+
+[Illustration: FIG. 54.]
+
+The commutator A consists of a metallic bar _a c_, bearing the
+suspension fork of one of the telephones F′ below its point of
+articulation: it ends in two pins _a_ and _c_, below which the two
+contacts of the commutator are fixed, and a spring compresses the
+lower arm of the bar, so as to cause the other arm to rest constantly
+on the higher contact. For greater security a steel tongue _a b_ is
+fastened to the lower end of the bar, and rubs against the small shaft
+_b_, which is provided with two insulated contacts, corresponding to
+those of the board. The bar is in communication with the line wire
+by means of the call-push, and the upper of the two contacts we have
+just described corresponds with one of the telephone wires which is
+inserted in the same circuit, while the other corresponds with the bell
+system S, which is in communication with earth. It follows from this
+arrangement, that when the right telephone presses its whole weight
+on the support, the bar of the commutator is inclined on the lower
+contact, and consequently the line is in direct communication with
+the bell, so that the call can be made. When, on the other hand, the
+telephone is removed from its support, the bar rests on the higher
+contact, and the telephones are connected with the line.
+
+Pressure on the sending push serves to call the corresponding station:
+the connection of the line with the telephones is then broken, and it
+is established with the battery of the sending station, which sends
+its current through the bell of the corresponding station. In order
+to obtain this double effect, the contact spring of the sending push
+generally rests upon a contact fastened to a piece of wood shaped like
+a joiner’s rule, which covers it in front, and below this spring there
+is a second contact, which communicates with the positive pole of the
+station battery. The other contact corresponds with the line wire,
+and a connection takes place between the earth wire and the negative
+pole of the station battery, so that the earth wire is common to three
+circuits:
+
+1st. To the telephone circuit. 2nd. To that of the bell system. 3rd. To
+that of the local battery.
+
+The second fork, which supports the telephone on the right, is fixed to
+the board, and is independent of any electric current.
+
+It is clear that this arrangement may be varied in a thousand ways, but
+the model we have just described is the most practical.
+
+
+_Edison’s System._--The problem becomes more complex in the case of
+battery telephones, since the battery must be common to both systems,
+and the induction coil must be inserted in two distinct circuits. Fig.
+55 represents the model adopted in Mr. Edison’s telephone.
+
+[Illustration: FIG. 55.]
+
+In this arrangement, there is a small stand C on the mahogany board on
+which the bases of the two telephones rest. The bell system S is worked
+by an electro-magnetic speaker P, which serves, when a Morse key is
+added to the system, for exchange of correspondence in the Morse code,
+if there should be any defect in the telephones, or to put them in
+working order. Above the speaker there is a commutator with a stopper D
+to adapt the line for sending or receiving, with or without the bell;
+and below the stand C the induction coil, destined to transform the
+voltaic currents into induced currents, is arranged in a small closed
+box E.
+
+When the commutator is at reception, the line is in immediate
+correspondence either with the speaker or with the receiving telephone,
+according to the hole in which the stopper is inserted; when, on the
+other hand, it is at sending, the line corresponds to the secondary
+circuit of the induction coil. Under these conditions the action is
+no longer automatic; but since this kind of telephone can only be
+usefully employed for telegraphy, in which case those who work it are
+acquainted with electric apparatus, there is no inconvenience in this
+complication.
+
+
+
+
+CALL-BELLS AND ALARUMS.
+
+
+The call-bells applied to telegraphic service have been arranged in
+different ways. When the vibrating bells are in use, like those of
+which we have just spoken, it is necessary to use a battery, and
+the advantages offered by telephones with induced currents are thus
+sensibly diminished. In order to dispense with the battery, the use of
+the electro-magnetic bell has been suggested.
+
+In this case there are usually two bells, with a hammer oscillating
+between them, and a support formed of the polarised armature of an
+electro-magnet. The electro-magnetic instrument is placed below this
+system; it is turned by a winch, and sends the currents, alternately
+reversed, which are necessary to communicate the vibratory movement
+to the hammer, and this movement is enough to make the two bells
+tinkle. Below the winch of this electro-magnetic instrument there is a
+commutator with two contacts, which adapts the instrument for sending
+or receiving.
+
+M. Mandroux has simplified this system, and has reduced it to small
+dimensions by the following arrangement. He fixes two magnetic cores,
+furnished with coils, on each of the two poles of a horseshoe magnet,
+composed of two bars connected by an iron coupler, and between the
+poles expanded by these four cores he inserts an armature, within
+which there is a steel spring fastened to one of these poles. In this
+way the armature is polarised, and oscillates under the influence of
+the reversed currents transmitted by an instrument of the same kind
+provided with an induction system. These oscillations may have the
+effect of producing the sound of a call-bell, and the induction system
+may consist of a manipulating key, fastened to a duplex system of
+armature, regularly applied to the magnetic cores, taken in pairs. On
+communicating a series of movements to this manipulator, a series of
+induced currents in an inverse direction are produced, which cause the
+armature of the corresponding station to act as we have already seen,
+and which may even, when necessary, furnish a series of Morse signals
+for a suitable manipulation. On account of the small size of this
+system, it might be applied to the telephonic service of the army.
+
+The Bell Telephone Company in Paris has arranged another little
+call-system which is quite satisfactory and has the advantage of
+acting as a telephone at the same time. The model resembles the one
+we have termed a snuff-box telephone, and it has a button commutator
+by means of which the instrument is placed in communication with the
+electro-magnetic system of the instrument, or with a battery which is
+able to make the telephone vibrate with some force. To make a call,
+the button must be pressed, and the battery current is communicated
+to the corresponding instrument, which begins to vibrate when the call
+is made; and when notice is given of the receipt of the signal, the
+pressure on the button is removed, and it becomes possible to speak and
+receive as in ordinary telephones.
+
+[Illustration: FIG. 56.]
+
+
+_M. de Weinhold’s System._--M. Zetzche speaks highly of an alarum
+devised by Professor A. de Weinhold, which resembles that by M. Lorenz,
+represented in fig. 56. Its organ of sound consists of a steel bell T,
+from 13 to 14 centimètres in diameter, and toned to give about 420
+double vibrations in a second. ‘Its diameter and tone,’ he says, ‘are
+important, and any great departure from the rule laid down diminishes
+the effect. The opening of the bell is below, and it is fixed on a
+stand by its centre. A slightly curved bar magnet, provided at its two
+ends with iron appendices enclosed in a coil, traverses the stand.
+The bar magnet of the telephone also terminates in an iron appendix
+enclosed in a coil. In both cases the changes produced in the magnetic
+condition appear to be more intense than they are in magnets without
+appendices. The bar magnet is placed within the bell in the direction
+of one of its diameters, so that the appendices almost touch its sides.
+
+‘When the bell is struck on a spot about 90° from this diameter with
+a wooden clapper M, which acts with a spring, and is withdrawn by
+stretching the spring and then letting it go, as in a bell for the
+dinner-table, the vibrations imparted to it send currents into the
+coils, and these currents produce identical vibrations on the iron
+disk of the telephone, which are intensified by a conical resonator
+fitted to the telephone, so as to be easily heard some paces off. For
+ordinary use, the bell coil is broken into a short circuit by means of
+a metallic spring R, and consequently, when the bell is struck, the
+spring must be opened so as not to break the circuit. An instrument of
+the same kind has also been devised by Herr W. E. Fein at Stuttgardt.’
+
+[Illustration: FIG. 57.]
+
+[Illustration: FIG. 58.]
+
+
+_MM. Dutertre and Gouault’s System._--One of the most ingenious
+solutions of the problem of making the telephone call has recently been
+proposed by MM. Dutertre and Gouault. Figs. 57 and 58 represent the
+opposite faces of the instrument. It consists of a kind of snuff-box
+telephone, like the one shown in fig. 26, and it is so arranged as to
+send or receive the call, according to the way in which it is placed on
+its stand, which is only an ordinary bracket fastened to the wall. When
+it is placed on the bracket so as to have the telephone mouthpiece on
+the outside, it is adapted for receiving, and can then give the call.
+When, on the other hand, its position on the bracket is reversed, it
+permits the other station to make the call, by producing vibrations
+on a vibrator under the influence of a battery, and these vibrations
+reverberate in the corresponding instrument with sufficient force to
+produce the call. If the instrument is taken up, and the finger is
+placed on a small spring button, it may then be used as an ordinary
+telephone.
+
+In this instrument, the magnet N S (fig. 57) is snail-shaped, like
+others we have mentioned, but the core of soft iron S, to which the
+coil E is fastened, can produce two different effects on its two
+extremities. On the one side, it reacts on a small armature which is
+fastened to the end of a vibrating disk C, fig. 58; the armature is
+placed against a contact fastened to the bridge B, and constitutes an
+electro-magnetic vibrator. For this purpose the bridge is in metallic
+communication with the coil wire, of which the other end corresponds
+with the line wire, and the spring C is mounted on an upright A, which
+also supports another spring D G acting on two contacts, one placed at
+G, and corresponding to the earth wire, the other at H, and connected
+with the positive pole of the battery. A small moveable button, which
+passes through a hole in the lid of the box, and projects beyond it, is
+fixed at G, and all this part of the instrument faces the bottom of the
+box. The upper part consists of the vibrating disk and the mouthpiece,
+so that the mechanism we have described is all mounted on an inner
+partition forming a false bottom to the box.
+
+When the box rests upon its base, on the side shown in fig. 58, the
+button at G presses on the spring D G, and raises it so as to break the
+connection with the battery; the coil of the instrument is then united
+to the circuit, and consequently receives the transmitted currents,
+which follow this route: line wire, coil E, bridge B, spring C, spring
+D G, earth contact. If these currents are transmitted by a vibrator,
+they are strong enough to produce a noise which can be heard in all
+parts of a room, and consequently the call may be given in this way.
+If the currents are due to telephonic transmission, the instrument is
+applied to the ear, care being taken to put the finger on the button
+G, and the exchange of correspondence takes place as in ordinary
+instruments; but it is simpler and more manageable to insert a second
+telephone in the circuit for this purpose. When the box is inverted on
+its mouthpiece, and the button G ceases to press on the spring D G, the
+battery current reacts on the vibrator of the instrument, and sends the
+call to the corresponding station, following this route: I D A C B E,
+line, earth and battery; and the call goes on until the correspondent
+breaks the current by taking up his instrument, thus warning the other
+that he is ready to listen.
+
+
+_System of M. Puluj._--There is yet another call system, devised
+by M. Puluj. It consists of two telephones without mouthpieces,
+connected together, and with coils placed opposite the branches of two
+tuning-forks, tuned as nearly as possible to the same tone. A small
+metal bell is fixed between the opposite faces of the tuning-forks, and
+a wire stretched near them is provided with a small ball in contact
+with their branches. When the tuning-fork at the sending station is put
+in vibration by striking it with an iron hammer covered with skin, the
+tuning fork at the other station vibrates also, and its ball strikes
+upon the bell. As soon as the signal is returned by the second station,
+mouthpieces with iron diaphragms are fastened to the telephones, and
+the correspondence begins. It seems that, by the use of a resonator,
+the sound which reaches the receiving station may be so intensified as
+to become audible in a large hall, and the bell signal may be heard in
+an adjoining room, even through a closed door.
+
+
+_Mr. Alfred Chiddey’s System._--This arrangement consists of a slender
+copper tube, eight inches long, and with an orifice of 1/30 of an inch,
+of which the lower end is soldered to the diaphragm of a telephone. A
+branch joint, to which an india-rubber tube is fitted, connects it with
+a gas jet, which is lighted and surrounded with a lamp shade, in such
+a way as to make it produce, under given conditions, sounds resembling
+those of the singing flames. A perfectly similar system is arranged
+at the other end of the line, in such a way that the sounds emitted
+in each case shall be precisely in unison. If the two systems are so
+regulated as not to emit sounds in their normal condition, they can
+be made to sing by causing a tuning-fork in the vicinity of one or the
+other to vibrate the same note, and then the corresponding flame will
+begin to sing, producing a vibration in the diaphragm of the telephone
+with which it is in correspondence, and hence will follow the vibration
+of the diaphragm of the other telephone, and consequently the vibration
+of the flame of the calling instrument. In this way the call signal may
+be made without the intervention of any battery.
+
+
+
+
+APPLICATIONS OF THE TELEPHONE.
+
+
+The applications of the telephone are much more numerous than might
+be supposed at the first glance. As far as the telegraphic service
+is concerned, its use must evidently be rather limited, since it
+cannot register the messages sent, and the speed of transmission is
+inferior to that of the improved system of telegraphs; yet in many
+cases it would be very valuable, even for a telegraphic system, since
+it is possible to work it without any special telegraphic training.
+The first comer may send and receive with the telephone, and this is
+certainly not the case even with the simplest forms of telegraphic
+instruments. This system is therefore already in use in public offices
+and factories, for communication in mines, for submarine works, for
+the navy, especially when several vessels manœuvre in the same
+waters, some towed by others; finally, for military purposes, either
+to transmit orders to different corps, or to communicate with schools
+of artillery and rifle practice. In America the municipal telegraphic
+service and that of telegraphs limited to the area of towns are
+conducted in this way, and it is probable that this system will soon
+be adopted in Europe. Indeed, a service of this kind was established
+in Germany last autumn at the telegraph offices of some towns, and the
+London Post Office is now thinking of establishing it in England.
+
+But, besides its use for the purposes of correspondence, the telephone
+can be useful to the telegraphic service itself by affording one of
+the simplest means of obtaining a number of simultaneous transmissions
+through the same wire, and even of being combined in duplex with
+the Morse telegraphs. Its applications in the microphonic form are
+incalculable, and the proverb which declares that ‘walls have ears’
+may in this way be literally true. It is alarming to think of the
+consequences of such an indiscreet organ. Diplomatists must certainly
+redouble their reserve, and tender confidences will no longer be made
+with the same frankness. On this point we cannot think that much will
+be gained, but on the other hand the physician will probably soon make
+use of this invention to ascertain more readily the processes going on
+within the human body.
+
+
+APPLICATION OF THE TELEPHONE TO SIMULTANEOUS TELEGRAPHIC TRANSMISSIONS.
+
+The simultaneous transmission of several messages through the same wire
+is one of the most curious and important applications of the telephone
+to telegraphic instruments which can be made, and we have seen that it
+was this application which led Messrs. Gray and Bell to the invention
+of speaking telephones. The admiration which these instruments have
+excited has thrown the original idea into the background, although it
+has perhaps a more practical importance. We will now consider these
+systems.
+
+An articulating telephone is not necessary in order to obtain
+simultaneous transmission: the musical telephones devised by MM.
+Petrina, Gray, Froment, &c., are quite sufficient, and a brief
+explanation of their principle will make this intelligible.
+Suppose that there are seven electro-magnetic vibrators at the two
+corresponding stations, which are tuned with the same tuning-fork
+on the different notes of the scale, and suppose that a key-board,
+resembling the Morse telegraph key, is arranged so that, by lowering
+the keys, electric reaction takes place on each vibrator: it is easy
+to see that these vibrators may be made to react in the same way on
+the corresponding vibrators of the opposite station; but they must be
+tuned on the same note, and the sounds emitted will continue while the
+keys are lowered. By keeping them down for a shorter or longer time,
+the long or short sounds which constitute the elements of telegraphic
+language in the Morse system may be obtained, and consequently an
+audible transmission becomes possible. Let us now suppose that a
+telegraphist accustomed to this mode of transmission is placed before
+each of the vibrators, and that they transmit different messages at the
+same moment in this way: the telegraphic wire will be instantaneously
+traversed by seven currents, broken and massed upon each other, and
+they might be expected to produce a medley of confused sounds on the
+vibrators at the receiving station; but since they each harmonise with
+the corresponding vibrator, they have no sensible influence except on
+those for which they are intended. The dominant sound may be made still
+more distinct by applying a Helmholtz resonator to each vibrator,[18]
+that is, an acoustic instrument which will only vibrate under the
+influence of the note to which it is tuned. In this way it is possible
+to select the transmitted sounds, and only to allow each _employé_ to
+hear that which is intended for him. Consequently, however confused
+the sounds may be on the receiving vibrators, the person to whom _do_
+is assigned will only receive _do_ sounds, the person to whom _sol_ is
+assigned will only receive _sol_ sounds, so that correspondence may be
+carried on as well as if they had each a special wire.
+
+In the mode we have described, this telegraphic system only admits
+of audible transmissions, and consequently cannot register messages.
+To supply this defect, it has been suggested to make the receiving
+vibrators react on registers, so arranging the latter that their
+electric organ may present such magnetic inertia, that, when it is
+influenced by the vibrations of sound, its effect may be maintained
+throughout the time of vibration. Experiments show that a Morse
+receiver, worked by the current of a local battery, will be enough for
+this purpose; so that if the musical vibrator is made to react as a
+relay, that is, on a contact in connection with the local battery and
+the receiver, the dots and dashes may be obtained on it which are the
+constituent elements of the Morse code.
+
+On these principles, and considering that the musical spaces
+separating the different notes of the scale are such as may be easily
+distinguished by the resonator, seven simultaneous transmissions may be
+obtained on the same wire; but experience shows that it is necessary to
+be content with a much smaller number. Yet this number may easily be
+doubled by applying the mode of transmission in an opposite direction
+to the system.
+
+Mr. Bell states that the idea of applying the telephone to multiple
+electric transmissions occurred simultaneously to M. Paul Lacour of
+Copenhagen, to Mr. Elisha Gray of Chicago, to Mr. Varley of London,
+and to Mr. Edison of New York; but there is some confusion here, for
+we have already seen, from reference to the patents, that Mr. Varley’s
+system dates from 1870, that of M. Paul Lacour from September 1874,
+that of Mr. Elisha Gray from February 1875, and those of Messrs.
+Bell and Edison were still later. Yet it appears from Mr. Gray’s
+specification that he was the first to conceive and execute instruments
+of the kind. In fact, in a specification drawn up on August 6, 1874,
+he distinctly put forward the system we have described, and which is
+the basis of those of which we have still to speak. This specification
+was only an addition to two others made out in April and June 1874.
+Mr. Varley’s system has only an indirect relation to the one we have
+described. It appears from what Mr. Bell said on the subject in a paper
+addressed to the Society of Telegraphic Engineers in London, that he
+himself only attaches a secondary interest to this invention.
+
+He said that he had been struck with the idea that the greater or
+less duration of a musical sound might represent the dot and dash of
+the telegraphic alphabet, and it occurred to him that simultaneous
+telegraphic transmissions, of which the number should only be
+limited by the delicacy of the sense of hearing, might be obtained
+by suitable combinations of long and short sounds, and that these
+should be effected by a keyboard of tuning-forks applied to one end
+of a telegraphic line, and so arranged as to react electrically on
+electro-magnetic instruments striking on the strings of a piano. For
+this purpose it would be necessary to assign an employé to each of
+the keys for the service of transmission, and to arrange that his
+correspondent should only distinguish his peculiar note among all
+those transmitted. It was this idea, Mr. Bell adds, which led to his
+researches in telephony.
+
+For several years he sought for the best mode of reproducing musical
+sounds at a distance by means of vibrating rheotomes: the best results
+were given by a steel plate vibrating between two contacts, of which
+the vibrations were electrically produced and maintained by an
+electro-magnet and a local battery. In consequence of its vibration,
+the two contacts were touched alternately, and the two circuits
+were alternately broken; the local circuit which kept the plate in
+vibration, and the other which was connected with the line, and reacted
+on the distant receiver, so as to effect simultaneous vibrations in
+it. A Morse key was placed in the latter circuit near the sending
+instrument, and when it was lowered, vibrations were sent through the
+line; when it was raised, these vibrations ceased, and it is easy to
+see that, by lowering the key for a longer or shorter time, the short
+and long sounds necessary for the different combinations of telegraphic
+language could be obtained. Moreover, if the vibrating plate of the
+receiving instrument were so regulated as to vibrate in unison with the
+sending instrument in correspondence, it would vibrate better with this
+sender than with another whose plate was not so adjusted.
+
+It is evident that different sounds might be simultaneously transmitted
+with several plates by this arrangement of contact breaker, and that
+at the receiving station the sounds might be distinguished by each
+employé, since the one which corresponds to the fundamental note of
+each vibrating plate is reproduced by that plate. Consequently, the
+sounds produced by the vibrating plate of _do_, for example, will only
+be audible at the receiving station on the plate tuned to _do_, and the
+same will be the case with the other plates; so that the sounds will
+reach their destination, if not without confusion, yet with sufficient
+clearness to be distinguished by the employés.
+
+Mr. Bell sums up the defects still existing in his system as
+follows:--1st. The receiver of the messages must have a good musical
+ear, in order to distinguish the value of sounds. 2nd. Since the
+signals can only take place when the transmitted currents are in
+the same direction, two wires must be employed in order to exchange
+messages on each side.
+
+He surmounted the first difficulty by providing the receiver with an
+instrument which he called the vibrating contact breaker, and which
+registered automatically the sounds produced. This contact breaker was
+placed in the circuit of a local battery, which could work a Morse
+instrument under certain conditions. When the sounds emitted by the
+instrument did not correspond with those for which it had been tuned,
+the contact breaker had no effect on the telegraphic instrument: it
+only acted when the sounds were those which were to be interpreted, and
+its action necessarily corresponded to the length of the sounds.
+
+Mr. Bell adds that he applied the system to electro-chemical
+telegraphs; but we need not dwell on this part of the invention, since,
+as we have said, it is no longer his special study.
+
+
+_System of M. Lacour of Copenhagen._--M. Lacour’s system was patented
+on the 2nd September, 1874, but his experiments were commenced on the
+5th June of the same year. Since M. Lacour believed that the vibrations
+would be imperceptible on long lines, his first attempts were made on
+a somewhat short line; but in November 1874 fresh experiments were made
+between Fredericia and Copenhagen on a line 225 miles in length, and
+it was ascertained that vibratory effects could be easily transmitted,
+even under the influence of a rather weak battery.
+
+[Illustration: FIG. 59.]
+
+In M. Lacour’s system, the sending instrument is a simple tuning-fork,
+placed in a horizontal position, and one of its arms reacts on a
+contact breaker, which can produce precisely the same number of
+discharges of currents as there are vibrations of the tuning-fork. If
+a Morse manipulator is inserted in the circuit, it is evident that
+if it is worked so as to produce the dots and dashes of the Morse
+alphabet, the same signals will be reproduced at the opposite station,
+and the signals will be manifested by long and short sounds, if an
+electro-magnetic receiver is connected with the circuit. This sender is
+shown fig. 59.
+
+Fig. 60 represents M. Lacour’s receiver. It consists of a tuning-fork F
+made of soft iron, not of steel like the sending tuning-fork, and each
+of its branches is inserted in the bobbin of an electro-magnetic coil
+C C; two distinct electro-magnets M M react close to the extremities
+of the fork, in such a way that the polarities developed on the two
+branches of the fork under the influence of the coils C C should be of
+contrary signs to those of the electro-magnets M M.
+
+[Illustration: FIG. 60.]
+
+If this double electro-magnetic system is inserted in a line circuit,
+it follows that, for each discharge of the transmitted current, a
+corresponding attraction of the branches of the tuning-fork will take
+place, and consequently there will be a vibration, producing a sound,
+if the discharges are numerous. This sound will naturally be short or
+long in proportion to the duration of the sender’s action, and it
+will be the same as that of the tuning-fork in that instrument. Again,
+if one branch of the tuning-fork reacts on a contact P inserted in
+the circuit of the local battery communicating with a Morse receiver,
+traces will be produced on this receiver of length varying with the
+duration of the sounds, for the Morse electro-magnet will be so quickly
+affected by the successive breaks in the current that its armature
+will remain stationary throughout each vibration. ‘I have not yet been
+able,’ said M. Lacour in an address delivered before the Danish Academy
+of Science in 1875, ‘to calculate the time necessary for the production
+of definite vibrations in the tuning-fork. Different factors have to be
+considered, but experiment has shown that the time which elapses before
+the local circuit is broken is such a small fraction of a second as to
+be almost inappreciable, even when the current is very weak.
+
+‘Since intermittent currents only affect a tuning-fork on condition
+that it vibrates in unison with the one which produces them, it follows
+that if a series of sending tuning-forks, tuned to the different notes
+of the scale, is placed at one end of a circuit, and if a similar
+series of electro-magnetic tuning-forks, in exact accordance with the
+first, is placed at the other end of the circuit, the intermittent
+currents transmitted by the sending tuning-forks will be added to each
+other without becoming confused, and each of the receiving tuning-forks
+will only be affected by the currents emitted by the tuning-fork in
+unison with it. In this way the combinations of elementary signals
+representing a word may be telegraphed simultaneously.’
+
+M. Lacour enumerates the ways in which this system may be applied as
+follows: ‘If the keys in connection with the sending tuning-forks
+are placed side by side, and are lowered in succession, or two or
+three together, it will be enough to play on the keys as on a musical
+instrument, in order that the air may be heard at the receiving
+station, or the signals transmitted simultaneously may each belong to
+a different message. This system will therefore allow the furthest
+station on a line to communicate with one or several intermediate
+stations, and _vice versa_, without disturbing the communication
+at other stations. In this way two stations can exchange signals,
+unperceived by the rest. The power of sending many signals at once
+affords a good means of improving the autographic telegraph. In the
+instruments now in use, such as those of Caselli and D’Arlincourt,
+there is only one tracing stylus, and this stylus must pass over the
+whole surface of the telegram in order to obtain a copy of it, but with
+the telephone a certain number of styli may be placed side by side
+in the form of a comb, and this comb need only be drawn in a certain
+direction to pass over the surface of the telegram. In this way a more
+faithful copy will be obtained in a shorter time.’
+
+M. Lacour also observes that his system possesses a merit already
+pointed out by Mr. Varley, namely, that the instruments permit the
+passage of ordinary currents without revealing their presence, whence
+it follows that the accidental currents which often disturb telegraphic
+transmissions will have no effect on these systems.
+
+M. Lacour began without applying an electro-magnetic system to his
+instrument in order to maintain the movement of the tuning-fork,
+but he soon saw that this accessory was indispensable, and he made
+the tuning-forks themselves electro-magnetic. It also occurred to
+him to convert the transmitted currents into pulsatory currents by
+inserting an induction coil in the circuit, which was also done by
+Mr. Elisha Gray. Finally, in order to obtain the immediate action
+of the tuning-forks and the immediate cessation of their action, he
+constructed them so as to reduce their inertia as much as possible.
+This was effected by inserting the two branches of the tuning-fork in
+the same coil and by lengthening its handle, and turning it back so
+that it might pass through a second coil, dividing into two branches
+and embracing the two vibrating branches, but without touching them.
+When a current traverses both coils, it produces, in the kind of
+horseshoe magnet formed by the two systems, opposite polarities which
+provoke a double reaction in the vibrating branches--a reaction by
+repulsion exerted by the two branches in virtue of the same polarity,
+and a reaction by attraction by the other two branches in virtue of
+their opposite polarities; and this double action is repeated by the
+movements of a contact breaker applied to one of the vibrating branches
+of the tuning-fork.
+
+[Illustration: FIG. 61.]
+
+
+_Mr. Elisha Gray’s System._--According to the system originally
+patented, each sender, represented fig. 61, consists of an
+electro-magnet M M resting below a small copper tablet B S, in such a
+way that its poles pass through this tablet and are on a level with
+its upper surface. A steel plate A S is fixed above these poles; its
+tension can be regulated by means of a screw S; and another screw _c_
+is placed on the plate, and is in electric communication with a local
+battery R′ by means of a Morse key. Below the plate A S there is a
+contact _d_ connected with the line wire L; this contact is met by
+the plate at the moment of its attraction by the electro-magnet, and
+breaks the current of a line battery P, which acts on the receiver of
+the opposite station. Finally, the electric communication established
+between the local battery R′ and the electro-magnet, as may be seen
+in the figure, produces vibrations in the steel plate A S at each
+lowering of the key, as in the case of ordinary vibrations--vibrations
+which, with a suitable tension of the plate and a given intensity of
+the battery R′, can produce a definite musical note. Moreover, since
+at each vibration the plate A S meets the contact, discharges of the
+line current take place through the line L, and react on the receiving
+instrument, causing it to reproduce exactly the same vibrations as
+those of the sending instrument.
+
+[Illustration: FIG. 62.]
+
+The receiving instrument represented fig. 62 exactly resembles the one
+we have just described, except that there is no contact _d_ below the
+vibrating plate A S, and the contact _c_, instead of communicating
+with the line wire, is in electric connection with a register E and
+a local battery P. It follows from this arrangement that when the
+plate A S vibrates under the influence of the broken currents passing
+through the electro-magnet M M, similar vibrations are sent through
+the register; but if the electro-magnetic organ of this register is
+properly regulated, these vibrations can only produce the effect of
+a continuous current, and hence the length of the traces left on the
+instrument will vary with the duration of the sounds produced. In this
+way the registration of the dashes and dots which constitute the signs
+of the Morse vocabulary will be effected.
+
+If it is remembered that the plate A S vibrates under the influence
+of electro-magnetic attractions more readily in proportion to their
+approximation in number to the vibrations corresponding to the
+fundamental sound it can emit, it becomes clear that if this plate is
+tuned to the same note as that of the corresponding instrument, it
+will be rendered peculiarly sensitive to the vibrations transmitted
+by the sender, and the other vibrations which may affect it will only
+act faintly. Moreover, a resonator placed above the plate will greatly
+increase this predisposition; so that if several systems of this kind,
+tuned to different notes, produce simultaneous transmissions, the
+sounds corresponding to the different vibrations will be in a certain
+sense selected and distributed, in spite of their combination, into the
+receivers for which they are specially adapted, and each of them may
+retain the traces of the sounds emitted by adding the register, which
+may be so arranged as to act as an ordinary Morse receiver. Mr. Gray
+states that the number of sending instruments and independent local
+circuits may be equal to that of the tones and semitones of two or more
+octaves, provided that each vibrating plate be tuned to a different
+note of the scale. The instruments may be placed side by side, and
+their respective local keys, arranged like the keys of a piano, will
+make it easy to play an air combining notes and chords; there may also
+be an interval between the instruments, which may be sufficiently far
+from each other to allow the employés to work without being distracted
+by sounds not intended for them.
+
+In a new arrangement, exhibited at the Paris Exhibition, 1878, Mr. Gray
+considerably modified the way of working the various electro-magnetic
+organs which we have just described. In this case, the plates consist
+of tuning-forks with one branch kept in continual vibration at both
+stations, and the signals only become perceptible by intensifying the
+sounds produced. This arrangement follows from the necessity of keeping
+the line circuit always closed for multiple transmissions of this
+nature, so as to react with pulsatory currents, which are alone able,
+as we have already seen, to retain the individual character of several
+sounds simultaneously transmitted.
+
+[Illustration: FIG. 63.]
+
+Under these conditions, the sender consists, as we see (fig. 63), of
+a bar tuning-fork, _a_, which is grooved for the passage of a runner,
+heavy enough to tune the fork to the desired note, and it oscillates
+between two electro-magnets _e_ and _f_ and two contacts I and G. The
+difference of resistance in the electro-magnets is very great: in the
+one _f_ the resistance is equal to 2¾ miles of telegraphic wire, in
+the other it does not exceed 440 yards. When electric communication is
+established as we see in the figure, the following effect takes place.
+Since the current of the local battery through the two electro-magnets
+is broken by the rest-contact of the Morse key H, the plate _a_ is
+subject to two contrary actions; but since the electro-magnet _f_ has
+more turns than the electro-magnet _e_, its action is preponderant,
+and the plate is attracted towards _f_, and produces a contact with
+the spring G, which opens a way of less resistance for the current.
+Since the current then passes almost wholly through G, _b_, 1, 2, B,
+the electro-magnet is now able to act; the plate _a_ is then attracted
+towards _e_, and, by producing a contact on the spring I, it sends
+the current of the line B P through the telegraphic line, if the key
+H is at the same time lowered on the sending contact: if not, there
+will be no effect in this direction, but since the plate _a_ has left
+the spring G, the first effect of attraction by the electro-magnet
+_f_ will be repeated, and this tends to draw the plate again towards
+_f_. This state of things is repeated indefinitely so as to maintain
+the vibration of the plate, and to send out signals corresponding with
+these vibrations whenever the key H is lowered. The elastic nature of
+the plate makes these vibrations more easy, and it ought also to be put
+in mechanical vibration at the outset.
+
+The receiver, represented fig. 64, consists of an electro-magnet
+M, mounted on a sounding-box C, and having an armature formed by a
+tuning-fork L L firmly buttressed on the box by a cross bar T. There
+is a runner P on the armature, sliding in a groove, which makes it
+possible to tune the vibrations of the tuning-fork to the fundamental
+note of the sounding-box C, which is so arranged as to vibrate
+in unison with it. Under these conditions, the box as well as the
+tuning-fork will act as an analyser of the vibrations transmitted by
+the currents, and may set the register at work by itself reacting on
+a breaker of the local current. To obtain this result, a membrane of
+gold-beater’s skin or parchment must be stretched before the opening
+of the box, and a platinum contact must be applied to it, so arranged
+as to meet a metallic spring connected with any kind of register or a
+Morse instrument, when the membrane vibrates. As, however, in America
+the messages are generally received by sound, this addition to the
+system is not in use.
+
+[Illustration: FIG. 64.]
+
+The instrument is not only regulated by the runner P, but also by a
+regulating screw V which allows the electro-magnet M to be properly
+adjusted. The regulating system is made more exact by the small screw
+V, and the instrument is connected with the line by the binding screw
+B. Of course this double arrangement is necessary for each of the
+sending systems.
+
+As I have already said, seven different messages might theoretically be
+sent at once in this way, but Mr. Gray has only adapted his instrument
+for four; he has, however, made use of the duplex system, which allows
+him to double the number of transmissions, so that eight messages may
+be sent at the same time, four in one direction, and four in another.
+
+Mr. Hoskins asserts that this system has been worked with complete
+success on the lines of the Western Union Telegraph Company, from
+Boston to New York, and from Chicago to Milwaukee. Since these
+experiments were made, fresh improvements have rendered it possible to
+send a much larger number of messages.
+
+Mr. Gray has also, aided by Mr. Hoskins, devised a system by which
+telephonic messages may be sent on a wire previously used for Morse
+instruments. Mr. Varley had already solved this problem, but Mr. Gray’s
+system seems to have produced important results, and has therefore a
+claim to our attention. We do not, however, describe it here, since it
+is not within the lines marked out for us, and those who are interested
+in the subject will find all the necessary details in a paper inserted
+in the ‘Journal of the Society of Telegraphic Engineers, London,’ vol.
+vi.
+
+
+_Mr. Varley’s System._--This system is evidently the earliest in date,
+since it was patented in 1870, and the patent describes the principle
+of most of the arrangements which have since been adopted by Messrs.
+Lacour, Gray, and Bell. It is based upon the use of his own musical
+telephone, which we have already described, but with some variations in
+its arrangement, which make it somewhat like the Reiss system.
+
+It was Mr. Varley’s aim to make his telephone work in conjunction with
+instruments with ordinary currents, by the addition of rapid electric
+waves, incapable of making any practical change in the mechanical
+or chemical capacity of the currents which serve for the ordinary
+signals, yet able to make distinct signals, perceptible to the ear and
+even to the eye. He says: ‘An electro-magnet offers at first a great
+resistance to the passage of an electric current, and may consequently
+be regarded as a partially opaque body with respect to the transmission
+of very rapid inverse currents or of electric waves. Therefore, if a
+tuning-fork, or an instrument with a vibrating plate, tuned to a given
+note, be placed at the sending station, and so arranged as to be kept
+in constant vibration by magnetic influence, the current which acts
+upon it must be passed into two helices placed one above the other so
+as to constitute the primary helix of an induction coil: in this way
+it will be possible to obtain in two distinct circuits two series of
+rapidly broken currents, which will correspond to the two directions of
+the vibrations of the tuning-fork, and we shall also have the induced
+currents produced in the secondary helix by these currents, which may
+act on a third circuit. This third circuit may be placed in connection
+with a telegraphic line previously used by an ordinary telegraphic
+system, if a condenser is applied to it, and in this way two different
+transmissions may be obtained simultaneously.’
+
+[Illustration: FIG. 65.]
+
+Fig. 65 represents the arrangement of this system. D is the vibrating
+plate of the tuning-fork designed to produce the electric contacts
+necessary to maintain it in motion. These contacts are at S and S′, and
+the electro-magnets which affect it are at M and M′. The induction coil
+is at I′, and the three helices of which it is composed are indicated
+by the circular lines which surround it. There is a Morse manipulator
+at A, another at A′, and the two batteries which work the system are at
+P and P′. The condenser is at C, and the telephone is at the end of the
+line L.
+
+When the vibration of the plate D tends to the right, and the electric
+contact takes place at S′, the current of the battery P′, after
+traversing the primary helix, reaches the electro-magnets M M′, which
+give it an impulse in the contrary direction. When, on the other hand,
+it tends to the left, the current is sent through the second primary
+circuit, which will be balanced by the first. Consequently there will
+be a series of reversed currents in the induced circuit corresponding
+to the key A′, which will alternately charge and discharge the
+condenser C, thus sending into the line a corresponding series of
+electric undulations which will react on the telephone placed at the
+end of the line; and as the duration of the transmitted currents
+will vary with the time that the key A′ is lowered, a correspondence
+in the Morse code may be obtained in the telephone, while another
+correspondence is exchanged with the key A and the ordinary Morse
+receivers.
+
+In order to render the vibratory signals visible, Mr. Varley proposes
+to use a fine steel wire, stretched through a helix and facing a narrow
+slit, to reproduce the vibrations. A light, which is intercepted by the
+wire, is placed behind the slit. As soon as a current passes, the wire
+vibrates and the light appears. A lens is placed so as to magnify the
+image of the luminous slit, and project it on a white screen while the
+wire is in vibration.
+
+
+
+
+VARIOUS USES OF THE TELEPHONE.
+
+
+_Its domestic application._--We have seen that telephones may be used
+with advantage in public and private offices: they can be set up
+at a much less expense than acoustic tubes, and in cases where the
+latter would never be employed. With the aid of the calls we have
+described, they offer the same advantages, and the connection between
+the instruments is more easily concealed. The difference of price in
+establishing them is in the ratio of one to seven.
+
+For this purpose electro-magnetic telephones are evidently the best,
+since they require no battery and are always ready to work. They are
+already in use in many Government offices, and it is probable that they
+will soon be combined with electric bells for the service of hotels and
+of large public and private establishments: they may even be used in
+private houses for giving orders to servants and porters, who may thus
+save visitors from the fatigue of a useless ascent of several storeys.
+
+In factories, telephones will certainly soon replace the telegraphic
+communication which has already become general. They may not only be
+used for ordinary messages, but to call for help in case of fire,
+and they will become an integral part of several systems already
+established for this purpose.
+
+In countries which have free telegraphic communication, the telephone
+has already replaced in great measure the private telegraph instruments
+which have hitherto been in use; and if the same privilege is extended
+to France, no other mode of correspondence will be used.
+
+
+_Its application to telegraphic service._--The advantage to be derived
+by the telegraphic service from the telephone is rather limited, since,
+as far as the speed of transmission is concerned, it is of less value
+than many of the telegraphic instruments now in use, and the messages
+which it produces cannot be registered. Yet in municipal offices not
+overburdened with messages they offer the advantage of not requiring a
+trained service. On longer lines their use would be of little value.
+The ‘Berne Telegraphic Journal’ has published some interesting remarks
+on this subject, of which the following is a summary.
+
+1st. In order to send a message with the special advantages of the
+system, the sender ought to be able to address his correspondent
+without the intervention of an official. Those who are acquainted with
+the network of wires know this to be impossible. Intermediate offices
+for receiving messages are essential, and the public cannot be admitted
+to those set apart for sending and receiving; consequently the sender
+must deliver a written message.
+
+2nd. If the message is written, the chief advantage of the instrument
+is lost, since it must be read and uttered aloud, which could not
+be done if expressed in a language with which the employés were
+unacquainted.
+
+3rd. The instruments now in use at the telegraph offices can transmit
+messages more quickly than if they were spoken.
+
+In Germany, however, a telephone service has been established in
+several telegraph offices, and its possible advantages are enumerated
+as follows in the official circular which created it:
+
+‘The offices which will be opened to the public for the service
+of telephonic messages in Germany will be regarded as independent
+establishments; yet they will be in connection with the ordinary
+telegraph offices, which will undertake to send telephonic messages
+through their wires.
+
+‘The transmission will take place as follows: The sending office will
+request the receiving office to prepare the instrument; as soon as
+the tubes are adjusted, the sending office will give the signal for
+despatching the verbal message.
+
+‘The sender must speak slowly and clearly, without raising his voice;
+each syllable must be distinctly pronounced; the final syllables
+especially must be well articulated, and there must be a pause after
+each word, in order to give the receiver time to write it down.
+
+‘When the telegram has been received, the employé at the receiving
+office must verify the number of words; then he must repeat through the
+telephone the whole message without pausing, so as to make sure that
+there is no mistake.
+
+‘In order to ensure secrecy, the telephones are placed apart, where
+persons unconnected with the service cannot hear the verbal message,
+and the employés are forbidden to reveal to anyone the names of the
+correspondents.
+
+‘The charge for telephonic messages, as for the ordinary telegraphic
+services, is at the rate of so much a word.’
+
+The use of the telephone has also been suggested for verifying the
+perfect junction of telegraphic wires. It is certain that, if the
+junction is complete, no abnormal sounds will be heard, or only those
+which result from accidental currents; but if the junction is bad, the
+imperfect contacts which take place produce variations in electric
+intensity which are translated into the more or less marked sounds
+observed in the telephone.
+
+M. Mauborgne, the electrician attached to the Northern Railway of
+France, has lately used the telephone instead of the galvanometer to
+ascertain the condition of the circuits in correspondence with the
+instruments in use for electric signals. The reactions produced on
+the galvanometer needle by the pieces of iron which are placed at the
+sides of the railway often make its indications uncertain, and a strong
+wind produces irregular movements in the instrument which interfere
+with observations. It was also necessary to place the galvanometer
+with due regard to the points of the compass, and to wait for the
+needle to settle, which involved loss of time. The operation is easily
+accomplished with the telephone, since the strokes of the call-bell are
+distinctly reproduced; it is made to ring by working the contacts which
+need verification, and in the same way the condition of the battery can
+be ascertained.
+
+_Application to military purposes._--Since the telephone was invented,
+numerous experiments have been made in different countries to ascertain
+whether it would be of use in military operations. These experiments
+have hitherto been only moderately satisfactory, on account of the
+noise inseparable from an army, which generally makes it impossible
+to hear the telephone, and every means of intensifying its sounds has
+been eagerly sought. It was at first supposed that the discovery of
+the microphone had solved the problem, and I received many enquiries
+from military schools on the subject, but I have not been able to see
+that anything has been gained from this point of view. The telephone
+is, however, of great use in schools of artillery and rifle practice.
+Now that firearms carry so far, it has become necessary to be informed
+by telegraph of the points hit on the target, in order to judge of
+the accuracy of aim, and for this purpose telegraphic targets were
+suggested; but telephones are much to be preferred, and they are now
+used with good effect.
+
+If the telephone is unsuited for the service of the flying telegraph in
+the field, it may be of great use in the defence of towns, to transmit
+the orders of the commandant to different batteries, and even for the
+exchange of correspondence with captive balloons sent to hover over
+fields of battle.
+
+In spite of the difficulties attending its use, the experiment was
+made by the Russians in the late war: the cable wire of communication
+was 500 or 600 yards long, and so light that it could be laid by one
+man. The ‘Telegraphic Journal’ of March 15, 1878, states that the bad
+weather did not interfere with the working of the instruments; but the
+noise made it difficult to hear, and it was necessary to cover the head
+with a hood to intercept external sounds. This cannot be considered a
+satisfactory result, yet the telephone may be of great service to an
+army by intercepting the enemy’s messages: a bold man, provided with a
+pocket telephone, who placed himself in a retired spot, might divert
+the current of the enemy’s telegraphic wire into his telephone, and get
+possession of all his despatches, as we saw was the case at Clermont.
+He might even do this by diverting the current to earth or to a rail of
+the railway line. These are suggestions for future research, and it is
+probable that they may some day be turned to practical account.
+
+_Its application to the navy._--The telephone may be of the greatest
+use in naval matters, for the service of electro-semaphores, for
+island forts and ships at anchor. M. Pollard says that ‘experiments
+made between the Préfecture Maritime at Cherbourg, the semaphores and
+the forts on the mole, demonstrate the advantage there would be in
+establishing telephones at these stations, since they would ensure an
+easy communication between the vessels of a squadron and the land they
+are approaching. By sinking small cables which come to the surface
+of the water along mooring chains, and terminate in buoys or cases
+which remain permanently in the harbour, the ships of war may in this
+way place themselves in communication with the Préfecture Maritime as
+they cast anchor, and, by temporarily connecting the vessels together
+with light cables, the admiral may communicate freely with the whole
+squadron.’
+
+The telephone has been tried on board ship for transmitting orders, but
+without success, on account of the noise always going on in a vessel.
+
+The telephone may be usefully applied to the service of submarine
+torpedoes. We have already seen how it may be applied in connection
+with the microphone, but it may also be used in firing the torpedoes
+after the exact position of the enemy’s ship has been ascertained from
+two reconnaissances taken from different parts of the coast.
+
+The telephone, again, makes it possible to verify the condition of
+torpedoes, and to ascertain if there is any fault in the circuit within
+the explosives. For this purpose a very weak current has been used,
+and a galvanometer is not always able to indicate the fault, while the
+extreme sensitiveness of the telephone will do so in the simplest way.
+
+Captain M’Evoy, of the American Army, suggested a way of ascertaining,
+while on shore, the condition of torpedoes under water, by connecting
+the buoys which support them with the land by means of a telephonic
+line. By inserting, in the buoy which supports the torpedo, metallic
+disks, so arranged as to vibrate with every movement caused by the
+waves upon the buoy, a continuous noise will be heard in the telephone,
+after the circuit has been completed by the metallic disks; and the
+noise will go on as long as the disks continue to oscillate, and will
+cease as soon as the buoy is completely covered by the water. When it
+ceases, therefore, if not affected by some accidental cause, it may be
+supposed that the enemy’s ship is passing over the buoy.
+
+M. Trève, again, has shown that the telephone might be used with
+advantage for the telegraphic communication between vessels in tow, and
+M. des Portes has applied it with good effect to diving operations. In
+this instance, one of the glass panes in the helmet is replaced by a
+copper plate in which the telephone is framed, so that the diver need
+only make a slight movement of his head in order to receive or address
+communications to those in charge of the apparatus. With this system
+the keels of vessels may be examined, and an account given of their
+condition, without bringing up the divers, which has hitherto been
+necessary.
+
+M. de Parville, the able and learned editor of the _Journal
+Scientifique_ and the science department of the _Journal des Débats_,
+has suggested a new and interesting application of the telephone. It
+concerns the possibility of making use of it to determine the precise
+position of the magnetic meridian, that is, the true direction of the
+magnetised needle.
+
+For this purpose a Bell telephone is necessary, of which the
+magnetic core is formed of an iron rod a mètre in length, kept, by
+a suitable suspension, at nearly the same angle of inclination as a
+dipping-needle. This rod will be magnetised under the influence of
+terrestrial magnetism, and the telephone will be able to transmit
+the sounds produced by some sort of vibrator placed near its
+mouthpiece. These sounds will be strong in proportion to the degree
+of magnetisation of the bar; and if the telephone is turned round the
+horizon, keeping the bar at the same angle of inclination, the sounds
+transmitted to the receiving telephone will be greatest when the axis
+of the bar is in the plane of the magnetic meridian, and least when
+it is at 90°. It will therefore be possible to ascertain from the
+direction of the axis at the moment when the sounds are no longer
+heard, the exact inclination of the magnetic needle from north to
+south, for it will be given by the perpendicular to the line which is
+followed by the axis of the iron bar at that moment.
+
+It is possible that, with this system, the disturbing influence on the
+magnetic needle of the mass of iron in iron-plated vessels might be
+almost destroyed, and a more exact orientation than that of the compass
+might be obtained. The same process may make it possible to estimate
+and measure the variations of terrestrial magnetism. M. de Parville has
+not himself tried to apply this system; but Mr. Blake’s experiments, of
+which we spoke in an early part of this work, make it probable that it
+might be done with advantage.
+
+_Application to industry._--One of the earliest and most important
+applications of the telephone is that which was first made to the
+service of mines in England and America in the autumn of 1877. The
+great length of the galleries is well known, and had already involved
+the use of the electric telegraph for transmitting orders; but the
+miners did not understand how to work these instruments, and the
+service was ill performed. Thanks to the telephone, through which the
+first corner can send and receive a message, there is no longer any
+difficulty in the communication between the galleries and the surface
+of the mine.
+
+The ventilation of mines can also be regulated by the aid of
+telephones. If one of these instruments is placed near a wheel kept
+in motion by the air which passes through the ventilating shaft, and
+another is placed in the inspector’s office he can ascertain by the
+sound if the ventilation is duly carried on, and if the machine works
+regularly.
+
+_Application to scientific research._--M. d’Arsonval’s experiments,
+which we have already mentioned, show that the telephone can be used
+as an extremely sensitive galvanoscope; but since it can only produce
+sounds under the influence of broken currents, the circuit on which the
+experiment is made must be divided at rather close intervals. It has
+been seen that it is not even necessary to insert the telephone in the
+circuit: it may be influenced, when at a distance, either immediately
+or by the induction of the broken current on a circuit placed parallel
+to the first, and the force of these effects may be increased by the
+reaction of a core of iron, round which the inducing circuit is wound.
+The drawback to this system is that the direction of the current is
+not ascertained, so that it cannot be used as a measuring instrument;
+but, on the other hand, it is so sensitive, so easy to arrange, and so
+inexpensive, that it might be of the greatest use as a galvanoscope.
+
+Mr. Warren de La Rue has also made use of the telephone in his
+researches into the electric discharges of high-tension batteries,
+in order to follow the different phases of the discharge during the
+luminous phenomena which it produces. In this way he ascertained
+that when a condenser is placed in connection with a battery formed
+of a considerable number of insulated elements, and is gradually
+discharged through a Geissler tube, a dull and faint sound is heard
+in the telephone, as long as the stratifications of light appear to
+be perfectly stable; but the sound becomes considerably stronger,
+and sometimes even piercing, in proportion to the diffusion of these
+stratifications, and to their approach to the point of extinction:
+whence it is shown that the discharge of a battery into tubes in which
+a vacuum has been made is intermittent.
+
+Mr. Spottiswoode has repeated the same experiments with the discharges
+of Holtz machines, and with large condensers, and he found that the
+most piercing sounds produced by the telephone coincided with the
+greatest development of the stratifications. These sounds, however,
+sometimes ceased for a moment. It was even possible to ascertain,
+from the intensity of the sounds produced, the differences of tension
+which might be manifested in the charge of the condenser and the
+slackening of the machine’s motion, and the differences of intensity
+in these sounds might in some cases exceed an octave. The fall in the
+scale generally appeared in half-tones instead of gradually, and the
+introduction of resistances into the circuit modified the sounds very
+much: they might even be intensified by approaching the finger to the
+discharging tube.
+
+From experiments made with the telephone between Calais and Boulogne,
+it appears that this instrument might be applied with advantage to the
+science of projectiles. In fact, in some artillery practice which took
+place on the shore at Boulogne, a telephone was placed close to the
+gun, and the explosion was heard at a distance of nearly two miles,
+where the projectile fell. It was possible to estimate its velocity by
+measuring the lapse of time between the moment when the projectile left
+the gun, and its fall. This calculation is usually made by observing
+the flash from the cannon’s mouth; but in some cases, as in a fog or in
+practice at long ranges, the telephone may be usefully substituted for
+ocular observation. On the field of battle, an observer, provided with
+a telephone and placed on a hill, might rectify from a distance the aim
+of his battery, which is generally established in a sheltered and less
+elevated place.
+
+
+
+
+THE PHONOGRAPH.
+
+
+Mr. Edison’s Phonograph, which has for the last year attracted so much
+attention, is an instrument which not only registers the different
+vibrations produced by speech on a vibrating plate, but reproduces the
+same words in correspondence with the traces registered. The first
+function of this instrument is not the result of a new discovery.
+Physicists have long sought to solve the problem of registering
+speech, and in 1856 Mr. Leo Scott invented an instrument well known to
+physicists under the name of Phonautograph, which completely solved
+the difficulty: this instrument is described in all the more detailed
+treatises on physics. But the second function of the Edison instrument
+was not realised nor even mentioned by Mr. Scott, and we are surprised
+that this able inventor should have regarded Mr. Edison’s invention as
+an injurious act of spoliation. We regret on his own account, since no
+one has wished to deprive him of the credit he deserves, that he should
+have published a pamphlet on the subject, couched in terms of such
+asperity, which proves nothing, and only states facts which were well
+known to all physicists. If any other person could claim the invention
+of the phonograph, at least in its most curious property of reproducing
+speech, it would certainly be M. Charles Cros; for in a sealed paper
+deposited at the Académie des Sciences, April 30, 1877, he pointed
+out the principle of an instrument by means of which speech might be
+reproduced in accordance with the marks traced on a register like that
+of the phonautograph.[19] Mr. Edison’s patent, in which the principle
+of the phonograph is first indicated, is dated July 31, 1877, and he
+was still only occupied with the repetition of the Morse signals. In
+this patent Mr. Edison described a mode of registering these signals by
+means of indentations traced with a stylus on a sheet of paper wound
+round a cylinder, and this cylinder had a spiral groove cut on its
+surface. The tracings thus produced were to be used for the automatic
+transmission of the same message, by passing it again under a stylus
+which should react on a current breaker. In this patent, therefore,
+nothing is said of the registration of speech or of its reproduction;
+but, as the ‘Telegraphic Journal’ of May 1, 1878, observes, the
+foregoing invention gave him the means of solving this double problem
+as soon as it was suggested to him. If we may believe the American
+journals, this suggestion soon came, and it was the result of an
+accident.
+
+In the course of some experiments Mr. Edison was making with the
+telephone, a stylus attached to the diaphragm pierced his finger at
+the moment when the diaphragm began to vibrate under the influence of
+the voice, and the prick was enough to draw blood. It then occurred
+to him that if the vibrations of the diaphragm enabled the stylus to
+pierce the skin, they might produce on a flexible surface such distinct
+outlines as to represent all the undulations produced by the voice, and
+even that the same outlines might mechanically reproduce the vibrations
+which had caused them, by reacting on a plate capable of vibrating in
+the same way as that which he had already used for the reproduction
+of the Morse signals. From that moment the phonograph was discovered,
+since there was only a step between the idea and its realisation, and
+in less than two days the instrument was made and tried.
+
+This is an ingenious story, yet we would rather believe that the
+discovery was made in a more serious spirit. In fact, such an inventor
+as Mr. Edison, who had discovered the electro-motograph, and had
+applied it to the telephone, was already on the way to discover the
+phonograph, and we think too well of his powers to attach much credit
+to this American romance. Besides, Mr. Edison was well acquainted with
+Mr. Scott’s phonautograph.
+
+Mr. Edison’s phonograph was only patented in January 1877.
+Consequently, when we look at the principle of the invention, M. Cros
+undoubtedly may claim priority; but it is a question whether the
+system described in his sealed paper, and published in the _Semaine
+du Clergé_, October 8, 1877, would have been capable of reproducing
+speech. Our doubt seems justified by the unsuccessful attempts of the
+Abbé Leblanc to carry out M. Cros’ idea. When we have to do with such
+undulating and complex vibrations as those involved in the reproduction
+of articulate words, it is necessary that the stereotyping should in
+some sense be effected by the words themselves, and their artificial
+reproduction will necessarily fail to mark the slight differences
+which distinguish the delicate combinations of speech. Besides, the
+movements performed by a point confined to a groove that follows a
+sinusoidal curve cannot be effected with all the freedom necessary for
+the development of sounds, and the friction exerted on the two edges of
+the groove will often be of a nature to stifle them. A distinguished
+member of the Société de Physique, when I exhibited the phonograph to
+that society, justly said that Mr. Edison’s whole invention consisted
+in the thin metallic sheet on which the vibrations are inscribed; this
+sheet permits the movements of the vibrating plate to be directly
+stereotyped, and thereby the problem is solved. It was necessary to
+find such an expedient, and it was done by Mr. Edison, who is therefore
+the inventor of the phonograph.
+
+After M. Cros, and before Mr. Edison, MM. Napoli and Marcel Deprez
+attempted to make a phonograph, but with so little success that they
+believed at one time the problem to be insoluble, and threw doubts
+on Mr. Edison’s invention when it was announced to the Société de
+Physique. They subsequently resumed their labours, and lead us to
+hope that they may eventually produce a phonograph of more perfect
+construction than that of Mr. Edison. We shall have more to say on this
+subject.
+
+In conclusion, the mechanical reproduction of speech was first effected
+by Mr. Edison, and in so doing he has accomplished one of the most
+curious and important discoveries of our time, since it has shown that
+this reproduction was much less complicated than had been supposed. Yet
+the theoretical consequences of the discovery must not be exaggerated,
+since I do not consider it by any means proved that our theories on the
+voice are incorrect. There is in fact a great difference between the
+reproduction of a sound which has been uttered, and the mode in which
+the same sound was produced. The reproduction may be easily effected,
+as M. Bourseul has remarked, as soon as a mode has been discovered of
+transmitting the vibrations of air, however complex they may be; but in
+order to produce the complex vibrations of speech by the voice, several
+special organs must be exercised--first, the muscles of the throat;
+secondly, the tongue, the lips, and even the teeth--and for this reason
+an articulating machine is necessarily very complex.
+
+Surprise was expressed that the speaking machine, which was brought
+from America two years ago, and exhibited at the Grand Hôtel, Paris,
+was so extremely complicated, since the phonograph solved the problem
+in such a simple way. This is because the latter instrument only
+reproduces speech, while the former utters it, and the inventor of
+the speaking machine had to employ in his mechanism all the organs
+which are necessary in our organism for the reproduction of speech.
+The problem was infinitely more complex, and this invention has
+not attracted all the attention it deserved. We shall speak of it
+presently. We must now describe the phonograph and the different
+applications which have been, or which may be, made of it.
+
+_Description of Phonograph, and mode of using it._--The first and best
+known model of this instrument, which we represent in fig. 66, simply
+consists of a registering cylinder R, set in motion with the hand by
+a winch M, before which a vibrating plate is placed, furnished on its
+face with a telephone mouthpiece E, and on the reverse side with a
+tracing point. This tracing point, which is seen at _s_ in the section
+of the instrument given in fig. 68, is not fixed directly on the plate;
+it rests on a spring _r_, and a caoutchouc pad _c_ is placed between
+it and the vibrating disk. This pad is formed of the end of a tube
+which is designed to send the vibrations of the plate to the point _s_
+without stifling them. Another pad _a_, placed between the plate L L
+and the rigid support of the point, moderates in some degree these
+vibrations, which, without this precaution, would generally be too
+powerful.
+
+[Illustration: FIG. 66.]
+
+The cylinder, of which the axis A A (fig. 66) is cut at one end
+like a screw, to enable it to make a lateral progressive movement
+simultaneously with the rotatory movement effected on itself, has on
+its surface a narrow screw-thread coinciding with that of the axis, and
+when the tracing point is inserted, it is able to pass along it for a
+distance corresponding to the time occupied in turning the cylinder.
+A sheet of tinfoil or of very thin copper is carefully applied to the
+surface of the cylinder, and it should be slightly pressed down upon
+it, so as to show a faint tracing of the groove, and to allow the point
+of the vibrating disk to be placed in a proper position. The point
+rests on the foil under a pressure which must be regulated, and for
+this purpose, as well as to detach the cylinder when it is desired
+to place or take away the tinfoil, there is the articulated system
+S N which sustains the support S of the vibrating disk. This system
+consists of a jointed lever in which there is a nut screw for the screw
+R. The handle N at the end of the lever allows the tracing system to
+be turned aside when the screw R is loosened. In order to regulate the
+pressure of the tracing point on the sheet of tinfoil, it is enough to
+turn the screw R loosely in its socket, and to tighten it as soon as
+the right degree of pressure is obtained.
+
+This is the simple system by which speech can engrave itself on a
+plate in durable characters, and it works in the following manner.
+
+[Illustration: FIG. 67.]
+
+The speaker stands before the mouthpiece E, as before a telephone or
+an acoustic tube, and speaks in a strong, emphatic voice, with his
+lips pressed against the walls of the mouthpiece, as we see in fig.
+67; at the same moment he turns the handle of the cylinder, which is
+provided with a heavy fly-wheel in order that the movement may be
+regular. Influenced by the voice, the plate L L begins to vibrate, and
+sets the tracing point at work, which presses on the tinfoil at each
+vibration, and produces a furrow whose depth varies along its course in
+correspondence with the unequal vibrations of the disk. The cylinder
+which moves at the same time presents the different parts of the groove
+of which we have spoken to the tracing point in succession; so that
+when the spoken sentence comes to an end, the design which has been
+pricked out, consisting of a succession of reliefs and depressions,
+represents the registration of the sentence itself. The first part of
+the operation is therefore accomplished, and by detaching the sheet
+from the instrument the words may be put away in a portfolio. We have
+now to see how the instrument is able to reproduce what has been so
+easily inscribed.
+
+For this purpose it is only necessary to repeat the process, and the
+identical effect will be reproduced in an inverse sense. The tracing
+stylus is replaced at the end of the groove it has already traversed,
+and the cylinder is again set in motion. When the engraved track passes
+again under the point, it has a tendency to raise it and to impart to
+it movements which must necessarily be the repetition of those which
+first produced the tracing. The vibrating plate is obedient to these
+movements, and begins to vibrate, thus producing the same sounds, and
+consequently the same words; yet since there is necessarily a loss of
+power in this double transformation of mechanical effects, the speaking
+tube C is attached to the mouthpiece E in order to intensify the
+effects. Under these conditions the words reproduced by the instrument
+may be heard in all parts of a hall, and it is startling to hear this
+voice--somewhat shrill, it must be admitted--which seems to utter its
+sentences from beyond the grave. If this invention had taken place
+in the middle ages, it would certainly have been applied to ghostly
+apparitions, and it would have been invaluable to miracle-mongers.
+
+[Illustration: FIG. 68.]
+
+As the height of the notes of the musical scale depends on the number
+of vibrations effected by a vibrating substance in a given time,
+speaking will be reproduced in a tone of which the pitch will depend
+on the velocity of rotation given to the cylinder on which the tinfoil
+is wound. If the velocity is the same as that which was used in
+registration, the tone of the words reproduced is the same as that
+in which they were uttered. If the velocity is greater, the tone is
+higher; if less, the tone is lower; but the accent of the speaker may
+always be recognised. Owing to this peculiarity the reproduction of
+songs is nearly always defective in instruments turned by the hand;
+they sing out of tune. This is not the case when the instrument is
+moved by a well-regulated system of clockwork, and in this way a
+satisfactory reproduction of a duet has been obtained.
+
+The words registered on tinfoil can be often reproduced; but the sounds
+become fainter and more indistinct at each repetition, since the
+tracings in relief are gradually effaced. The reproduction on copper
+is more successful, but if intended to be permanent the sheets must
+be stereotyped, and in this case the instrument must be differently
+arranged.
+
+An attempt has been made to obtain speech from the phonograph by taking
+the words registered inversely to their true direction. In this way the
+sounds obtained were necessarily quite unlike the words uttered; yet
+Messrs. Fleeming Jenkin and Ewing have observed that not only are the
+vowels unchanged by this inverse action, but consonants, syllables, and
+even whole words may be reproduced with the accent they would have if
+spoken backwards.
+
+The sounds produced by the phonograph, although fainter than those of
+the voice which produced the registered tracing, are strong enough to
+react on the ordinary string telephone, and even on a Bell telephone;
+and as in this case the sounds do not go beyond the instrument, and can
+only be heard by the person who is using it, it is easy to ascertain
+that the sound has not been produced by trickery.
+
+Mr. Edison presented his phonograph to the Académie des Sciences
+through me, March 11, 1878, and when his agent, M. Puskas, caused
+the wonderful instrument to speak, a murmur of admiration was heard
+from all parts of the hall--a murmur succeeded by repeated applause.
+A letter appeared in the newspapers from one of the persons present,
+in which he said that ‘the learned Academy, generally so cold, had
+never before abandoned itself to such enthusiasm. Yet some members
+of a sceptical turn of mind, instead of examining the physical fact,
+ascribed it to moral causes, and a report soon ran through the room
+which seemed to accuse the Academy of having been mystified by a
+clever ventriloquist. Certainly the spirit of ancient Gaul is still
+to be found among the French, and even in the Academy. One said
+that the sounds emitted by the instrument were precisely those of a
+ventriloquist. Another asked if the movements of M. Puskas’ face and
+lips as he turned the instrument did not resemble the grimaces of a
+ventriloquist. A third admitted that the phonograph might emit sounds,
+but believed that it was much helped by the manipulator. Finally, the
+Academy requested M. du Moncel to try the experiment, and as he was not
+accustomed to speak into the instrument, it was unsuccessful, to the
+great joy of the incredulous. Some members of the Academy, however,
+desiring to ascertain the real nature of the effects, begged M. Puskas
+to repeat the experiments before them in the secretary’s office under
+such conditions as they should lay down. M. Puskas complied with this
+request, and they were absolutely satisfied with the result. Yet others
+remained incredulous, and it was necessary that they should make the
+experiment for themselves before they accepted the fact that speech
+could be reproduced in so simple a way.’
+
+The anecdote I have just related cannot be interpreted to the discredit
+of the Académie des Sciences, since it is especially bound to preserve
+the true principles of science intact, and only to accept startling
+facts after a careful examination. Owing to this attitude, all which
+emanates from the Academy can be received with complete confidence; and
+we cannot approve too highly of reserve which does not give way to the
+first impulse of enthusiasm and admiration.
+
+The failure of my experiment at the Academy was simply due to the fact
+that I spoke at too great a distance from the vibrating disk, and that
+my lips did not touch the sides of the mouthpiece. Some days later, at
+the request of several of my colleagues, I made repeated trials of
+the instrument, and I soon succeeded in making it speak as well as the
+supposed ventriloquist; but I learned at the same time that practice
+is necessary to ensure success. Some words are reproduced more readily
+than others; those which include many vowels and many _r_’s come out
+better than those which abound in consonants, and especially in _s_’s.
+It is therefore not surprising that, even in the case of an experienced
+manipulator like Mr. Edison’s agent, some of the sentences uttered by
+him are more audible than others.
+
+The simultaneous repetition of several sentences in different languages
+by registering one over the other is one of the most surprising effects
+of the phonograph. As many as three different sentences have been
+obtained; but in order to distinguish them through the confused sounds
+which result from placing one over the other, it is necessary that
+different persons, giving special attention to a particular sentence,
+should thus separate them and understand their sense. Vocal airs may,
+in the same way, be registered over the word tracings, and in this case
+it is more easy to distinguish them.
+
+There are several models of phonographs. The one represented in fig.
+66 has been chiefly used for public experiments, but there is a small
+model, generally sold to the public, in which the cylinder is much
+longer, and serves at once for register and fly-wheel. This instrument
+gives good results, but can only be used for short sentences. In this
+model, as indeed in the other, the words are more easily registered
+by fastening a small tube in the form of a prolonged speaking-trumpet
+to the mouthpiece; the vibrations of the air are thus concentrated
+on the vibrating disk, and act with greater energy. The tenuity of
+the vibrating disk adds to the efficiency of the instrument, and the
+tracing point may be fitted directly to this disk.
+
+[Illustration: FIG. 69.]
+
+I need not describe particularly the phonograph which acts by
+clockwork. The instrument resembles the one represented fig. 66, except
+that it is mounted on a rather high table, to give room for the descent
+of the weight which moves the clockwork; the mechanism is applied
+directly to the axis of the cylinder, supplying the place of the winch,
+and is regulated by a small fly-wheel. The wheel used in an English
+system has been adopted, but we prefer that of M. Villarceau, which has
+small wings.
+
+Since it is always difficult to fit the tinfoil to the cylinder, Mr.
+Edison has tried, with good success, to obtain the tracing on a plane
+surface of tinfoil, by means of the arrangement represented fig. 69.
+In this new model, the plate on which the tin or copper sheet is to
+be applied has a spiral grooving, of which one end corresponds to the
+centre of the plate, and the other to its outer edges. The plate is set
+in motion by a powerful system of clockwork, of which the velocity is
+regulated with reference to the length of the turns of the spiral. The
+vibrating disk is arranged as in the former instrument, and is placed
+above this plate; the tracing point may, by means of a movement of
+progression imparted to the system, follow the spiral groove from the
+centre of the plate to its circumference.
+
+It must not be supposed that all the tinfoil used for phonographic
+registration is equally good. The foil must be of a definite thickness,
+and combined with a definite amount of lead. That which is used for
+wrapping chocolate, and indeed all foil of French manufacture, is too
+thin and too exclusively made of tin to produce good results, and
+M. Puskas was obliged to import some from America to continue his
+experiments. The relative proportion of lead and tin has not yet been
+defined, and the selection of foil has been made empirically; but as
+the use of the phonograph becomes more general, this proportion must be
+ascertained, and it may easily be done by analysing the composition of
+the foil which gives the best results.
+
+[Illustration: FIG. 70.]
+
+The arrangement of the tracing point is also of much importance for
+the successful action of the phonograph. It must be very slender and
+very short (not exceeding a millimètre in length), so as to register
+distinctly the smallest vibrations of the vibrating disk without
+deviating from the normal direction of the cylinder, which might be
+the case, if it were long, on account of the unequal friction exerted
+on the tinfoil. It must also be made of a metal which has no tendency
+to tear the metallic sheet. Iron appears to combine most of the
+conditions demanded.
+
+The phonograph is still in its infancy, and it is probable that it may
+soon be enabled to register speech without the necessity of speaking
+into a mouthpiece. According to the newspapers, Mr. Edison has already
+discovered a way of collecting, without the aid of an acoustic tube,
+the sounds uttered at a distance of three or four feet from the
+instrument, and of printing them on a metallic sheet. From this there
+is only a step to the power of inscribing a speech uttered in a large
+hall at any distance from the phonograph; and if this step is taken,
+phonography may be substituted with advantage for shorthand. We add
+in a note the instructions given by M. Roosevelt to the purchasers of
+phonographs, so as to enable them to work the instrument.[20]
+
+_Considerations on the theory._--Although the explanation we have given
+will make the effects of the phonograph intelligible, it leads to a
+curious question which has greatly interested physicists--namely, how
+it is that the tracing made on so yielding a surface as tin can, when
+retraced by the stylus, of which the rigidity is relatively great,
+produce a vibratory movement without being completely destroyed. To
+this we reply that the retracing is effected with such extreme rapidity
+that the effects of active force which are developed only manifest
+themselves locally, and that under these conditions the mechanical
+effects exerted are as energetic in soft as in hard substances. The
+curious experiment, related in so many books on physics, must be
+remembered, of a plank pierced when a candle serves as the projectile
+of a gun. The various accidents caused by the discharge of paper
+waddings must also be remembered. Under such conditions the motion
+imparted to the molecules which receive the shock has not time to be
+transmitted to the whole mass of the substance to which they belong,
+and these molecules are compelled to separate from it, or at any rate
+to produce, when the substance is capable of vibration, a centre of
+vibration which diffuses waves throughout its surface, and produces
+sounds.
+
+Several scientific men, among others Messrs. Preece and Mayer, have
+carefully studied the form of the tracing left by the voice on the
+tinfoil of the phonograph, and they observe that it greatly resembles
+the outline of the singing flames so well shown by Herr Koenig’s
+instruments. Mr. Mayer wrote on this subject in the ‘Popular Science
+Monthly Review’ of April 1878.
+
+He said that he had been successful in reproducing a splendid tracing
+on smoked glass, which gave in profile the outline of the vibrations
+of sound registered on the tinfoil with their varying curves. For this
+purpose he fastened to the spring support of the tracing point of
+the phonograph a slender rod, terminating in a point, which pressed
+obliquely against the plate of smoked glass, and, since the latter was
+in a vertical position, a movement imparted to the rod enabled it to
+produce a sinusoidal tracing. By this arrangement, when the phonograph
+was at work, two systems of tracings were produced at the same moment,
+of which one was the profile of the other.
+
+Mr. Mayer had not, at the time he wrote, been long enough in possession
+of the instrument to make many experiments with it, but from a study of
+some of its curves it appeared to him that the registered outlines bore
+a strong resemblance to those of Koenig’s singing flames.
+
+[Illustration: FIG. 71.]
+
+Fig. 71 represents the tracing which corresponds to the letter _a_
+when pronounced as in _bat_, in the three systems of registration.
+That corresponding to line A is an enlarged reproduction of the
+tracing left on the tinfoil; that corresponding to line B represents
+its profile on the sheet of smoked glass. Finally, line C shows the
+outline of Koenig’s singing flames, when the same sound is produced
+quite close to the membrane of the register. It must be quite close,
+since the form of the tracing produced by a pointer attached to a
+vibrating membrane, when influenced by composite sounds, depends on
+the distance intervening between the membrane and the source of sound,
+and an infinite variety in the form of the tracing may be obtained
+by modifying the distance. In fact, when this distance is increased,
+the waves of sound which result from composite sounds react on the
+membrane at different moments of their emission. For example, if the
+composite sound is formed of six harmonics, the displacement of the
+source of vibration from the first harmonic by ¼ the length of a wave
+will respectively remove the second, third, fourth, fifth, and sixth
+harmonics ½, ¾, 1, 1¼, 1½ the length of a wave, and consequently the
+outline resulting from the combination of waves will no longer be
+the same as it was before the displacement of the source of sound,
+although the perception of the sounds remains the same in both cases.
+This principle is clearly demonstrated by Koenig’s instrument, by
+lengthening and shortening an extensible tube, inserted between the
+resonator and the vibrating membrane, which is placed close to the
+flame; and this explains the disagreement of physicists as to the
+composition of vocal sounds which they have analysed by means of the
+singing flames.
+
+Mr. Mayer adds that these facts further show that we cannot hope to
+read the impressions and tracings of the phonograph, which not only
+vary with the nature of the voice, but also with the different moments
+at which the harmonics of the voice are emitted, and with the relative
+differences in the intensities of these harmonics.
+
+Notwithstanding this assertion, we reproduce (fig. 72) an extremely
+curious tracing sent to us by Mr. Blake, which represents the
+vibrations produced by the words ‘Brown, University: how do you do?’
+They were photographed by means of an index fastened to a vibrating
+disk on which a ray of light was thrown. The word ‘how’ is particularly
+remarkable for the combined forms of the inflections of the vibrations.
+
+Recent experiments seem to show that the more the vibrating membrane
+of the phonograph resembles the human ear in its construction, the
+better it repeats and registers the sound vibrations: it should be
+stretched, as far as possible, in the same way as the tympanum is
+stretched by the hammer of the ear, and moreover it should have the
+same form, since the vibrations of air are in this case much more
+effective.
+
+[Illustration: FIG. 72.]
+
+Mr. Edison considers that the size of the opening of the mouthpiece has
+considerable influence on the distinct articulation of speech. When
+the sounds are pronounced before the whole surface of the diaphragm,
+some hissing sounds are lost. They are, on the contrary, intensified
+when these sounds reach the diaphragm through a narrow orifice with
+sharp rims. If the opening is toothed on its flattened rims, the
+hissing consonants are delivered more clearly. Speech is reproduced
+more perfectly when the mouthpiece has a covering of some thickness,
+so arranged as to deaden the sounds arising from the friction of the
+tracing point on the tin.
+
+Mr. Hardy has rendered the registration of phonographic tracings more
+easy by adding a small ebonite tube, resembling the mouthpiece of a
+wind instrument, to the mouthpiece of the phonograph.
+
+
+
+
+USES OF THE PHONOGRAPH AND ITS FUTURE.
+
+Mr. Edison has lately published in the ‘North American Review’ of
+May-June 1878 an article on the future of the phonograph, in which he
+himself discusses the different applications which may be made of this
+instrument. Without sharing all his anticipations, which appear to us
+to be very premature, we think that some extracts from his paper may be
+interesting.
+
+‘In order to furnish a basis on which the reader may take his stand ...
+a few categorical questions and answers are given upon the essential
+features of the principle involved.
+
+‘1. Is a vibrating plate or disk capable of receiving a complex motion
+which shall correctly represent the peculiar property of each and all
+the multifarious vocal and other sound waves?
+
+‘The telephone answers affirmatively.
+
+‘2. Can such complex movement be transmitted from such plate by means
+of a single embossing point attached thereto, to effect a record upon a
+plastic material, by indentation, with such fidelity as to give to such
+indentations the same varied and complex form? And if so, will this
+embossing point, upon being passed over the record thus made, follow
+it with such fidelity as to transmit to the disk the same variety of
+movement, and thus effect a restoration or reproduction of the vocal or
+other sound waves, without loss of any property essential to producing
+on the ear the same sensation as if coming direct from the original
+source?
+
+‘The answer to this may be summed up in a statement of the fact that
+... the writer has at various times during the past weeks reproduced
+these waves with such degree of accuracy in each and every detail as
+to enable his assistants to read, without the loss of a word, one or
+more columns of a newspaper article unfamiliar to them, and which
+were spoken into the apparatus when they were not present. The only
+perceptible loss was found to be in the quality of the utterance, a
+non-essential in the practical application of the instrument. Indeed,
+the articulation of some individuals has been perceptibly improved by
+passage through the phonograph, the original utterance being mutilated
+by some imperfection of lip and mouth formation, and these mutilations
+corrected or eliminated by the mechanism of the phonograph.[21]
+
+‘3. Can a record be removed from the apparatus on which it was made,
+and replaced upon a second without mutilation or loss of effective
+power to vibrate the second plate?
+
+‘This is a mere mechanical detail, presenting no greater obstacle
+than having proper regard for the perfect interchangeableness of the
+various working parts of the apparatus--not so nice a problem as the
+manufacture of the American watch.
+
+‘4. What as to the facility of placing and removing the second sheet,
+and as to its transportation by mail?
+
+‘But ten or fifteen seconds suffice for such placing or removing. A
+special envelope will probably be required, the weight and form of
+which, however, will but slightly increase the cost of postage.
+
+‘5. What as to durability?
+
+‘Repeated experiments have proved that the indentations possess
+wonderful enduring power, even when the reproduction has been effected
+by the comparatively rigid plate used for their production. It is
+proposed, however, to use a more flexible plate for reproducing,
+which, with a perfectly smooth stone point--diamond or sapphire--will
+render the record capable of from fifty to one hundred repetitions,
+enough for all practical purposes.
+
+‘6. What as to duplication of a record and its permanence?
+
+‘Many experiments have been made, with more or less success, in
+the effort to obtain electrotypes of a record, and the writer is
+informed that it has very recently been successfully accomplished. He
+can certainly see no great practical obstacle in the way. This, of
+course, permits of an indefinite multiplication of a record, and its
+preservation for all time.
+
+‘7. What is the requisite force of wave impinging upon the diaphragm,
+and the proximity of the mouth to the diaphragm, to effect a record?
+
+‘These depend in great measure upon the volume of sound desired in
+the reproduction. If the reproduction is to be made audible to an
+assembly, considerable force is requisite in the original utterance;
+if for the individual ear, only the ordinary conversational tone (even
+a whisper has been reproduced). In both cases the original utterances
+are delivered directly in the mouthpiece of the instrument. An audible
+reproduction may, however, be had by speaking at the instrument from a
+distance of from two to three feet in loud tone. The application of a
+flaring tube or funnel to collect the sound waves, and the construction
+of an especially delicate diaphragm and embossing point, &c., are the
+simple means which suggest themselves to effect this....
+
+‘The foregoing presentment of the stage of development reached by the
+several essential features of the phonograph demonstrates the following
+_faits accomplis_:
+
+‘1. The captivity of all manner of sound waves, hitherto designated as
+“fugitive,” and their retention.
+
+‘2. Their reproduction with all their original characteristics, without
+the presence or consent of the original source, and after the lapse of
+any period of time.
+
+‘3. The transmission of such captive sounds through the ordinary
+channels of commercial intercourse and trade in a material form, for
+purposes of communication.
+
+‘4. Indefinite multiplication and preservation of such sounds, without
+regard to the existence or non-existence of the original source.
+
+‘5. The captivation of sounds, with or without the knowledge or consent
+of the source of their origin...
+
+‘The apparatus now being perfected in mechanical details will be the
+standard phonograph, and may be used for all purposes, except such
+as require special form of matrix, such as toys, clocks, &c., for
+an indefinite repetition of the same thing. The main utility of the
+phonograph being, however, for the purposes of letter-writing and
+other forms of dictation, the design is made with a view to its utility
+for that purpose.
+
+‘The general principles of construction are, a flat plate or disk, with
+spiral groove on the face, worked by clockwork underneath the plate;
+the grooves are cut very closely together, so as to give a great total
+length to each length of surface--a close calculation gives as the
+capacity of each sheet of foil nearly 40,000 words. The sheets being
+but ten inches square, the cost is so trifling that but a hundred words
+might be put on a single sheet economically....
+
+‘The practical application of this form of phonograph is very simple.
+A sheet of foil is placed in the phonograph, the clockwork set in
+motion, and the matter dictated into the mouthpiece without other
+effort than when dictating to a stenographer. It is then removed,
+placed in suitable form of envelope, and sent through the ordinary
+channels to the correspondent for whom it is designed. He, placing it
+upon his phonograph, starts his clockwork, and _listens_ to what his
+correspondent has to say.’
+
+Since this paper by Mr. Edison appeared in June 1878, he has applied
+the phonograph to several other purposes, among which we may mention
+that of registering the force of sounds on railways, and especially
+on the metropolitan atmospheric railway in New York. The instrument
+which he has made for this purpose resembles that by Mr. Leo Scott, and
+bears the same name. It is described and represented in the ‘Daily
+Graphic’ of July 19, 1878, as well as the aerophone, the megaphone, and
+the microtasimeter, which is adapted for astronomical observations. We
+should exceed the limits laid down for this volume, if we were to give
+a more detailed account of these inventions.
+
+M. Lambrigot, one of the officials on the telegraphic lines in France,
+and the author of various improvements in the Caselli telegraph, has
+shown me a phonographic system of his own invention in which it is
+reduced to its simplest form. He sent me the following description of
+his system.
+
+‘The instrument consists of a wooden slab placed vertically on a stand
+and firmly fixed upon it. There is a round opening in the middle of the
+slab, covered by a tightly stretched sheet of parchment bearing a steel
+knife, which, like the tracing point of the phonograph, is intended to
+trace the vibrations. A solid block rises from the stand to the middle
+of the slab, and supports a slide on which a runner can move in front
+of the slab. There is a strip of glass on this runner, of which one
+side is covered with stearine. When the runner is moved to and fro, the
+stearine comes in contact with the knife and takes the mould of its
+form, which is curved throughout.
+
+‘A sound places the sheet of parchment in vibration, and imparts its
+movement to the knife, which traces various lines on the surface of
+the stearine.
+
+‘The reproduction thus obtained on the strip of glass is subjected to
+the ordinary processes of metallisation. By galvanism a deposit of
+copper is obtained which reproduces the lines in an inverse way. In
+order to make the metallic plate speak, it is necessary to pass a point
+of ivory, wood, or horn lightly over the signs, and, by moving it more
+or less quickly, the different tones can be heard, just as they were
+spoken.
+
+‘Since copper is relatively harder than lead, the copper plate on
+which the vibrations are traced will afford an unlimited number of
+reproductions. To obtain this result, a lead wire must be applied
+to the plate, and due pressure must be exerted on it. The wire is
+flattened and takes the impression of all the traces which then appear
+in relief. If the edge of a card is passed through this impressed
+tracing, the same sounds are produced as those which are obtained from
+the copper plate.’
+
+M. Lambrigot suggests that the speaking plates might be useful in
+many ways: for example, they might make it easy to learn the correct
+pronunciation of foreign languages, since a sufficient number might be
+collected to make a sort of vocabulary which would give the accent of
+the words most in use in a given language.
+
+By this simple process M. Lambrigot has been able to obtain a strong
+impression, within a copper groove, of the vibrations caused by the
+voice, and they are so distinctly engraved that whole sentences may be
+heard, if they are retraced by the sharpened point of a match. It is
+true that the reproduction is imperfect, and that those words are only
+to be distinguished which were previously known; but it is possible
+that better results will be obtained from improvements in the system,
+and at any rate the distinct impression of the vibrations of the voice
+on a hard metal is a really interesting discovery.
+
+I have made one somewhat important observation in the working of the
+phonograph--namely, that if speech is registered on the instrument
+in a very hot room, and it is then carried to a colder room, the
+reproduction of speech is imperfect in proportion to the difference
+of temperature. This is probably owing to considerable modifications
+in the elasticity of the caoutchouc pad which is inserted between the
+tracing point and the vibrating disk: perhaps differences of expansion
+in the tinfoil have also some effect.
+
+
+FABER’S AMERICAN SPEAKING MACHINE.
+
+About two years ago the newspapers announced with some pomp that a
+speaking machine had reached Paris, which far surpassed Vaucanson’s
+duck, and which would attract general attention. Unfortunately the
+invention was not in the first instance brought forward with any
+scientific authority, and was soon relegated to take a place among
+the curiosities exhibited by conjurors. In a country so essentially
+critical and sceptical as France, there are always those who profess
+incredulity, and who will even resist evidence, and it was asserted
+that the machine only spoke because its exhibitor was an able
+ventriloquist. This is an old assertion which has lately been made
+with reference to the phonograph. Some scientific papers echoed the
+absurdity, and the speaking machine was so discredited that it is now
+unnoticed, although it is a most ingenious and interesting conception.
+When will our country be cured of the error of denying everything
+without due examination?
+
+Since we ourselves only judge of things after having seriously
+considered them, we think it just to vindicate the truth as to Mr.
+Faber’s machine, and this can only be done by an exact description of
+it.
+
+As I said in the last chapter, there is a great difference between
+the production and the reproduction of a sound, and a machine
+like the phonograph, adapted for the reproduction of sound, may
+differ essentially from a machine which really speaks. In fact, the
+reproduction even of articulate sounds may be very simple, as soon as
+we possess the means of stereotyping the vibrations of air necessary to
+transmit these sounds; but in order to produce them, and especially to
+emit the complex vibrations which constitute speech, it is necessary
+to set in motion a number of special organs, fulfilling more or less
+exactly the functions of the larynx, the mouth, the tongue, the lips,
+and even the nose. For this reason, a speaking machine is necessarily
+very complicated, and this is precisely the case with the machine we
+are now considering. Such a machine is not now made for the first time,
+and the Academy has lately been reminded of a speaking head which was
+in the possession of the philosopher Albertus Magnus in the thirteenth
+century, and which was destroyed by St. Thomas Aquinas as a diabolical
+invention.
+
+Mr. Faber’s speaking machine was exhibited two years ago at the Grand
+Hôtel, and may now be seen in the room adjoining M. Robert Houdin’s
+theatre, the same room in which Mr. Giffard exhibited the telephone. It
+consists of three distinct parts: 1st, of a large bellows worked by a
+pedal, which produces the currents of air necessary for the production
+of sounds, and to some extent acts as the lungs; 2nd, a vocal
+instrument, consisting of a larynx accompanied by diaphragms of various
+forms to modify the sounds, of a mouth with caoutchouc lips and tongue,
+and of a tube with an outlet somewhat resembling the nasal cavities;
+3rd, of a system of jointed levers and of pedals, terminating in keys
+like those of a piano.
+
+The most interesting part of the machinery, of which we represent the
+principle fig. 73, is the vocal apparatus, which involved the severest
+study of physics in order to succeed in the production of articulate
+sounds. It consists, first, of a rather thick caoutchouc tube, within
+which there is a kind of whistle L, as in a clarionet. The whistle
+consists of a small caoutchouc cylinder with a longitudinal slit, and
+before this is placed a very thin ivory plate lined with caoutchouc.
+This plate is fixed at one end to the cylinder, and deviates slightly
+from it at its free end, so as to permit the current of air projected
+from the bellows S to penetrate between the two parts, and to cause the
+vibrations in the ivory plate necessary for the production of a sound.
+The extremity of the caoutchouc cylinder is closed on this side, and is
+fitted to an iron rod _t_ which comes out of the pipe, and is connected
+with a system of bars, corresponding to the keyboard of a piano, by
+which the force of sounds can be regulated. This force depends on the
+width of the opening between the tongue and the cylinder.
+
+[Illustration: FIG. 73.]
+
+The whistle, which plays the part of the larynx, is necessarily placed
+opposite the opening of the bellows, and a sort of tourniquet M is
+fastened to the opening itself, which is able to move on certain
+conditions, so that it may produce the rolling sound of _r_. This is
+done by fastening before the opening a diaphragm in which there is a
+somewhat wide and long slit, and this slit can be almost closed by a
+little bar of the same size M, revolving on a transverse axis which
+supports it by its centre. In its normal condition, this little bar is
+kept in a slanting position by cords attached to the keyboard, and the
+air ejected by the bellows readily traverses the slit in order to reach
+the larynx; but two dampers are fastened to the rods which transmit
+movement, with which the cords just mentioned are also connected. On
+lowering the notes of the key-board, the passage of air is contracted,
+and the little plate begins to oscillate and to press against a band of
+leather, producing by its vibration an action similar to that produced
+by the cricket. This little tourniquet only begins to act when the
+dampers are lowered by a pedal worked by the hand; and this is also
+the case with the iron rod _t_, which modifies the acuteness of the
+sounds passing through the larynx.[22]
+
+Below the larynx tube, which is only five centimètres in length,
+there is another pipe G, also of caoutchouc, which terminates in a
+spherical cavity connected with the outer air by a caoutchouc tube I,
+slightly raised, and closed by a valve, of which the movements are
+regulated by a pedal worked by the keyboard. When the valve is open,
+the sounds emitted through the larynx are somewhat nasal.[23] The
+larynx communicates with the mouth through a square funnel-shaped pipe,
+to which six metallic diaphragms D are fastened; the diaphragms are
+placed in a vertical position behind each other, and have indentations
+on their lower end, which are intended to diminish more or less the
+orifice for the current of air, and to impede its passage with greater
+or less force. The diaphragms, which we represent separately fig. 74,
+are connected with the keyboard by jointed iron rods _t_, and, for the
+emission of most articulate sounds, several of the diaphragms are
+moved at the same moment and at different heights. We shall return to
+this subject.
+
+[Illustration: FIG. 74.]
+
+The mouth consists of a caoutchouc cavity O, somewhat resembling the
+human mouth, and forming a continuation to the channel we have just
+described. The tongue C, likewise modelled on the human tongue, is
+placed within the mouth, and connected with two jointed rods _t_,
+_t_, fastened to its two opposite ends, so as to enable the tongue to
+raise its tip, or touch the palate, in obedience to the notes of the
+keyboard. The lower caoutchouc lip A can also be more or less closed,
+according to the action of the keyboard on its special rod. Finally,
+a circular metallic piece E, following the shape of the mouth, is
+placed above the upper lip, with a small opening in it to admit of the
+pronunciation of the letter _f_.
+
+The keyboard has fourteen notes, of different lengths, producing the
+following letters when lowered, _a_, _o_, _u_, _i_, _e_, _l_, _r_,
+_v_, _f_, _s_, _ch_, _b_, _d_, _g_. The longest corresponds to _g_,
+and the shortest to _a_. There are two pedals below the _g_ note and
+those of _b_ and _d_, corresponding with the opening of the tube which
+produces nasal sounds, and to the rod which regulates the opening of
+the larynx, and this makes it possible to obtain _p_, _t_, and _k_ from
+the notes _b_, _d_, _g_. The mechanical effects produced by lowering
+the different notes in succession are as follows:--
+
+1. The _a_ note moves the first five diaphragms.
+
+2. _o_ also moves these five diaphragms, but varies the pitch, and
+closes the mouth a little.
+
+3. _u_ does the same, only further closing the mouth.
+
+4. _t_ moves a single diaphragm, raises the tip of the tongue, and
+opens the mouth more widely.
+
+5. _e_ moves six diaphragms, throws the tongue further back, and opens
+the mouth still more.
+
+6. _l_ moves five diaphragms, sends the tongue against the palate, and
+further opens the mouth.
+
+7. _r_ moves six diaphragms and the tourniquet, lowers the tongue, and
+somewhat closes the mouth.
+
+8. _v_ moves five diaphragms, almost closes the mouth, and keeps the
+tongue down.
+
+9. _f_ lowers the circular appendix of the upper lip, and almost
+entirely closes the mouth.
+
+10. _s_ moves three diaphragms, half closes the mouth, and half raises
+the tongue.
+
+11. _ch_ moves three diaphragms, keeps the mouth half closed, and
+further lowers the tongue.
+
+12. _b_ moves five diaphragms, closes the mouth, and keeps the tongue
+completely down.
+
+13. _d_ moves six diaphragms, keeps the mouth three parts closed, and
+raises the tongue a little.
+
+14. _g_ moves five diaphragms, keeps the mouth three parts closed, and
+the tongue completely down.
+
+_m_ is produced by lowering note _b_ and opening the valve of the pipe
+which gives nasal sounds.
+
+_n_ is obtained by lowering note _d_ and opening the same valve.
+
+_h_ is obtained from note _s_ by lowering the pedal which acts upon the
+larynx, and half closing it.
+
+Since the other letters of the alphabet are compound sounds, they can
+be produced by combinations of the preceding letters.
+
+Although the words pronounced by this machine are distinct, they are
+spoken in a uniform, drawling tone, which might, I should have thought,
+have excluded the idea of imposition. Some of them are indeed far from
+distinct, yet the results are not less remarkable; and when we consider
+the amount of study and experience which must have been applied to
+the combination of all these arrangements, it seems surprising that
+physicists have not given more attention to such an interesting machine.
+
+As for the mechanical execution, it is impossible to admire too highly
+the simple and ingenious manner in which all the complicated movements
+of the different vocal organs have been connected with the keyboard,
+of which the mechanism has been so calculated as only to produce the
+precise action of the organ which is required for any given effect. For
+this purpose, the notes of the keyboard regularly increase in length,
+so as to produce at a single touch different mechanical effects on the
+rods which act upon the mechanism; and since most of the notes are
+required to react simultaneously on the whole mechanism, the rods which
+transmit the movement are fastened to a series of jointed levers which
+cross the notes of the keyboard at right angles. Pegs of different
+length are fastened to the notes at this junction, so as to produce the
+simultaneous action of the different organs of the machine.
+
+The public will believe that the assertions of ventriloquism are
+unfounded when I add that I myself have made the machine speak.
+
+
+
+
+APPENDIX.
+
+
+_The Perrodon System of Telephonic Alarum._--Captain Perrodon, of
+the French Artillery, has lately improved the system invented by MM.
+Dutertre and Gouault, by a self-acting call. For this purpose he has
+fastened a spring contact before the diaphragm, combined with the
+diaphragm and the electro-magnetic system so as to form a vibrator. The
+vibrations thus produced are strong enough to resound in an ordinary
+telephone, so as to make the call audible in spite of external noises.
+
+The system has been arranged in different ways. In one arrangement, a
+small plate of tinfoil is glued to the outer surface of the diaphragm,
+and the end of the telephone coil wire is connected, below the inner
+surface of the mouthpiece, with a silver wire soldered to a spring
+plate, which constitutes the contact of the vibrator. This spring
+plate, slightly curved, is fixed below one of the binding-screws of
+the telephone, and terminates at its free end in a regulating screw
+by which the interval between the contacts can be regulated, and the
+instrument can be arranged as a telephonic organ. To do this, the
+screw can be withdrawn, and inserted in a nut which establishes direct
+connection between the line and the telephone coil. It is easy to
+adapt an ordinary telephone to this system.
+
+In another arrangement M. Courtot’s mirror telephone has been employed,
+and a sort of spring pedal is inserted in the wood of the mouthpiece,
+which terminates in a bent silver wire, supporting an index adapted
+to make a contact with a square plate soldered to the diaphragm. The
+battery is placed in connection with the spring of the pedal, and
+one end of the telephone coil-wire communicates as before with the
+diaphragm. When a call is to be made, the pedal must be pressed, and
+the battery immediately communicates with the silver wire which, with
+the diaphragm, constitutes the vibrator, and an electric vibration
+is sent through the circuit, and produces the call. For receiving,
+the pedal is allowed to revert to its normal position, and the index
+of the pedal, touching the contact in connection with the diaphragm,
+establishes direct communication between the two telephones, while
+breaking the contact of the silver wire with the diaphragm, so that the
+battery cannot act.
+
+It appears that experiments made at the musketry school at Orleans for
+a distance of 370 miles have been very successful.
+
+_M. Varey’s Microphone Speaker._--M. Varey has recently arranged
+a successful microphonic speaker, in which the principle of the
+microphone represented in fig. 39 is maintained. The system of three
+vertical carbons is arranged inside a sort of snuff-box, of which the
+lid is made of a thin plate of mica, horn, or ebonite. The snuff-box
+is provided with two hinged arms, so that it may be placed in the
+most convenient position for speaking, and at the same time the
+sensitiveness of the instrument can be regulated. A small battery,
+consisting of two Gaiffe cells of chloride of silver, is placed in the
+pedestal on which the instrument stands, and sets the microphone at
+work without further trouble. In this way the speaker can be used like
+an ordinary telephone, and is not affected by vibrations of air. Only
+vibrations of sound react upon it.
+
+_Microphonic Speaker by Fitch._--Mr. Pope states that this speaker
+has produced excellent results in America. It is merely Edison’s
+carbon telephone reduced to its simplest form. It consists of a small
+cylindrical box, which has a mouthpiece like the one represented
+fig. 28. The box contains two carbon disks of the same diameter as
+itself, and is lined with a kind of felt. Metal wires, inlaid in a
+groove scooped on the circumference of the carbons, place them in
+communication with the circuit and battery, and transmission takes
+place by means of the vibrations of the upper carbon, which is directly
+influenced by the voice without the intervention of any diaphragm.
+These vibrations, which can be freely developed in consequence of the
+elasticity of the felt pad which supports the lower carbon, produce
+on the surface of contact of the two carbons the modifications of
+intensity of current necessary for the reproduction of speech, in the
+same way as other microphones.
+
+An induction coil is necessarily employed for a long circuit, and
+the effects of induction in the adjacent wires are modified by two
+rheostats introduced into the circuit at its two extremities.
+
+_Further remarks on the theory of the Telephone._--Following the
+example of a certain sceptic in the Académie des Sciences, Colonel
+Navez continues to maintain the theory first formed as to the mode
+in which the telephone acts, in spite of the clearest proofs of its
+insufficiency; but most scientific men who consider the question have
+come round to our opinion, and admit the concurrence of several causes
+in the reproduction of speech by this remarkable instrument. Mr.
+Fleeming Jenkin writes to this effect in the new edition of a treatise
+on Electricity and Magnetism.
+
+He observes that a singular fact has been discovered by several
+persons, who have ascertained that not merely non-magnetic and
+non-conducting bodies can be substituted for the diaphragms of
+receiving telephones, but that they will act without a diaphragm at
+all. In this case it is evident that we have to do with the sounds
+discovered by Page, and that they are produced by the magnet itself,
+in which each molecular movement constitutes the source of the sound
+produced. This sound becomes articulate as soon as its increase and
+decrease can follow the increasing or decreasing action of the voice
+which produces it at the sending station. It is certain that when the
+transmitted currents are due to the action of the Bell diaphragm, the
+sounds due to the Page effects ought to correspond with those which
+would be given by iron diaphragms adapted to the receiving instruments;
+so that, when a telephone has an iron diaphragm, there are in fact two
+voices, that of the diaphragm, which is strong, and that of the magnet,
+which is weak. When a disk of wood is substituted for one of iron, it
+acts as a sounding board for the Page effect, and when the disk is of
+metal, induction is developed by the magnetic modifications, and tends
+to produce vibration, thus developing a third source of sound, which
+may be called the Ampère effect. Finally, a fourth source of sound
+may result from the induced effects produced in the wire itself in
+consequence of changes in the intensity of current. These sounds, first
+observed by M. de la Rive, have since been studied by Mr. Fergusson of
+Edinburgh (vide ‘Telegraphic Journal’ of November 1, 1878).
+
+Mr. Fleeming Jenkin’s opinion only differs from mine in his ascribing
+the energy of sound acquired by a telephone with an iron diaphragm to
+the preponderance of sounds in the latter, whereas I consider it to
+be chiefly due to the increase of energy in the whole magnetic system
+produced by the reaction of the two magnetic parts on each other. If
+the two effects could be taken singly, it is probable that the sounds
+produced by each of them separately would be similar, since in magnetic
+effects the reaction and action are equal. But as they are combined,
+it becomes difficult to assign to each the share which belongs to
+it in the general effect observed. Besides, it is quite possible
+that the sounds of the diaphragm may appear to be stronger and more
+distinct because it is nearer to the ear than the magnet, and because
+the effects of magnetisation and demagnetisation are then more easily
+produced in consequence of the mass of the magnetic body being smaller.
+
+Mr. Fleeming Jenkin goes on to say that the question of the
+displacement of surface in the diaphragm and magnet is very complex,
+but that he thinks it impossible to deny the existence of such
+displacement, since the air which acts as the vehicle of sound between
+the ear and the source of sound is placed in vibration; yet this
+displacement maybe effected quite otherwise than by flexion. Suppose
+that the magnetic molecules of these bodies are drawn together by
+magnetisation, which tends to diminish the intermolecular space which
+separates them, the points of surface of the substance corresponding
+to these intervals will be elevated in a manner equivalent to a
+displacement of surface, and the effect of this will be the same as a
+flexion movement. At the moment of demagnetisation a depression instead
+of an elevation will take place, and the vibratory movements will
+thus be produced without any electro-magnetic attraction, and it is
+precisely these vibrations which Mr. Fleeming Jenkin terms molecular
+vibrations. He evidently does not mean that such attractions cannot
+take place: they may react, together with the molecular vibrations,
+when the electric force is capable of producing them. He adds that the
+reproduction of sounds by a condenser, by simple coils, and by a carbon
+microphone, has convinced him that the action just analysed requires
+generalisation.
+
+We have recently seen an article by Mr. Hughes in the ‘Telegraphic
+Journal,’ Nov. 15, 1878, in which, to our surprise, he not only opposes
+all the theories he has hitherto held, but cites experiments which
+are quite inconclusive, since they were performed under conditions in
+which electro-magnetic effects must necessarily be displayed. He made
+use of voltaic currents produced by a battery of three Daniell cells.
+In order to estimate the transverse effects resulting in such a case
+from attraction, the experiments he mentions are wholly unnecessary:
+they may be felt with the hand. On the other hand, he has evidently
+forgotten that the currents employed in a Bell telephone have no
+influence on a very sensitive galvanometer.
+
+_M. Pollard’s Microphone._--This microphone, which has been arranged in
+several ways, essentially consists of a carbon rod kept in a horizontal
+position by a wire, and resting on two other vertical carbons. The
+upright of the arm which holds the wire can revolve together with
+this arm, and is thus able to regulate the pressure of the horizontal
+carbon on the two vertical carbons. It appears that this instrument
+is extremely sensitive, and that the regulation effected on the two
+contacts is better than when it is effected on one only. It is fair to
+add that M. Voisin previously sent me the sketch of a somewhat similar
+arrangement.
+
+M. Dutertre has also made use of such an arrangement in what he calls
+the Dolmen microphone. Three pieces of coke in the form of a dolmen,
+that is, two uprights, supporting a third and horizontal carbon, are
+placed in circuit. M. Gouault has informed me that speech was well
+transmitted by this instrument, and it is, like that of Mr. Blyth,
+which succeeded it, of wonderful simplicity.
+
+This microphone, as well as one composed of two pieces of lead-pencil
+placed in a watch-case, and connected by a piece of money, were
+exhibited to the Industrial Society at Rouen, February 1, 1878, of
+which an account was published in the Bulletin of that society.
+
+_M. Ader’s Electrophone._--M. Ader has recently constructed a
+remarkable telephonic instrument, which reproduces speech and song in a
+quite exceptional and simple way. It consists of a drum 15 centimètres
+in diameter, covered with parchment at one end only. Six small tin
+armatures, one centimètre in length and two millimètres in width,
+are fixed in the centre of the parchment in a circle six centimètres
+in diameter. Six microscopic electro-magnets, whose distance from
+the armatures can be regulated by a screw, are placed opposite the
+armatures within a wooden circle. The magnets are horseshoe, with
+branches 12 millimètres long and 4 millimètres in diameter, including
+the coils, and the magnetic core is 1½ millimètre thick. They are all
+in connection, and act simultaneously under the sole influence of the
+battery current. The sender is the same as that of M. Ader described
+before. With this instrument speech may be heard at a distance of six
+or seven yards, and songs are much more distinctly heard than in the
+singing condenser. Owing to the simplicity of the arrangement, the
+instrument is not costly.
+
+The extraordinary effects of this telephone are due to the small size
+of the electro-magnets, which, as we believe, produce much more rapid
+magnetic effects than those of larger size. M. Ader has also made a
+small ordinary telephone based on this principle, of which the sounds
+are much stronger than in others.
+
+_Modification of Bell Telephone._--Mr. Gower has recently made a new
+system of telephone without a battery, which not only reproduces
+speech loudly enough to be heard at the distance of eight or nine
+yards from the instrument, but will also transmit it when the speaker
+is at a moderate distance from the sending instrument. In this latter
+case, indeed, the receiving telephone must be brought close to the
+ear. Although this double problem had already been solved by the use
+of telephones with microphonic senders, the results furnished by the
+instruments in question are still more curious, since they are obtained
+without batteries, and are even more distinct.
+
+In this new system, which is only an improvement on Bell’s square
+model, the horseshoe magnet is of a peculiar form, which renders it
+more powerful. It is formed of a kind of half-circle of magnetised
+steel, with its two ends turned back, so as to form a diameter of the
+circle, only this diameter is divided in the centre: so that the two
+poles of the magnet are placed one before the other, as in Faraday’s
+electro-magnet. The poles are tipped with iron, terminating in front in
+two thin iron plates, on which are placed the electro-magnetic coils,
+which are oblong, and constitute the magnetic core. The diaphragm,
+thicker than the ordinary diaphragms, is of tin, and is fixed firmly
+to the edges of the circular box which encloses the whole, and which
+forms a kind of sounding-box. The box is made of copper, and the
+diaphragm is so firmly fastened to it as to become homogeneous with it,
+and to give out a sound when the box is touched, which is not the case
+in ordinary telephones. This is one of the conditions which make the
+instrument a better conductor of sound. The magnet is also much more
+powerful. It is magnetised by a current from a powerful Gramme machine,
+which acts upon it for almost twenty minutes. The instrument has,
+strictly speaking, no mouthpiece: the lid of the box which supports the
+diaphragm, and is separated from it by a space of two millimètres, has
+merely a hole bored in it above the centre of the diaphragm, and into
+this hole either a tin trumpet, 50 centimètres in length, is screwed,
+when the instrument is required to reproduce or transmit speech to a
+distance, or an acoustic tube when it is to be used like an ordinary
+telephone. The remarkable part of the system is that the instrument
+can itself give a very loud call by only breathing into it instead of
+speaking.
+
+For this purpose a small oblong opening is made in the diaphragm at a
+half diameter from its centre, and behind this the reed of an harmonium
+is applied to a square copper plate fixed on the diaphragm itself. On
+using the bellows the expelled air passes through this little hole,
+and, on reaching the reed, sets it in vibration, and produces a sound
+of which the acuteness depends on the conditions of the vibrating
+plate. This addition to the diaphragm in no way alters its properties
+in the reproduction of speech, so that, after using the bellows,
+conversation may begin, and the receiving telephone repeats what is
+said after emitting a sound somewhat resembling the note of a bugle.
+The instrument is then provided with the speaking tube of which we
+have spoken.
+
+Nothing can be more remarkable than this power of listening to
+conversation while seated in an armchair six or seven yards from
+the instrument, nor is it necessary to move in order to reply. The
+correspondent, indeed, must be close to the acoustic tube in order
+to speak and listen, and he must speak rather loud in order to be
+heard at any distance from the other station. But the listener
+receives the sounds so amplified that it might be supposed that a
+giant was speaking, and conversation held in a low tone may even be
+distinguished. These results are really extraordinary, and even to
+those familiar with such effects this incessant progress is surprising.
+
+These results may be ascribed to the following causes:--
+
+1. First, that the conditions of the magnet are better than those of
+ordinary instruments.
+
+2. That the diaphragm is also thicker, larger, and better stretched.
+
+3. That the box is of metal, and calculated to act as a sounding-box.
+
+4. The speaking trumpet magnifies the sounds.
+
+5. The acoustic tubes concentrate the sound waves on the centre of the
+diaphragm.
+
+
+_Note on some fresh Experiments with Telephones without any Diaphragm._
+
+In a paper published March 4, 1878, I made some suggestions on
+the theory of the sounds produced in the telephone, and on the
+contradictory assertions of physicists as to the transmission of speech
+by ordinary telephones when devoid of diaphragm. These remarks induced
+M. Ader to undertake some experiments which not only demonstrate the
+truth of my opinion, but bring to light some fresh facts which may be
+of great importance to acoustic science.
+
+M. Ader has in fact not only succeeded in making a telephone without
+a diaphragm speak, but he has made it speak more loudly and with less
+alteration of the voice than we find to be the case with a small model
+of the ordinary telephone. No one, therefore, can now maintain that the
+sounds produced by the magnetic cores are so faint that they cannot be
+taken into account among the effects produced, and that it is at any
+rate impossible for them to reproduce articulate sounds.
+
+To obtain this result, M. Ader reduced the size of the magnetic core to
+that of a simple iron wire, one millimètre in diameter, and he fastened
+it by one of its ends to a small wooden board. Under these conditions,
+it was enough to fasten a small helix of fine wire on this iron wire,
+and to apply the board to the ear in order to hear speech distinctly,
+with the aid of a microphonic speaker actuated by a voltaic current.
+But the range of sound was considerably increased if a mass of metal
+was applied to the free end of the iron wire: in this case it was
+possible to hear when the wooden board was removed to a distance of ten
+or fifteen centimètres from the ear.
+
+If the wire is in contact with masses of metal at each end, the effect
+is further increased; but the two masses must not be in metallic
+communication with each other, and must be to some extent insulated by
+a more or less elastic medium. If the metallic masses are soldered to
+the wire, the effects are still greater.
+
+M. Ader was also able to reproduce speech by using a simple coil
+without a magnetic core, but in this case the spirals must be open, and
+not pressed together. If they are steeped in gum, no sound is heard,
+but speech will become instantly audible if a wire or a magnetised
+needle is inserted in the coil, or even if a second metallic helix is
+placed in the circuit: always provided that one of the ends of these
+magnetic organs rests upon, or is fastened to, the board on which the
+coil is fixed.
+
+M. Ader has likewise obtained a very distinct reproduction of speech
+at a distance of two or three yards from the instrument by inserting
+between the two stretched membranes of two tambourines a bent wire
+which acts as a spring and passes through an electro-magnetic coil.
+Under these conditions, magnetisation of the wire in a greater or less
+degree affects its elasticity and causes vibrations which are magnified
+by the membranes, and transmitted sounds are reproduced with intensity.
+Unfortunately articulate speech is less distinct with this system than
+with the one I described before.
+
+M. Ader has often had occasion to make one curious remark, namely,
+that the _timbre_ of the voice and its high or low key varies with the
+degree of tension given to the wire; but if the fundamental note of
+the wire is deadened by pressing it between the fingers, the sounds
+reproduced then become dull and monotonous. They are also somewhat
+fainter.
+
+Signor Carlo Resio has also observed that in a telephone sender the
+variations of intensity in the current correspond with the vibrations
+caused by speech, and these are reproduced by corresponding variations
+in a liquid column, which may thus act as a telephone receiver,
+and consequently may reproduce speech without any electro-magnetic
+organ, as in a microphone speaker. Under these conditions, however, a
+layer of water is inserted between the platinum electrodes and the
+surrounding air, and consequently this liquid layer must be put in
+vibration under the influence of varying intensities of current.
+
+Mr. Edison has also now made a practical application of the chemical
+telephone we have mentioned before. The trials made with it have been
+very satisfactory, showing that sounds transmitted in this way can be
+heard in a large room.
+
+
+                               PRINTED BY
+                SPOTTISWOODE AND CO., NEW-STREET SQUARE
+                                 LONDON
+
+
+
+
+FOOTNOTES
+
+
+[1] Mr. Gray, in an article inserted in the _Telegrapher_ of October
+7, 1876, enters into full details of this mode of transmitting sounds
+by the tissues of the human body, and he gives the following as the
+conditions in which it must be placed to obtain a favourable result: 1.
+The electricity must be of a high tension, in order to have an effect
+perceptible to the ear.
+
+2. The substance employed to touch the metallic plate must be soft,
+flexible, and a good conductor, up to the point of contact: it must
+then interpose a slight resistance, neither too great nor too small.
+
+3. The disk and the hand, or any other tissue, must not only be in
+contact, but the contact must result from rubbing or gliding over the
+surface.
+
+4. The parts in contact must be dry, so as to maintain the required
+degree of resistance.
+
+[2] He cites the following names in his account of electric
+telephony:--Page, Marrian, Beatson, Gassiot, De la Rive, Matteucci,
+Guillemin, Wertheim, Wartmann, Janniar, Joule, Laborde, Legat, Reiss,
+Poggendorf, Du Moncel, Delezenne, Gore, &c. Vide Mr. Bell’s paper, in
+the _Journal of the Society of Telegraphic Engineers_ in London, vol.
+vi. pp. 390, 391.
+
+[3] This statement is disputed by Mr. Elisha Gray, owing, as we shall
+see, to a misunderstanding as to the word _undulatory_ current.
+
+[4] _Elisha Gray._ Eng. Pat. Spec. No. 2646, Aug. 1874.
+
+[5] This property has long been known, but not applied. In 1856, in the
+second edition of my _Exposé des applications d’Electricité_, I pointed
+them out in speaking of the contact-breakers. I also spoke of them in
+a paper on electro-magnets (published in the _Annales télégraphiques_,
+1865), and in several articles laid before the _Académie des Sciences_
+in 1872 and 1875 on the conductivity of filings and conducting powders.
+M. Clérac, in 1865, also used them to obtain variable resistances.
+
+[6] In 1865 I was able to verify this observation when tightening the
+spirals of an electro-magnet on a naked wire. The greater the number
+of spirals under pressure, the more definite were the differences of
+resistance in the magnetising helix.
+
+[7] M. Hellesen communicated the plan of his instrument to me on May 3,
+1878, and his experiments were made in Copenhagen three weeks earlier.
+
+[8] M. M. J. Page had already noticed that if a telephone is placed
+in the circuit of the primary helix of an induction coil, while the
+secondary helix of this instrument is placed in the circuit of one of
+M. Lippmann’s capillary electrometers, a movement of the mercurial
+column of the electrometer takes place at each word, and this movement
+is effected towards the capillary end of the tube, in whatever
+direction the current is sent by the telephone. This is because the
+mercury always tends to move more rapidly at its capillary end than at
+the other extremity.
+
+[9] Mr. Edison, in a letter written November 25, 1877, writes that
+he has made two telephones which act with copper diaphragms, based
+on Arago’s effects of magnetism by rotation. He ascertained that a
+copper diaphragm might replace the iron plate, if its thickness did not
+exceed 1/32 of an inch. The effect produced is slight when the copper
+diaphragm is placed between two corresponding instruments; but when the
+sender only is furnished with the copper diaphragm, and the receiver is
+arranged as usual, communication becomes easy.
+
+Mr. Preece repeated these experiments, but he only obtained very slight
+and indistinct effects: he consequently believes that they are of no
+practical use, although very interesting in theory.
+
+[10] Mr. Bell had previously made a like experiment, which suggested to
+him that molecular vibrations had as much to do with the action of the
+telephone as mechanical vibrations.
+
+[11] M. Bosscha, who has published in the _Archives néerlandaises_
+an interesting paper on the intensity of electric currents in the
+telephone, says that the minimum intensity of currents necessary to
+produce a sound in a telephone by the vibration of its diaphragm may
+be less than 100/1000 of a Daniell element, and the displacement of
+the centre of the diaphragm would then be invisible. He was unable
+to measure exactly the range of movements produced in the diaphragm
+by the influence of the voice, but he believes it to be less than
+the thousandth part of a millimètre; and from this it follows that,
+for a sound of 880 vibrations, the intensity of the induced currents
+developed would be 0·0000792 of the unit of electro-magnetic intensity.
+
+[12] Mr. Warwick describes his experiments as follows: ‘The magnets
+employed were nearly of the usual size, 1½ inch in diameter, and nearly
+eight times as long. At first I employed iron disks, but I found
+them to be unnecessary. When I had discarded them, I tried several
+substances: first a thin disk of iron, which answered perfectly both
+for sender and receiver. A disk of sheet iron, about ⅒ of an inch
+in thickness, did not act so well, but all that was said was quite
+understood. In making experiments with the disks, I simply placed them
+above the instrument, without fixing them in any way: the wooden cover
+and the conical cavity were also laid aside, because the transmission
+and reception could be effected as well without them. This part of the
+instrument seems to be superfluous, since, when the disk is simply
+placed level to the ear, the sound seems to be increased by being
+brought nearer. Although iron acts better than anything, it appears
+that iron disks are not absolutely necessary, and that diamagnetic
+substances also act perfectly. I wished that my assistant, who was at
+some distance, and could not hear any direct sound, should continue
+his calculations. I took away the iron disk and placed across the
+instrument a wide iron bar, an inch thick. On applying my ear to it, I
+could hear every sound distinctly, but somewhat more faintly. A piece
+of copper, three inches square, was substituted for it: although the
+sound was still distinct, it was fainter than before. Thick pieces of
+lead, zinc, and steel were alternately tried. The steel acted in almost
+the same way as the iron, and, as in the other cases, each word was
+heard faintly but distinctly. Some of these metals are diamagnetic,
+and yet the action took place. Some non-metallic substances were next
+tried; first a piece of window-glass, which acted very well. The action
+was faint with a piece of a wooden match-box; but on using pieces
+of gradually increasing thickness the sound was sensibly increased,
+and with a piece of solid wood, 1½ inch in thickness, the sound was
+perfectly distinct. I next replaced it by an empty wooden box, which
+acted very well. A piece of cork, ½ inch thick, acted, but somewhat
+faintly. A block of razor-stone, 2 inches thick, was placed upon the
+instrument; and, on applying the ear to it, it was quite easy to
+follow the speaker. I then tried to hear without the insertion of any
+substance, and, on applying my ear quite close to the coil and magnet,
+I heard a faint sound, and on listening attentively I understood all
+that was said. In all these experiments the sounds were perceived,
+but the sounds transmitted or attempted did not act precisely alike.
+The sound of a tuning-fork, placed on the iron disk itself or on
+the case of the instrument, was clearly heard: thin iron disks were
+more effective for articulate speech. With other substances, stone,
+solid wood, glass, zinc, &c., the sound of the tuning-fork was heard,
+whether it rested upon them, or the vibrating fork was held above
+them. These substances were not adapted for transmitting the sound
+of the voice. These were all laid aside, and the sounding instrument
+was held directly above the pole of the magnet: the sound was clearly
+heard, although there was nothing but air between the end of the
+magnet and the tuning-fork. The sound was perhaps less intense when
+the tuning-fork was held directly above the pole, than when it was at
+the end of the magnet. I next tried if my voice could be heard with
+this arrangement. The result was rather doubtful, but I think that
+some action must have taken place, for the tuning-fork was heard when
+it was simply vibrated near the pole. The effect of the voice can only
+have differed in the degree of intensity: it was too faint to be heard
+at the other extremity. I repeated these effects; I assured myself of
+them, and I succeeded in transmitting sounds distinctly on the pole
+without a disk, and, on the other hand, by applying my ear to the
+instrument, I was able to hear distinctly all that was said, although
+there was no disk.’
+
+[13] These are his own words: ‘The articulation produced from the
+instrument was remarkably clear, but its great defect consisted in the
+fact that it could not be used as a sending instrument, and thus two
+telephones were required at each station, one for transmitting and one
+for receiving spoken messages.’
+
+[14] These carbons are made by heating, in a temperature gradually
+raised to white heat, fragments of deal of a close fibre, which is
+enclosed in an iron tube or box hermetically sealed.
+
+[15] Mr. Willoughby Smith varied this experiment by placing a packet
+of silk threads coated with copper on the disconnected ends of the
+circuit, which were arranged at right angles with each other. Under
+these conditions the instrument became so sensitive, that the current
+of air produced by a lamp placed above the system, caused a decided
+crackling noise in the telephone.
+
+[16] Mr. Hughes observes on this subject that carbon is a valuable
+material for such purposes, since it does not oxidise, and its effects
+are greater when combined with mercury. He takes the prepared charcoal
+used by artists, brings it to a white heat, and suddenly plunges it in
+a bath of mercury, of which the globules instantly penetrate the pores
+of charcoal, and may be said to metallise it. He also tried charcoal
+coated with a deposit of platinum, or impregnated with chloride of
+platinum, but this was not more successful than the former method. If
+the charcoal of fir-wood is brought to a white heat in an iron tube,
+containing tin and zinc, or any other metal which readily evaporates,
+it is metallised, and is adapted for use if the metal is subdivided in
+the pores of charcoal and not combined with it. When iron is introduced
+into carbon in this way it is one of the most effective metals. The
+charcoal of fir-wood, in itself a bad conductor, may thus acquire great
+conducting power.
+
+[17] Mr. Hughes remarks that the vibrations which affect the
+microphone, even in speaking at a distance from the instrument, do
+not proceed from the direct action of the sound waves on the contacts
+of the microphone, but from the molecular vibrations produced by it
+on the board which serves to support the instrument; he shows, in
+fact, that the intensity of sounds produced by the microphone is in
+proportion to the size of the surface of this board, and when the
+sending microphone is enclosed in a cylindrical case, its sensitiveness
+is not much diminished if the surface of the box enclosing the whole is
+sufficiently large. From this point of view he has sought to increase
+the sensitiveness of his instruments by fixing the frame on which the
+moveable parts of the sender and receiver revolve on a spring plate.
+
+[18] Helmholtz’s resonator is based upon the principle that a volume
+of air contained in an open vase emits a certain note when placed in
+vibration, and that the height of the note depends on the size of the
+vase and of its opening. Helmholtz makes use of a globe with a large
+opening on one side and a small one on the other, and the small one is
+applied to the ear. If a series of musical notes take place in the air,
+the one which is in harmony with the fundamental note of the globe is
+intensified, and can be distinguished from the rest. The same effect
+takes place when, on singing to a piano accompaniment, some strings are
+heard to vibrate more strongly than others, namely, those which vibrate
+in unison with the sounds emitted. The resonators are made in various
+ways; those most generally used are cases of different lengths which
+also serve as sounding-boxes.
+
+[19] I give the text of M. Cros’ sealed paper, opened by his request,
+at the Académie des Sciences, December 3, 1877:--‘Speaking generally,
+my process consists in obtaining traces of the movement to and fro of
+a vibrating membrane, and in using this tracing to reproduce the same
+movements, with their intrinsic relations of duration and intensity,
+either on the same membrane or on one adapted to give out the sounds
+which result from this series of movements.
+
+‘It is therefore necessary that an extremely delicate tracing, such as
+may be obtained by passing a needle over a surface blackened by fire,
+should be transformed into a tracing, capable of sufficient resistance
+to guide an index which will transmit its movements to the membrane of
+sound.
+
+‘A light index is fastened to the centre of a vibrating membrane; it
+terminates in a point (a metallic wire or tip of a feather) which rests
+on a surface which has been blackened by fire. This surface forms part
+of a disk, to which the double action of rotation and rectilinear
+progression has been given. If the membrane is at rest, the point
+will trace a simple spiral; if the membrane vibrates, there will be
+undulations in the spiral, and these undulations will represent the
+precise movements of the membrane in their duration and intensity.
+
+‘By a well-known photographic process a transparent tracing of the
+undulations of the spiral can be represented by a line of similar
+dimensions on some resisting substance, tempered steel for example.
+
+‘When this is done, this resisting surface is placed in a turning
+machine which causes it to revolve and advance with a velocity and
+motion similar to those by which the registering surface was actuated.
+A metallic point if the tracing is concave, or a grooved index if it
+is in relief, is kept upon the tracing by a spring, and the index
+which supports this point is connected with the centre of the membrane
+which produces the sounds. Under these conditions, the membrane will
+be actuated not by the vibrating air, but by the tracing which guides
+the index, and the impulses will be precisely similar in duration and
+intensity to those to which the registering membrane was subjected.
+
+‘The spiral tracing represents equal successions of time by increasing
+or decreasing lengths. There is no inconvenience in this, since the
+turns of the spiral are very close together, if only the circumference
+of the turning circle is used; but then the central surface is lost.
+
+‘In all cases the tracing of the helix on a cylinder is much more
+satisfactory, and I am now trying to make this idea practicable.’
+
+[20] Never make a contact between the stylus and the cylinder until the
+latter is covered with the tinfoil. Do not begin to turn the cylinder
+until assured that everything is in its place. Take care, when the
+stylus returns to the point of departure, to bring the mouthpiece
+forward. Always leave a margin of from five to ten millimètres on the
+left and at the beginning of the sheet of tinfoil; for if the stylus
+describes the curve on the extreme edge of the cylinder, it may tear
+the sheet or come out of the groove. Be careful not to detach the
+spring of the caoutchouc pad.
+
+To fix the tinfoil, apply varnish to the end with a paint-brush; take
+this end between the finger and thumb of the left hand, with the sticky
+part towards the cylinder; raise it with the right hand and apply it
+quite smoothly to the cylinder; bring round the sticky end, and join
+them firmly.
+
+To adjust the stylus and place it in the centre of the groove, bring
+the cylinder to the right, so as to place the stylus opposite the
+left extremity of the tinfoil; bring forward the cylinder gently and
+by degrees, until the stylus touches the tinfoil with force enough to
+imprint a mark. Observe if this mark is quite in the centre of the
+groove (in order to do this, make a mark with the nail across the
+cylinder), and if it is not, adjust the stylus to the right or left by
+means of the little screw placed above the mouthpiece. The depth of the
+impression made by the stylus should be ⅓ millimètre, just enough for
+it to leave a slight tracing, whatever the range of vibrations may be.
+
+To reproduce the words, the winch must be turned with the same velocity
+as when they were inscribed. The average velocity should be about
+eighty turns a minute.
+
+In speaking, the lips must touch the mouthpiece, and deep guttural
+sounds are better heard than those which are shrill. In reproducing,
+the tightening screw must be loosened and brought in front of the
+mouthpiece, the cylinder must be brought back to its point of
+departure, the contact between the stylus and the foil must be renewed,
+and the cylinder must again be turned in the same direction as when the
+sentence was spoken.
+
+To increase the volume of reproduced sound, a tube of cardboard, wood,
+or horn may be applied to the mouthpiece; it must be of a conical form,
+and its lower end should be rather larger than the opening of the
+mouthpiece.
+
+The stylus consists of a No. 9 needle, somewhat flattened on its two
+sides by friction on an oiled stone. The caoutchouc pad which connects
+the plate with the disk serves to weaken the vibrations of the plate.
+If this pad should come off, heat the head of a small nail, apply it to
+the wax which fastens the pad to the plate or to the spring, so as to
+soften it; then press the caoutchouc lightly, until it adheres to the
+place from which it was detached. The pads must be renewed from time to
+time, as they lose their elasticity. Care must be taken in replacing
+them not to injure the vibrating plate, either by too strong a pressure
+or by grazing it with the instrument employed to fix the pad.
+
+The first experiments should be with single words or very short
+sentences, which can be extended as the ear becomes accustomed to the
+instrument’s peculiar tone.
+
+The tone is varied by accelerating or slackening the rotatory movement
+of the cylinder. The cries of animals may be imitated. Instrumental
+music may be reproduced by placing a cardboard tube before the
+mouthpiece. The airs should be played in rapid time, since, when there
+is no system of clockwork, they will be more perfectly reproduced than
+those which are played slowly.
+
+[21] We confess that we find it difficult to believe in this property
+of the phonograph, from which we have only heard the harsh and
+unpleasant voice of Punch.
+
+[22] The action of this pedal is effected by two little rockers, so
+connected that the upper damper is lowered a little before the lower
+damper is raised--a condition necessary to produce the quivering motion
+of the plate which furnishes the rolling _r_.
+
+[23] The arrangement of this part of the instrument is remarkable in
+this particular, that in the case of certain letters the air is ejected
+with more or less force through the pipe I, while in the case of other
+letters the air is drawn into the same tube. Since I was unable to
+see the internal arrangement of these cavities, I can only give an
+imperfect account of the mechanism at work.
+
+
+
+
+Transcriber’s Notes
+
+
+Punctuation, hyphenation, and spelling were made consistent when a
+predominant preference was found in the original book; otherwise they
+were not changed.
+
+Simple typographical errors were corrected; unbalanced quotation
+marks were remedied when the change was obvious, and otherwise left
+unbalanced.
+
+Illustrations in this eBook have been positioned between paragraphs and
+outside quotations.
+
+Footnotes, originally at the bottoms of the pages that referenced them,
+have been collected, sequentially renumbered, and placed near the end
+of the book.
+
+The Table of Contents is not well-coordinated with the actual text. The
+Transcriber has not added missing entries, but has attempted to correct
+page number discrepancies.
+
+Several diagrams use labels with prime marks, but the accompanying
+explanations do not always include the prime marks.
+
+
+
+*** END OF THE PROJECT GUTENBERG EBOOK 75683 ***
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+<div style='text-align:center'>*** START OF THE PROJECT GUTENBERG EBOOK 75683 ***</div>
+
+<div class="transnote section">
+<p class="center larger">Transcriber’s Note</p>
+
+<p>Larger versions of most illustrations may be seen by right-clicking them
+and selecting an option to view them separately, or by double-tapping and/or
+stretching them.</p>
+
+<p><a href="#Transcribers_Notes">Additional notes</a> will be found near the end of this ebook.</p>
+<div>                                                                                                                                                                                                                           </div>
+</div>
+
+<div class="section">
+<h1><span class="smaller">THE</span> <br>TELEPHONE, MICROPHONE, &amp; PHONOGRAPH</h1>
+<hr class="chap x-ebookmaker-drop">
+<div>                                                                                                                                                                                                                           </div>
+</div>
+
+<div class="section center vspace wspace">
+<p class="xxlarge">
+THE TELEPHONE<br>
+THE MICROPHONE &amp; THE PHONOGRAPH</p>
+
+<p class="p2">BY<br>
+<span class="larger">COUNT DU MONCEL</span><br>
+<span class="small">MEMBRE DE L’INSTITUT</span></p>
+
+<p class="p2 smaller"><i>AUTHORISED TRANSLATION<br>
+WITH ADDITIONS AND CORRECTIONS BY THE AUTHOR</i></p>
+
+<p class="p2">WITH 70 ILLUSTRATIONS ON WOOD</p>
+
+<p class="p2 larger"><i>FOURTH EDITION</i></p>
+
+<p class="p2"><span class="larger">LONDON</span><br>
+KEGAN PAUL, TRENCH, TRÜBNER, &amp; CO. <span class="smcap">Ltd.</span><br>
+<span class="smaller">PATERNOSTER HOUSE, CHARING CROSS ROAD<br>
+1892</span>
+</p>
+<hr class="chap x-ebookmaker-drop">
+</div>
+
+<div class="section p4 center">
+<p><span class="pagenum" id="Page_v">v</span></p>
+<p>(<i>The rights of translation and of reproduction are reserved</i>)</p>
+<div>                                                                                                                                                                                                                           </div>
+</div>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h2 class="nobreak" id="CONTENTS"><i>CONTENTS.</i></h2>
+</div>
+
+<table id="toc">
+<tr class="xsmall">
+  <td></td>
+  <td class="tdr">PAGE</td>
+</tr>
+<tr>
+  <td class="tdl">History of the telephone</td>
+  <td class="tdr"><a href="#Page_1">1</a></td>
+</tr>
+<tr>
+  <td class="tdc chap" colspan="2"><i><a href="#toclink_11">MUSICAL TELEPHONES</a>.</i></td>
+</tr>
+<tr>
+  <td class="tdl">Reiss’s telephone</td>
+  <td class="tdr"><a href="#Page_11">11</a></td>
+</tr>
+<tr>
+  <td class="tdl">Wray’s telephone</td>
+  <td class="tdr"><a href="#Page_15">15</a></td>
+</tr>
+<tr>
+  <td class="tdl">Electric harmonica</td>
+  <td class="tdr"><a href="#Page_18">18</a></td>
+</tr>
+<tr>
+  <td class="tdl">Gray’s telephone</td>
+  <td class="tdr"><a href="#Page_21">21</a></td>
+</tr>
+<tr>
+  <td class="tdl">Pollard and Garnier’s singing condenser</td>
+  <td class="tdr"><a href="#Page_26">26</a></td>
+</tr>
+<tr>
+  <td class="tdc chap" colspan="2"><i><a href="#toclink_30">SPEAKING TELEPHONES</a>.</i></td>
+</tr>
+<tr>
+  <td class="tdl">String telephones</td>
+  <td class="tdr"><a href="#Page_31">31</a></td>
+</tr>
+<tr>
+  <td class="tdl">Bell’s electric telephone</td>
+  <td class="tdr"><a href="#Page_35">35</a></td>
+</tr>
+<tr>
+  <td class="tdl">Gray’s share in invention of telephone</td>
+  <td class="tdr"><a href="#Page_62">62</a></td>
+</tr>
+<tr>
+  <td class="tdc chap" colspan="2"><i><a href="#toclink_67">FUNDAMENTAL PRINCIPLES OF BELL TELEPHONE</a>.</i></td>
+</tr>
+<tr>
+  <td class="tdl">Explanation of principles</td>
+  <td class="tdr"><a href="#Page_67">67</a></td>
+</tr>
+<tr>
+  <td class="tdc chap" colspan="2"><i><a href="#toclink_71">ORDINARY ARRANGEMENT OF BELL TELEPHONE</a>.</i></td>
+</tr>
+<tr>
+  <td class="tdl">Description and illustrations</td>
+  <td class="tdr"><a href="#Page_71">71</a><span class="pagenum" id="Page_vi">vi</span></td>
+</tr>
+<tr>
+  <td class="tdc chap" colspan="2"><i><a href="#toclink_83">BATTERY TELEPHONES</a>.</i></td>
+</tr>
+<tr>
+  <td class="tdl">Edison’s telephone</td>
+  <td class="tdr"><a href="#Page_83">83</a></td>
+</tr>
+<tr>
+  <td class="tdl">Edison’s chemical telephone</td>
+  <td class="tdr"><a href="#Page_90">90</a></td>
+</tr>
+<tr>
+  <td class="tdl">Navez’ telephone</td>
+  <td class="tdr"><a href="#Page_93">93</a></td>
+</tr>
+<tr>
+  <td class="tdl">Pollard and Garnier’s telephone</td>
+  <td class="tdr"><a href="#Page_97">97</a></td>
+</tr>
+<tr>
+  <td class="tdl">Hellesen’s telephone</td>
+  <td class="tdr"><a href="#Page_100">100</a></td>
+</tr>
+<tr>
+  <td class="tdl">Thomson and Houston’s telephone</td>
+  <td class="tdr"><a href="#Page_101">101</a></td>
+</tr>
+<tr>
+  <td class="tdl">Telephones with liquid senders</td>
+  <td class="tdr"><a href="#Page_103">103</a></td>
+</tr>
+<tr>
+  <td class="tdl">Telephones with voltaic arcs</td>
+  <td class="tdr"><a href="#Page_107">107</a></td>
+</tr>
+<tr>
+  <td class="tdl">Mercury telephones</td>
+  <td class="tdr"><a href="#Page_110">110</a></td>
+</tr>
+<tr>
+  <td class="tdl">Friction telephones</td>
+  <td class="tdr"><a href="#Page_113">113</a></td>
+</tr>
+<tr>
+  <td class="tdc chap" colspan="2"><i><a href="#toclink_114">MODIFICATION OF BELL TELEPHONES</a>.</i></td>
+</tr>
+<tr>
+  <td class="tdl">Telephones with several diaphragms</td>
+  <td class="tdr"><a href="#Page_114">114</a></td>
+</tr>
+<tr>
+  <td class="tdl">Gray’s system</td>
+  <td class="tdr"><a href="#Page_118">118</a></td>
+</tr>
+<tr>
+  <td class="tdl">Phelps’s system</td>
+  <td class="tdr"><a href="#Page_118">118</a></td>
+</tr>
+<tr>
+  <td class="tdl">Cox Walker’s system</td>
+  <td class="tdr"><a href="#Page_121">121</a></td>
+</tr>
+<tr>
+  <td class="tdl">Trouvé’s system</td>
+  <td class="tdr"><a href="#Page_121">121</a></td>
+</tr>
+<tr>
+  <td class="tdl">Demoget’s system</td>
+  <td class="tdr"><a href="#Page_124">124</a></td>
+</tr>
+<tr>
+  <td class="tdl">Mac Tighe’s system</td>
+  <td class="tdr"><a href="#Page_125">125</a></td>
+</tr>
+<tr>
+  <td class="tdl">Modifications of telephonic organs</td>
+  <td class="tdr"><a href="#Page_125">125</a></td>
+</tr>
+<tr>
+  <td class="tdl">Righi’s system</td>
+  <td class="tdr"><a href="#Page_126">126</a></td>
+</tr>
+<tr>
+  <td class="tdl">Ader’s system</td>
+  <td class="tdr"><a href="#Page_129">129</a></td>
+</tr>
+<tr>
+  <td class="tdl">Jorgenson’s system</td>
+  <td class="tdr"><a href="#Page_131">131</a></td>
+</tr>
+<tr>
+  <td class="tdc chap" colspan="2"><i><a href="#toclink_132">EXPERIMENTS WITH THE TELEPHONE</a>.</i></td>
+</tr>
+<tr>
+  <td class="tdl">On the effects of voltaic and induced currents</td>
+  <td class="tdr"><a href="#Page_132">132</a></td>
+</tr>
+<tr>
+  <td class="tdl">On the effects of different telephonic organs</td>
+  <td class="tdr"><a href="#Page_139">139</a></td>
+</tr>
+<tr>
+  <td class="tdl">Edison’s experiments</td>
+  <td class="tdr"><a href="#Page_140">140</a></td>
+</tr>
+<tr>
+  <td class="tdl">Canestrelli’s experiments</td>
+  <td class="tdr"><a href="#Page_142">142</a></td>
+</tr>
+<tr>
+  <td class="tdl">Hughes’s and Roy’s experiments</td>
+  <td class="tdr"><a href="#Page_143">143</a></td>
+</tr>
+<tr>
+  <td class="tdl">Bréguet’s experiments</td>
+  <td class="tdr"><a href="#Page_149">149</a><span class="pagenum" id="Page_vii">vii</span></td>
+</tr>
+<tr>
+  <td class="tdl">Luvini’s experiments</td>
+  <td class="tdr"><a href="#Page_149">149</a></td>
+</tr>
+<tr>
+  <td class="tdl">Warwick’s experiments</td>
+  <td class="tdr"><a href="#Page_151">151</a></td>
+</tr>
+<tr>
+  <td class="tdl">Experiments on the effects of mechanical shocks</td>
+  <td class="tdr"><a href="#Page_154">154</a></td>
+</tr>
+<tr>
+  <td class="tdl">Des Portes’ experiments</td>
+  <td class="tdr"><a href="#Page_154">154</a></td>
+</tr>
+<tr>
+  <td class="tdl">Thompson’s experiments</td>
+  <td class="tdr"><a href="#Page_158">158</a></td>
+</tr>
+<tr>
+  <td class="tdl">Theory of telephone</td>
+  <td class="tdr"><a href="#Page_159">159</a></td>
+</tr>
+<tr>
+  <td class="tdl">Nature of vibrations</td>
+  <td class="tdr"><a href="#Page_160">160</a></td>
+</tr>
+<tr>
+  <td class="tdl">Action of diaphragm</td>
+  <td class="tdr"><a href="#Page_163">163</a></td>
+</tr>
+<tr>
+  <td class="tdl">Action of magnet</td>
+  <td class="tdr"><a href="#Page_167">167</a></td>
+</tr>
+<tr>
+  <td class="tdl">Action of currents</td>
+  <td class="tdr"><a href="#Page_169">169</a></td>
+</tr>
+<tr>
+  <td class="tdl">Wiesendanger’s thermophone</td>
+  <td class="tdr"><a href="#Page_171">171</a></td>
+</tr>
+<tr>
+  <td class="tdc chap" colspan="2"><i><a href="#toclink_173">OTHER EXPERIMENTS WITH THE TELEPHONE</a>.</i></td>
+</tr>
+<tr>
+  <td class="tdl">D’Arsonval’s experiments</td>
+  <td class="tdr"><a href="#Page_173">173</a></td>
+</tr>
+<tr>
+  <td class="tdl">Eick’s experiments</td>
+  <td class="tdr"><a href="#Page_175">175</a></td>
+</tr>
+<tr>
+  <td class="tdl">Demoget’s experiments</td>
+  <td class="tdr"><a href="#Page_176">176</a></td>
+</tr>
+<tr>
+  <td class="tdl">Sensitiveness of telephone</td>
+  <td class="tdr"><a href="#Page_179">179</a></td>
+</tr>
+<tr>
+  <td class="tdl">Hellesen’s experiments</td>
+  <td class="tdr"><a href="#Page_180">180</a></td>
+</tr>
+<tr>
+  <td class="tdl">Zetsche’s experiments</td>
+  <td class="tdr"><a href="#Page_181">181</a></td>
+</tr>
+<tr>
+  <td class="tdc chap" colspan="2"><i><a href="#toclink_182">THE MICROPHONE</a>.</i></td>
+</tr>
+<tr>
+  <td class="tdl">History of microphone</td>
+  <td class="tdr"><a href="#Page_182">182</a></td>
+</tr>
+<tr>
+  <td class="tdl">Different systems</td>
+  <td class="tdr"><a href="#Page_187">187</a></td>
+</tr>
+<tr>
+  <td class="tdl">Hughes’s microphone</td>
+  <td class="tdr"><a href="#Page_188">188</a></td>
+</tr>
+<tr>
+  <td class="tdl">Gaiffe’s system</td>
+  <td class="tdr"><a href="#Page_190">190</a></td>
+</tr>
+<tr>
+  <td class="tdl">Carette’s system</td>
+  <td class="tdr"><a href="#Page_191">191</a></td>
+</tr>
+<tr>
+  <td class="tdl">Ducretet’s system</td>
+  <td class="tdr"><a href="#Page_192">192</a></td>
+</tr>
+<tr>
+  <td class="tdl">Ducretet’s speaker</td>
+  <td class="tdr"><a href="#Page_193">193</a></td>
+</tr>
+<tr>
+  <td class="tdl">Boudet’s speaker</td>
+  <td class="tdr"><a href="#Page_195">195</a></td>
+</tr>
+<tr>
+  <td class="tdl">Gaiffe’s thermoscope</td>
+  <td class="tdr"><a href="#Page_197">197</a></td>
+</tr>
+<tr>
+  <td class="tdl">Blyth’s system</td>
+  <td class="tdr"><a href="#Page_199">199</a></td>
+</tr>
+<tr>
+  <td class="tdl">Microphone as a speaking instrument</td>
+  <td class="tdr"><a href="#Page_200">200</a></td>
+</tr>
+<tr>
+  <td class="tdl">Hughes’s system</td>
+  <td class="tdr"><a href="#Page_203">203</a></td>
+</tr>
+<tr>
+  <td class="tdl">Other arrangements of microphones</td>
+  <td class="tdr"><a href="#Page_205">205</a><span class="pagenum" id="Page_viii">viii</span></td>
+</tr>
+<tr>
+  <td class="tdl">Varcy’s and Trouvé’s microphones</td>
+  <td class="tdr"><a href="#Page_207">207</a></td>
+</tr>
+<tr>
+  <td class="tdl">Lippens’s microphone</td>
+  <td class="tdr"><a href="#Page_209">209</a></td>
+</tr>
+<tr>
+  <td class="tdl">Hughes’s experiments</td>
+  <td class="tdr"><a href="#Page_211">211</a></td>
+</tr>
+<tr>
+  <td class="tdl">Hughes’s theory</td>
+  <td class="tdr"><a href="#Page_215">215</a></td>
+</tr>
+<tr>
+  <td class="tdl">Microphone used as thermoscope</td>
+  <td class="tdr"><a href="#Page_217">217</a></td>
+</tr>
+<tr>
+  <td class="tdl">Edison’s thermoscope</td>
+  <td class="tdr"><a href="#Page_219">219</a></td>
+</tr>
+<tr>
+  <td class="tdl">Experiments in London</td>
+  <td class="tdr"><a href="#Page_220">220</a></td>
+</tr>
+<tr>
+  <td class="tdl">Experiment at Bellinzona</td>
+  <td class="tdr"><a href="#Page_223">223</a></td>
+</tr>
+<tr>
+  <td class="tdc chap" colspan="2"><i><a href="#toclink_225">APPLICATIONS OF MICROPHONE</a>.</i></td>
+</tr>
+<tr>
+  <td class="tdl">Its application to scientific research</td>
+  <td class="tdr"><a href="#Page_226">226</a></td>
+</tr>
+<tr>
+  <td class="tdl">Application to telephonic relays</td>
+  <td class="tdr"><a href="#Page_229">229</a></td>
+</tr>
+<tr>
+  <td class="tdl">Application to surgery</td>
+  <td class="tdr"><a href="#Page_232">232</a></td>
+</tr>
+<tr>
+  <td class="tdl">Various applications</td>
+  <td class="tdr"><a href="#Page_236">236</a></td>
+</tr>
+<tr>
+  <td class="tdc chap" colspan="2"><i><a href="#toclink_238">EXTERNAL INFLUENCE ON TELEPHONIC TRANSMISSIONS</a>.</i></td>
+</tr>
+<tr>
+  <td class="tdl">Disturbing influences</td>
+  <td class="tdr"><a href="#Page_239">239</a></td>
+</tr>
+<tr>
+  <td class="tdl">Confusion of circuits</td>
+  <td class="tdr"><a href="#Page_241">241</a></td>
+</tr>
+<tr>
+  <td class="tdl">Induced reactions</td>
+  <td class="tdr"><a href="#Page_243">243</a></td>
+</tr>
+<tr>
+  <td class="tdl">Mr. Preece’s suggestions</td>
+  <td class="tdr"><a href="#Page_245">245</a></td>
+</tr>
+<tr>
+  <td class="tdl">Effects of heat and moisture</td>
+  <td class="tdr"><a href="#Page_249">249</a></td>
+</tr>
+<tr>
+  <td class="tdc chap" colspan="2"><i><a href="#toclink_251">ESTABLISHMENT OF TELEPHONE STATION</a>.</i></td>
+</tr>
+<tr>
+  <td class="tdl">Pollard and Garnier’s system</td>
+  <td class="tdr"><a href="#Page_252">252</a></td>
+</tr>
+<tr>
+  <td class="tdl">Bréguet and Roosevelt’s system</td>
+  <td class="tdr"><a href="#Page_254">254</a></td>
+</tr>
+<tr>
+  <td class="tdl">Edison’s system</td>
+  <td class="tdr"><a href="#Page_257">257</a></td>
+</tr>
+<tr>
+  <td class="tdc chap" colspan="2"><i><a href="#toclink_260">CALL-BELLS AND ALARUMS</a>.</i></td>
+</tr>
+<tr>
+  <td class="tdl">Weinhold’s system</td>
+  <td class="tdr"><a href="#Page_262">262</a></td>
+</tr>
+<tr>
+  <td class="tdl">Dutertre and Gouault’s system</td>
+  <td class="tdr"><a href="#Page_264">264</a><span class="pagenum" id="Page_ix">ix</span></td>
+</tr>
+<tr>
+  <td class="tdl">Puluj’s system</td>
+  <td class="tdr"><a href="#Page_266">266</a></td>
+</tr>
+<tr>
+  <td class="tdl">Chiddey’s system</td>
+  <td class="tdr"><a href="#Page_267">267</a></td>
+</tr>
+<tr>
+  <td class="tdc chap" colspan="2"><i><a href="#toclink_268">APPLICATIONS OF TELEPHONE</a>.</i></td>
+</tr>
+<tr>
+  <td class="tdl">Its application to simultaneous transmissions</td>
+  <td class="tdr"><a href="#Page_270">270</a></td>
+</tr>
+<tr>
+  <td class="tdl">Bell’s system</td>
+  <td class="tdr"><a href="#Page_273">273</a></td>
+</tr>
+<tr>
+  <td class="tdl">Lacour’s system</td>
+  <td class="tdr"><a href="#Page_276">276</a></td>
+</tr>
+<tr>
+  <td class="tdl">Gray’s system</td>
+  <td class="tdr"><a href="#Page_282">282</a></td>
+</tr>
+<tr>
+  <td class="tdc chap" colspan="2"><i><a href="#toclink_293">VARIOUS USES OF THE TELEPHONE</a>.</i></td>
+</tr>
+<tr>
+  <td class="tdl">Its use in offices</td>
+  <td class="tdr"><a href="#Page_293">293</a></td>
+</tr>
+<tr>
+  <td class="tdl">Its use in telegraphic service</td>
+  <td class="tdr"><a href="#Page_294">294</a></td>
+</tr>
+<tr>
+  <td class="tdl">Its application to military purposes</td>
+  <td class="tdr"><a href="#Page_297">297</a></td>
+</tr>
+<tr>
+  <td class="tdl">Its application to industry</td>
+  <td class="tdr"><a href="#Page_302">302</a></td>
+</tr>
+<tr>
+  <td class="tdl">Its application to scientific research</td>
+  <td class="tdr"><a href="#Page_303">303</a></td>
+</tr>
+<tr>
+  <td class="tdc chap" colspan="2"><i><a href="#toclink_307">THE PHONOGRAPH</a>.</i></td>
+</tr>
+<tr>
+  <td class="tdl">Edison’s patent</td>
+  <td class="tdr"><a href="#Page_309">309</a></td>
+</tr>
+<tr>
+  <td class="tdl">Description of phonograph</td>
+  <td class="tdr"><a href="#Page_313">313</a></td>
+</tr>
+<tr>
+  <td class="tdl">Several systems</td>
+  <td class="tdr"><a href="#Page_322">322</a></td>
+</tr>
+<tr>
+  <td class="tdl">Theory of phonograph</td>
+  <td class="tdr"><a href="#Page_327">327</a></td>
+</tr>
+<tr>
+  <td class="tdc chap" colspan="2"><i><a href="#toclink_333">USES OF PHONOGRAPH</a>.</i></td>
+</tr>
+<tr>
+  <td class="tdl">Account by Edison</td>
+  <td class="tdr"><a href="#Page_333">333</a></td>
+</tr>
+<tr>
+  <td class="tdl">Lainbrigot’s system</td>
+  <td class="tdr"><a href="#Page_339">339</a></td>
+</tr>
+<tr>
+  <td class="tdl chap"><i>FABER’S SPEAKING MACHINE</i></td>
+  <td class="tdr"><a href="#Page_341">341</a><span class="pagenum" id="Page_x">x</span></td>
+</tr>
+<tr>
+  <td class="tdc chap" colspan="2"><i><a href="#toclink_351">APPENDIX</a>.</i></td>
+</tr>
+<tr>
+  <td class="tdl">Perrodon’s system of telephonic alarum</td>
+  <td class="tdr"><a href="#Page_351">351</a></td>
+</tr>
+<tr>
+  <td class="tdl">Varey’s microphone speaker</td>
+  <td class="tdr"><a href="#Page_352">352</a></td>
+</tr>
+<tr>
+  <td class="tdl">Fitch’s microphone speaker</td>
+  <td class="tdr"><a href="#Page_353">353</a></td>
+</tr>
+<tr>
+  <td class="tdl">Theory of telephone</td>
+  <td class="tdr"><a href="#Page_353">353</a></td>
+</tr>
+<tr>
+  <td class="tdl">Pollard’s microphone</td>
+  <td class="tdr"><a href="#Page_356">356</a></td>
+</tr>
+<tr>
+  <td class="tdl">Ader’s electrophone</td>
+  <td class="tdr"><a href="#Page_357">357</a></td>
+</tr>
+<tr>
+  <td class="tdl">Gower’s new telephone</td>
+  <td class="tdr"><a href="#Page_358">358</a></td>
+</tr>
+<tr>
+  <td class="tdl">Transmission of speech by telephones without diaphragm</td>
+  <td class="tdr"><a href="#Page_360">360</a></td>
+</tr>
+</table>
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<p><span class="pagenum" id="Page_1">1</span></p>
+
+<h2 class="nobreak" id="THE_TELEPHONE">THE TELEPHONE,<br>
+
+<span class="subhead"><i>&amp;c.</i></span></h2>
+
+<hr class="narrow">
+
+<h2 class="nobreak" id="HISTORY_OF_THE_TELEPHONE"><i>HISTORY OF THE TELEPHONE.</i></h2>
+</div>
+
+<p class="in0"><span class="firstword">Strictly</span> speaking, the telephone is merely an
+instrument adapted for the transmission of sound
+to a distance, and this idea of transmitting sound
+is as old as the world itself. The Greeks made
+use of means which might effect it, and there is no
+doubt that these means were sometimes used for
+the pagan oracles. But such transmission of sound
+was within somewhat narrow limits, and certainly
+did not exceed those of a speaking-tube. Mr.
+Preece considers that the earliest document in
+which this transmission of sound to a distance is
+distinctly formulated, dates from 1667: he refers
+to a paper by one Robert Hooke, who writes to
+this effect: ‘It is not impossible to hear a whisper
+at a furlong’s distance, it having been already done;
+and perhaps the nature of the thing would not make<span class="pagenum" id="Page_2">2</span>
+it more impossible, though that furlong should be
+ten times multiply’d. And though some famous
+authors have affirm’d it impossible to hear through
+the thinnest plate of Muscovy glass; yet I know a
+way, by which ’tis easie enough to hear one speak
+through a wall a yard thick. It has not yet been
+thoroughly examin’d how far otacousticons may be
+improv’d, nor what other wayes there may be of
+quickning our hearing, or conveying sound through
+other bodies than the air; for that is not the only
+medium I can assure the reader, that I have, by the
+help of a distended wire, propagated the sound to a
+very considerable distance in an instant, or with as
+seemingly quick a motion as that of light, at least
+incomparably quicker than that which at the same
+time was propagated through the air; and this not
+only in a straight line or direct, but in one bended
+in many angles.’</p>
+
+<p>This plan for the transmission of sound is the
+principle of the string telephones which have attracted
+attention for some years, and it remained
+in the stage of simple experiment until 1819, when
+Sir Charles Wheatstone applied it to his magic
+lyre. In this instrument, sounds were transmitted
+through a long strip of deal, with one end in connection
+with a sounding board: one step more led
+to the use of the membrane employed in string
+telephones. It would be difficult to say with whom
+this idea originated, since it is claimed, as if beyond
+dispute, by several telephone-makers. If we may<span class="pagenum" id="Page_3">3</span>
+believe some travellers, it has long been used in
+Spain for the correspondence of lovers. However
+this may be, it was not to be found among the
+scientific appliances of some years ago, and it was
+even supposed by many persons that the cord
+consisted of an acoustic tube of slender diameter.
+Although the instrument has become a child’s toy,
+it has great scientific importance, for it proves that
+vibrations capable of reproducing speech may be
+extremely minute, since they can be mechanically
+transmitted more than a hundred yards.</p>
+
+<p>From the telegraphic point of view, however, the
+problem of transmitting sounds to a distance was
+far from being solved in this way, and the idea of
+applying electricity to this mode of transmission
+naturally arose as soon as the wonderful effects of
+electric telegraphy were observed, that is, in the
+years subsequent to 1839. A surprising discovery
+made in America by Mr. Page, in 1837, and afterwards
+investigated by MM. Wertheim, De la Rive,
+and others, must also have led up to it: for it was
+observed that a magnetic bar could emit sounds
+when rapidly magnetised and demagnetised, and
+these sounds corresponded with the number of
+currents which produced them. Again, the electric
+vibrators devised by MM. Macaulay, Wagner,
+Neef, etc., and adapted to produce musical sounds,
+between 1847–1852, by MM. Froment and Pétrina,
+showed that the problem of transmitting sounds
+to a distance was not insoluble. Yet, up to 1854,<span class="pagenum" id="Page_4">4</span>
+no one had ventured to admit the possibility
+of transmitting speech by electricity, and when
+M. Charles Bourseul published in that year a paper
+on the electric transmission of speech, the idea
+was regarded as a fanciful dream. I confess
+that I myself thought it incredible, and when I
+produced the paper in the first edition of my account
+of the applications of electricity, published
+in 1854, I felt bound to add that the scheme
+seemed more than doubtful. Yet, as the paper
+was thoughtfully written, I had no hesitation in
+publishing it, affixing the signature of CH. B.
+Events justified this daring idea, and although it
+did not include the only principle which could lead
+to the reproduction of articulate sounds, yet it was
+the germ of the fertile invention which has made
+the names of Graham Bell and Elisha Gray famous.
+For this reason I will again quote M. Charles
+Bourseul’s paper.</p>
+
+<p>‘After the telegraphic marvels which can reproduce
+at a distance hand-writings, or even more
+or less complicated drawings, it may appear impossible
+to penetrate further into the region of the
+marvellous. Yet we will try to advance a few
+steps further. I have, for example, asked myself
+whether speech itself may not be transmitted by
+electricity—in a word, if what is spoken in Vienna
+may not be heard in Paris. The thing is practicable
+in this <span class="locked">way:—</span></p>
+
+<p>‘We know that sounds are made by vibrations,<span class="pagenum" id="Page_5">5</span>
+and are adapted to the ear by the same vibrations
+which are reproduced by the intervening medium.
+But the intensity of the vibrations diminishes very
+rapidly with the distance: so that it is, even with
+the aid of speaking-tubes and trumpets, impossible
+to exceed somewhat narrow limits. Suppose that
+a man speaks near a moveable disk, sufficiently
+flexible to lose none of the vibrations of the voice,
+that this disk alternately makes and breaks the
+currents from a battery: you may have at a
+distance another disk, which will simultaneously
+execute the same vibrations.</p>
+
+<p>‘It is true that the intensity of the sounds produced
+will be variable at the point of departure, at
+which the disk vibrates by means of the voice, and
+constant at the point of arrival, where it vibrates by
+means of electricity; but it has been shown that
+this does not change the sounds. It is, moreover,
+evident that the sounds will be reproduced at the
+same pitch.</p>
+
+<p>‘The present state of acoustic science does not
+permit us to declare <i lang="la">à priori</i> if this will be precisely
+the case with syllables uttered by the human voice.
+The mode in which these syllables are produced
+has not yet been sufficiently investigated. It is
+true that we know that some are uttered by the
+teeth, others by the lips, and so on; but this is
+all.</p>
+
+<p>‘However this may be, observe that the syllables
+can only reproduce upon the sense of hearing the<span class="pagenum" id="Page_6">6</span>
+vibrations of the intervening medium: reproduce
+precisely these vibrations, and you will reproduce
+precisely these syllables.</p>
+
+<p>‘It is, at all events, impossible in the present
+condition of science to prove the impossibility of
+transmitting sound by electricity. Everything
+tends to show, on the contrary, that there is such
+a possibility. When the application of electro-magnetism
+to the transmission of messages was
+first discussed, a man of great scientific attainments
+treated the idea as utopian, and yet there is now
+direct communication between London and Vienna
+by means of a simple wire. Men declared it to be
+impossible, but so it is.</p>
+
+<p>‘It need not be said that numerous applications
+of the highest importance will immediately arise
+from the transmission of speech by electricity.
+Any one who is not deaf and dumb may use this
+mode of transmission, which would require no apparatus,
+except an electric battery, two vibrating
+disks, and a wire. In many cases, as for example
+in large establishments, orders might be transmitted
+in this way, although transmission by
+electricity will not be used while it is necessary to
+go from letter to letter, and to make use of telegraphs
+which require use and apprenticeship.
+However this may be, it is certain that in a more
+or less distant future, speech will be transmitted by
+electricity. <em>I have made some experiments in this
+direction</em>: they are delicate, and demand time and<span class="pagenum" id="Page_7">7</span>
+patience, but <em>the approximations obtained</em> promise a
+favourable result.’</p>
+
+<p>This description is certainly not full enough to
+enable us to discern from it the arrangement
+which would lead to the solution of the problem,
+and if the vibrations of the disk at the receiving
+station were to follow from making and breaking
+the current at the sending-station, under the
+influence of vibrations caused by the voice, they
+would only produce musical, and not articulate
+sounds. Yet the idea was magnificent, as Mr.
+Preece said, even when he thought it impossible to
+realise it. Besides, it is easy to see that M. Bourseul
+himself was not deceived as to the difficulties
+of the problem, as far as articulate sounds are
+concerned, for he points out, as we have seen, the
+difference existing between the simple vibrations
+which produce musical sounds, and the complex
+vibrations which cause articulate sounds; but,
+as he justly said: ‘Reproduce at the one end of
+the line the vibrations of air caused at the other,
+and speech will be transmitted, however complex
+the mechanism may be by which it is effected.’
+We shall presently see how the problem was solved,
+and it is probable that some attempts had already
+enabled M. Bourseul to anticipate the solution of
+the question; but there is nothing in his paper to
+show what were the means he proposed, so that
+the discovery of the electric transmission of speech
+cannot reasonably be ascribed to him, and we do<span class="pagenum" id="Page_8">8</span>
+not understand why we should be reproached for
+having at that time failed to appreciate the importance
+of a discovery which seemed to be then
+only within the range of fancy.</p>
+
+<p>It was not until 1876 that the problem of the
+electric transmission of speech was finally solved,
+and the discovery has lately given rise to an interesting
+controversy as to priority between Mr.
+Elisha Gray, of Chicago, and Mr. Graham Bell, on
+which we must say a few words.</p>
+
+<p>As early as 1874 Mr. Elisha Gray was occupied
+with a system of musical telephone, which he
+wished to apply to manifold telegraphic transmissions,
+and the investigations which he made,
+in order to establish this system under the best
+possible conditions, gave him a glimpse of the
+possibility of transmitting articulate words by electricity.
+While carrying on his experiments on the
+telegraphic system, he arranged in fact, about the
+15th January, 1876, a system of <em>speaking telephone</em>,
+and he deposited the specification and drawings in
+the American Patent Office, in the form of a
+<i lang="la">caveat</i> or provisional specification. The deposit
+was made on the 14th February, 1876: on the very
+same day, Mr. Graham Bell also deposited, in the
+American Patent Office, a request for a patent in
+which he spoke of an instrument of the same kind,
+but with special application to simultaneous telegraphic
+transmissions by means of a telephonic
+apparatus; and the few words which could, in this<span class="pagenum" id="Page_9">9</span>
+specification, refer to a telephone with articulate
+sounds, applied to an instrument which, by Mr.
+Bell’s own admission, had not produced any satisfactory
+results. In Mr. Gray’s <i lang="la">caveat</i>, on the
+contrary, the application of the instrument to the
+electric transmission of speech alone is indicated,
+the description of the system is complete, and the
+drawings which accompany it are so exact, that a
+telephone made from them would work perfectly:
+this was proved by Mr. Gray himself, when, some
+time afterwards, he finished his instruments, which
+differed in no respect from the one described in Mr.
+Bell’s statement as worked by a battery. On these
+grounds Mr. Elisha Gray would certainly have
+obtained the patent, if the expiration of his <i lang="la">caveat</i>
+had not been the result of an omission of form in
+the Patent Office, which, as we know, decides the
+priority of inventions in America. An action on the
+ground of this omission has lately been brought
+against Mr. Bell, in the Supreme Court of the
+American Patent Office, to set aside the patent
+granted to him. If Mr. Gray did not appeal before,
+it was because he was then wholly occupied with
+experiments on the system of harmonic telephone,
+applied to telegraphic communication, and he had
+no time to attend to the matter.</p>
+
+<p>However this may be, Mr. Bell did not begin
+to give serious attention to the speaking telephone
+until he had obtained his patent, and his efforts
+were soon crowned with success: a few months<span class="pagenum" id="Page_10">10</span>
+later, he exhibited his speaking telephone at
+Philadelphia, which has from that time attracted so
+much public attention, and which, when perfected
+in a practical point of view, reached Europe in the
+autumn of 1877 under the form we know.</p>
+
+<p>To complete this summary account of the
+telephone, we ought to say that since its success
+a good many claims of priority have arisen, as if
+by enchantment. Mr. John Camack, of English
+origin, has among others claimed the invention
+of the telephone, not merely relying on the description
+he gave of the instrument in 1865, but on the
+drawings he executed; he even adds, that if he had
+not lacked means for its construction, this would
+have been the date of the discovery of the telephone.
+A similar pretension has been put forward
+by Mr. Dolbear, a fellow countryman of Mr. Bell,
+of whose claim we shall speak presently.</p>
+
+<p>Signor Manzetti, of Aosta, says the same thing,
+asserting that his telephonic invention was described
+in several newspapers of 1865, among others in
+‘Le Petit Journal,’ of Paris, on the 22nd November,
+1865; ‘Il Diritto’ at Rome, 16th July, 1865;
+‘L’Echo d’Italia,’ New York, 9th August, 1865;
+‘L’Italia,’ Florence, 10th August, 1865; ‘La Comuna
+d’Italia,’ Genoa, 1st December, 1865; ‘La
+Verità,’ Novara, 4th January, 1866; ‘Il Commercio,’
+Genoa, 6th January, 1866. It is true that
+no description of the system was given, and that the
+journals in question only asserted that experiments<span class="pagenum" id="Page_11">11</span>
+had been made, which proved that the practical solution
+of the problem of transmitting speech by electricity
+became possible by this system. At any rate
+M. Charles Bourseul must still have the credit of the
+priority of the idea, and, in our opinion, all claims
+made after the fact only merit slight consideration.</p>
+
+<p>Before considering Bell’s telephone, and the
+different modifications which have been applied to
+it, it seems worth while, in order to make the
+reader perfectly familiar with these kinds of instruments,
+to study the electro-musical telephones
+which preceded it, and especially that of M. Reiss,
+which was made in 1860, and became the starting
+point of all the others. We shall find that these
+instruments have very important applications, and
+that telegraphy will probably be one day much
+advanced by their use.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h2 class="nobreak" id="MUSICAL_TELEPHONES"><span id="toclink_11"></span>MUSICAL TELEPHONES.</h2>
+</div>
+
+<p><i>Telephone of M. Reiss.</i>—This telephone is, as
+far as the reproduction of sound is concerned,
+based upon Mr. Page’s discoveries in 1837, and, as
+regards electric transmission, it is based on the
+vibrating membrane of which Mr. L. Scott made
+use in his phonautograph, in 1855. This instrument
+is composed, like telegraphic systems, of two
+distinct parts, a sender and a receiver, as represented
+in <a href="#il_1">fig. 1</a>.</p>
+
+<p><span class="pagenum" id="Page_12">12</span></p>
+
+<figure id="il_1" class="figcenter" style="max-width: 26em;">
+  <img src="images/i_p012.jpg" width="1016" height="889" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 1.</span>
+  </figcaption>
+</figure>
+
+<p>The sender was virtually composed of a sounding
+box <span class="allsmcap">K</span>, having on its upper surface a large
+circular opening, across which a membrane was
+stretched, and in its centre there was fitted a thin
+disk of platinum <i>o</i>, above which a metallic point <i>c</i>
+was fixed, and this, together with the disk, constituted
+the contact-breaker. On one face of the
+sounding-box <span class="allsmcap">K</span>, there was a sort of speaking-tube,
+for the purpose of collecting the sound, and directing
+it to the interior of the box, in order that it<span class="pagenum" id="Page_13">13</span>
+might then react upon the membrane. Part of
+the box <span class="allsmcap">K</span> is broken away in the plate, in order
+that the different parts of which it is made may be
+seen.</p>
+
+<p>The rods <i>a</i>, <i>c</i>, which support the platinum point
+<i>b</i>, are in metallic contact with a Morse key <i>t</i>,
+placed on the side of the box <span class="allsmcap">K</span>, and with an electro-magnet
+<span class="allsmcap">A</span>, which belongs to a telegraphic system,
+intended to exchange the signals required to start
+the action of the two instruments at their respective
+stations.</p>
+
+<p>The receiver consists of a sounding-box <span class="allsmcap">B</span>, on
+which rest two supports <i>d</i>, <i>d</i>, bearing an iron rod
+of the thickness of a knitting needle. An induction
+coil of insulated wire <i>g</i> is wound round this rod, and
+the whole is enclosed by the lid <span class="allsmcap">D</span>, which concentrates
+the sound already increased by the sounding-box:
+for this purpose the box is provided with
+two openings below the coil.</p>
+
+<p>The circuit is completed through the primary
+of this coil by the two terminals 3 and 4, and a
+Morse key <i>t</i> is placed at the side of box <span class="allsmcap">B</span>, in order
+to exchange signals.</p>
+
+<p>In order to work this system, the speaking
+instrument should be placed before the opening
+<span class="allsmcap">T</span>, and this instrument may be a flute, a violin,
+or even the human voice. The vibrations of air
+occasioned by these instruments cause the telephonic
+membrane to vibrate in unison, and the
+latter, rapidly moving the platinum disk <i>o</i> to and<span class="pagenum" id="Page_14">14</span>
+from the point <i>b</i>, causes a series of breaks in the
+current, which are repeated in the iron wire <i>d d</i>,
+and transformed into metallic vibrations, of which
+the number is equal to that of the sounds successively
+produced.</p>
+
+<p>According to this mode of action, the possibility
+of transmitting sounds with their relative value
+becomes intelligible: but it is equally clear that
+sounds thus transmitted will not have the <em>timbre</em>
+of those which produce them, since the <em>timbre</em> is
+independent of the number of vibrations, and it
+must be added that the sounds produced by M.
+Reiss’s instrument were as shrill as those of a
+child’s penny trumpet, and by no means attractive.
+The problem of transmitting musical sounds by
+electricity was, however, really solved, and it can be
+said with truth that an air or a melody could be
+heard at any given distance.</p>
+
+<p>The invention of this telephone dates, as we
+have seen, from 1860, and Professor Heisler speaks
+of it in his treatise of technical physics, published
+at Vienna in 1866; he even asserts, in the article
+which he devotes to the subject, that although the
+instrument was still in its infancy, it was capable
+of transmitting vocal melodies, and not merely
+musical sounds. The system was afterwards perfected
+by M. Van der Weyde, who, after reading
+the account published by M. Heisler, sought to
+make the box of the sender more sonorous, and
+to strengthen the sounds produced by the receiver.<span class="pagenum" id="Page_15">15</span>
+He writes as follows in the ‘American Scientific
+Journal:’</p>
+
+<p>‘In 1868, I caused two telephones to be made,
+similar to those I have described, and I exhibited
+them at a meeting of the Polytechnic Club of the
+American Institute. The transmitted sounds were
+produced at the farthest extremity of the Cooper
+Institute, quite outside the hall in which the
+audience sat: the receiver was placed on a table
+in the hall itself. The vocal airs were faithfully
+reproduced, but the sound was rather weak and
+nasal. I then tried to improve the instrument, and
+I first obtained stronger vibrations in the box <span class="allsmcap">K</span>
+by causing reverberation from the sides of the
+box, by means of hollow partitions. I next intensified
+the sounds produced by the receiver,
+by introducing several iron wires into the coil,
+instead of one. These improvements were submitted
+to the meeting of the American Association
+for the Advancement of Science, which was held in
+1869, and it was considered that the invention
+contained the germ of a new method of telegraphic
+transmission which might lead to important results.’
+This opinion was soon afterwards justified by the
+discoveries of Bell and Elisha Gray.</p>
+
+<p><i>Messrs. Cecil and Leonard Wray’s Telephone.</i>—This
+system, represented in <a href="#il_2">figs. 2</a> and <a href="#il_3">3</a>, is simply
+an improvement on that of M. Reiss, with the
+object of intensifying the effects produced. The
+sender is provided with two membranes, instead<span class="pagenum" id="Page_16">16</span>
+of one; and its receiver, instead of being formed of
+a single iron wire covered with a magnetising
+coil, is composed of two distinct coils <span class="allsmcap">H</span>, <span class="allsmcap">H′</span> (<a href="#il_2">fig. 2</a>),
+placed in the same straight line, and within which
+are two iron rods. These rods are fastened by one
+of their ends to two copper disks <span class="allsmcap">A</span>, <span class="allsmcap">B</span>; these disks
+are maintained in a fixed position by screws <span class="allsmcap">I</span>, <span class="allsmcap">I′</span>,
+and the two other extremities of the rods, between
+the coils, are opposite each other, not touching,
+but divided by a very small interval. The instrument
+is set upon a sounding-box, in which there is
+a hole <span class="allsmcap">T</span> in the space corresponding to the interval
+between the coils: these coils communicate with
+four terminals, which are connected with the electric
+current in such a way that the adjacent poles of
+the two rods are of opposite polarity, thus forming
+a single magnet, divided in the centre. It seems
+that by this arrangement the sound produced becomes
+much more distinct.</p>
+
+<figure id="il_2" class="figcenter" style="max-width: 20em;">
+  <img src="images/i_p016.jpg" width="765" height="377" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 2.</span>
+  </figcaption>
+</figure>
+
+<figure id="il_3" class="figcenter" style="max-width: 23em;">
+  <img src="images/i_p017.jpg" width="904" height="779" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 3.</span>
+  </figcaption>
+</figure>
+
+<p>The form of the sender also is somewhat<span class="pagenum" id="Page_17">17</span>
+different from the one we have previously described:
+the upper part, instead of being horizontal, is rather
+inclined, as it appears in <a href="#il_3">fig. 3</a>, and the opening <span class="allsmcap">E</span>
+through which the sound has to communicate with
+the vibrating membrane, occupies a great part of
+the upper surface of the box, which consequently
+appears to be somewhat oblique. The second
+membrane <span class="allsmcap">G</span>, which is of caoutchouc, forms a sort
+of partition which divides the box in two, starting
+from the upper end of the opening: the inventor
+states that this will protect the outer membrane <span class="allsmcap">D</span>
+from the breath and other injurious effects, while
+increasing the force of the vibrations produced on<span class="pagenum" id="Page_18">18</span>
+the first membrane, as in a drum. The contact-breaker
+itself also differs from the one in M. Reiss’s
+instrument. The platinum disk <i>b</i> is only placed
+in circuit by means of two slender wires of platinum
+or steel, which are immersed in two small cups,
+filled with mercury, and connected with the circuit.
+In this way, the movements of the membrane <span class="allsmcap">D</span>
+are free, and its vibration is rendered more easy.</p>
+
+<p>The circuit is also broken by a little platinum
+point resting on a lever with a spring-joint, <span class="allsmcap">K H</span>,
+which is above the disk: one end of the lever,
+which is fixed below a kind of Morse key <span class="allsmcap">M I</span>,
+makes it possible to close the circuit with the
+hand, so as to give the signal for setting the
+apparatus to work.</p>
+
+<p><i>Electric Harmonica.</i>—Long before M. Reiss’s
+invention, and consequently still longer before that
+of Mr. Elisha Gray, I mentioned a sort of electric
+harmonica, and described it as follows in the first
+edition of my ‘Exposé des applications de l’Electricité,’
+published in <span class="locked">1853:—</span></p>
+
+<p>‘The power possessed by electricity to set
+metallic plates in motion and cause their vibration
+has been used for the production of distinct sounds,
+which can be combined and harmonised; but in
+addition to this purely physical application, electro-magnetism
+has come to the aid of certain instruments,
+such as pianos, organs, &amp;c., rendering
+them capable of being played at a distance. So
+that this extraordinary force may be turned to<span class="pagenum" id="Page_19">19</span>
+account in arts which are apparently the least susceptible
+of any application of electricity.</p>
+
+<p>‘We have already spoken of M. de la Rive’s
+contact-breaker. It is, as we know, an iron disk,
+soldered to a steel spring, and maintained in a
+fixed position opposite to an electro-magnet by
+another spring in connection with one branch of
+the current. As the other branch, after passing
+into the wire of the electro-magnet, terminates
+in the iron disk itself, the electro-magnet is only
+active at the moment when the disk touches the
+terminal spring; at the moment of leaving it, the
+magnetism ceases, and the iron disk returns to its
+normal position, and then leaves it again. In this
+way a vibration is produced, rapid in proportion
+to the small size of the vibrating disk, and to the
+greatness of the force produced by the approach of
+the disk to the electro-magnet.</p>
+
+<p>‘In order to increase the acuteness of the
+sounds, one or other of these expedients must be
+employed. The simplest way is to use a screw
+which can be tightened or relaxed at pleasure,
+and which in this manner removes the vibrating disk
+to a greater or less distance from the electro-magnet.
+This is the case in M. Froment’s instrument, and
+by this means he has obtained sounds of extraordinary
+acuteness, although not unpleasant to
+the ear.</p>
+
+<p>‘M. Froment has not applied the apparatus to
+a musical instrument, but it is evident that it would<span class="pagenum" id="Page_20">20</span>
+be easy to do so; it would only be necessary to
+make the notes of a key-board act on metallic
+levers, of a length corresponding to the position
+required by the disk for the vibration of different
+tones. These different levers, resting on the disk,
+would act as a point of contact, but the point
+would vary in position, according to the touch.</p>
+
+<p>‘If the current were constant, such an instrument
+would certainly have many advantages over
+the pipe instruments which are in use, since the
+vibration might be prolonged at will in the case of
+each note, and the sounds would be softer; unfortunately
+the irregular action of the battery
+makes it difficult in practice. These kinds of
+instruments are therefore only used as a means of
+regulating by ear the force of the battery, a much
+more convenient regulator than the rheometers,
+since it is possible to estimate by them the variations
+of the battery during an experiment without
+any distraction of the mind.’</p>
+
+<p>In 1856 M. Pétrina, of Prague, invented an
+analogous arrangement, to which he gave the name
+of electric harmonica, although, strictly speaking, he
+had not thought of it as a musical instrument. This
+is what I have said on the subject in vol. iv. of the
+second edition of my ‘Exposé des applications de
+l’Electricité,’ published in <span class="locked">1859:—</span></p>
+
+<p>‘The principle of this instrument is similar to
+that of Neef’s rheotome, in which the hammer is
+replaced by slender rods, whose vibrations produce<span class="pagenum" id="Page_21">21</span>
+a sound. Four of these rods are placed side by
+side, and when moved by keys, and arrested by
+levers, produce combined sounds of which the origin
+may be easily shown.’</p>
+
+<p>It is true that nothing is said in this passage
+of the capability possessed by these instruments
+of being played at a distance; but this idea was
+quite legitimate, and German periodicals assert
+that it was accomplished by M. Pétrina even before
+1856. It was the result of what I said at the outset:
+‘that electro-magnetism may come to the aid of
+certain instruments, such as pianos, organs, &amp;c.,
+<em>in order to enable them to be played at a distance</em>,’ and
+I also pointed out the expedients employed for the
+purpose, and even for setting them at work, under
+the influence of a small musical box. I did not,
+however, ascribe importance to the matter, and it is
+only by way of historical illustration that I speak
+of these systems.</p>
+
+<p><i>Telephone by Mr. Elisha Gray, of Chicago.</i>—This
+system, invented in 1874, is in reality only an instrument
+of the nature of those which preceded it, but
+with important modifications, which made it possible
+to apply it usefully to telegraphy. In an early
+model, he made use of an induction coil, with
+two helices, one over the other: the contact-breaker,
+which was vibrating, was multiple, and so arranged
+as to produce vibrations numerous enough to emit
+sounds. These sounds may, as we have seen, be
+modified by this arrangement, according to the<span class="pagenum" id="Page_22">22</span>
+mode in which the instrument is adjusted, and if
+there are a certain number of such contact-breakers
+side by side, with vibrating disks so ordered as to
+produce the different notes of the scale on several
+octaves, it becomes possible, by a combination of
+certain notes, to execute on this new kind of instrument
+a piece of music such as may be produced
+by an harmonium, an accordion, or any other instrument
+with blowers. The contact-breakers are set
+in motion by means of the primary current of
+the induction coil, as it circulates through one or
+other of the electro-magnets of these contact-breakers,
+actuated by the lowering of the notes of
+a key-board connected with them, and the secondary
+currents which arise in the coil, in consequence
+of the interruptions in the primary currents,
+transmit the corresponding vibrations to a remote
+receiver. There is an analogy between this instrument
+and the telephones of which we have already
+spoken by Reiss and Wray, but the effect is increased
+by Mr. Gray’s modifications.</p>
+
+<p>We represent in <a href="#il_4">fig. 4</a> the arrangement of the
+first system. The vibrators are <span class="allsmcap">A</span> and <span class="allsmcap">A′</span>, the
+key-board <span class="allsmcap">M</span> and <span class="allsmcap">M′</span>, the induction coil <span class="allsmcap">B</span>, and
+the receiver <span class="allsmcap">C</span>. This receiver consists, as we
+see, of a simple electro-magnet <span class="allsmcap">N N′</span>: above its
+poles there is a metal cylindrical case <span class="allsmcap">C</span>, of which
+the bottom is made of iron, to serve as an armature.
+This box, like a violin, is pierced with
+two holes in the form <span class="allsmcap">S</span>, to serve as a sounding-board;<span class="pagenum" id="Page_23">23</span>
+and Mr. Elisha Gray has ascertained that
+the molecular motion which takes place in the
+magnetic core and its armature, under the influence
+of alternate magnetisation and demagnetisation,
+sufficed to produce vibrations corresponding
+to the velocity of these alternations, and to emit
+sounds which became audible when they were magnified
+by the sounding-board.</p>
+
+<figure id="il_4" class="figcenter" style="max-width: 23em;">
+  <img src="images/i_p023.jpg" width="891" height="862" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 4.</span>
+  </figcaption>
+</figure>
+
+<p>It is quite intelligible that the effect obtained
+in this system might be reproduced, if, instead of
+contact-breakers or electric rheotomes, mechanical<span class="pagenum" id="Page_24">24</span>
+contact-breakers were used at the sending station,
+so arranged as to furnish the requisite number
+of breaks in the current which communicates the
+vibrations of the different notes of the scale. In
+this way also it would be possible to dispense
+with the induction coil, by causing the current
+which has been broken by the mechanical contact-breaker
+to react upon the receiver. Mr. Elisha
+Gray has moreover made a different arrangement
+of this telephonic system, which he has applied to
+telegraphy for simultaneous electric transmissions,
+of which we shall speak presently.</p>
+
+<p>If we may believe Mr. Elisha Gray, the vibrations
+transmitted by the secondary currents would
+be capable, by the intervention of the human body,
+of causing the sounds to be reproduced at a distance
+by conducting disks, which vibrate readily, and are
+placed on a sounding-box. In this way musical
+sounds may be evoked from copper cylinders placed
+upon a table, from a metallic disk fastened to a kind
+of violin, from a membrane stretched on a drum, or
+from any other resonant substance, by touching any
+of these objects with one hand, while holding the
+end of the line with the other. These sounds,
+of which the quality must vary with the substance
+touched, would reproduce the transmitted note with
+the precise number of vibrations which belong to it.<a id="FNanchor_1" href="#Footnote_1" class="fnanchor">1</a></p>
+
+<p><span class="pagenum" id="Page_25">25</span></p>
+
+<p><i>Mr. Varley’s Telephone.</i>—This is, strictly speaking,
+merely a musical telephone of the same kind
+as that of Mr. Gray, but the arrangement of the
+receiver is original and interesting. This part of
+the instrument essentially consists of a drum of
+large size (three or four feet in diameter), within
+which is a condenser formed of four sheets of tinfoil,
+divided by sheets of some insulating material,
+and with a surface of about half the size of the
+drum. The plates of the condenser are placed
+parallel to the membranes of the drum, and very
+little removed from its surface.</p>
+
+<p>If an electric charge is communicated to one of
+the series of conducting plates of the condenser,
+those which correspond to it are attracted, and if
+they were movable they might communicate to
+the intervening strata of air a movement which, on
+reaching the membranes of the drum, might, by a
+series of charges in rapid succession, cause the
+membranes to vibrate, and thus produce sounds:
+these sounds would correspond to the number of<span class="pagenum" id="Page_26">26</span>
+charges and discharges which had occurred. Since
+these charges and discharges are determined by the
+contact of the two plates of the condenser, at the
+extremities of the secondary circuit of an induction
+coil, of which the primary circuit has been duly
+broken, it becomes evident that, in order to cause
+the drum to emit any given sound, it will be enough
+to produce the number of vibrations in the contact-breaker
+of the induction coil which are required for
+this sound.</p>
+
+<p>The means employed by Mr. Varley to produce
+these interruptions are the same which are in use
+in several electrical instruments, and especially in
+chronographs—an electro-magnetic tuning-fork, regulated
+so as to emit the sound required. This
+tuning-fork may, by acting as contact-breaker, react
+on the primary current of the induction coil; if the
+number of the tuning-forks equals that of the musical
+notes which are to be transmitted, and if the electro-magnets
+which set them in motion are connected
+with the key-board of a piano, it would be possible
+to transmit a melody to a distance by this system,
+as well as by that of Mr. Elisha Gray.</p>
+
+<p>The peculiarity of this system consists in the
+reproduction of sounds by the action of a condenser,
+and we shall presently see that this idea, adopted
+by Messrs. Pollard and Gamier, led to interesting
+results.</p>
+
+<p><i>Singing Condenser of MM. Pollard and Garnier.</i>—This
+instrument, which astonishes all who<span class="pagenum" id="Page_27">27</span>
+hear it, attracted public attention in London some
+time ago. It is difficult to say why its fame was
+not greater, since much attention has been bestowed
+on less curious instruments. It is a fact that we
+have been able, thanks to MM. Pollard and Garnier,
+to hear songs issue from a sort of copy-book, so as
+to become audible throughout the room. The
+songs thus reproduced are certainly not always
+perfectly true; yet when the person who sings into
+the sender is a musician, and understands how
+to make use of it, the condenser in question will
+emit sounds somewhat resembling those of the
+violoncello or the hautbois.</p>
+
+<p>The singing instrument consists of a condenser
+<span class="allsmcap">K</span>, formed of thirty sheets of paper, laid one over
+the other, from nine to thirteen centimètres in
+thickness: between these, twenty-eight sheets of
+tinfoil, from six to twelve centimètres thick, are
+intercalated, so joined as to form the two plates
+of the condenser. For this purpose the pair sheets
+are joined together at one end of the copy-book,
+and the odd sheets at the other end. This system
+is fastened to a stiff <em>carton</em>, after taking care to bind
+it with a strip of paper, and the sheets of tinfoil
+are joined to the two ends of the condenser by two
+copper rims <span class="allsmcap">D</span>, <span class="allsmcap">D</span>, which are provided with terminals
+for the circuit wire, and in this way the singing
+instrument is constructed. A somewhat heavy
+weight, placed upon the condenser to compress the
+sheets, does not in any way prevent it from working;<span class="pagenum" id="Page_28">28</span>
+and this vitiates the theory first put forward
+to explain its effects, that the sheets were moved
+by attraction.</p>
+
+<figure id="il_5" class="figcenter" style="max-width: 22em;">
+  <img src="images/i_p028.jpg" width="865" height="1079" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 5.</span>
+  </figcaption>
+</figure>
+
+<p>The sending instrument consists of a sort
+of telephone without a handle, <span class="allsmcap">E</span>, of which the
+vibrating disk is formed of a very thin plate of tin.
+A cylindrical piece of carbon <span class="allsmcap">C</span> is fastened to its
+centre, and is supported by another cylinder of the<span class="pagenum" id="Page_29">29</span>
+same material <span class="allsmcap">H</span>. This rests on a transverse piece
+of wood <span class="allsmcap">A B</span>, jointed on the side <span class="allsmcap">A</span>, on the edge
+opposite to the box, by means of a regulating screw
+<span class="allsmcap">V</span>. An arched spring <span class="allsmcap">R</span> (the end of a watch spring)
+placed across this piece of wood gives it a certain
+elasticity beneath the pressure, and this elasticity is
+necessary in order that the instrument may act
+properly, and it thus becomes a sort of microphone
+with a diaphragm.</p>
+
+<p>The tin plate is put into communication with
+one pole of a battery <span class="allsmcap">P</span>, of six Leclanché cells, and
+the lower carbon cylinder <span class="allsmcap">H</span> corresponds to the
+primary helix of an induction coil <span class="allsmcap">M</span>, previously
+connected with the second pole of the battery:
+Finally, the two extremities of the secondary helix
+of the coil, <i>a</i> and <i>b</i>, are in immediate connection
+with the two plates <span class="allsmcap">D</span>, <span class="allsmcap">D</span>, of the condenser.</p>
+
+<p>This secondary helix should consist of twenty
+strands of wire No. 32, covered with silk, and the
+primary helix is made of five strands of wire No.
+16. The length of the coil should not exceed
+seven centimètres and the diameter of the core of
+fine iron wire ought to be about one centimètre.</p>
+
+<p>In order to produce song on the condenser,
+the sender must be so regulated that the two
+carbons <span class="allsmcap">C</span> and <span class="allsmcap">H</span> do not touch each other in their
+normal condition, but they should be so close that
+in singing the vibrations of the disk <span class="allsmcap">L L</span> may effect
+the needful contacts. The adjustment can be easily
+made by the touch, and by uttering the same note<span class="pagenum" id="Page_30">30</span>
+until it is repeated by the condenser. If three
+notes, given in succession, are faithfully reproduced,
+the instrument may be assumed to be properly
+regulated, and, in order to make it work, it is enough
+to apply the mouth to the mouthpiece as it is
+applied to a reed pipe.</p>
+
+<p>In order to obtain a satisfactory result, the disk
+of the instrument must be heard to vibrate, as in a
+<i lang="fr">flûte à l’oignon</i>. Instead of carbons, contacts of
+platinum may be used; but when arranged as we
+have described, the instrument may be employed
+for several purposes, as we shall see presently.
+This instrument is made by MM. Chardin and
+Prayer. M. Janssens has made the system more
+portable by fastening the sender, represented in
+<a href="#il_5">fig. 5</a>, to a handle in which the induction coil is
+placed: the instrument then resembles an ordinary
+telephone, and the vibration of the diaphragm is
+made more easy by piercing two holes in it. On
+the side of the sending-box, above and below the
+diaphragm, there are binding screws in connection
+with the end of the handle, since the instrument
+may be used as an ordinary telephonic sender, and
+even as a telephonic receiver.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h2 class="nobreak" id="SPEAKING_TELEPHONES"><span id="toclink_30"></span>SPEAKING TELEPHONES.</h2>
+</div>
+
+<p>We have seen that the telephones just described
+can only transmit musical sounds, since they can
+merely repeat simple vibrations, in greater or less<span class="pagenum" id="Page_31">31</span>
+number, it is true, but not in simultaneous combinations
+like those which reproduce articulate sounds.
+Up to the time of Mr. Bell’s invention, the transmission
+of speech could only take place with the aid of
+acoustic tubes, or of the string telephones of which
+we have spoken. Although these instruments have
+no connection with the object of our study in this
+work, we have thought it necessary to say a few
+words about them, since they may sometimes be
+combined with electric telephones, and also represent
+the first stage of the invention.</p>
+
+<p><i>String Telephones.</i>—These instruments, which
+have flooded the cities of Europe for several years,
+since the date of the invention was 1867, are interesting
+in themselves, and we are surprised that they
+have not hitherto taken a place in the collections of
+physical science. They are made of two metal or
+cardboard tubes, in the form of a cylindrical cone:
+one end is closed by a tightly stretched membrane
+of parchment, in the centre of which the cord or
+string intended to connect the two cylinders is
+fastened by a knot. When two such tubes are connected
+in this way, and the cord is tightly stretched,
+as in <a href="#il_6">fig. 6</a>, it is only necessary to apply one tube
+to the ear, while another speaks into the opening
+of the other tube: the words spoken by the latter
+are instantly transmitted, and it is even possible to
+converse in quite an undertone. Under these conditions
+the vibrations of the membrane affected by
+the voice are mechanically transmitted to the other<span class="pagenum" id="Page_32">32</span>
+membrane by the string, which, as Robert Hooke
+declared in 1667, is a better transmitter of sound
+than the air. In this way it is possible to communicate
+at a distance of 170 yards, and the size and
+nature of the cord have some influence. The sellers
+of these instruments say that the best results are
+obtained from silken cords, and the worst from
+those made of hemp. Cords of plaited cotton are
+usually employed for the sake of cheapness.</p>
+
+<figure id="il_6" class="figcenter" style="max-width: 23em;">
+  <img src="images/i_p032.jpg" width="887" height="729" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 6.</span>
+  </figcaption>
+</figure>
+
+<p>In some patterns, the tubes are so arranged as
+to present, between the membrane and the mouth,
+a diaphragm pierced with a hole, and the instrument
+somewhat resembles a bell with its base bored and<span class="pagenum" id="Page_33">33</span>
+closed again a little above the parchment membrane;
+but I have not observed that this pattern
+is decidedly superior to the others.</p>
+
+<p>It has also been asserted that horn-shaped tubes
+of nickel silver are to be preferred, of which I am
+equally doubtful. At any rate, these instruments
+have produced unexpected results; and although
+their practical use is very limited, they are interesting
+from a scientific point of view, and are
+instructive toys for children.</p>
+
+<p>Mr. Millar, of Glasgow, declares that the effect
+produced by these telephones depends very much
+on the nature of the string, the way in which it is
+attached, and the way in which the membrane is
+fastened to the mouthpiece.</p>
+
+<p><i>Improvements made in the String Telephone.</i>—The
+amazing effects of the Bell telephones have lately
+brought the string telephones, which were only regarded
+as children’s toys, again into fashion. Since
+they have made it possible to transmit to several
+persons the words reproduced by an electric telephone,
+means have been sought for combining
+them usefully with the latter, and the best mode of
+making them speak on a string presenting several
+angles has been sought for: it has been shown that,
+under the usual conditions, these instruments only
+speak distinctly when the string is stretched in
+a right line. To solve this problem, it occurred
+to M. A. Bréguet to make use of a sort of tambourine
+for the supports, with the string passed<span class="pagenum" id="Page_34">34</span>
+through their centre; the sound conveyed by that
+part of the string which is in connection with the
+speaking-horn causes the membrane of the tambourine
+to vibrate, which again communicates the
+vibration to the next portion of string. In this
+way the angles may be multiplied at will, and the
+string may be supported throughout the length compatible
+with this kind of telephone, which does not
+exceed 112 yards.</p>
+
+<p>M. A. Bréguet has also invented a system of relays
+to accomplish the same object. He makes the
+strings terminate in two membranes which close
+the two openings of a brass cylinder. The sounds
+reproduced on one of these membranes react
+upon the other, which vibrates under its influence,
+as if it were affected by the voice. The cylinder
+then acts as an ordinary acoustic tube, and its form
+may be varied at pleasure.</p>
+
+<p>M. A. Badet, on February 1, 1878, succeeded
+in making string telephones in an analogous
+way, and he used parchment stretched upon
+frames which acted as resonant boards. The string
+was fixed in the centre of the membrane, and made
+with it the angle desired.</p>
+
+<p>Several scientific men, among others Messrs.
+Wheatstone, Cornu, and Mercadier, have long been
+occupied about these ways of transmission by wire,
+and Messrs. Millar, Heaviside, and Nixon have
+lately made some interesting experiments, on
+which we must say a few words. Mr. Millar<span class="pagenum" id="Page_35">35</span>
+ascertained that by means of a telegraphic wire,
+stretched and connected by two copper wires with
+two vibrating disks, musical sounds might be
+conveyed to a distance exceeding 160 yards, and
+that by stretching these wires through a house,
+and connecting them with mouth-and-ear holes in
+different rooms, communication between them
+became perfectly easy.</p>
+
+<p>For the vibrating disks he employed wood,
+metal, or gutta-percha, in the form of a drum, with
+wires fixed in the centre. The sound seems to
+become more intense in proportion to the thickness
+of the wire.</p>
+
+<p>Messrs. Heaviside and Nixon, in their experiments
+at Newcastle-on-Tyne, have ascertained that
+the most effective wire was No. 4 of the English
+gauge. They employed wooden disks ⅛ inch in
+thickness, and these may be placed in any part of the
+length of the wire. When the wire was well stretched
+and motionless, it was possible to hear what was
+said at a distance of 230 yards, and it seems that
+Mr. Huntley, by using very thin iron diaphragms,
+and by insulating the line wire on glass supports,
+was able to transmit speech for 2,450 feet, in spite
+of the zigzags made by the line on its supports.</p>
+
+<p><i>Mr. Graham Bell’s Electric Telephone.</i>—Telephonic
+instruments were at this stage when Bell’s telephone
+was shown at the Philadelphia Exhibition of
+1876. Sir William Thompson did not hesitate to
+call it ‘the wonder of wonders,’ and it instantly<span class="pagenum" id="Page_36">36</span>
+attracted universal attention, although there was at
+first much incredulity as to its genuineness. This
+telephone, in fact, reproduced articulate words, a
+result which surpassed all the conceptions of physicists.
+In this case it was no longer a conception,
+to be treated as visionary until there was proof to
+the contrary: the instrument spoke, and even
+spoke so loudly that it was not necessary to apply
+the ear. Sir William Thompson spoke to this effect
+on the subject at the meeting of the British Association
+at Glasgow in September <span class="locked">1876:—</span></p>
+
+<p>‘In the department of telegraphs in the United
+States I saw and heard Mr. Elisha Gray’s electric
+telephone, of wonderful construction, which can
+repeat four despatches at the same time in the
+Morse code, and, with some improvements in
+detail, this instrument is evidently capable of a
+fourfold delivery. In the Canadian department
+I heard “To be or not to be? There’s the rub,”
+uttered through a telegraphic wire, and its pronunciation
+by electricity only made the rallying tone of
+the monosyllables more emphatic. The wire also repeated
+some extracts from New York papers. With
+my own ears I heard all this, distinctly articulated
+through the slender circular disk formed by the
+armature of an electro-magnet. It was my fellow-juryman,
+Professor Watson, who, at the other
+extremity of the line, uttered these words in a
+loud and distinct voice, while applying his mouth
+to a tightly stretched membrane provided with a<span class="pagenum" id="Page_37">37</span>
+small piece of soft iron, which executed movements
+corresponding to the sound vibrations of the air
+close to an electro-magnet introduced into the
+circuit. This discovery, the wonder of wonders
+in electric telegraphy, is due to a young fellow-countryman
+of our own, Mr. Graham Bell, a
+native of Edinburgh and now naturalised in New
+York.</p>
+
+<p>‘It is impossible not to admire the daring invention
+by which we have been able to realise with
+these simple expedients the complex problem of
+reproducing by electricity the tones and delicate
+articulations of voice and speech; and it was
+necessary, in order to obtain this result, to find out
+the means of varying the intensity of the current in
+the same proportion as the inflections of the sound
+emitted by the voice.’</p>
+
+<p>If we are to believe Mr. Graham Bell, the invention
+of the telephone was not due to a spontaneous
+and fortunate conception: it was the result of
+his long and patient studies in acoustic science, and
+of the labours of the physicists who preceded him.<a id="FNanchor_2" href="#Footnote_2" class="fnanchor">2</a>
+His father, Mr. Alexander Melville Bell, of Edinburgh,
+had studied this science deeply, and had
+even succeeded in representing with great ingenuity<span class="pagenum" id="Page_38">38</span>
+the adaptation of the vocal organs for the
+emission of sound. It was natural that he should
+instil a taste for his favourite studies into his son’s
+mind, and they made together numerous researches
+in order to discover the relations which
+exist between the different elements of speech in
+different languages, and the musical relations of
+vowels. It is true that several of these researches
+had been made by M. Helmholtz, and under
+more favourable conditions; but these studies
+were of great use to Mr. Bell when he was afterwards
+occupied with the telephone, and Helmholtz’s
+experiments, which he repeated with one of
+his friends, Mr. Hellis of London, concerning the
+artificial reproduction of vowels by means of
+electric tuning-forks, launched him into the study of
+the application of electricity to acoustic instruments.
+He first invented a system of an electric
+harmonica with a key-board, in which the different
+sounds of the scale were reproduced by electric
+diapasons of different forms, adapted to different
+notes, and which, when set in motion by the successive
+lowering of the keys, could reproduce
+sounds corresponding to the notes touched, just as
+in an ordinary piano.</p>
+
+<p>He next, as he tells us, turned his attention to
+telegraphy, and thought of making the Morse
+telegraphs audible by causing the electro-magnetic
+organ to react on sounding contacts. It is true
+that this result had already been obtained in the<span class="pagenum" id="Page_39">39</span>
+sounders used in telegraphy, but he thought that
+by applying this system to his electric harmonica,
+and by employing such an intensifying instrument
+as Helmholtz’s resonator at the receiving station,
+it would be possible to obtain through a single
+wire simultaneous transmissions which should be
+due to the action of the voice. We shall see
+presently that this idea was realised almost at the
+same time by several inventors, among others by
+M. Paul Lacour, of Copenhagen, Mr. Elisha Gray,
+of Chicago, and Messrs. Edison and Varley.</p>
+
+<p>Mr. Bell’s study of electric telephones really
+dates from this time, and he passed from complex
+to simple instruments, making a careful study of
+the different modes of vibration which arise from
+different modes of electric action. The following is an
+abstract, with the omission of more technical details,
+of the paper read by Mr. Bell to the Society of
+Telegraphic Engineers, London, October 31, 1877.</p>
+
+<p>If the intensity of an electric current is represented
+by the ordinates of a curve, and the duration
+of breaks in the current by the abscissæ, the
+given curve may represent the waves of the positive
+or negative current respectively, above and below
+the line of <span class="allsmcap">X</span>, and these waves will be more or less
+accentuated, just as the transmitted currents are
+more or less instantaneous.</p>
+
+<p>If the currents which are interrupted to produce
+a sound are quite instantaneous in their manifestation,
+the curve represents a series of isolated indentations,<span class="pagenum" id="Page_40">40</span>
+as we see in <a href="#il_7">fig. 7</a>; and if the interruptions
+are so made as only to produce differences of
+intensity, the curve is presented under the form of
+<a href="#il_8">fig. 8</a>. Finally, if the emissions of current are so
+ordered that their intensity alternately increases
+and diminishes, the curve takes the form represented
+in <a href="#il_9">fig. 9</a>. In the first case, the currents are <em>intermittent</em>;
+in the second, <em>pulsatory</em>; in the third
+case, they are <em>undulatory</em>.</p>
+
+<figure id="il_7" class="figcenter" style="max-width: 24em;">
+  <img src="images/i_p040.jpg" width="935" height="635" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 7.</span>
+  </figcaption>
+</figure>
+
+<figure id="il_8" class="figcenter" style="max-width: 26em;">
+  <img src="images/i_p041.jpg" width="1024" height="655" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 8.</span>
+  </figcaption>
+</figure>
+
+<figure id="il_9" class="figcenter" style="max-width: 26em;">
+  <img src="images/i_p041b.jpg" width="1024" height="753" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 9.</span>
+  </figcaption>
+</figure>
+
+<p>These currents are necessarily positive or negative,
+according to their position above or below the
+line <i>x</i>, and if they are alternately reversed, the
+curves present the form given in <a href="#il_10">fig. 10</a>, curves
+which essentially differ from the first, not merely
+in the different form of the indentations, but
+especially in the suppression of the extra current,<span class="pagenum" id="Page_42">42</span>
+which is always found in the pulsatory and undulatory
+currents.</p>
+
+<figure id="il_10" class="figcenter" style="max-width: 25em;">
+  <img src="images/i_p042.jpg" width="993" height="741" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 10.</span>
+  </figcaption>
+</figure>
+
+<p>The two former systems of currents have long
+been in use for the electric transmission of musical
+sounds, of which we have an interesting example
+in Reiss’s telephone already described. But Mr.
+Bell claims to have been the first to employ the
+undulatory currents, which made it possible to solve
+the problem of transmitting speech.<a id="FNanchor_3" href="#Footnote_3" class="fnanchor">3</a> In order to
+estimate the importance of this discovery, it will be
+enough to analyse the effects produced with these<span class="pagenum" id="Page_43">43</span>
+different systems of currents when several notes of
+varying pitch are to be combined.</p>
+
+<p><a href="#il_7">Fig. 7</a> shows a combination in which the styles
+<i>a</i>, <i>a′</i>, of two sending instruments cause the interruption
+of the current from the same battery
+<span class="allsmcap">B</span>, so that the given vibrations should be between
+them in the relation of a tierce major, that is in the
+relation of four to five. Under such conditions, the
+currents are intermittent, and four contacts of <i>a</i> are
+produced in the same space of time as the five
+contacts of <i>a′</i>, and the corresponding electric intensities
+will be represented by the indentations we
+see in <span class="allsmcap">A</span><sup>2</sup> and in <span class="allsmcap">B</span><sup>2</sup>: the combination of these intensities
+<span class="allsmcap">A</span><sup>2</sup> + <span class="allsmcap">B</span><sup>2</sup> will produce the indentations at
+unequal intervals which may be observed on the
+third line. It is evident that although the current
+maintains a uniform intensity, there is less time
+for the breaks when the interrupting styles act
+together than when they act separately, so that
+when there are a number of contacts effected simultaneously
+by styles working at different degrees
+of velocity, the effects produced will have the effect
+of a continuous current. The maximum number
+of distinct effects which can be produced in this
+way will, however, greatly depend on the relation
+which exists between the durations of the make
+and break of the current. The shorter the contacts
+are, and the longer the breaks, the more numerous
+will be the effects transmitted without confusion,
+and <i lang="la">vice versâ</i>.</p>
+
+<p><span class="pagenum" id="Page_44">44</span></p>
+
+<p>By the aid of pulsatory currents the transmission
+of musical sounds is effected in the way indicated
+in <a href="#il_8">fig. 8</a>, and it is seen that when they are produced
+simultaneously, the result <span class="allsmcap">A</span><sup>2</sup> + <span class="allsmcap">B</span><sup>2</sup> is analogous to
+that which would be produced by a continuous
+current of minimum intensity.</p>
+
+<p>In the case of undulatory currents the result is
+different, but in order to produce them it is necessary
+to have recourse to inductive effects, and <a href="#il_9">fig. 9</a>
+indicates the manner in which the experiment
+should be made. In this case, ‘the current from
+the battery <span class="allsmcap">B</span> is thrown into waves by the inductive
+action of iron or steel reeds <span class="allsmcap">M</span>, <span class="allsmcap">M</span>, vibrated in front
+of electro-magnets <i>e</i>, <i>e</i>, placed in circuit with the
+battery: <span class="allsmcap">A</span><sup>2</sup> and <span class="allsmcap">B</span><sup>2</sup> represent the undulations caused
+in the current by the vibration of the magnetised
+bodies, and it will be seen that there are four undulations
+of <span class="allsmcap">B</span><sup>2</sup> in the same time as five undulations
+of <span class="allsmcap">A</span><sup>2</sup>. The resultant effect upon the main line is
+expressed by the curve <span class="allsmcap">A</span><sup>2</sup> + <span class="allsmcap">B</span><sup>2</sup>, which is the algebraical
+sum of the sinusoidal curves <span class="allsmcap">A</span><sup>2</sup> and <span class="allsmcap">B</span><sup>2</sup>. A
+similar effect is produced when reversed undulatory
+currents are employed, as in <a href="#il_10">fig. 10</a>, where the current
+is produced by the vibration of permanent magnets
+united upon a circuit, without a voltaic battery.</p>
+
+<p>‘It will be understood from <a href="#il_9">figs. 9</a> and <a href="#il_10">10</a> that
+the effect of transmitting musical signals of different
+pitches simultaneously along a single wire
+is not to obliterate the vibratory character of the
+current, as in the case of intermittent and pulsatory<span class="pagenum" id="Page_45">45</span>
+currents, but to change the shapes of the electrical
+undulations. In fact, the effect produced upon the
+current is precisely analogous to the effect produced
+in the air by the vibration of the inducing
+bodies <span class="allsmcap">M</span>, <span class="allsmcap">M′</span>. Hence it should be possible to
+transmit as many musical tones simultaneously
+through a telegraph wire as through the air.’</p>
+
+<figure id="il_11" class="figcenter" style="max-width: 24em;">
+  <img src="images/i_p046.jpg" width="932" height="760" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 11.</span>
+  </figcaption>
+</figure>
+
+<p>After applying these principles to the construction
+of a telegraphic system for multiple transmissions,
+Mr. Bell lost no time in making use of
+his researches to improve the vocal training of deaf
+mutes. ‘It is well known,’ he said, ‘that deaf
+mutes are dumb merely because they are deaf,
+and that there is no defect in their vocal organs to
+incapacitate them from utterance. Hence it was
+thought that my father’s system of pictorial symbols,
+popularly known as visible speech, might prove a
+means whereby we could teach the deaf and dumb
+to use their vocal organs and to speak. The great
+success of these experiments urged upon me the
+advisability of devising methods of exhibiting the
+vibrations of sound optically, for use in teaching
+the deaf and dumb. For some time I carried on
+experiments with the manometric capsule of Koenig,
+and with the phonautograph of Léon Scott. The
+scientific apparatus in the Institute of Technology
+in Boston was freely placed at my disposal for
+these experiments, and it happened that at that
+time a student of the Institute of Technology, Mr.
+Maurey, had invented an improvement upon the<span class="pagenum" id="Page_46">46</span>
+phonautograph. He had succeeded in vibrating
+by the voice a stylus of wood about a foot in length
+which was attached to the membrane of the phonautograph,
+and in this way he had been enabled to
+obtain enlarged tracings upon a plane surface of
+smoked glass. With this apparatus I succeeded in
+producing very beautiful tracings of the vibrations
+of the air for vowel sounds. Some of these tracings
+are shown in <a href="#il_11">fig. 11</a>. I was much struck with this
+improved form of apparatus, and it occurred to me
+that there was a remarkable likeness between the
+manner in which this piece of wood was vibrated
+by the membrane of the phonautograph and the<span class="pagenum" id="Page_47">47</span>
+manner in which the <i lang="la">ossiculæ</i> of the human ear
+were moved by the tympanic membrane. I determined
+therefore to construct a phonautograph
+modelled still more closely upon the mechanism
+of the human ear, and for this purpose I sought
+the assistance of a distinguished aurist in Boston,<span class="pagenum" id="Page_48">48</span>
+Dr. Clarence J. Blake. He suggested the use of the
+human ear itself as a phonautograph, instead of
+making an artificial imitation of it. The idea was
+novel, and struck me accordingly, and I requested
+my friend to prepare a specimen for me, which he
+did. The apparatus, as finally constructed, is
+shown in <a href="#il_12">fig. 12</a>. The <em>stapes</em> was removed, and a
+stylus of hay about an inch in length was attached
+to the end of the <em>incus</em>. Upon moistening
+the <em>membrana tympani</em> and the <em>ossiculæ</em> with
+a mixture of glycerine and water, the necessary
+mobility of the parts was obtained; and upon singing
+into the external artificial ear the stylus of hay
+was thrown into vibration, and tracings were obtained
+upon a plane surface of smoked glass passed
+rapidly underneath. While engaged in these experiments
+I was struck with the remarkable disproportion
+in weight between the membrane and
+the bones that were vibrated by it. It occurred to
+me that if a membrane as thin as tissue paper
+could control the vibration of bones that were,
+compared to it, of immense size and weight, why
+should not a larger and thicker membrane be able
+to vibrate a piece of iron in front of an electro-magnet,
+in which case the complication of steel
+rods shown in my first form of telephone, could be
+done away with, and a simple piece of iron attached
+to a membrane be placed at either end of the
+telegraphic circuit?</p>
+
+<figure id="il_12" class="figcenter" style="max-width: 24em;">
+  <img src="images/i_p047.jpg" width="948" height="1141" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 12.</span>
+  </figcaption>
+</figure>
+
+<p>‘For this purpose I attached the reed <span class="allsmcap">A</span> (<a href="#il_13">fig. 13</a>)<span class="pagenum" id="Page_49">49</span>
+loosely by one extremity to the uncovered pole
+<i>h</i> of the magnet, and fastened the other extremity
+to the centre of a stretched membrane of goldbeaters’
+skin <i>n</i>. I presumed that upon speaking in
+the neighbourhood of the membrane <i>n</i>, it would be
+thrown into vibration and cause the steel reed <span class="allsmcap">A</span>
+to move in a similar manner, occasioning undulations
+in the electrical current that would correspond
+to the changes in the density of the air during the
+production of the sound; and I further thought
+that the change of the intensity of the current at
+the receiving end would cause the magnet there to
+attract the reed <span class="allsmcap">A′</span> in such a manner that it should
+copy the motion of the reed <span class="allsmcap">A</span>, in which case its
+movements would occasion a sound from the membrane
+<i>n′</i> similar in <em>timbre</em> to that which had occasioned
+the original vibration.</p>
+
+<figure id="il_13" class="figcenter" style="max-width: 19em;">
+  <img src="images/i_p049.jpg" width="729" height="313" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 13.</span>
+  </figcaption>
+</figure>
+
+<figure id="il_14" class="figcenter" style="max-width: 24em;">
+  <img src="images/i_p050.jpg" width="923" height="563" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 14.</span>
+  </figcaption>
+</figure>
+
+<p>‘The results, however, were unsatisfactory and
+discouraging. My friend Mr. Thomas A. Watson,
+who assisted me in this first experiment, declared
+that he heard a faint sound proceed from the telephone
+at his end of the circuit, but I was unable<span class="pagenum" id="Page_50">50</span>
+to verify his assertion. After many experiments
+attended by the same only partially successful
+results, I determined to reduce the size and weight
+of the spring as much as possible. For this purpose
+I fastened a piece of clock spring, about the size
+and shape of my thumbnail, firmly to the centre of
+the diaphragm, and had a similar instrument at the
+other end (<a href="#il_14">fig. 14</a>); we were then enabled to obtain
+distinctly audible effects. I remember an experiment
+made with this telephone, which at the time
+gave me great satisfaction and delight. One of
+the telephones was placed in my lecture-room in
+the Boston University, and the other in the basement
+of the adjoining building. One of my
+students repaired to the distant telephone to observe
+the effects of articulate speech, while I uttered
+the sentence, “Do you understand what I say?”<span class="pagenum" id="Page_51">51</span>
+into the telephone placed in the lecture-hall. To
+my delight an answer was returned through the
+instrument itself, articulate sounds proceeded from
+the steel spring attached to the membrane, and I
+heard the sentence, “Yes, I understand you perfectly.”
+It is a mistake, however, to suppose that
+the articulation was by any means perfect, and expectancy
+no doubt had a great deal to do with my
+recognition of the sentence; still, the articulation
+was there, and I recognised the fact that the indistinctness
+was entirely due to the imperfection of
+the instrument. I will not trouble you by detailing
+the various stages through which the apparatus
+passed, but shall merely say that after a time I
+produced the form of instrument shown in <a href="#il_15">fig. 15</a>,
+which served very well as a receiving telephone.
+In this condition my invention was exhibited at the
+Centennial Exhibition in Philadelphia. The telephone
+shown in <a href="#il_14">fig. 14</a> was used as a transmitting<span class="pagenum" id="Page_52">52</span>
+instrument, and that in <a href="#il_15">fig. 15</a> as a receiver, so
+that vocal communication was only established in
+one direction.</p>
+
+<figure id="il_15" class="figcenter" style="max-width: 21em;">
+  <img src="images/i_p051.jpg" width="823" height="489" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 15.</span>
+  </figcaption>
+</figure>
+
+<p>‘The articulation produced from the instrument
+shown in <a href="#il_15">fig. 15</a> was remarkably distinct, but its
+great defect consisted in the fact that it could not
+be used as a transmitting instrument, and thus two
+telephones were required at each station, one for
+transmitting and one for receiving spoken messages.</p>
+
+<p>‘It was determined to vary the construction of
+the telephone, and I sought by changing the size
+and tension of the membrane, the diameter and
+thickness of the steel spring, the size and power of
+the magnet, and the coils of insulated wire around
+their poles, to discover empirically the exact effect
+of each element of the combination, and thus to
+deduce a more perfect form of apparatus. It was
+found that a marked increase in the loudness of the
+sounds resulted from shortening the length of the
+coils of wire, and by enlarging the iron diaphragm
+which was glued to the membrane. In the latter
+case, also, the distinctness of the articulation was
+improved. Finally, the membrane of goldbeaters’
+skin was discarded entirely, and a simple iron plate
+was used instead, and at once intelligible articulation
+was obtained. The new form of instrument is
+that shown in <a href="#il_16">fig. 16</a>, and, as had been long anticipated,
+it was proved that the only use of the battery
+was to magnetise the iron core of the magnet, for<span class="pagenum" id="Page_53">53</span>
+the effects were equally audible when the battery
+was omitted and a rod of magnetised steel substituted
+for the iron core of the magnet.</p>
+
+<p>‘It was my original intention, and it was always
+claimed by me, that the final form of telephone
+would be operated by permanent magnets in place
+of batteries, and numerous experiments had been
+carried on by Mr. Watson and myself privately for
+the purpose of producing this effect.</p>
+
+<figure id="il_16" class="figcenter" style="max-width: 20em;">
+  <img src="images/i_p053.jpg" width="769" height="433" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 16.</span>
+  </figcaption>
+</figure>
+
+<p>‘At the time the instruments were first exhibited
+in public the results obtained with permanent
+magnets were not nearly so striking as when a
+voltaic battery was employed, wherefore we thought
+it best to exhibit only the latter form of instrument.</p>
+
+<p>‘The interest excited by the first published
+accounts of the operation of the telephone led many
+persons to investigate the subject, and I doubt not
+that numbers of experimenters have independently<span class="pagenum" id="Page_54">54</span>
+discovered that permanent magnets might be employed
+instead of voltaic batteries. Indeed one
+gentleman, Professor Dolbear, of Tufts College,
+not only claims to have discovered the magneto-electric
+telephone, but I understand charges me
+with having obtained the idea from him through the
+medium of a mutual friend.</p>
+
+<figure id="il_17" class="figcenter" style="max-width: 13em;">
+  <img src="images/i_p054.jpg" width="503" height="325" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 17.</span>
+  </figcaption>
+</figure>
+
+<p>‘A still more powerful form of apparatus was
+constructed by using a powerful compound horseshoe
+magnet in place of the straight rod which had
+been previously used (see <a href="#il_17">fig. 17</a>). Indeed the
+sounds produced by means of this instrument were
+of sufficient loudness to be faintly audible to a
+large audience, and in this condition the instrument
+was exhibited in the Essex Institute, in Salem,
+Massachusetts, on February 12, 1877, on which
+occasion a short speech shouted into a similar
+telephone in Boston, sixteen miles away, was heard
+by the audience in Salem. The tones of the
+speaker’s voice were distinctly audible to an
+audience of 600 people, but the articulation was<span class="pagenum" id="Page_55">55</span>
+only distinct at a distance of about 6 feet. On the
+same occasion, also, a report of the lecture was
+transmitted by word of mouth from Salem to
+Boston, and published in the papers the next
+morning.</p>
+
+<figure id="il_18" class="figcenter" style="max-width: 21em;">
+  <img src="images/i_p055.jpg" width="815" height="453" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 18.</span>
+  </figcaption>
+</figure>
+
+<p>‘From the form of telephone shown in <a href="#il_16">fig. 16</a>
+to the present form of the instrument (<a href="#il_18">fig. 18</a>) is
+but a step. It is in fact the arrangement of <a href="#il_16">fig. 16</a>
+in a portable form, the magnet <span class="allsmcap">N S</span> being placed
+inside the handle, and a more convenient form of
+mouthpiece provided.</p>
+
+<p>‘And here I wish to express my indebtedness
+to several scientific friends in America for their co-operation
+and assistance. I would specially mention
+Professor Peirce and Professor Blake, of Brown
+University, Dr. Channing, Mr. Clarke, and Mr.
+Jones. It was always my belief that a certain ratio
+would be found between the several parts of a
+telephone, and that the size of the instrument was<span class="pagenum" id="Page_56">56</span>
+immaterial; but Professor Peirce was the first to
+demonstrate the extreme smallness of the magnets
+which might be employed. The convenient form
+of mouthpiece shown in <a href="#il_17">fig. 17</a>, now adopted by
+me, was invented solely by my friend Professor
+Peirce.’</p>
+
+<figure id="il_19" class="figcenter" style="max-width: 20em;">
+  <img src="images/i_p056.jpg" width="781" height="840" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 19.</span>
+  </figcaption>
+</figure>
+
+<p>Another form of transmitting telephone exhibited
+in Philadelphia, intended for use with the
+receiving telephone (<a href="#il_15">fig. 15</a>), is represented by <a href="#il_19">fig. 19</a>.</p>
+
+<p>A platinum wire attached to a stretched membrane
+completed a voltaic circuit by dipping into
+water. Upon speaking to the membrane, articulate<span class="pagenum" id="Page_57">57</span>
+sounds proceeded from the telephone in the distant
+room. The sounds produced by the telephone
+became louder when dilute sulphuric acid, or a
+saturated solution of salt, was substituted for the
+water. Audible effects were also produced by the
+vibration of plumbago in mercury, in a solution of
+bichromate of potash, in salt and water, in dilute
+sulphuric acid, and in pure water.</p>
+
+<p>Mr. Bell goes on to say:</p>
+
+<p>‘I have found also that a musical tone proceeds
+from a piece of plumbago or retort carbon when
+an intermittent current of electricity is passed
+through it, and I have observed the most curious
+audible effects produced by the passage of reversed
+intermittent currents through the human body. A
+rheotome was placed in circuit with the primary
+wires of an induction coil, and the fine wires were
+connected with two strips of brass. One of
+these strips was held closely against the ear, and a
+loud sound proceeded from it whenever the other
+slip was touched with the other hand. The
+strips of brass were next held one in each hand. The
+induced currents occasioned a muscular tremor in
+the fingers. Upon placing my forefinger to my
+ear a loud crackling noise was audible, seemingly
+proceeding from the finger itself. A friend who
+was present placed my finger to his ear, but heard
+nothing. I requested him to hold the strips himself.
+He was then distinctly conscious of a noise
+(which I was unable to perceive) proceeding from<span class="pagenum" id="Page_58">58</span>
+his finger. In this case a portion of the induced
+currents passed through the head of the observer
+when he placed his ear against his own finger; and it
+is possible that the sound was occasioned by a vibration
+of the surfaces of the ear and finger in contact.</p>
+
+<p>‘When two persons receive a shock from a
+Ruhmkorff’s coil by clasping hands, each taking
+hold of one wire of the coil with the free hand, a
+sound proceeds from the clasped hands. The
+effect is not produced when the hands are moist.
+When either of the two touches the body of the
+other, a loud sound comes from the parts in contact.
+When the arm of one is placed against the arm of
+the other, the noise produced can be heard at a
+distance of several feet. In all these cases a
+slight shock is experienced so long as the contact
+is preserved. The introduction of a piece of paper
+between the parts in contact does not materially
+interfere with the production of the sounds, but
+the unpleasant effects of the shock are avoided.</p>
+
+<p>‘When an intermittent current from a Ruhmkorff’s
+coil is passed through the arms, a musical
+note can be perceived when the ear is closely
+applied to the arm of the person experimented
+upon. The sound seems to proceed from the
+muscles of the fore-arm and from the biceps
+muscle. Mr. Elisha Gray<a id="FNanchor_4" href="#Footnote_4" class="fnanchor">4</a> has also produced
+audible effects by the passage of electricity through
+the human body.</p>
+
+<p><span class="pagenum" id="Page_59">59</span></p>
+
+<p>‘An extremely loud musical note is occasioned
+by the spark of a Ruhmkorff’s coil when the
+primary circuit is made and broken with sufficient
+rapidity; when two rheotomes of different pitch are
+caused simultaneously to open and close the primary
+circuit, a double tone proceeds from the spark.</p>
+
+<p>‘A curious discovery, which may be of interest
+to you, has been made by Professor Blake. He
+constructed a telephone in which a rod of soft iron,
+about six feet in length, was used instead of a permanent
+magnet. A friend sang a continuous
+musical tone into the mouthpiece of a telephone,
+like that shown in <a href="#il_17">fig. 17</a>, which was connected
+with the soft iron instrument alluded to above.
+It was found that the loudness of the sound produced
+in this telephone varied with the direction in
+which the iron rod was held, and that the maximum
+effect was produced when the rod was in the position
+of the dipping-needle. This curious discovery
+of Professor Blake has been verified by myself.</p>
+
+<p>‘When a telephone is placed in circuit with a
+telegraph line, the telephone is found seemingly to
+emit sounds on its own account. The most extraordinary
+noises are often produced, the causes of
+which are at present very obscure. One class of
+sounds is produced by the inductive influence of
+neighbouring wires and by leakage from them, the
+signals of the Morse alphabet passing over neighbouring
+wires being audible in the telephone, and
+another class can be traced to earth currents upon<span class="pagenum" id="Page_60">60</span>
+the wire, a curious modification of this sound revealing
+the presence of defective joints in the wire.</p>
+
+<p>‘Professor Blake informs me that he has been
+able to use the railroad track for conversational
+purposes in place of a telegraph-wire, and he
+further states that when only one telephone was
+connected with the track the sounds of Morse
+operating were distinctly audible in the telephone,
+although the nearest telegraph-wires were at least
+forty feet distant; and Professor Peirce has observed
+the most curious sounds produced from a telephone
+in connection with a telegraph-wire during the
+aurora borealis.’</p>
+
+<p>Mr. Bell went on to describe instances in
+which airs sung or played upon a musical instrument
+are transmitted by a telephone, when it is
+not known whence they come; but the strongest
+proof of the extraordinary sensibility of this
+instrument consists in its becoming possible by its
+means to transmit speech through bodies which
+might be supposed to be non-conductors. Thus
+communication with the earth through the human
+body can be made in spite of the intervention of
+shoes and stockings; and it may even be effected
+if, instead of standing on the ground, the person
+stands on a brick wall. Only hewn stone and
+wood are a sufficient hindrance to communication,
+and if the foot touches the adjoining ground, or
+even a blade of grass, it is enough to produce
+electric manifestations.</p>
+
+<p><span class="pagenum" id="Page_61">61</span></p>
+
+<p>Mr. Bell says in conclusion:</p>
+
+<p>‘The question will naturally arise, Through
+what length of wire can the telephone be used?
+In reply to this, I may say that the maximum
+amount of resistance through which the undulatory
+current will pass, and yet retain sufficient force to
+produce an audible sound at the distant end, has
+yet to be determined; no difficulty has, however,
+been experienced in laboratory experiments in
+conversing through a resistance of 60,000 ohms,
+which has been the maximum at my disposal.
+On one occasion, not having a rheostat at hand, I
+may mention having passed the current through
+the bodies of sixteen persons, who stood hand in
+hand. The longest length of real telegraph line
+through which I have attempted to converse has
+been about 250 miles. On this occasion no
+difficulty was experienced so long as parallel lines
+were not in operation. Sunday was chosen as the
+day on which it was probable other circuits would
+be at rest. Conversation was carried on between
+myself in New York, and Mr. Thomas A. Watson
+in Boston, until the opening of business upon the
+other wires. When this happened the vocal
+sounds were very much diminished, but still audible.
+It seemed, indeed, like talking through a storm.
+Conversation, though possible, could be carried on
+with difficulty, owing to the distracting nature of
+the interfering currents.</p>
+
+<p>‘I am informed by my friend Mr. Preece that<span class="pagenum" id="Page_62">62</span>
+conversation has been successfully carried on
+through a submarine cable, sixty miles in length,
+extending from Dartmouth to the Island of
+Guernsey, by means of hand telephones.’</p>
+
+<figure id="il_20" class="figcenter" style="max-width: 23em;">
+  <img src="images/i_p062.jpg" width="906" height="742" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 20.</span>
+  </figcaption>
+</figure>
+
+<p><i>Mr. Elisha Gray’s Share in the Invention of the
+Telephone.</i>—We have seen that if Mr. Bell was the
+first to construct the speaking telephone in a practical
+form, Mr. Gray had at the same time conceived
+the idea of an instrument also capable of reproducing
+speech, and the description given of it in
+his <i lang="la">caveat</i> was so precise that if it had been made
+from his design, it would have acted perfectly.
+This was, in fact, afterwards proved by him. In
+order that our readers may judge from their own<span class="pagenum" id="Page_63">63</span>
+knowledge of the share which should be ascribed to
+Mr. Elisha Gray in the invention of the telephone,
+we reproduce in <a href="#il_20">fig. 20</a> the drawing which accompanied
+the <i lang="la">caveat</i> in question.</p>
+
+<p>The sender, as we see, is composed of a sort
+of tube, closed at its lower end by a membrane
+to which a platinum wire is fixed; this wire dips
+into a liquid of moderate conducting power, and
+an electrode made of platinum, in communication
+with a battery, is fixed at the bottom of the
+vessel containing the liquid. The receiver is composed
+of an electro-magnet, of which the armature
+is fixed to the centre of a membrane, stretched
+on a kind of resonator or ear-trumpet which is
+held to the ear, and the two instruments are united
+by the line wire as we see in the plate.</p>
+
+<p>Under these conditions, the undulatory currents
+necessary for the reproduction of speech were obtained
+in a mode analogous to that pointed out by
+Mr. Bell in his specification, that is, by the variations
+of resistance in the liquid layer interposed
+between the platinum wires of the transmitter;
+and their action, exerted on an electro-magnet, of
+which the armature was fixed on the diaphragm of
+the resonator, was produced under more favourable
+conditions than in Mr. Bell’s specification (see
+<a href="#il_13">fig. 13</a>), since that gentleman regards this arrangement
+(represented in <a href="#il_14">fig. 14</a>) as an important improvement
+on his first conception.</p>
+
+<p>The whole importance of the invention rests<span class="pagenum" id="Page_64">64</span>
+on the intervention of undulatory currents, which,
+as we have seen, are indispensable for the reproduction
+of speech, and it concerns us to know
+whether it was Mr. Bell or Mr. Gray who first declared
+their importance; for in both the specifications
+deposited on February 14, 1876, the use of
+undulatory currents was declared to be indispensable.
+Mr. Gray asserts that he had recognised
+their importance for the transmission of combined
+sounds as early as 1874; but Mr. Bell believes that
+the undulatory currents mentioned by Mr. Gray at
+that time were only currents analogous to those he
+had designated under the name of pulsatory currents,
+which we have represented in <a href="#il_8">fig. 8</a>. We
+have seen that since these currents only represent
+the abrupt elevations and depressions of intensity,
+they are unfit for the reproduction of articulate
+sounds, which, on the contrary, demand that the
+variations of intensity should result from successive
+efforts, in exact correspondence with all the
+inflections of the sonorous vibrations effected by
+the voice. Mr. Bell’s claim to priority on this question
+has been recognised by the American Patent
+Office, since he has been placed in possession of
+the patent. However this may be, Mr. Gray’s
+telephonic system was complete, and we see in it,
+as we have already said, the origin of the battery
+telephones, which have recently produced such important
+results. Let us now consider the relation
+which this system bears to Mr. Bell’s.</p>
+
+<p><span class="pagenum" id="Page_65">65</span></p>
+
+<p>The Bell system, as we have seen, although
+making use of a battery in the first instance, only
+obtained the diminution and increase of electric
+force necessary for the articulation of words by
+means of induction currents produced by the
+movements of an armature of soft iron, currents
+of which the intensity was consequently due to the
+range and inflections of these movements. The
+battery only intervened in order to communicate
+magnetic force to the inducer. This use of induced
+currents in telephonic transmissions was
+already of great importance, since various experiments
+subsequently made have proved their superiority
+to voltaic currents for this purpose. But
+experience soon convinced Mr. Bell that a powerful
+inductive apparatus worked by a battery was
+not only unnecessary for the action of this apparatus,
+but that a permanent magnet, very small and
+weak, would provide sufficient currents. This discovery,
+in which, as we have seen, Mr. Peirce had
+some share, was of great importance, since it became
+possible to reduce the size of the instrument considerably,
+so as to make it portable and adapted
+for sending and receiving; and it was shown that
+the telephone was the most sensitive of all instruments
+in revealing the action of currents. If,
+therefore, Mr. Bell was not the first to employ the
+successful mode of transmitting articulate words, it
+must be said that he sought, like Mr. Gray, to solve
+the problem by means of undulatory currents, and<span class="pagenum" id="Page_66">66</span>
+that he obtained these currents by the effect of induction,
+a system which, as soon as it was perfected,
+led to the important results with which we are all
+acquainted. If he had only given to the astonished
+world an instrument capable of reproducing
+speech telegraphically, his fame would be great;
+for this problem had hitherto been regarded as
+insoluble.</p>
+
+<p>Mr. Gray’s claims to the invention of the telephone
+are given in the following summary from
+a very interesting work, entitled ‘Experimental
+Researches on Electro-harmonic Telegraphy and
+Telephony:’</p>
+
+<p>‘1. I was the first to discover the means of
+transmitting compound sounds and variable inflections
+through a closed circuit by means of two or
+more electric waves.</p>
+
+<p>‘2. I assert that I was the first to discover and
+utilise the mode of reproducing vibrations by the
+use of a magnet receiver constantly supplied with
+electric action.</p>
+
+<p>‘3. I also assert that I was the first to construct
+an instrument consisting of a magnet with a circular
+diaphragm of magnetic substance, supported by
+its edge at a little distance from the poles of a
+magnet, and capable of being applied to the transmission
+and reception of articulate sounds.’</p>
+
+<p>It is a curious fact, worth recording here, that
+Mr. Yates, of Dublin, in 1865, when trying to improve
+Reiss’s telephone, realised to a certain extent<span class="pagenum" id="Page_67">67</span>
+Mr. Gray’s conception of the liquid transmitter; for
+he introduced into the platinum contacts of Mr.
+Reiss’s instrument a drop of water which adapted
+it for the reproduction of articulate sounds. However,
+no notice was then taken of this result.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h2 class="nobreak" id="EXAMINATION_INTO_THE_FUNDAMENTAL_PRINCIPLES"><span id="toclink_67"></span>EXAMINATION INTO THE FUNDAMENTAL PRINCIPLES
+ON WHICH BELL’S TELEPHONE IS BASED.</h2>
+</div>
+
+<p>Although the preceding account would suffice
+to make the principle of Bell’s telephone intelligible
+to persons acquainted with electric science,
+this would not be the case with the majority of
+our readers, and we therefore think it necessary
+to enter into some details as to the source of the
+electric currents which are employed in telephonic
+transmissions. These details seem to us the more
+necessary, since many persons still believe that
+Bell’s telephones are not electric, because they do
+not require a battery, and they are often confounded
+with string telephones, so that the difference
+of price between Bell’s instruments and
+those hawked in the streets seems astonishing.</p>
+
+<p>Without defining what is meant by an electric
+current, which would be too elementary, we may
+say that electric currents can be produced by different
+causes, and that, in addition to those which
+are due to batteries, strong currents are also produced
+by the force exerted by magnets on a conducting
+circuit properly arranged. Such currents<span class="pagenum" id="Page_68">68</span>
+are called induction currents, and are used in Bell’s
+telephone. In order to understand how they are
+developed under these conditions, it will be enough
+to examine what takes place when the pole of a
+magnet is brought near to, and withdrawn from, a
+closed circuit. To do this, let us suppose a copper
+wire attached to a galvanometer in the form of a
+circle, and that one pole of a permanent magnet is
+directed towards the centre of the circle. Now
+observe what happens:</p>
+
+<p>1. At the moment when the magnet approaches
+an electric current arises, causing the galvanometer
+to deviate to one side. This deviation will be great
+in proportion to the extent of the movement, and
+the tension of the current will be great in proportion
+to the abruptness of the movement. The
+current will however be only instantaneous.</p>
+
+<p>2. At the moment when the magnet is withdrawn,
+a fresh current of the same nature will arise,
+but it will appear in an opposite direction from the
+former. It will be what is called a direct current,
+because it is in the same direction as the magnetic
+current of the magnet which produces it, while the
+other current is called <em>inverse</em>.</p>
+
+<p>3. If, instead of advancing or withdrawing the
+magnet by means of a single movement, it is
+advanced in jerks, a succession of currents in the
+same direction is produced, of which the existence
+can be ascertained by the galvanometer when
+there is a sufficient interval between the movements,<span class="pagenum" id="Page_69">69</span>
+but when the intervals are very slight the currents
+are interfused; and since inverse effects take place
+when the magnet is moved in a contrary direction,
+the needle of the galvanometer follows the movements
+of the magnet, and to a certain extent
+stereotypes them.</p>
+
+<p>4. If, instead of reacting on a simple closed
+circuit, the magnet exerts its force on a considerable
+number of circumvolutions of this circuit, that
+is, on a bobbin of coiled wire, the effects will be considerably
+increased, and they will be still greater
+if there be a magnetic core within the bobbin,
+since the inducing action will then be more effectually
+exerted throughout the bobbin. As the
+magnetic core, when it is magnetised and demagnetised
+under the influence of its approach to or
+withdrawal from the inducing magnet, is subject to
+the reaction from all the fluctuations which occur in
+the movements of the magnet, the induced currents
+which ensue are perfectly defined.</p>
+
+<p>5. If, instead of a movable magnet, we suppose
+it to be fixed in the centre of the coil, the
+induced currents of which we have spoken may
+then be determined by modifying its force. In
+order to do so, it is enough that an iron armature
+should react upon its poles. When this armature
+is brought close to one of the poles, or to both at
+once, it acquires force, and produces an inverse
+current, that is, a current in the direction which
+would have corresponded to an approach of the<span class="pagenum" id="Page_70">70</span>
+magnet to the closed circuit. On its withdrawal
+the inverse effect is produced; but in both cases the
+induced currents correspond with the extent and
+direction of the movements accomplished by the
+armature, and consequently they may reproduce
+its movements by their effects. If this armature is
+an iron plate, which vibrates under the influence
+of any sound in this disposition of the electro-magnetic
+system, the alternate movements of the
+plate will be transformed into the induced currents,
+and these will be stronger or weaker, more or less
+definite, according to the range and complexity of
+the vibrations: they will, however, be undulatory,
+since they will always result from successive and
+continuous movements, and will consequently be
+in the conditions which, as we have seen, are required
+for the transmission of speech.</p>
+
+<p>As for the action produced upon the receiver,
+that is, on the instrument for reproducing speech,
+it is somewhat complex, and we shall have occasion
+to speak of it presently; but we can get a general
+impression of it, if we consider that the effects
+produced by the induced currents of variable
+intensity, which traverse the coil of the electro-magnetic
+system, must determine, by the magnetisations
+and demagnetisations which ensue, the
+vibrations of the armature disk; these vibrations,
+more or less amplified and defined, exactly represent
+those of the disk before which the speaker
+stands, and can only be obtained from them. The<span class="pagenum" id="Page_71">71</span>
+effects are, however, in reality more complex,
+although they are produced under analogous conditions,
+and we shall have more to say about
+them when we come to speak of the experiments
+made with the telephone. It must meanwhile be
+observed that, for the reproduction of speech, it is
+not necessary that the magnetic core should be of
+soft iron, since the vibratory effects may follow
+from differential as well as from direct magnetisation.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h2 class="nobreak" id="ORDINARY_ARRANGEMENT_OF_THE_BELL"><span id="toclink_71"></span>ORDINARY ARRANGEMENT OF THE BELL
+TELEPHONE.</h2>
+</div>
+
+<p>The arrangement most generally adopted for
+the telephone is the one represented in <a href="#il_21">fig. 21</a>.
+It consists of a kind of circular wooden box, fitted
+to the extremity of a handle <span class="allsmcap">M</span>, which is also of
+wood, and contains the magnetic bar <span class="allsmcap">N S</span>. This
+bar is fixed by means of a screw <i>t</i>, and is so
+arranged as to be moved forward and backward by
+tightening or loosening the screw, a condition
+necessary in order to regulate the instrument. At
+the free extremity of the bar the magnetic coil
+<span class="allsmcap">B</span> is fixed; this must, according to MM. Pollard
+and Garnier, be made of wire No. 42, so as to present
+a considerable number of spirals. The ends
+of this coil generally terminate at the lower end of
+the handle in two copper rods <i>f</i>, <i>f</i>, which traverse
+its length, and are fastened to two binding-screws<span class="pagenum" id="Page_72">72</span>
+<span class="allsmcap">I</span>, <span class="allsmcap">I′</span>, where the line wires <span class="allsmcap">C</span>, <span class="allsmcap">C</span> are fixed. In the
+instruments made by M. Bréguet there are, however,
+no binding-screws, but a little twist, made of
+two flexible wires covered with gutta-percha and
+silk, is fastened to the two rods. A wooden cap is
+screwed to the end of the handle, and the twist
+passes through a hole made in this cap, so that
+there is no inconvenience in working the instrument.
+By laying hold of the ends of the wire twist
+with pliers it is possible to join them to the circuit.
+This instrument is represented in <a href="#il_22">fig. 22</a>.</p>
+
+<figure id="il_21" class="figcenter" style="max-width: 21em;">
+  <img src="images/i_p072.jpg" width="807" height="457" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 21.</span>
+  </figcaption>
+</figure>
+
+<p>By another arrangement, the wires of the coil
+end immediately in the binding-screws which are
+placed below the wooden box, but this arrangement
+is inconvenient.</p>
+
+<p>Above the pole of the magnetic bar is placed
+the iron vibrating plate <span class="allsmcap">L L</span>, which is coated either
+with black or yellow varnish, with tin or blue oxide,
+but which must always be very thin. This plate<span class="pagenum" id="Page_73">73</span>
+is in the form of a disk, and by its rim, resting on a
+caoutchouc ring, it is firmly fixed to the circular
+edges of the wooden box, which is for this purpose
+made in two pieces. These pieces are adjusted to<span class="pagenum" id="Page_74">74</span>
+each other, either by screws or by spirals cut in
+half the thickness of the wood. This disk ought to
+be as near as possible to the polar end of the
+magnet, yet not so near as to produce contact
+between the two by the vibrations of the voice.
+Finally, the mouthpiece <span class="allsmcap">R R′</span> (<a href="#il_21">fig. 21</a>), which is in
+form of a wide funnel, terminates the upper part of
+the box, and should be so arranged as to leave a
+certain space between the disk and the edges of
+the hole <span class="allsmcap">V</span>, which is open in its centre. The size of
+the box should be so calculated as to permit of its
+acting as a sounding-box, without however provoking
+echoes and a confusion of sounds.</p>
+
+<figure id="il_22" class="figcenter" style="max-width: 12em;">
+  <img src="images/i_p073.jpg" width="616" height="1263" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 22.</span>
+  </figcaption>
+</figure>
+
+<p>When the instrument is properly made, it will
+produce very marked effects; and M. Pollard, one
+of the first Frenchmen to take up the study of
+telephones, has written as follows on the subject:</p>
+
+<p>‘The instrument which I have prepared gives
+results which are truly astonishing. In the first
+place, when considering the resistance, the introduction
+into the circuit of five or six persons does
+not sensibly diminish the intensity of sounds. On
+putting an instrument to each ear, the sensation is
+precisely the same as if the correspondent were
+speaking some yards behind. The intensity, the
+clearness, the purity of tone are irreproachable.</p>
+
+<p>‘I can speak to my colleague in quite an undertone,
+scarcely breathing as I may say, and persons
+placed within two yards of me will be unable to
+catch a single word of our conversation.</p>
+
+<p><span class="pagenum" id="Page_75">75</span></p>
+
+<p>‘On the part of the receiver, if anyone raises
+his voice to call me, I hear the call in all parts of
+my office, at least when silence prevails there; at
+any rate, when I am seated at my table with the
+instrument some yards off, I can always hear
+the call. In order to increase the intensity of
+sound, I fitted the mouthpiece with a copper
+horn of conical shape, and under these conditions
+words spoken in my bureau two or three yards
+from the mouthpiece can be heard at the other
+end of the line; from my station, a little more than
+a yard from the tube, I can hear and speak to my
+colleague without effort.’</p>
+
+<p>In using the ordinary Bell telephone, it is
+necessary to speak distinctly before the mouthpiece
+of the telephone which is handled, while the
+listener placed at the corresponding station keeps
+the mouthpiece of the receiver to his ear. These
+two instruments form a closed circuit with the two
+wires which connect them, but one is enough to
+make the transmission perfect, if care is taken to
+place both instruments in connection with the
+earth, which thus takes the place of the second
+wire. M. Bourbouze asserts that the intensity of
+sound in the telephone is much increased by employing
+this expedient, but we believe that this
+increase depends upon the conditions of the circuit,
+although he asserts that the fact can be proved in a
+circuit not exceeding eighty yards.</p>
+
+<p>For practical purposes it is necessary to have<span class="pagenum" id="Page_76">76</span>
+two telephones at each station, so as to hold one to
+the ear while speaking through the other, as in <a href="#il_23">fig. 23</a>.
+It is also much more easy to hear with a
+telephone applied to each ear, in which case they
+are held as in <a href="#il_24">fig. 24</a>. In order not to fatigue the
+arms, an arrangement has been made by which they
+are held before the ears by a strap and spring which
+goes round the head.</p>
+
+<figure id="il_23" class="figcenter" style="max-width: 16em;">
+  <img src="images/i_p076.jpg" width="623" height="741" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 23.</span>
+  </figcaption>
+</figure>
+
+<p>The sending power of the telephone varies
+with different voices. Mr. Preece asserts that
+shouting has no effect, and that, in order to obtain
+a favourable result, the intonation must be clear,
+the articulation distinct, and the sounds emitted
+must resemble musical sounds as much as possible.</p>
+
+<p><span class="pagenum" id="Page_77">77</span></p>
+
+<p>Mr. Wilmot, one of the electricians employed
+by the Post Office, says that he has been able to
+make himself heard on circuits through which no
+other voices were audible. The vowel sounds are
+most readily transmitted, and among other letters <i>e</i>,
+<i>g</i>, <i>j</i>, <i>k</i>, and <i>q</i> are always repeated more imperfectly.
+The ear requires practice, and the faculty of hearing
+varies in a surprising degree in different people.
+Singing is very distinctly heard, as well as wind
+instruments, especially the cornet-à-piston, which,
+when played in London, was heard by thousands of
+people in the Corn Exchange at Basingstoke.</p>
+
+<figure id="il_24" class="figcenter" style="max-width: 19em;">
+  <img src="images/i_p077.jpg" width="737" height="688" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 24.</span>
+  </figcaption>
+</figure>
+
+<p>According to Mr. Rollo Russell, it is not
+necessary to isolate the circuit of a telephone when<span class="pagenum" id="Page_78">78</span>
+the distance is relatively slight; thus, with a circuit
+of about 430 yards, it is possible to use a simple
+copper wire, laid on the grass, without destroying
+the telephonic transmission from a small musical
+box, as long as the two wires do not touch each
+other. Transmission took place, even when the
+circuit was buried in moist earth for a length of
+thirty-five yards, or immersed in a well for a length
+of forty-eight yards. The words transmitted under
+such conditions did not differ from those transmitted
+by an isolated circuit.</p>
+
+<p>The telephone may be heard at the same
+moment by several listeners, either by connecting
+the wires which unite the telephones in correspondence
+(near the receiving telephone) with
+branch wires of other telephones, which may be
+done up to the number of five or six, in short
+circuits; or by means of a little sounding-box
+closed by two thin membranes, one of which is
+fixed on the vibrating disk. When a certain
+number of acoustic tubes are connected with the
+membrane, Mr. M’Kendrick asserts that several
+people can hear distinctly.</p>
+
+<p>Telephones may also transmit speech to different
+stations simultaneously, by inserting them on
+the same circuit, and experiments made at New
+York showed that five instruments placed in
+different parts of the same telegraphic line could be
+made to speak in this way. In the telephonic experiments
+made on the canal lines in the department<span class="pagenum" id="Page_79">79</span>
+of the Yonne, it was ascertained that on a wire
+seven miles and a half in length, on which several
+telephones were placed at varying distances, three
+or four persons were able to converse with each
+other through the telephones, and each could
+hear what the other was saying. The questions
+and answers could be understood, even in crossing.
+It was also possible, by placing a telephone on a
+second wire, a little over five miles in length, and
+half a yard distant from the other, to hear the conversation
+exchanged on the first wire by following
+it to a distance not exceeding a mile and a quarter.
+Even the different voices of the two speakers could
+be distinguished.</p>
+
+<p>Since the telephone made its appearance in
+Europe, several inventors have asserted that they
+are able to make a telephone speak so as to be
+audible in all parts of a large hall. It has been
+shown that this was accomplished by Mr. Bell, and
+in this respect we do not see that those who have
+attempted to improve the telephone have attained
+results of greater importance. It is certain that
+the ordinary telephone can emit musical sounds
+which become perfectly audible in a tolerably
+large room, while the instrument is still attached
+to the wall. We should also remember the results
+obtained by MM. Pollard and Garnier in the
+experiments made at Cherbourg to connect the
+mole with the <i lang="fr">Préfecture Maritime</i>.</p>
+
+<p>The mole at Cherbourg is, as we know, a kind<span class="pagenum" id="Page_80">80</span>
+of artificial island thrown up before the town in
+order to make an anchorage. The forts which
+have been constructed on the mole are connected by
+submarine cables with the military port and with
+the <i lang="fr">Préfecture Maritime</i>. On one occasion, after
+making experiments in the Préfet’s study on one
+of the cables applied to a telephone, several persons
+were talking together in the room, and were much
+surprised to hear the bugle sound the retreat, the
+sound appearing to come from one part of the
+room. It was found, on examination, that the
+telephone hung to the wall was occupied with
+this performance. On enquiry, it appeared that
+one of the manipulators on the mole station had
+amused himself by sounding the bugle before the
+telephone on that station. The mole is more than
+three miles from Cherbourg, and the <i lang="fr">Préfecture Maritime</i>
+is in the centre of the town. Yet these telephones
+had been roughly made in the dockyard
+workshops; and we have here another proof of the
+small amount of accuracy required for the successful
+working of these instruments.</p>
+
+<figure id="il_25" class="figcenter" style="max-width: 12em;">
+  <img src="images/i_p081.jpg" width="540" height="1120" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 25.</span>
+  </figcaption>
+</figure>
+
+<p>Telephones of various construction on the
+Bell model are to be seen at M.&nbsp;C. Roosevelt’s,
+Mr. Bell’s agent in Paris, 1, Rue de la Bourse.
+They are, for the most part, constructed by M.
+Bréguet, and the model in the greatest request,
+exclusive of the one we have described, is the
+great square model, with a horseshoe magnet enclosed
+in a flat box, and a horn on its upper side,<span class="pagenum" id="Page_81">81</span>
+which serves as a mouthpiece. This system is
+represented in <a href="#il_25">fig. 25</a>, and it has been neatly constructed
+at Boston under the best conditions. In
+this new model, made by Mr. Gower, the magnet
+is composed of several plates terminated by magnetic
+cores of iron, to which the coils are fixed,<span class="pagenum" id="Page_82">82</span>
+and the whole is covered with a thick layer of
+paraffin. The sounds thus reproduced are much
+stronger and more distinct. Mr. Gower, who is
+now Mr. Roosevelt’s partner, has made considerable
+improvements in the different forms of Mr.
+Bell’s instrument. There is one model in the form
+of a snuff-box, in which the magnet is twisted into
+a spiral, so as to maintain its length in a circular
+form. The pole, which is in the centre of the
+spiral, is furnished with an iron core, to which the
+induction coil is fastened, and the cover of the
+snuff-box supports the vibrating disk as well as
+the mouthpiece: this model is represented in <a href="#il_26">fig. 26</a>.
+In another model, called the mirror telephone,
+the preceding arrangement is fitted on to a handle<span class="pagenum" id="Page_83">83</span>
+like the glass of a portable mirror, and there is a
+mouthpiece on one of the lateral faces, so that the
+speaker uses the instrument as if he were speaking
+before a chimney screen.</p>
+
+<figure id="il_26" class="figcenter" style="max-width: 26em;">
+  <img src="images/i_p082.jpg" width="1003" height="599" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 26.</span>
+  </figcaption>
+</figure>
+
+<p>Mr. Bailey has different models of telephones
+worked by a battery or by the Edison carbon of
+which we shall speak presently, and these, as well
+as the telephones by Messrs. Gray and Phelps,
+are more successful in conveying sound on a long
+line of wire.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<h2>DIFFERENT ARRANGEMENTS OF TELEPHONES.</h2>
+
+<p>The prodigious results attained with the Bell
+telephones, which were at first discredited by many
+scientific men, necessarily provoked, as soon as their
+authenticity was proved, innumerable researches
+on the part of inventors, and even of those who
+were originally the most incredulous. A host of
+improvements and modifications have consequently
+been suggested, which are evidently not without
+interest, and must now be considered by us.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h2 class="nobreak" id="BATTERY_TELEPHONES"><span id="toclink_83"></span>BATTERY TELEPHONES.</h2>
+</div>
+
+<p><i>The Edison Telephone.</i>—One of the earliest and
+most interesting improvements made in the Bell
+telephone is that introduced by Mr. Edison in
+the early part of the year 1876. This system is
+indeed more complicated than the one we have<span class="pagenum" id="Page_84">84</span>
+just considered, since it requires a battery, and
+the sending instrument differs from the receiving
+instrument; but it is less apt to be affected by
+external causes, and transmits sound to a greater
+distance.</p>
+
+<p>The Edison telephone, like Mr. Gray’s, which
+we have already had occasion to mention, is based
+upon the action of undulatory currents, determined
+by the variations in the resistance of a conductor
+of moderate conducting power, which is inserted in
+the circuit, and the vibrations of a diaphragm before
+which the speaker stands react upon it. Only, instead
+of employing a liquid conductor, which is
+practically useless, Mr. Edison has attempted to use
+semi-conducting solid bodies. Those which were
+most suitable from this point of view were graphite
+and carbon, especially the carbon extracted from
+compressed lamp-black. When these substances
+are introduced into a circuit between two conducting
+plates, one of which is moveable, they are capable
+of modifying the resistance of the circuit almost in
+the same proportion as the pressure exerted upon
+them by the moveable plate,<a id="FNanchor_5" href="#Footnote_5" class="fnanchor">5</a> and it was seen that,<span class="pagenum" id="Page_85">85</span>
+in order to obtain the undulatory currents necessary
+for the production of articulate sounds, it was
+enough to introduce a disk of plumbago or of lamp-black
+between the vibrating plate of a telephone
+and a platinum plate placed in connection with
+the battery. When the telephone disk is placed
+in circuit, its vibrations before the disk of carbon
+produce a series of increasing and decreasing
+pressures, thus causing corresponding effects in
+the intensity of the transmitted current, and these
+effects react in an analogous manner on the undulatory<span class="pagenum" id="Page_86">86</span>
+currents determined by induction in the
+Bell system. In order to obtain good results,
+however, several accessory arrangements were
+necessary, and we represent in <a href="#il_27">fig. 27</a> one of the
+arrangements made in this part of Mr. Edison’s
+telephonic system.</p>
+
+<figure id="il_27" class="figcenter" style="max-width: 16em;">
+  <img src="images/i_p085.jpg" width="626" height="851" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 27.</span>
+  </figcaption>
+</figure>
+
+<p>In <a href="#il_27">this figure</a> a section of the instrument is
+given, and its form greatly resembles that of Bell.
+<span class="allsmcap">L L</span> is the vibrating disk; <span class="allsmcap">O′ O</span>, the mouthpiece; <span class="allsmcap">M</span>,
+the opening to the mouthpiece; <span class="allsmcap">N N N</span>, the case for
+the instrument, which is, like the mouthpiece, made
+of ebonite, and below the disk it presents a rather
+large cavity, and a tubular hole which is scooped in
+the handle. In its upper part this tube terminates
+in a cylindrical rim, furnished with a worm on which
+is screwed a little rod with a ridge on its inner side,
+and the rheostatic system is placed within this tube.
+The system consists, first, of a piston <span class="allsmcap">E</span>, fitted to
+the end of a long screw <span class="allsmcap">E F</span>, and the turning of the
+button will move the piston up or down within a
+certain limit. Above this piston there is fitted a
+very thin platinum plate <span class="allsmcap">A</span>, connected by a flexible
+chain and a wire with a binding-screw <span class="allsmcap">P′</span>. Another
+plate <span class="allsmcap">B</span>, exactly similar, is connected with the
+binding-screw <span class="allsmcap">P</span>, and the carbon disk <span class="allsmcap">C</span> is placed
+between these two plates. This disk is composed
+of compressed lamp-black and petroleum, and its
+resistance is one <em>ohm</em>, or 110 yards, of telegraphic
+wire. Finally, an ebonite disk is fastened to the
+upper platinum plate, and an elastic pad, composed<span class="pagenum" id="Page_87">87</span>
+of a piece of caoutchouc tube <span class="allsmcap">G</span>, and of a cork
+disk <span class="allsmcap">H</span>, is interposed between the vibrating plate
+<span class="allsmcap">L L</span> and the disk <span class="allsmcap">B</span>, in order that the vibrations of
+the plate may not be checked by the rigid obstacle
+formed by the whole rheostatic system. When
+these different parts are in position, the instrument
+is regulated by the screw <span class="allsmcap">F</span>, and this is easily
+done by screwing or unscrewing it until the receiving
+telephone gives out its maximum of sound.</p>
+
+<figure id="il_28" class="figcenter" style="max-width: 16em;">
+  <img src="images/i_p087.jpg" width="602" height="331" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 28.</span>
+  </figcaption>
+</figure>
+
+<p>In another model, represented in <a href="#il_28">fig. 28</a>, which
+has produced the best results in the distinctness
+with which sounds are transmitted, the vibrating
+plate <span class="allsmcap">L L</span> is supported on the disks of the secondary
+carbon conductor <span class="allsmcap">C</span> by means of a little iron
+cylinder <span class="allsmcap">A</span>, instead of the caoutchouc pad, and
+the pressure is regulated by a screw placed below
+<i>e</i>. The mouthpiece <span class="allsmcap">E</span> of the instrument is more
+prominent, and its opening is larger. Finally, the
+instrument, which is cased in nickel silver, is without
+a handle. The rigid disk <i>b</i>, resting on the<span class="pagenum" id="Page_88">88</span>
+first platinum plate <i>p</i>, is of aluminium instead of
+ebonite.</p>
+
+<figure id="il_29" class="figcenter" style="max-width: 14em;">
+  <img src="images/i_p088.jpg" width="535" height="855" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 29.</span>
+  </figcaption>
+</figure>
+
+<p>The receiving telephone somewhat resembles
+that of Mr. Bell, yet it presents some differences
+which can be understood from the examination of
+<a href="#il_29">fig. 29</a>. The magnet <span class="allsmcap">N S</span> is horseshoe in form,
+and the magnetising coil <span class="allsmcap">E</span> only covers one of
+the poles, <span class="allsmcap">N</span>: this pole is precisely in the centre of
+the vibrating plate <span class="allsmcap">L L</span>, while the second pole is
+near the edge of this plate. The size of the plate
+itself is considerably reduced: its superficies is
+about the same as that of a five-franc piece, and it<span class="pagenum" id="Page_89">89</span>
+is enclosed in a kind of circular groove, which keeps
+it in a definite position. In consequence of this
+arrangement the handle of the instrument is of
+solid wood, and the vacant space for the electro-magnetic
+system is somewhat larger than in the
+Bell model; but an arrangement is made for subduing
+the echo, and there is a kind of sounding-box
+to magnify the sound. It is evident that the relation
+which the electro-magnetic system bears to the
+vibrating disk must increase the sensitiveness of
+the instrument; for as the pole <span class="allsmcap">S</span> is in close contact
+with the disk <span class="allsmcap">L L</span>, the latter is polarised, and
+becomes more susceptible to the magnetic influence
+of the second pole <span class="allsmcap">N</span>, which is separated from it
+by an interval not exceeding the thickness of a
+sheet of coarse paper. In Mr. Edison’s two
+instruments, the receiver and sender, the upper
+part <span class="allsmcap">C C</span>, corresponding to the vibrating disk, instead
+of being fixed by screws to the handle, is
+screwed on to the handle itself, which makes it
+much more easy to dismount the instrument.</p>
+
+<p>Mr. Edison has varied the form of his instruments
+in many ways, and their cases have of late
+been made of metal with a funnel-shaped mouthpiece
+of ebonite.</p>
+
+<p>When Mr. Edison had ascertained, as indeed
+Mr. Elisha Gray had done before him, that induced
+currents are more favourable to telephonic
+transmissions than voltaic currents, he transformed
+the currents from the battery which passed through<span class="pagenum" id="Page_90">90</span>
+his sender into induced currents by making them
+pass through the primary circuit of a carefully insulated
+induction coil; the line wire was then put
+into communication with the secondary wire of the
+coil. We shall afterwards describe some experiments
+which show the advantages of this combination:
+for the present we can only point out the fact,
+for it is now an integral quality of almost all the
+systems of battery telephones.</p>
+
+<p><i>Edison’s Chemical Telephone.</i>—The curious and
+really useful effects produced by Mr. Edison with
+his <em>electro-motograph</em> prompted, about the beginning
+of the year 1877, his idea of applying the principle of
+this instrument to the telephone for the reproduction
+of transmitted sounds; and he obtained such
+interesting results that the author of an article on
+telephones, published in the ‘Telegraphic Journal,’
+August 15, 1877, put forward this invention as one
+of the finest of the nineteenth century. It certainly
+appears to have given birth to the phonograph,
+which has lately become famous, and has so much
+astonished men of science.</p>
+
+<p>To understand the principle of this telephone,
+we must give some account of Mr. Edison’s electro-motograph,
+discovered in 1872. This instrument
+is based upon the principle that if a sheet of paper,
+prepared with a solution of hydrate of potash, is
+fastened on a metallic plate which is united to the
+positive pole of a battery, and if a point of lead
+or platinum connected with the negative pole is<span class="pagenum" id="Page_91">91</span>
+moved about the paper, the friction which this
+point encounters ceases after the passage of the
+current, and it is then able to slide as if upon a
+mirror until the current is interrupted. Now, as
+this reaction may be effected instantaneously under
+the influence of extremely weak currents, the
+mechanical effects produced by these alternations
+of arrest and motion may, by a suitable arrangement
+of the instrument, determine vibrations in
+correspondence with the interruptions of current
+produced by the transmitter.</p>
+
+<p>In this system the telephonic receiver consists
+of a resonator and a drum mounted on an axis and
+turned by a winch. A paper band, wound upon a
+reel, passes over the drum, of which the surface is
+rough, and a point tipped with platinum, and fitted
+to the end of a spring which is fixed in the centre
+of the resonator, presses strongly on the paper.
+The current from the battery, first directed on the
+spring, passes by the platinum point through the
+chemical paper, and returns by the drum to the
+battery. On turning the winch, the paper moves
+forward, and the normal friction which is produced
+between the paper and the platinum point pushes
+the point forward, while producing by means of
+the spring a tension on one side of the resonator;
+but since the friction ceases at each passage of the
+current through the paper, the spring is no longer
+drawn out, and the resonator returns to its normal
+position. Since this double effect is produced by<span class="pagenum" id="Page_92">92</span>
+each vibration made in the sender, a series of
+vibrations takes place in the resonator, repeating
+those of the sender, and consequently the musical
+sounds which affected the sender are reproduced
+to a certain extent. According to the American
+journals, the results produced by this instrument
+are astonishing: the weakest currents, which would
+have no effect on an electro-magnet, become perfectly
+efficacious in this way. The instrument can
+even reproduce with great intensity the highest
+notes of the human voice, notes which can hardly
+be distinguished by the use of electro-magnets.</p>
+
+<p>The sender nearly resembles the one we have
+previously described, except that, when it is used
+for musical sounds, a platinum point is employed
+instead of the disk of carbon, and it ought not to
+be in constant contact with the vibrating plate.
+According to the ‘Telegraphic Journal,’ it consists
+simply of a long tube, two inches in diameter,
+having one end covered with a diaphragm formed
+of a thin sheet of copper, and kept in its place by
+an elastic ring. A small platinum disk is riveted
+to the centre of the copper diaphragm, and a point
+of the same metal, fitted with a firm support, is
+adjusted before the disk. When the singer stands
+before the diaphragm, its vibration causes it to
+touch the platinum point, and produces the number
+of breaks in the current which corresponds to the
+vibration of the notes uttered.</p>
+
+<p>The experiments lately made in America, in<span class="pagenum" id="Page_93">93</span>
+order to decide on the merits of various telephonic
+systems, show that Mr. Edison’s telephone gives
+the best results. The ‘Telegraphic Journal,’ May 1,
+1878, states that on April 2 Mr. Edison’s carbon
+telephone was tested between New York and Philadelphia
+on one of the numerous lines of the West
+Union. The length of the line was 106 miles, and
+ran parallel to other wires almost throughout
+its length. The effects of induction caused by
+telegraphic transmissions through the adjacent
+wires were enough to make speech inaudible
+through the other telephones, but they had no
+influence on Edison’s telephone, which was worked
+with a battery of two cells and a small induction
+coil, and Messrs. Batchelor, Phelps, and Edison
+were able to converse with ease. Mr. Phelps’
+magnetic telephone, which is considered to be the
+most powerful of its kind, did not afford such good
+results.</p>
+
+<p>In the experiments made between the Paris
+Exhibition building and Versailles, the jury commission
+was able to ascertain that the results were
+equally favourable.</p>
+
+<p><i>Telephones by Colonel Navez.</i>—Colonel Navez
+of the Belgian Artillery, inventor of the well-known
+balistic chronograph, has endeavoured to improve
+the Edison telephone by employing several disks
+of carbon instead of one. He considers that the
+variations of electric resistance produced by carbon
+disks under the influence of unequal pressure depend<span class="pagenum" id="Page_94">94</span>
+chiefly on their surface of contact, and he
+consequently believes that the more these surfaces
+are multiplied, the greater the differences in question
+will be, just as it happens when light is polarised
+through ice. He adds that these disks act
+well by their surfaces of contact, since, if they are
+separated by copper disks, the speech reproduced
+ceases to be articulate.<a id="FNanchor_6" href="#Footnote_6" class="fnanchor">6</a></p>
+
+<p>I am not surprised to learn that Colonel Navez
+has found a limit to the number of carbon disks,
+for the reproduction of speech in this system is
+due both to the greatness of the differences of
+resistance in the circuit, and to the intensity of
+the transmitted current. If therefore the instrument’s
+sensitiveness to articulate sounds is increased
+by increasing the number of imperfect contacts
+in the circuit, the intensity of the transmitted
+sounds is diminished, and thus sounds lose their
+power. There is consequently a limit to be observed
+in the number of carbon disks placed upon
+each other; and it depends on the nature of the
+imperfect contacts which are employed, and on the
+tension of the electric generator.</p>
+
+<p>In order to stop the unpleasant musical vibrations
+which accompany telephonic transmissions,
+Colonel Navez employs for the vibrating plate of<span class="pagenum" id="Page_95">95</span>
+the sender a silver-plated copper disk, and for
+the vibrating plate of the receiver an iron disk
+lined with brass and soldered together. He also
+employs caoutchouc tubes with mouthpieces and
+ear-tubes for the transmission and reception of
+sound, and these instruments are placed level on a
+table. For this purpose the magnetised bar of the
+receiving telephone is replaced by two horizontal
+magnets, acting through a pole of the same nature
+on a little iron core which carries the coil, and
+which is placed vertically between the two magnets.<span class="pagenum" id="Page_96">96</span>
+He necessarily makes use of a small Ruhmkorff
+coil to transform the electricity of the battery into
+induced electricity.</p>
+
+<figure id="il_30" class="figcenter" style="max-width: 19em;">
+  <img src="images/i_p095.jpg" width="758" height="864" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 30.</span>
+  </figcaption>
+</figure>
+
+<figure id="il_31" class="figcenter" style="max-width: 17em;">
+  <img src="images/i_p096.jpg" width="658" height="858" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 31.</span>
+  </figcaption>
+</figure>
+
+<p><a href="#il_30">Figs. 30</a> and <a href="#il_31">31</a> represent the two parts of this
+telephonic system. The carbon battery is in <span class="allsmcap">C</span>
+(<a href="#il_30">fig. 30</a>), the vibrating disk in <span class="allsmcap">L L</span>, and the mouthpiece
+<span class="allsmcap">E</span>, fitted to a caoutchouc tube <span class="allsmcap">T E</span>, corresponds
+at the lower end to the vibrating disk. The carbon
+battery is placed in metallic contact with the circuit
+by a platinum rod <span class="allsmcap">E C</span>, and the vibrating disk
+also communicates with the circuit through a binding-screw.<span class="pagenum" id="Page_97">97</span>
+In the receiving telephone (<a href="#il_31">fig. 31</a>) the
+upper part is arranged much as in the ordinary
+telephones, except that, instead of a mouthpiece,
+the instrument is fitted with an ear-tube <span class="allsmcap">T O</span>. The
+two horseshoe magnets, <span class="allsmcap">A</span>, <span class="allsmcap">A</span>, which communicate a
+uniform polarity to the iron core <span class="allsmcap">N</span>, support the
+induction coil <span class="allsmcap">B</span>. The two terminals of this
+receiver are connected with the supplementary
+wire of the induction coil, and the two terminals of
+the sender are connected with the two ends of
+the primary of this coil, and with the battery which
+is inserted in the circuit near this instrument.</p>
+
+<p><i>The Pollard and Garnier Telephones.</i>—The
+battery telephone made by MM. Pollard and
+Garnier differs from the foregoing in this particular:
+it simply employs two points of graphite, mounted
+in metallic porte-crayons, and these points are
+directly applied against the vibrating plate with a
+pressure which must be regulated. <a href="#il_32">Fig. 32</a> represents
+the arrangement adopted, which, however,
+may be infinitely varied.</p>
+
+<p><span class="allsmcap">L L</span> is the vibrating tin plate, above which is the
+mouthpiece <span class="allsmcap">E</span>, and <span class="allsmcap">P</span>, <span class="allsmcap">P′</span> are the two graphite points
+with their porte-crayons. There is a screw on the
+lower part of the porte-crayons which is fixed in a
+hole pierced in a metallic plate <span class="allsmcap">C C</span>, and by this
+means the pressure of the pencils against the disk
+<span class="allsmcap">L L</span> can be regulated. The metallic plate <span class="allsmcap">C C</span> is
+made in two pieces, placed side by side, but
+insulated from each other, so that they may be placed<span class="pagenum" id="Page_98">98</span>
+in communication with a cylindrical commutator,
+and by its means the circuit can be arranged in
+different ways. Since the commutator consists of
+five sheets, the transition from one combination to
+another is instantaneous, and these combinations
+are as follows:</p>
+
+<p>1. The current enters by the pencil <span class="allsmcap">P</span>, passes
+into the plate, and so to line.</p>
+
+<p>2. The current enters by the pencil <span class="allsmcap">P′</span>, passes
+into the plate, and so to line.</p>
+
+<p>3. The current comes simultaneously by the two
+pencils <span class="allsmcap">P</span> and <span class="allsmcap">P′</span>, goes into the plate, and thence to
+line.</p>
+
+<p>4. The current comes by the pencil <span class="allsmcap">P</span>, goes
+thence to the plate, then into the pencil <span class="allsmcap">P′</span>, and so
+to line.</p>
+
+<figure id="il_32" class="figcenter" style="max-width: 12em;">
+  <img src="images/i_p098.jpg" width="459" height="305" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 32.</span>
+  </figcaption>
+</figure>
+
+<p>By this means there are two elements of combination,
+which may be employed separately, or by
+coupling them for tension or quantity.</p>
+
+<p>When the pencils are properly regulated and
+give a regular transmission of equal intensity, the
+effects produced in the transition from one combination<span class="pagenum" id="Page_99">99</span>
+to another may be easily studied, and it has
+been ascertained: first, that in a short circuit there
+is no appreciable change, whatever be the combination
+employed; secondly, that when the circuit
+is long, or of great resistance, the tension arrangement
+is the best, and this in proportion to the length
+of the line.</p>
+
+<p>This telephonic system, like the two preceding
+ones, requires an inducing machine to transform
+voltaic into induced currents: we shall presently
+speak of this important accessory of these instruments.</p>
+
+<p>Besides this arrangement, MM. Pollard and
+Garnier have employed the one we have represented
+in <a href="#il_5">fig. 5</a>, which has given better results. We shall
+see presently that it can be used as the receiving
+organ of sounds. In each case the two carbons
+must be placed in contact, and subjected to a
+certain initial pressure, which should be regulated
+by the screw fitted to the support of the lower
+carbon.</p>
+
+<p>As for the receiving telephone, the arrangement
+adopted by MM. Pollard and Garnier is the same
+as Bell’s, except that they employ tin plates and
+helices of greater resistance. This resistance ranges
+in fact from 100 to 125 miles. ‘We have always
+held,’ these gentlemen say, ‘that whatever may
+be the resistance of the outer circuit, there is an
+advantage in increasing the number of spirals,<span class="pagenum" id="Page_100">100</span>
+even when using wire No. 42, which is the one we
+prefer.’</p>
+
+<figure id="il_33" class="figcenter" style="max-width: 23em;">
+  <img src="images/i_p100.jpg" width="901" height="690" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 33.</span>
+  </figcaption>
+</figure>
+
+<p><i>M. Hellesen’s Reaction Telephone.</i>—M. Hellesen
+believed that the vibrations produced by the voice
+on the carbon of a telephonic sender would be
+magnified if the moveable part of the rheotome
+were subjected to an electro-magnetic action resulting
+from the vibrations themselves, and he has
+contrived a sender, which is based on the principle
+shown in <a href="#il_33">fig. 33</a>, and which has the merit of forming
+in itself the inducing apparatus intended to transform
+the voltaic currents employed. This instrument is
+composed of a vertical iron tube, supported on a
+magnetic bar <span class="allsmcap">N S</span>, and surrounded by a magnetising<span class="pagenum" id="Page_101">101</span>
+coil <span class="allsmcap">B B</span>, above which is fixed an inducing
+helix of fine wire <span class="allsmcap">I I</span>, communicating with
+the circuit. Within the tube there is a lead pencil
+<span class="allsmcap">C</span>, held by a porte-crayon which can be raised or
+lowered by means of a screw <span class="allsmcap">V</span> fixed below the
+magnetic bar. Finally, above this pencil, there is
+an iron vibrating plate <span class="allsmcap">L L</span>, with a platinum point
+in communication with the battery in its centre;
+the local circuit communicates with the pencil by
+means of the magnetising helix <span class="allsmcap">B</span>, and for this
+purpose one end is soldered to the iron tube.</p>
+
+<p>From this arrangement it follows that the
+vibrations of the plate <span class="allsmcap">L L</span>, at the moment when it
+comes nearest to the pencil, tend to become greater
+in consequence of the attractive force exerted on
+the plate, and as the pressure of the lead pencil is
+increased, it increases the differences of resistance
+which result from it, and consequently causes
+greater variations in the intensity of the transmitted
+currents.</p>
+
+<p><i>Reaction Telephone of Messrs. Thomson and
+Houston.</i>—The telephonic arrangement we have
+described has lately been adopted by Mr. Elihu
+Thomson and Mr. Edwin J. Houston, who, on
+June 21, 1878, two months after M. Hellesen explained
+his system to me,<a id="FNanchor_7" href="#Footnote_7" class="fnanchor">7</a> published an article in
+‘The English Mechanic and World of Science’<span class="pagenum" id="Page_102">102</span>
+about an instrument very similar to that of M.
+Hellesen.</p>
+
+<p>In their instrument, the current, which passes
+through a body of moderately conducting capacity,
+acts on an electro-magnet provided with an induction
+coil, and this electro-magnet reacts on the
+diaphragm, in order to increase the range of its
+vibrations, and to create at the same moment two
+electric actions in the same direction: the only
+difference lies in the arrangement of the contact of
+this indifferent conductor with the vibrating plate.
+Instead of a simple contact effected by pressure
+between this plate and a carbon pencil, a fragment of
+the same substance with a sharpened point is fixed
+on the vibrating plate, and it dips into a drop of
+mercury which has been poured into the receptacle
+made for it at the upper end of the electro-magnet.
+In other respects, the arrangement of the instrument
+is that of an ordinary telephone, and the iron rod
+of the electro-magnet represents the magnetised
+bar of the Bell telephone. The inventors assert
+that this instrument can be used both as a sender
+and receiver, and it is in the following manner
+that it is worked in each case.</p>
+
+<p>When the instrument is transmitting, the morsel
+of carbon dips more or less into the mercury, and
+consequently differences are produced in the surfaces
+of contact, according to the range of vibrations
+made by the plate; the current varies in
+intensity in proportion to this range, and induced<span class="pagenum" id="Page_103">103</span>
+currents in the induction coil result from these variations;
+the induced currents react on the receiving
+telephone, as in Bell’s instrument, and are further
+strengthened by those which are produced electrically
+by the movement of the diaphragm before
+the induction coil, and the iron of the electro-magnet.</p>
+
+<p>When the instrument is used as a receiver, the
+usual effects are displayed, for since the iron of the
+electro-magnet is magnetised by the current, its
+conditions are precisely those of the ordinary Bell
+telephone, and the induced currents reach it in the
+same manner, only with greater intensity. Messrs.
+Thomson and Houston assert that their system has
+produced excellent results, and that by it the sound
+of the voice is much less altered than in other
+telephones.</p>
+
+<p><i>Telephones with batteries and liquid senders.</i>—We
+have seen that in 1867 Mr. Gray conceived
+the idea of a telephonic system based on the
+differences of resistance effected in a circuit completed
+by a liquid, when the layer of liquid interposed
+between the electrodes varies in thickness
+under the influence of the vibrations of the telephonic
+plate which is in communication with one
+of these electrodes. This system has since been the
+subject of study by several inventors, among others
+by MM. Richemond and Salet; and I give some of
+the accounts which have been published respecting
+their researches.</p>
+
+<p><span class="pagenum" id="Page_104">104</span></p>
+
+<p>Another telephone for the reproduction of
+articulate sounds, which M. Richemond terms the
+<em>electro-hydro telephone</em>, has been recently patented
+in the United States. It resembles that of Mr.
+Edison in some respects, but instead of making use
+of carbon disks to modify the resistance of the
+circuit, water is employed, and this water is placed
+in communication with the circuit and battery by
+means of two platinum points, one of which is fixed
+on the metallic diaphragm which vibrates under the
+influence of the voice. As the vibrations of the diaphragm
+transport the point which is attached to it to
+different parts of the interpolar layer of liquid, they
+diminish or increase the electric resistance of this
+layer, and cause corresponding variations in the
+intensity of the current traversing the circuit. The
+receiving telephone is of the usual kind. (See
+‘Telegraphic Journal,’ September 15, 1877.)</p>
+
+<p>M. Salet writes: ‘I thought it would be interesting
+to construct a telephone in which there
+should be absolute solidarity in the movements
+of the two membranes, and for this purpose I
+have availed myself of the great resistance of
+liquids. Mr. Bell had already obtained some
+results by attaching to the vibrating membrane a
+platinum wire communicating with a battery, and
+dipping more or less into a metallic vessel, itself
+connected by the line with the receiving telephone
+and containing some acidulated water. I have substituted
+for the platinum wire a small aluminium<span class="pagenum" id="Page_105">105</span>
+lever supporting a disk of platinum, and at a very
+slight distance from it there is a second disk in connection
+with the line. The vibrations of the membrane,
+tripled or quadrupled in their range, are not
+altered in form, thanks to the small size and light
+weight of the lever: they cause variations in the
+thickness of the liquid layer traversed by the
+current, and consequently in its intensity, and these
+variations cause corresponding differences in the
+attractive force of the receiving electro-magnet.
+Under its influence the receiving membrane executes
+movements which are identical with those of
+the sending membrane. The sound transmitted
+is very distinct, and its <em>timbre</em> is perfectly maintained,
+a result which might have been anticipated.
+The consonants, however, are not so clearly pronounced
+as those transmitted by Mr. Bell’s instrument.
+This inconvenience is most apparent when
+the lever is heavy, and might easily be obviated.
+The electrolysis also produces a continual murmur,
+but this does not interfere with the distinctness of
+the sound.</p>
+
+<p>‘Since on this system the voice is not required
+to <em>produce</em>, but only to <em>direct</em> the electric current
+generated by a battery, the intensity of the sound
+received might in theory be increased at pleasure.
+I have in fact been able to make the receiver emit
+very powerful sounds, and I think that this advantage
+greatly counterbalances the necessity of employing
+a battery, and a somewhat delicate sending<span class="pagenum" id="Page_106">106</span>
+instrument. Unfortunately it can only be
+used for moderate distances. Assuming that any
+displacement of the transmitting membrane increases
+the resistance to a degree equivalent to
+five or six hundred yards of wire: if the line is five
+hundred yards long, the intensity of the current
+will be reduced by one half, and the receiving
+membrane will take up a fresh position, considerably
+differing from the first; but if the line is three
+hundred miles in length, the intensity of the current
+will only be modified by a thousandth part. An
+immense battery must therefore be employed in
+order that this variation may be translated by a
+sensible change in the position of the receiving
+membrane.’ (See ‘Comptes Rendus de l’Académie
+des Sciences,’ February 18, 1878.)</p>
+
+<p>M. J. Luvini, in an article inserted in ‘Les
+Mondes,’ March 7, 1878, has suggested a system
+of rheotome by means of a current, for battery
+telephones, which, although complicated, possibly
+offers some advantages, since it produces currents
+alternately reversed. In this system, the vibrating
+disk of the sender, which should be in a vertical
+position, reacts on a moveable horizontal wire,
+turned back at a right angle, and supporting on
+each of its branches two platinum points which
+dip into two bulbs, filled with a liquid of moderate
+conducting capacity. The two branches of this
+wire, insulated from each other, are placed in communication
+with the two poles of the battery, and<span class="pagenum" id="Page_107">107</span>
+the four cups into which the platinum wire dips
+communicate inversely with the line and the
+earth by means of platinum wires immoveably
+fixed in the cups. It follows from this arrangement,
+that when the distances are duly regulated
+between the fixed and moveable wires, two equal
+currents will be opposed to each other across
+the line circuit when the diaphragm is motionless;
+but as soon as it vibrates, the respective
+distances of the wires will vary, and it follows from
+this that there will be a differential current, of which
+the intensity will correspond with the extent of the
+displacement of the system, or with the range of
+vibrations, and the direction will vary with the
+movements above or below the line of the nodes of
+vibration. In this way the advantage of the induced
+currents is obtained.</p>
+
+<p><i>Telephones with a battery and voltaic arcs.</i>—In
+order to obtain variations of resistance of still
+greater sensitiveness than is the case with liquids
+or pulverised substances, the idea has been suggested
+of employing conductors of heated gas,
+and several arrangements of battery telephones
+have been made in which the circuit was completed
+by a stratum of air, separating the vibrating disk
+from a platinum point, which serves to excite an
+electric discharge of high tension. Under these
+conditions, the stratum of air becomes the conductor,
+and the intensity of the current which
+traverses it corresponds to its thickness. This<span class="pagenum" id="Page_108">108</span>
+problem has been solved, either by means of
+voltaic currents of high tension, or by a Ruhmkorff
+coil.</p>
+
+<p>The former system was arranged by M. Trouvé,
+and he writes as follows on the subject in the
+journal ‘La Nature’ of April 6, 1878: ‘A metallic
+vibrating membrane forms one of the poles of a
+high tension battery; the other pole is fastened
+before the disk by a micrometer screw which can
+be adjusted so as to vary the distance from the disk
+according to the tension of the battery, but without
+ever coming in contact with it. The distance
+must not in any case exceed that to which the
+discharge of the battery can extend. Under these
+conditions, the membrane which vibrates under the
+influence of the waves of sound has the effect of
+constantly modifying the distance between the
+two poles, and thus of continually varying the intensity
+of the current: consequently the receiving
+instrument (a Bell telephone, or telephone with an
+electro-magnet) is subjected to magnetic variations,
+corresponding to the variations of the current which
+affect it, and this has the effect of making the
+receiving instrument vibrate at the same moment.
+This kind of telephonic instrument relies, therefore,
+on the possibility of varying within wide limits the
+resistance of the outer circuit of a high-tension
+battery, in which the poles are not in contact. In
+order to vary the conditions of this resistance, it is
+also possible to interpose some vapour or other<span class="pagenum" id="Page_109">109</span>
+medium, such as air, or gas of greater or less
+rarity.’</p>
+
+<p>M. Trouvé thinks that he was successful with
+his battery of small disks, moistened with sulphate
+of copper and sulphate of zinc, arranging these
+elements, to the number of five or six hundred, in
+glass tubes of small diameter. It is well known
+that it is unnecessary for the elements to be of
+large size in order to obtain tension currents.</p>
+
+<p>M. de Lalagade has suggested an analogous
+mode by employing for the formation of the arc
+a current of which the tension is increased by inserting
+a strong electro-magnet into the circuit.
+This electro-magnet acts on a Hughes magnet in
+order to produce induction currents capable of
+making the receiving instrument act. M. de
+Lalagade says that a Bunsen battery, or one of six
+cells with bichromate of potash, will be enough
+to produce a continuous voltaic arc between the
+vibrating plate of a telephone and a platinum
+point which is sufficiently remote to avoid contact.
+It is necessary, however, to begin with a contact, in
+order to produce the formation of this arc. In M.
+de Lalagade’s system, the vibrating plate should
+have in its centre a small platinum plate, in order
+to obviate the oxidising effects of the spark. The
+inventor asserts that sounds transmitted in this
+way, and reproduced in a telephone of which the
+electro-magnetic system is set upon a sounding-box,
+will have greater intensity than the sounds<span class="pagenum" id="Page_110">110</span>
+transmitted by an ordinary telephone, and the
+speaker will appear to be close to the ear.</p>
+
+<p><i>Mercury Telephones.</i>—These systems are based
+on the physical principle discovered by M. Lippmann,
+that if a layer of acidulated water is placed above
+mercury, and connected with it by an electrode
+and wire, every mechanical action which exerts
+pressure on the surface of the mercury, and alters
+the form of its meniscus, will cause an electric
+reaction, capable of producing a current with a
+force which corresponds to the mechanical action
+exerted. Conversely, every electric action produced
+on the circuit of such a system will occasion
+a displacement of the meniscus, and consequently
+its movement, which will be more marked in proportion
+to the smallness of the tube in which the
+mercury is placed, and to the greatness of the
+electric action. This electric action may result
+from a difference of potential in the electric condition
+of the two extremities of the circuit, which
+communicate with the electric source employed, or
+with some electric generator.<a id="FNanchor_8" href="#Footnote_8" class="fnanchor">8</a></p>
+
+<p><span class="pagenum" id="Page_111">111</span></p>
+
+<figure id="il_34" class="figcenter" style="max-width: 24em;">
+  <img src="images/i_p111.jpg" width="933" height="535" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 34.</span>
+  </figcaption>
+</figure>
+
+<p>In accordance with these effects, it is intelligible
+that if two tubes <span class="allsmcap">T</span> <span class="allsmcap">T</span>, pointed at the end, and containing
+mercury, are plunged into two vessels <span class="allsmcap">V</span> <span class="allsmcap">V</span>
+(<a href="#il_34">fig. 34</a>) containing acidulated water and mercury,
+and metallic wires, <span class="allsmcap">P P</span>, <span class="allsmcap">Q Q</span>, are used, first to connect
+the columns of mercury in the tubes, and secondly
+the layers of mercury at the bottom of the two vessels,
+the tubes being a little removed from the surface of
+the mercury in the vessels, we shall then have a
+metallic circuit, completed by two electrolytes,
+one of which will be subjected to the mechanical
+or electrical effects produced in the other. If two
+vibratory plates <span class="allsmcap">B</span> <span class="allsmcap">B</span> are placed above the tubes,
+and one of these is caused to vibrate, the other
+will reproduce these vibrations, influenced by the
+vibratory movements communicated by the corresponding<span class="pagenum" id="Page_112">112</span>
+column of mercury. The vibrations
+themselves will be in connection with the electrical
+discharges resulting from the movements of the
+column of mercury in the first tube, which are
+mechanically produced. If an electric generator is
+introduced into the circuit, the effect which we
+have just analysed will be caused by modifications
+in the potential of this generator, in consequence
+of electro-capillary effects. But if no generator
+is employed, the action will result from electric
+currents determined by the electro-capillary attraction
+itself. In the latter case, however, the instrument
+must be more delicately made, in order to
+obtain more sensitive electric reaction, and M.&nbsp;A.
+Bréguet describes his instrument as follows.</p>
+
+<p>‘The instrument consists of a tube of thin
+glass, a few centimètres in length, containing alternate
+drops of mercury and acidulated water, so as to
+constitute so many electro-capillary elements, connected
+in tension. The two ends of the tube are
+fused together, yet so as to allow a platinum wire
+to touch the nearest drop of mercury on each side.
+A small circle of thin deal is fixed at right angles to
+the tube by its centre, thus providing a surface of
+some extent, which can be applied to the ear when
+the instrument is a receiver, and to make the tube
+more mobile under the influence of the voice
+when the instrument is a sender. The following
+are the advantages offered by instruments of this
+<span class="locked">construction:—</span></p>
+
+<p><span class="pagenum" id="Page_113">113</span></p>
+
+<p>‘1. They do not involve the use of a battery.</p>
+
+<p>‘2. The disturbing influence of the resistance of
+a long line is almost destroyed in these instruments,
+although it is still appreciable in the Bell
+telephone.</p>
+
+<p>‘3. Two mercury telephones, coupled together
+as we described above, are absolutely correlative,
+in this sense, that even different positions in the
+equilibrium of the mercury in one of them produce
+different positions of equilibrium in the
+opposite instrument. It is therefore possible to
+reproduce at a distance, without a battery, not
+merely faithful indications of oscillatory movements,
+which is done by the Bell telephone, but
+also the exact image of the most general movements.’</p>
+
+<p><i>Friction Telephones.</i>—Mr. E. Gray has quite
+recently applied the principle of producing sounds
+by the friction of animal tissues to the construction
+of a speaking telephone which may be heard
+through a whole room, like the singing condenser.
+He obtains this result by means of clockwork,
+which causes the rotation of the metallic disk of
+which we have spoken (p. 23), and on which a piece
+of skin is so arranged as to produce friction. A
+carbon or liquid telephone is placed at the sending
+station, in such a way as to react on an induction
+coil, as in the systems of Edison, Navez, or
+Pollard, and speech is reproduced on the rotating
+disk, and is audible, as we have said, without<span class="pagenum" id="Page_114">114</span>
+the necessity of approaching the ear to the instrument.</p>
+
+<p>The best arrangement of the metallic disk on
+which the animal tissue rubs is that of a cylindrical
+box, of which the outer lid is made of a thin sheet
+of zinc with a highly polished, slightly oxidised
+surface; for the agent of friction, glove-leather
+slightly moistened with acidulated water may be
+used, or a sinew of an ox, or skin taken from the
+ear or tail of a pig.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h2 class="nobreak" id="MODIFICATIONS_INTRODUCED_IN_THE_CONSTRUCTION"><span id="toclink_114"></span>MODIFICATIONS INTRODUCED IN THE CONSTRUCTION
+OF THE BELL TELEPHONES.</h2>
+</div>
+
+<p>The modifications which we have been considering
+relate to the principle of the instrument;
+those which we have now to consider are only
+modifications in the form and arrangement of the
+different organs which form the Bell telephone
+itself, and which have been designed with the
+object of increasing the intensity and distinctness
+of the sounds produced.</p>
+
+<p><i>Telephones with several diaphragms.</i>—When we
+remember that the induced currents caused in a
+magnet result from the vibratory movements of
+the diaphragm, and that these are produced by the
+vibrations of the stratum of air interposed between
+this diaphragm and the vocal organ, it necessarily
+follows that if these vibrations of the air react on
+several diaphragms, each attached to its electro-magnetic
+organ, several induced currents might be<span class="pagenum" id="Page_115">115</span>
+caused simultaneously, and if these were properly
+connected, their effects on the receiver would be
+so much the more intense, since the sounds produced
+would result from the combination of
+several sources of sound. Several inventors, starting
+from this argument, have planned instruments
+of varying ingenuity, which we will now describe,
+but without being able to declare who was the
+first to realise this idea. It is in fact so simple,
+that it probably suggested itself to the minds
+of several inventors at the same time, and we see
+that while M. Trouvé proposed this improvement
+in France in November 1877, it was tried
+in America and discussed in England, where
+indeed it was not expected to produce very
+favourable results. Mr. Preece wrote on the subject
+in a paper entitled ‘On some Physical Points connected
+with the Telephone,’ which was published in
+April 1878. He observes that all the attempts
+to improve the telephone have ended in disappointment
+and failure. One of the first attempts
+of the kind was made by Mr. Wilmot, who expected
+to obtain favourable results by augmenting
+the number of diaphragms, helices, and magnets,
+connecting the helices in a series, and causing them
+to act simultaneously, so as to increase the energy
+of the currents developed by the influence of the
+voice; but experience showed that when the instrument
+acted directly, the vibratory effect of
+each of the diaphragms decreased in proportion to<span class="pagenum" id="Page_116">116</span>
+their number, and the general effect remained the
+same as with a single diaphragm. Mr. Wilmot’s
+instrument was made in the beginning of October
+1877, and that of M. Trouvé was only an imitation
+of it.</p>
+
+<p>On the other hand, we see that if the telephones
+with several membranes were not successful in
+England, this was not the case in America, for the
+telephones which experience has shown to give the
+best results in that country are those of Mr. Elisha
+Gray and Mr. Phelps, and these have several diaphragms.
+It is evident that there are details of construction
+in these instruments which may appear
+insignificant in theory, and which are notwithstanding
+very important from a practical point of
+view, and we believe that it is to this circumstance
+that instruments of this kind owe their success or
+failure. Thus, for example, it seems that the
+vibrations of air caused in the mouthpiece ought to
+be immediately directed on the surface of the diaphragms
+by means of distinct channels; it is
+necessary that the empty space round each diaphragm
+should be sufficiently limited to prevent
+echoes and interruptions, unless the case is so large
+that there is no danger of such effects. Above all, it
+is necessary that the organs should be fixed in some
+material unsusceptible of reverberation, and for this
+reason a preference is given to iron or ebonite. It is
+certain that when the instrument is properly made,
+its effects are superior to those of the Bell telephones,<span class="pagenum" id="Page_117">117</span>
+and it is asserted in the ‘Telegraphic Journal’ that
+experiments were made with one of these instruments
+before the Royal Society, in London, May
+1, 1878, and that the intensity of sound was in
+proportion to the number of diaphragms. This
+instrument was designed by Mr. Cox Walker, of
+York, and possessed eight diaphragms. He considers
+that this is the arrangement which gives the
+best results.</p>
+
+<figure id="il_35" class="figcenter" style="max-width: 20em;">
+  <img src="images/i_p117.jpg" width="761" height="987" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 35.</span>
+  </figcaption>
+</figure>
+
+<p><span class="pagenum" id="Page_118">118</span></p>
+
+<p><i>Mr. Elisha Gray’s System.</i>—Mr. Elisha Gray’s
+last system, which we represent in <a href="#il_35">fig. 35</a>, is one
+of those which have given the best effects. It
+is made, as we see, of two telephones, side by side,
+to which correspond two tubes, issuing from a common
+mouthpiece <span class="allsmcap">E</span>. One of these telephones is seen
+in section in the plate, the other in elevation, and
+they correspond to the two branches of a nickel-plated
+horseshoe magnet <span class="allsmcap">N U S</span>, which may serve as
+a suspension ring. In that part of the plate which
+represents the section, the induction coil is shown
+in <span class="allsmcap">B</span>, and the magnetic core, of soft iron, in <span class="allsmcap">A</span>,
+which is screwed to the polar end of the magnet <span class="allsmcap">S</span>;
+the vibrating plate is in <span class="allsmcap">L L</span>, and, as we see, the
+tube of the mouthpiece terminates on its surface.</p>
+
+<p>In another model there are four telephones side
+by side, instead of two, and the effects produced
+are still more marked.</p>
+
+<p><i>Mr. Phelps’s System.</i>—This system is only deduced
+from the last, but there are two models of it.
+In the larger one, which makes it possible to hear
+as distinctly as if the person with whom conversation
+is held were speaking in a loud voice in the
+same room, the two telephones are placed parallel
+to each other, and so as to present their diaphragms
+vertically; the space between these two diaphragms
+is occupied by a vertical tube, terminating at its
+lower end in a horizontal tube corresponding to
+the centres of the two diaphragms, and on this
+tube the mouthpiece is fitted, which projects outside<span class="pagenum" id="Page_119">119</span>
+the box in which the instrument is enclosed.
+The induction coils, and the magnetic cores which
+traverse them, follow the axis of the system, and
+seem to constitute the axis of a wheel which
+is polarised by the poles of a horseshoe magnet,
+of which the position with reference to the surface
+of the diaphragms can be regulated by moveable
+screws. The appearance of the instrument somewhat
+resembles a gyroscope, resting by a horizontal
+axis on two shafts which issue from a flattened
+horseshoe magnet.</p>
+
+<p>Above this system there is the electro-magnetic
+apparatus of the call-bell, in which there is nothing
+peculiar, and which is like the German
+alarums of which we shall speak at the end of this
+account. This instrument is remarkable for strength
+and clearness of sound, and especially for its freedom
+from the Punch and Judy voice so displeasing
+in other telephones.</p>
+
+<p>Mr. Phelps’s small model is in the form of an
+oblong or elliptical snuff-box, of which the two
+centres are occupied by two telephonic systems,
+influenced by the same magnet. This magnet is
+placed in a horizontal position below the snuff-box,
+and its poles correspond to the magnetic cores of
+the coils. These cores are made of iron tubes,
+split longitudinally in order to destroy irregular
+induction reactions, and the iron diaphragms rest on
+five spiral springs, which raise them above the
+magnetic system. On their other surface the diaphragms<span class="pagenum" id="Page_120">120</span>
+are provided with rings of some semi-elastic
+substance, which prevent the central vibrations
+of the disks from becoming complicated by
+those of their edges. The lid, hollowed out in
+very shallow cavities, is next placed upon the disks,
+and there are channels of communication in it to
+serve as a sounding-box. The mouthpiece corresponds
+to one of these cavities, and the other is closed
+by a small metallic stopper, which can be withdrawn
+to regulate the instrument when necessary.
+Since the vibrations of air are transmitted by the
+channels to both cavities, the two telephones act
+together, although at first sight only one of them
+seems to be required to produce the effect.</p>
+
+<p>Mr. Phelps praises the simultaneous effects produced
+on the two instruments, which he ascribes,
+first, to the semi-elastic ring surrounding the rim of
+each disk, and acting as the hammer of the ear,
+that is, as a damper; then, to the longitudinal splits
+of the magnetic core, and lastly to the small size of
+the cavities left above the vibrating disks. The
+instrument is made of ebonite, grooved on the
+surface in order to give a better grasp to the
+hand.</p>
+
+<p>Mr. Phelps has a new model, called <em>the crown
+telephone</em>, which is now in use in America, together
+with Mr. Edison’s carbon sender. In it each of
+the two systems of the large model we have
+described is worked by six horseshoe magnets
+radiating round the magnetic core, and so arranged<span class="pagenum" id="Page_121">121</span>
+that the north poles correspond to this core, and
+the other poles to the circular rim of the diaphragm.
+In this way the magnetic field is considerably
+enlarged, and the sound much intensified.</p>
+
+<p>In experiments recently made at Dr. Wells’s
+church, New York, an assembly of three hundred
+people were able to hear speech and vocal or
+instrumental music distinctly in different parts of
+the hall.</p>
+
+<p><i>Mr. Cox Walker’s System.</i>—This system, on
+which we have already said a few words, has
+exactly the arrangement of that by Mr. Elisha
+Gray. The magnets which act upon the diaphragms
+are horseshoe, and separate pipes, issuing from a
+common mouthpiece, direct the vibrations of air
+on the diaphragms. These, indeed, are only
+defined parts of one diaphragm, bounded in a circle
+by mouthpieces corresponding to the air-pipes, and
+sufficiently restricted on their edges to limit the
+field of vibration.</p>
+
+<p><i>M. Trouvé’s System.</i>—M. Trouvé has simplified
+the arrangement of telephones with a double
+diaphragm, by designing the instrument so as to
+make Bell’s bar magnet react by both poles at
+once on several disks. For this purpose, he
+employs a tubular magnet, and winds a helix
+throughout its whole length, as we see in <a href="#il_36">fig. 36</a>.
+This magnet is maintained in a fixed position in
+the centre of a small cylindrical box, of which the
+base is slightly funnel-shaped, thus acting as a<span class="pagenum" id="Page_122">122</span>
+mouthpiece and acoustic tube. It is consequently
+pierced in the centre with a hole larger at <i>a</i>, the
+station for speaking, than on the opposite side <i>b</i>.
+Between the base and the poles of the magnet
+there are two vibrating iron plates, <span class="allsmcap">M</span>, <span class="allsmcap">M′</span>, one of
+which, <span class="allsmcap">M</span>, is pierced with a hole <i>a</i> of the same
+diameter as the hollow part of the magnet, and
+consequently smaller than that of the mouthpiece.
+Finally, several other plates <i>n</i>, <i>n</i>, <i>n</i>, are ranged in
+parallel lines between these two plates, so that the
+magnet and its helix may pass through them.</p>
+
+<figure id="il_36" class="figcenter" style="max-width: 18em;">
+  <img src="images/i_p122.jpg" width="697" height="505" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 36.</span>
+  </figcaption>
+</figure>
+
+<p>When anything is said before the mouthpiece
+<i>a</i>, the waves of sound encountering the edges of
+the plate <span class="allsmcap">M</span> place it in vibration, and, continuing
+their passage inside the tubular magnet, they cause
+the plate <span class="allsmcap">M</span>′ to vibrate at the same time as <span class="allsmcap">M</span>. A
+double inducing action therefore takes place on the<span class="pagenum" id="Page_123">123</span>
+tubular magnet, and this is translated by the
+induced currents developed in the helix, which
+have greater energy since each of the plates intensifies
+the magnetic effects produced at the pole
+opposite to the one they influence, which is always
+the case with bar magnets when the inactive pole
+is provided with an armature. This advantage
+may even be obtained in the case of ordinary
+telephones, if the screw which holds the magnet is
+placed in contact with a mass of soft iron.</p>
+
+<p>In M. Trouvé’s arrangement, the induced
+currents therefore possess greater energy; but he
+adds that the sounds reproduced will also be
+strengthened by the multiplicity of vibratory
+effects, and by the enlargement of the magnetic
+effects, which results from a better arrangement of
+the magnets.</p>
+
+<p>‘When the ear is placed at <i>a</i>,’ M. Trouvé writes,
+‘it perceives immediately the sounds produced by
+the first plate <span class="allsmcap">M</span>, and those of the second plate
+reach the ear through the interior of the magnet.
+This new arrangement is well adapted for an
+experimental comparison of the results produced
+by a telephone with a single membrane (a Bell
+telephone), and those produced by a telephone with
+several membranes. It is in fact enough to listen at
+the two faces of the telephone alternately, in order
+to perceive at once the difference of intensity in
+the sounds produced. Those collected at <i>a</i>, on
+the side of the pierced iron plate, appear manifestly<span class="pagenum" id="Page_124">124</span>
+doubled in intensity compared with those
+collected at <i>b</i> on the side of the simple membrane
+which forms the ordinary telephone.</p>
+
+<p>‘The difference is still more striking if, in
+transmitting or receiving a sound of invariable
+intensity through a multiple telephone, the unbroken
+membrane <span class="allsmcap">M′</span> is repeatedly prevented from
+vibrating.’</p>
+
+<p>Before making this arrangement M. Trouvé had
+planned another, which he presented to the Académie
+des Sciences, November 26, 1877, and which
+we have glanced at in the beginning of this chapter.
+He describes it in these <span class="locked">terms:—</span></p>
+
+<p>‘In order to increase the intensity of the effects
+produced in the Bell telephone, I have substituted
+for the single membrane a cubic chamber, of which
+each face is, with one exception, formed of a vibrating
+membrane. Each of these membranes, put in
+vibration by the same sound, influences a fixed magnet,
+which is also provided with an electric circuit.
+In this way, by connecting all the currents generated
+by the magnets, a single intensity is obtained,
+which increases in proportion to the number of magnets
+influenced. The cube might be replaced by a
+polyhedron, of which the faces might be formed of
+an indefinite number of vibrating membranes, so as
+to obtain the desired intensity.’</p>
+
+<p><i>M. Demoget’s System.</i>—Several other systems of
+telephones with multiple membranes have been
+proposed. One of them, planned by M. Demoget,<span class="pagenum" id="Page_125">125</span>
+consists in placing before the vibrating disk of the
+ordinary Bell telephone, separated by the space of
+a millimètre, one or two similar vibrating disks,
+taking care to pierce in the centre of the first a
+circular hole of the same diameter as that of the bar
+magnet, and to pierce a larger hole in the second
+membrane. The inventor asserts that the distinctness
+as well as the intensity of sounds is increased
+in this way.</p>
+
+<p>‘By this arrangement,’ says M. Demoget, ‘since
+the vibrating magnetic mass is larger in proportion
+to the magnet, the electro-motive force of the
+currents generated is increased, and consequently
+the vibrations of the disks of the second telephone
+are more perceptible.’</p>
+
+<p><i>Mr. McTighe’s Telephone.</i>—In this telephone,
+which has several diaphragms, there is a horseshoe
+magnet, and instead of placing the coils upon the
+poles, there is a single coil fastened to an iron
+core, which is inserted between wide polar appendices
+fitted to the two poles of the magnet. These
+appendices consist of thin plates, which act as
+vibrating plates.</p>
+
+<p><i>Modifications in the arrangement of Telephonic
+Organs.</i>—We see that the forms given to the Bell
+telephone are very varied, and this is still more
+the case with its constituent organs, without, however,
+producing any remarkable improvements.
+Mr. Preece observes that little has been gained by
+varying the size and strength of the magnets, and<span class="pagenum" id="Page_126">126</span>
+the best effects have been obtained by using the
+horseshoe magnets directed by Mr. Bell himself.
+The telephone was certainly introduced into Europe
+with the arrangement which is theoretically the
+best, although Mr. Bell is still occupied in improving
+it. This is also the opinion of M. Hellesen, who,
+like Mr. Preece, has made many experiments on
+this point; but this has not deterred several
+people from declaring that they have discovered
+the way of making a telephone speak so as to be
+audible to an assembly of people.</p>
+
+<p>Of the different instruments made with this object,
+that of M. Righi seems to be the most important.
+It was lately tried with success at the Académie
+des Sciences, the Conservatoire des Arts et Métiers,
+and the Press pavilion of the Exhibition.</p>
+
+<figure id="il_37" class="figcenter" style="max-width: 20em;">
+  <img src="images/i_p127.jpg" width="770" height="803" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 37.</span>
+  </figcaption>
+</figure>
+
+<p>The receiver is only a Bell telephone of large
+size, with a diaphragm of parchment <span class="allsmcap">L L</span> (<a href="#il_37">fig. 37</a>),
+in the centre of which there is a sheet-iron disk <span class="allsmcap">F</span>.
+This membrane is stretched on a large funnel <span class="allsmcap">E</span>,
+which is fixed on a box <span class="allsmcap">C C</span>, containing the electro-magnetic
+coil <span class="allsmcap">B</span>: and the magnet <span class="allsmcap">N S</span>, much larger
+than in the ordinary instruments, issues from the
+box, and serves as its support.</p>
+
+<figure id="il_38" class="figcenter" style="max-width: 23em;">
+  <img src="images/i_p127b.jpg" width="902" height="515" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 38.</span>
+  </figcaption>
+</figure>
+
+<p>The sender resembles the one represented
+in <a href="#il_19">fig. 19</a>, except that, instead of liquid, M. Righi
+employs plumbago mixed with powdered silver,
+and the platinum needle is replaced by a metallic
+disk <span class="allsmcap">D</span> (<a href="#il_38">fig. 38</a>). The receiver <span class="allsmcap">I</span>, which contains the
+powder, is supported on a spring <span class="allsmcap">R</span>, which can be<span class="pagenum" id="Page_128">128</span>
+pushed up and down by a regulating screw <span class="allsmcap">V</span>, and
+the whole is fitted into a box <span class="allsmcap">C C</span>, and supported
+on a foot <span class="allsmcap">P</span>. The speaker places himself above
+the mouthpiece <span class="allsmcap">E</span>, and the vibrations transmitted
+to the membrane <span class="allsmcap">L L</span> cause the variations of resistance
+in <span class="allsmcap">I</span> which are necessary for the transmission
+of speech, as in the Edison system. Two
+Bunsen cells are enough to set the instrument
+at work, and it will make the sound of a trumpet
+or flute audible throughout a room. Vocal music,
+which is less intense, is necessarily transmitted to
+a rather less distance, and words spoken in the
+natural voice are heard by those standing about
+two yards and a half from the instrument.</p>
+
+<p>The maximum distance at which the instrument
+has been worked with the battery only is
+twenty-eight miles, the distance between Bologna
+and Ferrara, and for greater distances it is necessary
+to have recourse to induction coils.</p>
+
+<p>In this case, an induction coil is introduced
+into the circuit at each station, and its primary
+wire is traversed by a current from the local battery,
+and so also is the sender, which is elsewhere
+connected with the receiver by a commutator.
+The secondary circuit of these coils is completed
+through the earth and line wire. From
+this arrangement it follows that the induced
+current which influences the receiver in correspondence,
+only produces its effect after a second
+induction, produced on the primary wire of the<span class="pagenum" id="Page_129">129</span>
+local coil, and it appears that this is a sufficient
+effect; but the advantage of this arrangement is,
+that it is possible to receive and transmit sounds
+without the aid of anything but the commutator.</p>
+
+<p>Among other arrangements which have been
+suggested, we may mention one in which, instead
+of the bar magnet, a horseshoe magnet is used,
+with a vibrating plate placed between its poles.
+For this purpose the poles are tipped with iron, and
+one of them is pierced with a hole which corresponds
+to the mouthpiece of the instrument. The
+two branches of the magnet are also furnished with
+magnetising helices. When anything is spoken
+before the hole, the vibrating plate causes induced
+currents in the two helices: these currents would
+be of opposite direction if the poles were of like
+nature, but, since the magnetic poles are of contrary
+nature, they are in the same direction. The
+vibrating plate then acts like the two plates of
+M. Trouvé’s instrument, which we have described
+above.</p>
+
+<p>In another arrangement, lately made by Ader,
+the receiver is only an ordinary two-branched
+magnet, of which the armature is supported, at
+about two millimètres from its poles, by a glass
+plate to which it is glued, and the plate itself is
+fastened to two rigid supports. In order to hear it
+is only necessary to apply the ear to the plate. The
+sender is a moveable rod of iron or carbon, which<span class="pagenum" id="Page_130">130</span>
+rests on a fixed piece of carbon, with no pressure
+except its own weight, and it supports a concave
+disk, to which the speaker applies his mouth.
+These two parts are so arranged as to move horizontally,
+so that, when the instrument is suspended,
+the circuit is forcibly disconnected by the fact of its
+position, and is therefore closed until anyone takes
+it up to speak. Speech is well reproduced by this
+system, and may be transmitted to some distance if
+it is made on a larger scale.</p>
+
+<p>Again, an anonymous inventor, in a little note
+inserted in ‘Les Mondes,’ February 7, 1878, writes
+as follows: ‘Since the intensity of the currents
+produced in the telephone is in proportion to the
+mass of soft iron which vibrates before the pole of
+the magnet, and since, on the other hand, the plate
+is sensitive in proportion to its tenuity, I employ,
+instead of the ordinary plate, one reduced by nitric
+acid to the least possible thickness, and I fix it to
+a circle of soft iron, which keeps it stretched and
+forms part of the same substance. This circle is
+placed in a circular opening made inside the compartment.
+The intensity of a telephone is much
+increased when such a system replaces the ordinary
+plate, even at one end of the line.’</p>
+
+<p>In order to obtain vibrating plates of extreme
+tenuity, M.&nbsp;E. Duchemin thought of employing
+very thin plates of mica, sprinkled with pulverised
+iron fixed to the plate by a layer of silicate of
+potash. The inventor asserts that it is possible to<span class="pagenum" id="Page_131">131</span>
+correspond in a low voice with the aid of this system;
+but it has this inconvenience, that the plate
+will be broken by speaking too loud.</p>
+
+<p>Professor Jorgenson, of Copenhagen, has also
+made a Bell telephone which produces very
+intense sounds, and which has permitted him to
+observe some curious effects. In this instrument,
+the magnet is made in a mode analogous to Nicklès’
+tubular magnets. There is first a cylindrical
+magnet with a core of soft iron at its upper end,
+to which the coil is fitted; next, a magnetised tube,
+formed of a steel ring, which encloses the first magnetic
+system, and is connected with it by an iron
+tube. Finally, above the polar extremities of this
+system, there is the vibrating disk, with the same
+arrangement as that of ordinary telephones, and
+of which the superficies is large. If this plate is
+only a millimètre in thickness, the words spoken
+can be heard throughout a room; but the sounds
+lose their clearness when the ear is approached to
+the vibrating plate, the words are confused, and there
+is the reverberation which is observed on speaking
+in a place apt to produce echoes: the listener is, in
+fact, stunned by the sounds produced. On using a
+thicker plate—one, for example, of three or four
+millimètres—the telephone only produces the effect
+of the ordinary instruments, and it is necessary
+to apply the ear to it.</p>
+
+<p>M. Marin Maillet, of Lyons, has suggested that
+the sounds reproduced by the telephone might be<span class="pagenum" id="Page_132">132</span>
+increased by reflecting them through a certain
+number of reflectors, which, by concentrating them
+in a focus on a resonator, would considerably
+enlarge them. Since this idea was not accompanied
+by experiments, it can hardly be regarded as
+serious.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h2 class="nobreak" id="TELEPHONIC_EXPERIMENTS"><span id="toclink_132"></span>TELEPHONIC EXPERIMENTS.</h2>
+</div>
+
+<p>Since Mr. Bell’s experiments of which an account
+has been given in the early part of this
+work, much study has been given by men of
+science and inventors to the effects produced in
+this curious instrument, so as to ascertain its theory
+and deduce improvements in its construction. We
+will take a glance at these researches in succession.</p>
+
+<p><i>Experiments on the Effects produced by Voltaic
+and Induced Currents.</i>—The comparative study of
+the effects produced in the telephone by voltaic and
+induced currents was one of the first and most
+important. In 1873, as we have seen, Mr. Elisha
+Gray converted the voltaic currents, which he
+employed to cause the vibrations of his transmitting
+plate, into induced currents by means of an
+induction coil, such as Ruhmkorff’s. The voltaic
+currents then traversed the primary helix of the
+coil, and the induced currents reacted on the
+receiving instrument, producing on its electro-magnetic
+system the vibrations excited at the sending
+station. When Mr. Edison designed his battery<span class="pagenum" id="Page_133">133</span>
+telephone, he had recourse to the same means to
+work his receiving telephone, since he had ascertained
+that induced currents were superior to voltaic
+currents. But this peculiarity of Mr. Edison’s
+arrangement was not clearly understood from the
+descriptions which reached Europe, so that several
+persons believed that they had invented this arrangement—among
+others, Colonel Navez and MM.
+Pollard and Garnier.</p>
+
+<p>Colonel Navez, in an interesting paper on the
+new telephonic system, presented to the Belgian
+Royal Academy, February 2, 1878, only suggests
+this arrangement as a mode of reproducing speech
+at a great distance; but he quotes no experiment
+which distinctly shows the advantages of this combination.
+Twenty days later, MM. Pollard and
+Garnier, unacquainted with Colonel Navez’s
+researches, sent to me the results they had obtained
+by similar means, and these results appeared
+to me so interesting that I communicated them to
+the Académie des Sciences, February 25, 1878.
+In order that the importance of these results may
+be clearly understood, I will repeat the text of M.
+Pollard’s letter, addressed to me on February 20,
+1878:</p>
+
+<p>‘With the object of increasing the variations of
+electric intensity in the Edison system, we induce
+a current in the circuit of a small Ruhmkorff coil,
+and we fix the receiving telephone to the extremities
+of the induced wire. The current received has the<span class="pagenum" id="Page_134">134</span>
+same intensity as that of the inducing current, and
+consequently the variations produced in the current
+which works the telephone have a much wider
+range. The intensity of the transmitted sounds is
+strongly increased, and the value of this increase
+depends upon the relative number of spirals in the
+inducing and induced circuits. Our attempts to
+determine the best proportions have been laborious,
+since it is necessary to make a coil for each experiment;
+we have hitherto obtained excellent results
+with a small Ruhmkorff coil reduced to its simplest
+form, that is, without condenser or contact-breaker.
+The inducing wire is No. 16, and is wound in five
+layers; the induced wire is No. 32, and in twenty
+layers. The length of the coil is seven centimètres.</p>
+
+<p>‘The following is the most remarkable and
+instructive experiment: When setting the sender
+to work with a single Daniell cell, there is no
+appreciable effect at the receiving station, at least
+in the telephone which I have made, when it is
+in immediate connection with the circuit; after
+inserting the small induction coil, sounds become
+distinctly audible, and their intensity equals that
+of good ordinary telephones. Since the battery
+current is only moderately intense, the points of
+plumbago are not worn down, and the regulating
+apparatus lasts for a long while. When a stronger
+battery is used, consisting of six cells of bichromate
+of potash (in tension) or twelve Leclanché<span class="pagenum" id="Page_135">135</span>
+cells, sufficient intensity is obtained by the direct
+action to make sounds nearly as audible as
+in ordinary telephones; but when the induction
+coil is inserted, the sounds become much more
+intense, and may be heard at a distance of from
+fifty to sixty centimètres from the mouthpiece.
+Songs may, under such circumstances, be heard
+at a distance of several yards; but the relative
+increase does not appear to be so great as in the
+case of the single Daniell cell.’</p>
+
+<p>On the other hand, ‘Les Mondes,’ March 7,
+1878, contains an account of a series of experiments
+made by Signor Luvini, Professor of Physics
+at the Military Academy of Turin, which proved
+that the introduction of electro-magnets into the
+circuit which connects the two telephones sensibly
+increases the intensity of sound. The maximum
+effect is produced by placing one close to the transmitting,
+and the other close to the receiving
+telephone, and the introduction of other magnets
+is of no use. The inducing wire of a Ruhmkorff
+coil, when introduced into such a circuit, excited
+no sensible effects of induction in the induced
+circuit, and consequently could not set the telephone
+in connection with this circuit at work. But
+the current of a Clarke machine produces sounds
+resembling the beats of a drum, which are deafening
+when the ear is applied to the instrument:
+they become very faint, however, at the distance of
+a mètre. The currents of a Ruhmkorff machine are<span class="pagenum" id="Page_136">136</span>
+still more energetic, and the sound fills a whole
+room. By modifying the position of the lever of
+the coil, the sound passes through different tones,
+which are always in unison with the breaks of the
+current, at least up to a certain pitch.</p>
+
+<p>This property of currents induced by the
+Ruhmkorff coil has enabled M. Gaiffe to obtain by
+their means a very simple mode of regulating
+telephones, so as to produce in them the maximum
+amount of sensibility. For this purpose he places
+the telephone he proposes to regulate in the circuit
+of an induction instrument with moveable helices
+and graduated intensities. The sounds which
+result from the vibrator are then reverberated from
+the telephone, and are audible at a distance from
+the instrument; by using a screw-driver, it is
+possible to adjust the screw to which the free end
+of the bar magnet of the instrument is fixed. It
+can be tightened or loosened, so as to advance or
+withdraw the other end of the magnet from the
+vibrating plate of the telephone, and the process is
+repeated until the maximum intensity of sound is
+obtained.</p>
+
+<p>On the other hand, as the sounds given out by
+the two telephones in correspondence are intense in
+proportion to the degree of unison in the vibrations
+produced by them, it is necessary to select those
+which emit the same sounds for the same given
+note; and the mode we have just described may be
+employed with advantage, since it will be enough<span class="pagenum" id="Page_137">137</span>
+to observe what instruments give the same note
+in the condition of maximum sensibility, when
+regulated in the same way by the induction machine.</p>
+
+<p>It is very important that the telephones in
+correspondence should be well matched, not only to
+ensure clear transmissions, but also with reference
+to the tone of voice of those who are to use it.
+The sound becomes more audible when the tone
+of voice corresponds to the telephonic tone; and
+for this reason some telephones repeat the voices
+of women and children better than those of men,
+and with others the reverse takes place.</p>
+
+<p>The telephonic vibrations vary in different
+instruments, and these variations may be noted in
+the way we have indicated.</p>
+
+<p>The advantages of induced currents in telephonic
+transmissions may be easily understood, if
+we consider that the variations of resistance in the
+circuit, resulting from the greater or less range in
+the vibrations of the transmitting plate, are of constant
+value, and can only manifest their effects
+distinctly in short circuits; consequently the articulate
+sounds which result from them can only be
+really appreciable in circuits of great resistance.
+According to Mr. Warren de la Rue’s experiments
+(reported in the ‘Telegraphic Journal,’ March 1,
+1878), the currents produced by the vibrations
+of the voice in an ordinary telephone represent
+in intensity those of a Daniell cell traversing<span class="pagenum" id="Page_138">138</span>
+100 megohms of resistance (or 10,000,000 kilomètres);
+and it is plain that the simple question of
+greater or less intensity in the currents acting on
+the receiving telephone is not the only thing we
+have to consider. With an energetic battery, it is
+evident, in fact, that the differential currents will
+always be more intense than the induced currents
+produced by the action of the instrument. I
+myself am inclined to believe that induced currents
+owe the advantages they possess to the succession
+of inverse currents and their brief duration. These
+currents, of which M. Blaserna considers that the
+duration does not exceed 1/200 of a second, are much
+more susceptible than voltaic currents of the multiplied
+vibrations which are characteristic of phonetic
+vibrations, and especially since the succession
+of inverse currents which take place discharge the
+line, reverse the magnetic effects, and contribute to
+make the action more distinct and rapid. We
+cannot therefore be surprised that the induced
+currents of the induction coil, which can be produced
+under excellent conditions at the sending
+station, since the circuit of the voltaic current
+is then very short, are able to furnish results, not
+only more effective than the voltaic currents from
+which they take their origin, but even than the induced
+currents resulting from the action of the Bell
+telephone, since they are infinitely more energetic.</p>
+
+<p>As for the effects produced by the currents of
+Bell telephones, which are relatively great when we<span class="pagenum" id="Page_139">139</span>
+consider their size, they are easily explained from
+the fact that they are produced under the influence
+of the vibrations of the telephone plate, so that
+their variations of intensity always maintain the
+same proportion, whatever may be the resistance of
+the circuit, and consequently they are not effaced
+by the distance which divides the two telephones.</p>
+
+<p><i>Experiments on the part taken by the different
+telephonic organs in the transmission of speech.</i>—In
+order to introduce all the improvements of which a
+telephone is capable, it is important to be quite
+decided as to the effects produced in the several
+parts of which it is composed, and as to the part
+taken by the several organs which are at work. To
+attain this object several men of science and
+engineers have undertaken a series of experiments
+which have produced very interesting results.</p>
+
+<p>One of the points on which it was most important
+to throw light was that of ascertaining
+whether the vibrating plate used in their telephone
+receivers by Messrs. Bell and Gray is the only cause
+of the complex vibrations which reproduce speech,
+or if the different parts of the electro-magnetic
+system of the instrument all conduce to this effect.
+The experiments made by Mr. Page in 1837 on the
+sounds produced by the resonant electro-magnetic
+rods, and the researches pursued in 1846 by Messrs.
+de la Rive, Wertheim, Matteucci, &amp;c., on this curious
+phenomenon, allow us to state the question, which
+is certainly more complex than it at first appears.</p>
+
+<p><span class="pagenum" id="Page_140">140</span></p>
+
+<p>In order to start from a fixed point, it must
+first be ascertained whether a telephone can transmit
+speech without a vibrating plate. Experiments
+made by Mr. Edison<a id="FNanchor_9" href="#Footnote_9" class="fnanchor">9</a> in November 1877, with
+telephones provided with copper diaphragms, which
+produced sounds, make the hypothesis credible; and
+it received greater weight from the experiments
+made by Mr. Preece and Mr. Blyth. The fact was
+placed beyond a doubt by Mr. Spottiswoode (see
+the ‘Telegraphic Journal’ of March 1, 1878), who
+assures us that the vibrating plate of the telephone
+may be entirely suppressed without preventing the
+transmission of speech, provided that the polar extremity
+of the magnet be placed quite close to the
+ear; and it was after this that I presented to the
+Académie des Sciences my paper on the theory
+of the telephone, which led to an interesting discussion
+of which I shall speak presently. At first
+the authenticity of these results was denied, and
+then an attempt was made to explain the sounds
+heard by Mr. Spottiswoode as a mechanical transmission<span class="pagenum" id="Page_141">141</span>
+of the vibrations, effected after the manner
+of string telephones; but the numerous experiments
+which have subsequently been made by Messrs.
+Warwick, Rossetti, Hughes, Millar, Lloyd, Buchin,
+Canestrelli, Wiesendanger, Varley, and many others,
+show that this is not the case, and that a telephone
+without a diaphragm can transmit speech electrically.</p>
+
+<p>Colonel Navez himself, who had first denied
+the fact, now admits that a telephone without a
+diaphragm can emit sounds, and even, under certain
+exceptional conditions, can reproduce the human
+voice; but he still believes that it is impossible to
+distinguish articulate words.</p>
+
+<p>This uncertainty as to the results obtained by
+the different physicists who have studied the
+matter shows that at any rate the sounds thus
+reproduced are not clearly defined, and that in
+physical phenomena, only appreciable to our senses,
+the appreciation of an effect so undefined must
+depend on the perfection of our organs. We shall
+presently see that this very slight effect can be
+largely increased by the arrangement adopted by
+Messrs. Bell and Gray, and we shall also see that,
+by a certain mode of magnifying the vibrations, it
+has been decisively proved that a telephone without
+a diaphragm can readily reproduce speech. I
+proceed to give the description of such a telephone,
+which was shown by Mr. Millar at the meeting of
+the British Association at Dublin in August 1878.</p>
+
+<p><span class="pagenum" id="Page_142">142</span></p>
+
+<p>This instrument consists of a small bar magnet,
+three inches in length and 5/16 of an inch in width
+and thickness, and a copper helix (No. 30) of
+about six mètres in length is wound round the bar.
+It is fixed in a box of rather thick pasteboard,
+fitted above and below with two zinc plates, which
+render it very portable. With a telephonic battery
+sender and a single Leclanché cell, speech can
+be perfectly transmitted; the whistling of an air,
+a song, and even the act of respiration become
+audible. It seems also that the instrument can
+act without a magnet, merely with a piece of iron
+surrounded by the helix; but the sounds are then
+much fainter.</p>
+
+<p>Signor Ignace Canestrelli obtained the same
+results by making one of the carbon telephonic
+senders react on a telephone without a diaphragm,
+by means of an induction coil influenced
+by two Bunsen cells. He writes as follows on
+the subject:</p>
+
+<p>‘With this arrangement I was able to hear the
+sound of any musical instrument on a telephone
+without a diaphragm: singing, speaking, and
+whistling were perfectly audible. Whistling could
+be heard, even when the telephone without a
+diaphragm was placed at some distance from the
+ear. In some cases, depending on the pitch of the
+voice, on the distance of the sending station, and on
+the joint pressure exerted by the carbons, I could
+even distinguish words.</p>
+
+<p><span class="pagenum" id="Page_143">143</span></p>
+
+<p>‘I finally discharged the currents of the transmitter
+into the coils of insulated copper wire with
+which the two poles of a magnet were provided.
+This magnet was placed on a musical box, made
+of very thin slips of wood, and on placing the ear
+at the opening of the box I obtained the same
+results as with the ordinary telephones without a
+diaphragm.’</p>
+
+<p>M. Buchin, after repeating experiments of the
+same kind as the above, intimates that it is easy
+to hear the sounds produced by a telephone without
+a diaphragm, by introducing into the ear the
+end of an iron rod, of which the other end is applied
+to the active pole of the bar magnet of the
+telephone. (See ‘Le Journal d’Electricité,’ October
+5, 1878.)</p>
+
+<p>I repeat finally the account of some experiments
+made by Mr. Hughes and M. Paul Roy
+which are interesting from our present point of
+view.</p>
+
+<p>1. If an armature of soft iron is applied to the
+poles of an electro-magnet, with its two branches
+firmly fixed on a board, and if pieces of paper are
+inserted between this armature and the magnetic
+poles, so as to obviate the effects of condensed
+magnetism; if, finally, this electro-magnet is connected
+with a speaking microphone, of the form
+given in <a href="#il_39">fig. 39</a>, it is possible to hear the words
+spoken in the microphone on the board which
+supports the electro-magnet.</p>
+
+<p><span class="pagenum" id="Page_144">144</span></p>
+
+<p>2. If two electro-magnets are placed in communication
+with a microphone, with their poles of
+contrary signs opposite to each other, and if their
+poles are separated by pieces of paper, speech will
+be distinctly reproduced, without employing armature
+or diaphragm. These experiments are, however,
+delicate, and demand a practised ear.</p>
+
+<p>3. If, instead of causing the current produced
+by a microphone to pass through the helix of a
+receiving telephone, it is sent directly into the bar
+magnet of this telephone in the direction of its axis—that
+is, from one pole to another—the words pronounced
+in the microphone may be distinctly heard.
+This experiment by M. Paul Roy indicates, if it
+is exact, that the electric pulsations which traverse
+a magnet longitudinally will modify its magnetic
+intensity. The experiment, however, demands
+verification.</p>
+
+<p>Another point was obscure. It was important
+to know whether the diaphragm of a telephone
+really vibrates, or at least if its vibrations could
+involve its displacement, such as occurs in an
+electric vibrator, or in wind instruments which
+vibrate with a current of air. M. Antoine Bréguet
+has made some interesting experiments on the
+subject, which show that such a movement cannot
+take place, since speech was reproduced with great
+distinctness from telephones with vibrating plates
+of various degrees of thickness, and he carried the
+experiment so far as to employ plates fifteen centimètres<span class="pagenum" id="Page_145">145</span>
+in thickness.<a id="FNanchor_10" href="#Footnote_10" class="fnanchor">10</a> When pieces of wood,
+caoutchouc, and other substances were laid upon
+these thick plates, the results were the same. In
+this case it cannot be supposed that the plates
+were moved to and fro. I have moreover ascertained,
+by placing a layer of water or of mercury on
+these plates, and even on thin diaphragms, that no
+sensible movement took place, at least when the
+induced currents produced by the action of speaking
+were used as the electric source. No ripples
+could be seen on the surface of the liquid, even
+when luminous reflectors were employed to detect
+them. And indeed it can hardly be admitted that
+a current not more intense than that of a Daniell
+element, which has traversed 10,000,000 kilomètres
+of telegraphic wire—a current which can only
+show deviation on a Thomson galvanometer—should
+be powerful enough to make an iron plate as
+tightly stretched as that of a telephone vibrate by
+attraction, even if we grant that the current was
+produced by laying a finger on the diaphragm.</p>
+
+<p>Very nice photographic experiments do, however,
+show that vibrations are produced on the
+diaphragm of the receiving telephone; they are
+indeed excessively slight, but Mr. Blake asserts
+that they are enough to cause a very light index,
+resting on the diaphragm, to make slight inflections<span class="pagenum" id="Page_146">146</span>
+on a line which it describes on a register.
+Yet this small vibration of the diaphragm does not
+show that it is due to the effect of attraction, for it
+may result from the act of magnetisation itself in
+the centre of the diaphragm.<a id="FNanchor_11" href="#Footnote_11" class="fnanchor">11</a> An interesting experiment
+by Mr. Hughes, repeated under different
+conditions by Mr. Millar, confirms this opinion.</p>
+
+<p>If the magnet of a receiving telephone consists
+of two magnetised bars, perfectly equal, separated
+from each other by a magnetic insulator,
+and they are so placed in the coil as to bring
+alternately the poles of the same and of contrary
+signs opposite to the diaphragm, it is known that
+the telephone will reproduce speech better in the
+latter case than in the former. Now, if the effects
+were due to attraction, this would not be the case;
+for the actions are in disagreement when the poles
+of contrary signs are subjected to the same electric
+influence, while they are in agreement when these
+poles are of like signs.</p>
+
+<p>On the other hand, it is known that if several<span class="pagenum" id="Page_147">147</span>
+iron plates are put together in order to form the
+diaphragm of the receiver, the transmission of
+sounds is much stronger than with a simple diaphragm;
+and yet the attraction, if it has anything
+to do with it, could only be exerted on one of the
+diaphragms.</p>
+
+<p>It further appears that it is not merely the
+magnetic core which emits sounds, but that they
+are also produced with some distinctness by the
+helices. Signor Rossetti had already ascertained
+this fact, and had even remarked that they could be
+animated by a slight oscillatory movement along
+the bar magnet, when they were not fixed upon it.
+Several observers, among others M. Paul Roy, Herr
+Wiesendanger, and Signor Canestrelli, have since
+mentioned similar facts, which are really interesting.</p>
+
+<p>‘If,’ writes M. Paul Roy, ‘a coil of fine wire,
+which is at the extremity of the bar magnet of a
+Bell telephone, receives the pulsatory currents
+transmitted by a carbon telephone, it is only necessary
+to bring the coil close to the ear in order to
+hear the sounds.</p>
+
+<p>‘The sounds received in this way are very faint,
+but become much stronger if a piece of iron is introduced
+into the circuit coil. A magnet acts with
+still greater force, even when it consists of a simple
+magnetised needle. Finally, the sound assumes its
+maximum intensity when an iron disk is inserted
+between the ear and the coil.</p>
+
+<p>‘By placing the end of the coil to the ear, and<span class="pagenum" id="Page_148">148</span>
+sending a current through it from the bar magnet,
+it is ascertained that the sound is at its minimum
+when the neutral line of the magnet is enclosed by
+the coil, and that it increases until attaining its
+maximum, when the magnet is moved until one of
+its poles corresponds to the coil.</p>
+
+<p>‘This fact of the reproduction of sounds by a
+helix is universal. Every induction coil and every
+electro-magnet are capable of reproducing sound
+when the currents of the sender are of sufficient
+intensity.’</p>
+
+<p>Signor Canestrelli writes as follows: ‘With the
+combination of a carbon telephone and one without
+diaphragm or magnet—that is, with only a
+simple coil—I was able to hear whistling through
+the coil, placed close to the ear. This coil was of
+very fine copper wire, and the currents were produced
+through an induction coil by two Bunsen
+elements. The contacts of the telephone were
+in carbon, and it was inserted in the primary
+circuit.</p>
+
+<p>‘I fastened the coil to the middle of a tightly
+stretched membrane which served as the base of a
+short metal cylinder. When a magnet was placed
+near this part of the coil, the sounds were intensified,
+and when I fixed the magnet in this position,
+I could hear what was said.</p>
+
+<p>‘I afterwards substituted for the magnet a
+second coil, fastened to a wooden bar, and on
+causing the induced currents to pass into both coils<span class="pagenum" id="Page_149">149</span>
+at once I was able to hear articulate speech, although
+not without difficulty.</p>
+
+<p>‘Under these latter conditions I found it possible
+to construct a telephone without a magnet,
+but it required a strong current, and it was necessary
+to speak into the sender in a special manner,
+so as to produce strong and concentrated sounds.’</p>
+
+<p>Another very interesting experiment by M.&nbsp;A.
+Bréguet shows that all the constituent parts of the
+telephone—the handle, the copper rims, and the
+case, as well as the diaphragm and the electro-magnet—can
+transmit sounds. M. Bréguet ascertained
+this fact by the use of string telephones,
+which he attached to different parts of the telephone
+on which the experiment was made. In
+this way he was not only able to establish a correspondence
+between the person who worked the
+electric telephone and the one who was listening
+through the string telephone, but he also made
+several string telephones act, which were attached
+to different parts of the electric telephone.</p>
+
+<p>These two series of experiments show that
+sounds may be obtained from different parts of the
+telephone without any very appreciable vibratory
+movements. But Signor Luvini wished for a further
+assurance of the fact, by ascertaining whether the
+magnetisation of any magnetic substance, followed
+by its demagnetisation, would involve a variation
+in the form and dimensions of this substance. He
+consequently caused a large tubular electro-magnet<span class="pagenum" id="Page_150">150</span>
+to be made, which he filled with a quantity of
+water, so that, when its two ends were corked, the
+liquid should rise in a capillary tube fitted to one
+of the corks. In this way the slightest variations
+in the capacity of the hollow part of the electro-magnet
+were revealed by the ascent or descent of
+the liquid column. He next sent an electric
+current of varying intensity through the electro-magnet,
+but he was never able to detect any
+change in the level of the water in the tube;
+although by this arrangement he could measure a
+change of volume of 1/30 of a cubic millimètre. It
+appears from this experiment that the vibrations
+produced in a magnetic substance under the influence
+of successive magnetisations and demagnetisations,
+are wholly molecular. Yet other experiments
+made by M. Canestrelli seem to show that
+these vibrations are so far sensible as to produce
+sounds which can be detected by the microphone.
+He writes as follows on the subject:</p>
+
+<p>‘When the broken currents of an induction
+coil are discharged into a coil placed on a sounding-box,
+it is possible to hear at a little distance the
+sounds produced by the induced currents thus
+generated. On approaching the magnet to the
+opening of the coil, these sounds are intensified,
+and the vibrations of the magnet become sensible
+to the touch; this vibration might even be made
+visible by suspending the magnet inserted into
+the coil to a metallic wire, which is fitted to a membrane<span class="pagenum" id="Page_151">151</span>
+stretched on a drum, and the latter will
+then reproduce sounds. When the same magnet
+is suspended to a microphone, it is possible, with
+the aid of a telephone, to ascertain the same effects,
+which are then increased.’</p>
+
+<p>We shall presently consider how these different
+deductions are to be interpreted, so as to render
+the true theory of the telephone intelligible; but,
+before doing so, we will mention some other experiments
+which are not without interest.</p>
+
+<p>We have seen that the experiments of Messrs.
+Edison, Blyth, and Preece, show that sounds may
+be reproduced by a telephone with a diaphragm
+made of some unmagnetic substance, and they also
+show, which is still more curious, that these sounds
+may be transmitted under the influence of induced
+currents produced by these diaphragms when they
+are placed in vibration before the magnet. Messrs.
+Edison and Blyth had already adduced this fact,
+which was received with incredulity, but it has
+been confirmed by Mr. Warwick in an article
+published in the ‘English Mechanic.’ He writes
+that in order to act upon the magnet, so as to produce
+induced currents, something possessed of
+greater energy than gas must first be made to
+vibrate. It is not, however, necessary that this
+substance should be magnetic, for diamagnetic
+substances act perfectly.<a id="FNanchor_12" href="#Footnote_12" class="fnanchor">12</a> Mr. Preece sought for<span class="pagenum" id="Page_152">152</span>
+the cause in the induced currents developed in
+any conducting body when a magnet is moved<span class="pagenum" id="Page_153">153</span>
+before it, currents which give rise to the phenomenon
+discovered by Arago and known by the
+name of magnetism by rotation. Yet these facts do
+not appear to us to be sufficiently well established
+to make the theory worthy of serious consideration,
+and it is possible that the effects observed resulted
+from simple mechanical transmissions.</p>
+
+<p>To conclude the account of these experiments,
+we will add that Mr. W.&nbsp;F. Barrett thinks it somewhat
+difficult to define the mode of vibration of the
+diaphragm, since, while a certain amount of compression
+exerted on the iron destroys the sounds<span class="pagenum" id="Page_154">154</span>
+resulting from the peculiar effects of magnetisation,
+a still stronger compression causes them to reappear.
+It is certain that the question is full of
+obscurity, and demands great research: it is enough
+to have shown that the theory hitherto held is insufficient.</p>
+
+<p>On the other hand, Colonel Navez considers
+that the intensity of sound reproduced in a telephone
+depends not only on the range of vibrations,
+but also on the vibrating surface and the effect it
+produces on the stratum of air which transmits the
+sound. (See paper by Colonel Navez in the
+‘Bulletin de l’Académie de Belgique,’ July 7,
+1878.)</p>
+
+<p><i>Experiments on the Effects which result from
+Mechanical Shocks communicated to different parts
+of a Telephone.</i>—If a piece of iron is applied to the
+screw which holds the magnet of the ordinary telephone,
+it is observed that the transmitted sounds are
+more distinct, owing to the force supplied to the
+active pole of the magnet; but at the moment when
+the piece of iron is applied to the screw a distinct
+noise is heard, which seems to be due to the mechanical
+vibrations caused in the magnet at the moment
+of the shock. M. des Portes, a lieutenant in the
+French navy, has lately made some interesting
+experiments on this class of phenomena. He has
+observed that if, in a telephonic circuit of 90
+yards completed by the earth, the sending telephone
+is reduced to a simple magnet, provided<span class="pagenum" id="Page_155">155</span>
+with the coil which constitutes its electro-magnetic
+organ, and if this magnet is suspended vertically
+by a silken thread, with the coil above it, a blow
+struck upon the magnet, either by a copper rod or
+a piece of wood, will cause distinct sounds to be
+produced in the receiving telephone—sounds which
+will increase in intensity when the blow is struck
+close to the coil, and which will become still
+stronger, but less clear, if a vibrating plate of soft
+iron is placed in contact with the upper pole of the
+magnet.</p>
+
+<p>When the striking instrument is made of iron,
+the sounds in question are more strongly marked
+than if it is of wood, and when the magnet has a
+vibrating disk applied to its active pole, a vibration
+of the disk takes place at the moment when the
+shock is heard.</p>
+
+<p>If the striking body is a magnet, the sounds
+produced resemble those obtained when it is of
+iron, if the effect is produced between poles of the
+same nature; but if the poles are of contrary
+natures, a second noise is heard after each blow,
+which is produced by drawing away the magnet,
+and which appears to be a blow struck with much
+less force. The sound is of course increased if the
+magnet is provided with its vibrating disk.</p>
+
+<p>If words are uttered on the vibrating disk of
+the sending telephone, when it is applied to the
+pole of the magnet, various sounds are heard on
+the receiving telephone, somewhat similar to those<span class="pagenum" id="Page_156">156</span>
+produced by vibrating one of the strings of a
+violin, and the sound made in withdrawing the
+disk from contact with the magnet is distinctly
+heard in the receiver.</p>
+
+<p>The person who applies his ear to the vibrating
+disk of the sender when it is arranged as above,
+may hear the voice of anyone who speaks into
+the receiver, but cannot distinguish the words,
+owing, no doubt, to the condensed magnetism at
+the point of contact between the magnet and the
+vibrating disk, which slackens the magnetic variations
+and makes it more difficult for them to take
+place.</p>
+
+<p>A coil is not necessary in order to perceive the
+blows struck upon the magnet with a rod of soft
+iron. It is enough to wind three turns of naked
+conducting wire, which acts as line wire, round one
+end of the magnet, and the sounds perceived cease,
+as in other experiments, when the circuit is broken,
+plainly showing that they are not due to mechanical
+transmission. It is a still more curious fact
+that if the magnet is placed in the circuit, so as to
+form an integral part of it, and if the two ends of
+the conducting wire are wound round the ends of
+the magnet, the blows struck upon the latter with
+the soft iron rod are perceived in the telephone
+as soon as one pole of the magnet is provided with
+a vibrating disk.</p>
+
+<p>I have myself repeated M. des Portes’ experiments
+by simply striking on the screw which, in<span class="pagenum" id="Page_157">157</span>
+ordinary telephones, fastens the magnet to the instrument,
+and I have ascertained that, whenever the
+circuit was complete, the blows struck with an ivory
+knife were repeated by the telephone: they were, it
+is true, very faint when the vibrating disk was removed,
+but very marked when the disk was in its
+place. On the other hand, no sound was perceived
+when the circuit was broken. These sounds
+were louder when the blows were struck upon the
+screw than when they were struck on the pole of
+the magnet itself above the coil: for this reason,
+that in the first case the magnet could vibrate
+freely, while in the second the vibrations were
+stifled by the fixed position of the bar magnet.</p>
+
+<p>These effects may be to some extent explained
+by saying that the vibrations caused in the magnet
+by the shock produce undulatory displacements of
+the magnetised particles in the whole length of the
+bar, and that induced currents would, according to
+Lenz’s law, result in the helix from these displacements—currents
+of which the force would increase
+when the power of the magnet was further excited
+by the reaction of the diaphragm, which acts as an
+armature, and also by that of the striking instrument
+when it also is magnetic. Yet it is more difficult to
+explain M. des Portes’ later experiments, and the
+effect may be produced by something more than
+the ordinary induced currents.</p>
+
+<p>These are not the only experiments which
+show the effects produced under the influence of<span class="pagenum" id="Page_158">158</span>
+molecular disturbance of various kinds. Mr.
+Thompson, of Bristol, has observed that if a piece
+of iron and a tin rod placed perpendicularly on the
+iron are introduced into the circuit of an ordinary
+telephone, it is enough to strike the tin rod in
+order to produce a loud sound in the telephone.
+He has also shown that if the two ends of a bar
+magnet are enclosed by two induction coils which
+are placed in connection with the circuit of a telephone,
+and if the flame of a spirit lamp is moved
+below the magnet in the space dividing the two
+coils, a distinct sound is heard as soon as the flame
+exerts its influence on the bar magnet. This effect
+is undoubtedly due to the weakening of the magnetic
+force of the bar which is produced by the
+action of heat. I have myself observed that a
+scratching sound on one of the wires which connect
+the telephones is heard in both of them, at
+whatever point in the circuit the scratch is made.
+The sounds produced are indeed very faint, but they
+can be distinctly heard, and they become more
+intense when the scratch is made on the binding-screws
+of the telephone wires. These sounds
+cannot result from the mechanical transmission of
+vibrations, since they are imperceptible when the
+circuit is broken. From these experiments it appears
+that some sounds which have been observed
+in telephones tried on telegraph stations may
+arise from the friction of the wires on their supports—a
+friction which produces those very intense<span class="pagenum" id="Page_159">159</span>
+sounds which are sometimes heard on telegraphic
+wires.</p>
+
+<p><i>Theory of the Telephone.</i>—It appears from the
+several experiments of which we have spoken
+that the explanation generally given of the effects
+produced in the telephone is very imperfect, and
+that the transmission of speech, instead of resulting
+from the repetition by the membrane of the
+receiving telephone (influenced by electro-magnetism)
+of vibrations caused by the voice on the
+membrane of the transmitting membrane, is due
+to molecular vibrations produced in the whole
+electro-magnetic system, and especially on the
+magnetic core contained in the helix. These vibrations
+must be of the same nature as those
+which have been observed in resonant electro-magnetic
+rods by MM. Page, de la Rive, Wertheim,
+Matteucci, &amp;c., and these have been employed
+in telephones by Reiss, by Cecil and Leonard
+Wray, and by Vanderweyde.</p>
+
+<p>According to this hypothesis, the principal
+office of the vibrating plate consists in its reaction,
+in order to produce the induced currents when the
+voice has placed it in vibration, and by this reaction
+on the polar extremity of the bar magnet it
+strengthens the magnetic effects caused in the
+centre of the bar when it vibrates under the electro-magnetic
+influence, or at least when it is affected
+by the magnet. Since the range of these vibrations
+for a single note is great in proportion to the<span class="pagenum" id="Page_160">160</span>
+flexibility of the note, and since, on the other hand,
+the variations in the magnetic condition of the
+plate are rapid in proportion to the smallness of
+its mass, the advantage of employing, as Mr.
+Edison has done, very thin and relatively small
+plates is readily understood. In the case of transmission,
+the wider range of vibration increases the
+intensity of the induced currents transmitted. In
+the case of reception the variations in the magnetising
+force which produces the sounds are rendered
+clearer and more distinct, both in the armature
+membrane and in the bar magnet: something
+is gained, therefore, in each case. This hypothesis
+by no means excludes the phonetic effects of the
+mechanical and physical vibrations which may be
+produced in the armature plate under the influence
+of magnetisation and demagnetisation to which it
+is subjected, and these join their influence to that
+of the magnetic core.</p>
+
+<p>What is the nature of the vibrations sent into
+the receiving telephone? This question is still
+obscure, and those who have studied it are far
+from being in agreement: as early as 1846 it was
+the subject of an interesting discussion between
+MM. Wertheim and de la Rive, and the new discoveries
+render it still more complex. M. Wertheim
+considers that these vibrations are at once
+longitudinal and transverse, and arise from attractions
+exchanged between the spirals of the
+magnetising helix and the magnetic particles of<span class="pagenum" id="Page_161">161</span>
+the core. M. de la Rive holds that in the case we
+are considering the vibrations are simply longitudinal,
+and result from molecular contractions and
+expansions produced by the different combinations
+assumed by the magnetic molecules under the
+influence of magnetisation and demagnetisation.
+This appears to us to be the most natural explanation,
+and it seems to be confirmed by the
+experiment made by M. Guillemin in 1846. M.
+Guillemin ascertained that if a flexible iron rod,
+surrounded by a magnetising helix, is kept in position
+by a vice at one end, and bent back by a weight
+at the other, it can be made to return instantly to
+its normal position by sending a current through
+the magnetising helix. This recovery can in such
+a case be due to nothing but the contraction
+caused by the magnetic molecules, which, under the
+influence of their magnetisation, tend to produce
+intermolecular attractions, and to modify the elastic
+conditions of the metal. It is known that when
+iron is thus magnetised it becomes as hard as steel,
+and a file makes no impression on its surface.</p>
+
+<p>It is at any rate impossible to dispute that
+sounds are produced in the magnetic core, as well
+as in the armature, under the influence of intermittent
+electric action. These sounds may be
+musical or articulate; for as soon as the sender has
+produced the electric action required, there is no
+reason why vibrations which are effected in a
+transverse or longitudinal direction should transmit<span class="pagenum" id="Page_162">162</span>
+the one more than the other. These vibrations
+may, as we have seen, be termed microscopic.</p>
+
+<p>Signor Luvini, who shares our opinion of the
+foregoing theory, does not, however, think it wholly
+satisfactory, unless account is taken of the reaction
+caused by the bar magnet on the helix which surrounds
+it. ‘There cannot,’ he says, ‘be <em>action</em> without
+<em>reaction</em>, and consequently the molecular action
+produced in the magnet ought to cause corresponding
+variations in the helix, and these two effects ought to
+contribute to the production of sounds.’ He supports
+this remark by a reference to Professor Rossetti’s experiment,
+of which we have spoken above.</p>
+
+<p>We believe, however, that this double reaction
+of which Signor Luvini speaks is not indispensable,
+for we have seen that insulated helices can produce
+sounds; it is true that the spirals, reacting on each
+other, may be the cause of this.</p>
+
+<p>The difficulty of explaining the production of
+sounds in an electro-magnetic organ destitute of
+armature caused the authenticity of the experiments
+we have described to be at first denied, and
+Colonel Navez started a controversy with us which
+is not likely to be soon terminated; yet one result
+of this controversy is that Colonel Navez was obliged
+to admit <em>that the sound of the human voice may be
+reproduced by a telephonic receiver without a disk</em>.
+But he still believes that this reproduction is so faint
+that it is not possible to recognise articulate words,
+and he maintains that the transverse vibrations of<span class="pagenum" id="Page_163">163</span>
+the disk, which are due to effects of attraction, are
+the only ones to reproduce articulate speech with
+such intensity as to be of any use.</p>
+
+<p>It is certain that the articulation of speech
+requires a somewhat intense vibration which cannot
+easily be produced in a telephone without a
+diaphragm; for it must be remembered that in an
+instrument so arranged, the magnetic effects are
+reduced in a considerable ratio, which is that of the
+magnetic force developed in the magnet, multiplied
+by itself, and that so faint an action as that effected
+in a telephone becomes almost null when, in consequence
+of the suppression of the armature, it is
+only represented by the square root of the force
+which produced it. It is therefore possible that
+the sounds which are hardly perceptible in a telephone
+without a diaphragm become audible when
+the cause which provokes them is multiplied by
+itself, and when there are in addition the vibrations
+produced in the heart of the armature itself, influenced
+by the magnetisations and demagnetisations
+to which it is subjected.</p>
+
+<p>In order to show that the action of the
+diaphragm is less indispensable than Colonel
+Navez seems to imagine, and that its vibrations
+are not due to electro-magnetic attractions, it will
+be enough to refer to Mr. Hughes’s experiments,
+which we have mentioned above. It is certain
+that if this were the effect produced, we should
+hear better when the two bar magnets present<span class="pagenum" id="Page_164">164</span>
+their poles of the same nature before the diaphragm,
+than when they present the poles of
+contrary natures, since the whole action would then
+converge in the same direction. Again, the more
+marked effects obtained with multiple diaphragms
+in juxtaposition completely exclude this hypothesis.
+It is, however, possible that in electro-magnetic
+telephones the iron diaphragm, in virtue of the rapid
+variations of its magnetic condition, may contribute
+to render the sounds clearer and more distinct; it
+may react in the way the tongue does; but we
+believe that the greater or less distinctness of the
+articulate sounds must be chiefly due to the range
+of vibrations. Thus Mr. Hughes has shown that
+the carbons of metallised wood employed in his
+microphonic speakers were to be preferred to
+retort carbons for the transmission of speech, for
+the very reason that they had less conductivity,
+so that the differences of resistance which result
+from differences of pressure are more marked,
+and consequently it is easier to seize the different
+degrees of vocal sounds which constitute articulate
+speech.</p>
+
+<p>It must be clearly understood that what we
+have just said only applies to the Bell telephone,
+that is, to a telephone in which the electric currents
+have such a faint intensity that it cannot be supposed
+there is any external attractive effect. When
+these currents are so energetic as to produce such
+an effect, a transverse electro-magnetic vibration<span class="pagenum" id="Page_165">165</span>
+certainly takes place, which is added to the molecular
+vibration, and helps to increase the sounds
+produced. But it is no less true that this transverse
+vibration by attraction or by movement of
+the diaphragm is not necessary for the reproduction
+of sounds, whether musical or articulate.</p>
+
+<p>We are not now concerned with the discussion
+of magnetic effects; there has been an advance in
+science since Colonel Navez started the controversy,
+and we must ask how his theory of the movements
+of the telephone diaphragm by attraction
+will explain the reproduction of speech by a
+receiving microphone destitute of any electro-magnetic
+organ, and I can assert that my experiments
+show that there can be no mechanical
+transmission of vibrations, since no sound is
+heard when the circuit is broken or deprived of
+its battery. Colonel Navez must therefore accept
+the molecular vibrations. This certainly gives us
+a new field for study; but it is because European
+men of science persist in remaining bound by
+incomplete theories that we have allowed the
+Americans who despise them to reap the glory of
+the great discoveries by which we have lately been
+astonished.</p>
+
+<p>The experiments quoted above show that
+sounds may be reproduced not only by simple
+helices without an electro-magnetic organ, but
+also by the plates of a condenser, in spite of the
+pressure exerted upon them; and when we add<span class="pagenum" id="Page_166">166</span>
+to this the effects I have just pointed out, it may
+be supposed that vibrations of sound must result
+from every reaction between two bodies which has
+the effect of producing abruptly and at close intervals
+modifications in the condition of their
+electric or magnetic equilibrium. It is known that
+the presence of ponderable matter is necessary for
+the production of electric effects, and it is possible
+that the molecular vibrations of which I have
+spoken may be the result of molecular movements,
+due to the variations of the electric force which
+holds the molecules in a special condition of reciprocal
+equilibrium.</p>
+
+<p>In conclusion, the theory of the telephone and
+microphone, considered as reproductive organs of
+speech, is still far from being perfectly clear, and
+it would be imprudent to be too positive on questions
+of such recent origin.</p>
+
+<p>The theory of the electric transmission of
+sounds in electro-magnetic telephones is somewhat
+complex. It has been seen that they can be
+obtained from diaphragms of non-magnetic substance,
+and even from simple mechanical vibrations
+produced by shocks. Are we to ascribe them in
+the first case to the inductive reaction of the
+magnet on the vibrating plate, and in the second
+case to the movements of magnetic particles before
+the spirals of the helix? The matter is still very
+obscure; yet it is conceivable that the modifications
+of the inducing action of the magnet on the<span class="pagenum" id="Page_167">167</span>
+vibrating diaphragm may involve variations in the
+magnetic intensity, just as we can admit an effect
+of the same kind due to the approach and withdrawal
+of the magnetic particles of the spirals of
+the helix; M. Trève, however, believes that there
+is in the latter case a special action, which he has
+already had occasion to study under other circumstances,
+and he sees in the current thus caused the
+effect of the transformation of the mechanical
+labour produced amidst the magnetic molecules.
+The question is complicated by the fact that these
+effects are often produced by purely mechanical
+transmissions.</p>
+
+<p>There is another point to consider, on which
+Colonel Navez has made some interesting remarks;
+that is, whether the effects in the receiver
+are stronger with permanent than with temporary
+magnets. In the first model of the telephone,
+exhibited by Mr. Bell at Philadelphia, the receiver
+was, as I have said, made of a tubular electro-magnet,
+furnished with a vibrating disk at its
+cylindrical pole; but this arrangement was abandoned
+by Mr. Bell, with the object, as he states
+in his paper, of rendering his instrument both
+a receiver and a sender.<a id="FNanchor_13" href="#Footnote_13" class="fnanchor">13</a> Yet Colonel Navez
+maintains that the magnet plays an important<span class="pagenum" id="Page_168">168</span>
+part, and is even indispensable under the present
+conditions of its form. ‘It is possible,’ he says,
+‘under certain circumstances, and by making the
+instrument in a special way, to make a Bell receiver
+speak without a permanent magnet, yet with an
+instrument of the usual construction the sound
+ceases when the magnet is withdrawn and replaced
+by a cylinder of soft iron. In order to restore the
+voice of the telephone, it is enough to approach
+the pole of a permanent magnet to the cylinder
+of soft iron. It follows from these experiments
+that a Bell telephone cannot act properly unless
+the disk is subjected to an initial magnetic tension
+obtained by means of a permanent magnet. It
+is easy to deduce this assertion from a consideration
+of the theory.’</p>
+
+<p>The assertion may be true in the case of Bell
+telephones, which are worked by extremely weak
+currents, but when these currents are relatively
+strong, all electro-magnets will reproduce speech
+perfectly, and we have seen that M. Ader made
+a telephone with the ordinary electro-magnet
+which acted perfectly.</p>
+
+<p>The action of the currents sent through the
+helix of a telephone can be easily explained.
+Whatever may be the magnetic conditions of the
+bar, the induced currents of different intensity
+which act upon it produce modifications in its
+magnetic state, and hence the molecular vibrations
+follow from contraction and expansion. These<span class="pagenum" id="Page_169">169</span>
+vibrations are likewise produced in the armature
+under the influence of the magnetisations and demagnetisations
+which are produced by the magnetic
+action of the core, and they contribute to the
+vibrations of the core itself, while at the same
+time the modifications in the magnetic condition
+of the system are increased by the reaction of the
+two magnetic parts upon each other.</p>
+
+<p>When the bar is made of soft iron, the induced
+currents act by creating magnetisations of greater
+or less energy, followed by demagnetisations which
+are the more prompt since inverse currents always
+succeed to those which have been active, and this
+causes the alternations of magnetisation and demagnetisation
+to be more distinct and rapid.
+When the bar is magnetised, the action is differential,
+and may be exerted in either direction, according
+as the induced currents corresponding to
+the vibrations which are effected pass through the
+receiving coil in the same or opposite direction as
+the magnetic current of the bar. If these currents
+are in the same direction, the action is strengthening,
+and the modifications are effected as if a
+magnetisation had taken place. If these currents
+are of opposite direction, the inverse effect is
+produced; but, whatever the effects may be,
+the molecular vibrations maintain the same
+reciprocal relations and the same height in
+the scale of musical sounds. If the question
+is considered from the mathematical point of<span class="pagenum" id="Page_170">170</span>
+view, we find the presence of a constant, corresponding
+with the intensity of the current, which
+does not exist in mechanical vibrations, and which
+may possibly be the cause of the peculiar tone of
+speech reproduced by the telephone, a tone which
+has been compared to the voice of Punch. M.
+Dubois Raymond has published an interesting
+paper on this theory, which appeared in ‘Les
+Mondes,’ February 21, 1878, but we do not reproduce
+it here, since his remarks are too scientific
+for the readers for whom this work is intended.
+We will only add that Mr. C.&nbsp;W. Cunningham
+asserts that the vibrations produced in a telephone
+cannot be manifested under precisely the same conditions
+as those which affect the tympanum of the
+ear, because the latter has a peculiar funnel-shaped
+form, which excludes every fundamental note, specially
+adapted to it, and this is not the case with
+the bars and magnetic plates which possess fundamental
+notes capable of greatly altering the half-tones
+of the voice. He considers the alteration of
+the voice observed in the telephone must be ascribed
+to these fundamental notes.</p>
+
+<p><i>M. Wiesendanger’s Thermophone.</i>—M. Wiesendanger,
+in an article inserted in the ‘English
+Mechanic and World of Science,’ September 13,
+1878, ascribes the reproduction of speech in certain
+telephones to vibratory movements resulting from
+molecular expansions and contractions produced
+by variations of temperature, and these variations<span class="pagenum" id="Page_171">171</span>
+would follow from the currents of varying intensity
+which are transmitted through the telephonic
+circuits. He was conscious of one objection to
+this theory, namely, that the movements of expansion
+and contraction due to heat are slowly
+produced, and consequently are not capable of
+substantial action, rapid enough to produce vibrations;
+but he considers that molecular effects need
+not take place under the same conditions as those
+which are displayed in the case of material substances.</p>
+
+<p>M. Wiesendanger believes that this hypothesis
+will explain the reproduction of speech in the
+receiving microphones of Mr. Hughes, and that it
+may even be applied to the theory of the electro-magnetic
+telephone, if we consider that a magnetising
+helix, as well as a magnetic core, round
+which an electric current circulates, is more or
+less heated, according to the intensity of the
+current which traverses it, especially when the wire
+of the helix and the core are bad conductors of
+electricity and of magnetism. Pursuing this idea,
+M. Wiesendanger has sought to construct telephones
+in which calorific effects are more fully
+developed, and with this object he used very fine
+wire of German silver and platinum to make the
+coils. He ascertained that these coils could produce
+sounds themselves, and, to increase their intensity,
+he put them between disks of iron, or on
+tin tubes, placed on resonant surfaces close to the<span class="pagenum" id="Page_172">172</span>
+disks. In this way he says that he was able to
+make a good receiving telephone without employing
+magnets. He afterwards arranged the instrument
+in different ways, of which the two following
+are the most noteworthy.</p>
+
+<p>In the first, the electro-magnetic system was
+simply formed by a magnetic disk with a helix
+wound round it, of which the wire was in connection
+with the circuit of a microphone, and which
+was fastened to the centre of the parchment membrane
+of an ordinary string telephone; the disk
+consisted of two iron plates separated by a carbon
+disk of smaller diameter, and the whole was so
+compressed as to form a solid mass.</p>
+
+<p>In the second, the helix was wound on a tin
+tube, six inches long and five-eighths of an inch in
+diameter, which was soldered by merely a point to
+the centre of the diaphragm of an ordinary telephone.</p>
+
+<p>The inventor asserts that the tube and diaphragm
+only act as resonators, and that the sounds
+produced by this instrument are nearly the same
+as those obtained from the ordinary string telephone:
+the tunes of a musical box were heard,
+and the reproduction of speech was perfect, both
+in intensity and in distinctness of sound; it even
+appeared that telephonic sounds were audible with
+the tin tube alone, surrounded by the helix. M.
+Wiesendanger says that ‘these different receiving
+telephones show clearly that the diaphragm and<span class="pagenum" id="Page_173">173</span>
+magnet are not essential, but merely accessory,
+parts of a telephone.’</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h2 class="nobreak" id="VARIOUS_EXPERIMENTS_MADE_WITH_THE"><span id="toclink_173"></span>VARIOUS EXPERIMENTS MADE WITH THE
+TELEPHONE.</h2>
+</div>
+
+<p>We must now consider a series of experiments
+which demonstrate the wonderful properties of the
+telephone, and which may also give some indication
+of the importance of the influences by which it is
+liable to be affected.</p>
+
+<p><i>Experiments by M. d’Arsonval.</i>—We have seen
+that the telephone is an extremely sensitive instrument,
+but its sensitiveness could scarcely be appreciated
+by ordinary means. In order to gauge it, M.
+d’Arsonval has compared it to the nerve of a frog,
+which has hitherto been regarded as the most
+perfect of all galvanoscopes, and it appears from
+his experiments that the sensitiveness of the
+telephone is two hundred times greater than that of
+the frog’s nerve. M. d’Arsonval has given the
+following account of his researches in the records of
+the Académie des Sciences, April 1, 1878:</p>
+
+<p>‘I prepared a frog in Galvani’s manner. I
+took Siemens’ instrument of induction, used in
+physiology under the name of the chariot instrument.
+I excited with the ordinary pincers the
+sciatic nerve, and I withdrew the induced coil until
+the nerve no longer responded to the electric excitement.
+I then substituted the telephone for
+the nerve, and the induced current, which had<span class="pagenum" id="Page_174">174</span>
+ceased to excite the latter, made the instrument
+vibrate strongly. I withdrew the induced coil, and
+the telephone continued to vibrate.</p>
+
+<p>‘In the stillness of night I could hear the
+vibration of the telephone when the induced coil
+was at a distance fifteen times greater than the
+minimum at which the excitement of the nerve
+took place; consequently, if the same law of inverse
+squares applies to induction and to distance,
+it is evident that the sensitiveness of the telephone
+is two hundred times greater than that of the nerve.</p>
+
+<p>‘The sensitiveness of the telephone is indeed
+exquisite. We see how much it exceeds that
+of the galvanoscopic frog’s leg, and I have thought
+of employing it as a galvanoscope. It is very
+difficult to study the muscular and nervous currents
+with a galvanometer of 30,000 turns, because
+the instrument is deficient in instantaneous action,
+and the needle, on account of its inertia, cannot
+display the rapid succession of electric variations,
+such as are effected, for example, in a muscle thrown
+into electric convulsion. The telephone is free from
+this inconvenience, and it responds by vibration to
+each electric change, however rapid it may be. The
+instrument is therefore well adapted for the study
+of electric tetanus in the muscle. It is certain that
+the muscular current will excite the telephone, since
+this current excites the nerve, which is less sensitive
+than the telephone. But for this purpose some
+special arrangement of the instrument is required.</p>
+
+<p><span class="pagenum" id="Page_175">175</span></p>
+
+<p>‘It is true that the telephone can only reveal
+the variations of an electric current, however faint
+they may be; but I have been able, by the use
+of a very simple expedient, to reveal by its means
+the presence of a continuous current, also of extreme
+faintness. I send the current in question
+into the telephone, and, to obtain its variations, I
+break this current mechanically with a tuning-fork.
+If no current is traversing the telephone, it remains
+silent. If, on the other hand, the faintest current
+exists, the telephone vibrates in unison with the
+tuning-fork.’</p>
+
+<p>Professor Eick, of Wurzburg, has also used the
+telephone for physiological researches, but in a
+direction precisely opposite to that explored by
+M. d’Arsonval. He ascertained that when the
+nerves of a frog were placed in connection with a
+telephone, they were forcibly contracted when anyone
+was speaking into the instrument, and the force
+of the contractions chiefly depended on the words
+pronounced. For instance, the vowels <i>a</i>, <i>e</i>, <i>i</i> produced
+hardly any effect, while <i>o</i> and especially <i>u</i>
+caused a very strong contraction. The words <em>Liege
+still</em>, pronounced in a loud voice, only produced a faint
+movement, while the word <em>Tucker</em>, even when
+spoken in a low voice, strongly agitated the frog.
+These experiments, reminding us of those by
+Galvani, were necessarily based on the effects produced
+by the induced currents developed in the
+telephone, and they show that if this instrument is<span class="pagenum" id="Page_176">176</span>
+a more sensitive galvanoscope than the nerve of a
+frog, the latter is more susceptible than the most
+perfect galvanometer.</p>
+
+<p><i>Experiments by M. Demoget.</i>—In order that he
+might compare the intensity of the sounds transmitted
+by the telephone with the intensity of
+original sounds, M. Demoget placed two telephones
+in an open space. He held the first to
+his ear, while his assistant withdrew to a distance,
+constantly repeating the same syllable with the
+same intensity of tone in the second instrument.
+He first heard the sound transmitted by the telephone,
+and then the sound which reached him
+directly, so that comparison was easy, and he
+obtained the following results.</p>
+
+<p>At a distance of 93 yards the original and the
+transmitted sounds were received with equal intensity,
+while the vibrating disk was about 5 centimètres
+from the ear. At this moment, therefore,
+the relative intensity was as 25 to 81,000,000. In
+other words, the sound transmitted by the telephone
+was only 1/3000000 of the emitted sound. ‘But,’
+said M. Demoget, ‘since the stations at which we
+worked could not be regarded as two points freely
+vibrating in space, the ratio may be reduced by
+one half on account of the influence of the earth,
+and the sound transmitted by the telephone may
+be supposed to be 1,500,000 times weaker than
+that emitted by the voice.</p>
+
+<p>‘Again, since we know that the intensity of the<span class="pagenum" id="Page_177">177</span>
+two sounds is in proportion to the square of the
+range of vibrations, it may be concluded that the
+vibrations of the two telephone disks were in direct
+proportion to the distance, that is, as 5 to 9,000,
+or that the vibrations of the sending telephone
+were eighteen hundred times greater than those
+of the receiving telephone. These latter may
+therefore be compared to molecular vibrations, since
+the range of those of the sending telephone was
+extremely small.</p>
+
+<p>‘Without in any degree detracting from the
+merit of Bell’s remarkable invention,’ continues M.
+Demoget, ‘it follows from what I have said above
+that the telephone, considered as a sending instrument,
+leaves much to be desired, since it only
+transmits the 18/100 part of the original power; and
+if it has produced such unexpected results, this
+is due to the perfection of the organ of hearing,
+rather than to the perfection of the instrument itself.’</p>
+
+<p>M. Demoget considers this loss of power which
+takes place in the telephone to be chiefly owing
+to the eight transformations in succession to which
+sound is subjected before reaching the ear, setting
+aside the loss due to the electric resistance of the
+line, which might in itself suffice to absorb the
+whole force.</p>
+
+<p>In order to estimate the force of the induced
+currents which act upon a telephone, M. Demoget
+has attempted to compare them with currents of
+which the intensity is known, and which produce<span class="pagenum" id="Page_178">178</span>
+vibrations of like nature and force: for this purpose
+he has made use of two telephones, <span class="allsmcap">A</span> and <span class="allsmcap">B</span>, communicating
+through a line 22 yards in length.
+He placed a small file in slight contact with the
+vibrating disk of the telephone <span class="allsmcap">A</span>, and caused friction
+between the file and a metallic plate: the sound
+thus produced was necessarily transmitted by the
+telephone <span class="allsmcap">B</span>, with an intensity which could be
+estimated. He then substituted a battery for the
+telephone <span class="allsmcap">A</span>, and the file was introduced into
+the circuit by connecting it with one of the poles.
+The current could only be closed by the friction of
+the file with the plate, which had a spring, and was
+in communication with the other end of the circuit.
+In this way broken currents were obtained, which
+caused vibration in the telephone <span class="allsmcap">B</span>, and produced
+a sound of which the intensity varied with the
+strength of the battery current. In this way M.
+Demoget endeavoured to find the electric intensity
+capable of producing a sound similar to that of the
+telephone <span class="allsmcap">A</span>, and he ascertained that it corresponded
+in intensity to that produced in a small thermo-electric
+battery formed of an iron and a copper
+wire, two millimètres in diameter, flattened at the
+end, and soldered to the tin: the faint current produced
+by this battery only caused a short wire
+galvanometer to deviate two degrees.</p>
+
+<p>This estimate does not appear to us to unite so
+many conditions of accuracy as to enable us to
+deduce from it the degree of sensitiveness possessed<span class="pagenum" id="Page_179">179</span>
+by a telephone, a sensitiveness which the experiments
+of Messrs. Warren de la Rue, Brough, and
+Peirce show to be much greater. Mr. Warren de la
+Rue, as we have seen, used Thomson’s galvanometer,
+and compared the deviation produced on
+the scale of this galvanometer with that caused by
+a Daniell cell traversing a circle completed by
+a rheostat: he ascertained that the currents discharged
+by an ordinary Bell telephone are equivalent
+to those of a Daniell cell traversing 100
+megohms of resistance, that is, 6,200,000 miles
+of telegraphic wire. Mr. Brough, the Director
+of Indian Telegraphs, considers that the strongest
+current which at any given moment causes a Bell
+telephone to work does not exceed 1/1000000 of the
+unit of current, that is, one Weber, and the current
+transmitted to the stations on the Indian telegraphic
+line is 400,000 times as strong. Finally,
+Professor Peirce, of Boston, compares the effects
+of the telephonic current with those which would
+be produced by an electric source of which the
+electro-motive force should be 1/200000 part of a volt,
+or one Daniell cell. Mr. Peirce justly remarks
+that it is difficult to estimate the real value of
+these kinds of currents at any precise sum, since it
+essentially varies according to the intensity of the
+sounds produced on the transmitting telephone; but
+it may be affirmed that it is less than the 1/1000000 part
+of the current usually employed to work the instruments
+on telegraphic lines.</p>
+
+<p><span class="pagenum" id="Page_180">180</span></p>
+
+<p>Signor Galileo Ferraris, who has recently published
+an interesting treatise on this question in the
+‘Atti della Reale Accademia delle Scienze di
+Torino’ (June 13, 1878), states that the intensity of
+the currents produced by the ordinary Bell telephone
+varies with the pitch of the sound emitted.</p>
+
+<p><i>Experiments by M. Hellesen, of Copenhagen.</i>—In
+order to estimate the reciprocal effects of different
+parts of a telephone, M. Hellesen has made telephones
+of the same size with three different arrangements
+which act inversely to each other. The first
+was of the ordinary form, the second like that of Bell’s
+first system, that is, with a membrane supporting a
+small iron armature on its centre, instead of a vibrating
+disk, and the third telephone consisted of a
+hollow cylindrical magnet, with the vibrating disk
+fixed to one of its poles, and the disk was adapted
+to move before a flat, snail-shaped spiral, of which
+the number of spirals equalled those of the two other
+helices. In this last arrangement, the induced
+currents resulting from the vibrations of the voice
+might be assimilated to those which follow from
+the approximation and withdrawal of the two
+parallel spirals, one of which should be traversed by
+a current. It is this last arrangement which Mr.
+Bell has adopted as producing the best effects, and
+it is rare in the history of discoveries that an
+inventor hits at once on the best arrangement of his
+instrument.</p>
+
+<p><i>Experiments by M. Zetsche.</i>—There are always a<span class="pagenum" id="Page_181">181</span>
+few perverse minds, impelled by a spirit of contradiction
+to deny evidence, and thus they attempt to
+depreciate a discovery of which the glory irritates
+them. The telephone and the phonograph have
+been the objects of such unworthy criticism. It has
+been said that electric action had nothing to do
+with the effects produced in the telephone, and that
+it only acted under the influence of mechanical
+vibrations transmitted by the conducting wire, just
+as in a string telephone. It was in vain to demonstrate
+to these obstinate minds that no sound
+is produced when the circuit is broken, and in order
+to convince them M. Zetsche has made some experiments
+to show, from the mode in which sound
+is propagated, that it is absurd to ascribe the sound
+produced in a telephone to mechanical vibration.
+He wrote to this effect in an article inserted in the
+‘Journal Télégraphique,’ Berne, January 25, 1878:</p>
+
+<p>‘The correspondence by telephone between
+Leipzig and Dresden affords another proof that
+the sounds which reproduce words at the receiving
+station are due to electric currents, and not to
+mechanical vibrations. The velocity with which
+sound is transmitted by vibrations on the wire, in
+the case of longitudinal undulations, may be estimated
+at three miles one furlong a second, so that
+the sound ought to traverse the distance from
+Leipzig to Dresden in 25 seconds. The same time
+ought to elapse before receiving the answer. Consequently
+there should be an interval of more than<span class="pagenum" id="Page_182">182</span>
+three-quarters of a minute allowed for each exchange
+of communication, which is by no means the case.’</p>
+
+<p><i>Experiments which may be made by anyone.</i>—We
+will conclude this chapter, devoted to the
+account of the different experiments made with
+the telephone, by the mention of a singular experiment,
+which, although easily performed, has only
+been suggested a few months ago by a Pennsylvanian
+newspaper. It consists in the transmission
+of speech by a telephone simply laid on some part
+of the human body adjacent to the chest. It has
+been asserted that any part of the body will produce
+this effect, but according to my experience,
+I could only succeed when the telephone was firmly
+applied to my chest. Under such conditions, and
+even through my clothes, I could make myself
+heard when speaking in a very loud voice, from
+which it appears that the whole of the human body
+takes part in the vibrations produced by the voice.
+In this case, the vibrations are mechanically
+transmitted to the diaphragm of the sending telephone,
+not by the air, but by the body itself acting
+on the outside of the telephone.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h2 class="nobreak" id="THE_MICROPHONE"><span id="toclink_182"></span>THE MICROPHONE.</h2>
+</div>
+
+<p>The microphone is in fact only the sender
+of a battery telephone, but with such distinctive
+characteristics that it may be regarded as an
+original invention which is entitled to a special<span class="pagenum" id="Page_183">183</span>
+name. The invention has lately given rise to an
+unfortunate controversy between its inventor, Mr.
+Hughes, and Mr. Edison, the inventor of the carbon
+telephone and the phonograph—a controversy
+which has been embittered by the newspapers, and
+for which there were no grounds. For although
+the scientific principle of the microphone may
+appear to be the same as that of Mr. Edison’s
+carbon sender, its arrangement is totally different,
+its mode of action is not the same, and the effect
+required of it is of quite another kind. Less than
+this is needed to constitute a new invention.
+Besides, a thorough examination of the very
+principle of the instrument must make us wonder
+at Mr. Edison’s claim to priority. He cannot
+in fact regard as his exclusive possession the discovery
+of the property possessed by some substances
+of moderate conductivity of having this
+power modified by pressure. In 1856, and often
+subsequently, as for example in 1864, 1872, 1874,
+and 1875, I made numerous experiments on this
+point, which are described in the first volume of
+the second edition of my ‘Exposé des applications
+de l’Electricité,’ and also in several papers presented
+to the Académie des Sciences, and inserted in their
+<i lang="fr">Comptes rendus</i>. M. Clarac again, in 1865, employed
+a tube made of plumbago, and provided
+with a moveable electrode, to produce variable
+resistances in a telegraphic circuit. Besides, in
+Mr. Edison’s telephonic sender, the carbon disk, as<span class="pagenum" id="Page_184">184</span>
+we have seen, must be subjected to a certain
+initial pressure, in order that the current may
+not be broken by the vibrations of the plate on
+which it rests, and consequently the modifications
+of resistance in the circuit which produce articulate
+sounds are only caused by greater or less increase
+and diminution of pressure, that is, by differential
+actions. We shall presently see that this is not
+the case with the microphone. In the first place,
+the carbon contact is effected in the latter instrument
+on other carbons and not with platinum
+disks, and these contacts are multiple. In the
+second place, the pressure exerted on all the points
+of contact is excessively slight, so that the resistances
+can be varied in an infinitely greater ratio than in
+Mr. Edison’s system; and for this very reason it
+is possible to magnify the sounds. In the third
+place, a microphone can be made of other substances
+besides carbon. Finally, no vibrating disk
+is needed to make the microphone act; the simple
+medium of air is enough, so that it is possible to
+work the instrument from some little distance.</p>
+
+<p>We do not therefore see the grounds for Mr.
+Edison’s assertions, and especially for the way in
+which he has spoken of Messrs. Hughes and
+Preece, who are well known in science and are in
+all respects honourable men. I repeat my regret
+that Mr. Edison should have made this ill-judged
+attack on them, since it must injure himself, and is
+unworthy of an inventor of such distinction. If we<span class="pagenum" id="Page_185">185</span>
+look at the question from another point of view,
+we must ask Mr. Edison why, if he invented the
+microphone, he did not make us acquainted with
+its properties and results. These results are indeed
+startling, since the microphone has in so short a time
+attracted general attention; and it is evident that
+the clear-sighted genius of this celebrated American
+inventor would have made the most of the discovery
+if it were really his. The only justification for Mr.
+Edison’s claim consists in his ignorance of the
+purely scientific discoveries made in Europe, so
+that he supposed the invention of the microphone
+to be wholly involved in the principle which he
+regards as his peculiar discovery.</p>
+
+<p>In Mr. Hughes’s instrument which we are now
+considering, the sounds, instead of reaching the
+receiving stations much diminished, which is the
+case with ordinary telephones, and even with that
+of Mr. Edison, are often remarkably increased, and
+it is for this reason that Mr. Hughes has given to
+this telephonic system the name of Microphone,
+since it can be employed to discover very faint
+sounds. Yet we must add that this increase really
+takes place only when the sounds result from
+mechanical vibrations transmitted by solid substances
+to the sending instrument. The sounds
+propagated through the air are undoubtedly a
+little more intense than in the ordinary system,
+but they lose some of their force, and therefore it
+cannot be said that in this case the microphone<span class="pagenum" id="Page_186">186</span>
+has the same effect upon sounds as the microscope
+has on objects on which light is thrown. It is true
+that with this system it is possible to speak at a
+distance from the instrument, and I have even been
+able to transmit conversation in a loud voice, when
+standing at a distance of nine yards from the
+microphone. When close to the instrument, I was
+also perfectly able to make myself heard at the
+receiving station while speaking in a low voice, and
+even to send the sounds to a distance of ten or
+fifteen centimètres from the mouthpiece of the
+receiving telephone by raising the voice a little;
+but the increase of sound is not really very evident
+unless it is produced by a mechanical action transmitted
+to the standard of the instrument.</p>
+
+<p>Thus the steps of a fly walking on the stand
+are clearly heard, and give the sensation of a
+horse’s tread; and even a fly’s scream, especially at
+the moment of death, is said by Mr. Hughes to be
+audible. The rustling of a feather or of a piece of
+stuff on the board of the instrument, sounds
+completely inaudible in ordinary circumstances, are
+distinctly heard in the microphone. It is the same
+with the ticking of a watch placed upon the
+stand, which may be heard at ten or fifteen
+centimètres from the receiver. A small musical
+box placed upon the instrument gives out so
+much sound, in consequence of its vibratory
+movements, that it is impossible to distinguish the
+notes, and in order to do so it is necessary to<span class="pagenum" id="Page_187">187</span>
+place the box close to the instrument, without
+allowing it to come in contact with any of its
+constituent parts. It therefore appears that the
+instrument is affected by the vibrations of air, and
+the transmitted sounds are fainter than those heard
+close to the box. On the other hand, the
+vibrations produced by the pendulum of a clock,
+when placed in communication with the standard
+of the instrument by means of a metallic rod, are
+heard perfectly, and may even be distinguished
+when the connection is made by the intervention of
+a copper wire. A current of air projected on the
+system gives the sensation of a trickle of water heard
+in the distance. Finally, the rumbling of a carriage
+outside the house is transformed into a very intense
+crackling noise, which may combine with the ticking
+of a watch, and will often overpower it.</p>
+
+<p><i>Different Systems of Microphones.</i>—The microphone
+has been made in several ways, but the one
+represented in <a href="#il_39">fig. 39</a> is the arrangement which
+renders it the most sensitive. In this system, two
+small carbon cubes, <span class="allsmcap">A</span>, <span class="allsmcap">B</span>, are placed one above the
+other on a vertical wooden prism; two holes are
+pierced in the cubes to serve as sockets for a spindle-shaped
+carbon pencil, that is, with the points fined
+off at the two ends, and about four centimètres
+long: if of a large size, the inertia will be too
+great. One end of this pencil is in the cavity of
+the lower carbon, and the other must move freely
+in the upper cavity which maintains it in a position<span class="pagenum" id="Page_188">188</span>
+approaching to that of instable equilibrium, that
+is, in a vertical position. Mr. Hughes states that the
+carbons become more effective if they are steeped
+in a bath of mercury at red heat, but they will act
+well without undergoing this process. The two
+carbon cubes are also provided with metallic contacts
+which admit of their being placed in connection
+with the circuit of an ordinary telephone in
+which a Leclanché battery has been placed, or one,
+two, or three Daniell cells, with an additional resistance
+introduced into the circuit.</p>
+
+<figure id="il_39" class="figcenter" style="max-width: 20em;">
+  <img src="images/i_p188.jpg" width="789" height="895" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 39.</span>
+  </figcaption>
+</figure>
+
+<p><span class="pagenum" id="Page_189">189</span></p>
+
+<p>In order to use this instrument, it is placed on
+a table, with the board which serves to support it,
+taking care to deaden any extraneous vibrations
+by interposing between this board and the table
+several folds of stuff so arranged as to form a
+cushion, or, which is better, a belt of wadding, or
+two caoutchouc tubes: what is said by a person
+standing before this system is immediately reproduced
+in the telephone, and if a watch is placed on
+the stand, or a box with a fly enclosed in it, all
+its movements are heard. The instrument is so
+sensitive that words said in a low voice are most
+easily heard, and it is possible, as I have already
+said, to hear the speaker when he is standing
+nine yards from the microphone. Yet some precautions
+are necessary in order to obtain good
+results with this system, and besides the cushions
+placed beneath the instrument to guard it from the
+extraneous vibrations which might ensue from any
+movements communicated to the table, it is also
+necessary to regulate the position of the carbon
+pencil. It must always rest on some point of the
+rim of the upper cavity; but as the contact may be
+more or less satisfactory, experience alone will
+show when it is in the best position, and it is a
+good plan to make use of a watch to ascertain
+this. The ear is then applied to the telephone,
+and the pencil is placed in different positions until
+the maximum effect is obtained. To avoid the
+necessity of regulating the instrument in this way,<span class="pagenum" id="Page_190">190</span>
+which must be done repeatedly by this arrangement,
+MM. Chardin and Berjot, who are ingenious
+in the construction of telephones on this
+pattern, have added to it a small spring-plate, of
+which the pressure can be regulated, and which
+rests against the carbon pencil itself. This system
+works well.</p>
+
+<figure id="il_40" class="figcenter" style="max-width: 26em;">
+  <img src="images/i_p190.jpg" width="1009" height="667" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 40.</span>
+  </figcaption>
+</figure>
+
+<p>M. Gaiffe, by constructing it like a scientific
+instrument, has given the instrument a more elegant
+form. <a href="#il_40">Fig. 40</a> represents one of his two models.
+In this case, the cubes or carbon dice are supported
+by metallic holders, and the upper one <span class="allsmcap">E</span> is made
+to move up and down a copper column <span class="allsmcap">G</span>, so as to be
+placed in the right position by tightening the screw <span class="allsmcap">V</span>.<span class="pagenum" id="Page_191">191</span>
+In this way the carbon pencil can be made to
+incline more or less, and its pressure on the upper
+carbon can be altered at pleasure. When the pencil
+is in a vertical position, the instrument transmits
+articulate sounds with difficulty, on account of the
+instability of the points of contact, and rustling
+sounds are heard. When the inclination of the
+pencil is too great, the sounds are purer and more
+distinct, but the instrument is less sensitive. The
+exact degree of inclination should be ascertained,
+which is easily done by experiment. In another
+model M. Gaiffe substitutes for the carbon pencil
+a very thin square plate of the same material,
+bevelled on its lower and upper surfaces, and revolving
+in a groove cut in the lower carbon. This
+plate must be only slightly inclined in order to
+touch the upper carbon, and under these conditions
+it transmits speech more loudly and distinctly.</p>
+
+<p>I must also mention another arrangement, devised
+by Captain Carette of the French Engineers,
+which is very successful in transmitting inarticulate
+sounds. In this case the vertical carbon is pear-shaped,
+and its larger end rests in a hole made in
+the lower carbon; its upper and pointed end goes
+into a small hole made in the upper carbon, but so
+as hardly to touch it, and there is a screw to regulate
+the distance between the two carbons. Under
+such conditions, the contacts are so unstable that
+almost anything will put an end to them, and consequently
+the variations in the intensity of the<span class="pagenum" id="Page_192">192</span>
+transmitted current are so strong that the sounds
+produced by the telephone may be heard at the
+distance of several yards.</p>
+
+<figure id="il_41" class="figcenter" style="max-width: 25em;">
+  <img src="images/i_p192.jpg" width="964" height="771" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 41.</span>
+  </figcaption>
+</figure>
+
+<p><a href="#il_41">Fig. 41</a> represents another arrangement, devised
+by M. Ducretet. The two carbon blocks are
+at <span class="allsmcap">D</span> <span class="allsmcap">D′</span>, the moveable carbon pencil is at <span class="allsmcap">C</span>, the telephone
+at <span class="allsmcap">T</span>, and the binding screws at <span class="allsmcap">B</span> <span class="allsmcap">B′</span>. An
+enlarged figure of the arrangement of the carbons
+is given on the left. The arm which holds the
+upper carbon <span class="allsmcap">D</span> is fastened to a rod, bearing a plate
+<span class="allsmcap">P′</span>, of which the surface is rough, and a little cage
+<span class="allsmcap">C′</span>, made of wire netting, can be placed upon the<span class="pagenum" id="Page_193">193</span>
+plate, so as to enable us to study the movements
+of living insects.</p>
+
+<p>When speech is to be transmitted with a force
+which can make the telephone audible in a large
+room, the microphone must have a special arrangement,
+and <a href="#il_42">fig. 42</a> represents the one which Mr.
+Hughes considers the most successful, to which
+he has given the name of <em>speaker</em>.</p>
+
+<figure id="il_42" class="figcenter" style="max-width: 22em;">
+  <img src="images/i_p193.jpg" width="847" height="481" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 42.</span>
+  </figcaption>
+</figure>
+
+<p>In this new form, the moveable carbon which is
+required to produce the variable contacts is at <span class="allsmcap">C</span>, at
+the end of a horizontal bar <span class="allsmcap">B A</span>, properly balanced
+so as to move up and down on its central point.
+The support on which the bar oscillates is fastened
+to the end of a spring plate in order that it may
+vibrate more easily, and the lower carbon is placed
+at <span class="allsmcap">D</span> below the first. It consists of two pieces laid
+upon each other, so as to increase the sensitiveness
+of the instrument, and we represent the upper piece<span class="pagenum" id="Page_194">194</span>
+at <span class="allsmcap">E</span>, which is raised so as to show that when it is
+desired only one of these carbons need be used.
+For this purpose the carbon <span class="allsmcap">E</span> is fastened to a
+morsel of paper, which is fixed to the little board
+and contributes to the articulation. A spring <span class="allsmcap">R</span>, of
+which the tension can be regulated by the screw <i>t</i>,
+serves to regulate the pressure of the two carbons.
+Mr. Hughes recommends the use of metallised charcoal
+prepared from deal.<a id="FNanchor_14" href="#Footnote_14" class="fnanchor">14</a> The whole is then enclosed
+in a semi-cylindrical case <span class="allsmcap">H I G</span>, made of
+very thin pieces of deal, and the system is fixed,
+together with another similar system, in a flat box,
+<span class="allsmcap">M J L I</span>, which, on the side <span class="allsmcap">M I</span>, presents an opening
+before which the speaker stands, taking care to
+keep his lower lip at a distance of two centimètres
+from the bottom of the box. If the two telephones
+are connected for strength, and if the battery
+employed consists of two cells of bichromate of
+potash, it is possible to act so strongly on the current,
+that, after traversing an induction coil only
+six centimètres long, a telephone of Bell’s square
+model can be made to speak, so as to be heard
+from all parts of a room; a speaking tube, about a
+yard long, must indeed be applied to it. Mr.
+Hughes asserts that the sounds produced by it are
+nearly as loud as those of the phonograph, and
+this is confirmed by Mr. Thomson.</p>
+
+<p><span class="pagenum" id="Page_195">195</span></p>
+
+<p>M. Boudet de Paris has lately invented a
+microphone speaker of the same kind, with which
+it is possible to make a small telephone utter a loud
+sound. An induction coil, influenced by a single
+Leclanché cell, must be employed.</p>
+
+<p>Suppose that a very small carbon rod with
+pointed ends is placed at the bottom of a box, of
+about the size of a watch. One end of the rod
+rests against a morsel of carbon, which is fastened
+to a very thin steel diaphragm, placed before a
+mouthpiece which acts as a lid to the box, and is
+screwed above it. Next suppose that a small piece
+of paper, folded in two, in the shape of the letter
+V, is fixed above that part of the carbon in contact
+with the carbon of the diaphragm. This constitutes
+the instrument, and in order to work it, it
+must be held in a vertical position before the mouth,
+at a distance of about three centimètres, and it is
+necessary to speak in the ordinary tone. If the
+telephone is placed in direct communication with
+this instrument, it will send the voice to a distance.
+Without employing a Leclanché cell, the voice
+may be heard at the distance of ten yards, if one of
+the carbons used for the phonograph is placed
+before the mouthpiece of the telephone.</p>
+
+<p>In this system, the sensitiveness of the instrument
+is entirely due to the slightness of the contact
+between the two carbons, and the slight elasticity
+of the folded paper constitutes the contact. Perhaps
+the paper itself has some influence; at any rate the<span class="pagenum" id="Page_196">196</span>
+most delicate spiral spring is incapable of producing
+the same effect, and it is necessary to suspend the
+instrument vertically, in order that the weight of
+the moveable carbon may not affect it. It can be
+regulated by depressing or elevating that part of
+the paper which rests on the carbon rod.</p>
+
+<p>Although it is possible to work all telephones
+with this instrument, some are more effective than
+others. The mouthpiece must be concave, and the
+diaphragm must be close to its rim, and must be
+made of a particular kind of tin. The ordinary
+diaphragm does not act well, and M. Boudet de
+Paris has tried several, so as to obtain the maximum
+effect.</p>
+
+<p>It is certain that when the instruments are as
+well regulated as those which the inventor has
+deposited with me, their results are really surprising.
+It is even possible, by using several microphones at
+the sending station, to obtain the reproduction of
+duets, and even of trios, with remarkable effect.</p>
+
+<p>With this kind of microphone speaker M.
+Boudet de Paris is able to transmit speech into a
+snuff-box telephone, merely consisting of a flat
+helix of wire, placed before a slightly magnetised
+steel plate, and without insertion of a magnetic
+core. A single Leclanché cell was enough. An
+experiment of the same nature was tried in England,
+but it was found necessary to use six Leclanché
+cells.</p>
+
+<figure id="il_43" class="figcenter" style="max-width: 17em;">
+  <img src="images/i_p197.jpg" width="643" height="347" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 43</span>
+  </figcaption>
+</figure>
+
+<figure id="il_44" class="figcenter" style="max-width: 25em;">
+  <img src="images/i_p197b.jpg" width="965" height="371" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 44.</span>
+  </figcaption>
+</figure>
+
+<p>The microphone may also be made of morsels<span class="pagenum" id="Page_197">197</span>
+of carbon pressed into a box between two metallic
+electrodes, or enclosed in a tube with two electrodes
+represented by two elongated fragments of carbon.
+In the latter case the carbons ought to be as cylindrical
+as possible, and those made by M. Carré for
+the Jablochkoff candles are very suitable. <a href="#il_43">Fig. 43</a>
+represents an instrument of this kind which M.
+Gaiffe arranged for me, and which, as we shall see,
+serves as a thermoscope (<a href="#il_44">fig. 44</a>). It is composed
+of a quill filled with morsels of carbon, and those
+at the two ends are tipped with metal. One of
+these metal tips ends in a large-headed screw which,
+by means of its supports <span class="allsmcap">A B</span>, is able to press more
+or less on the morsels of carbon in the tube, and
+consequently to establish a more or less intimate<span class="pagenum" id="Page_198">198</span>
+contact between them. When the instrument is
+properly regulated, speech can be reproduced by
+speaking above the tube. It is therefore a microphone
+as well as a thermoscope. Mr. Hughes has
+remarked one curious fact, namely, that if the different
+letters of the alphabet are pronounced separately
+before this sort of microphone, some of them
+are much more distinctly heard than others, and it
+is precisely those which correspond to the breathings
+of the voice.</p>
+
+<p>A microphone of this kind may be made by
+substituting for the carbon powders of more or
+less conductivity, or even metal filings. I have
+shown in my paper on the action of substances of
+moderate conductivity, that such power varies considerably
+with the pressure and the temperature;
+and as the microphone is based on the differences
+of conducting power which result from differences
+of pressure, we can understand that these powders
+may be used as a means of telephonic transmission.
+In a recent arrangement of this system Mr. Hughes
+has made the powder adhere together with a sort
+of gum, and has thus made a cylindrical pencil
+which, when connected with two electrodes which
+are good conductors, can produce effects analogous
+to those we have just described. As I have said,
+it is possible to use metal filings, but Mr. Hughes
+prefers powdered charcoal.</p>
+
+<p>Mr. Blyth states that a flat box, about 15 inches
+by 9, filled with coke, and with two tin electrodes<span class="pagenum" id="Page_199">199</span>
+fixed to the two ends, is one of the best arrangements
+for a microphone. He says that three of
+these instruments, hung like pictures against the
+wall of a room, would suffice, when influenced
+by a single Leclanché cell, to make all the sounds
+produced in a telephone audible, and especially
+vocal airs. Mr. Blyth even asserts that a microphone
+capable of transmitting speech can be made
+with a simple piece of coke, connected with the
+circuit by its two ends, but it must be coke: a retort
+carbon, with electrodes, will not act.</p>
+
+<p>It is a remarkable property of these kinds of
+microphones that they can act without a battery,
+at least when they are so arranged as to form a
+voltaic element for themselves, and this can be
+done by throwing water on the carbons. Mr. Blyth,
+who was the first to speak of this system, does not
+distinctly indicate its arrangement, and we may
+assume that his instrument did not differ from the
+one we have already described, to which water
+must have been added. In this way, indeed, I have
+been able to transmit not only the ticking of a
+watch and the sounds of a musical box, but speech
+itself, which was often more distinctly expressed
+than in an ordinary microphone, since it was free
+from the sputtering sound which is apt to accompany
+the latter. Mr. Blyth also asserts that sounds
+may be transmitted without the addition of water,
+but in this case he considers that the result is due
+to the moisture of the breath. Certainly much<span class="pagenum" id="Page_200">200</span>
+moisture is not required to set a voltaic couple in
+action, especially when a telephone is the instrument
+of manifestation. The ordinary microphone
+may be used without a battery, if the circuit in
+which it is inserted is in communication with the
+earth by means of earthen cakes; the currents
+which then traverse the circuit will suffice to make
+the tickings of a watch placed upon the microphone
+perfectly audible. M. Cauderay, of Lausanne,
+in a paper sent to the Académie des Sciences,
+July 8, 1878, informs us that he made this experiment
+on a telegraphic wire which unites the Hôtel
+des Alpes at Montreux with a <i lang="fr">châlet</i> on the hill—a
+distance of about 550 yards.</p>
+
+<p><i>The Microphone used as a Speaking Instrument.</i>—The
+microphone can not only transmit speech,
+but it can also under certain conditions reproduce
+it, and consequently supply the place of the receiving
+telephone. This seems difficult to understand,
+since a cause for the vibratory motion
+produced in part of the circuit itself can only be
+sought in the variations in intensity of the current,
+and the effects of attraction and magnetisation have
+nothing to do with it. Can the action be referred
+to the repulsions reciprocally exerted by the contiguous
+elements of the same current? Or are we
+to consider it to be of the same nature as that
+which causes the emission of sounds from a wire
+when a broken current passes through it, so that
+an electric current is itself a vibratory current, as<span class="pagenum" id="Page_201">201</span>
+Mr. Hughes believes? It is difficult to reply to
+these questions in the present state of science; we
+can only state the fact, which has been published
+by Messrs. Hughes, Blyth, Robert Courtenay, and
+even by Mr. Edison himself. I have been able to
+verify the fact myself under the experimental conditions
+indicated by Mr. Hughes, but I was not so
+successful in the attempt to repeat Mr. Blyth’s experiments.
+This gentleman stated that in order to
+hear speech in a microphone it would be enough to
+use the model made from fragments of carbon, as
+we have described, to join to it a second microphone
+of the same kind, and to introduce into the circuit
+a battery consisting of two Grove elements. If
+anyone then speaks above the carbons of one of
+the microphones, what is said should be distinctly
+heard by the person who puts his ear to the other,
+and the importance of the sounds thus produced
+will correspond with the intensity of the electric
+source employed. As I have said, I was unable
+by following this method to hear any sound, still
+less articulate speech; and if other experiments had
+not convinced me, I should have doubted the correctness
+of the statement. But this negative experiment
+does not in fact prove anything, since it
+is possible that my conditions were wrong, and that
+the cinders which I employed were not subject to
+the same conditions as Mr. Blyth’s fragments of
+coke.</p>
+
+<figure id="il_45" class="figcenter" style="max-width: 15em;">
+  <img src="images/i_p202.jpg" width="564" height="737" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 45.</span>
+  </figcaption>
+</figure>
+
+<p>With respect to Mr. Hughes’s experiments, I<span class="pagenum" id="Page_202">202</span>
+have repeated them with the microphone made by
+MM. Chardin and Berjot, using that by M. Gaiffe
+as the sender, and I ascertained that with a battery
+of only four Leclanché cells, a scratch made
+on the sender, and even the tremulous motion
+and the airs played in a little musical box placed
+on the sender, were reproduced—very faintly,
+it is true—in the second microphone; in order
+to perceive them, it was enough to apply the ear
+to the vertical board of the instrument. It is true
+that speech was not reproduced, but of this Mr.
+Hughes had warned me; it was evident that with<span class="pagenum" id="Page_203">203</span>
+this arrangement the instrument was not sufficiently
+sensitive.</p>
+
+<p>A different arrangement of the microphone is
+required for the transmission and the reproduction
+of speech by this system, and a section of the one
+which Mr. Hughes found most successful is given
+in <a href="#il_45">fig. 45</a>. It somewhat resembles Mr. Hughes’s
+microphone speaker, placed in a vertical position,
+and the fixed carbon is fastened to the centre of
+the stretched membrane of a string telephone.
+The ear or mouth tube is at <span class="allsmcap">A</span>, the membrane at
+<span class="allsmcap">D D</span>, the carbon just mentioned at <span class="allsmcap">C</span>: this carbon is of
+metallised charcoal prepared from deal, and so also is
+the double carbon <span class="allsmcap">E</span>, which is in contact with it and is
+fastened to the upper end of the little bar <span class="allsmcap">G I</span>.
+The whole is enclosed in a small box, and the
+pressure exerted on the contact of the two carbons is
+regulated by a spring <span class="allsmcap">R</span> and a screw <span class="allsmcap">H</span>. The tube
+of the telephone serves as an acoustic tube for
+the listener, and Mr. Hughes’s speaker, described
+above, acts as sender. It is hardly necessary to say
+that the two instruments are placed at each end of
+the circuit, that the carbons are connected with the
+two poles of a battery of one or two cells of bichromate
+of potash, or two Bunsen or six Leclanché cells,
+and the two instruments are connected by the line
+wire. Under such conditions, conversation may be
+exchanged, but the sounds are always much less
+distinct than they are in a telephone.</p>
+
+<p>I was able to ascertain this fact with a roughly<span class="pagenum" id="Page_204">204</span>
+made instrument brought from England by Mr.
+Hughes. MM. Berjot, Chardin, and de Méritens,
+who were also present at the experiments, were
+able with me to hear speech perfectly, and I have
+since successfully repeated the experiment alone,
+but it does not always succeed, and under its present
+conditions the instrument has no importance
+in a scientific point of view. It is evident that the
+instrument can dispense with any support, and the
+little box then forms the handle of the instrument;
+in this case the two binding screws are placed at the
+end of this handle, as in a telephone. The microphone
+speaker with a disk, represented in <a href="#il_5">fig. 5</a>,
+which acts as sender to the singing condenser, can
+be used, when properly regulated, as a receiving
+microphone. M. Berjot has obtained good results
+from a little instrument of the same kind as that
+in <a href="#il_45">fig. 45</a>, but with a metal diaphragm, and the
+microphonic system consists of a cylindrical piece of
+carbon resting on a small disk of the same substance,
+which is galvanised and soldered to the
+diaphragm. The whole is enclosed in a small
+round box, with its upper part cut in the form of a
+mouthpiece.</p>
+
+<p>It seems that all microphone senders with disks
+can reproduce speech more or less perfectly; it is
+a question of adjusting and refining the carbon
+points of contact. A weak battery, consisting of a
+single Leclanché cell, is better for these instruments
+than a strong battery, precisely because<span class="pagenum" id="Page_205">205</span>
+of the effects of oxidation and polarisation, which
+are so energetically produced at these points of
+contact when the battery is strong.</p>
+
+<p>The effects of the microphone receiver explain
+the sounds, often very intense, produced by
+the Jablochkoff candles when they are influenced
+by electro-magnetic machines. These sounds
+always vibrate in unison with those emitted by the
+machine itself, and they result, as I have already
+shown, from the rapid magnetisations and demagnetisations
+which are effected by the machine.
+These effects, observed by M. Marcel Deprez,
+were particularly marked in M. de Méritens’ first
+machines.</p>
+
+<p><i>Other Arrangements of Microphones.</i>—An arrangement
+such as we have just described has
+been employed by M. Carette to form an extremely
+powerful microphone speaker. The only difference
+is that the stretched membrane is replaced by
+a thin metallic disk: he fastens one of the carbons
+to the centre of this disk, and applies to it the
+other carbon, which is pointed, and held by a
+<i lang="fr">porte-carbon</i> with a regulating screw, so that the
+pressure which takes place between the two carbons
+may be regulated at pleasure. By this arrangement
+speech may be heard at a distance from
+the telephone. In other respects it resembles the
+telephone sender represented in <a href="#il_5">fig. 5</a>.</p>
+
+<p>M. de Méritens has executed the system represented,
+<a href="#il_45">fig. 45</a>, on a large scale, forming the tube<span class="pagenum" id="Page_206">206</span>
+<span class="allsmcap">A B</span> of a zinc funnel a yard in length, and in this
+way he has been able to magnify the sounds, so
+that a conversation held in a low voice, three or
+four yards from the instrument, has been produced
+in a telephone with more sonorous distinctness. The
+instrument was placed on the floor of the apartment,
+with the opening of the funnel above, and
+the telephone was in the cellars of the house.</p>
+
+<p>The form of the microphone has been varied
+in a thousand ways, to suit the purposes to which
+it was to be applied. In the ‘English Mechanic
+and World of Science,’ June 28, 1878, we see the
+drawings of several arrangements, one of which is
+specially adapted for hearing the steps of a fly. It
+is a box, with a sheet of straw paper stretched on
+its upper part; two carbons, separated by a morsel
+of wood, and connected with the two circuit wires,
+are fastened to it, and a carbon pencil, placed
+crosswise between the two, is kept in this position
+by a groove made in the latter. A very weak
+battery will be enough to set the instrument at
+work, and when the fly walks over the sheet of
+paper it produces vibrations strong enough to
+react energetically on an ordinary telephone.
+The instrument must be covered with a glass globe.
+When a watch is placed on the membrane, with its
+handle applied to the morsel of wood which divides
+the two carbons, the noise of its ticking may be
+heard through a whole room. Two carbon cubes
+placed side by side, and only divided by a playing-card,<span class="pagenum" id="Page_207">207</span>
+may also be used instead of the arrangement
+of carbons described above. A semicircular
+cavity, made in the upper part of the two carbons,
+in which are placed some little carbon balls,
+smaller than a pea and larger than a mustard seed,
+will make it possible to obtain multiple contacts
+which are very mobile and peculiarly fit for telephonic
+transmissions. This arrangement has been
+made by Mr. T. Cuttriss.</p>
+
+<p>Several other arrangements of microphones
+have been devised by different makers and inventors,
+such as those of Messrs. Varey, Trouvé,
+Vereker, de Combettes, Loiseau, Lippens, de
+Courtois, Pollard, Voisin, Dumont, Jackson, Paterson,
+Taylor, &amp;c., and they are more or less satisfactory.
+The instruments of MM. Varey, Trouvé,
+Lippens, and de Courtois are the most interesting,
+and we will describe them.</p>
+
+<p>M. Varey’s microphone consists of a sounding
+box of deal, mounted in a vertical position on a
+stand, and two microphones are arranged on
+either side of it, with vertical carbons united for
+tension. A small Gaiffe cell of chloride of silver,
+without liquid, is applied to the standard of the
+instrument, and is enough to make it work perfectly.
+This system is extremely sensitive.</p>
+
+<p>M. Trouvé’s microphones, represented in <a href="#il_46">figs. 46</a>,
+<a href="#il_47">47</a>, <a href="#il_48">48</a>, are extremely simple, so that he is able
+to sell them at a very moderate price. They
+generally consist of a small vertical cylindrical<span class="pagenum" id="Page_208">208</span>
+box, as we see in the figure, with disks of carbon
+at its two ends, which are united by a carbon rod,
+or by a metallic tube tipped with carbon. This
+rod or tube turns freely in two cavities made in
+the carbons, and the box, while acting as a sounding
+box, becomes at the same time a prison for the
+insects whose movements and noises are the objects
+of study.</p>
+
+<figure id="il_46" class="figcenter" style="max-width: 21em;">
+  <img src="images/i_p208.jpg" width="805" height="433" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 46.</span>
+  </figcaption>
+</figure>
+
+<p>These boxes may be suspended on a cross-bar
+(<a href="#il_47">fig. 47</a>) by the two communicating wires, so as to be
+completely insulated. In this case the ticking of a
+watch placed upon the board, friction, and external
+shocks are hardly heard, but on the other hand the
+sound vibrations of the air alone are transmitted,
+and they acquire great distinctness. We have often
+repeated these experiments, and have always found
+that the tones of the voice were perfectly preserved.</p>
+
+<p><span class="pagenum" id="Page_209">209</span></p>
+
+<p>The model represented <a href="#il_48">fig. 48</a> is still more
+simple, and appears to be the latest development
+of this kind of instrument. It consists of a stand
+and a disk united by a central rod. The upper
+disk moves round the central rod, and permits
+the vertical carbon to assume any inclination
+which is desired. It is evident that the instrument
+will become less sensitive when the carbon
+is more oblique.</p>
+
+<figure id="il_47" class="figcenter" style="max-width: 21em;">
+  <img src="images/i_p209.jpg" width="818" height="637" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 47.</span>
+  </figcaption>
+</figure>
+
+<p>We must also mention a very successful microphone
+devised by M. Lippens. It is a slightly
+made box, like that of M. Varey, and on its
+opposite faces there are applied, on two frames
+left empty for the purpose, two thin plates of
+hardened caoutchouc, in the centre of which inside<span class="pagenum" id="Page_210">210</span>
+the box, two carbons are fastened, and on their
+outer surface a half-sphere is hollowed.</p>
+
+<figure id="il_48" class="figcenter" style="max-width: 21em;">
+  <img src="images/i_p210.jpg" width="813" height="437" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 48.</span>
+  </figcaption>
+</figure>
+
+<p>The interval between the two carbons hardly
+amounts to two millimètres, and a carbon ball is
+inserted into the two cavities which form its
+spherical case. This ball is supported by a spiral
+spring which can be extended more or less by means
+of a wire wound on a windlass which is fixed
+above the instrument, like the spring of an electric
+telegraph instrument. By means of this spring,
+the pressure of the carbon ball against the sides of
+the cavity which contains it can be regulated at
+pleasure, and the sensitiveness of the instrument
+and its capacity for transmitting speech can be
+adjusted. Under these conditions, the vibrations
+of the caoutchouc plates directly affect the microphone,
+and the currents of air have no influence
+on it, so that the effects are more distinct. It is so
+sensitive that it is best for the speaker to place<span class="pagenum" id="Page_211">211</span>
+himself at the distance of at least 50 centimètres
+from the instrument. M. Lippens’ instrument is a
+pretty one, mounted on a wooden stand, which is
+neatly turned.</p>
+
+<p>In order to put an end to the sputtering usual
+in microphones, it occurred to M. de Courtois to
+prevent any cessation of contact between the
+carbons by keeping them close together, and to
+effect the variations of resistance necessary for
+articulate sounds by making them slide over each
+other, so as to insert a shorter or longer portion of
+the carbon in the circuit. For this purpose a
+vibrating disk is placed in a vertical position in a
+rigid frame, and a small conducting rod, terminated
+by a pointed carbon, is applied to it, with this
+carbon point resting on another flat piece of carbon
+placed below it. Influenced by the vibrations of
+the disk, the carbon point moves to and fro, effecting
+more or less extensive contacts with the lower
+carbon, and thus producing variations of resistance
+which almost correspond to the range of
+vibrations on the disk.</p>
+
+<p><i>Experiments made with the Microphone.</i>—I must
+now mention the interesting experiments which led
+Mr. Hughes to the invention of the remarkable
+instrument of which we have spoken, as well as
+those undertaken by other scientific men, either
+from a scientific or a practical point of view.</p>
+
+<p>Believing that light and heat can modify the
+conductivity of bodies, Mr. Hughes went on to<span class="pagenum" id="Page_212">212</span>
+consider whether sound vibrations, transmitted to
+a conductor traversed by a current, would not
+also modify this conductivity by provoking the
+contraction and expansion of the conducting molecules,
+which would be equivalent to the shortening
+or lengthening of the conductor thus affected. If
+such a property existed, it would make it possible
+to transmit sounds to a distance, since variations in
+the conductivity would result from variations corresponding
+to the intensity of the current acting on
+the telephone. The experiment which he made
+on a stretched metal wire did not, however, fulfil
+his expectation, and it was only when the wire
+vibrated so strongly as to break, that he heard a
+sound at the moment of its fracture. When he
+again joined the two ends of the wire, another
+sound was produced, and he soon perceived that
+imperfect contact between the two broken ends of
+wire would enable him to obtain a sound. Mr.
+Hughes was then convinced that the effects he
+wished to produce could only be obtained with a
+divided conductor, and by means of imperfect
+contacts.</p>
+
+<p>He then sought to discover the degree of
+pressure which it was most expedient to exert
+between the two adjacent ends of the wire, and for
+this purpose he effected the pressure by means of
+weights. He ascertained that when the pressure
+did not exceed the weight of an ounce on the
+square inch at the point of connection, the sounds<span class="pagenum" id="Page_213">213</span>
+were reproduced with distinctness, but somewhat
+imperfectly. He next modified the conditions of the
+experiment, and satisfied himself that it was unnecessary
+to join the wires end to end in order to
+obtain this result. They might be placed side by
+side on a board, or even separated (with a conductor
+placed crosswise between them), provided that the
+conductors were of iron, and that they were kept in
+metallic connection by a slight and constant pressure.
+The experiment was made with three Paris points,
+and arranged as it appears in <a href="#il_49">fig. 49</a>, and it has
+since been repeated under very favourable conditions
+by Mr. Willoughby Smith with three of the
+so-called rat-tail files, which made it possible to
+transmit even the faint sound of the act of
+respiration.<a id="FNanchor_15" href="#Footnote_15" class="fnanchor">15</a></p>
+
+<figure id="il_49" class="figcenter" style="max-width: 22em;">
+  <img src="images/i_p213.jpg" width="871" height="525" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 49.</span>
+  </figcaption>
+</figure>
+
+<p><span class="pagenum" id="Page_214">214</span></p>
+
+<p>He afterwards tried different combinations of
+the same nature, which offered several solutions of
+continuity, and a steel chain produced fairly good
+results, but slight inflections, like those caused by
+the <em>timbre</em> of the voice, were not reproduced, and
+he tried other arrangements. He first sought to
+apply metallic powders to the points of contact;
+powdered zinc and tin, known in commerce under
+the name of white bronze, greatly increased the
+effects obtained; but they were unstable, on
+account of the oxidation of the contacts; and it
+was in seeking to solve this difficulty, as well as
+to discover the most simple means of obtaining a
+slight and constant pressure on the contacts, that
+Mr. Hughes was led to the arrangement, previously
+described, of carbons impregnated with mercury,
+and he thus obtained the maximum effect.<a id="FNanchor_16" href="#Footnote_16" class="fnanchor">16</a></p>
+
+<p><span class="pagenum" id="Page_215">215</span></p>
+
+<p>Mr. Hughes considers that the successful effects
+of the microphone depend on the number and
+perfection of the contacts, and this is doubtless the
+reason why some arrangements of the carbon
+pencil in the instrument described above were
+more favourable than others.</p>
+
+<p>In order to reconcile these experiments with
+his preconceived ideas, Mr. Hughes thought that,
+since the differences of resistance proceeding from
+the vibrations of the conductor were only produced
+when it was broken, the molecular movements were
+arrested by the lateral resistances which were equal
+and opposite, but that if one of these resistances
+were destroyed, the molecular movement could be
+freely developed. He considers that an imperfect
+contact is equivalent to the suppression of one of
+these resistances, and as soon as this movement
+can take place, the molecular expansions and
+contractions which result from the vibrations must
+correspond to the increase or diminution of resistance
+in the circuit. We need not pursue Mr.
+Hughes’s theory further, since it would take too
+long to develope it, and we must continue our
+examination of the different properties of the
+microphone.<a id="FNanchor_17" href="#Footnote_17" class="fnanchor">17</a></p>
+
+<p><span class="pagenum" id="Page_216">216</span></p>
+
+<p>Carbon, as we have said, is not the only
+substance which can be employed to form the
+sensitive organ of this system of transmission.
+Mr. Hughes has tried other substances, including
+those which are good conductors, such as metals.
+Iron afforded rather good results, and the effect
+produced by surfaces of platinum when it was
+greatly subdivided was equal, if not superior, to
+that furnished by the mercurised carbon. Yet
+since the difficulty of making instruments with this
+metal is greater, he prefers the carbon, which
+resembles it in being incapable of oxidation.</p>
+
+<p>We have already said that the microphone may
+be used as a thermoscope, in which case it must
+have the special arrangement represented in <a href="#il_43">fig. 43</a>.
+Under these conditions, heat, reacting on
+the conductivity of these contacts, may cause
+such variations in the resistance of the circuit that
+the current of three Daniell cells will be annulled
+by approaching the hand to the tube. In
+order to estimate the relative intensity of the
+different sources of heat, it will be enough to<span class="pagenum" id="Page_217">217</span>
+introduce into the circuit of the two electrodes <span class="allsmcap">A</span>
+and <span class="allsmcap">B</span>, <a href="#il_43">fig. 43</a>, a battery <span class="allsmcap">P</span>, of one or two Daniell
+cells, and a moderately sensitive galvanometer
+<span class="allsmcap">G</span>. For this purpose one of 120 turns will suffice.
+When the deviation decreases, it shows that the
+source of heat is superior to the surrounding atmosphere;
+and conversely, that it is inferior when
+the deviation increases. Mr. Hughes says that the
+effects resulting from the intervention of sunshine
+and shadow are shown on the instrument by considerable
+variations in the deviations of the galvanometer.
+Indeed it is so sensitive to the slightest
+variations of temperature that it is impossible to
+maintain it in repose.</p>
+
+<p>I have repeated Mr. Hughes’s experiments
+with a single Leclanché cell, and for this purpose
+I employed a quill, filled with five fragments
+of carbon, taken from the cylindrical carbons
+of small diameter which are made by M. Carré for
+the electric light. I have obtained the results
+which are mentioned by Mr. Hughes, but I ought
+to say that the experiment is a delicate one.
+When the pressure of the fragments of carbon
+against each other is too great, the current traverses
+them with too much force to allow the calorific
+effects to vary the deviation of the galvanometer,
+and when the pressure is too slight, the current
+will not pass through them. A medium degree of
+pressure must therefore be effected to ensure the
+success of the experiment, and when it is obtained,<span class="pagenum" id="Page_218">218</span>
+it is observed that on the approach of the hand to
+the tube, a deviation of 90° will, after a few
+seconds, diminish, so that it seems to correspond
+with the approach or withdrawal of the hand.
+But breathing produces the most marked effects,
+and I am disposed to believe that the greater
+or less deviations produced by the emission of
+articulate sounds when the different letters of the
+alphabet are pronounced separately, are due to
+more or less direct emissions of heated gas from
+the chest. It is certain that the letters which require
+the most strongly marked sounds, such as A, F, H,
+I, K, L, M, N, O, P, R, S, W, Y, Z, produce the
+greatest deviations of the galvanometric needle.</p>
+
+<p>In my paper on the conductivity of such bodies
+as are moderately good conductors, I had already
+pointed out this effect of heat upon divided substances,
+and I also showed that after a retrograde
+movement, which is always produced at once,
+a movement takes place in an inverse direction to
+the index of the galvanometer when heat has been
+applied for some instants, and this deviation is
+much greater than the one which is first indicated.</p>
+
+<p>In a paper published in the ‘American Scientific
+Journal,’ June 28, 1878, Mr. Edison gives some
+interesting details on the application of his system
+of a telephonic sender to measuring pressures,
+expansions, and other forces capable of varying the
+resistance of the carbon disk by means of greater
+or less compression. Since his experiments on<span class="pagenum" id="Page_219">219</span>
+this subject date from December 1877, he again
+claims priority in the invention of using the microphone
+as a thermoscope; but we must observe that
+according to Mr. Hughes’s arrangement of his
+instrument, the effect produced by heat is precisely
+the reverse of the effect described by Mr. Edison.
+In fact, in the arrangement adopted by the latter,
+heat acts by increasing the conductivity acquired
+by the carbon under the increased pressure produced
+by the expansion of a body sensitive to heat:
+in Mr. Hughes’s system, the effect produced by
+heat is precisely the contrary, since it then acts
+only on the contacts, and not by means of pressure.
+Therefore the resistance of the microphone-thermoscope
+is increased under the influence of
+heat, instead of being diminished. This contrary
+effect is due to the division of some substance
+which is only a moderate conductor, and I have
+shown that under such conditions these bodies,
+when only slightly heated, always diminish the
+intensity of the current which they transmit. I
+believe that Mr. Edison’s arrangement is the best
+for the thermoscopic instrument, and makes it
+possible to measure much less intense sources of
+heat. Indeed he asserts that by its aid the heat of
+the luminous rays of the stars, moon, and sun may
+be measured, and also the variations of moisture in
+the air, and barometric pressure.</p>
+
+<p>This instrument, which we give <a href="#il_50">fig. 50</a>, with
+its several details, and with the rheostatic arrangement<span class="pagenum" id="Page_220">220</span>
+employed for measuring, consists of a
+metallic piece <span class="allsmcap">A</span> fixed on a small board <span class="allsmcap">C</span>, and on
+one of its sides there is the system of platinum
+disks and carbons shown in <a href="#il_28">fig. 28</a>. A rigid piece
+<span class="allsmcap">G</span>, furnished with a socket, serves as the external
+support of the system, and into this socket is
+introduced the tapering end of some substance
+which is readily affected by heat, moisture, or
+barometric pressure. The other extremity is
+supported by another socket <span class="allsmcap">I</span>, fitted to a screw-nut
+<span class="allsmcap">H</span>, which may be more or less tightened by a
+regulating screw. If this system is introduced into
+a galvanometric circuit <i>a, b, c, i, g</i>, provided with
+all the instruments of the electric scale of measure,
+the variations in length of the substance inserted
+are translated by greater or less deviations of the
+galvanometric needle, which follow from the differences
+of pressure resulting from the lengthening
+or shortening of the surface capable of expansion
+which is inserted in the circuit.</p>
+
+<figure id="il_50" class="figcenter" style="max-width: 20em;">
+  <img src="images/i_p221.jpg" width="939" height="1290" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 50.</span>
+  </figcaption>
+</figure>
+
+<p>The experiments on the microphone made in
+London at the meeting of the Society of Telegraphic
+Engineers on May 25, 1878, were wonderfully
+successful, and they were the subject of an
+interesting article in the ‘Engineer’ of May 31,
+which asserts that the whole assembly heard the
+microphone speak, and that its voice was very like
+that of the phonograph. When the meeting was
+informed that these words had been uttered at
+some distance from the microphone, the Duke of<span class="pagenum" id="Page_221">221</span>
+Argyll, who was present, while admiring the important
+discovery, could not help exclaiming that
+this invention might have terrible consequences,
+since, for instance, if one of Professor Hughes’s<span class="pagenum" id="Page_222">222</span>
+instruments were placed in the room in Downing
+Street, in which Her Majesty’s ministers hold their
+cabinet council, their secrets might be heard in the
+room in which the present meeting took place.
+He added that if one of these little instruments
+were in the pocket of Count Schouvaloff, or of
+Lord Salisbury, we should at once be in possession
+of the secrets for which all Europe was anxiously
+waiting. If these instruments were able to repeat
+all the conversations held in the room in which they
+stood, they might be really dangerous, and the
+Duke thought that Professor Hughes, who had
+invented such a splendid yet perilous instrument,
+ought next to seek an antidote for his discovery.
+Dr. Lyon Playfair, again, thought that the microphone
+ought to be applied to the aërophone, so
+that by placing these instruments in the two Houses
+of Parliament, the speeches of great orators might
+be heard by the whole population within five or six
+square miles.</p>
+
+<p>The experiments lately made with the microphone
+at Halifax show that the Duke of Argyll’s
+predictions were fully justified. It seems that a
+microphone was placed on a pulpit-desk in a church
+in Halifax, and connected by a wire about two
+miles long with a telephone placed close to the bed
+of a sick person, who was able to hear the prayers,
+the chanting, and the sermon. This fact was communicated
+to me by Mr. Hughes, who heard it
+from a trustworthy source, and it is said that<span class="pagenum" id="Page_223">223</span>
+seven patients have subscribed for the expense of an
+arrangement by which they may hear the church
+services at Halifax without fatigue.</p>
+
+<p>The microphone has also lately been applied to
+the transmission of a whole opera, as we learn from
+the following account in the ‘Journal Télégraphique,’
+Berne, July 25, <span class="locked">1878:—</span></p>
+
+<p>‘A curious micro-telephonic experiment took
+place on June 19 at Bellinzona, Switzerland. A
+travelling company of Italian singers was to perform
+Donizetti’s opera, “Don Pasquale,” at the theatre of
+that town. M. Patocchi, a telegraphic engineer,
+took the opportunity of making experiments on
+the combined effects of Hughes’s carbon microphone
+as the sending instrument, and Bell’s telephone
+as the receiver. With this object he placed a
+Hughes microphone in a box on the first tier, close
+to the stage, and connected it by two wires, from
+one to half a millimètre in thickness, to four Bell
+receivers, which were placed in a billiard-room
+above the vestibule of the theatre, and inaccessible
+to sounds within the theatre itself. A small battery
+of two cells, of the ordinary type used in the
+Swiss telegraphic service, was inserted in the circuit,
+close to the Hughes microphone.</p>
+
+<p>‘The result was completely successful. The
+telephones exactly reproduced, with wonderful
+purity and distinctness, the instrumental music of
+the orchestra, as well as the voices of the singers.
+Several people declared that they did not lose a<span class="pagenum" id="Page_224">224</span>
+note of either, that the words were heard perfectly;
+the airs were reproduced in a natural key, with
+every variation, whether <i lang="la">piano</i> or <i lang="la">forte</i>, and several
+amateurs assured M. Patocchi that by listening to
+the telephone they were able to estimate the musical
+beauty, the quality of the singers’ voices, and the
+general effect of the piece, as completely as if they
+had been among the audience within the theatre.</p>
+
+<p>‘The result was the same when resistances
+equivalent to 10 kilomètres were introduced into
+the circuit, without increasing the number of cells
+in the battery. We believe that this is the first
+experiment of the kind which has been made in
+Europe, at least in a theatre, and with a complete
+opera; and those who are acquainted with the
+delicacy and grace of the airs in “Don Pasquale” will
+be able to appreciate the sensitiveness of the combined
+instruments invented by Hughes and Bell,
+which do not suffer the most delicate touches of
+this music to be lost.’</p>
+
+<p>Although experiments with the microphone are
+of such recent date, they have been very various,
+and among other curious experiments we learn
+from the English newspapers that the attempt has
+been made to construct an instrument on the same
+principle as the telephone, which shall be sensitive
+to the variations of light. It is known that some
+substances, and particularly selenium, are electrically
+affected by light, that is, that their conductivity
+varies considerably with the greater or less<span class="pagenum" id="Page_225">225</span>
+amount of light which is shed upon them. If,
+therefore, a circuit in which a substance of this
+nature is inserted, is abruptly subjected to a somewhat
+intense light, the increase of resistance which
+results from it ought to produce a powerful sound
+in a telephone inserted in the circuit. This fact has
+been verified by experiment, and Mr. Willoughby
+Smith infers from it, as we have already suggested,
+that the effects produced in the microphone
+are due to variations of resistance in the circuit,
+which are produced by more or less close contacts
+between imperfect conductors.</p>
+
+<p>In order to obtain this effect under the most
+favourable conditions, Mr. Siemens employs two
+electrodes, consisting of network of very fine platinum
+wire, fitting into each other like two forks, of
+which the prongs are interlaced. These electrodes
+are inserted between two glass plates, and a drop
+of selenium, dropped in the centre of the two pieces
+of network, connects them on a circular surface large
+enough to establish sufficient conductivity in the
+circuit. It is on this flattened drop that the ray of
+light must be projected.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h2 class="nobreak" id="APPLICATIONS_OF_THE_MICROPHONE"><span id="toclink_225"></span>APPLICATIONS OF THE MICROPHONE.</h2>
+</div>
+
+<p>The applications of the microphone increase
+in number every day, and in addition to those of
+which we have just spoken, there are others of
+really scientific and even of practical interest.
+Among the number is the use which can be made<span class="pagenum" id="Page_226">226</span>
+of it as a system of relays for telegraphy, in
+science for the study of vibrations imperceptible to
+our senses, in medicine and surgery, and even in
+manufactures.</p>
+
+<p><i>Its application to Scientific Research.</i>—We have
+seen that several physicists, including Messrs.
+Spottiswoode, Warwick, Rossetti, Canestrelli,
+Wiesendanger, Lloyd, Millar, Buchin, and Blyth,
+have been able to hear what is said in a telephone
+which has no iron diaphragm, but it was so difficult
+to establish the fact that it has been often disputed.
+More certain evidence was desirable, and the
+microphone is an opportune agent for affording it.</p>
+
+<p>The ‘Telegraphic Journal’ of September 1, 1878,
+observes that M. du Moncel, in order to claim the
+victory in his controversy with Colonel Navez,
+had still to show that the sounds which appeared
+to be inarticulate in telephones without a diaphragm
+might become intelligible if they were
+intensified. This has been done for him by the
+use of Mr. Hughes’s microphone, and the following
+experiments were made for the purpose.</p>
+
+<p>1. If a magnetising coil, surrounding a bar of
+soft iron, is inserted in the circuit of a microphone,
+with a battery of three cells, the ticking of a
+watch and other sounds of the same kind may be
+heard on approaching the ear to the electro-magnet
+which has been thus constituted. It is true
+that these sounds are very faint when they are
+not amplified, but if the electro-magnet is fastened<span class="pagenum" id="Page_227">227</span>
+to a board, and a second microphone is fixed to the
+same board, the sounds produced by the electro-magnet
+are magnified, and become distinctly audible
+in the telephone which is placed in connection with
+this second microphone.</p>
+
+<p>2. These sounds may be further amplified by
+resting one of the extremities of the core of the
+electro-magnet on one of the poles of a permanent
+magnet, which is fixed upon the board. Articulate
+speech may then be heard in the telephone which
+is placed in connection with the microphone resting
+on the board, and the point at issue between
+MM. Navez and Du Moncel is completely decided
+in this way: for the auxiliary microphone can
+only propagate and amplify the vibration of
+articulate sounds, which are communicated by
+the bar magnet of the coil to the board on which
+the two instruments are placed. In this way it
+would be possible to render articulate sounds perceptible
+to M. Navez, when transmitted by the
+bar magnet of a telephone without a diaphragm.</p>
+
+<p>3. When a second bar magnet rests on the
+free pole of the electro-magnet, so as to present to
+it a pole of the same nature as the one with which
+it is already in communication—in a word, if a bar
+is placed between the two poles of a horseshoe
+electro-magnet, the effects are still more marked,
+and hence it may be assumed that the bar reacts
+as an armature, by concentrating the lines of magnetic
+force in the vicinity of the helix.</p>
+
+<p><span class="pagenum" id="Page_228">228</span></p>
+
+<p>4. When the two poles of a horseshoe magnet
+are inserted together inside a coil, their effects are
+equally energetic, although by this arrangement
+one of the poles might be expected to neutralise
+the effect of the other: but the most important
+effects have been obtained by placing an armature
+of soft iron across the poles of the magnet which
+has been already inserted in the coil. Under these
+conditions articulate sounds are distinctly heard.</p>
+
+<p>These experiments were confirmed by Mr. F.
+Varley, in a letter published in the ‘Telegraphic
+Journal’ of September 15, 1878, and among the
+fresh experiments mentioned by him, we will quote
+those which he made with an iron tube inserted in
+a helix, in which the two opposite poles of two bar
+magnets are introduced. These poles are only
+separated from each other by the interval of an
+inch, so that the centre of the iron tube may be
+strongly magnetised.</p>
+
+<p>Mr. Varley says that this last arrangement
+reproduces the articulate sounds which issue from a
+sending microphone, and this experiment is more
+decisive than that of Professor Hughes, in which
+case it might be supposed that the bar magnet,
+resting on the polar end of an electro-magnetic
+bar, was only a modification of the disk in the
+Bell telephone, set in vibration by the alternate
+currents passing through the helix, and that these
+vibrations were communicated to the board, and
+became sensible when enlarged by the microphone.<span class="pagenum" id="Page_229">229</span>
+But such an objection cannot be alleged in the
+case of the arrangement described above, for since
+the sound is produced between the current passing
+into the helix and the magnetic current of the bar,
+it can only be the result of a vibration produced
+by a disturbance of the reciprocal relations subsisting
+between these two elements. Mr. Varley
+adds that these experiments confirm M. du Moncel’s
+researches, which have thrown considerable light
+upon the causes which are at work in the action of
+the speaking telephone, and with which we have
+hitherto been imperfectly acquainted.</p>
+
+<p><i>Its application to Telephonic Relays.</i>—In February
+1878, I first began to consider the mode of forming
+telephonic relays, but I was checked by the discovery
+that there was no vibration in the receiving
+telephone, and I made the following communication
+on the subject to the Académie des Sciences
+on February 25:—‘If the vibrations of the disk in
+the receiving telephone were the same as those of
+the sending telephone, it is easy to see that if a
+telephone with a local battery, acting both as
+sender and receiver, were substituted for the receiving
+telephone, it might, by the intervention of
+the induction coil, act as a relay, and might therefore
+not only amplify the sound, but also transmit
+it to any distance. It is, however, doubtful whether
+the vibrations of the two corresponding disks are
+of the same nature, and if the sound be due to
+molecular contractions and expansions, the solution<span class="pagenum" id="Page_230">230</span>
+of the problem becomes much more difficult. Here
+is therefore a field for experiments.’ These experiments
+have been successfully made by Mr.
+Hughes, who acquainted me with them early in
+June 1878, and they led to the discovery of a most
+interesting system of microphonic relays.</p>
+
+<p>On a wooden board of moderate size, such as a
+drawing board, he placed a microphone with a
+carbon brought to a fine point at each end, and fixed
+in a vertical position. One or more telephones were
+placed in the circuit, with their membranes facing
+the board, and a continuous sound was heard,
+sometimes resembling a musical note, sometimes
+the singing of boiling water in an oven; and the
+sound, which could be heard at a distance, went
+on indefinitely, as long as the electric force was exerted.
+Mr. Hughes explains this phenomenon in
+the following way.</p>
+
+<p>The slightest shock which affects the microphone
+has the effect of sending currents, more or
+less broken, through the telephones, which transform
+them into sound vibrations, and since these
+are mechanically transmitted by the board to
+the microphone, they maintain and even amplify
+its action, and produce fresh vibrations on the
+telephones. Thus a fresh action is exerted on
+the microphone, and so on indefinitely. Again,
+if a second microphone, in connection with another
+telephonic circuit, be placed upon the same
+board, we have an instrument which acts as a<span class="pagenum" id="Page_231">231</span>
+telephonic relay, that is, it transmits to a distance
+the sounds communicated to the board, and these
+sounds may serve either as a call, or as the elements
+of a message in the Morse code, if a Morse
+manipulator is placed in the circuit of the first
+microphone. Mr. Hughes adds that he has made
+several very successful experiments with this system
+of instruments, although he only employed a
+Daniell battery of six cells without any induction
+coil. By fastening a pasteboard tube, 40
+centimètres in length, to the receiving telephone,
+he was able to hear in all parts of a large room
+the continuous sound of the relay, the ticking of a
+watch, and the scratching of a pen upon paper.
+He did not try to transmit speech, since it would
+not have been reproduced with sufficient distinctness
+under such conditions.</p>
+
+<p>Since this first attempt, Mr. Hughes has arranged
+another and still more curious system of microphonic
+relays, for which two microphones with
+vertical carbons are required. He places two
+microphones of this description on a board, and
+connects one of them with a third microphone,
+which acts as a sender, while the second is in communication
+with a telephone and a second battery:
+in this way the words uttered before the sender are
+heard in the telephone, without employing any
+electro-magnetic organ for the telephonic relay.</p>
+
+<p>In August 1878, Messrs. Houston and Thomson
+likewise arranged a system of telephonic relays<span class="pagenum" id="Page_232">232</span>
+which only differs from that of Mr. Hughes in the
+particular of having the microphone fixed on the
+diaphragm of the telephone, and not on the board
+beside it. The system consists of three vertical
+microphones, which can be combined for tension or
+quantity, according to the conditions for which they
+are required. The model of this instrument was
+represented in the ‘Telegraphic Journal’ of August
+15, 1878, to which we must refer our readers, if
+they wish for further information on the subject.</p>
+
+<p><i>Its application to Medicine and Surgery.</i>—The
+extreme sensitiveness of the microphone suggested
+its use for the observation of sounds produced
+within the human body, so that it might serve as a
+stethoscope for listening to the action of the lungs
+and heart. Dr. Richardson and Mr. Hughes are
+now busy in the attempt to carry out this idea, but
+so far the result is not very satisfactory, although
+they still hope to succeed. Meanwhile, M. Ducretet
+has made a very sensitive stethoscopic microphone,
+which we represent in <a href="#il_51">fig. 51</a>. It consists
+of a carbon microphone <span class="allsmcap">C P</span>, with a simple contact,
+of which the lower carbon <span class="allsmcap">P</span> is fitted to one of M.
+Marais’ tambourines with a vibrating membrane <span class="allsmcap">T</span>.
+This tambourine is connected with another <span class="allsmcap">T′</span>, by a
+caoutchouc tube, which is to be applied to the
+different parts of the body which demand auscultation,
+and which is therefore termed the <i lang="fr">tambour
+explorateur</i>. The sensitiveness of the instrument is
+regulated by means of a counterpoise <span class="allsmcap">P O</span>, which is<span class="pagenum" id="Page_233">233</span>
+screwed upon the arm of a bent lever, and to
+this the second carbon <span class="allsmcap">C</span> is fixed. The extreme
+sensitiveness of M. Marais’ tambourines in transmitting
+vibrations is well known, and since their
+sensitiveness is further increased by the microphone,
+the instrument becomes almost too impressionable,
+since it reveals all sorts of sounds, which
+it is difficult to distinguish from each other. Such<span class="pagenum" id="Page_234">234</span>
+an instrument can only be of use when entrusted
+to experienced hands, and a special education of
+the organ of hearing is needful, in order to turn it
+to account.</p>
+
+<figure id="il_51" class="figcenter" style="max-width: 26em;">
+  <img src="images/i_p233.jpg" width="1037" height="1065" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 51.</span>
+  </figcaption>
+</figure>
+
+<p>In a work lately published by M. Giboux on
+the application of the microphone to medicine, this
+stethoscopic system is rather severely criticised, and
+not without reason if, as M. Giboux asserts, it is
+only sensitive to the movements which take place
+on the surface of the body, and those which are
+internal are either lost or altogether changed in
+character. But without pronouncing on the improvements
+which may ultimately be made in the
+instrument, M. Giboux thinks that its most important
+use in medical practice consists in its allowing
+a certain number of students to observe with the
+professor the different sounds of the body, to study
+them with him in their different phases, and thus
+to profit more readily by his teaching. A microphonic
+circuit might bifurcate between several telephones,
+so that each person might hear for himself
+what is heard by others.</p>
+
+<p>The most important application of the instrument
+to surgical purposes has lately been made by
+Sir Henry Thompson, aided by Mr. Hughes, for
+the examination of the bladder in cases of stone.
+It enables him to ascertain the presence and
+precise position of calculi, however small they may
+be. For the purpose of research, he uses a sound,
+made of a Maillechort rod, a little bent at the end,<span class="pagenum" id="Page_235">235</span>
+and placed in communication with a sensitive
+carbon microphone. When the sound is moved
+about in the bladder, the rod comes in contact with
+stony particles, even if they are no
+larger than a pin’s head, and friction
+ensues, producing in the telephone
+vibrations which can be easily distinguished
+from those caused by the
+simple friction of the rod on the
+soft tissues of the sides of the
+bladder. The arrangement of the
+instrument is shown in <a href="#il_52">fig. 52</a>.
+The microphone is placed in the
+handle which contains the sound,
+and is the same as that given in
+<a href="#il_42">fig. 42</a>, but of smaller size, and
+the two conducting wires <i>e</i> which
+lead to the telephone, issue from
+the handle by the end <i>a</i> opposite
+to that <i>bb</i> to which the sound <i>dd</i>
+is screwed. As this instrument
+is not intended to reproduce speech,
+retort carbons instead of wood
+carbons may be used.</p>
+
+<figure id="il_52" class="figright" style="max-width: 5em;">
+  <img src="images/i_p235.jpg" width="223" height="1164" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 52.</span>
+  </figcaption>
+</figure>
+
+<p>Some deaf people, whose sense
+of hearing is not completely destroyed,
+have been able to hear by
+an expedient based upon the principle of the microphone.
+For this purpose two telephones, connected
+by a metallic crown, which is placed on the temples,<span class="pagenum" id="Page_236">236</span>
+are applied to the ears of the deaf person, and the
+telephones are placed in communication with a
+battery microphone, which hangs to the end of a
+double conducting wire. The deaf man keeps the
+microphone in his pocket, and presents it as an
+acoustic tube to the person who wishes to converse
+with him. Mr. Hughes’s speaker, represented
+<a href="#il_42">fig. 42</a>, is the one used.</p>
+
+<p><i>Various Applications.</i>—The microphone may be
+used in many other ways, some of which are suggested
+in the ‘English Mechanic’ of June 21,
+1878. The article states that by means of this
+instrument, engineers will be able to estimate the
+effects of the vibrations caused on old and new
+buildings by the passage of heavy loads; a soldier
+will be able to discover the enemy’s approach when
+he is several miles off, and may even ascertain
+whether he has to do with artillery or cavalry; the
+approach of ships to the neighbourhood of torpedoes
+may be automatically heralded on the coast
+by this means, so that an explosion may be produced
+at the right moment.</p>
+
+<p>It has also been proposed to use the microphone
+to give notice of an escape of gas in coal-mines.
+The gas, in escaping from between the
+seams of coal, makes a whistling noise, which might,
+with the aid of the microphone and telephone, be
+heard at the top of the shaft. Again, it has been
+suggested that the microphone might be used as a
+seismograph to reveal the subterranean noises<span class="pagenum" id="Page_237">237</span>
+which generally precede earthquakes and volcanic
+eruptions, and which would be much intensified by
+this instrument. It might even be of use to Signor
+Palmieri for his observations in the Vesuvius
+Observatory.</p>
+
+<p>The microphone has also been used by Mr.
+Chandler Roberts to render the diffusion of gaseous
+molecules through a porous membrane sensible to
+the ear.</p>
+
+<p>As might have been expected, the acclamation
+with which Mr. Hughes’s invention was received
+led to the assertion of other claims to priority, and
+in addition to that of Mr. Edison, on which we
+have already given our opinion, there are several
+others, showing that if some microphonic effects
+were discovered at different times before the date
+of Mr. Hughes’s discovery, they could not have
+been considered important, since they were not
+even announced. Among the number was that of
+Mr. Wentworth Lascelles Scott, specified in the
+‘Electrician’ of May 25, 1878, and that of M. Weyher,
+presented to the Société de Physique, Paris,
+in June 1878. Another, made by M. Dutertre, is
+of somewhat greater importance, for his experiments
+were reported in the Rouen papers in
+February of the same year: yet there is no just
+ground for such claims, since the earliest date of
+his experiments is subsequent to the experiments
+first made by Mr. Hughes. These began early in
+December 1877, and in January 1878 they were<span class="pagenum" id="Page_238">238</span>
+exhibited to officials of the Submarine Telegraph
+Company, as Mr. Preece declared in a letter addressed
+to the several scientific men.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h2 class="nobreak" id="EXTERNAL_INFLUENCE_ON_TELEPHONIC"><span id="toclink_238"></span>EXTERNAL INFLUENCE ON TELEPHONIC
+TRANSMISSIONS.</h2>
+</div>
+
+<p>The obstacles which occur in telephonic transmissions
+proceed from three causes: 1. The intensity
+of sound is diminished by the loss of current in
+transmission—a loss which is much greater in the
+case of induced currents than in those received from
+a battery. 2. Confusion is caused by the influence of
+adjacent currents. 3. The induction from one wire
+to another. This last influence is much greater
+than is usually supposed. If two perfectly insulated
+wires are placed side by side, one in communication
+with the circuit of an electric bell, and the
+other with the circuit of a telephone, the latter
+will repeat the sounds of the bell with an intensity
+often great enough to act as a call without applying
+the instrument to the ear. MM. Pollard and
+Garnier, in their interesting experiments with the
+induced currents of the Ruhmkorff coil, have
+ascertained that in this way not merely sounds may
+be obtained which correspond with the induced
+currents resulting from the action of the primary
+current, but also those which result from the action
+of the secondary current on other helices, which
+are termed currents of the second order. These<span class="pagenum" id="Page_239">239</span>
+different reactions frequently cause the telephonic
+transmissions made on telegraphic lines to be disturbed
+by irregular sounds, arising from the electric
+transmissions on adjoining lines; but it does not
+appear that these influences altogether neutralise
+each other, so that conversation held in the ordinary
+way and a message sent in the Morse code may be
+heard simultaneously.</p>
+
+<p>At the Artillery School, Clermont, a telephonic
+communication has been established, for the sake
+of experiments, between the school and the butts,
+which are at a distance of about eight miles. Another
+communication of the same kind has been
+established between the Clermont Observatory and
+the one at Puy-de-Dôme, which is nearly nine miles
+from the former. These two lines are carried on
+the same posts for a course of six miles, together with
+an ordinary telegraphic wire, and for a distance of
+330 yards there are seven other such wires. The two
+telephonic wires are separated from each other by
+a space of 85 centimètres. The following facts
+have been observed under these conditions.</p>
+
+<p>1. The school telephone is perfectly able to
+read off from their sound the Morse messages
+which pass through the two adjacent telegraph
+wires, and the ticking of the instrument does not
+at all interfere with the vocal communication of
+the telephone, nor render it inaudible.</p>
+
+<p>2. The two adjacent telegraphic lines, although
+not in contact, confuse their messages together, and<span class="pagenum" id="Page_240">240</span>
+it has sometimes been possible to hear messages
+from Puy-de-Dôme at the school through the wire
+which runs to the butts, although the distance
+between the two lines is nowhere less than 85
+centimètres.</p>
+
+<p>These inconveniences have been in some degree
+remedied by inserting strong resistances in the
+circuit, or by putting the current to earth at some
+distance from the telephonic stations.</p>
+
+<p>M. Izarn, Professor of Physics at the Lycée,
+Clermont, holds that telephonic electric currents
+may readily be turned aside by the earth, especially
+if in the course of their passage they encounter
+metallic conductors, such as gas or water pipes.
+He writes as follows on the subject, in a paper
+addressed to the Académie des Sciences, on May
+13, 1878:—‘I set up a telephone in the Clermont
+Lycée with a single wire, more than 50 yards in
+length, which crosses the court-yard of the Lycée,
+and goes from the laboratory, where it is suspended
+to a gas-burner, to a room near the porter’s lodge,
+where it is suspended to another gas-burner.
+When I applied my ear to the telephone, I could
+distinctly hear the telegraphic signals, Morse or
+otherwise, which came either from the telegraph
+office at Clermont, or from the telephone office
+which was at work between the School of Artillery
+and the butts below Puy-de-Dôme, a distance of
+eight miles. I could overhear words, and especially
+the military orders issued at the butts for the<span class="pagenum" id="Page_241">241</span>
+purpose of being heard at the school. Yet my
+wire is perfectly independent of those used for
+signalling, and is even very remote from them; but
+as the wires of the telegraph office and of the
+School of Artillery go to earth at a little distance
+from the gas-pipes, it is probable that this phenomenon
+is caused by a diversion of the current produced
+in my wire, by means of the earth and the
+network of metal pipes.’</p>
+
+<p>Mr. Preece made the same remark in his notice
+of ‘some physical points connected with the
+telephone.’ Again, we read in the ‘Telegraphic
+Journal’ of June 15, 1878, that in a telephonic
+concert transmitted from Buffalo to New York, the
+singers at Buffalo were heard in an office placed
+outside the telegraphic circuit in which the transmission
+was effected. On enquiry, it was ascertained
+that the wire through which the telephonic
+transmission took place, was at one point in its
+course close to the one which directly transmitted
+the musical sounds, but the distance between the
+two wires was not less than ten feet.</p>
+
+<p>When the circuits are altogether metallic, there
+is much less risk of confusion, and M. Zetzche
+declares that sounds proceeding from other wires
+are in this case little heard, and then only
+momentarily, so that it is much more easy to hear
+with this arrangement than with the one in
+ordinary use. ‘It is not,’ he says, ‘the resistances
+of the wire, but rather the diversions of the current<span class="pagenum" id="Page_242">242</span>
+near the posts, which interfere with telephonic
+correspondence on long lines above ground. This
+was proved by the following experiments:—I
+connected the telegraphic line from Dresden to
+Chemnitz with a line from Chemnitz to Leipzig
+(54 miles), which made a circuit of 103 miles, going
+to earth at its two extremities. There was no
+communication between Dresden and Leipzig, but
+Leipzig and Dresden could communicate with
+ease, in spite of the greater extent of line. I broke
+the connection with earth, first at Leipzig, then
+simultaneously at Leipzig and Dresden, and I
+observed the following effects. When insulation
+took place at Leipzig only, the telephone could be
+heard at the stations of Dresden, Riesa, and
+Wurzen; when the line was insulated at both ends,
+the communication was good between the two
+latter stations, but it was observed that at the
+intermediate station the words spoken at Wurzen
+were more distinctly heard than the words spoken
+at Riesa were heard at Wurzen. Since the distance
+from Wurzen to Leipzig is little more than half
+that from Riesa to Dresden, there are consequently
+nearly twice as many posts on the latter line, which
+carry the currents to earth, and hence I conclude
+that these diversions of current explain the
+possibility of conversing on an insulated line, and
+also why sounds are more distinctly heard at the
+Riesa station in consequence of the greater intensity
+of current still remaining on the line.’</p>
+
+<p><span class="pagenum" id="Page_243">243</span></p>
+
+<p>Some vibrations also result from the action of
+currents of air on telegraphic wires, which produce
+the humming sound so well known on some lines,
+and these may also react on the telephone; but
+they are in this case generally mechanically
+transmitted, and they may be distinguished from
+the others, if the sounds which ensue are heard
+after the telephone is excluded from the circuit by
+a break with a short circuit and after the communication
+to earth established behind the telephone
+has been broken.</p>
+
+<p>The induced reactions caused by the line wires
+on each other are not the only ones which may be
+observed on a telephonic circuit: every manifestation
+of electricity near a telephone may produce
+sounds of greater or less force. Of this we have
+already given a proof in M. d’Arsonval’s experiments,
+and others by M. Demoget demonstrate the
+fact still more clearly. In fact, if a small bar
+magnet provided with a vibrator be placed before
+one of the telephones of a telephonic circuit, and
+the vibrating plate of the telephone be removed, in
+order to draw away the sound produced by the
+vibrator, its humming noise may be distinctly
+heard on the second telephone of the circuit; a
+noise which attains its maximum when the two extremities
+of the electro-magnet are at their nearest
+point to the telephone without a diaphragm, and it
+is at its minimum when this electro-magnet is
+presented to it along its neutral line. M. Demoget<span class="pagenum" id="Page_244">244</span>
+supposes that the action which is exerted in this
+instance is that of a magnet exerting two inducing
+actions which are opposite and symmetrical, with
+a field limited by a double paraboloid and with an
+axis, according to his experiments, which extended
+55 centimètres beyond the magnetic core, and a
+vertical diameter of 60 centimètres. He believes
+that in this way it would be easy to telegraph on
+the Morse system, and that, in order to do so, it
+would only be necessary to apply a key to the inducing
+electro-magnet.</p>
+
+<p>Mr. Preece points out three ways of overcoming
+the difficulty presented by the induced reactions
+caused by the wires on each other.</p>
+
+<p>1. By increasing the intensity of the transmitted
+currents, so as to make them decidedly stronger
+than the induced currents, and to reduce the
+sensitiveness of the receiving telephone.</p>
+
+<p>2. To place the telephonic wire beyond the
+range of induction.</p>
+
+<p>3. To neutralise the effects of induction.</p>
+
+<p>The first mode may be effected by Edison’s
+battery system, and we have seen that it is very
+successful.</p>
+
+<p>In order to put the second mode in practice,
+Mr. Preece says that it would be necessary to
+study the two kinds of induction which are
+developed on telegraphic lines: electro-static
+induction, analogous to that produced on submarine
+cables, and electro-dynamic induction, resulting<span class="pagenum" id="Page_245">245</span>
+from electricity in motion. In the former
+case, Mr. Preece proposes to interpose between the
+telephone wire and the other wires a conducting
+body in communication with the earth, capable of
+becoming a screen to the induction by itself absorbing
+the electro-static effects. He says that this
+might be accomplished by surrounding the telegraphic
+wires adjacent to the telephonic wire with
+a metallic envelope, and then plunging them in
+water. He adds that the effects of static induction
+are not completely destroyed in this way, since the
+substance used is a bad conductor, but they are
+considerably reduced, as he has proved by experiments
+between Dublin, Holyhead, Manchester, and
+Liverpool. In the second case, Mr. Preece admits
+that an iron envelope might paralyse the electro-dynamic
+effects produced by absorbing them, so
+that if insulated wires were employed, covered with
+an iron case, and communicating with the earth, the
+two induced reactions would be annulled. We will
+not follow Mr. Preece in his theory as to these
+effects—a theory which seems to us open to question,
+but we content ourselves with pointing out
+his proposed mode of attenuation.</p>
+
+<p>In order to carry out the third expedient, it
+might be thought that it would be enough to
+employ a return wire instead of going to earth, for
+under such conditions the currents induced on one
+of the wires would be neutralised by those resulting
+from the same induction on the second wire,<span class="pagenum" id="Page_246">246</span>
+which would then act in an opposite direction; but
+this mode would only be successful when there is
+a very small interval between the two telephone
+wires, and they are at a considerable distance from
+the other wires. When this is not the case, and
+they are all close together, as in submarine or
+subterranean cables, consisting of several wires,
+this mode is quite inefficient. A small cable,
+including two conductors, insulated with gutta-percha,
+may be successfully carried through the
+air.</p>
+
+<p>The use of two conductors has the further
+advantage of avoiding the inconvenience of stray
+currents on the line and through the earth, which,
+when the communications to earth are imperfect,
+permit the line current to pass more or less easily
+into the telephonic line.</p>
+
+<p>In addition to the disturbing causes in telephonic
+transmission we have just mentioned, there
+are others which are also very appreciable, and
+among them are the accidental currents which are
+continually produced on telegraphic lines. These
+currents may proceed from several causes, at one
+time from atmospheric electricity, at another from
+terrestrial magnetism, at another from thermo-electric
+effects produced upon the lines, at another
+from the hydro-electric reactions produced on the
+wires and disks in communication with the earth.
+These currents are always very unstable, and
+consequently they are likely, by reacting on the<span class="pagenum" id="Page_247">247</span>
+transmitted currents, to modify them so as to
+produce sounds upon the telephone. Mr. Preece
+asserts that the sound proceeding from earth
+currents somewhat resembles that of falling water.
+The discharges of atmospheric electricity, even
+when the storm is remote, produce a sound which
+varies with the nature of the discharge. When it
+is diffused and the clap takes place near at hand,
+Dr. Channing, of Providence, U.S., says that the
+sound resembles that produced by a drop of fused
+metal when it falls into water, or, still more, that of
+a rocket discharged at a distance: in this case it
+might seem that the sound would be heard before
+the appearance of the flash, which clearly shows
+that the electric discharges of the atmosphere only
+take place in consequence of an electric disturbance
+in the air. Mr. Preece adds that a wailing
+sound is sometimes heard, which has been compared
+to that of a young bird, and which must
+proceed from the induced currents which terrestrial
+magnetism produces in the metallic wires when
+placed in vibration by currents of air.</p>
+
+<p>M. Gressier, in a communication made to the
+Académie des Sciences on May 6, 1878, has
+spoken of some of these sounds, but he is totally
+mistaken in the source to which he ascribes them.</p>
+
+<p>‘In addition to the crackling sound caused by
+the working of telegraph instruments on the
+adjacent lines, a confused murmur takes place in
+the telephone, a friction so intense that it might<span class="pagenum" id="Page_248">248</span>
+sometimes be thought that the vibrating disk was
+splitting. This murmur is heard more by night
+than by day, and is sometimes intolerable, since it
+becomes impossible to understand the telephone,
+although nothing is going on in the office to disturb
+the sound. The same noise is heard when
+only one telephone is used. A good galvanometer
+inserted in the circuit reveals the presence of
+sensible currents, sometimes in one direction, sometimes
+in another.’</p>
+
+<p>I studied these currents for a long time with
+the galvanometer, and made them the subject of
+four papers which were laid before the Académie
+des Sciences in 1872, and I am convinced that
+they have in general nothing to do with atmospheric
+electricity, but result either from thermo-electric
+or hydro-electric influence. They take
+place constantly and in all weathers on telegraph
+lines, whether these lines are insulated at one end,
+or in contact with the earth at both ends. In the
+first case, the polar electrodes of the couple are
+formed by the telegraph wire and the earth plate,
+generally of the same nature, and the intermediate
+conducting medium is represented by the posts
+which support the wire and the earth which completes
+the circuit. In the second case, the couple
+is formed in almost the same way, but the difference
+in the chemical composition of the ground at
+the two points where the earth plates are buried, and
+sometimes their different temperature, exert a<span class="pagenum" id="Page_249">249</span>
+strong influence. If only the first case be considered,
+it generally happens that on fine summer
+days the currents produced during the day are
+inverse to those which are produced by night, and
+vary with the surrounding temperature in one or
+the other direction. The presence or absence of
+the sun, the passage of clouds, the currents of air
+involve abrupt and strongly marked variations,
+which may be easily followed on the galvanometer,
+and which cause more or less distinct sounds in the
+telephone.</p>
+
+<p>During the day, the currents are directed from
+the telegraph line to the earth plate, because
+the heat of the wire is greater than that of the
+plate, and these currents are then thermo-electric.
+During the night, on the other hand, the wire
+is cooled by the dew, which causes a greater oxidation
+on the wire than that which takes place on the
+plate, and the currents then become hydro-electric.</p>
+
+<p>I say more about these currents because, in
+consequence of a mistaken belief as to their origin,
+it has been supposed that the telephone might
+serve for the study of the variations of the atmospheric
+electricity generally diffused through the air.
+Such an application of the telephone would, under
+these conditions, be not only useless, but also misleading,
+by inducing the study of very complex
+phenomena, which could lead to nothing more
+than I have already stated in my different papers
+on the subject.</p>
+
+<p><span class="pagenum" id="Page_250">250</span></p>
+
+<p>Certain local influences will also produce sounds
+in the telephone. Thus the distension of the
+diaphragm by the moist heat of the breath, when
+the instrument is held before the mouth in speaking,
+causes a perceptible murmur.</p>
+
+<p>From the electro-static reactions, so strongly
+produced on the submarine cables, in consequence
+of electric transmissions, it might be supposed
+that it would not be easy to hold telephonic correspondence
+through this kind of conductor, and, to
+ascertain the fact, an experiment was made on the
+cable between Guernsey and Dartmouth, a distance
+of sixty miles. Articulate speech, only a little indistinct,
+was, however, perfectly transmitted. Other
+experiments, made by Messrs. Preece and Wilmot,
+on an artificial submarine cable, placed in conditions
+analogous to those of the Atlantic cable,
+showed that a telephonic correspondence might be
+kept up at a distance of a hundred miles, although
+the effects of induction were apparent. At the distance
+of 150 miles, it was somewhat difficult to hear,
+and the sounds were very faint, as if some one were
+speaking through a thick partition. The sound diminished
+rapidly until the distance of 200 miles was
+reached, and after that it became perfectly indistinct,
+although singing could still be heard. It was
+even possible to hear through the whole length of
+the cable, that is, for 3,000 miles, but Mr. Preece
+believed this to be due to the induction of the condenser
+on itself: he holds, however, that singing<span class="pagenum" id="Page_251">251</span>
+may be heard at a much greater distance than
+speech, owing to the more regular succession of
+electric waves.</p>
+
+<p>Mr. Preece also made experiments on the subterranean
+telegraphs between Manchester and
+Liverpool, a distance of 30 miles, and found no
+difficulty in exchanging correspondence; and it
+was the same with the cable from Dublin to Holyhead,
+a distance of 67 miles. This cable had seven
+conducting wires, and when the telephone was connected
+with one of them, the sound was repeated
+through all the others, but in a fainter degree.
+When the currents of the telegraphic instruments
+passed through the wires, the induction was apparent,
+but not so great as to prevent telephonic
+communication.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h2 class="nobreak" id="ESTABLISHMENT_OF_A_TELEPHONIC_STATION"><span id="toclink_251"></span>ESTABLISHMENT OF A TELEPHONIC STATION.</h2>
+</div>
+
+<p>Although the telephonic system of telegraphy
+is very simple, yet certain accessory arrangements
+are indispensable for its use. Thus, for example,
+an alarum call is necessary, in order to know when
+the exchange of correspondence is to take place,
+and information that the call has been heard is
+likewise necessary. An electric bell is therefore
+an indispensable addition to the telephone, and
+since the same circuit may be employed for both
+systems, if a commutator is used, it was necessary
+to find a mode of making the commutator act automatically,<span class="pagenum" id="Page_252">252</span>
+so as to maintain the simple action of
+the system which constitutes its principal merit.</p>
+
+<p><i>MM. Pollard and Garnier’s System.</i>—With
+this object, MM. Pollard and Garnier devised a
+very successful arrangement last March, which
+employs the weight of the instrument to act upon
+the commutator.</p>
+
+<p>For this purpose, they suspended the instrument
+to the end of a spring plate, fastened between
+the two contacts of the commutator. The circuit
+wire corresponds with this plate, and the two contacts
+correspond, the one with the telephone, the
+other with the bell. When the telephone hangs
+below the spring-support, that is, when it is not at
+work, its weight lowers the spring plate on the
+lower contact, and the communication of the line
+with the bell is established: when, on the other
+hand, the telephone is raised for use, the spring
+plate touches the higher contact, and communication
+is established between the line and telephone.
+In order to make the bell sound, it is only
+necessary to establish, on the wire which connects
+the line with the bell contact of the commutator,
+a breaker which can both join and break the
+current, and which communicates on one side with
+the contact of the bell, and on the other with
+its battery. The ordinary push of an electric
+bell will be sufficient, if it is supplied with a
+second contact, but MM. Pollard and Garnier
+wished to make this action also automatic, and consequently<span class="pagenum" id="Page_253">253</span>
+they devised the arrangement represented in
+<a href="#il_53">fig. 53</a>.</p>
+
+<figure id="il_53" class="figcenter" style="max-width: 23em;">
+  <img src="images/i_p253.jpg" width="916" height="623" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 53.</span>
+  </figcaption>
+</figure>
+
+<p>In this system, as well as in those which have
+since been devised, two telephones are employed,
+one of which is constantly applied to the ear, and
+the other to the mouth, so as to make it possible to
+speak while listening. The telephones are supported
+by three wires, two of which contain flexible conductors,
+while the third only acts as a support.</p>
+
+<p>Two of the four wires of the two telephones are
+connected with each other, and the other two are
+connected with the two binding screws of the
+commutator <i>t</i>, <i>t′</i>: the wires without conductors are
+suspended to the extremities of the two flexible
+plates <i>l</i>, <i>l′</i>, which correspond with earth and line.</p>
+
+<p><span class="pagenum" id="Page_254">254</span></p>
+
+<p>When at rest, the weight of the telephones
+presses the two plates <i>l</i>, <i>l′</i>, on the lower contacts
+<span class="allsmcap">S</span>, <span class="allsmcap">S′</span>, but when the instruments are taken up
+these plates press against the higher contacts.</p>
+
+<p>The two bell wires terminate on the lower
+contacts, those of the telephones on the higher contacts,
+and one of the poles of the battery is
+connected with the lower contact on the left <span class="allsmcap">S′</span>, the
+other with the higher contact on the right <span class="allsmcap">T</span>.</p>
+
+<p>When at rest, the system is applied to the
+electric bell, and the current sent from the opposite
+station will follow the circuit <span class="allsmcap">L</span> <i>l</i> <span class="allsmcap">S S′ S′</span> <i>l′</i> <span class="allsmcap">T</span>, so that
+the call will be made. On taking up the two
+telephones, the circuit of the bell system is broken,
+and that of the telephones is established, so that the
+current follows the course <span class="allsmcap">L</span> <i>l</i> <span class="allsmcap">T</span> <i>t t′</i> <span class="allsmcap">T′</span> <i>l′</i> <span class="allsmcap">T</span>. If only
+one telephone is held at a time, the current is sent
+into the bell system of the opposite station, and
+follows the route + <span class="allsmcap">P S</span> <i>l</i> <span class="allsmcap">L T</span> <i>l′</i> <span class="allsmcap">T′</span> <i>t</i> <span class="allsmcap">P</span> —. In this
+way the three actions necessary for calling, corresponding,
+and enabling the corresponding instrument
+to give a call, are almost involuntarily made.</p>
+
+<p><i>System by MM. Bréguet and Roosevelt.</i>—In the
+system established by the Paris agents of the Bell
+company, the arrangement resembles the one just
+described, except that there is only one spring
+commutator, and the call is made with the push of
+an ordinary electric bell. A mahogany board is
+suspended from the wall, and on it are arranged,
+first, the ordinary electric bell system, with a sending<span class="pagenum" id="Page_255">255</span>
+push fixed below it; second, two forks supporting
+two telephones, one of which is fastened to the<span class="pagenum" id="Page_256">256</span>
+bar of a commutator, arranged as a Morse key.
+The two telephones are connected by two conducting
+wires, so arranged as to be capable of extension,
+and two of their four binding screws are in immediate
+connection with each other, and the other
+two with the earth, line, and battery, by means of
+the commutator, the sending push, and the bell
+system. The arrangement is shown in <a href="#il_54">fig. 54</a>.</p>
+
+<figure id="il_54" class="figcenter" style="max-width: 20em;">
+  <img src="images/i_p255.jpg" width="967" height="1353" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 54.</span>
+  </figcaption>
+</figure>
+
+<p>The commutator A consists of a metallic bar
+<i>a c</i>, bearing the suspension fork of one of the telephones
+<span class="allsmcap">F′</span> below its point of articulation: it ends in
+two pins <i>a</i> and <i>c</i>, below which the two contacts of
+the commutator are fixed, and a spring compresses
+the lower arm of the bar, so as to cause
+the other arm to rest constantly on the higher
+contact. For greater security a steel tongue <i>a b</i>
+is fastened to the lower end of the bar, and rubs
+against the small shaft <i>b</i>, which is provided
+with two insulated contacts, corresponding to
+those of the board. The bar is in communication
+with the line wire by means of the call-push,
+and the upper of the two contacts we have just
+described corresponds with one of the telephone
+wires which is inserted in the same circuit, while
+the other corresponds with the bell system <span class="allsmcap">S</span>,
+which is in communication with earth. It follows
+from this arrangement, that when the right telephone
+presses its whole weight on the support, the
+bar of the commutator is inclined on the lower
+contact, and consequently the line is in direct<span class="pagenum" id="Page_257">257</span>
+communication with the bell, so that the call can
+be made. When, on the other hand, the telephone
+is removed from its support, the bar rests on the
+higher contact, and the telephones are connected
+with the line.</p>
+
+<p>Pressure on the sending push serves to call the
+corresponding station: the connection of the line
+with the telephones is then broken, and it is
+established with the battery of the sending station,
+which sends its current through the bell of the
+corresponding station. In order to obtain this
+double effect, the contact spring of the sending
+push generally rests upon a contact fastened to a
+piece of wood shaped like a joiner’s rule, which
+covers it in front, and below this spring there is a
+second contact, which communicates with the positive
+pole of the station battery. The other contact
+corresponds with the line wire, and a connection
+takes place between the earth wire and the negative
+pole of the station battery, so that the earth wire
+is common to three circuits:</p>
+
+<p>1st. To the telephone circuit. 2nd. To that of
+the bell system. 3rd. To that of the local battery.</p>
+
+<p>The second fork, which supports the telephone
+on the right, is fixed to the board, and is independent
+of any electric current.</p>
+
+<p>It is clear that this arrangement may be varied
+in a thousand ways, but the model we have just
+described is the most practical.</p>
+
+<p><i>Edison’s System.</i>—The problem becomes more<span class="pagenum" id="Page_259">259</span>
+complex in the case of battery telephones, since
+the battery must be common to both systems, and
+the induction coil must be inserted in two distinct
+circuits. <a href="#il_55">Fig. 55</a> represents the model adopted in
+Mr. Edison’s telephone.</p>
+
+<figure id="il_55" class="figcenter" style="max-width: 20em;">
+  <img src="images/i_p258.jpg" width="901" height="1493" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 55.</span>
+  </figcaption>
+</figure>
+
+<p>In this arrangement, there is a small stand <span class="allsmcap">C</span>
+on the mahogany board on which the bases of
+the two telephones rest. The bell system <span class="allsmcap">S</span> is
+worked by an electro-magnetic speaker <span class="allsmcap">P</span>, which
+serves, when a Morse key is added to the system,
+for exchange of correspondence in the Morse code,
+if there should be any defect in the telephones, or
+to put them in working order. Above the speaker
+there is a commutator with a stopper <span class="allsmcap">D</span> to adapt
+the line for sending or receiving, with or without
+the bell; and below the stand <span class="allsmcap">C</span> the induction coil,
+destined to transform the voltaic currents into
+induced currents, is arranged in a small closed
+box <span class="allsmcap">E</span>.</p>
+
+<p>When the commutator is at reception, the line is
+in immediate correspondence either with the speaker
+or with the receiving telephone, according to the
+hole in which the stopper is inserted; when, on the
+other hand, it is at sending, the line corresponds to
+the secondary circuit of the induction coil. Under
+these conditions the action is no longer automatic;
+but since this kind of telephone can only be usefully
+employed for telegraphy, in which case those
+who work it are acquainted with electric apparatus,
+there is no inconvenience in this complication.</p>
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<p><span class="pagenum" id="Page_260">260</span></p>
+
+<h2 class="nobreak" id="CALL-BELLS_AND_ALARUMS"><span id="toclink_260"></span>CALL-BELLS AND ALARUMS.</h2>
+</div>
+
+<p>The call-bells applied to telegraphic service
+have been arranged in different ways. When the
+vibrating bells are in use, like those of which we
+have just spoken, it is necessary to use a battery,
+and the advantages offered by telephones with
+induced currents are thus sensibly diminished. In
+order to dispense with the battery, the use of the
+electro-magnetic bell has been suggested.</p>
+
+<p>In this case there are usually two bells, with a
+hammer oscillating between them, and a support
+formed of the polarised armature of an electro-magnet.
+The electro-magnetic instrument is placed
+below this system; it is turned by a winch, and
+sends the currents, alternately reversed, which are
+necessary to communicate the vibratory movement
+to the hammer, and this movement is enough to
+make the two bells tinkle. Below the winch of this
+electro-magnetic instrument there is a commutator
+with two contacts, which adapts the instrument
+for sending or receiving.</p>
+
+<p>M. Mandroux has simplified this system, and
+has reduced it to small dimensions by the following
+arrangement. He fixes two magnetic cores,
+furnished with coils, on each of the two poles of a
+horseshoe magnet, composed of two bars connected
+by an iron coupler, and between the
+poles expanded by these four cores he inserts an<span class="pagenum" id="Page_261">261</span>
+armature, within which there is a steel spring
+fastened to one of these poles. In this way the
+armature is polarised, and oscillates under the
+influence of the reversed currents transmitted by
+an instrument of the same kind provided with an
+induction system. These oscillations may have
+the effect of producing the sound of a call-bell, and
+the induction system may consist of a manipulating
+key, fastened to a duplex system of armature,
+regularly applied to the magnetic cores, taken in
+pairs. On communicating a series of movements
+to this manipulator, a series of induced currents
+in an inverse direction are produced, which cause
+the armature of the corresponding station to act
+as we have already seen, and which may even,
+when necessary, furnish a series of Morse signals
+for a suitable manipulation. On account of the
+small size of this system, it might be applied to
+the telephonic service of the army.</p>
+
+<p>The Bell Telephone Company in Paris has
+arranged another little call-system which is quite
+satisfactory and has the advantage of acting as a
+telephone at the same time. The model resembles
+the one we have termed a snuff-box telephone,
+and it has a button commutator by means of
+which the instrument is placed in communication
+with the electro-magnetic system of the instrument,
+or with a battery which is able to make the telephone
+vibrate with some force. To make a call,
+the button must be pressed, and the battery<span class="pagenum" id="Page_262">262</span>
+current is communicated to the corresponding
+instrument, which begins to vibrate when the call
+is made; and when notice is given of the receipt of
+the signal, the pressure on the button is removed,
+and it becomes possible to speak and receive as in
+ordinary telephones.</p>
+
+<figure id="il_56" class="figcenter" style="max-width: 29em;">
+  <img src="images/i_p262.jpg" width="1122" height="851" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 56.</span>
+  </figcaption>
+</figure>
+
+<p><i>M. de Weinhold’s System.</i>—M. Zetzche speaks
+highly of an alarum devised by Professor A. de
+Weinhold, which resembles that by M. Lorenz,
+represented in <a href="#il_56">fig. 56</a>. Its organ of sound consists
+of a steel bell <span class="allsmcap">T</span>, from 13 to 14 centimètres in<span class="pagenum" id="Page_263">263</span>
+diameter, and toned to give about 420 double
+vibrations in a second. ‘Its diameter and tone,’ he
+says, ‘are important, and any great departure from
+the rule laid down diminishes the effect. The
+opening of the bell is below, and it is fixed on a
+stand by its centre. A slightly curved bar magnet,
+provided at its two ends with iron appendices enclosed
+in a coil, traverses the stand. The bar
+magnet of the telephone also terminates in an iron
+appendix enclosed in a coil. In both cases the
+changes produced in the magnetic condition appear
+to be more intense than they are in magnets without
+appendices. The bar magnet is placed within
+the bell in the direction of one of its diameters, so
+that the appendices almost touch its sides.</p>
+
+<p>‘When the bell is struck on a spot about 90°
+from this diameter with a wooden clapper M, which
+acts with a spring, and is withdrawn by stretching
+the spring and then letting it go, as in a bell for
+the dinner-table, the vibrations imparted to it send
+currents into the coils, and these currents produce
+identical vibrations on the iron disk of the telephone,
+which are intensified by a conical resonator
+fitted to the telephone, so as to be easily
+heard some paces off. For ordinary use, the bell
+coil is broken into a short circuit by means of a
+metallic spring <span class="allsmcap">R</span>, and consequently, when the bell is
+struck, the spring must be opened so as not to break
+the circuit. An instrument of the same kind has
+also been devised by Herr W.&nbsp;E. Fein at Stuttgardt.’</p>
+
+<p><span class="pagenum" id="Page_264">264</span></p>
+
+<figure id="il_57" class="figleft" style="max-width: 10em;">
+  <img src="images/i_p264.jpg" width="399" height="553" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 57.</span>
+  </figcaption>
+</figure>
+
+<figure id="il_58" class="figright" style="max-width: 10em;">
+  <img src="images/i_p264r.jpg" width="397" height="553" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 58.</span>
+  </figcaption>
+</figure>
+
+<p><i>MM. Dutertre and Gouault’s System.</i>—One of
+the most ingenious solutions of the problem of
+making the telephone call has recently been
+proposed by MM. Dutertre and Gouault. <a href="#il_57">Figs. 57</a>
+and <a href="#il_58">58</a> represent the opposite faces of the
+instrument. It consists of a kind of snuff-box
+telephone, like the one shown in <a href="#il_26">fig. 26</a>, and it is
+so arranged as to send or receive the call, according
+to the way in which it is placed on its stand,
+which is only an ordinary bracket fastened to the
+wall. When it is placed on the bracket so as to
+have the telephone mouthpiece on the outside, it is
+adapted for receiving, and can then give the call.
+When, on the other hand, its position on the
+bracket is reversed, it permits the other station to
+make the call, by producing vibrations on a
+vibrator under the influence of a battery, and<span class="pagenum" id="Page_265">265</span>
+these vibrations reverberate in the corresponding
+instrument with sufficient force to produce the call.
+If the instrument is taken up, and the finger is
+placed on a small spring button, it may then be
+used as an ordinary telephone.</p>
+
+<p>In this instrument, the magnet <span class="allsmcap">N S</span> (<a href="#il_57">fig. 57</a>) is
+snail-shaped, like others we have mentioned, but
+the core of soft iron <span class="allsmcap">S</span>, to which the coil <span class="allsmcap">E</span> is
+fastened, can produce two different effects on its
+two extremities. On the one side, it reacts on a
+small armature which is fastened to the end of a
+vibrating disk <span class="allsmcap">C</span>, <a href="#il_58">fig. 58</a>; the armature is placed
+against a contact fastened to the bridge <span class="allsmcap">B</span>, and
+constitutes an electro-magnetic vibrator. For this
+purpose the bridge is in metallic communication
+with the coil wire, of which the other end corresponds
+with the line wire, and the spring <span class="allsmcap">C</span> is
+mounted on an upright <span class="allsmcap">A</span>, which also supports
+another spring <span class="allsmcap">D G</span> acting on two contacts, one
+placed at <span class="allsmcap">G</span>, and corresponding to the earth wire,
+the other at <span class="allsmcap">H</span>, and connected with the positive
+pole of the battery. A small moveable button,
+which passes through a hole in the lid of the box,
+and projects beyond it, is fixed at <span class="allsmcap">G</span>, and all this
+part of the instrument faces the bottom of the box.
+The upper part consists of the vibrating disk and
+the mouthpiece, so that the mechanism we have
+described is all mounted on an inner partition
+forming a false bottom to the box.</p>
+
+<p>When the box rests upon its base, on the side<span class="pagenum" id="Page_266">266</span>
+shown in <a href="#il_58">fig. 58</a>, the button at <span class="allsmcap">G</span> presses on the
+spring <span class="allsmcap">D G</span>, and raises it so as to break the connection
+with the battery; the coil of the instrument
+is then united to the circuit, and consequently
+receives the transmitted currents, which follow this
+route: line wire, coil <span class="allsmcap">E</span>, bridge <span class="allsmcap">B</span>, spring <span class="allsmcap">C</span>, spring
+<span class="allsmcap">D G</span>, earth contact. If these currents are transmitted
+by a vibrator, they are strong enough to
+produce a noise which can be heard in all parts of
+a room, and consequently the call may be given in
+this way. If the currents are due to telephonic
+transmission, the instrument is applied to the ear,
+care being taken to put the finger on the button <span class="allsmcap">G</span>,
+and the exchange of correspondence takes place
+as in ordinary instruments; but it is simpler and
+more manageable to insert a second telephone in
+the circuit for this purpose. When the box is
+inverted on its mouthpiece, and the button <span class="allsmcap">G</span>
+ceases to press on the spring <span class="allsmcap">D G</span>, the battery current
+reacts on the vibrator of the instrument, and
+sends the call to the corresponding station, following
+this route: <span class="allsmcap">I D A C B E</span>, line, earth and battery;
+and the call goes on until the correspondent
+breaks the current by taking up his instrument,
+thus warning the other that he is ready to
+listen.</p>
+
+<p><i>System of M. Puluj.</i>—There is yet another call
+system, devised by M. Puluj. It consists of two
+telephones without mouthpieces, connected together,
+and with coils placed opposite the branches<span class="pagenum" id="Page_267">267</span>
+of two tuning-forks, tuned as nearly as possible to
+the same tone. A small metal bell is fixed between
+the opposite faces of the tuning-forks, and a
+wire stretched near them is provided with a small
+ball in contact with their branches. When the
+tuning-fork at the sending station is put in vibration
+by striking it with an iron hammer covered with
+skin, the tuning fork at the other station vibrates
+also, and its ball strikes upon the bell. As soon as
+the signal is returned by the second station, mouthpieces
+with iron diaphragms are fastened to the telephones,
+and the correspondence begins. It seems
+that, by the use of a resonator, the sound which
+reaches the receiving station may be so intensified
+as to become audible in a large hall, and the bell
+signal may be heard in an adjoining room, even
+through a closed door.</p>
+
+<p><i>Mr. Alfred Chiddey’s System.</i>—This arrangement
+consists of a slender copper tube, eight
+inches long, and with an orifice of 1/30 of an inch,
+of which the lower end is soldered to the diaphragm
+of a telephone. A branch joint, to which an india-rubber
+tube is fitted, connects it with a gas jet,
+which is lighted and surrounded with a lamp shade,
+in such a way as to make it produce, under given
+conditions, sounds resembling those of the singing
+flames. A perfectly similar system is arranged at
+the other end of the line, in such a way that the
+sounds emitted in each case shall be precisely in
+unison. If the two systems are so regulated as<span class="pagenum" id="Page_268">268</span>
+not to emit sounds in their normal condition, they
+can be made to sing by causing a tuning-fork in the
+vicinity of one or the other to vibrate the same note,
+and then the corresponding flame will begin to sing,
+producing a vibration in the diaphragm of the
+telephone with which it is in correspondence, and
+hence will follow the vibration of the diaphragm of
+the other telephone, and consequently the vibration
+of the flame of the calling instrument. In this way
+the call signal may be made without the intervention
+of any battery.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h2 class="nobreak" id="APPLICATIONS_OF_THE_TELEPHONE"><span id="toclink_268"></span>APPLICATIONS OF THE TELEPHONE.</h2>
+</div>
+
+<p>The applications of the telephone are much
+more numerous than might be supposed at the first
+glance. As far as the telegraphic service is concerned,
+its use must evidently be rather limited,
+since it cannot register the messages sent, and the
+speed of transmission is inferior to that of the
+improved system of telegraphs; yet in many cases
+it would be very valuable, even for a telegraphic
+system, since it is possible to work it without any
+special telegraphic training. The first comer may
+send and receive with the telephone, and this is
+certainly not the case even with the simplest forms
+of telegraphic instruments. This system is therefore
+already in use in public offices and factories, for communication
+in mines, for submarine works, for the
+navy, especially when several vessels manœuvre<span class="pagenum" id="Page_269">269</span>
+in the same waters, some towed by others; finally,
+for military purposes, either to transmit orders to
+different corps, or to communicate with schools of
+artillery and rifle practice. In America the municipal
+telegraphic service and that of telegraphs
+limited to the area of towns are conducted in this
+way, and it is probable that this system will soon
+be adopted in Europe. Indeed, a service of this
+kind was established in Germany last autumn at
+the telegraph offices of some towns, and the
+London Post Office is now thinking of establishing
+it in England.</p>
+
+<p>But, besides its use for the purposes of correspondence,
+the telephone can be useful to the telegraphic
+service itself by affording one of the
+simplest means of obtaining a number of simultaneous
+transmissions through the same wire,
+and even of being combined in duplex with the
+Morse telegraphs. Its applications in the microphonic
+form are incalculable, and the proverb which
+declares that ‘walls have ears’ may in this way be
+literally true. It is alarming to think of the consequences
+of such an indiscreet organ. Diplomatists
+must certainly redouble their reserve, and tender
+confidences will no longer be made with the same
+frankness. On this point we cannot think that
+much will be gained, but on the other hand the
+physician will probably soon make use of this
+invention to ascertain more readily the processes
+going on within the human body.</p>
+
+<p><span class="pagenum" id="Page_270">270</span></p>
+
+<p>APPLICATION OF THE TELEPHONE TO SIMULTANEOUS
+TELEGRAPHIC TRANSMISSIONS.</p>
+
+<p>The simultaneous transmission of several
+messages through the same wire is one of the most
+curious and important applications of the telephone
+to telegraphic instruments which can be made, and
+we have seen that it was this application which led
+Messrs. Gray and Bell to the invention of speaking
+telephones. The admiration which these instruments
+have excited has thrown the original idea
+into the background, although it has perhaps a
+more practical importance. We will now consider
+these systems.</p>
+
+<p>An articulating telephone is not necessary in
+order to obtain simultaneous transmission: the
+musical telephones devised by MM. Petrina, Gray,
+Froment, &amp;c., are quite sufficient, and a brief explanation
+of their principle will make this intelligible.
+Suppose that there are seven electro-magnetic
+vibrators at the two corresponding stations, which
+are tuned with the same tuning-fork on the
+different notes of the scale, and suppose that a
+key-board, resembling the Morse telegraph key, is
+arranged so that, by lowering the keys, electric
+reaction takes place on each vibrator: it is easy to
+see that these vibrators may be made to react in
+the same way on the corresponding vibrators of the
+opposite station; but they must be tuned on the<span class="pagenum" id="Page_271">271</span>
+same note, and the sounds emitted will continue
+while the keys are lowered. By keeping them
+down for a shorter or longer time, the long or
+short sounds which constitute the elements of
+telegraphic language in the Morse system may be
+obtained, and consequently an audible transmission
+becomes possible. Let us now suppose that a
+telegraphist accustomed to this mode of transmission
+is placed before each of the vibrators, and
+that they transmit different messages at the same
+moment in this way: the telegraphic wire will be
+instantaneously traversed by seven currents, broken
+and massed upon each other, and they might be
+expected to produce a medley of confused sounds
+on the vibrators at the receiving station; but since
+they each harmonise with the corresponding vibrator,
+they have no sensible influence except on
+those for which they are intended. The dominant
+sound may be made still more distinct by applying
+a Helmholtz resonator to each vibrator,<a id="FNanchor_18" href="#Footnote_18" class="fnanchor">18</a> that
+is, an acoustic instrument which will only vibrate
+under the influence of the note to which it is tuned.<span class="pagenum" id="Page_272">272</span>
+In this way it is possible to select the transmitted
+sounds, and only to allow each <i lang="fr">employé</i> to hear
+that which is intended for him. Consequently,
+however confused the sounds may be on the receiving
+vibrators, the person to whom <em>do</em> is assigned will
+only receive <em>do</em> sounds, the person to whom <em>sol</em> is
+assigned will only receive <em>sol</em> sounds, so that correspondence
+may be carried on as well as if they had
+each a special wire.</p>
+
+<p>In the mode we have described, this telegraphic
+system only admits of audible transmissions, and
+consequently cannot register messages. To supply
+this defect, it has been suggested to make the
+receiving vibrators react on registers, so arranging
+the latter that their electric organ may present such
+magnetic inertia, that, when it is influenced by the
+vibrations of sound, its effect may be maintained
+throughout the time of vibration. Experiments
+show that a Morse receiver, worked by the current
+of a local battery, will be enough for this purpose;
+so that if the musical vibrator is made to react as
+a relay, that is, on a contact in connection with the
+local battery and the receiver, the dots and dashes
+may be obtained on it which are the constituent
+elements of the Morse code.</p>
+
+<p>On these principles, and considering that the<span class="pagenum" id="Page_273">273</span>
+musical spaces separating the different notes of the
+scale are such as may be easily distinguished by
+the resonator, seven simultaneous transmissions
+may be obtained on the same wire; but experience
+shows that it is necessary to be content with a
+much smaller number. Yet this number may
+easily be doubled by applying the mode of transmission
+in an opposite direction to the system.</p>
+
+<p>Mr. Bell states that the idea of applying the
+telephone to multiple electric transmissions occurred
+simultaneously to M. Paul Lacour of Copenhagen,
+to Mr. Elisha Gray of Chicago, to Mr. Varley
+of London, and to Mr. Edison of New York; but
+there is some confusion here, for we have already
+seen, from reference to the patents, that Mr.
+Varley’s system dates from 1870, that of M. Paul
+Lacour from September 1874, that of Mr. Elisha
+Gray from February 1875, and those of Messrs. Bell
+and Edison were still later. Yet it appears from
+Mr. Gray’s specification that he was the first to
+conceive and execute instruments of the kind. In
+fact, in a specification drawn up on August 6,
+1874, he distinctly put forward the system we
+have described, and which is the basis of those
+of which we have still to speak. This specification
+was only an addition to two others made
+out in April and June 1874. Mr. Varley’s system
+has only an indirect relation to the one we have
+described. It appears from what Mr. Bell said on
+the subject in a paper addressed to the Society<span class="pagenum" id="Page_274">274</span>
+of Telegraphic Engineers in London, that he himself
+only attaches a secondary interest to this
+invention.</p>
+
+<p>He said that he had been struck with the idea
+that the greater or less duration of a musical sound
+might represent the dot and dash of the telegraphic
+alphabet, and it occurred to him that simultaneous
+telegraphic transmissions, of which the number
+should only be limited by the delicacy of the sense
+of hearing, might be obtained by suitable combinations
+of long and short sounds, and that these
+should be effected by a keyboard of tuning-forks
+applied to one end of a telegraphic line, and so
+arranged as to react electrically on electro-magnetic
+instruments striking on the strings of a piano.
+For this purpose it would be necessary to assign
+an employé to each of the keys for the service of
+transmission, and to arrange that his correspondent
+should only distinguish his peculiar note among all
+those transmitted. It was this idea, Mr. Bell adds,
+which led to his researches in telephony.</p>
+
+<p>For several years he sought for the best mode
+of reproducing musical sounds at a distance by
+means of vibrating rheotomes: the best results were
+given by a steel plate vibrating between two contacts,
+of which the vibrations were electrically produced
+and maintained by an electro-magnet and a
+local battery. In consequence of its vibration, the
+two contacts were touched alternately, and the two
+circuits were alternately broken; the local circuit<span class="pagenum" id="Page_275">275</span>
+which kept the plate in vibration, and the other
+which was connected with the line, and reacted on
+the distant receiver, so as to effect simultaneous
+vibrations in it. A Morse key was placed in the
+latter circuit near the sending instrument, and
+when it was lowered, vibrations were sent through
+the line; when it was raised, these vibrations
+ceased, and it is easy to see that, by lowering the
+key for a longer or shorter time, the short and long
+sounds necessary for the different combinations of
+telegraphic language could be obtained. Moreover,
+if the vibrating plate of the receiving instrument
+were so regulated as to vibrate in unison with the
+sending instrument in correspondence, it would
+vibrate better with this sender than with another
+whose plate was not so adjusted.</p>
+
+<p>It is evident that different sounds might be
+simultaneously transmitted with several plates
+by this arrangement of contact breaker, and that
+at the receiving station the sounds might be distinguished
+by each employé, since the one which
+corresponds to the fundamental note of each vibrating
+plate is reproduced by that plate. Consequently,
+the sounds produced by the vibrating plate of <em>do</em>,
+for example, will only be audible at the receiving
+station on the plate tuned to <em>do</em>, and the same will
+be the case with the other plates; so that the
+sounds will reach their destination, if not without
+confusion, yet with sufficient clearness to be distinguished
+by the employés.</p>
+
+<p><span class="pagenum" id="Page_276">276</span></p>
+
+<p>Mr. Bell sums up the defects still existing in
+his system as follows:—1st. The receiver of the
+messages must have a good musical ear, in order to
+distinguish the value of sounds. 2nd. Since the
+signals can only take place when the transmitted
+currents are in the same direction, two wires must
+be employed in order to exchange messages on
+each side.</p>
+
+<p>He surmounted the first difficulty by providing
+the receiver with an instrument which he called
+the vibrating contact breaker, and which registered
+automatically the sounds produced. This contact
+breaker was placed in the circuit of a local battery,
+which could work a Morse instrument under certain
+conditions. When the sounds emitted by the instrument
+did not correspond with those for which
+it had been tuned, the contact breaker had no
+effect on the telegraphic instrument: it only acted
+when the sounds were those which were to be interpreted,
+and its action necessarily corresponded to
+the length of the sounds.</p>
+
+<p>Mr. Bell adds that he applied the system to
+electro-chemical telegraphs; but we need not dwell
+on this part of the invention, since, as we have said,
+it is no longer his special study.</p>
+
+<p><i>System of M. Lacour of Copenhagen.</i>—M.
+Lacour’s system was patented on the 2nd September,
+1874, but his experiments were commenced on
+the 5th June of the same year. Since M. Lacour
+believed that the vibrations would be imperceptible<span class="pagenum" id="Page_277">277</span>
+on long lines, his first attempts were made on a
+somewhat short line; but in November 1874 fresh
+experiments were made between Fredericia and
+Copenhagen on a line 225 miles in length, and it
+was ascertained that vibratory effects could be
+easily transmitted, even under the influence of a
+rather weak battery.</p>
+
+<figure id="il_59" class="figcenter" style="max-width: 20em;">
+  <img src="images/i_p277.jpg" width="765" height="313" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 59.</span>
+  </figcaption>
+</figure>
+
+<p>In M. Lacour’s system, the sending instrument
+is a simple tuning-fork, placed in a horizontal
+position, and one of its arms reacts on a contact
+breaker, which can produce precisely the same
+number of discharges of currents as there are vibrations
+of the tuning-fork. If a Morse manipulator
+is inserted in the circuit, it is evident that if it is
+worked so as to produce the dots and dashes of the
+Morse alphabet, the same signals will be reproduced
+at the opposite station, and the signals will
+be manifested by long and short sounds, if an
+electro-magnetic receiver is connected with the
+circuit. This sender is shown <a href="#il_59">fig. 59</a>.</p>
+
+<p><a href="#il_60">Fig. 60</a> represents M. Lacour’s receiver. It
+consists of a tuning-fork <span class="allsmcap">F</span> made of soft iron, not of<span class="pagenum" id="Page_278">278</span>
+steel like the sending tuning-fork, and each of its
+branches is inserted in the bobbin of an electro-magnetic
+coil <span class="allsmcap">C C</span>; two distinct electro-magnets <span class="allsmcap">M M</span>
+react close to the extremities of the fork, in such a
+way that the polarities developed on the two
+branches of the fork under the influence of the
+coils <span class="allsmcap">C C</span> should be of contrary signs to those of the
+electro-magnets <span class="allsmcap">M M</span>.</p>
+
+<figure id="il_60" class="figcenter" style="max-width: 23em;">
+  <img src="images/i_p278.jpg" width="920" height="652" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 60.</span>
+  </figcaption>
+</figure>
+
+<p>If this double electro-magnetic system is inserted
+in a line circuit, it follows that, for each discharge
+of the transmitted current, a corresponding
+attraction of the branches of the tuning-fork will take
+place, and consequently there will be a vibration,
+producing a sound, if the discharges are numerous.
+This sound will naturally be short or long in proportion
+to the duration of the sender’s action, and<span class="pagenum" id="Page_279">279</span>
+it will be the same as that of the tuning-fork in that
+instrument. Again, if one branch of the tuning-fork
+reacts on a contact <span class="allsmcap">P</span> inserted in the circuit of the
+local battery communicating with a Morse receiver,
+traces will be produced on this receiver of length
+varying with the duration of the sounds, for the
+Morse electro-magnet will be so quickly affected
+by the successive breaks in the current that its
+armature will remain stationary throughout each
+vibration. ‘I have not yet been able,’ said M.
+Lacour in an address delivered before the Danish
+Academy of Science in 1875, ‘to calculate the
+time necessary for the production of definite vibrations
+in the tuning-fork. Different factors have to be
+considered, but experiment has shown that the
+time which elapses before the local circuit is broken
+is such a small fraction of a second as to be almost
+inappreciable, even when the current is very weak.</p>
+
+<p>‘Since intermittent currents only affect a
+tuning-fork on condition that it vibrates in unison
+with the one which produces them, it follows that
+if a series of sending tuning-forks, tuned to the
+different notes of the scale, is placed at one end of
+a circuit, and if a similar series of electro-magnetic
+tuning-forks, in exact accordance with the first, is
+placed at the other end of the circuit, the intermittent
+currents transmitted by the sending tuning-forks
+will be added to each other without becoming
+confused, and each of the receiving tuning-forks
+will only be affected by the currents emitted by the<span class="pagenum" id="Page_280">280</span>
+tuning-fork in unison with it. In this way the combinations
+of elementary signals representing a
+word may be telegraphed simultaneously.’</p>
+
+<p>M. Lacour enumerates the ways in which this
+system may be applied as follows: ‘If the keys in
+connection with the sending tuning-forks are placed
+side by side, and are lowered in succession, or two
+or three together, it will be enough to play on the
+keys as on a musical instrument, in order that the
+air may be heard at the receiving station, or the
+signals transmitted simultaneously may each belong
+to a different message. This system will
+therefore allow the furthest station on a line to
+communicate with one or several intermediate
+stations, and <i lang="la">vice versa</i>, without disturbing the
+communication at other stations. In this way two
+stations can exchange signals, unperceived by the
+rest. The power of sending many signals at once
+affords a good means of improving the autographic
+telegraph. In the instruments now in use, such as
+those of Caselli and D’Arlincourt, there is only
+one tracing stylus, and this stylus must pass over the
+whole surface of the telegram in order to obtain a
+copy of it, but with the telephone a certain number
+of styli may be placed side by side in the form
+of a comb, and this comb need only be drawn in a
+certain direction to pass over the surface of the
+telegram. In this way a more faithful copy will
+be obtained in a shorter time.’</p>
+
+<p>M. Lacour also observes that his system<span class="pagenum" id="Page_281">281</span>
+possesses a merit already pointed out by Mr.
+Varley, namely, that the instruments permit the
+passage of ordinary currents without revealing
+their presence, whence it follows that the accidental
+currents which often disturb telegraphic transmissions
+will have no effect on these systems.</p>
+
+<p>M. Lacour began without applying an electro-magnetic
+system to his instrument in order to
+maintain the movement of the tuning-fork, but he
+soon saw that this accessory was indispensable,
+and he made the tuning-forks themselves electro-magnetic.
+It also occurred to him to convert the
+transmitted currents into pulsatory currents by inserting
+an induction coil in the circuit, which was
+also done by Mr. Elisha Gray. Finally, in order
+to obtain the immediate action of the tuning-forks
+and the immediate cessation of their action, he
+constructed them so as to reduce their inertia as
+much as possible. This was effected by inserting
+the two branches of the tuning-fork in the same
+coil and by lengthening its handle, and turning
+it back so that it might pass through a second
+coil, dividing into two branches and embracing
+the two vibrating branches, but without touching
+them. When a current traverses both coils, it
+produces, in the kind of horseshoe magnet formed
+by the two systems, opposite polarities which provoke
+a double reaction in the vibrating branches—a
+reaction by repulsion exerted by the two
+branches in virtue of the same polarity, and a<span class="pagenum" id="Page_282">282</span>
+reaction by attraction by the other two branches
+in virtue of their opposite polarities; and this
+double action is repeated by the movements of
+a contact breaker applied to one of the vibrating
+branches of the tuning-fork.</p>
+
+<figure id="il_61" class="figcenter" style="max-width: 23em;">
+  <img src="images/i_p282.jpg" width="897" height="369" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 61.</span>
+  </figcaption>
+</figure>
+
+<p><i>Mr. Elisha Gray’s System.</i>—According to the
+system originally patented, each sender, represented
+<a href="#il_61">fig. 61</a>, consists of an electro-magnet <span class="allsmcap">M M</span> resting
+below a small copper tablet <span class="allsmcap">B S</span>, in such a way
+that its poles pass through this tablet and are on
+a level with its upper surface. A steel plate <span class="allsmcap">A S</span>
+is fixed above these poles; its tension can be regulated
+by means of a screw <span class="allsmcap">S</span>; and another screw
+<i>c</i> is placed on the plate, and is in electric communication
+with a local battery <span class="allsmcap">R′</span> by means of a
+Morse key. Below the plate <span class="allsmcap">A S</span> there is a contact
+<i>d</i> connected with the line wire <span class="allsmcap">L</span>; this contact is
+met by the plate at the moment of its attraction
+by the electro-magnet, and breaks the current of a
+line battery <span class="allsmcap">P</span>, which acts on the receiver of the
+opposite station. Finally, the electric communication<span class="pagenum" id="Page_283">283</span>
+established between the local battery <span class="allsmcap">R′</span> and
+the electro-magnet, as may be seen in the figure,
+produces vibrations in the steel plate <span class="allsmcap">A S</span> at each
+lowering of the key, as in the case of ordinary vibrations—vibrations
+which, with a suitable tension of
+the plate and a given intensity of the battery <span class="allsmcap">R′</span>, can
+produce a definite musical note. Moreover, since
+at each vibration the plate <span class="allsmcap">A S</span> meets the contact,
+discharges of the line current take place through
+the line <span class="allsmcap">L</span>, and react on the receiving instrument,
+causing it to reproduce exactly the same vibrations
+as those of the sending instrument.</p>
+
+<figure id="il_62" class="figcenter" style="max-width: 23em;">
+  <img src="images/i_p283.jpg" width="883" height="363" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 62.</span>
+  </figcaption>
+</figure>
+
+<p>The receiving instrument represented <a href="#il_62">fig. 62</a>
+exactly resembles the one we have just described,
+except that there is no contact <i>d</i> below the vibrating
+plate <span class="allsmcap">A S</span>, and the contact <i>c</i>, instead of communicating
+with the line wire, is in electric connection
+with a register <span class="allsmcap">E</span> and a local battery <span class="allsmcap">P</span>. It
+follows from this arrangement that when the plate
+<span class="allsmcap">A S</span> vibrates under the influence of the broken<span class="pagenum" id="Page_284">284</span>
+currents passing through the electro-magnet <span class="allsmcap">M M</span>,
+similar vibrations are sent through the register;
+but if the electro-magnetic organ of this register
+is properly regulated, these vibrations can only
+produce the effect of a continuous current, and hence
+the length of the traces left on the instrument will
+vary with the duration of the sounds produced.
+In this way the registration of the dashes and dots
+which constitute the signs of the Morse vocabulary
+will be effected.</p>
+
+<p>If it is remembered that the plate <span class="allsmcap">A S</span> vibrates
+under the influence of electro-magnetic attractions
+more readily in proportion to their approximation
+in number to the vibrations corresponding to
+the fundamental sound it can emit, it becomes clear
+that if this plate is tuned to the same note as that of
+the corresponding instrument, it will be rendered
+peculiarly sensitive to the vibrations transmitted by
+the sender, and the other vibrations which may
+affect it will only act faintly. Moreover, a resonator
+placed above the plate will greatly increase this
+predisposition; so that if several systems of this
+kind, tuned to different notes, produce simultaneous
+transmissions, the sounds corresponding to
+the different vibrations will be in a certain sense
+selected and distributed, in spite of their combination,
+into the receivers for which they are specially
+adapted, and each of them may retain the traces
+of the sounds emitted by adding the register, which
+may be so arranged as to act as an ordinary Morse<span class="pagenum" id="Page_285">285</span>
+receiver. Mr. Gray states that the number of
+sending instruments and independent local circuits
+may be equal to that of the tones and semitones
+of two or more octaves, provided that each vibrating
+plate be tuned to a different note of the scale.
+The instruments may be placed side by side, and
+their respective local keys, arranged like the keys
+of a piano, will make it easy to play an air combining
+notes and chords; there may also be an
+interval between the instruments, which may be
+sufficiently far from each other to allow the employés
+to work without being distracted by sounds
+not intended for them.</p>
+
+<p>In a new arrangement, exhibited at the Paris
+Exhibition, 1878, Mr. Gray considerably modified
+the way of working the various electro-magnetic
+organs which we have just described. In this case,
+the plates consist of tuning-forks with one branch
+kept in continual vibration at both stations, and
+the signals only become perceptible by intensifying
+the sounds produced. This arrangement follows
+from the necessity of keeping the line circuit always
+closed for multiple transmissions of this nature, so
+as to react with pulsatory currents, which are alone
+able, as we have already seen, to retain the individual
+character of several sounds simultaneously
+transmitted.</p>
+
+<figure id="il_63" class="figcenter" style="max-width: 18em;">
+  <img src="images/i_p286.jpg" width="719" height="880" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 63.</span>
+  </figcaption>
+</figure>
+
+<p>Under these conditions, the sender consists,
+as we see (<a href="#il_63">fig. 63</a>), of a bar tuning-fork, <i>a</i>, which
+is grooved for the passage of a runner, heavy<span class="pagenum" id="Page_286">286</span>
+enough to tune the fork to the desired note, and it
+oscillates between two electro-magnets <i>e</i> and <i>f</i> and
+two contacts <span class="allsmcap">I</span> and <span class="allsmcap">G</span>. The difference of resistance
+in the electro-magnets is very great: in the one <i>f</i>
+the resistance is equal to 2¾ miles of telegraphic wire,
+in the other it does not exceed 440 yards. When
+electric communication is established as we see in
+the figure, the following effect takes place. Since the
+current of the local battery through the two electro-magnets
+is broken by the rest-contact of the Morse
+key <span class="allsmcap">H</span>, the plate <i>a</i> is subject to two contrary<span class="pagenum" id="Page_287">287</span>
+actions; but since the electro-magnet <i>f</i> has more
+turns than the electro-magnet <i>e</i>, its action is preponderant,
+and the plate is attracted towards <i>f</i>, and
+produces a contact with the spring <span class="allsmcap">G</span>, which opens
+a way of less resistance for the current. Since the
+current then passes almost wholly through <span class="allsmcap">G</span>, <i>b</i>, 1,
+2, <span class="allsmcap">B</span>, the electro-magnet is now able to act; the
+plate <i>a</i> is then attracted towards <i>e</i>, and, by producing
+a contact on the spring <span class="allsmcap">I</span>, it sends the current
+of the line <span class="allsmcap">B P</span> through the telegraphic line, if the
+key <span class="allsmcap">H</span> is at the same time lowered on the sending
+contact: if not, there will be no effect in this direction,
+but since the plate <i>a</i> has left the spring <span class="allsmcap">G</span>, the
+first effect of attraction by the electro-magnet <i>f</i>
+will be repeated, and this tends to draw the plate
+again towards <i>f</i>. This state of things is repeated
+indefinitely so as to maintain the vibration of the
+plate, and to send out signals corresponding with
+these vibrations whenever the key <span class="allsmcap">H</span> is lowered.
+The elastic nature of the plate makes these vibrations
+more easy, and it ought also to be put in
+mechanical vibration at the outset.</p>
+
+<p>The receiver, represented <a href="#il_64">fig. 64</a>, consists of an
+electro-magnet <span class="allsmcap">M</span>, mounted on a sounding-box <span class="allsmcap">C</span>,
+and having an armature formed by a tuning-fork
+<span class="allsmcap">L L</span> firmly buttressed on the box by a cross bar <span class="allsmcap">T</span>.
+There is a runner <span class="allsmcap">P</span> on the armature, sliding in a
+groove, which makes it possible to tune the vibrations
+of the tuning-fork to the fundamental note of
+the sounding-box <span class="allsmcap">C</span>, which is so arranged as to<span class="pagenum" id="Page_288">288</span>
+vibrate in unison with it. Under these conditions,
+the box as well as the tuning-fork will act as an
+analyser of the vibrations transmitted by the currents,
+and may set the register at work by itself
+reacting on a breaker of the local current. To
+obtain this result, a membrane of gold-beater’s
+skin or parchment must be stretched before the
+opening of the box, and a platinum contact must be
+applied to it, so arranged as to meet a metallic
+spring connected with any kind of register or a
+Morse instrument, when the membrane vibrates. As,
+however, in America the messages are generally
+received by sound, this addition to the system is
+not in use.</p>
+
+<figure id="il_64" class="figcenter" style="max-width: 23em;">
+  <img src="images/i_p288.jpg" width="907" height="728" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 64.</span>
+  </figcaption>
+</figure>
+
+<p><span class="pagenum" id="Page_289">289</span></p>
+
+<p>The instrument is not only regulated by the
+runner <span class="allsmcap">P</span>, but also by a regulating screw <span class="allsmcap">V</span> which
+allows the electro-magnet <span class="allsmcap">M</span> to be properly
+adjusted. The regulating system is made more
+exact by the small screw <span class="allsmcap">V</span>, and the instrument is
+connected with the line by the binding screw <span class="allsmcap">B</span>.
+Of course this double arrangement is necessary for
+each of the sending systems.</p>
+
+<p>As I have already said, seven different messages
+might theoretically be sent at once in this way,
+but Mr. Gray has only adapted his instrument for
+four; he has, however, made use of the duplex
+system, which allows him to double the number of
+transmissions, so that eight messages may be sent
+at the same time, four in one direction, and four in
+another.</p>
+
+<p>Mr. Hoskins asserts that this system has been
+worked with complete success on the lines of the
+Western Union Telegraph Company, from Boston
+to New York, and from Chicago to Milwaukee.
+Since these experiments were made, fresh improvements
+have rendered it possible to send a much
+larger number of messages.</p>
+
+<p>Mr. Gray has also, aided by Mr. Hoskins,
+devised a system by which telephonic messages
+may be sent on a wire previously used for Morse
+instruments. Mr. Varley had already solved this
+problem, but Mr. Gray’s system seems to have
+produced important results, and has therefore a
+claim to our attention. We do not, however, describe<span class="pagenum" id="Page_290">290</span>
+it here, since it is not within the lines marked out
+for us, and those who are interested in the subject
+will find all the necessary details in a paper inserted
+in the ‘Journal of the Society of Telegraphic Engineers,
+London,’ vol. vi.</p>
+
+<p><i>Mr. Varley’s System.</i>—This system is evidently
+the earliest in date, since it was patented in 1870,
+and the patent describes the principle of most of the
+arrangements which have since been adopted by
+Messrs. Lacour, Gray, and Bell. It is based upon
+the use of his own musical telephone, which we
+have already described, but with some variations
+in its arrangement, which make it somewhat like
+the Reiss system.</p>
+
+<p>It was Mr. Varley’s aim to make his telephone
+work in conjunction with instruments with ordinary
+currents, by the addition of rapid electric waves,
+incapable of making any practical change in the
+mechanical or chemical capacity of the currents
+which serve for the ordinary signals, yet able to
+make distinct signals, perceptible to the ear and
+even to the eye. He says: ‘An electro-magnet
+offers at first a great resistance to the passage of
+an electric current, and may consequently be regarded
+as a partially opaque body with respect to
+the transmission of very rapid inverse currents or
+of electric waves. Therefore, if a tuning-fork, or an
+instrument with a vibrating plate, tuned to a given
+note, be placed at the sending station, and so
+arranged as to be kept in constant vibration by<span class="pagenum" id="Page_291">291</span>
+magnetic influence, the current which acts upon it
+must be passed into two helices placed one above
+the other so as to constitute the primary helix of
+an induction coil: in this way it will be possible to
+obtain in two distinct circuits two series of rapidly
+broken currents, which will correspond to the two
+directions of the vibrations of the tuning-fork,
+and we shall also have the induced currents produced
+in the secondary helix by these currents,
+which may act on a third circuit. This third
+circuit may be placed in connection with a telegraphic
+line previously used by an ordinary telegraphic
+system, if a condenser is applied to it, and
+in this way two different transmissions may be
+obtained simultaneously.’</p>
+
+<figure id="il_65" class="figcenter" style="max-width: 21em;">
+  <img src="images/i_p291.jpg" width="823" height="311" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 65.</span>
+  </figcaption>
+</figure>
+
+<p><a href="#il_65">Fig. 65</a> represents the arrangement of this
+system. <span class="allsmcap">D</span> is the vibrating plate of the tuning-fork
+designed to produce the electric contacts necessary
+to maintain it in motion. These contacts are at <span class="allsmcap">S</span>
+and <span class="allsmcap">S′</span>, and the electro-magnets which affect it are
+at <span class="allsmcap">M</span> and <span class="allsmcap">M′</span>. The induction coil is at <span class="allsmcap">I′</span>, and the
+three helices of which it is composed are indicated<span class="pagenum" id="Page_292">292</span>
+by the circular lines which surround it. There is a
+Morse manipulator at <span class="allsmcap">A</span>, another at <span class="allsmcap">A′</span>, and the
+two batteries which work the system are at <span class="allsmcap">P</span> and
+<span class="allsmcap">P′</span>. The condenser is at <span class="allsmcap">C</span>, and the telephone is at
+the end of the line <span class="allsmcap">L</span>.</p>
+
+<p>When the vibration of the plate <span class="allsmcap">D</span> tends to the
+right, and the electric contact takes place at <span class="allsmcap">S′</span>,
+the current of the battery <span class="allsmcap">P′</span>, after traversing the
+primary helix, reaches the electro-magnets <span class="allsmcap">M M′</span>,
+which give it an impulse in the contrary direction.
+When, on the other hand, it tends to the left, the
+current is sent through the second primary circuit,
+which will be balanced by the first. Consequently
+there will be a series of reversed currents in the induced
+circuit corresponding to the key <span class="allsmcap">A′</span>, which will
+alternately charge and discharge the condenser <span class="allsmcap">C</span>,
+thus sending into the line a corresponding series of
+electric undulations which will react on the telephone
+placed at the end of the line; and as the
+duration of the transmitted currents will vary with
+the time that the key <span class="allsmcap">A′</span> is lowered, a correspondence
+in the Morse code may be obtained
+in the telephone, while another correspondence is
+exchanged with the key <span class="allsmcap">A</span> and the ordinary Morse
+receivers.</p>
+
+<p>In order to render the vibratory signals visible,
+Mr. Varley proposes to use a fine steel wire,
+stretched through a helix and facing a narrow slit,
+to reproduce the vibrations. A light, which is
+intercepted by the wire, is placed behind the slit.<span class="pagenum" id="Page_293">293</span>
+As soon as a current passes, the wire vibrates and
+the light appears. A lens is placed so as to
+magnify the image of the luminous slit, and project
+it on a white screen while the wire is in vibration.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h2 class="nobreak" id="VARIOUS_USES_OF_THE_TELEPHONE"><span id="toclink_293"></span>VARIOUS USES OF THE TELEPHONE.</h2>
+</div>
+
+<p><i>Its domestic application.</i>—We have seen that
+telephones may be used with advantage in public
+and private offices: they can be set up at a much
+less expense than acoustic tubes, and in cases
+where the latter would never be employed. With
+the aid of the calls we have described, they offer
+the same advantages, and the connection between
+the instruments is more easily concealed. The
+difference of price in establishing them is in the
+ratio of one to seven.</p>
+
+<p>For this purpose electro-magnetic telephones
+are evidently the best, since they require no battery
+and are always ready to work. They are already
+in use in many Government offices, and it is probable
+that they will soon be combined with electric
+bells for the service of hotels and of large public
+and private establishments: they may even be
+used in private houses for giving orders to servants
+and porters, who may thus save visitors from the
+fatigue of a useless ascent of several storeys.</p>
+
+<p>In factories, telephones will certainly soon replace
+the telegraphic communication which has already
+become general. They may not only be used
+for ordinary messages, but to call for help in case of<span class="pagenum" id="Page_294">294</span>
+fire, and they will become an integral part of several
+systems already established for this purpose.</p>
+
+<p>In countries which have free telegraphic communication,
+the telephone has already replaced in
+great measure the private telegraph instruments
+which have hitherto been in use; and if the same
+privilege is extended to France, no other mode of
+correspondence will be used.</p>
+
+<p><i>Its application to telegraphic service.</i>—The
+advantage to be derived by the telegraphic service
+from the telephone is rather limited, since, as far as
+the speed of transmission is concerned, it is of less
+value than many of the telegraphic instruments
+now in use, and the messages which it produces
+cannot be registered. Yet in municipal offices not
+overburdened with messages they offer the advantage
+of not requiring a trained service. On longer
+lines their use would be of little value. The ‘Berne
+Telegraphic Journal’ has published some interesting
+remarks on this subject, of which the following is a
+summary.</p>
+
+<p>1st. In order to send a message with the special
+advantages of the system, the sender ought to be
+able to address his correspondent without the intervention
+of an official. Those who are acquainted
+with the network of wires know this to be impossible.
+Intermediate offices for receiving messages
+are essential, and the public cannot be admitted to
+those set apart for sending and receiving; consequently
+the sender must deliver a written message.</p>
+
+<p><span class="pagenum" id="Page_295">295</span></p>
+
+<p>2nd. If the message is written, the chief advantage
+of the instrument is lost, since it must
+be read and uttered aloud, which could not be
+done if expressed in a language with which the
+employés were unacquainted.</p>
+
+<p>3rd. The instruments now in use at the telegraph
+offices can transmit messages more quickly
+than if they were spoken.</p>
+
+<p>In Germany, however, a telephone service has
+been established in several telegraph offices, and its
+possible advantages are enumerated as follows in
+the official circular which created it:</p>
+
+<p>‘The offices which will be opened to the public
+for the service of telephonic messages in Germany
+will be regarded as independent establishments;
+yet they will be in connection with the ordinary
+telegraph offices, which will undertake to send
+telephonic messages through their wires.</p>
+
+<p>‘The transmission will take place as follows:
+The sending office will request the receiving office
+to prepare the instrument; as soon as the tubes
+are adjusted, the sending office will give the signal
+for despatching the verbal message.</p>
+
+<p>‘The sender must speak slowly and clearly,
+without raising his voice; each syllable must be
+distinctly pronounced; the final syllables especially
+must be well articulated, and there must be a pause
+after each word, in order to give the receiver time
+to write it down.</p>
+
+<p>‘When the telegram has been received, the<span class="pagenum" id="Page_296">296</span>
+employé at the receiving office must verify the
+number of words; then he must repeat through the
+telephone the whole message without pausing, so
+as to make sure that there is no mistake.</p>
+
+<p>‘In order to ensure secrecy, the telephones are
+placed apart, where persons unconnected with the
+service cannot hear the verbal message, and the
+employés are forbidden to reveal to anyone the
+names of the correspondents.</p>
+
+<p>‘The charge for telephonic messages, as for the
+ordinary telegraphic services, is at the rate of so
+much a word.’</p>
+
+<p>The use of the telephone has also been suggested
+for verifying the perfect junction of telegraphic
+wires. It is certain that, if the junction is complete,
+no abnormal sounds will be heard, or only those
+which result from accidental currents; but if the
+junction is bad, the imperfect contacts which take
+place produce variations in electric intensity which
+are translated into the more or less marked sounds
+observed in the telephone.</p>
+
+<p>M. Mauborgne, the electrician attached to the
+Northern Railway of France, has lately used the
+telephone instead of the galvanometer to ascertain
+the condition of the circuits in correspondence with
+the instruments in use for electric signals. The
+reactions produced on the galvanometer needle by
+the pieces of iron which are placed at the sides of
+the railway often make its indications uncertain,
+and a strong wind produces irregular movements<span class="pagenum" id="Page_297">297</span>
+in the instrument which interfere with observations.
+It was also necessary to place the galvanometer
+with due regard to the points of the compass,
+and to wait for the needle to settle, which
+involved loss of time. The operation is easily
+accomplished with the telephone, since the strokes
+of the call-bell are distinctly reproduced; it is
+made to ring by working the contacts which need
+verification, and in the same way the condition of
+the battery can be ascertained.</p>
+
+<p><i>Application to military purposes.</i>—Since the
+telephone was invented, numerous experiments
+have been made in different countries to ascertain
+whether it would be of use in military operations.
+These experiments have hitherto been only
+moderately satisfactory, on account of the noise
+inseparable from an army, which generally makes it
+impossible to hear the telephone, and every means
+of intensifying its sounds has been eagerly sought.
+It was at first supposed that the discovery of
+the microphone had solved the problem, and I
+received many enquiries from military schools on
+the subject, but I have not been able to see that
+anything has been gained from this point of view.
+The telephone is, however, of great use in schools of
+artillery and rifle practice. Now that firearms carry
+so far, it has become necessary to be informed by
+telegraph of the points hit on the target, in order to
+judge of the accuracy of aim, and for this purpose
+telegraphic targets were suggested; but telephones<span class="pagenum" id="Page_298">298</span>
+are much to be preferred, and they are now used
+with good effect.</p>
+
+<p>If the telephone is unsuited for the service of
+the flying telegraph in the field, it may be of great
+use in the defence of towns, to transmit the orders
+of the commandant to different batteries, and even
+for the exchange of correspondence with captive
+balloons sent to hover over fields of battle.</p>
+
+<p>In spite of the difficulties attending its use, the
+experiment was made by the Russians in the late
+war: the cable wire of communication was 500 or
+600 yards long, and so light that it could be laid
+by one man. The ‘Telegraphic Journal’ of March
+15, 1878, states that the bad weather did not
+interfere with the working of the instruments; but
+the noise made it difficult to hear, and it was
+necessary to cover the head with a hood to intercept
+external sounds. This cannot be considered
+a satisfactory result, yet the telephone may be of
+great service to an army by intercepting the
+enemy’s messages: a bold man, provided with a
+pocket telephone, who placed himself in a retired
+spot, might divert the current of the enemy’s
+telegraphic wire into his telephone, and get possession
+of all his despatches, as we saw was the case
+at Clermont. He might even do this by diverting
+the current to earth or to a rail of the railway line.
+These are suggestions for future research, and it is
+probable that they may some day be turned to
+practical account.</p>
+
+<p><span class="pagenum" id="Page_299">299</span></p>
+
+<p><i>Its application to the navy.</i>—The telephone may
+be of the greatest use in naval matters, for the
+service of electro-semaphores, for island forts and
+ships at anchor. M. Pollard says that ‘experiments
+made between the Préfecture Maritime at
+Cherbourg, the semaphores and the forts on the
+mole, demonstrate the advantage there would be in
+establishing telephones at these stations, since they
+would ensure an easy communication between the
+vessels of a squadron and the land they are
+approaching. By sinking small cables which come
+to the surface of the water along mooring chains,
+and terminate in buoys or cases which remain
+permanently in the harbour, the ships of war may
+in this way place themselves in communication with
+the Préfecture Maritime as they cast anchor, and,
+by temporarily connecting the vessels together
+with light cables, the admiral may communicate
+freely with the whole squadron.’</p>
+
+<p>The telephone has been tried on board ship for
+transmitting orders, but without success, on account
+of the noise always going on in a vessel.</p>
+
+<p>The telephone may be usefully applied to the
+service of submarine torpedoes. We have already
+seen how it may be applied in connection with the
+microphone, but it may also be used in firing the
+torpedoes after the exact position of the enemy’s
+ship has been ascertained from two reconnaissances
+taken from different parts of the coast.</p>
+
+<p>The telephone, again, makes it possible to<span class="pagenum" id="Page_300">300</span>
+verify the condition of torpedoes, and to ascertain
+if there is any fault in the circuit within the explosives.
+For this purpose a very weak current
+has been used, and a galvanometer is not always
+able to indicate the fault, while the extreme sensitiveness
+of the telephone will do so in the simplest
+way.</p>
+
+<p>Captain M’Evoy, of the American Army, suggested
+a way of ascertaining, while on shore, the
+condition of torpedoes under water, by connecting
+the buoys which support them with the land by
+means of a telephonic line. By inserting, in the
+buoy which supports the torpedo, metallic disks,
+so arranged as to vibrate with every movement
+caused by the waves upon the buoy, a continuous
+noise will be heard in the telephone, after the
+circuit has been completed by the metallic disks;
+and the noise will go on as long as the disks
+continue to oscillate, and will cease as soon as the
+buoy is completely covered by the water. When
+it ceases, therefore, if not affected by some accidental
+cause, it may be supposed that the
+enemy’s ship is passing over the buoy.</p>
+
+<p>M. Trève, again, has shown that the telephone
+might be used with advantage for the telegraphic
+communication between vessels in tow, and
+M. des Portes has applied it with good effect to
+diving operations. In this instance, one of the
+glass panes in the helmet is replaced by a copper
+plate in which the telephone is framed, so that the<span class="pagenum" id="Page_301">301</span>
+diver need only make a slight movement of his
+head in order to receive or address communications
+to those in charge of the apparatus. With this
+system the keels of vessels may be examined, and
+an account given of their condition, without bringing
+up the divers, which has hitherto been necessary.</p>
+
+<p>M. de Parville, the able and learned editor
+of the <i lang="fr">Journal Scientifique</i> and the science department
+of the <i lang="fr">Journal des Débats</i>, has suggested a
+new and interesting application of the telephone.
+It concerns the possibility of making use of it to
+determine the precise position of the magnetic
+meridian, that is, the true direction of the magnetised
+needle.</p>
+
+<p>For this purpose a Bell telephone is necessary,
+of which the magnetic core is formed of an iron
+rod a mètre in length, kept, by a suitable suspension,
+at nearly the same angle of inclination as a
+dipping-needle. This rod will be magnetised under
+the influence of terrestrial magnetism, and the
+telephone will be able to transmit the sounds produced
+by some sort of vibrator placed near its
+mouthpiece. These sounds will be strong in proportion
+to the degree of magnetisation of the bar;
+and if the telephone is turned round the horizon,
+keeping the bar at the same angle of inclination, the
+sounds transmitted to the receiving telephone will
+be greatest when the axis of the bar is in the plane
+of the magnetic meridian, and least when it is at
+90°. It will therefore be possible to ascertain from<span class="pagenum" id="Page_302">302</span>
+the direction of the axis at the moment when
+the sounds are no longer heard, the exact inclination
+of the magnetic needle from north to south, for
+it will be given by the perpendicular to the line
+which is followed by the axis of the iron bar at
+that moment.</p>
+
+<p>It is possible that, with this system, the disturbing
+influence on the magnetic needle of the mass of
+iron in iron-plated vessels might be almost destroyed,
+and a more exact orientation than that of
+the compass might be obtained. The same process
+may make it possible to estimate and measure the
+variations of terrestrial magnetism. M. de Parville
+has not himself tried to apply this system; but Mr.
+Blake’s experiments, of which we spoke in an early
+part of this work, make it probable that it might
+be done with advantage.</p>
+
+<p><i>Application to industry.</i>—One of the earliest
+and most important applications of the telephone
+is that which was first made to the service of
+mines in England and America in the autumn
+of 1877. The great length of the galleries is
+well known, and had already involved the use of
+the electric telegraph for transmitting orders; but
+the miners did not understand how to work these
+instruments, and the service was ill performed.
+Thanks to the telephone, through which the first
+corner can send and receive a message, there is no
+longer any difficulty in the communication between
+the galleries and the surface of the mine.</p>
+
+<p><span class="pagenum" id="Page_303">303</span></p>
+
+<p>The ventilation of mines can also be regulated
+by the aid of telephones. If one of these instruments
+is placed near a wheel kept in motion by
+the air which passes through the ventilating shaft,
+and another is placed in the inspector’s office he
+can ascertain by the sound if the ventilation is duly
+carried on, and if the machine works regularly.</p>
+
+<p><i>Application to scientific research.</i>—M. d’Arsonval’s
+experiments, which we have already mentioned,
+show that the telephone can be used as an extremely
+sensitive galvanoscope; but since it can
+only produce sounds under the influence of broken
+currents, the circuit on which the experiment is
+made must be divided at rather close intervals. It
+has been seen that it is not even necessary to insert
+the telephone in the circuit: it may be influenced,
+when at a distance, either immediately or by the
+induction of the broken current on a circuit placed
+parallel to the first, and the force of these effects
+may be increased by the reaction of a core of
+iron, round which the inducing circuit is wound.
+The drawback to this system is that the direction
+of the current is not ascertained, so that it cannot
+be used as a measuring instrument; but, on the
+other hand, it is so sensitive, so easy to arrange,
+and so inexpensive, that it might be of the greatest
+use as a galvanoscope.</p>
+
+<p>Mr. Warren de La Rue has also made use of the
+telephone in his researches into the electric discharges
+of high-tension batteries, in order to<span class="pagenum" id="Page_304">304</span>
+follow the different phases of the discharge during
+the luminous phenomena which it produces. In
+this way he ascertained that when a condenser is
+placed in connection with a battery formed of a
+considerable number of insulated elements, and is
+gradually discharged through a Geissler tube, a
+dull and faint sound is heard in the telephone, as
+long as the stratifications of light appear to be
+perfectly stable; but the sound becomes considerably
+stronger, and sometimes even piercing,
+in proportion to the diffusion of these stratifications,
+and to their approach to the point of
+extinction: whence it is shown that the discharge
+of a battery into tubes in which a vacuum has been
+made is intermittent.</p>
+
+<p>Mr. Spottiswoode has repeated the same experiments
+with the discharges of Holtz machines,
+and with large condensers, and he found that the
+most piercing sounds produced by the telephone
+coincided with the greatest development of the
+stratifications. These sounds, however, sometimes
+ceased for a moment. It was even possible to
+ascertain, from the intensity of the sounds produced,
+the differences of tension which might be
+manifested in the charge of the condenser and
+the slackening of the machine’s motion, and the
+differences of intensity in these sounds might in
+some cases exceed an octave. The fall in the
+scale generally appeared in half-tones instead of
+gradually, and the introduction of resistances into<span class="pagenum" id="Page_305">305</span>
+the circuit modified the sounds very much: they
+might even be intensified by approaching the
+finger to the discharging tube.</p>
+
+<p>From experiments made with the telephone
+between Calais and Boulogne, it appears that this
+instrument might be applied with advantage to the
+science of projectiles. In fact, in some artillery
+practice which took place on the shore at Boulogne,
+a telephone was placed close to the gun, and the
+explosion was heard at a distance of nearly two
+miles, where the projectile fell. It was possible to
+estimate its velocity by measuring the lapse of
+time between the moment when the projectile left
+the gun, and its fall. This calculation is usually
+made by observing the flash from the cannon’s
+mouth; but in some cases, as in a fog or in practice
+at long ranges, the telephone may be usefully
+substituted for ocular observation. On the field
+of battle, an observer, provided with a telephone
+and placed on a hill, might rectify from a distance
+the aim of his battery, which is generally established
+in a sheltered and less elevated place.</p>
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<p><span class="pagenum" id="Page_307">307</span></p>
+
+<h2 class="nobreak" id="THE_PHONOGRAPH"><span id="toclink_307"></span>THE PHONOGRAPH.</h2>
+</div>
+
+<p>Mr. Edison’s Phonograph, which has for the last
+year attracted so much attention, is an instrument
+which not only registers the different vibrations
+produced by speech on a vibrating plate, but reproduces
+the same words in correspondence with the
+traces registered. The first function of this instrument
+is not the result of a new discovery. Physicists
+have long sought to solve the problem of registering
+speech, and in 1856 Mr. Leo Scott invented an
+instrument well known to physicists under the
+name of Phonautograph, which completely solved the
+difficulty: this instrument is described in all the
+more detailed treatises on physics. But the second
+function of the Edison instrument was not realised
+nor even mentioned by Mr. Scott, and we are surprised
+that this able inventor should have regarded
+Mr. Edison’s invention as an injurious act of spoliation.
+We regret on his own account, since no
+one has wished to deprive him of the credit he
+deserves, that he should have published a pamphlet
+on the subject, couched in terms of such asperity,<span class="pagenum" id="Page_308">308</span>
+which proves nothing, and only states facts which
+were well known to all physicists. If any other
+person could claim the invention of the phonograph,
+at least in its most curious property of reproducing
+speech, it would certainly be M. Charles Cros; for
+in a sealed paper deposited at the Académie des
+Sciences, April 30, 1877, he pointed out the
+principle of an instrument by means of which
+speech might be reproduced in accordance with
+the marks traced on a register like that of the
+phonautograph.<a id="FNanchor_19" href="#Footnote_19" class="fnanchor">19</a> Mr. Edison’s patent, in which the<span class="pagenum" id="Page_309">309</span>
+principle of the phonograph is first indicated, is
+dated July 31, 1877, and he was still only
+occupied with the repetition of the Morse signals.
+In this patent Mr. Edison described a mode of
+registering these signals by means of indentations
+traced with a stylus on a sheet of paper wound
+round a cylinder, and this cylinder had a spiral
+groove cut on its surface. The tracings thus
+produced were to be used for the automatic transmission
+of the same message, by passing it again
+under a stylus which should react on a current
+breaker. In this patent, therefore, nothing is said<span class="pagenum" id="Page_310">310</span>
+of the registration of speech or of its reproduction;
+but, as the ‘Telegraphic Journal’ of May 1, 1878,
+observes, the foregoing invention gave him the
+means of solving this double problem as soon as
+it was suggested to him. If we may believe the
+American journals, this suggestion soon came, and
+it was the result of an accident.</p>
+
+<p>In the course of some experiments Mr. Edison
+was making with the telephone, a stylus attached
+to the diaphragm pierced his finger at the moment
+when the diaphragm began to vibrate under the
+influence of the voice, and the prick was enough to
+draw blood. It then occurred to him that if the
+vibrations of the diaphragm enabled the stylus
+to pierce the skin, they might produce on a flexible
+surface such distinct outlines as to represent all the
+undulations produced by the voice, and even that
+the same outlines might mechanically reproduce the
+vibrations which had caused them, by reacting on
+a plate capable of vibrating in the same way as
+that which he had already used for the reproduction
+of the Morse signals. From that moment the
+phonograph was discovered, since there was only a
+step between the idea and its realisation, and in
+less than two days the instrument was made and
+tried.</p>
+
+<p>This is an ingenious story, yet we would rather
+believe that the discovery was made in a more
+serious spirit. In fact, such an inventor as Mr.
+Edison, who had discovered the electro-motograph,<span class="pagenum" id="Page_311">311</span>
+and had applied it to the telephone, was already
+on the way to discover the phonograph, and we
+think too well of his powers to attach much credit
+to this American romance. Besides, Mr. Edison
+was well acquainted with Mr. Scott’s phonautograph.</p>
+
+<p>Mr. Edison’s phonograph was only patented in
+January 1877. Consequently, when we look at the
+principle of the invention, M. Cros undoubtedly
+may claim priority; but it is a question whether the
+system described in his sealed paper, and published
+in the <i lang="fr">Semaine du Clergé</i>, October 8, 1877, would
+have been capable of reproducing speech. Our
+doubt seems justified by the unsuccessful attempts
+of the Abbé Leblanc to carry out M. Cros’ idea.
+When we have to do with such undulating and
+complex vibrations as those involved in the reproduction
+of articulate words, it is necessary that
+the stereotyping should in some sense be effected
+by the words themselves, and their artificial reproduction
+will necessarily fail to mark the slight differences
+which distinguish the delicate combinations
+of speech. Besides, the movements performed by
+a point confined to a groove that follows a sinusoidal
+curve cannot be effected with all the freedom
+necessary for the development of sounds, and the
+friction exerted on the two edges of the groove
+will often be of a nature to stifle them. A distinguished
+member of the Société de Physique, when
+I exhibited the phonograph to that society, justly<span class="pagenum" id="Page_312">312</span>
+said that Mr. Edison’s whole invention consisted in
+the thin metallic sheet on which the vibrations are
+inscribed; this sheet permits the movements of the
+vibrating plate to be directly stereotyped, and
+thereby the problem is solved. It was necessary to
+find such an expedient, and it was done by Mr.
+Edison, who is therefore the inventor of the phonograph.</p>
+
+<p>After M. Cros, and before Mr. Edison, MM.
+Napoli and Marcel Deprez attempted to make a
+phonograph, but with so little success that they
+believed at one time the problem to be insoluble,
+and threw doubts on Mr. Edison’s invention
+when it was announced to the Société de Physique.
+They subsequently resumed their labours, and lead
+us to hope that they may eventually produce a
+phonograph of more perfect construction than that
+of Mr. Edison. We shall have more to say on this
+subject.</p>
+
+<p>In conclusion, the mechanical reproduction of
+speech was first effected by Mr. Edison, and in so
+doing he has accomplished one of the most curious
+and important discoveries of our time, since it has
+shown that this reproduction was much less complicated
+than had been supposed. Yet the theoretical
+consequences of the discovery must not be
+exaggerated, since I do not consider it by any
+means proved that our theories on the voice are
+incorrect. There is in fact a great difference
+between the reproduction of a sound which has<span class="pagenum" id="Page_313">313</span>
+been uttered, and the mode in which the same
+sound was produced. The reproduction may be
+easily effected, as M. Bourseul has remarked, as
+soon as a mode has been discovered of transmitting
+the vibrations of air, however complex they
+may be; but in order to produce the complex
+vibrations of speech by the voice, several special
+organs must be exercised—first, the muscles of the
+throat; secondly, the tongue, the lips, and even the
+teeth—and for this reason an articulating machine
+is necessarily very complex.</p>
+
+<p>Surprise was expressed that the speaking
+machine, which was brought from America two
+years ago, and exhibited at the Grand Hôtel, Paris,
+was so extremely complicated, since the phonograph
+solved the problem in such a simple way.
+This is because the latter instrument only reproduces
+speech, while the former utters it, and the
+inventor of the speaking machine had to employ
+in his mechanism all the organs which are
+necessary in our organism for the reproduction of
+speech. The problem was infinitely more complex,
+and this invention has not attracted all the attention
+it deserved. We shall speak of it presently.
+We must now describe the phonograph and the
+different applications which have been, or which
+may be, made of it.</p>
+
+<p><i>Description of Phonograph, and mode of using
+it.</i>—The first and best known model of this instrument,
+which we represent in <a href="#il_66">fig. 66</a>, simply consists<span class="pagenum" id="Page_314">314</span>
+of a registering cylinder <span class="allsmcap">R</span>, set in motion with the
+hand by a winch <span class="allsmcap">M</span>, before which a vibrating plate
+is placed, furnished on its face with a telephone
+mouthpiece <span class="allsmcap">E</span>, and on the reverse side with a tracing
+point. This tracing point, which is seen at <i>s</i>
+in the section of the instrument given in <a href="#il_68">fig. 68</a>, is
+not fixed directly on the plate; it rests on a spring
+<i>r</i>, and a caoutchouc pad <i>c</i> is placed between it and
+the vibrating disk. This pad is formed of the end
+of a tube which is designed to send the vibrations
+of the plate to the point <i>s</i> without stifling them.
+Another pad <i>a</i>, placed between the plate <span class="allsmcap">L L</span> and
+the rigid support of the point, moderates in some
+degree these vibrations, which, without this precaution,
+would generally be too powerful.</p>
+
+<figure id="il_66" class="figcenter" style="max-width: 28em;">
+  <img src="images/i_p314.jpg" width="1088" height="676" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 66.</span>
+  </figcaption>
+</figure>
+
+<p><span class="pagenum" id="Page_315">315</span></p>
+
+<p>The cylinder, of which the axis <span class="allsmcap">A A</span> (<a href="#il_66">fig. 66</a>) is
+cut at one end like a screw, to enable it to make
+a lateral progressive movement simultaneously
+with the rotatory movement effected on itself, has
+on its surface a narrow screw-thread coinciding
+with that of the axis, and when the tracing point is
+inserted, it is able to pass along it for a distance
+corresponding to the time occupied in turning the
+cylinder. A sheet of tinfoil or of very thin copper
+is carefully applied to the surface of the cylinder,
+and it should be slightly pressed down upon it,
+so as to show a faint tracing of the groove, and
+to allow the point of the vibrating disk to be placed
+in a proper position. The point rests on the foil
+under a pressure which must be regulated, and for
+this purpose, as well as to detach the cylinder when
+it is desired to place or take away the tinfoil, there
+is the articulated system <span class="allsmcap">S N</span> which sustains the
+support <span class="allsmcap">S</span> of the vibrating disk. This system consists
+of a jointed lever in which there is a nut
+screw for the screw <span class="allsmcap">R</span>. The handle <span class="allsmcap">N</span> at the end of
+the lever allows the tracing system to be turned
+aside when the screw <span class="allsmcap">R</span> is loosened. In order to
+regulate the pressure of the tracing point on the
+sheet of tinfoil, it is enough to turn the screw <span class="allsmcap">R</span>
+loosely in its socket, and to tighten it as soon as
+the right degree of pressure is obtained.</p>
+
+<p>This is the simple system by which speech can
+engrave itself on a plate in durable characters, and
+it works in the following manner.</p>
+
+<p><span class="pagenum" id="Page_316">316</span></p>
+
+<figure id="il_67" class="figcenter" style="max-width: 21em;">
+  <img src="images/i_p316.jpg" width="818" height="642" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 67.</span>
+  </figcaption>
+</figure>
+
+<p>The speaker stands before the mouthpiece <span class="allsmcap">E</span>,
+as before a telephone or an acoustic tube, and
+speaks in a strong, emphatic voice, with his lips
+pressed against the walls of the mouthpiece, as we
+see in <a href="#il_67">fig. 67</a>; at the same moment he turns the
+handle of the cylinder, which is provided with a
+heavy fly-wheel in order that the movement may
+be regular. Influenced by the voice, the plate <span class="allsmcap">L L</span>
+begins to vibrate, and sets the tracing point at work,
+which presses on the tinfoil at each vibration, and
+produces a furrow whose depth varies along its
+course in correspondence with the unequal vibrations
+of the disk. The cylinder which moves at the same
+time presents the different parts of the groove of
+which we have spoken to the tracing point in succession;<span class="pagenum" id="Page_317">317</span>
+so that when the spoken sentence comes
+to an end, the design which has been pricked out,
+consisting of a succession of reliefs and depressions,
+represents the registration of the sentence itself.
+The first part of the operation is therefore accomplished,
+and by detaching the sheet from the instrument
+the words may be put away in a portfolio.
+We have now to see how the instrument is
+able to reproduce what has been so easily inscribed.</p>
+
+<p>For this purpose it is only necessary to repeat
+the process, and the identical effect will be reproduced
+in an inverse sense. The tracing stylus is
+replaced at the end of the groove it has already
+traversed, and the cylinder is again set in motion.
+When the engraved track passes again under the
+point, it has a tendency to raise it and to impart to
+it movements which must necessarily be the repetition
+of those which first produced the tracing.
+The vibrating plate is obedient to these movements,
+and begins to vibrate, thus producing the same
+sounds, and consequently the same words; yet
+since there is necessarily a loss of power in this
+double transformation of mechanical effects, the
+speaking tube <span class="allsmcap">C</span> is attached to the mouthpiece <span class="allsmcap">E</span>
+in order to intensify the effects. Under these conditions
+the words reproduced by the instrument
+may be heard in all parts of a hall, and it is startling
+to hear this voice—somewhat shrill, it must
+be admitted—which seems to utter its sentences
+from beyond the grave. If this invention had<span class="pagenum" id="Page_318">318</span>
+taken place in the middle ages, it would certainly
+have been applied to ghostly apparitions, and it
+would have been invaluable to miracle-mongers.</p>
+
+<figure id="il_68" class="figcenter" style="max-width: 28em;">
+  <img src="images/i_p318.jpg" width="1087" height="906" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 68.</span>
+  </figcaption>
+</figure>
+
+<p>As the height of the notes of the musical scale
+depends on the number of vibrations effected by a
+vibrating substance in a given time, speaking will
+be reproduced in a tone of which the pitch will
+depend on the velocity of rotation given to the cylinder
+on which the tinfoil is wound. If the velocity
+is the same as that which was used in registration,<span class="pagenum" id="Page_319">319</span>
+the tone of the words reproduced is the
+same as that in which they were uttered. If the
+velocity is greater, the tone is higher; if less, the
+tone is lower; but the accent of the speaker may
+always be recognised. Owing to this peculiarity
+the reproduction of songs is nearly always defective
+in instruments turned by the hand; they sing out
+of tune. This is not the case when the instrument
+is moved by a well-regulated system of clockwork,
+and in this way a satisfactory reproduction of a
+duet has been obtained.</p>
+
+<p>The words registered on tinfoil can be often reproduced;
+but the sounds become fainter and more
+indistinct at each repetition, since the tracings in
+relief are gradually effaced. The reproduction on
+copper is more successful, but if intended to be
+permanent the sheets must be stereotyped, and in
+this case the instrument must be differently arranged.</p>
+
+<p>An attempt has been made to obtain speech
+from the phonograph by taking the words registered
+inversely to their true direction. In this way
+the sounds obtained were necessarily quite unlike
+the words uttered; yet Messrs. Fleeming Jenkin and
+Ewing have observed that not only are the vowels
+unchanged by this inverse action, but consonants,
+syllables, and even whole words may be reproduced
+with the accent they would have if spoken
+backwards.</p>
+
+<p>The sounds produced by the phonograph,<span class="pagenum" id="Page_320">320</span>
+although fainter than those of the voice which produced
+the registered tracing, are strong enough to
+react on the ordinary string telephone, and even on
+a Bell telephone; and as in this case the sounds do
+not go beyond the instrument, and can only be
+heard by the person who is using it, it is easy to ascertain
+that the sound has not been produced by
+trickery.</p>
+
+<p>Mr. Edison presented his phonograph to the
+Académie des Sciences through me, March 11, 1878,
+and when his agent, M. Puskas, caused the wonderful
+instrument to speak, a murmur of admiration was
+heard from all parts of the hall—a murmur succeeded
+by repeated applause. A letter appeared in the
+newspapers from one of the persons present, in
+which he said that ‘the learned Academy, generally
+so cold, had never before abandoned itself to such
+enthusiasm. Yet some members of a sceptical turn
+of mind, instead of examining the physical fact,
+ascribed it to moral causes, and a report soon ran
+through the room which seemed to accuse the
+Academy of having been mystified by a clever ventriloquist.
+Certainly the spirit of ancient Gaul is
+still to be found among the French, and even in
+the Academy. One said that the sounds emitted
+by the instrument were precisely those of a ventriloquist.
+Another asked if the movements of M.
+Puskas’ face and lips as he turned the instrument
+did not resemble the grimaces of a ventriloquist. A
+third admitted that the phonograph might emit<span class="pagenum" id="Page_321">321</span>
+sounds, but believed that it was much helped by
+the manipulator. Finally, the Academy requested
+M. du Moncel to try the experiment, and as he
+was not accustomed to speak into the instrument,
+it was unsuccessful, to the great joy of the incredulous.
+Some members of the Academy, however,
+desiring to ascertain the real nature of the effects,
+begged M. Puskas to repeat the experiments before
+them in the secretary’s office under such conditions
+as they should lay down. M. Puskas complied with
+this request, and they were absolutely satisfied with
+the result. Yet others remained incredulous, and
+it was necessary that they should make the experiment
+for themselves before they accepted the fact
+that speech could be reproduced in so simple a way.’</p>
+
+<p>The anecdote I have just related cannot be interpreted
+to the discredit of the Académie des
+Sciences, since it is especially bound to preserve
+the true principles of science intact, and only to
+accept startling facts after a careful examination.
+Owing to this attitude, all which emanates from the
+Academy can be received with complete confidence;
+and we cannot approve too highly of reserve which
+does not give way to the first impulse of enthusiasm
+and admiration.</p>
+
+<p>The failure of my experiment at the Academy
+was simply due to the fact that I spoke at too
+great a distance from the vibrating disk, and that
+my lips did not touch the sides of the mouthpiece.
+Some days later, at the request of several of my<span class="pagenum" id="Page_322">322</span>
+colleagues, I made repeated trials of the instrument,
+and I soon succeeded in making it speak as
+well as the supposed ventriloquist; but I learned
+at the same time that practice is necessary to ensure
+success. Some words are reproduced more readily
+than others; those which include many vowels
+and many <i>r</i>’s come out better than those which
+abound in consonants, and especially in <i>s</i>’s. It is
+therefore not surprising that, even in the case of an
+experienced manipulator like Mr. Edison’s agent,
+some of the sentences uttered by him are more audible
+than others.</p>
+
+<p>The simultaneous repetition of several sentences
+in different languages by registering one over the
+other is one of the most surprising effects of the
+phonograph. As many as three different sentences
+have been obtained; but in order to distinguish
+them through the confused sounds which result
+from placing one over the other, it is necessary that
+different persons, giving special attention to a particular
+sentence, should thus separate them and
+understand their sense. Vocal airs may, in the
+same way, be registered over the word tracings, and
+in this case it is more easy to distinguish them.</p>
+
+<p>There are several models of phonographs. The
+one represented in <a href="#il_66">fig. 66</a> has been chiefly used for
+public experiments, but there is a small model,
+generally sold to the public, in which the cylinder
+is much longer, and serves at once for register
+and fly-wheel. This instrument gives good
+results, but can only be used for short sentences.<span class="pagenum" id="Page_323">323</span>
+In this model, as indeed in the other, the words are
+more easily registered by fastening a small tube in
+the form of a prolonged speaking-trumpet to the
+mouthpiece; the vibrations of the air are thus
+concentrated on the vibrating disk, and act with
+greater energy. The tenuity of the vibrating disk
+adds to the efficiency of the instrument, and the
+tracing point may be fitted directly to this disk.</p>
+
+<figure id="il_69" class="figcenter" style="max-width: 22em;">
+  <img src="images/i_p323.jpg" width="869" height="525" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 69.</span>
+  </figcaption>
+</figure>
+
+<p>I need not describe particularly the phonograph
+which acts by clockwork. The instrument resembles
+the one represented <a href="#il_66">fig. 66</a>, except that it is mounted
+on a rather high table, to give room for the descent
+of the weight which moves the clockwork; the mechanism
+is applied directly to the axis of the cylinder,
+supplying the place of the winch, and is regulated
+by a small fly-wheel. The wheel used in an
+English system has been adopted, but we prefer
+that of M. Villarceau, which has small wings.</p>
+
+<p><span class="pagenum" id="Page_324">324</span></p>
+
+<p>Since it is always difficult to fit the tinfoil to
+the cylinder, Mr. Edison has tried, with good
+success, to obtain the tracing on a plane surface of
+tinfoil, by means of the arrangement represented
+<a href="#il_69">fig. 69</a>. In this new model, the plate on which the
+tin or copper sheet is to be applied has a spiral
+grooving, of which one end corresponds to the
+centre of the plate, and the other to its outer
+edges. The plate is set in motion by a powerful
+system of clockwork, of which the velocity is regulated
+with reference to the length of the turns of
+the spiral. The vibrating disk is arranged as in
+the former instrument, and is placed above this
+plate; the tracing point may, by means of a
+movement of progression imparted to the system,
+follow the spiral groove from the centre of the plate
+to its circumference.</p>
+
+<p>It must not be supposed that all the tinfoil
+used for phonographic registration is equally good.
+The foil must be of a definite thickness, and combined
+with a definite amount of lead. That which
+is used for wrapping chocolate, and indeed all foil
+of French manufacture, is too thin and too exclusively
+made of tin to produce good results, and M.
+Puskas was obliged to import some from America
+to continue his experiments. The relative proportion
+of lead and tin has not yet been defined, and
+the selection of foil has been made empirically;
+but as the use of the phonograph becomes more
+general, this proportion must be ascertained, and<span class="pagenum" id="Page_325">325</span>
+it may easily be done by analysing the composition
+of the foil which gives the best results.</p>
+
+<figure id="il_70" class="figcenter" style="max-width: 22em;">
+  <img src="images/i_p325.jpg" width="850" height="831" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 70.</span>
+  </figcaption>
+</figure>
+
+<p>The arrangement of the tracing point is also of
+much importance for the successful action of the
+phonograph. It must be very slender and very
+short (not exceeding a millimètre in length), so as
+to register distinctly the smallest vibrations of the
+vibrating disk without deviating from the normal
+direction of the cylinder, which might be the case,
+if it were long, on account of the unequal friction
+exerted on the tinfoil. It must also be made of a
+metal which has no tendency to tear the metallic<span class="pagenum" id="Page_326">326</span>
+sheet. Iron appears to combine most of the conditions
+demanded.</p>
+
+<p>The phonograph is still in its infancy, and it is
+probable that it may soon be enabled to register
+speech without the necessity of speaking into a
+mouthpiece. According to the newspapers, Mr.
+Edison has already discovered a way of collecting,
+without the aid of an acoustic tube, the sounds uttered
+at a distance of three or four feet from the
+instrument, and of printing them on a metallic sheet.
+From this there is only a step to the power of inscribing
+a speech uttered in a large hall at any
+distance from the phonograph; and if this step is
+taken, phonography may be substituted with advantage
+for shorthand. We add in a note the instructions
+given by M. Roosevelt to the purchasers
+of phonographs, so as to enable them to work the
+instrument.<a id="FNanchor_20" href="#Footnote_20" class="fnanchor">20</a></p>
+
+<p><span class="pagenum" id="Page_327">327</span></p>
+
+<p><i>Considerations on the theory.</i>—Although the explanation
+we have given will make the effects of the<span class="pagenum" id="Page_328">328</span>
+phonograph intelligible, it leads to a curious question
+which has greatly interested physicists—namely,
+how it is that the tracing made on so yielding a
+surface as tin can, when retraced by the stylus, of
+which the rigidity is relatively great, produce a
+vibratory movement without being completely
+destroyed. To this we reply that the retracing is
+effected with such extreme rapidity that the effects
+of active force which are developed only manifest
+themselves locally, and that under these conditions
+the mechanical effects exerted are as energetic in
+soft as in hard substances. The curious experiment,
+related in so many books on physics, must
+be remembered, of a plank pierced when a candle
+serves as the projectile of a gun. The various accidents
+caused by the discharge of paper waddings
+must also be remembered. Under such conditions
+the motion imparted to the molecules which receive
+the shock has not time to be transmitted to the
+whole mass of the substance to which they belong,
+and these molecules are compelled to separate from
+it, or at any rate to produce, when the substance is
+capable of vibration, a centre of vibration which
+diffuses waves throughout its surface, and produces
+sounds.</p>
+
+<p><span class="pagenum" id="Page_329">329</span></p>
+
+<p>Several scientific men, among others Messrs.
+Preece and Mayer, have carefully studied the form
+of the tracing left by the voice on the tinfoil of the
+phonograph, and they observe that it greatly resembles
+the outline of the singing flames so well
+shown by Herr Koenig’s instruments. Mr. Mayer
+wrote on this subject in the ‘Popular Science
+Monthly Review’ of April 1878.</p>
+
+<p>He said that he had been successful in reproducing
+a splendid tracing on smoked glass, which
+gave in profile the outline of the vibrations of sound
+registered on the tinfoil with their varying curves.
+For this purpose he fastened to the spring support
+of the tracing point of the phonograph a slender
+rod, terminating in a point, which pressed obliquely
+against the plate of smoked glass, and, since the
+latter was in a vertical position, a movement imparted
+to the rod enabled it to produce a sinusoidal
+tracing. By this arrangement, when the phonograph
+was at work, two systems of tracings were
+produced at the same moment, of which one was
+the profile of the other.</p>
+
+<p>Mr. Mayer had not, at the time he wrote, been
+long enough in possession of the instrument to
+make many experiments with it, but from a study
+of some of its curves it appeared to him that the
+registered outlines bore a strong resemblance to
+those of Koenig’s singing flames.</p>
+
+<figure id="il_71" class="figcenter" style="max-width: 21em;">
+  <img src="images/i_p330.jpg" width="813" height="347" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 71.</span>
+  </figcaption>
+</figure>
+
+<p><a href="#il_71">Fig. 71</a> represents the tracing which corresponds
+to the letter <i>a</i> when pronounced as in <em>bat</em>, in the<span class="pagenum" id="Page_330">330</span>
+three systems of registration. That corresponding
+to line A is an enlarged reproduction of the tracing
+left on the tinfoil; that corresponding to line B
+represents its profile on the sheet of smoked glass.
+Finally, line C shows the outline of Koenig’s singing
+flames, when the same sound is produced quite
+close to the membrane of the register. It must be
+quite close, since the form of the tracing produced
+by a pointer attached to a vibrating membrane,
+when influenced by composite sounds, depends on
+the distance intervening between the membrane
+and the source of sound, and an infinite variety in
+the form of the tracing may be obtained by modifying
+the distance. In fact, when this distance is
+increased, the waves of sound which result from
+composite sounds react on the membrane at
+different moments of their emission. For example,
+if the composite sound is formed of six harmonics,
+the displacement of the source of vibration from
+the first harmonic by ¼ the length of a wave will
+respectively remove the second, third, fourth, fifth,<span class="pagenum" id="Page_331">331</span>
+and sixth harmonics ½, ¾, 1, 1¼, 1½ the length of a
+wave, and consequently the outline resulting from the
+combination of waves will no longer be the same as
+it was before the displacement of the source of sound,
+although the perception of the sounds remains the
+same in both cases. This principle is clearly
+demonstrated by Koenig’s instrument, by lengthening
+and shortening an extensible tube, inserted
+between the resonator and the vibrating membrane,
+which is placed close to the flame; and this explains
+the disagreement of physicists as to the composition
+of vocal sounds which they have analysed by
+means of the singing flames.</p>
+
+<p>Mr. Mayer adds that these facts further show
+that we cannot hope to read the impressions and
+tracings of the phonograph, which not only vary
+with the nature of the voice, but also with the
+different moments at which the harmonics of the
+voice are emitted, and with the relative differences
+in the intensities of these harmonics.</p>
+
+<p>Notwithstanding this assertion, we reproduce
+(<a href="#il_72">fig. 72</a>) an extremely curious tracing sent to us by
+Mr. Blake, which represents the vibrations produced
+by the words ‘Brown, University: how do
+you do?’ They were photographed by means of
+an index fastened to a vibrating disk on which a
+ray of light was thrown. The word ‘how’ is
+particularly remarkable for the combined forms of
+the inflections of the vibrations.</p>
+
+<p>Recent experiments seem to show that the more<span class="pagenum" id="Page_332">332</span>
+the vibrating membrane of the phonograph
+resembles the human ear in its construction, the
+better it repeats and registers the sound vibrations:
+it should be stretched, as far as possible, in the
+same way as the tympanum is stretched by the
+hammer of the ear, and moreover it should have
+the same form, since the vibrations of air are in
+this case much more effective.</p>
+
+<figure id="il_72" class="figcenter" style="max-width: 24em;">
+  <img src="images/i_p332.jpg" width="931" height="795" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 72.</span>
+  </figcaption>
+</figure>
+
+<p>Mr. Edison considers that the size of the opening
+of the mouthpiece has considerable influence
+on the distinct articulation of speech. When the
+sounds are pronounced before the whole surface of<span class="pagenum" id="Page_333">333</span>
+the diaphragm, some hissing sounds are lost. They
+are, on the contrary, intensified when these sounds
+reach the diaphragm through a narrow orifice with
+sharp rims. If the opening is toothed on its flattened
+rims, the hissing consonants are delivered
+more clearly. Speech is reproduced more perfectly
+when the mouthpiece has a covering of some thickness,
+so arranged as to deaden the sounds arising
+from the friction of the tracing point on the tin.</p>
+
+<p>Mr. Hardy has rendered the registration of
+phonographic tracings more easy by adding a small
+ebonite tube, resembling the mouthpiece of a wind
+instrument, to the mouthpiece of the phonograph.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h2 class="nobreak" id="USES_OF_THE_PHONOGRAPH_AND_ITS_FUTURE"><span id="toclink_333"></span>USES OF THE PHONOGRAPH AND ITS FUTURE.</h2>
+</div>
+
+<p>Mr. Edison has lately published in the ‘North
+American Review’ of May-June 1878 an article on
+the future of the phonograph, in which he himself
+discusses the different applications which may be
+made of this instrument. Without sharing all his
+anticipations, which appear to us to be very premature,
+we think that some extracts from his paper
+may be interesting.</p>
+
+<p>‘In order to furnish a basis on which the
+reader may take his stand ... a few categorical
+questions and answers are given upon the essential
+features of the principle involved.</p>
+
+<p>‘1. Is a vibrating plate or disk capable of receiving
+a complex motion which shall correctly represent<span class="pagenum" id="Page_334">334</span>
+the peculiar property of each and all the
+multifarious vocal and other sound waves?</p>
+
+<p>‘The telephone answers affirmatively.</p>
+
+<p>‘2. Can such complex movement be transmitted
+from such plate by means of a single embossing
+point attached thereto, to effect a record
+upon a plastic material, by indentation, with such
+fidelity as to give to such indentations the same
+varied and complex form? And if so, will this
+embossing point, upon being passed over the record
+thus made, follow it with such fidelity as to transmit
+to the disk the same variety of movement, and
+thus effect a restoration or reproduction of the
+vocal or other sound waves, without loss of any
+property essential to producing on the ear the
+same sensation as if coming direct from the original
+source?</p>
+
+<p>‘The answer to this may be summed up in
+a statement of the fact that ... the writer has
+at various times during the past weeks reproduced
+these waves with such degree of accuracy in each
+and every detail as to enable his assistants to read,
+without the loss of a word, one or more columns of a
+newspaper article unfamiliar to them, and which
+were spoken into the apparatus when they were
+not present. The only perceptible loss was found
+to be in the quality of the utterance, a non-essential
+in the practical application of the instrument.
+Indeed, the articulation of some individuals has
+been perceptibly improved by passage through the<span class="pagenum" id="Page_335">335</span>
+phonograph, the original utterance being mutilated
+by some imperfection of lip and mouth formation,
+and these mutilations corrected or eliminated by
+the mechanism of the phonograph.<a id="FNanchor_21" href="#Footnote_21" class="fnanchor">21</a></p>
+
+<p>‘3. Can a record be removed from the
+apparatus on which it was made, and replaced
+upon a second without mutilation or loss of
+effective power to vibrate the second plate?</p>
+
+<p>‘This is a mere mechanical detail, presenting
+no greater obstacle than having proper regard for
+the perfect interchangeableness of the various
+working parts of the apparatus—not so nice a
+problem as the manufacture of the American
+watch.</p>
+
+<p>‘4. What as to the facility of placing and removing
+the second sheet, and as to its transportation
+by mail?</p>
+
+<p>‘But ten or fifteen seconds suffice for such placing
+or removing. A special envelope will probably
+be required, the weight and form of which, however,
+will but slightly increase the cost of postage.</p>
+
+<p>‘5. What as to durability?</p>
+
+<p>‘Repeated experiments have proved that the
+indentations possess wonderful enduring power,
+even when the reproduction has been effected by
+the comparatively rigid plate used for their
+production. It is proposed, however, to use a<span class="pagenum" id="Page_336">336</span>
+more flexible plate for reproducing, which, with a
+perfectly smooth stone point—diamond or sapphire—will
+render the record capable of from fifty to
+one hundred repetitions, enough for all practical
+purposes.</p>
+
+<p>‘6. What as to duplication of a record and its
+permanence?</p>
+
+<p>‘Many experiments have been made, with
+more or less success, in the effort to obtain electrotypes
+of a record, and the writer is informed that it
+has very recently been successfully accomplished.
+He can certainly see no great practical obstacle in
+the way. This, of course, permits of an indefinite
+multiplication of a record, and its preservation for
+all time.</p>
+
+<p>‘7. What is the requisite force of wave impinging
+upon the diaphragm, and the proximity of the
+mouth to the diaphragm, to effect a record?</p>
+
+<p>‘These depend in great measure upon the
+volume of sound desired in the reproduction. If
+the reproduction is to be made audible to an
+assembly, considerable force is requisite in the
+original utterance; if for the individual ear, only
+the ordinary conversational tone (even a whisper
+has been reproduced). In both cases the original
+utterances are delivered directly in the mouthpiece
+of the instrument. An audible reproduction
+may, however, be had by speaking at the instrument
+from a distance of from two to three feet in loud
+tone. The application of a flaring tube or funnel
+to collect the sound waves, and the construction of<span class="pagenum" id="Page_337">337</span>
+an especially delicate diaphragm and embossing
+point, &amp;c., are the simple means which suggest
+themselves to effect this....</p>
+
+<p>‘The foregoing presentment of the stage of
+development reached by the several essential
+features of the phonograph demonstrates the
+following <i lang="fr">faits accomplis</i>:</p>
+
+<p>‘1. The captivity of all manner of sound
+waves, hitherto designated as “fugitive,” and their
+retention.</p>
+
+<p>‘2. Their reproduction with all their original
+characteristics, without the presence or consent
+of the original source, and after the lapse of any
+period of time.</p>
+
+<p>‘3. The transmission of such captive sounds
+through the ordinary channels of commercial intercourse
+and trade in a material form, for purposes of
+communication.</p>
+
+<p>‘4. Indefinite multiplication and preservation
+of such sounds, without regard to the existence or
+non-existence of the original source.</p>
+
+<p>‘5. The captivation of sounds, with or without the
+knowledge or consent of the source of their origin...</p>
+
+<p>‘The apparatus now being perfected in
+mechanical details will be the standard phonograph,
+and may be used for all purposes, except
+such as require special form of matrix, such as
+toys, clocks, &amp;c., for an indefinite repetition of the
+same thing. The main utility of the phonograph
+being, however, for the purposes of letter-writing<span class="pagenum" id="Page_338">338</span>
+and other forms of dictation, the design is made
+with a view to its utility for that purpose.</p>
+
+<p>‘The general principles of construction are, a flat
+plate or disk, with spiral groove on the face, worked
+by clockwork underneath the plate; the grooves are
+cut very closely together, so as to give a great total
+length to each length of surface—a close calculation
+gives as the capacity of each sheet of foil nearly
+40,000 words. The sheets being but ten inches
+square, the cost is so trifling that but a hundred words
+might be put on a single sheet economically....</p>
+
+<p>‘The practical application of this form of
+phonograph is very simple. A sheet of foil is
+placed in the phonograph, the clockwork set in
+motion, and the matter dictated into the mouthpiece
+without other effort than when dictating to a
+stenographer. It is then removed, placed in suitable
+form of envelope, and sent through the
+ordinary channels to the correspondent for whom
+it is designed. He, placing it upon his phonograph,
+starts his clockwork, and <em>listens</em> to what his
+correspondent has to say.’</p>
+
+<p>Since this paper by Mr. Edison appeared in
+June 1878, he has applied the phonograph to
+several other purposes, among which we may
+mention that of registering the force of sounds on
+railways, and especially on the metropolitan
+atmospheric railway in New York. The instrument
+which he has made for this purpose resembles
+that by Mr. Leo Scott, and bears the same name.<span class="pagenum" id="Page_339">339</span>
+It is described and represented in the ‘Daily
+Graphic’ of July 19, 1878, as well as the aerophone,
+the megaphone, and the microtasimeter, which is
+adapted for astronomical observations. We should
+exceed the limits laid down for this volume, if we
+were to give a more detailed account of these
+inventions.</p>
+
+<p>M. Lambrigot, one of the officials on the
+telegraphic lines in France, and the author of
+various improvements in the Caselli telegraph, has
+shown me a phonographic system of his own
+invention in which it is reduced to its simplest
+form. He sent me the following description of his
+system.</p>
+
+<p>‘The instrument consists of a wooden slab
+placed vertically on a stand and firmly fixed upon
+it. There is a round opening in the middle of the
+slab, covered by a tightly stretched sheet of
+parchment bearing a steel knife, which, like the
+tracing point of the phonograph, is intended to
+trace the vibrations. A solid block rises from
+the stand to the middle of the slab, and supports a
+slide on which a runner can move in front of the
+slab. There is a strip of glass on this runner, of
+which one side is covered with stearine. When the
+runner is moved to and fro, the stearine comes in
+contact with the knife and takes the mould of its
+form, which is curved throughout.</p>
+
+<p>‘A sound places the sheet of parchment in
+vibration, and imparts its movement to the knife,<span class="pagenum" id="Page_340">340</span>
+which traces various lines on the surface of the
+stearine.</p>
+
+<p>‘The reproduction thus obtained on the strip of
+glass is subjected to the ordinary processes of metallisation.
+By galvanism a deposit of copper is
+obtained which reproduces the lines in an inverse
+way. In order to make the metallic plate speak,
+it is necessary to pass a point of ivory, wood,
+or horn lightly over the signs, and, by moving it
+more or less quickly, the different tones can be
+heard, just as they were spoken.</p>
+
+<p>‘Since copper is relatively harder than lead, the
+copper plate on which the vibrations are traced
+will afford an unlimited number of reproductions.
+To obtain this result, a lead wire must be applied
+to the plate, and due pressure must be exerted on
+it. The wire is flattened and takes the impression
+of all the traces which then appear in relief.
+If the edge of a card is passed through this impressed
+tracing, the same sounds are produced as
+those which are obtained from the copper plate.’</p>
+
+<p>M. Lambrigot suggests that the speaking plates
+might be useful in many ways: for example, they
+might make it easy to learn the correct pronunciation
+of foreign languages, since a sufficient number
+might be collected to make a sort of vocabulary
+which would give the accent of the words most in
+use in a given language.</p>
+
+<p>By this simple process M. Lambrigot has been
+able to obtain a strong impression, within a copper<span class="pagenum" id="Page_341">341</span>
+groove, of the vibrations caused by the voice, and
+they are so distinctly engraved that whole sentences
+may be heard, if they are retraced by the sharpened
+point of a match. It is true that the reproduction
+is imperfect, and that those words are only to be
+distinguished which were previously known; but it
+is possible that better results will be obtained from
+improvements in the system, and at any rate
+the distinct impression of the vibrations of the
+voice on a hard metal is a really interesting discovery.</p>
+
+<p>I have made one somewhat important observation
+in the working of the phonograph—namely,
+that if speech is registered on the instrument in a
+very hot room, and it is then carried to a colder
+room, the reproduction of speech is imperfect in proportion
+to the difference of temperature. This is
+probably owing to considerable modifications in the
+elasticity of the caoutchouc pad which is inserted
+between the tracing point and the vibrating disk:
+perhaps differences of expansion in the tinfoil
+have also some effect.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<h2>FABER’S AMERICAN SPEAKING MACHINE.</h2>
+
+<p>About two years ago the newspapers announced
+with some pomp that a speaking machine had
+reached Paris, which far surpassed Vaucanson’s
+duck, and which would attract general attention.
+Unfortunately the invention was not in the first<span class="pagenum" id="Page_342">342</span>
+instance brought forward with any scientific
+authority, and was soon relegated to take a place
+among the curiosities exhibited by conjurors. In
+a country so essentially critical and sceptical as
+France, there are always those who profess incredulity,
+and who will even resist evidence, and it was
+asserted that the machine only spoke because its
+exhibitor was an able ventriloquist. This is an old
+assertion which has lately been made with reference
+to the phonograph. Some scientific papers echoed
+the absurdity, and the speaking machine was so
+discredited that it is now unnoticed, although it is a
+most ingenious and interesting conception. When
+will our country be cured of the error of denying
+everything without due examination?</p>
+
+<p>Since we ourselves only judge of things after
+having seriously considered them, we think it just
+to vindicate the truth as to Mr. Faber’s machine,
+and this can only be done by an exact description
+of it.</p>
+
+<p>As I said in the last chapter, there is a great
+difference between the production and the reproduction
+of a sound, and a machine like the phonograph,
+adapted for the reproduction of sound,
+may differ essentially from a machine which really
+speaks. In fact, the reproduction even of articulate
+sounds may be very simple, as soon as we possess
+the means of stereotyping the vibrations of air
+necessary to transmit these sounds; but in order
+to produce them, and especially to emit the complex<span class="pagenum" id="Page_343">343</span>
+vibrations which constitute speech, it is
+necessary to set in motion a number of special
+organs, fulfilling more or less exactly the functions
+of the larynx, the mouth, the tongue, the lips, and
+even the nose. For this reason, a speaking machine
+is necessarily very complicated, and this is precisely
+the case with the machine we are now considering.
+Such a machine is not now made for the first time,
+and the Academy has lately been reminded of a
+speaking head which was in the possession of the
+philosopher Albertus Magnus in the thirteenth
+century, and which was destroyed by St. Thomas
+Aquinas as a diabolical invention.</p>
+
+<p>Mr. Faber’s speaking machine was exhibited two
+years ago at the Grand Hôtel, and may now be seen
+in the room adjoining M. Robert Houdin’s theatre,
+the same room in which Mr. Giffard exhibited the
+telephone. It consists of three distinct parts: 1st,
+of a large bellows worked by a pedal, which produces
+the currents of air necessary for the production
+of sounds, and to some extent acts as the
+lungs; 2nd, a vocal instrument, consisting of a
+larynx accompanied by diaphragms of various
+forms to modify the sounds, of a mouth with
+caoutchouc lips and tongue, and of a tube with an
+outlet somewhat resembling the nasal cavities;
+3rd, of a system of jointed levers and of pedals,
+terminating in keys like those of a piano.</p>
+
+<p>The most interesting part of the machinery, of
+which we represent the principle <a href="#il_73">fig. 73</a>, is the<span class="pagenum" id="Page_344">344</span>
+vocal apparatus, which involved the severest study
+of physics in order to succeed in the production of
+articulate sounds. It consists, first, of a rather
+thick caoutchouc tube, within which there is a kind
+of whistle <span class="allsmcap">L</span>, as in a clarionet. The whistle consists
+of a small caoutchouc cylinder with a longitudinal
+slit, and before this is placed a very thin ivory
+plate lined with caoutchouc. This plate is fixed
+at one end to the cylinder, and deviates slightly
+from it at its free end, so as to permit the current
+of air projected from the bellows <span class="allsmcap">S</span> to penetrate
+between the two parts, and to cause the vibrations
+in the ivory plate necessary for the production of
+a sound. The extremity of the caoutchouc cylinder
+is closed on this side, and is fitted to an iron rod <i>t</i>
+which comes out of the pipe, and is connected
+with a system of bars, corresponding to the keyboard
+of a piano, by which the force of sounds
+can be regulated. This force depends on the width
+of the opening between the tongue and the cylinder.</p>
+
+<figure id="il_73" class="figcenter" style="max-width: 22em;">
+  <img src="images/i_p345.jpg" width="863" height="764" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 73.</span>
+  </figcaption>
+</figure>
+
+<p>The whistle, which plays the part of the
+larynx, is necessarily placed opposite the opening of
+the bellows, and a sort of tourniquet <span class="allsmcap">M</span> is fastened
+to the opening itself, which is able to move on
+certain conditions, so that it may produce the
+rolling sound of <i>r</i>. This is done by fastening before
+the opening a diaphragm in which there is a somewhat
+wide and long slit, and this slit can be almost
+closed by a little bar of the same size <span class="allsmcap">M</span>, revolving
+on a transverse axis which supports it by its<span class="pagenum" id="Page_345">345</span>
+centre. In its normal condition, this little bar is
+kept in a slanting position by cords attached to
+the keyboard, and the air ejected by the bellows
+readily traverses the slit in order to reach the
+larynx; but two dampers are fastened to the rods
+which transmit movement, with which the cords
+just mentioned are also connected. On lowering
+the notes of the key-board, the passage of air is contracted,
+and the little plate begins to oscillate and to
+press against a band of leather, producing by its
+vibration an action similar to that produced by the
+cricket. This little tourniquet only begins to act
+when the dampers are lowered by a pedal worked<span class="pagenum" id="Page_346">346</span>
+by the hand; and this is also the case with the iron
+rod <i>t</i>, which modifies the acuteness of the sounds
+passing through the larynx.<a id="FNanchor_22" href="#Footnote_22" class="fnanchor">22</a></p>
+
+<p>Below the larynx tube, which is only five
+centimètres in length, there is another pipe <span class="allsmcap">G</span>,
+also of caoutchouc, which terminates in a spherical
+cavity connected with the outer air by a caoutchouc
+tube <span class="allsmcap">I</span>, slightly raised, and closed by a valve, of
+which the movements are regulated by a pedal
+worked by the keyboard. When the valve is
+open, the sounds emitted through the larynx are
+somewhat nasal.<a id="FNanchor_23" href="#Footnote_23" class="fnanchor">23</a> The larynx communicates with
+the mouth through a square funnel-shaped pipe,
+to which six metallic diaphragms <span class="allsmcap">D</span> are fastened;
+the diaphragms are placed in a vertical position
+behind each other, and have indentations on their
+lower end, which are intended to diminish more or
+less the orifice for the current of air, and to impede
+its passage with greater or less force. The diaphragms,
+which we represent separately <a href="#il_74">fig. 74</a>, are
+connected with the keyboard by jointed iron rods <i>t</i>,
+and, for the emission of most articulate sounds,<span class="pagenum" id="Page_347">347</span>
+several of the diaphragms are moved at the same
+moment and at different heights. We shall return
+to this subject.</p>
+
+<figure id="il_74" class="figcenter" style="max-width: 18em;">
+  <img src="images/i_p347.jpg" width="719" height="726" alt="">
+  <figcaption class="caption"><span class="smcap">Fig. 74.</span>
+  </figcaption>
+</figure>
+
+<p>The mouth consists of a caoutchouc cavity <span class="allsmcap">O</span>,
+somewhat resembling the human mouth, and forming
+a continuation to the channel we have just described.
+The tongue <span class="allsmcap">C</span>, likewise modelled on the human
+tongue, is placed within the mouth, and connected
+with two jointed rods <i>t</i>, <i>t</i>, fastened to its two
+opposite ends, so as to enable the tongue to raise
+its tip, or touch the palate, in obedience to the
+notes of the keyboard. The lower caoutchouc lip
+<span class="allsmcap">A</span> can also be more or less closed, according to the<span class="pagenum" id="Page_348">348</span>
+action of the keyboard on its special rod. Finally,
+a circular metallic piece <span class="allsmcap">E</span>, following the shape of
+the mouth, is placed above the upper lip, with a
+small opening in it to admit of the pronunciation
+of the letter <i>f</i>.</p>
+
+<p>The keyboard has fourteen notes, of different
+lengths, producing the following letters when
+lowered, <i>a</i>, <i>o</i>, <i>u</i>, <i>i</i>, <i>e</i>, <i>l</i>, <i>r</i>, <i>v</i>, <i>f</i>, <i>s</i>, <i>ch</i>, <i>b</i>, <i>d</i>, <i>g</i>. The
+longest corresponds to <i>g</i>, and the shortest to <i>a</i>.
+There are two pedals below the <i>g</i> note and those
+of <i>b</i> and <i>d</i>, corresponding with the opening of the
+tube which produces nasal sounds, and to the rod
+which regulates the opening of the larynx, and
+this makes it possible to obtain <i>p</i>, <i>t</i>, and <i>k</i> from the
+notes <i>b</i>, <i>d</i>, <i>g</i>. The mechanical effects produced by
+lowering the different notes in succession are as
+<span class="locked">follows:—</span></p>
+
+<p>1. The <i>a</i> note moves the first five diaphragms.</p>
+
+<p>2. <i>o</i> also moves these five diaphragms, but
+varies the pitch, and closes the mouth a little.</p>
+
+<p>3. <i>u</i> does the same, only further closing the
+mouth.</p>
+
+<p>4. <i>t</i> moves a single diaphragm, raises the tip of
+the tongue, and opens the mouth more widely.</p>
+
+<p>5. <i>e</i> moves six diaphragms, throws the tongue
+further back, and opens the mouth still more.</p>
+
+<p>6. <i>l</i> moves five diaphragms, sends the tongue
+against the palate, and further opens the mouth.</p>
+
+<p>7. <i>r</i> moves six diaphragms and the tourniquet,
+lowers the tongue, and somewhat closes the mouth.</p>
+
+<p><span class="pagenum" id="Page_349">349</span></p>
+
+<p>8. <i>v</i> moves five diaphragms, almost closes the
+mouth, and keeps the tongue down.</p>
+
+<p>9. <i>f</i> lowers the circular appendix of the upper
+lip, and almost entirely closes the mouth.</p>
+
+<p>10. <i>s</i> moves three diaphragms, half closes the
+mouth, and half raises the tongue.</p>
+
+<p>11. <i>ch</i> moves three diaphragms, keeps the
+mouth half closed, and further lowers the tongue.</p>
+
+<p>12. <i>b</i> moves five diaphragms, closes the mouth,
+and keeps the tongue completely down.</p>
+
+<p>13. <i>d</i> moves six diaphragms, keeps the mouth
+three parts closed, and raises the tongue a little.</p>
+
+<p>14. <i>g</i> moves five diaphragms, keeps the mouth
+three parts closed, and the tongue completely down.</p>
+
+<p><i>m</i> is produced by lowering note <i>b</i> and opening
+the valve of the pipe which gives nasal sounds.</p>
+
+<p><i>n</i> is obtained by lowering note <i>d</i> and opening
+the same valve.</p>
+
+<p><i>h</i> is obtained from note <i>s</i> by lowering the pedal
+which acts upon the larynx, and half closing it.</p>
+
+<p>Since the other letters of the alphabet are compound
+sounds, they can be produced by combinations
+of the preceding letters.</p>
+
+<p>Although the words pronounced by this
+machine are distinct, they are spoken in a uniform,
+drawling tone, which might, I should have thought,
+have excluded the idea of imposition. Some of
+them are indeed far from distinct, yet the results
+are not less remarkable; and when we consider the
+amount of study and experience which must have<span class="pagenum" id="Page_350">350</span>
+been applied to the combination of all these
+arrangements, it seems surprising that physicists
+have not given more attention to such an interesting
+machine.</p>
+
+<p>As for the mechanical execution, it is impossible
+to admire too highly the simple and ingenious
+manner in which all the complicated movements
+of the different vocal organs have been connected
+with the keyboard, of which the mechanism has
+been so calculated as only to produce the precise
+action of the organ which is required for any
+given effect. For this purpose, the notes of the
+keyboard regularly increase in length, so as to
+produce at a single touch different mechanical
+effects on the rods which act upon the mechanism;
+and since most of the notes are required to react
+simultaneously on the whole mechanism, the rods
+which transmit the movement are fastened to a
+series of jointed levers which cross the notes of the
+keyboard at right angles. Pegs of different length
+are fastened to the notes at this junction, so as to
+produce the simultaneous action of the different
+organs of the machine.</p>
+
+<p>The public will believe that the assertions of
+ventriloquism are unfounded when I add that I
+myself have made the machine speak.</p>
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<p><span class="pagenum" id="Page_351">351</span></p>
+
+<h2 class="nobreak" id="APPENDIX"><span id="toclink_351"></span>APPENDIX.</h2>
+</div>
+
+<p><i>The Perrodon System of Telephonic Alarum.</i>—Captain
+Perrodon, of the French Artillery, has lately improved the
+system invented by MM. Dutertre and Gouault, by a
+self-acting call. For this purpose he has fastened a spring
+contact before the diaphragm, combined with the diaphragm
+and the electro-magnetic system so as to form a
+vibrator. The vibrations thus produced are strong
+enough to resound in an ordinary telephone, so as to
+make the call audible in spite of external noises.</p>
+
+<p>The system has been arranged in different ways. In
+one arrangement, a small plate of tinfoil is glued to the
+outer surface of the diaphragm, and the end of the telephone
+coil wire is connected, below the inner surface of
+the mouthpiece, with a silver wire soldered to a spring
+plate, which constitutes the contact of the vibrator. This
+spring plate, slightly curved, is fixed below one of the
+binding-screws of the telephone, and terminates at its
+free end in a regulating screw by which the interval
+between the contacts can be regulated, and the instrument
+can be arranged as a telephonic organ. To do this, the
+screw can be withdrawn, and inserted in a nut which
+establishes direct connection between the line and the<span class="pagenum" id="Page_352">352</span>
+telephone coil. It is easy to adapt an ordinary telephone
+to this system.</p>
+
+<p>In another arrangement M. Courtot’s mirror telephone
+has been employed, and a sort of spring pedal is inserted
+in the wood of the mouthpiece, which terminates in a
+bent silver wire, supporting an index adapted to make a
+contact with a square plate soldered to the diaphragm.
+The battery is placed in connection with the spring of the
+pedal, and one end of the telephone coil-wire communicates
+as before with the diaphragm. When a call is to be
+made, the pedal must be pressed, and the battery immediately
+communicates with the silver wire which, with
+the diaphragm, constitutes the vibrator, and an electric
+vibration is sent through the circuit, and produces the
+call. For receiving, the pedal is allowed to revert to its
+normal position, and the index of the pedal, touching
+the contact in connection with the diaphragm, establishes
+direct communication between the two telephones, while
+breaking the contact of the silver wire with the diaphragm,
+so that the battery cannot act.</p>
+
+<p>It appears that experiments made at the musketry
+school at Orleans for a distance of 370 miles have been
+very successful.</p>
+
+<p><i>M. Varey’s Microphone Speaker.</i>—M. Varey has
+recently arranged a successful microphonic speaker, in
+which the principle of the microphone represented in <a href="#il_39">fig. 39</a>
+is maintained. The system of three vertical carbons is
+arranged inside a sort of snuff-box, of which the lid is
+made of a thin plate of mica, horn, or ebonite. The
+snuff-box is provided with two hinged arms, so that it
+may be placed in the most convenient position for speaking,
+and at the same time the sensitiveness of the instrument
+can be regulated. A small battery, consisting of
+two Gaiffe cells of chloride of silver, is placed in the<span class="pagenum" id="Page_353">353</span>
+pedestal on which the instrument stands, and sets the
+microphone at work without further trouble. In this
+way the speaker can be used like an ordinary telephone,
+and is not affected by vibrations of air. Only vibrations
+of sound react upon it.</p>
+
+<p><i>Microphonic Speaker by Fitch.</i>—Mr. Pope states that
+this speaker has produced excellent results in America.
+It is merely Edison’s carbon telephone reduced to its
+simplest form. It consists of a small cylindrical box,
+which has a mouthpiece like the one represented <a href="#il_28">fig. 28</a>.
+The box contains two carbon disks of the same diameter
+as itself, and is lined with a kind of felt. Metal wires,
+inlaid in a groove scooped on the circumference of the
+carbons, place them in communication with the circuit
+and battery, and transmission takes place by means of the
+vibrations of the upper carbon, which is directly influenced
+by the voice without the intervention of any diaphragm.
+These vibrations, which can be freely developed in consequence
+of the elasticity of the felt pad which supports
+the lower carbon, produce on the surface of contact of
+the two carbons the modifications of intensity of current
+necessary for the reproduction of speech, in the same way
+as other microphones.</p>
+
+<p>An induction coil is necessarily employed for a long
+circuit, and the effects of induction in the adjacent
+wires are modified by two rheostats introduced into the
+circuit at its two extremities.</p>
+
+<p><i>Further remarks on the theory of the Telephone.</i>—Following
+the example of a certain sceptic in the Académie
+des Sciences, Colonel Navez continues to maintain the
+theory first formed as to the mode in which the telephone
+acts, in spite of the clearest proofs of its insufficiency;
+but most scientific men who consider the question have
+come round to our opinion, and admit the concurrence<span class="pagenum" id="Page_354">354</span>
+of several causes in the reproduction of speech by this
+remarkable instrument. Mr. Fleeming Jenkin writes to
+this effect in the new edition of a treatise on Electricity
+and Magnetism.</p>
+
+<p>He observes that a singular fact has been discovered
+by several persons, who have ascertained that not merely
+non-magnetic and non-conducting bodies can be substituted
+for the diaphragms of receiving telephones, but
+that they will act without a diaphragm at all. In this
+case it is evident that we have to do with the sounds
+discovered by Page, and that they are produced by the
+magnet itself, in which each molecular movement constitutes
+the source of the sound produced. This sound
+becomes articulate as soon as its increase and decrease
+can follow the increasing or decreasing action of the voice
+which produces it at the sending station. It is certain
+that when the transmitted currents are due to the action
+of the Bell diaphragm, the sounds due to the Page effects
+ought to correspond with those which would be given by
+iron diaphragms adapted to the receiving instruments;
+so that, when a telephone has an iron diaphragm, there are
+in fact two voices, that of the diaphragm, which is strong,
+and that of the magnet, which is weak. When a disk of
+wood is substituted for one of iron, it acts as a sounding
+board for the Page effect, and when the disk is of metal,
+induction is developed by the magnetic modifications, and
+tends to produce vibration, thus developing a third source
+of sound, which may be called the Ampère effect.
+Finally, a fourth source of sound may result from the
+induced effects produced in the wire itself in consequence
+of changes in the intensity of current. These sounds,
+first observed by M. de la Rive, have since been studied
+by Mr. Fergusson of Edinburgh (vide ‘Telegraphic
+Journal’ of November 1, 1878).</p>
+
+<p><span class="pagenum" id="Page_355">355</span></p>
+
+<p>Mr. Fleeming Jenkin’s opinion only differs from mine
+in his ascribing the energy of sound acquired by a telephone
+with an iron diaphragm to the preponderance of
+sounds in the latter, whereas I consider it to be chiefly
+due to the increase of energy in the whole magnetic
+system produced by the reaction of the two magnetic
+parts on each other. If the two effects could be taken
+singly, it is probable that the sounds produced by each
+of them separately would be similar, since in magnetic
+effects the reaction and action are equal. But as
+they are combined, it becomes difficult to assign to each
+the share which belongs to it in the general effect
+observed. Besides, it is quite possible that the sounds
+of the diaphragm may appear to be stronger and more
+distinct because it is nearer to the ear than the magnet,
+and because the effects of magnetisation and demagnetisation
+are then more easily produced in consequence of
+the mass of the magnetic body being smaller.</p>
+
+<p>Mr. Fleeming Jenkin goes on to say that the question
+of the displacement of surface in the diaphragm and
+magnet is very complex, but that he thinks it impossible
+to deny the existence of such displacement, since the air
+which acts as the vehicle of sound between the ear and
+the source of sound is placed in vibration; yet this displacement
+maybe effected quite otherwise than by flexion.
+Suppose that the magnetic molecules of these bodies are
+drawn together by magnetisation, which tends to diminish
+the intermolecular space which separates them, the points
+of surface of the substance corresponding to these intervals
+will be elevated in a manner equivalent to a displacement
+of surface, and the effect of this will be the
+same as a flexion movement. At the moment of demagnetisation
+a depression instead of an elevation will take
+place, and the vibratory movements will thus be produced<span class="pagenum" id="Page_356">356</span>
+without any electro-magnetic attraction, and it is precisely
+these vibrations which Mr. Fleeming Jenkin terms molecular
+vibrations. He evidently does not mean that such
+attractions cannot take place: they may react, together
+with the molecular vibrations, when the electric force is
+capable of producing them. He adds that the reproduction
+of sounds by a condenser, by simple coils, and by a
+carbon microphone, has convinced him that the action
+just analysed requires generalisation.</p>
+
+<p>We have recently seen an article by Mr. Hughes in
+the ‘Telegraphic Journal,’ Nov. 15, 1878, in which, to our
+surprise, he not only opposes all the theories he has
+hitherto held, but cites experiments which are quite
+inconclusive, since they were performed under conditions
+in which electro-magnetic effects must necessarily be displayed.
+He made use of voltaic currents produced by a
+battery of three Daniell cells. In order to estimate the
+transverse effects resulting in such a case from attraction,
+the experiments he mentions are wholly unnecessary:
+they may be felt with the hand. On the other hand, he
+has evidently forgotten that the currents employed in a
+Bell telephone have no influence on a very sensitive
+galvanometer.</p>
+
+<p><i>M. Pollard’s Microphone.</i>—This microphone, which
+has been arranged in several ways, essentially consists of
+a carbon rod kept in a horizontal position by a wire, and
+resting on two other vertical carbons. The upright of
+the arm which holds the wire can revolve together with
+this arm, and is thus able to regulate the pressure of the
+horizontal carbon on the two vertical carbons. It appears
+that this instrument is extremely sensitive, and that the
+regulation effected on the two contacts is better than when
+it is effected on one only. It is fair to add that M.<span class="pagenum" id="Page_357">357</span>
+Voisin previously sent me the sketch of a somewhat
+similar arrangement.</p>
+
+<p>M. Dutertre has also made use of such an arrangement
+in what he calls the Dolmen microphone. Three
+pieces of coke in the form of a dolmen, that is, two uprights,
+supporting a third and horizontal carbon, are
+placed in circuit. M. Gouault has informed me that
+speech was well transmitted by this instrument, and it is,
+like that of Mr. Blyth, which succeeded it, of wonderful
+simplicity.</p>
+
+<p>This microphone, as well as one composed of two
+pieces of lead-pencil placed in a watch-case, and connected
+by a piece of money, were exhibited to the
+Industrial Society at Rouen, February 1, 1878, of which
+an account was published in the Bulletin of that society.</p>
+
+<p><i>M. Ader’s Electrophone.</i>—M. Ader has recently constructed
+a remarkable telephonic instrument, which
+reproduces speech and song in a quite exceptional and
+simple way. It consists of a drum 15 centimètres in
+diameter, covered with parchment at one end only. Six
+small tin armatures, one centimètre in length and two
+millimètres in width, are fixed in the centre of the parchment
+in a circle six centimètres in diameter. Six
+microscopic electro-magnets, whose distance from the
+armatures can be regulated by a screw, are placed
+opposite the armatures within a wooden circle. The
+magnets are horseshoe, with branches 12 millimètres long
+and 4 millimètres in diameter, including the coils, and the
+magnetic core is 1½ millimètre thick. They are all in
+connection, and act simultaneously under the sole influence
+of the battery current. The sender is the same
+as that of M. Ader described before. With this instrument
+speech may be heard at a distance of six or seven<span class="pagenum" id="Page_358">358</span>
+yards, and songs are much more distinctly heard than in
+the singing condenser. Owing to the simplicity of the
+arrangement, the instrument is not costly.</p>
+
+<p>The extraordinary effects of this telephone are due to
+the small size of the electro-magnets, which, as we believe,
+produce much more rapid magnetic effects than those of
+larger size. M. Ader has also made a small ordinary
+telephone based on this principle, of which the sounds
+are much stronger than in others.</p>
+
+<p><i>Modification of Bell Telephone.</i>—Mr. Gower has recently
+made a new system of telephone without a battery,
+which not only reproduces speech loudly enough to be
+heard at the distance of eight or nine yards from the instrument,
+but will also transmit it when the speaker is at
+a moderate distance from the sending instrument. In
+this latter case, indeed, the receiving telephone must be
+brought close to the ear. Although this double problem
+had already been solved by the use of telephones with
+microphonic senders, the results furnished by the instruments
+in question are still more curious, since they are
+obtained without batteries, and are even more distinct.</p>
+
+<p>In this new system, which is only an improvement on
+Bell’s square model, the horseshoe magnet is of a
+peculiar form, which renders it more powerful. It is
+formed of a kind of half-circle of magnetised steel, with
+its two ends turned back, so as to form a diameter of the
+circle, only this diameter is divided in the centre: so that
+the two poles of the magnet are placed one before the
+other, as in Faraday’s electro-magnet. The poles are
+tipped with iron, terminating in front in two thin iron
+plates, on which are placed the electro-magnetic coils,
+which are oblong, and constitute the magnetic core.
+The diaphragm, thicker than the ordinary diaphragms, is
+of tin, and is fixed firmly to the edges of the circular box<span class="pagenum" id="Page_359">359</span>
+which encloses the whole, and which forms a kind of
+sounding-box. The box is made of copper, and the
+diaphragm is so firmly fastened to it as to become
+homogeneous with it, and to give out a sound when the
+box is touched, which is not the case in ordinary telephones.
+This is one of the conditions which make the
+instrument a better conductor of sound. The magnet is
+also much more powerful. It is magnetised by a current
+from a powerful Gramme machine, which acts upon it for
+almost twenty minutes. The instrument has, strictly
+speaking, no mouthpiece: the lid of the box which
+supports the diaphragm, and is separated from it by a
+space of two millimètres, has merely a hole bored in it
+above the centre of the diaphragm, and into this hole
+either a tin trumpet, 50 centimètres in length, is screwed,
+when the instrument is required to reproduce or transmit
+speech to a distance, or an acoustic tube when it is to
+be used like an ordinary telephone. The remarkable
+part of the system is that the instrument can itself give
+a very loud call by only breathing into it instead of
+speaking.</p>
+
+<p>For this purpose a small oblong opening is made in
+the diaphragm at a half diameter from its centre, and
+behind this the reed of an harmonium is applied to a
+square copper plate fixed on the diaphragm itself. On
+using the bellows the expelled air passes through this
+little hole, and, on reaching the reed, sets it in vibration,
+and produces a sound of which the acuteness
+depends on the conditions of the vibrating plate. This
+addition to the diaphragm in no way alters its properties
+in the reproduction of speech, so that, after using the
+bellows, conversation may begin, and the receiving telephone
+repeats what is said after emitting a sound somewhat
+resembling the note of a bugle. The instrument<span class="pagenum" id="Page_360">360</span>
+is then provided with the speaking tube of which we have
+spoken.</p>
+
+<p>Nothing can be more remarkable than this power of
+listening to conversation while seated in an armchair
+six or seven yards from the instrument, nor is it necessary
+to move in order to reply. The correspondent, indeed,
+must be close to the acoustic tube in order to speak and
+listen, and he must speak rather loud in order to be
+heard at any distance from the other station. But the
+listener receives the sounds so amplified that it might be
+supposed that a giant was speaking, and conversation
+held in a low tone may even be distinguished. These
+results are really extraordinary, and even to those
+familiar with such effects this incessant progress is surprising.</p>
+
+<p>These results may be ascribed to the following
+<span class="locked">causes:—</span></p>
+
+<p>1. First, that the conditions of the magnet are better
+than those of ordinary instruments.</p>
+
+<p>2. That the diaphragm is also thicker, larger, and
+better stretched.</p>
+
+<p>3. That the box is of metal, and calculated to act as
+a sounding-box.</p>
+
+<p>4. The speaking trumpet magnifies the sounds.</p>
+
+<p>5. The acoustic tubes concentrate the sound waves
+on the centre of the diaphragm.</p>
+
+<p><i>Note on some fresh Experiments with Telephones
+without any Diaphragm.</i></p>
+
+<p>In a paper published March 4, 1878, I made some
+suggestions on the theory of the sounds produced in the
+telephone, and on the contradictory assertions of
+physicists as to the transmission of speech by ordinary<span class="pagenum" id="Page_361">361</span>
+telephones when devoid of diaphragm. These remarks
+induced M. Ader to undertake some experiments which
+not only demonstrate the truth of my opinion, but bring
+to light some fresh facts which may be of great importance
+to acoustic science.</p>
+
+<p>M. Ader has in fact not only succeeded in making a
+telephone without a diaphragm speak, but he has made
+it speak more loudly and with less alteration of the voice
+than we find to be the case with a small model of the
+ordinary telephone. No one, therefore, can now maintain
+that the sounds produced by the magnetic cores are
+so faint that they cannot be taken into account among
+the effects produced, and that it is at any rate impossible
+for them to reproduce articulate sounds.</p>
+
+<p>To obtain this result, M. Ader reduced the size of the
+magnetic core to that of a simple iron wire, one millimètre
+in diameter, and he fastened it by one of its ends
+to a small wooden board. Under these conditions, it
+was enough to fasten a small helix of fine wire on this
+iron wire, and to apply the board to the ear in order to
+hear speech distinctly, with the aid of a microphonic
+speaker actuated by a voltaic current. But the range
+of sound was considerably increased if a mass of metal
+was applied to the free end of the iron wire: in this case
+it was possible to hear when the wooden board was
+removed to a distance of ten or fifteen centimètres from
+the ear.</p>
+
+<p>If the wire is in contact with masses of metal at each
+end, the effect is further increased; but the two masses
+must not be in metallic communication with each other,
+and must be to some extent insulated by a more or less
+elastic medium. If the metallic masses are soldered to
+the wire, the effects are still greater.</p>
+
+<p>M. Ader was also able to reproduce speech by using<span class="pagenum" id="Page_362">362</span>
+a simple coil without a magnetic core, but in this case
+the spirals must be open, and not pressed together. If they
+are steeped in gum, no sound is heard, but speech will
+become instantly audible if a wire or a magnetised needle
+is inserted in the coil, or even if a second metallic helix is
+placed in the circuit: always provided that one of the
+ends of these magnetic organs rests upon, or is fastened
+to, the board on which the coil is fixed.</p>
+
+<p>M. Ader has likewise obtained a very distinct reproduction
+of speech at a distance of two or three yards from
+the instrument by inserting between the two stretched
+membranes of two tambourines a bent wire which acts as
+a spring and passes through an electro-magnetic coil.
+Under these conditions, magnetisation of the wire in a
+greater or less degree affects its elasticity and causes
+vibrations which are magnified by the membranes, and
+transmitted sounds are reproduced with intensity. Unfortunately
+articulate speech is less distinct with this
+system than with the one I described before.</p>
+
+<p>M. Ader has often had occasion to make one curious
+remark, namely, that the <em>timbre</em> of the voice and its high
+or low key varies with the degree of tension given to the
+wire; but if the fundamental note of the wire is deadened
+by pressing it between the fingers, the sounds reproduced
+then become dull and monotonous. They are also
+somewhat fainter.</p>
+
+<p>Signor Carlo Resio has also observed that in a telephone
+sender the variations of intensity in the current
+correspond with the vibrations caused by speech, and
+these are reproduced by corresponding variations in a
+liquid column, which may thus act as a telephone
+receiver, and consequently may reproduce speech without
+any electro-magnetic organ, as in a microphone
+speaker. Under these conditions, however, a layer of<span class="pagenum" id="Page_363">363</span>
+water is inserted between the platinum electrodes and
+the surrounding air, and consequently this liquid layer
+must be put in vibration under the influence of varying
+intensities of current.</p>
+
+<p>Mr. Edison has also now made a practical application
+of the chemical telephone we have mentioned before.
+The trials made with it have been very satisfactory,
+showing that sounds transmitted in this way can be heard
+in a large room.</p>
+
+<p class="p4 center vspace wspace">
+<span class="small">PRINTED BY<br>
+SPOTTISWOODE AND CO., NEW-STREET SQUARE<br>
+LONDON</span>
+</p>
+
+<div class="chapter footnotes">
+<h2 class="nobreak" id="FOOTNOTES">FOOTNOTES</h2>
+
+<div class="footnote">
+
+<p class="fn1"><a id="Footnote_1" href="#FNanchor_1" class="label">1</a> Mr. Gray, in an article inserted in the <cite>Telegrapher</cite> of October
+7, 1876, enters into full details of this mode of transmitting sounds
+by the tissues of the human body, and he gives the following as the
+conditions in which it must be placed to obtain a favourable result:
+1. The electricity must be of a high tension, in order to have an
+effect perceptible to the ear.</p>
+
+<p>2. The substance employed to touch the metallic plate must be
+soft, flexible, and a good conductor, up to the point of contact: it
+must then interpose a slight resistance, neither too great nor too
+small.</p>
+
+<p>3. The disk and the hand, or any other tissue, must not only be
+in contact, but the contact must result from rubbing or gliding over
+the surface.</p>
+
+<p>4. The parts in contact must be dry, so as to maintain the required
+degree of resistance.</p>
+
+</div>
+
+<div class="footnote">
+
+<p class="fn1"><a id="Footnote_2" href="#FNanchor_2" class="label">2</a> He cites the following names in his account of electric telephony:—Page,
+Marrian, Beatson, Gassiot, De la Rive, Matteucci,
+Guillemin, Wertheim, Wartmann, Janniar, Joule, Laborde, Legat,
+Reiss, Poggendorf, Du Moncel, Delezenne, Gore, &amp;c. Vide Mr.
+Bell’s paper, in the <cite>Journal of the Society of Telegraphic Engineers</cite>
+in London, vol. vi. pp. 390, 391.</p>
+
+</div>
+
+<div class="footnote">
+
+<p class="fn1"><a id="Footnote_3" href="#FNanchor_3" class="label">3</a> This statement is disputed by Mr. Elisha Gray, owing, as we
+shall see, to a misunderstanding as to the word <em>undulatory</em> current.</p>
+
+</div>
+
+<div class="footnote">
+
+<p class="fn1"><a id="Footnote_4" href="#FNanchor_4" class="label">4</a> <cite>Elisha Gray.</cite> Eng. Pat. Spec. No. 2646, Aug. 1874.</p>
+
+</div>
+
+<div class="footnote">
+
+<p class="fn1"><a id="Footnote_5" href="#FNanchor_5" class="label">5</a> This property has long been known, but not applied. In 1856,
+in the second edition of my <cite lang="fr">Exposé des applications d’Electricité</cite>, I
+pointed them out in speaking of the contact-breakers. I also spoke
+of them in a paper on electro-magnets (published in the <cite lang="fr">Annales
+télégraphiques</cite>, 1865), and in several articles laid before the <cite lang="fr">Académie
+des Sciences</cite> in 1872 and 1875 on the conductivity of filings and
+conducting powders. M. Clérac, in 1865, also used them to obtain
+variable resistances.</p>
+
+</div>
+
+<div class="footnote">
+
+<p class="fn1"><a id="Footnote_6" href="#FNanchor_6" class="label">6</a> In 1865 I was able to verify this observation when tightening
+the spirals of an electro-magnet on a naked wire. The greater the
+number of spirals under pressure, the more definite were the differences
+of resistance in the magnetising helix.</p>
+
+</div>
+
+<div class="footnote">
+
+<p class="fn1"><a id="Footnote_7" href="#FNanchor_7" class="label">7</a> M. Hellesen communicated the plan of his instrument to me
+on May 3, 1878, and his experiments were made in Copenhagen
+three weeks earlier.</p>
+
+</div>
+
+<div class="footnote">
+
+<p class="fn1"><a id="Footnote_8" href="#FNanchor_8" class="label">8</a> M. M. J. Page had already noticed that if a telephone is placed
+in the circuit of the primary helix of an induction coil, while the
+secondary helix of this instrument is placed in the circuit of one of
+M. Lippmann’s capillary electrometers, a movement of the mercurial
+column of the electrometer takes place at each word, and this movement
+is effected towards the capillary end of the tube, in whatever
+direction the current is sent by the telephone. This is because the
+mercury always tends to move more rapidly at its capillary end than
+at the other extremity.</p>
+
+</div>
+
+<div class="footnote">
+
+<p class="fn1"><a id="Footnote_9" href="#FNanchor_9" class="label">9</a> Mr. Edison, in a letter written November 25, 1877, writes
+that he has made two telephones which act with copper diaphragms,
+based on Arago’s effects of magnetism by rotation. He ascertained
+that a copper diaphragm might replace the iron plate, if its thickness
+did not exceed 1/32 of an inch. The effect produced is slight when
+the copper diaphragm is placed between two corresponding instruments;
+but when the sender only is furnished with the copper
+diaphragm, and the receiver is arranged as usual, communication
+becomes easy.</p>
+
+<p>Mr. Preece repeated these experiments, but he only obtained
+very slight and indistinct effects: he consequently believes that they
+are of no practical use, although very interesting in theory.</p>
+
+</div>
+
+<div class="footnote">
+
+<p class="fn2"><a id="Footnote_10" href="#FNanchor_10" class="label">10</a> Mr. Bell had previously made a like experiment, which suggested
+to him that molecular vibrations had as much to do with the
+action of the telephone as mechanical vibrations.</p>
+
+</div>
+
+<div class="footnote">
+
+<p class="fn2"><a id="Footnote_11" href="#FNanchor_11" class="label">11</a> M. Bosscha, who has published in the <cite lang="fr">Archives néerlandaises</cite>
+an interesting paper on the intensity of electric currents in the telephone,
+says that the minimum intensity of currents necessary to
+produce a sound in a telephone by the vibration of its diaphragm
+may be less than 100/1000 of a Daniell element, and the displacement
+of the centre of the diaphragm would then be invisible. He was
+unable to measure exactly the range of movements produced in the
+diaphragm by the influence of the voice, but he believes it to be
+less than the thousandth part of a millimètre; and from this it follows
+that, for a sound of 880 vibrations, the intensity of the induced currents
+developed would be 0·0000792 of the unit of electro-magnetic
+intensity.</p>
+
+</div>
+
+<div class="footnote">
+
+<p class="fn2"><a id="Footnote_12" href="#FNanchor_12" class="label">12</a> Mr. Warwick describes his experiments as follows: ‘The magnets
+employed were nearly of the usual size, 1½ inch in diameter,
+and nearly eight times as long. At first I employed iron disks, but
+I found them to be unnecessary. When I had discarded them, I
+tried several substances: first a thin disk of iron, which answered
+perfectly both for sender and receiver. A disk of sheet iron,
+about ⅒ of an inch in thickness, did not act so well, but all that
+was said was quite understood. In making experiments with the
+disks, I simply placed them above the instrument, without fixing
+them in any way: the wooden cover and the conical cavity were
+also laid aside, because the transmission and reception could be
+effected as well without them. This part of the instrument seems to
+be superfluous, since, when the disk is simply placed level to the ear,
+the sound seems to be increased by being brought nearer. Although
+iron acts better than anything, it appears that iron disks are not
+absolutely necessary, and that diamagnetic substances also act
+perfectly. I wished that my assistant, who was at some distance,
+and could not hear any direct sound, should continue his calculations.
+I took away the iron disk and placed across the instrument a wide
+iron bar, an inch thick. On applying my ear to it, I could hear
+every sound distinctly, but somewhat more faintly. A piece of
+copper, three inches square, was substituted for it: although the
+sound was still distinct, it was fainter than before. Thick pieces of
+lead, zinc, and steel were alternately tried. The steel acted in
+almost the same way as the iron, and, as in the other cases, each
+word was heard faintly but distinctly. Some of these metals are
+diamagnetic, and yet the action took place. Some non-metallic
+substances were next tried; first a piece of window-glass, which
+acted very well. The action was faint with a piece of a wooden
+match-box; but on using pieces of gradually increasing thickness
+the sound was sensibly increased, and with a piece of solid wood,
+1½ inch in thickness, the sound was perfectly distinct. I next
+replaced it by an empty wooden box, which acted very well. A
+piece of cork, ½ inch thick, acted, but somewhat faintly. A block
+of razor-stone, 2 inches thick, was placed upon the instrument; and,
+on applying the ear to it, it was quite easy to follow the speaker.
+I then tried to hear without the insertion of any substance, and, on
+applying my ear quite close to the coil and magnet, I heard a faint
+sound, and on listening attentively I understood all that was said.
+In all these experiments the sounds were perceived, but the sounds
+transmitted or attempted did not act precisely alike. The sound of
+a tuning-fork, placed on the iron disk itself or on the case of the
+instrument, was clearly heard: thin iron disks were more effective
+for articulate speech. With other substances, stone, solid wood, glass,
+zinc, &amp;c., the sound of the tuning-fork was heard, whether it rested
+upon them, or the vibrating fork was held above them. These substances
+were not adapted for transmitting the sound of the voice.
+These were all laid aside, and the sounding instrument was held
+directly above the pole of the magnet: the sound was clearly heard,
+although there was nothing but air between the end of the magnet
+and the tuning-fork. The sound was perhaps less intense when the
+tuning-fork was held directly above the pole, than when it was at
+the end of the magnet. I next tried if my voice could be heard
+with this arrangement. The result was rather doubtful, but I think
+that some action must have taken place, for the tuning-fork was
+heard when it was simply vibrated near the pole. The effect of the
+voice can only have differed in the degree of intensity: it was too
+faint to be heard at the other extremity. I repeated these effects;
+I assured myself of them, and I succeeded in transmitting sounds
+distinctly on the pole without a disk, and, on the other hand, by
+applying my ear to the instrument, I was able to hear distinctly all
+that was said, although there was no disk.’</p>
+
+</div>
+
+<div class="footnote">
+
+<p class="fn2"><a id="Footnote_13" href="#FNanchor_13" class="label">13</a> These are his own words: ‘The articulation produced from the
+instrument was remarkably clear, but its great defect consisted in
+the fact that it could not be used as a sending instrument, and thus
+two telephones were required at each station, one for transmitting
+and one for receiving spoken messages.’</p>
+
+</div>
+
+<div class="footnote">
+
+<p class="fn2"><a id="Footnote_14" href="#FNanchor_14" class="label">14</a> These carbons are made by heating, in a temperature gradually
+raised to white heat, fragments of deal of a close fibre, which is
+enclosed in an iron tube or box hermetically sealed.</p>
+
+</div>
+
+<div class="footnote">
+
+<p class="fn2"><a id="Footnote_15" href="#FNanchor_15" class="label">15</a> Mr. Willoughby Smith varied this experiment by placing a
+packet of silk threads coated with copper on the disconnected ends
+of the circuit, which were arranged at right angles with each other.
+Under these conditions the instrument became so sensitive, that the
+current of air produced by a lamp placed above the system, caused
+a decided crackling noise in the telephone.</p>
+
+</div>
+
+<div class="footnote">
+
+<p class="fn2"><a id="Footnote_16" href="#FNanchor_16" class="label">16</a> Mr. Hughes observes on this subject that carbon is a valuable
+material for such purposes, since it does not oxidise, and its
+effects are greater when combined with mercury. He takes the
+prepared charcoal used by artists, brings it to a white heat, and
+suddenly plunges it in a bath of mercury, of which the globules instantly
+penetrate the pores of charcoal, and may be said to metallise
+it. He also tried charcoal coated with a deposit of platinum, or
+impregnated with chloride of platinum, but this was not more successful
+than the former method. If the charcoal of fir-wood is
+brought to a white heat in an iron tube, containing tin and zinc, or
+any other metal which readily evaporates, it is metallised, and is
+adapted for use if the metal is subdivided in the pores of charcoal
+and not combined with it. When iron is introduced into carbon
+in this way it is one of the most effective metals. The charcoal of
+fir-wood, in itself a bad conductor, may thus acquire great conducting
+power.</p>
+
+</div>
+
+<div class="footnote">
+
+<p class="fn2"><a id="Footnote_17" href="#FNanchor_17" class="label">17</a> Mr. Hughes remarks that the vibrations which affect the microphone,
+even in speaking at a distance from the instrument, do not
+proceed from the direct action of the sound waves on the contacts of
+the microphone, but from the molecular vibrations produced by it
+on the board which serves to support the instrument; he shows, in
+fact, that the intensity of sounds produced by the microphone is in
+proportion to the size of the surface of this board, and when the
+sending microphone is enclosed in a cylindrical case, its sensitiveness
+is not much diminished if the surface of the box enclosing the whole
+is sufficiently large. From this point of view he has sought to increase
+the sensitiveness of his instruments by fixing the frame on
+which the moveable parts of the sender and receiver revolve on a
+spring plate.</p>
+
+</div>
+
+<div class="footnote">
+
+<p class="fn2"><a id="Footnote_18" href="#FNanchor_18" class="label">18</a> Helmholtz’s resonator is based upon the principle that a volume
+of air contained in an open vase emits a certain note when
+placed in vibration, and that the height of the note depends on the
+size of the vase and of its opening. Helmholtz makes use of a globe
+with a large opening on one side and a small one on the other,
+and the small one is applied to the ear. If a series of musical notes
+take place in the air, the one which is in harmony with the fundamental
+note of the globe is intensified, and can be distinguished
+from the rest. The same effect takes place when, on singing to
+a piano accompaniment, some strings are heard to vibrate more
+strongly than others, namely, those which vibrate in unison with
+the sounds emitted. The resonators are made in various ways;
+those most generally used are cases of different lengths which also
+serve as sounding-boxes.</p>
+
+</div>
+
+<div class="footnote">
+
+<p class="fn2"><a id="Footnote_19" href="#FNanchor_19" class="label">19</a> I give the text of M. Cros’ sealed paper, opened by his
+request, at the Académie des Sciences, December 3, 1877:—‘Speaking
+generally, my process consists in obtaining traces of the
+movement to and fro of a vibrating membrane, and in using this
+tracing to reproduce the same movements, with their intrinsic
+relations of duration and intensity, either on the same membrane
+or on one adapted to give out the sounds which result from this
+series of movements.</p>
+
+<p>‘It is therefore necessary that an extremely delicate tracing, such
+as may be obtained by passing a needle over a surface blackened
+by fire, should be transformed into a tracing, capable of sufficient
+resistance to guide an index which will transmit its movements to
+the membrane of sound.</p>
+
+<p>‘A light index is fastened to the centre of a vibrating membrane;
+it terminates in a point (a metallic wire or tip of a feather) which
+rests on a surface which has been blackened by fire. This surface
+forms part of a disk, to which the double action of rotation and
+rectilinear progression has been given. If the membrane is at
+rest, the point will trace a simple spiral; if the membrane vibrates,
+there will be undulations in the spiral, and these undulations will
+represent the precise movements of the membrane in their duration
+and intensity.</p>
+
+<p>‘By a well-known photographic process a transparent tracing of
+the undulations of the spiral can be represented by a line of similar
+dimensions on some resisting substance, tempered steel for
+example.</p>
+
+<p>‘When this is done, this resisting surface is placed in a turning
+machine which causes it to revolve and advance with a velocity and
+motion similar to those by which the registering surface was
+actuated. A metallic point if the tracing is concave, or a grooved
+index if it is in relief, is kept upon the tracing by a spring, and the
+index which supports this point is connected with the centre of the
+membrane which produces the sounds. Under these conditions,
+the membrane will be actuated not by the vibrating air, but by the
+tracing which guides the index, and the impulses will be precisely
+similar in duration and intensity to those to which the registering
+membrane was subjected.</p>
+
+<p>‘The spiral tracing represents equal successions of time by
+increasing or decreasing lengths. There is no inconvenience in
+this, since the turns of the spiral are very close together, if only the
+circumference of the turning circle is used; but then the central
+surface is lost.</p>
+
+<p>‘In all cases the tracing of the helix on a cylinder is much
+more satisfactory, and I am now trying to make this idea practicable.’</p>
+
+</div>
+
+<div class="footnote">
+
+<p class="fn2"><a id="Footnote_20" href="#FNanchor_20" class="label">20</a> Never make a contact between the stylus and the cylinder until
+the latter is covered with the tinfoil. Do not begin to turn the
+cylinder until assured that everything is in its place. Take care,
+when the stylus returns to the point of departure, to bring the
+mouthpiece forward. Always leave a margin of from five to ten
+millimètres on the left and at the beginning of the sheet of tinfoil;
+for if the stylus describes the curve on the extreme edge of the
+cylinder, it may tear the sheet or come out of the groove. Be
+careful not to detach the spring of the caoutchouc pad.</p>
+
+<p>To fix the tinfoil, apply varnish to the end with a paint-brush;
+take this end between the finger and thumb of the left hand, with the
+sticky part towards the cylinder; raise it with the right hand and
+apply it quite smoothly to the cylinder; bring round the sticky end,
+and join them firmly.</p>
+
+<p>To adjust the stylus and place it in the centre of the groove,
+bring the cylinder to the right, so as to place the stylus opposite the
+left extremity of the tinfoil; bring forward the cylinder gently and
+by degrees, until the stylus touches the tinfoil with force enough to
+imprint a mark. Observe if this mark is quite in the centre of the
+groove (in order to do this, make a mark with the nail across the
+cylinder), and if it is not, adjust the stylus to the right or left by means
+of the little screw placed above the mouthpiece. The depth of the
+impression made by the stylus should be ⅓ millimètre, just enough for
+it to leave a slight tracing, whatever the range of vibrations may be.</p>
+
+<p>To reproduce the words, the winch must be turned with the
+same velocity as when they were inscribed. The average velocity
+should be about eighty turns a minute.</p>
+
+<p>In speaking, the lips must touch the mouthpiece, and deep
+guttural sounds are better heard than those which are shrill. In
+reproducing, the tightening screw must be loosened and brought in
+front of the mouthpiece, the cylinder must be brought back to its
+point of departure, the contact between the stylus and the foil must
+be renewed, and the cylinder must again be turned in the same
+direction as when the sentence was spoken.</p>
+
+<p>To increase the volume of reproduced sound, a tube of cardboard,
+wood, or horn may be applied to the mouthpiece; it must be
+of a conical form, and its lower end should be rather larger than
+the opening of the mouthpiece.</p>
+
+<p>The stylus consists of a No. 9 needle, somewhat flattened on its
+two sides by friction on an oiled stone. The caoutchouc pad which
+connects the plate with the disk serves to weaken the vibrations of
+the plate. If this pad should come off, heat the head of a small
+nail, apply it to the wax which fastens the pad to the plate or to the
+spring, so as to soften it; then press the caoutchouc lightly, until it
+adheres to the place from which it was detached. The pads must
+be renewed from time to time, as they lose their elasticity. Care must
+be taken in replacing them not to injure the vibrating plate, either
+by too strong a pressure or by grazing it with the instrument employed
+to fix the pad.</p>
+
+<p>The first experiments should be with single words or very short
+sentences, which can be extended as the ear becomes accustomed to
+the instrument’s peculiar tone.</p>
+
+<p>The tone is varied by accelerating or slackening the rotatory
+movement of the cylinder. The cries of animals may be imitated.
+Instrumental music may be reproduced by placing a cardboard
+tube before the mouthpiece. The airs should be played in rapid
+time, since, when there is no system of clockwork, they will be
+more perfectly reproduced than those which are played slowly.</p>
+
+</div>
+
+<div class="footnote">
+
+<p class="fn2"><a id="Footnote_21" href="#FNanchor_21" class="label">21</a> We confess that we find it difficult to believe in this property
+of the phonograph, from which we have only heard the harsh and
+unpleasant voice of Punch.</p>
+
+</div>
+
+<div class="footnote">
+
+<p class="fn2"><a id="Footnote_22" href="#FNanchor_22" class="label">22</a> The action of this pedal is effected by two little rockers, so
+connected that the upper damper is lowered a little before the lower
+damper is raised—a condition necessary to produce the quivering
+motion of the plate which furnishes the rolling <i>r</i>.</p>
+
+</div>
+
+<div class="footnote">
+
+<p class="fn2"><a id="Footnote_23" href="#FNanchor_23" class="label">23</a> The arrangement of this part of the instrument is remarkable
+in this particular, that in the case of certain letters the air is ejected
+with more or less force through the pipe <span class="allsmcap">I</span>, while in the case of
+other letters the air is drawn into the same tube. Since I was
+unable to see the internal arrangement of these cavities, I can only
+give an imperfect account of the mechanism at work.</p>
+
+</div>
+</div>
+
+<div class="chapter transnote">
+<h2 class="nobreak" id="Transcribers_Notes">Transcriber’s Notes</h2>
+
+<p>Punctuation, hyphenation, and spelling were made
+consistent when a predominant preference was found
+in the original book; otherwise they were not changed.</p>
+
+<p>Simple typographical errors were corrected; unbalanced
+quotation marks were remedied when the change was
+obvious, and otherwise left unbalanced.</p>
+
+<p>Illustrations in this eBook have been positioned
+between paragraphs and outside quotations.</p>
+
+<p>Footnotes, originally at the bottoms of the pages that referenced them,
+have been collected, sequentially renumbered, and placed near the end of
+the book.</p>
+
+<p>The Table of Contents is not well-coordinated
+with the actual text. The Transcriber has not
+added missing entries, but has attempted to
+correct page number discrepancies.</p>
+
+<p>Several diagrams use labels with prime marks, but
+the accompanying explanations do not
+always include the prime marks.
+</p>
+</div>
+
+<div style='text-align:center'>*** END OF THE PROJECT GUTENBERG EBOOK 75683 ***</div>
+</body>
+</html>
+
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diff --git a/LICENSE.txt b/LICENSE.txt
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+This book, including all associated images, markup, improvements,
+metadata, and any other content or labor, has been confirmed to be
+in the PUBLIC DOMAIN IN THE UNITED STATES.
+
+Procedures for determining public domain status are described in
+the "Copyright How-To" at https://www.gutenberg.org.
+
+No investigation has been made concerning possible copyrights in
+jurisdictions other than the United States. Anyone seeking to utilize
+this book outside of the United States should confirm copyright
+status under the laws that apply to them.
diff --git a/README.md b/README.md
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+Project Gutenberg (https://www.gutenberg.org) public repository for
+book #75683 (https://www.gutenberg.org/ebooks/75683)