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+Project Gutenberg's Electric Bells and All About Them, by S. R. Bottone
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever. You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Electric Bells and All About Them
+ A Practical Book for Practical Men
+
+Author: S. R. Bottone
+
+Release Date: March 4, 2012 [EBook #39053]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK ELECTRIC BELLS AND ALL ABOUT THEM ***
+
+
+
+
+Produced by Simon Gardner, Chris Curnow and the Online
+Distributed Proofreading Team at http://www.pgdp.net (This
+file was produced from images generously made available
+by The Internet Archive)
+
+
+
+
+
+
+
+Transcriber's Notes
+
+Inconsistent spellings (e.g. depolariser & depolarizer) and hyphenation
+(e.g. guttapercha & gutta-percha) are retained as in the original text.
+Minor punctuation errors are corrected without comment. Changes which
+have been made to the text (in the case of typographical errors) are
+listed at the end of the book.
+
+This version has been prepared using symbols from the ASCII and
+Latin-1 character sets only. Italic typeface is shown with surrounding
+_underscores_; small capital typeface is shown by ALL CAPS;
+superscript typeface is shown by a preceding caret (^). Subscripts in
+chemical formulae are shown with underscores and braces, e.g.
+H_{2}SO_{4}.
+
+The following are used to represent other special symbols:
+
+ [Lambda] sans-serif capital Lambda
+ [rotated S] S-like symbol rotated 90 deg.
+ [box open up] 3 sides of rectangular (open side up)
+ [box open down] 3 sides of rectangular (open side down)
+ [oe] oe-ligature
+ [battery] vertical lines (thick and thin)
+ [L], [U], [V] sans-serif letter shapes
+
+ * * * * *
+
+ ELECTRIC BELLS AND
+ ALL ABOUT THEM.
+
+ A Practical Book for Practical Men.
+
+ _WITH MORE THAN 100 ILLUSTRATIONS._
+
+ BY
+ S. R. BOTTONE,
+
+ CERTIFICATED BY SOUTH KENSINGTON (LATE OF THE COLLEGIO
+ DEL CARMINE, TURIN, AND OF THE ISTITUTO
+ BELLINO, NOVARA);
+
+ _Author of "The Dynamo," "Electrical Instruments for
+ Amateurs," &c._
+
+ LONDON:
+ WHITTAKER & CO., PATERNOSTER SQUARE, E.C.
+
+ 1889.
+
+ (_All rights reserved._)
+
+
+
+
+PREFACE.
+
+
+So rapidly has the use of electric bells and similiar signalling
+appliances extended, in modern houses, offices, hotels, lifts, and
+ships, that every bell-fitter must have felt the need of accurate
+knowledge of the manner in which these instruments act and are made.
+
+In the following pages the author has attempted to supply this need, by
+giving full details as to the construction of batteries, bells, pushes,
+detectors, etc., the mode of wiring, testing, connecting up, localizing
+faults, and, in point of fact, by directing careful attention to every
+case that can present itself to the electric-bell fitter.
+
+ CARSHALTON, SURREY,
+ _November, 1888_.
+
+
+
+
+CONTENTS.
+
+
+ CHAP. PAGE
+
+ I. PRELIMINARY CONSIDERATIONS 1
+
+ II. ON THE CHOICE OF BATTERIES FOR ELECTRIC BELL WORK 18
+
+ III. ON ELECTRIC BELLS AND OTHER SIGNALLING APPLIANCES 59
+
+ IV. ON CONTACTS, PUSHES, SWITCHES, KEYS, ALARMS, AND RELAYS 109
+
+ V. ON WIRING, CONNECTING UP, AND LOCALISING FAULTS 144
+
+
+
+
+LIST OF ILLUSTRATIONS.
+
+
+ FIG. PAGE
+
+ 1. Direction of current in cell 9
+
+ 2. " " out of cell 10
+
+ 3. Bar and horse-shoe magnets 14
+
+ 4. The Dynamo 16
+
+ 5. " Smee cell 28
+
+ 6. " Daniell cell 30
+
+ 7. " Gravity cell 32
+
+ 8. " Leclanché cell and parts 34
+
+ 9. " Agglomerate cell 40
+
+ 10. " Judson cell 42
+
+ 11. " Battery in box 43
+
+ 12. " Gent cell 44
+
+ 13. " Bichromate cell 48
+
+ 14. " Fuller cell 50
+
+ 15. " Cells coupled in series 54
+
+ 16. " " " Parallel 57
+
+ 17. Outline of electric bell 61
+
+ 18. Frame of bell 62
+
+ 19. E-shaped frame 63
+
+ 20. Electro-magnet, old form 64
+
+ 20A. " " modern form 65
+
+ 21. Magnet frame 66
+
+ 21A. Winder 72
+
+ 22. Mode of joining electromagnet wires 73
+
+ 23. Armature spring 74
+
+ 24. " " Another form 74
+
+ 25. Platinum tipped screw 75
+
+ 26. " " spring 76
+
+ 27. Binding screws 77
+
+ 28. Bell or gong 78
+
+ 29. Pillar and nuts 78
+
+ 30. Washers 78
+
+ 31. Trembling bell 81
+
+ 32. Bell action enclosed in case 88
+
+ 33. Ordinary trembling bells 90
+
+ 34. Single stroke bell 91
+
+ 35. Continuous ring bell 94
+
+ 36. Release action 95
+
+ 37. Continuous ringing with relay 96
+
+ 38. Continuous ringing action with indicator 97
+
+ 39. Relay and detent lever for indicator 97
+
+ 40. Callow's attachment 99
+
+ 40A. Thorpe's arrangement 101
+
+ 41. Jensen bell, _section_ 102
+
+ 42. " " _exterior_ 104
+
+ 43A. Circular bell 106
+
+ 43B. Mining bell 106
+
+ 44. Electric trumpet (Binswanger's) 107
+
+ 45. Various forms of pushes 110
+
+ 46. Pressel 111
+
+ 47. Pull 112
+
+ 48. Bedroom pull 113
+
+ 49A. " " Another form 114
+
+ 49B. Floor contact, ball form 114
+
+ 50. Burglar alarm 115
+
+ 51. " " Another form 115
+
+ 52. Floor contact 115
+
+ 53. Door contact 116
+
+ 54. Sash contact 117
+
+ 55. Shop door contact 117
+
+ 56A. Closed circuit system, _single_ 119
+
+ 56B. Closed circuit system, _double_ 119
+
+ 57. Modified gravity, Daniell 120
+
+ 58. Contact for closed circuit 121
+
+ 59. Thermometer alarm 122
+
+ 60. Fire alarm 123
+
+ 61A. " " Another form 123
+
+ 61B. " " " " in action 123
+
+ 62. Binswanger's "watch alarm" contact 125
+
+ 63. Watchman's electric tell-tale clock 126
+
+ 64. Lever switch, _two-way_ 128
+
+ 65. Morse key, _double contact_ 133
+
+ 66. Relay 134
+
+ 67. Indicator, drop 137
+
+ 68. " Semaphore 138
+
+ 69. " Fall back 139
+
+ 70. " Pendulum 140
+
+ 71. " Coupled up 142
+
+ 72. " Gent's tripolar 143
+
+ 73. Soldering iron and wires 148
+
+ 74. Push, interior of 151
+
+ 75. Bell, battery and push 159
+
+ 76. " " And earth return 160
+
+ 77. " and two pushes 161
+
+ 78. " two pushes and one pull 161
+
+ 79. Two bells in parallel 162
+
+ 80. " " Another mode 162
+
+ 81. " " with two-way switch 163
+
+ 82. Series coupler 163
+
+ 83. Bell with local battery and relay 164
+
+ 84. Continuous ringing bell with wire return 165
+
+ 85. Bells with Morse keys for signalling 165
+
+ 86. Bells with double contact pushes for signalling 166
+
+ 87. Bells with double contact with one battery only 167
+
+ 88. Two-way signalling with one battery only 168
+
+ 89. Complete installation of bells, batteries, pushes, etc. 169
+
+ 90. Mode of getting out plan or design 170
+
+ 91. Lift fitted with bells 173
+
+ 92. Magneto bell: generator 174
+
+ 93. " " Receiver 175
+
+ 94. " " Combined 176
+
+ 95. Detector or galvanometer 176
+
+
+
+
+ELECTRIC BELLS.
+
+
+
+
+CHAPTER I.
+
+PRELIMINARY CONSIDERATIONS.
+
+
+§ 1. ELECTRICITY.--The primary cause of all the effects which we are
+about to consider resides in a force known as _electricity_, from the
+Greek name of amber (electron), this being the body in which the
+manifestations were first observed. The ancients were acquainted with a
+few detached facts, such as the attractive power acquired by amber after
+friction; the benumbing shocks given by the torpedo; the aurora
+borealis; the lightning flash; and the sparks or streams of light which,
+under certain conditions, are seen to issue from the human body. Thales,
+a Grecian philosopher, who flourished about 600 years B.C., observed the
+former of these facts, but nearly twenty centuries elapsed before it was
+suspected that any connection existed between these phenomena.
+
+
+§ 2. According to the present state of our knowledge, it would appear
+that electricity is a mode of motion in the constituent particles (or
+atoms) of bodies very similar to, if not identical with, _heat_ and
+_light_. These, like _sound_, are known to be dependent on undulatory
+motion; but, whilst _sound_ is elicited by the vibration of a body _as a
+whole_, electricity appears to depend, in its manifestations, upon some
+motion (whether rotary, oscillatory, or undulatory, it is not known) of
+the atoms themselves.
+
+However this be, it is certain that whatever tends to set up molecular
+motion, tends also to call forth a display of electricity. Hence we have
+several practical means at our disposal for evoking electrical effects.
+These may be conveniently divided into three classes, viz.:--1st,
+mechanical; 2nd, chemical; 3rd, changes of temperature. Among the
+_mechanical_ may be ranged friction, percussion, vibration, trituration,
+cleavage, etc. Among the _chemical_ we note the action of acids and
+alkalies upon metals. Every chemical action is accompanied by electrical
+effects; but not all such actions are convenient sources of electricity.
+_Changes of temperature_, whether sudden or gradual, call forth
+electricity, but the displays are generally more striking in the former
+than in the latter case, owing to the accumulated effect being presented
+in a shorter time.
+
+
+§ 3. We may now proceed to study a few of these methods of evoking
+electricity, so as to familiarise ourselves with the leading properties.
+
+If we rub any resinous substance (such as amber, copal, resin,
+sealing-wax, ebonite, etc.) with a piece of warm, dry flannel, we shall
+find that it acquires the power of attracting light bodies, such as
+small pieces of paper, straw, pith, etc. After remaining in contact with
+the rubbed (or electrified) substance for a short time, the paper, etc.,
+will fly off as if repelled; and this apparent repulsion will be more
+evident and more quickly produced if the experiment be performed over a
+metal tray. If a small pith-ball, the size of a pea, be suspended from
+the ceiling by a piece of fine cotton, previously damped and then
+approached by an ebonite comb which has been briskly rubbed, it will be
+vigorously attracted, and never repelled; but if for the cotton there be
+substituted a thread or fibre of very fine dry silk, the pith-ball will
+be first _attracted_ and then _repelled_. This is owing to the fact that
+the damp cotton allows the electricity to escape along it: _id est_,
+damp cotton is a CONDUCTOR of electricity, while silk does not permit
+its dissipation; or, in other words, silk is a NON-CONDUCTOR. All bodies
+with which we are acquainted are found, on trial, to fall under one or
+other of the two heads--viz., conductors and non-conductors. Nature
+knows no hard lines, so that we find that even the worst conductors will
+permit the escape of some electricity, while the very best conductors
+oppose a measurable resistance to its passage. Between the limits of
+good conductors, on the one hand, and non-conductors (or insulators) on
+the other, we have bodies possessing varying degrees of conductivity.
+
+
+§ 4. As a knowledge of which bodies are, and which are not, conductors
+of electricity is absolutely essential to every one aspiring to apply
+electricity to any practical purpose, the following table is subjoined,
+giving the names of the commoner bodies, beginning with those which most
+readily transmit electricity, or are _good_ conductors, and ending with
+those which oppose the highest resistance to its passage, or are
+insulators, or non-conductors:--
+
+
+§ 5. TABLE OF CONDUCTORS AND INSULATORS.
+
+ -----------------+------------------------------+---------------------
+ Quality. | Name of Substance. | Relative Resistance.
+ -----------------+------------------------------+---------------------
+ Good {|Silver, annealed | 1.
+ Conductors {|Copper, annealed | 1.063
+ {|Silver, hard drawn | 1.086
+ {|Copper, hard drawn | 1.086
+ {|Gold, annealed | 1.369
+ {|Gold, hard drawn | 1.393
+ {|Aluminium, annealed | 1.935
+ {|Zinc, pressed | 3.741
+ {|Brass (variable) | 5.000
+ {|Platinum, annealed | 6.022
+ {|Iron | 6.450
+ {|Steel, soft | 6.500
+ {|Gold and silver alloy, 2 to 1 | 7.228
+ {|Nickel, annealed | 8.285
+ {|Tin, pressed | 8.784
+ {|Lead, pressed | 13.050
+ {|German silver (variable) | 13.920
+ {|Platinum-silver alloy, 1 to 2 | 16.210
+ {|Steel, hard | 25.000
+ {|Antimony, pressed | 23.600
+ {|Mercury | 62.730
+ {|Bismuth | 87.230
+ {|Graphite | 145.000
+ {|Nitric Acid | 976000.000
+ | |
+ Imperfect {|Hydrochloric acid | [1]
+ Conductors {|Sulphuric acid | 1032020.000
+ {|Solutions of metallic salts | varies with strength
+ {|Metallic sulphides | [1]
+ {|Distilled water | [1] 6754208.000
+ | |
+ Inferior {| Metallic salts, solid | [1]
+ Conductors. {| Linen } |
+ {| Cotton } and other forms of | [1]
+ {| Hemp } cellulose |
+ {| Paper } |
+ {| Alcohol | [1]
+ {| Ether | [1]
+ {| Dry Wood | [1]
+ {| Dry Ice | [1]
+ {| Metallic Oxides | [1]
+ | |
+ Non-conductors, {| Ice, at 25 c. | [1]
+ or {| Fats and oils | [1]
+ Insulators. {| Caoutchouc | 1000000000000.
+ {| Guttapercha | 1000000000000.
+ {| Dry air, gases, and vapours | [1]
+ {| Wool | [1]
+ {| Ebonite | 1300000000000.
+ {| Diamond | [1]
+ {| Silk | [1]
+ {| Glass | [1]
+ {| Wax | [1]
+ {| Sulphur | [1]
+ {| Resin | [1]
+ {| Amber | [1]
+ {| Shellac | [1]
+ {| Paraffin | 1500000000000.
+ -----------------+------------------------------+---------------------
+
+[Footnote 1: These have not been accurately measured.]
+
+The figures given as indicating the relative resistance of the above
+bodies to the passage of electricity must be taken as approximate only,
+since the conductivity of all these bodies varies very largely with
+their purity, and with the temperature. Metals become worse conductors
+when heated; liquids and non-metals, on the contrary, become better
+conductors.
+
+It must be borne in mind that _dry air_ is one of the _best
+insulators_, or worst _conductors_, with which we are acquainted; while
+damp air, on the contrary, owing to the facility with which it deposits
+_water_ on the surface of bodies, is highly conducive to the escape of
+electricity.
+
+
+§ 6. If the experiment described at § 3 be repeated, substituting a
+glass rod for the ebonite comb, it will be found that the pith-ball will
+be first attracted and then repelled, as in the case with the ebonite;
+and if of two similar pith-balls, each suspended by a fibre of silk, one
+be treated with the excited ebonite and the other with the glass rod,
+until repulsion occurs, and then approached to each other, the two balls
+will be found to attract each other. This proves that the electrical
+condition of the excited ebonite and of the excited glass must be
+different; for had it been the same, the two balls would have repelled
+one another. Farther, it will be found that the _rubber_ with which the
+ebonite or the glass rod have been excited has also acquired electrical
+properties, attracting the pith-ball, previously repelled by the rod.
+From this we may gather that when one body acting on another, either
+mechanically or chemically, sets up an electrical condition in one of
+the two bodies, a similar electrical condition, but in the opposite
+sense, is produced in the other: in point of fact, that it is impossible
+to excite any one body without exciting a corresponding but opposite
+state in the other. (We may take, as a rough mechanical illustration of
+this, the effect which is produced on the pile of two pieces of plush or
+fur, on being drawn across one another in opposite directions. On
+examination we shall find that both the piles have been laid down, the
+upper in the one direction, the lower in the other.) For a long time
+these two electrical states were held to depend upon two distinct
+electricities, which were called respectively _vitreous_ and _resinous_,
+to indicate the nature of the bodies from which they were derived. Later
+on (when it was found that the theory of a single electricity could be
+made to account for all the phenomena, provided it was granted that some
+electrified bodies acquired more, while others acquired less than their
+natural share of electricity), the two states were known as _positive_
+and _negative_; and these names are still retained, although it is
+pretty generally conceded that electricity is not an entity in itself,
+but simply a mode of motion.
+
+
+§ 7. It is usual, in treatises on electricity, to give a long list of
+the substances which acquire a positive or a negative condition when
+rubbed against one another. Such a table is of very little use, since
+the slightest modification in physical condition will influence very
+considerably the result. For example: if two similar sheets of glass be
+rubbed over one another, no change in electrical condition is produced;
+but if one be roughed while the other is left polished, this latter
+becomes positively, while the former becomes negatively, electrified.
+So, also, if one sheet of glass be warmed, while the other be left cold,
+the colder becomes positively, and the latter negatively, excited. As a
+general law, _that body, the particles of which are more easily
+displaced, becomes negatively electrified_.
+
+
+§ 8. As, however, the electricity set up by friction has not hitherto
+found any practical application in electric bell-ringing or signalling,
+we need not to go more deeply into this portion of the subject, but pass
+at once to the electricity elicited by the action of acids, or their
+salts, on metals.
+
+Here, as might be expected from the law enunciated above, the metal more
+acted on by the acid becomes negatively electrified, while the one less
+acted on becomes positive.[2] The following table, copied from Ganot,
+gives an idea of the electrical condition which the commoner metals and
+graphite assume when two of them are immersed at the same time in dilute
+acid:--
+
+ { v Zinc. ^ }
+ { v Cadmium. | }
+ { | Tin. | }
+ { | Lead. | }
+ { | Iron. | }
+ The portion { | Nickel. | } The portion out
+ immersed in the { | Bismuth. | } of the acid fluid
+ acid fluid. { | Antimony. | }
+ { | Copper. | }
+ { | Silver. | }
+ { | Gold. | }
+ { | Platinum. ^ }
+ { v Graphite. ^ }
+
+[Footnote 2: This refers, of course, to those portions of the metals
+which are out of the acid. For reasons which will be explained farther
+on, the condition of the metals in the acid is just the opposite to
+this.]
+
+The meaning of the above table is, that if we test the electrical
+condition of any two of its members when immersed in an acid fluid, we
+shall find that the ones at the head of the list are _positive_ to those
+below them, but negative to those above them, if the test have reference
+to the condition of the parts _within_ the fluid. On the contrary, we
+shall find that any member of the list will be found to be _negative_ to
+any one below it, or _positive_ to any above it, if tested from the
+portion NOT immersed in the acid fluid.
+
+[Illustration: Fig. 1.]
+
+[Illustration: Fig. 2.]
+
+
+§ 9. A very simple experiment will make this quite clear. Two strips,
+one of copper and the other of zinc, 1" wide by 4" long, have a 12"
+length of copper wire soldered to one extremity of each. A small flat
+piece of cork, about 1" long by 1" square section, is placed between the
+two plates, at the end where the wires have been soldered, this portion
+being then lashed together by a few turns of waxed string. (The plates
+should not touch each other at any point.) If this combination (which
+constitutes a very primitive galvanic couple) be immersed in a tumbler
+three-parts filled with water, rendered just sour by the addition of a
+few drops of sulphuric or hydrochloric acid, we shall get a
+manifestation of electrical effects. If a delicately poised magnetic
+needle be allowed to take up its natural position of north and south,
+and then the wires proceeding from the two metal strips twisted in
+contact, so as to be parallel to and over the needle, as shown in Fig.
+1, the needle will be impelled out of its normal position, and be
+deflected more or less out of the line of the wire. If the needle be
+again allowed to come to rest N. and S. (the battery or couple having
+been removed), and then the tumbler be held close over the needle, as in
+Fig. 2, so that the needle points from the copper to the zinc strip, the
+needle will be again impelled or deflected out of its natural position,
+but in this case in the opposite direction.
+
+
+§ 10. It is a well-known fact that if a wire, or any other conductor,
+along which the electric undulation (or, as is usually said, the
+electric current) is passing, be brought over and parallel to a
+suspended magnetic needle, pointing north and south, the needle is
+immediately deflected from this north and south position, and assumes a
+new direction, more or less east and west, according to the amplitude of
+the current and the nearness of the conductor to the needle. Moreover,
+the direction in which the north pole of the needle is impelled is found
+to be dependent upon the direction in which the electric waves (or
+current) enter the conducting body or wire. The law which regulates the
+direction of these deflections, and which is known, from the name of its
+originator, as Ampère's law, is briefly as follows:--
+
+
+§ 11. "If a current be caused to flow _over_ and parallel to a freely
+suspended magnetic needle, previously pointing north and south, the
+north pole will be impelled to the LEFT of the _entering_ current. If,
+on the contrary, the wire, or conductor, be placed _below_ the needle,
+the deflection will, under similar circumstances, be in the opposite
+direction, viz.: the north pole will be impelled to the RIGHT of the
+_entering_ current." In both these cases the observer is supposed to be
+looking along the needle, with its N. seeking pole pointing at him.
+
+
+§ 12. From a consideration of the above law, in connection with the
+experiments performed at § 9, it will be evident that inside the tumbler
+the zinc is _positive_ to the copper strip; while, viewed from the
+outside conductor, the copper is positive to the zinc strip.[3]
+
+[Footnote 3: From some recent investigations, it would appear that what
+we usually term the negative is really the point at which the undulation
+takes its rise.]
+
+
+§ 13. A property of current electricity, which is the fundamental basis
+of electric bell-ringing, is that of conferring upon iron and steel the
+power of attracting iron and similar bodies, or, as it is usually said,
+of rendering iron magnetic. If a soft iron rod, say about 4" long by
+1/2" diameter, be wound evenly from end to end with three or four layers
+of cotton-covered copper wire, say No. 20 gauge, and placed in proximity
+to a few iron nails, etc., no attractive power will be evinced; but let
+the two free ends of the wire be placed in metallic contact with the
+wires leading from the simple battery described at § 9, and it will be
+found that the iron has become powerfully magnetic, capable of
+sustaining several ounces weight of iron and steel, so long as the wires
+from the battery are in contact with the wire encircling the iron; or,
+in other words, "_the soft iron is a magnet, so long as an electric
+current flows round it_." If contact between the battery wires and the
+coiled wires be broken, the iron loses all magnetic power, and the
+nails, etc., drop off immediately. A piece of soft iron thus coiled with
+covered or "insulated" wire, no matter what its shape may be, is termed
+an "electro-magnet." Their chief peculiarities, as compared with the
+ordinary permanent steel magnets or lodestones, are, first, their great
+attractive and sustaining power; secondly, the rapidity, nay,
+instantaneity, with which they lose all attractive force on the
+cessation of the electric flow around them. It is on these two
+properties that their usefulness in bell-ringing depends.
+
+
+§ 14. If, instead of using a _soft_ iron bar in the above experiment, we
+had substituted one of _hard_ iron, or steel, we should have found two
+remarkable differences in the results. In the first place, the bar would
+have been found to retain its magnetism instead of losing it immediately
+on contact with the battery being broken; and, in the second place, the
+attractive power elicited would have been much less than in the case of
+soft iron. It is therefore of the highest importance, in all cases where
+rapid and powerful magnetisation is desired, that the _cores_ of the
+electro-magnets should be of the very softest iron. Long annealing and
+gradual cooling conduce greatly to the softness of iron.
+
+[Illustration: Fig. 3.
+
+MAGNETS, showing Lines of Force.]
+
+
+§ 15. There is yet another source of electricity which must be noticed
+here, as it has already found application in some forms of electric
+bells and signalling, and which promises to enter into more extended
+use. If we sprinkle some iron filings over a bar magnet, or a horse-shoe
+magnet, we shall find that the filings arrange themselves in a definite
+position along the lines of greatest attractive force; or, as scientists
+usually say, the iron filings arrange themselves in the direction of the
+lines of force. The entire space acted on by the magnet is usually known
+as its "field." Fig. 3 gives an idea of the distribution of the iron
+filings, and also of the general direction of the lines of force. It is
+found that if a body be moved before the poles of a magnet in such a
+direction as to cut the lines of force, electricity is excited in that
+body, and also around the magnet. The ordinary magneto-electric machines
+of the shops are illustrations of the application of this property of
+magnets. They consist essentially in a horse-shoe magnet, in front of
+which is caused to rotate, by means of appropriate gearing, or wheel and
+band, an iron bobbin, or pair of bobbins, coiled with wire. The ends of
+the wire on the bobbins are brought out and fastened to insulated
+portions of the spindle, and revolve with it. Two springs press against
+the spindle, and pick up the current generated by the motion of the iron
+bobbins before the poles of the magnet. It is quite indifferent whether
+we use permanent steel magnets or electro-magnets to produce this
+effect. If we use the latter, and more especially if we cause a portion
+of the current set up to circulate round the electro-magnet to maintain
+its power, we designate the apparatus by the name of DYNAMO.
+
+[Illustration: Fig. 4.
+
+TYPICAL DYNAMO, showing essential portions.]
+
+
+§ 16. Our space will not permit of a very extended description of the
+dynamo, but the following brief outline of its constructive details will
+be found useful to the student. A mass of soft iron (shape immaterial)
+is wound with many turns of insulated copper wire, in such a manner
+that, were an electrical current sent along the wire, the mass of iron
+would become strongly north at one extremity, and south at the other. As
+prolongations of the electro-magnet thus produced are affixed two masses
+of iron facing one another, and so fashioned or bored out as to allow a
+ring, or cylinder of soft iron, to rotate between them. This cylinder,
+or ring of iron, is also wound with insulated wire, two or more ends of
+which are brought out in a line with the spindle on which it rotates,
+and fastened down to as many insulated sections of brass cylinder placed
+around the circumference of the spindle. Two metallic springs,
+connected to binding screws which form the "terminals" of the machine,
+serve to collect the electrical wave set up by the rotation of the
+coiled cylinder (or "armature") before the poles of the electro-magnet.
+The annexed cut (Fig. 4) will assist the student in getting a clear idea
+of the essential portions in a dynamo:--E is the mass of wrought iron
+wound with insulated wire, and known as the _field-magnet_. N and S are
+cast-iron prolongations of the same, and are usually bolted to the
+field-magnet. When current is passing these become powerfully magnetic.
+A is the rotating iron ring, or cylinder, known as the _armature_, which
+is also wound with insulated wire, B, the ends of which are brought out
+and connected to the insulated brass segments known as the
+_commutator_, C. Upon this commutator press the two springs D and D',
+known as the _brushes_, which serve to collect the electricity set up by
+the rotation of the armature. These _brushes_ are in electrical
+connection with the two terminals of the machine F F', whence the
+electric current is transmitted where required; the latter being also
+connected with the wire encircling the field-magnet, E.
+
+When the iron mass stands in the direction of the earth's magnetic
+meridian, even if it have not previously acquired a little magnetism
+from the hammering, etc., to which it was subjected during fitting, it
+becomes weakly magnetic. On causing the armature to rotate by connecting
+up the pulley at the back of the shaft (not shown in cut) with any
+source of power, a very small current is set up in the wires of the
+armature, due to the weak magnetism of the iron mass of the
+field-magnet. As this current (or a portion of it) is caused to
+circulate around this iron mass, through the coils of wire surrounding
+the field-magnet, this latter becomes more powerfully magnetic (§ 13),
+and, being more magnetically active, sets up a more powerful electrical
+disturbance in the armature.
+
+This increased electrical activity in the armature increases the
+magnetism of this field-magnet as before, and this again reacts on the
+armature; and these cumulative effects rapidly increase, until a limit
+is reached, dependent partly on the speed of rotation, partly on the
+magnetic saturation of the iron of which the dynamo is built up, and
+partly on the amount of resistance in the circuit.
+
+
+
+
+CHAPTER II.
+
+ON THE CHOICE OF BATTERIES FOR ELECTRIC BELL WORK.
+
+
+§ 17. If we immerse a strip of ordinary commercial sheet zinc in dilute
+acid (say sulphuric acid 1 part by measure, water 16 parts by
+measure[4]), we shall find that the zinc is immediately acted on by the
+acid, being rapidly corroded and dissolved, while at the same time a
+quantity of bubbles of gas are seen to collect around, and finally to be
+evolved at the surface of the fluid in contact with the plate.
+Accompanying this chemical action, and varying in a degree proportionate
+to the intensity of the action of the acid on the zinc, we find a marked
+development of _heat_ and _electricity_. If, while the bubbling due to
+the extrication of gas be still proceeding, we immerse in the same
+vessel a strip of silver, or copper, or a rod of graphite, taking care
+that contact _does not_ take place between the two elements, no
+perceptible change takes place in the condition of things; but if we
+cause the two strips to touch, either by inclining the upper extremities
+so as to bring them in contact out of the fluid like a letter [Lambda],
+or by connecting the upper extremities together by means of a piece of
+wire (or other conductor of electricity), or by causing their lower
+extremities in the fluid to touch, we notice a very peculiar change. The
+extrication of bubbles around the zinc strip ceases entirely or almost
+entirely, while the other strip (silver, copper, or graphite) becomes
+immediately the seat of the evolution of the gaseous bubbles. Had these
+experiments been performed with chemically pure metallic zinc, instead
+of the ordinary impure commercial metal, we should have found some
+noteworthy differences in behaviour. In the first place, the zinc would
+have been absolutely unattacked by the acid before the immersion of the
+other strip; and, secondly, all evolution of gas would entirely cease
+when contact between the two strips was broken.
+
+[Footnote 4: In mixing sulphuric acid with water, the acid should be
+added in a fine stream, with constant stirring, to the water, and not
+the water to the acid, lest the great heat evolved should cause the acid
+to be scattered about.]
+
+As the property which zinc possesses of causing the extrication of gas
+(under the above circumstances) has a considerable influence on the
+efficiency of a battery, it is well to understand thoroughly what
+chemical action takes place which gives rise to this evolution of gas.
+
+
+§ 18. All acids may be conveniently regarded as being built up of two
+essential portions, viz.: firstly, a strongly electro-negative portion,
+which may either be a single body, such as _chlorine_, _iodine_,
+_bromine_, etc., or a compound radical, such as _cyanogen_; secondly,
+the strongly electro-positive body _hydrogen_.
+
+Representing, for brevity's sake, hydrogen by the letter H., and
+chlorine, bromine, iodine, etc., respectively by Cl., Br., and I., the
+constitution of the acids derived from these bodies may be conveniently
+represented by:--
+
+ H Cl H Br H I
+ ---- ---- ---
+ Hydrochloric[5] Hydrobromic Hydriodic
+ Acid. Acid. Acid.
+
+
+[Footnote 5: Spirits of salt.]
+
+and the more complex acids, in which the electro-negative component is a
+compound, such as sulphuric acid (built up of 1 atom of sulphur and 4
+atoms of oxygen, united to 2 atoms of hydrogen) or nitric acid
+(consisting of 1 nitrogen atom, 6 oxygen atoms, and 1 hydrogen atom),
+may advantageously be retained in memory by the aid of the
+abbreviations:--
+
+ H_{2}SO_{4} HNO_{6}
+ ----------- -------
+ Sulphuric and Nitric
+ Acid.[6] Acid.[7]
+
+
+[Footnote 6: Oil of vitriol.]
+
+[Footnote 7: Aquafortis.]
+
+When zinc _does_ act on an acid, it displaces the hydrogen contained in
+it, and takes its place; the acid losing at the same time its
+characteristic sourness and corrosiveness, becoming, as chemists say,
+_neutralized_. _One_ atom of zinc can replace _two_ atoms of hydrogen,
+so that one atom of zinc can replace the hydrogen in two equivalents of
+such acids as contain only one atom of hydrogen.
+
+This power of displacement and replacement possessed by zinc is not
+peculiar to this metal, but is possessed also by many other bodies, and
+is of very common occurrence in chemistry; and may be roughly likened to
+the substitution of a new brick for an old one in a building, or one
+girder for another in an arch.
+
+It will be well, therefore, to remember that in all batteries in which
+acids are used to excite electricity by their behaviour along with zinc,
+the following chemical action will also take place, according to which
+acid is employed:--
+
+ Hydrochloric Acid and Zinc, equal Zinc Chloride and Hydrogen Gas.
+
+ 2HCl + Zn = ZnCl_{2} + H_{2}
+
+or:--
+
+ Sulphuric Acid and Zinc, equal Zinc Sulphate and Hydrogen Gas.
+
+ H_{2}SO_{4} + Zn = ZnSO_{4} + H_{2}
+
+Or we may put this statement into a general form, covering all cases in
+which zinc is acted on by a compound body containing hydrogen,
+representing the other or electro-negative portion of the compound by
+X:--
+
+ Zn + H_{2}X = ZnX + H_{2}
+
+the final result being in every case the corrosion and solution of the
+zinc, and the extrication of the hydrogen gas displaced.
+
+
+§ 19. We learn from the preceding statements that no electricity can be
+manifested in a battery or cell (as such a combination of zinc acid and
+metal is called) without consumption of zinc. On the contrary, we may
+safely say that the more rapidly the _useful_ consumption of zinc takes
+place, the greater will be the electrical effects produced. But here it
+must be borne in mind that if the zinc is being consumed when we are
+_not_ using the cell or battery, that consumption is sheer waste, quite
+as much as if we were compelled to burn fuel in an engine whether the
+latter were doing work or not. For this reason the use of commercial
+zinc, in its ordinary condition, is not advisable in batteries in which
+acids are employed, since the zinc is consumed in such, whether the
+battery is called upon to do electrical work (by placing its plates in
+connection through some conducting circuit) or not. This serious
+objection to the employment of commercial zinc could be overcome by the
+employment of chemically purified zinc, were it not that the price of
+this latter is so elevated as practically to preclude its use for this
+purpose. Fortunately, it is possible to confer, on the ordinary crude
+zinc of commerce, the power of resisting the attacks of the acid (so
+long as the plates are not metallically connected; or, in other words,
+so long as the "circuit is broken"), by causing it to absorb
+superficially a certain amount of mercury (quicksilver). The modes of
+doing this, which is technically known as _amalgamating the zinc_, are
+various, and, as it is an operation which every one who has the care of
+batteries is frequently called upon to perform, the following working
+details will be found useful:--
+
+
+§ 20. To amalgamate zinc, it should first be washed with a strong
+solution of common washing soda, to remove grease, then rinsed in
+running water; the zinc plates, or rods, should then be dipped into a
+vessel containing acidulated water (§ 17), and as soon as bubbles of
+hydrogen gas begin to be evolved, transferred to a large flat dish
+containing water. While here, a few drops of mercury are poured on each
+plate, and caused to spread quickly over the surface of the zinc by
+rubbing briskly with an old nail-brush or tooth-brush. Some operators
+use a kind of mop, made of pieces of rag tied on the end of a stick, and
+there is no objection to this; others recommend the use of the fingers
+for rubbing in the mercury. This latter plan, especially if many plates
+have to be done, is very objectionable: firstly, on the ground of
+health, since the mercury is slowly but surely absorbed by the system,
+giving rise to salivation, etc.; and, secondly, because any jewellery,
+etc., worn by the wearer will be whitened and rendered brittle. When the
+entire surface of the zinc becomes resplendent like a looking-glass, the
+rubbing may cease, and the zinc plate be reared up on edge, to allow the
+superfluous mercury to drain off. This should be collected for future
+operations. It is important that the mercury used for this purpose
+should be pure. Much commercial mercury contains lead and tin. These
+metals can be removed by allowing the mercury to stand for some time in
+a vessel containing dilute nitric acid, occasional agitation being
+resorted to, in order to bring the acid into general contact with the
+mercury. All waste mercury, drainings, brushings from old plates, etc.,
+should be thus treated with nitric acid, and finally kept covered with
+water. Sprague, in his admirable work on electricity, says:--"Whenever
+the zinc shows a grey granular surface (or rather before this), brush
+it well and re-amalgamate, remembering that a saving of mercury is no
+economy, and a free use of it no waste; for it may all be recovered with
+a little care. Keep a convenient sized jar, or vessel, solely for
+washing zinc in, and brush into this the dirty grey powder which forms,
+and is an amalgam of mercury with zinc, lead, tin, etc., and forms
+roughnesses which reduce the protection of the amalgamation. Rolled
+sheet zinc should always be used in preference to cast. This latter is
+very hard to amalgamate, and has less electro-motive power[8]; but for
+rods for use in porous jars, and particularly with saline solutions,
+cast-zinc is very commonly used. In this case great care should be taken
+to use good zinc cuttings, removing any parts with solder on them, and
+using a little nitre as a flux, which will remove a portion of the
+foreign metals."
+
+[Footnote 8: Power to set up a current of electricity.]
+
+
+§ 21. Another and very convenient mode of amalgamating zinc, specially
+useful where solid rods or masses of zinc are to be used, consists in
+weighing up the zinc and setting aside four parts of mercury (by weight)
+for every hundred of the zinc thus weighed up. The zinc should then be
+melted in a ladle, with a little tallow or resin over the top as a flux.
+As soon as melted, the mercury should be added in and the mixture
+stirred with a stick. It should then be poured into moulds of the
+desired shape. This is, perhaps, the best mode of amalgamating cast
+zincs.
+
+
+§ 22. Some operators recommend the use of mercurial salts (such as
+mercury nitrate, etc.) as advantageous for amalgamating; but, apart
+from the fact that these salts are generally sold at a higher rate than
+the mercury itself, the amalgamation resulting, unless a very
+considerable time be allowed for the mercuric salts to act, is neither
+so deep nor so satisfactory as in the case of mercury alone. It may here
+be noted, that although the effect of mercury in protecting the zinc is
+very marked in those batteries in which acids are used as the exciting
+fluids, yet this action is not so observable in the cases in which
+solutions of _salts_ are used as exciters; and in a few, such as the
+Daniell cell and its congeners, the use of amalgamated zinc is
+positively a disadvantage.
+
+
+§ 23. If, having thus amalgamated the zinc plate of the little battery
+described and figured at § 9, we repeat the experiment therein
+illustrated, namely, of joining the wires proceeding from the two plates
+over a suspended magnetic needle, and leave them so united, we shall
+find that the magnetic needle, which was originally very much deflected
+out of the line of the magnetic meridian (north and south), will very
+quickly return near to its old and normal position; and this will be
+found to take place long before the zinc has been all consumed, or the
+acid all neutralised. Of course, this points to a rapid falling off in
+the transmission of the electric disturbance along the united wires; for
+had _that_ continued of the same intensity, the deflection of the needle
+would evidently have remained the same likewise. What, then, can have
+caused this rapid loss of power? On examining (without removing from
+the fluid) the surface of the copper plate, we shall find that it is
+literally covered with a coating of small bubbles of hydrogen gas, and,
+if we agitate the liquid or the plates, many of them will rise to the
+surface, while the magnetic needle will at the same time give a larger
+deflection. If we entirely remove the plates from the acid fluid, and
+brush over the surface of the copper plate with a feather or small
+pledget of cotton wool fastened to a stick, we shall find, on again
+immersing the plates in the acid, that the effect on the needle is
+almost, if not quite, as great as at first; thus proving that the sudden
+loss of electrical energy was greatly due to the adhesion of the free
+hydrogen gas to the copper plate. This peculiar phenomenon, which is
+generally spoken of as the _polarisation of the negative plate_, acts in
+a twofold manner towards checking the electrical energy of the battery.
+In the first place, the layer of hydrogen (being a bad conductor of
+electricity) presents a great resistance to the transmission of
+electrical energy from the zinc plate where it is set up to the copper
+(or other) plate whence it is transmitted to the wires, or _electrodes_.
+Again, the _copper_ or other receiving plate, in order that the electric
+energy should be duly received and transmitted, should be more
+electro-negative than the zinc plate; but the hydrogen gas which is
+evolved, and which thus adheres to the negative plate, is actually very
+highly electro-positive, and thus renders the copper plate incapable of
+receiving or transmitting the electric disturbance. This state of things
+may be roughly likened to that of two exactly equal and level tanks, Z
+and C, connected by a straight piece of tubing. If Z be full and C have
+an outlet, it is very evident that Z can and will discharge itself into
+C until exhausted; but if C be allowed to fill up to the same level as
+Z, then no farther flow can take place between the two.
+
+It is, therefore, very evident that to ensure anything like constancy in
+the working of a battery, at least until all the zinc be consumed or all
+the acid exhausted, some device for removing the liberated hydrogen must
+be put into practice. The following are some of the means that have been
+adopted by practical men:--
+
+
+§ 24. _Roughening the surface of the negative plate_, which renders the
+escape of the hydrogen gas easier. This mode was adopted by Smee in the
+battery which bears his name. It consists of a sheet of silver, placed
+between two plates of zinc, standing in a cell containing dilute
+sulphuric acid, as shown at Fig. 5.
+
+[Illustration: Fig. 5.]
+
+The silver sheet, before being placed in position, is _platinised_; that
+is to say, its surface is covered (by electro-deposition) with a coating
+of platinum, in the form of a fine black powder. This presents
+innumerable points of escape for the hydrogen gas; and for this reason
+this battery falls off much less rapidly than the plain zinc and smooth
+copper form. A modification of Smee's battery which, owing to the large
+negative surface presented, is very advantageous, is Walker's graphite
+cell. In this we have a plate of zinc between two plates of gas-carbon
+("scurf"), or graphite. The surface of this body is naturally much
+rougher than metal sheets; and this roughness of surface is further
+assisted by coating the surface with platinum, as in the case of the
+Smee. The chief objection to the use of graphite is its porosity, which
+causes it to suck up the acid fluid in which the plates stand, and this,
+of course, corrodes the brass connections, or binding screws.
+
+Other _mechanical_ means of removing the hydrogen have been suggested,
+such as brushing the surface of the plate, keeping the liquid in a state
+of agitation by boiling or siphoning; but the only really efficient
+practical means with which we are at present acquainted are _chemical_
+means. Thus, if we can have present at the negative plate some substance
+which is greedy of hydrogen, and which shall absorb it or combine with
+it, we shall evidently have solved the problem. This was first effected
+by Professor Daniell; and the battery known by his name still retains
+its position as one of the simplest and best of the "constant" forms of
+battery. The term "constant," as applied to batteries, does not mean
+that the battery is a constancy, and will run for ever, but simply that
+so long as there is in the battery any fuel (zinc, acid, etc.), the
+electrical output of that battery will be constant. The Daniell cell
+consists essentially in a rod or plate of zinc immersed in dilute
+sulphuric acid, and separated from the copper or collecting plate by a
+porous earthen pot or cell. Around the porous cell, and in contact with
+the copper plate, is placed a solution of sulphate of copper, which is
+maintained saturate by keeping crystals of sulphate of copper (blue
+stone, blue vitriol) in the solution. Sulphate of copper is a compound
+built up of copper Cu, and of sulphur oxide SO_{4}. When the dilute
+sulphuric acid acts on the zinc plate or rod (§ 18), sulphate of zinc is
+formed, which dissolves in the water, and hydrogen is given off:--
+
+ Zn + H_{2} SO_{4} = Zn SO_{4} + H_{2}.
+
+ Zinc and sulphuric acid produce zinc sulphate and free hydrogen.
+
+Now this free hydrogen, by a series of molecular interchanges, is
+carried along until it passes through the porous cell, and finds itself
+in contact with the solution of copper sulphate. Here, as the hydrogen
+has a greater affinity for, or is more greedy of, the sulphur oxide,
+SO_{4}, than the copper is, it turns the latter out, takes its place,
+setting the copper free, and forming, with the sulphur oxide, sulphuric
+acid. The liberated copper goes, and adheres to the copper plate, and,
+far from detracting from its efficacy, as the liberated hydrogen would
+have done, actually increases its efficiency, as it is deposited in a
+roughened form, which presents a large surface for the collection of the
+electricity. The interchange which takes place when the free hydrogen
+meets the sulphate of copper (outside the porous cells) is shown in the
+following equation:--
+
+ H_{2} + Cu SO_{4} = H_{2} SO_{4} + Cu.
+
+ Free hydrogen and copper sulphate produce sulphuric acid and free copper.
+
+[Illustration: Fig. 6. DANIELL CELL.]
+
+
+§ 25. The original form given to this, the Daniell cell, is shown at
+Fig. 6, in which Z is the zinc rod standing in the porous pot P, in
+which is placed the dilute sulphuric acid. A containing vessel, V, of
+glazed earthenware, provided with a perforated shelf, S, on which are
+placed the crystals of sulphate of copper, serves to hold the copper
+sheet, C, and the solution of sulphate of copper. T and T' are the
+terminals from which the electricity is led where desired.
+
+In another form, the copper sheet itself takes the form and replaces the
+containing vessel V; and since the copper is not corroded, but actually
+increases in thickness during action, this is a decided advantage. A
+modification, in which the porous cell is replaced by _sand_ or by
+_sawdust_, is also constructed, and known as "Minotto's" cell: this,
+owing to the greater thickness of the porous layer, offers more
+resistance, and gives, consequently, less current. By taking advantage
+of the greater specific gravity (_weight, bulk for bulk_) of the
+solution of sulphate of copper over that of water or dilute sulphuric
+acid, it is possible to construct a battery which shall act in a manner
+precisely similar to a Daniell, without the employment of any porous
+partition whatsoever. Fig. 7 illustrates the construction of one of
+these, known as "Gravity Daniells."
+
+[Illustration: Fig. 7. GRAVITY CELL.]
+
+In this we have a plate, disc, or spiral of copper, C, connected by an
+insulated copper wire to the terminal T'. Over this is placed a layer of
+crystals of copper sulphate; the jar is then filled nearly to the top
+with dilute sulphuric acid, or with a strong solution of sulphate of
+zinc (which is more lasting in its effects, but not so energetic as the
+dilute sulphuric acid), and on the surface of this, connected to the
+other terminal, T, is allowed to rest a thick disc of zinc, Z. Speaking
+of these cells, Professor Ayrton, in his invaluable "Practical
+Electricity," says:--"All gravity cells have the disadvantage that they
+cannot be moved about; otherwise the liquids mix, and the copper
+sulphate solution, coming into contact with the zinc plate, deposits
+copper on it. This impairs the action, by causing the zinc to act
+electrically, like a copper one. Indeed, without any shaking, the
+liquids mix by diffusion, even when a porous pot is employed; hence a
+Daniell's cell is found to keep in better order if it be always allowed
+to send a weak current when not in use, since the current uses up the
+copper sulphate solution, instead of allowing it to diffuse." The use of
+a solution of zinc sulphate to act on the zinc rod, or plate, is always
+to be preferred in the Daniell cell, when long duration is of more
+consequence than energetic action.
+
+
+§ 26. There are many other bodies which can be used in batteries to
+absorb the hydrogen set free. Of several of these we need only take a
+passing notice, as the batteries furnished by their use are unfit for
+electric bell work. Of these we may mention nitric acid, which readily
+parts with a portion of the oxygen (§ 18) and reconverts the free
+hydrogen into water. This acid is used as the "depolarizer"[9] in the
+"Grove" and in the "Bunsen" cell. Another very energetic "depolariser"
+is chromic acid, either in solution, in dilute sulphuric acid, or in the
+form of potassic dichromate (bichromate of potash: bichrome). As one
+form of chromic cell has found favour with some bell-fitters, we shall
+study its peculiarities farther on.
+
+[Footnote 9: Depolarizer is the technical name given to any body which,
+by absorbing the free hydrogen, removes the false polarity of the
+negative plate.]
+
+Another class of bodies which readily part with their oxygen, and thus
+act as depolarisers, are the oxides of lead and manganese. This latter
+oxide forms the basis of one of the most useful cells for electric bell
+work, namely: the one known as the "Leclanché." As the battery has been,
+and will probably remain, long a favourite, the next paragraph will be
+devoted to its consideration.
+
+
+§ 27. The Leclanché cell, in its original form, consists in a rod or
+block of gas carbon (retort scurf: graphite) standing in an upright
+porous pot. Around this, so as to reach nearly to the top of the porous
+cell, is tightly packed a mixture of little lumps of graphite and black
+oxide of manganese (manganic dioxide: black wad), the porous cell itself
+being placed in an outer containing vessel, which usually takes the form
+of a square glass bottle. A zinc rod stands in one corner of the
+bottle, and is prevented from coming into actual contact with the
+porous cell by having an indiarubber ring slipped over its upper and
+lower extremities. The glass containing vessel is then filled to about
+two-thirds of its height with a solution of ammonium chloride (sal
+ammoniac) in water, of the strength of about 2 oz. of the salt to each
+pint of water. This soon permeates the porous cell and reaches the
+mixture inside. The general appearance of the Leclanché cell is well
+shown at Fig. 8.
+
+[Illustration: Fig. 8.]
+
+In order to ensure a large surface of contact for the terminal of the
+carbon rod or plate, it is customary to cast a leaden cap on the top
+thereof; and, as the porosity of the graphite, or carbon, is very apt
+to allow the fluid in the battery to creep up to and corrode the
+terminal, and thus oppose resistance to the passage of electricity, the
+upper end of the carbon, before the lead cap is cast on, is soaked for
+some time in melted paraffin wax, at a temperature of 110° Centigrade:
+that is somewhat hotter than boiling water heat. This, if left on the
+outside, would prevent the passage of electricity almost entirely; so
+lateral holes are drilled into the carbon before the cap is finally cast
+on. The action that takes place in the Leclanché cell may be summarised
+as follows:--
+
+When the zinc, Zn, is acted on by the ammonium chloride, 2NH_{4}Cl, the
+zinc seizes the chlorine and forms with it zinc chloride, ZnCl_{2},
+while the ammonium, 2NH_{4}, is liberated. But this ammonium, 2NH_{4},
+does not escape. Being electro-positive, it is impelled towards the
+negative plate, and in its passage thereto meets with another molecule
+of ammonium chloride, from which it displaces the ammonium, in this
+wise: 2NH_{4} + 2NH_{4}Cl = 2NH_{4}Cl + 2NH_{4}; in other words, this
+electro-positive ammonium is able, by virtue of its electrical charge,
+to displace the ammonium from the combined chloride. In so doing, it
+sets the liberated ammonium in an electro-positive condition, as it was
+itself, losing at the same time its electrical charge. This interchange
+of molecules goes on (as we saw in the case of the Daniell's cell, § 24)
+until the surface of the carbon is reached. Here, as there is no more
+ammonium chloride to decompose, the ammonium 2NH_{4} immediately splits
+up into ammonia 2NH_{3} and free hydrogen H_{2}. The ammonia escapes,
+and may be detected by its smell; while the hydrogen H_{2}, finding
+itself in contact with the oxide of manganese, 2MnO_{2}, seizes one atom
+of its oxygen, O, becoming thereby converted into water H_{2}O; while
+the manganese dioxide, 2MnO_{2}, by losing one atom of oxygen, is
+reduced to the form of a lower oxide of manganese, known as manganese
+sesquioxide, Mn_{2}O_{3}. Expressed in symbols, this action may be
+formulated as below:--
+
+In the zinc compartment--
+
+ Zn + 2NH_{4}Cl = ZnCl_{2} + 2NH_{3} + H_{2}
+
+In the peroxide of manganese compartment--
+
+ H_{2} + 2MnO_{2} = Mn_{2}O_{3} + H_{2}O.
+
+Ammonia gas therefore slowly escapes while this battery is in action,
+and this corrodes all the brass work with which it comes into contact,
+producing a bluish green verdigris. If there be not sufficient ammonium
+chloride in solution, the water alone acts on the zinc: zinc oxide is
+produced, which renders the solution milky. Should this be the case,
+more sal ammoniac must be added. It is found that for every 50 grains of
+zinc consumed in this battery, about 82 grains of sal ammoniac and 124
+grains of manganese dioxide are needed to neutralize the hydrogen set
+free. It is essential for the efficient working of this battery that
+both the manganese dioxide and the carbon should be free from powder,
+otherwise it will cake together, prevent the passage of the liquid, and
+present a much smaller surface to the electricity, than if in a granular
+form. For this reason, that manganese dioxide should be preferred which
+is known as the "needle" form, and both this and the carbon should be
+sifted to remove dust.
+
+
+§ 28. In the admirable series of papers on electric bell fitting which
+was published in the _English Mechanic_, Mr. F. C. Allsop, speaking of
+the Leclanché cell, says:--"A severe and prolonged test, extending over
+many years, has proved that for general electric bell work the Leclanché
+has no equal; though, in large hotels, etc., where the work is likely to
+be very heavy, it may, perhaps, be preferable to employ a form of the
+Fuller bichromate battery. It is very important that the battery
+employed should be a thoroughly reliable one and set up in a proper
+manner, as a failure in the battery causes a breakdown in the
+communication throughout the whole building, whilst the failure of a
+push or wire only affects that portion of the building in which the push
+or wire is fixed. A common fault is that of putting in (with a view to
+economy) only just enough cells (when first set up) to do the necessary
+work. This is false economy, as when the cells are but slightly
+exhausted the battery power becomes insufficient; whereas, if another
+cell or two had been added, the battery would have run a much longer
+time without renewal, owing to the fact that each cell could have been
+reduced to a lower state of exhaustion, yet still the battery would have
+furnished the necessary power; and the writer has always found that the
+extra expense of the surplus cells is fully repaid by the increased
+length of time the battery runs without renewal."
+
+
+§ 29. Another form of Leclanché, from which great things were expected
+at its introduction, is the one known as the "Agglomerate block," from
+the fact that, instead of simply placing the carbon and manganese
+together loosely in a porous cell, solid blocks are formed by
+compressing these materials, under a pressure of several tons, around a
+central carbon core, to which the terminal is attached in the usual
+manner. The following are some of the compositions used in the
+manufacture of agglomerate blocks:--
+
+No. 1.
+
+ Manganese dioxide 40 parts.
+ Powdered gas carbon 55 "
+ Gum lac resin 5 "
+
+No. 2.
+
+ Manganese dioxide (pyrolusite) 40 parts.
+ Gas carbon (powdered) 52 "
+ Gum lac resin 5 "
+ Potassium bisulphate 3 "
+
+These are to be thoroughly incorporated, forced into steel moulds
+(containing the central carbon core) at a temperature of 100° C. (212°
+Fahr.), under a pressure of 300 atmospheres, say 4,500 lbs. to the
+square inch.
+
+No. 3.
+
+ _Barbier and Leclanché's Patent._
+
+ Manganese dioxide 49 parts.
+ Graphite 44 "
+ Pitch ("brai gras") 9 "
+ Sulphur 3/5 "
+ Water 2/5 "
+
+The materials having been reduced to fine powder, and the proportion of
+water stated having been added, are intimately mixed together by hand or
+mechanically. The moist mixture is moulded at the ordinary temperature,
+either by a simple compressing press, or by a press in which two pistons
+moving towards each other compress the block on two opposite faces; or
+the mixture may be compressed by drawing, as in the manufacture of
+electric light carbon. After compression, the products are sufficiently
+solid to be manipulated. They are then put in a stove, or oven, the
+temperature of which is gradually raised to about 350° C. (about 662°
+Fahr.); a temperature which is insufficient to decompose the
+depolarising substance (manganese dioxide), but sufficient to drive out
+first the volatile parts of the agglomerating material, and then to
+transform its fixed parts in a body unattackable by the ammonia of the
+cell. During the gradual heating, or baking, which lasts about two
+hours, what remains of the water in the agglomerate is driven off; then
+come the more volatile oils contained in the pitch, and finally the
+sulphur. The sulphur is added to the mixture, not as an agglomerative,
+but as a chemical re-agent (and this is a characteristic feature in the
+invention), acting on what remains of the pitch, as it acts on all
+carbo-hydrides at a high temperature, transforming it partially into
+volatile sulphuretted compounds, which are expelled by the heat, and
+partially into a fixed and unattackable body, somewhat similar to
+vulcanite. The action of the sulphur on the pitch can very well be
+likened to its action on caoutchouc (which is likewise a hydro-carbon)
+during the process of vulcanisation.
+
+These agglomerate blocks, however prepared, are placed in glass or
+porcelain containing vessels, as shown in Fig. 9, with a rod of zinc,
+separated from actual contact with the carbon by means of a couple of
+crossed indiarubber bands, which serve at the same time to hold the zinc
+rods upright. The exciting solution, as in the case of the ordinary
+Leclanché consists in a solution of ammonium chloride.
+
+[Illustration: Fig. 9.]
+
+Among the various advantages claimed for the agglomerate form of
+Leclanché over the ordinary type, may be mentioned the following:--
+
+1st.--The depolarising power of the manganese oxide is used to the best
+advantage, and that, owing to this, the electro-motive force of the
+battery is kept at the same point.
+
+2nd.--That, owing to the absence of the porous cell, there is less
+internal resistance in the battery and therefore more available current.
+
+3rd.--That the resistance of the battery remains pretty constant,
+whatever work be put upon it.
+
+4th.--That, owing to the fact that the liquid comes into contact with
+both elements immediately, the battery is ready for use directly on
+being charged.
+
+5th.--That the renewal or recharging is exceedingly easy, since the
+elements can be removed together, fresh solution added, or new
+depolarising blocks substituted.
+
+But when this battery came to be put to the test of practical work, it
+was found the block form could not be credited with all these
+advantages, and that their chief superiority over the old cell consisted
+rather in their lower internal resistance than in anything else. Even
+this is not an advantage in the case of bell work, except when several
+bells are arranged _in parallel_, so that a large current is required.
+The blocks certainly polarise more quickly than the old form, and it
+does not appear that they depolarise any more rapidly. Probably the
+enormous pressure to which the blocks are subjected, in the first two
+processes, renders the composition almost impermeable to the passage of
+the fluid, so that depolarisation cannot take place very rapidly.
+Another and serious objection to these blocks is that, after a little
+work, pieces break away from the blocks and settle on the zinc. This
+sets up a "short circuit," and the zincs are consumed whether the
+battery is in action or not.
+
+The author has had no opportunity for making any practical tests with
+the blocks prepared by process No. 3, but he is under the impression
+that the blocks would be even more friable than those prepared under
+greater pressure.
+
+
+§ 30. A third form of Leclanché, and one which has given considerable
+satisfaction, is the one known as "Judson's Patent." This consists, as
+shown at Fig. 10, in a cylinder of corrugated carbon encased in an outer
+coating of an insulating composition. Inside the cell are two or more
+thin carbon sheets, cemented to the sides of the cell by Prout's elastic
+glue, or some similar compound, so as to leave spaces, which are filled
+in with granular carbon and manganese. The surface of the plates is
+perforated, so as to allow ready access to the exciting fluid. The zinc
+rod, which is affixed to the cover, stands in the centre of the cell,
+touching it at no part. Owing to the very large surface presented by the
+corrugations in the carbon, and by the perforated carbon plates, the
+internal resistance of this form of battery is very low; hence the
+current, if employed against a small outer resistance, is large. But
+this, except in the case of bells arranged in parallel, is of no great
+advantage.
+
+[Illustration: Fig. 10.]
+
+
+§ 31. The ordinary form of Leclanché is found in market in three sizes,
+viz., No. 1, No. 2, and No. 3. Unfortunately, all makers do not use
+these numbers in the same manner, so that while some call the smallest,
+or _pint_ size, No. 1, others give this name to the largest, or
+_three-pint_, size. No. 2 is always quart size, and this is the one
+commonly employed. When several cells are employed to work a number of
+bells, it is well, in order that they may not receive injury, that they
+be enclosed in a wooden box. As it is necessary that the batteries
+should be inspected from time to time, boxes are specially made with
+doubled hinged top and side, so that when the catch is released these
+fall flat; thus admitting of easy inspection or removal of any
+individual cell. This form of battery box is shown at Fig. 11.
+
+[Illustration: Fig. 11. BATTERY IN BOX.]
+
+
+§ 32. There are certain ills to which the Leclanché cells are liable
+that require notice here. The first is _creeping_. By creeping is meant
+the gradual crystallisation of the sal ammonium up the inside and round
+the outside of the glass containing jar. There are two modes of
+preventing this. The first consists in filling in the neck with melted
+pitch, two small funnel-like tubes being previously inserted to admit of
+the addition of fresh sal ammoniac solution, and for the escape of gas.
+This mode cannot be recommended, as it is almost impossible to remove
+the pitch (in case it be required to renew the zinc, etc.) without
+breaking the glass vessel. The best way to remove the pitch is to place
+the cell in a large saucepan of cold water, and set it on a fire until
+the water boils. The pitch is, by this treatment, so far softened that
+the elements can be removed and the pitch scraped away with a knife.
+
+[Illustration: Fig. 12.]
+
+By far the better mode is to rub round the inside and outside of the
+neck of the jar with tallow, or melted paraffin wax, to the depth of an
+inch or thereabouts. This effectually prevents creeping and the
+consequent loss of current. Messrs. Gent, of Leicester, have introduced
+a very neat modification of the Leclanché cell, with a view to obviate
+altogether the evils deriving from creeping. This cell is illustrated at
+Fig. 12, and the following is the description supplied by the
+patentees:--"All who have had experience of batteries in which a
+solution of salts is used are aware of the difficulty experienced in
+preventing it creeping over the outside of the jar, causing local loss,
+and oftentimes emptying the jar of its solution. Many devices have been
+tried to prevent this, but the only effectual one is our patent
+insulated jar, in which a recess surrounds the top of the jar, this
+recess being filled with a material to which the salts will not adhere,
+thus keeping the outside of the jar perfectly clean. It is specially
+adapted for use in hot climates, and is the only cell in which jars may
+touch each other and yet retain their insulations. We confidently
+recommend a trial of this cell. Its price is but little in excess of the
+ordinary Leclanché." The battery should be set up in as cool a place as
+possible, as heat is very conducive to creeping. It is also important
+that the battery should be placed as near as convenient to the bell.
+
+Sometimes the zincs are seen to become coated with a black substance, or
+covered with crystals, rapidly wasting away at the same time, although
+doing little or no work; a strong smell of ammonia being given off at
+the same time. When this occurs, it points to an electrical leakage, or
+short circuit, and this, of course, rapidly exhausts the battery. It is
+of the utmost importance to the effective working of any battery that
+not the slightest leakage or _local action_ should be allowed to take
+place. However slight such loss be, it will eventually ruin the battery.
+This leakage may be taking place in the battery, as a porous cell may be
+broken, and carbon may be touching the zinc; or out of the battery,
+along the conducting wires, by one touching the other, or through
+partial conductivity of a damp wall, a metallic staple, etc., or by
+creeping. If loss or local action has taken place, it is best, after
+discovering and repairing the faults (see also _testing wires_), to
+replace the old zincs by new ones, which are not costly.
+
+
+§ 33. There is yet a modification of the Leclanché which is sometimes
+used to ring the large bells in hotels, etc., known as the Leclanché
+reversed, since the zinc is placed in the porous pot, this latter being
+stood in the centre of the stoneware jar, the space between the two
+being packed with broken carbon and manganese dioxide. By this means a
+very much larger negative surface is obtained. In the Grenet cell, the
+porous cell is replaced by a canvas bag, which is packed full of lumps
+of graphite and carbon dioxide, a central rod of carbon being used as
+the electrode. This may be used in out-of-the-way places where porous
+cells are not readily obtainable, but I cannot recommend them for
+durability.
+
+
+§ 34. The only other type of battery which it will be needful to notice
+in connection with bell work is one in which the depolariser is either
+chromic acid or a compound of chromic acid with potash or lime. Chromic
+acid consists of hydrogen united to the metal chromium and oxygen.
+Potassic dichromate (bichromate of potash: bichrome) contains potassium,
+chromium, and oxygen. If we represent potassium by K, chromium by Cr,
+and oxygen by O, we can get a fair idea of its constitution by
+expressing it as K_{2}Cr_{2}O_{7}, by which it is shown that one
+molecule of this body contains two atoms of potassium united to two
+atoms of chromium and seven atoms of oxygen. Bichromate of potash
+readily parts with its oxygen; and it is upon this, and upon the
+relatively large amount of oxygen it contains, that its efficiency as a
+depolariser depends. Unfortunately, bichromate of potash is not very
+soluble in water; one pint of water will not take up much more than
+three ounces of this salt. Hence, though the solution of potassium
+bichromate is an excellent depolariser as long as it contains any of the
+salt, it soon becomes exhausted. When bichromate of potash is used in a
+cell along with sulphuric acid and water, sulphate of potash and chromic
+acid are formed, thus:--
+
+ K_{2}Cr_{2}O_{7} + H_{2}SO_{4} + H_{2}O = K_{2}SO_{4} + 2H_{2}CrO_{4}
+ ---------------- ----------- ------ ----------- -------------
+ 1 molecule of & 1 molecule & 1 give 1 molecule & 2 molecules
+ bichrome. of molecule of of
+ sulphuric of sulphate chromic
+ acid. water. of potash. acid.
+
+From this we learn that before the potassium bichromate enters into
+action in the battery, it is resolved into chromic acid. Chromic acid is
+now prepared cheaply on a large scale, so that potassium bichromate may
+always be advantageously replaced by chromic acid in these batteries;
+the more so as chromic acid is extremely soluble in water. In the
+presence of the hydrogen evolved during the action of the battery (§ 18)
+chromic acid parts with a portion of its oxygen, forming water and
+sesquioxide of chromium, Cr_{2}O_{3}, and this, finding itself in
+contact with the sulphuric acid, always used to increase the
+conductivity of the liquid, forms sulphate of chromium. The action of
+the hydrogen upon the chromic acid is shown in the following equation:--
+
+ 2H_{2}CrO_{4} + 3H_{2} = 5H_{2}O + Cr_{2}O_{3}
+ ------------- ------ ------- -----------
+ 2 molecules of 3 molecules 5 molecules 1 molecule
+ chromic & of give of water. & of
+ acid. hydrogen. chromium
+ sesquioxide.
+
+[Illustration: Fig. 13.]
+
+
+§ 35. The "bottle" form of the bichromate or chromic acid battery (as
+illustrated at Fig. 13) is much employed where powerful currents of
+short duration are required. It consists of a globular bottle with a
+rather long wide neck, in which are placed two long narrow graphite
+plates, electrically connected to each other and to one of the binding
+screws on the top. Between these two plates is a sliding rod, carrying
+at its lower extremity the plate of zinc. This sliding rod can be
+lowered and raised, or retained in any position, by means of a set
+screw. The zinc is in metallic connection with the other binding screw.
+This battery (which, owing to the facility with which the zinc can be
+removed from the fluid, is extremely convenient and economical for short
+experiments) may be charged with either of the following fluids:--
+
+FIRST RECIPE.
+
+_Bichromate Solution._
+
+ Bichromate of potash (finely powdered) 3 oz.
+ Boiling water 1 pint.
+
+Stir with a glass rod, allow to cool, then add, in a fine stream, with
+constant stirring,
+
+ Strong sulphuric acid (oil of vitriol) 3 fluid oz.
+
+The mixture should be made in a glazed earthern vessel, and allowed to
+cool before using.
+
+SECOND RECIPE.
+
+_Chromic Acid Solution._
+
+ Chromic acid (chromic trioxide) 3 oz.
+ Water 1 pint.
+
+Stir together till dissolved, then add gradually, with stirring,
+
+ Sulphuric acid 3 oz.
+
+This also must not be used till cold.
+
+In either case the bottle must not be more than three parts filled with
+the exciting fluid, to allow plenty of room for the zinc to be drawn
+right out of the liquid when not in use.
+
+
+§ 36. The effects given by the above battery, though very powerful, are
+too transient to be of any service in continuous bell work. The
+following modification, known as the "Fuller" cell, is, however, useful
+where powerful currents are required, and, when carefully set up, may be
+made to do good service for five or six months at a stretch. The
+"Fuller" cell consists in an outer glass or glazed earthern vessel, in
+which stands a porous pot. In the porous pot is placed a large block of
+amalgamated zinc, that is cast around a stout copper rod, which carries
+the binding screw. This rod must be carefully protected from the action
+of the fluid, by being cased in an indiarubber tube. The amalgamation of
+the zinc must be kept up by putting a small quantity of mercury in the
+porous cell. The porous cells must be paraffined to within about half an
+inch of the bottom, to prevent too rapid diffusion of the liquids, and
+the cells themselves should be chosen rather thick and close in texture,
+as otherwise the zinc will be rapidly corroded. Water alone is used as
+the exciting fluid in the porous cell along with the zinc. Speaking of
+this form of cell, Mr. Perren-Maycock says:--"The base of the zinc is
+more acted on (when bichromate crystals are used), because the porous
+cells rest on the crystals; therefore let it be well paraffined, as also
+the top edge. Instead of paraffining the pot in strips all round (as
+many operators do) paraffin the pot all round, except at one strip about
+half an inch wide, and let this face the carbon plate. If this be done,
+the difference in internal resistance between the cell with paraffined
+pot and the same cell with pot unparaffined will be little; but if the
+portion that is unparaffined be turned away from the carbon, it will
+make very nearly an additional 1 ohm resistance. It is necessary to have
+an ounce or so of mercury in each porous cell, covering the foot of the
+zinc; or the zincs may be cast short, but of large diameter, hollowed
+out at the top to hold mercury, and suspended in the porous pot. The
+zinc is less acted on then, for when the bichromate solution diffuses
+into the porous pot, it obviously does so more at the bottom than at the
+top."
+
+[Illustration: Fig. 14.]
+
+Fig. 14 illustrates the form usually given to the modification of the
+Fuller cell as used for bell and signalling work.
+
+
+§ 37. Before leaving the subject of batteries, there are certain points
+in connection therewith that it is absolutely essential that the
+practical man should understand, in order to be able to execute any work
+satisfactorily. In the first place, it must be borne in mind that a cell
+or battery, when at work, is continually setting up electric
+undulations, somewhat in the same way that an organ pipe, when actuated
+by a pressure of air, sets up a continuous sound wave. Whatever sets up
+the electric disturbance, whether it be the action of sulphuric acid on
+zinc, or caustic potash on iron, etc., is called _electromotive force_,
+generally abbreviated E.M.F. Just in the same manner that the organ pipe
+could give no sound if the pressure of air were alike inside and out, so
+the cell, or battery, cannot possibly give _current_, or evidence of
+electric flow, unless there is some means provided to allow the
+_tension_, or increased atomic motion set up by the electromotive force,
+to distribute itself along some line of conductor or conductors not
+subjected to the same pressure or E.M.F. In other words, the "current"
+of electricity will always tend to flow from that body which has the
+highest tension, towards the body where the strain or tension is less.
+In a cell in which zinc and carbon, zinc and copper, or zinc and silver
+are the two elements, with an acid as an excitant, the zinc during the
+action of the acid becomes of higher "potential" than the other
+element, and consequently the undulations take place towards the
+negative plate (be it carbon, copper, or silver). But by this very
+action the negative plate immediately reaches a point of equal tension,
+so that no current is possible. If, however, we now connect the two
+plates together by means of any conductor, say a copper wire, then the
+strain to which the carbon plate is subjected finds its exit along the
+wire and the zinc plate, which is continually losing its strain under
+the influence of the acid, being thus at a lower potential (electrical
+level, strain) than the carbon, can and does actually take in and pass
+on the electric vibrations. It is therefore evident that no true
+"current" can pass unless the two elements of a battery are connected up
+by a conductor. When this connection is made, the circuit is called a
+"_closed circuit_." If, on the contrary, there is no electrical
+connection between the negative and positive plates of a cell or
+battery, the circuit is said to be open, or _broken_. It may be that the
+circuit is closed by some means that is not desirable, that is to say,
+along some line or at some time when and where the flow is not wanted;
+as, for instance, the outside of a cell may be _wet_, and one of the
+wires resting against it, when of course "leakage" will take place as
+the circuit will be closed, though no useful work will be done. On the
+other hand, we may actually take advantage of the practically unlimited
+amount of the earth's surface, and of its cheapness as a conductor to
+make it act as a portion of the conducting line. It is perfectly true
+that the earth is a very poor conductor as compared with metals. Let us
+say, for the sake of example, that damp earth conducts 100,000 times
+worse than copper. It will be evident that if a copper wire 1/20 of an
+inch in section could convey a given electric current, the same length
+of earth having a section of 5,000 inches would carry the same current
+equally well, and cost virtually nothing, beyond the cost of a metal
+plate, or sack of coke, presenting a square surface of a little over 70
+inches in the side at each end of the line. This mode of completing the
+circuit is known as "the earth plate."
+
+
+§ 38. The next point to be remembered in connection with batteries is,
+that the electromotive force (E.M.F.) depends on the _nature_ of the
+elements (zinc and silver, zinc and carbon, etc.) and the excitants used
+in the cell, and has absolutely nothing whatever to do with their
+_size_. This may be likened to difference of temperature in bodies.
+Thus, whether we have a block of ice as large as an iceberg or an inch
+square, the temperature will never exceed 32°F. as long as it remains
+ice; and whether we cause a pint or a thousand gallons of water to boil
+(under ordinary conditions), its temperature will not exceed 212°F. The
+only means we have of increasing the E.M.F., or "tension," or
+"potential," of any given battery, is by connecting up its constituent
+cells in _series_; that is to say, connecting the carbon or copper plate
+of the one cell to the zinc of the next, and so on. By this means we
+increase the E.M.F. just in the same degree as we add on cells. The
+accepted standard for the measure of electromotive force is called a
+VOLT, and 1 volt is practically a trifle less than the E.M.F. set up by
+a single Daniell's cell; the exact amount being 1·079 volt, or 1-1/12
+volt very nearly. The E.M.F. of the Leclanché is very nearly 1·6 volt,
+or nearly 1 volt and 2/3. Thus in Fig. 15, which illustrates 3 Leclanché
+cells set up in series, we should get
+
+ 1·6 volt
+ 1·6 "
+ 1·6 "
+ ---------
+ 4·8 volts
+
+as the total electromotive force of the combination.
+
+[Illustration: Fig. 15.]
+
+
+§ 39. The _current_, or amplitude of the continuous vibrations kept up
+in the circuit, depends upon two things: 1st, the electromotive force;
+2nd, the resistance in the circuit. There is a certain amount of
+resemblance between the flow of water under pressure and electricity in
+this respect. Let us suppose we have a constant "head" of water at our
+disposal, and allow it to flow through a tube presenting 1 inch
+aperture. We get a certain definite flow of water, let us say 100
+gallons of water per hour. More we do not get, owing to the resistance
+opposed by the narrowness of the tube to a greater flow. If now we
+double the capacity of the exit tube, leaving the pressure or "head" of
+water the same, we shall double the flow of water. Or we may arrive at
+the same result by doubling the "head" or pressure of water, which will
+then cause a double quantity of water to flow out against the same
+resistance in the tube, or conductor. Just in the same way, if we have a
+given pressure of electric strain, or E.M.F., we can get a greater or
+lesser flow or "current" by having less or more resistance in the
+circuit. The standard of flowing current is called an AMPÈRE; and 1
+ampère is that current which, in passing through a solution of sulphate
+of copper, will deposit 18·35 grains of copper per hour. The unit of
+resistance is known as an OHM. The resistance known as 1 ohm is very
+nearly that of a column of mercury 1 square millimètre (1/25 of an inch)
+in section, and 41-1/4 inches in height; or 1 foot of No. 41 gauge pure
+copper wire, 33/10000 of an inch in diameter, at a temperature of 32°
+Fahr., or 0° Centigrade.
+
+
+§ 40. Professor Ohm, who made a special study of the relative effects of
+the resistance inserted in the circuit, the electromotive force, and the
+current produced, enunciated the following law, which, after him, has
+been called "OHM'S LAW." It is that if we divide the number of
+electromotive force units (volts) employed by the number of resistance
+units (ohms) in the entire circuit, we get the number of current units
+(ampères) flowing through the circuit. This, expressed as an equation is
+shown below:
+
+E/R = C or Electromotive force/Resistance = Current.
+
+Or if we like to use the initials of volts, ampères, and ohms, instead
+of the general terms, E, R, and C, we may write V/R = A, or Volts/Ohms =
+Ampères.
+
+From this it appears that 1 volt will send a current of 1 ampère through
+a total resistance of 1 ohm, since 1 divided by 1 equals 1. So also 1
+volt can send a current of 4 ampères through a resistance of 1/4 of an
+ohm, since 1 divided by 1/4 is equal to 4. We can therefore always
+double the current by halving the resistance; or we may obtain the same
+result by doubling the E.M.F., allowing the resistance to remain the
+same. In performing this with batteries we must bear in mind that the
+metals, carbon, and liquids in a battery do themselves set up
+resistance. This resistance is known as "_internal resistance_," and
+must always be reckoned in these calculations. We can _halve_ the
+internal resistance by _doubling_ the size of the negative plate, or
+what amounts to the same thing by connecting two similar cells "_in
+parallel_;" that is to say, with both their zincs together, to form a
+positive plate of double size, and both carbons or coppers together to
+form a single negative of twice the dimensions of that in one cell. Any
+number of cells thus coupled together "_in parallel_" have their
+resistances reduced just in proportion as their number is increased;
+hence 8 cells, each having a resistance of 1 ohm if coupled together _in
+parallel_ would have a joint resistance of 1/8 ohm only. The E.M.F.
+would remain the same, since this does not depend on the size of the
+plate (see § 38). The arrangement of cells in parallel is shown at Fig.
+16, where three Leclanché cells are illustrated thus coupled. The
+following little table gives an idea of the E.M.F. in volts, and the
+internal resistance in ohms, of the cells mostly used in electric bell
+work.
+
+[Illustration: Fig. 16.]
+
+TABLE SHOWING E.M.F. AND R. OF BATTERIES.
+
+ ----------------+-------------------+-----------------+---------------
+ Name of Cell. | Capacity of Cell. | Electromotive | Resistance in
+ | | force in Volts. | Ohms.
+ ----------------+-------------------+-----------------+---------------
+ Daniell | 2 quarts | 1·079 | 1
+ " Gravity | 2 quarts | 1·079 | 10
+ Leclanché | 1 pint | 1·60 | 1·13
+ " | 2 pints | 1·60 | 1·10
+ " | 3 pints | 1·60 | 0·87
+ Agglomerate | 1 pint | 1·55 | 0·70
+ " | 2 pints | 1·55 | 0·60
+ " | 3 pints | 1·55 | 0·50
+ Fuller | 1 quart | 1·80 | 0·50
+ ----------------+-------------------+-----------------+---------------
+
+From this it is evident that if we joined up the two plates of a Fuller
+cell with a short wire presenting no appreciable resistance, we should
+get a current of (1·80 divided by 0·50) 3·6 ampères along the wire;
+whereas if a gravity Daniell were employed the current flowing in the
+same wire would only be a little over 1/10 of an ampère, since 1·079/10
+= 0·1079. But every wire, no matter how short or how thick, presents
+_some_ resistance; so we must always take into account both the internal
+resistance (that of the battery itself) and the external resistance
+(that of the wires, etc., leading to the bells or indicators) in
+reckoning for any given current from any cell or cells.
+
+
+
+
+CHAPTER III.
+
+ON ELECTRIC BELLS AND OTHER SIGNALLING APPLIANCES.
+
+
+§ 41. An electric bell is an arrangement of a cylindrical soft iron
+core, or cores, surrounded by coils of insulated copper wire. On causing
+a current of electricity to flow round these coils, the iron becomes,
+_for the time being_, powerfully magnetic (see § 13). A piece of soft
+iron (known as the _armature_), supported by a spring, faces the magnet
+thus produced. This armature carries at its free extremity a rod with a
+bob, clapper or hammer, which strikes a bell, or gong, when the
+armature, under the influence of the pull of the magnet, is drawn
+towards it. In connection with the armature and clapper is a device
+whereby the flow of the current can be rapidly interrupted, so that on
+the cessation of the current the iron may lose its magnetism, and allow
+the spring to withdraw the clapper from against the bell. This device is
+known as the "contact breaker" and varies somewhat in design, according
+to whether the bell belongs to the _trembling_, the _single stroke_, or
+the _continuous ringing_ class.
+
+
+§ 42. In order that the electric bell-fitter may have an intelligent
+conception of his work, he should _make_ a small electric bell himself.
+By so doing, he will gain more practical knowledge of what are the
+requisites of a good bell, and where defects may be expected in any he
+may be called upon to purchase or examine, than he can obtain from pages
+of written description. For this reason I reproduce here (with some
+trifling additions and modifications) Mr. G. Edwinson's directions for
+making an electric bell:--[10]
+
+_How to make a bell._--The old method of doing this was to take a piece
+of round iron, bend it into the form of a horse-shoe, anneal it (by
+leaving it for several hours in a bright fire, and allowing it to cool
+gradually as the fire goes out), wind on the wire, and fix it as a
+magnet on a stout board of beech or mahogany; a bell was then screwed to
+another part of the board, a piece of brass holding the hammer and
+spring being fastened to another part. Many bells made upon this plan
+are still offered for sale and exchange, but their performance is always
+liable to variation and obstruction, from the following causes:--To
+insure a steady, uniform vibratory stroke on the bell, its hammer must
+be nicely adjusted to move within a strictly defined and limited space;
+the least fractional departure from this adjustment results in an
+unsatisfactory performance of the hammer, and often a total failure of
+the magnet to move it. In bells constructed on the old plan, the wooden
+base is liable to expansion and contraction, varying with the change of
+weather and the humidity, temperature, etc., of the room in which the
+bells are placed. Thus a damp, foggy night may cause the wood to swell
+and place the hammer out of range of the bell, while a dry, hot day may
+alter the adjustment in the opposite direction. Such failures as these,
+from the above causes alone, have often brought electric bells into
+disrepute. Best made bells are, therefore, now made with metallic
+(practically inexpansible) bases, and it is this kind I recommend to my
+readers.
+
+[Footnote 10: "Amateur Work."]
+
+[Illustration: Fig. 17.]
+
+[Illustration: Fig. 18.]
+
+_The Base_, to which all the other parts are fastened, is made of 3/4
+in. mahogany or teak, 6 in. by 4 in., shaped as shown at Fig. 17, with a
+smooth surface and French polished. To this is attached the metallic
+base-plate, which may be cut out of sheet-iron, or sheet-brass (this
+latter is better, as iron disturbs the action of the magnet somewhat),
+and shaped as shown in Fig. 18; or it may be made of cast-iron, or cast
+in brass; or a substitute for it may be made in wrought-iron, or brass,
+as shown in Fig. 19. I present these various forms to suit the varied
+handicrafts of my readers; for instance, a worker in sheet metal may
+find it more convenient to manufacture his bell out of the parts
+sketched in Figs. 17, 18, 20^A, 21, 23, 24^A, and 25; but, on the other
+hand, a smith or engineer might prefer the improved form shown at Fig.
+31, and select the parts shown at Figs. 20^A, 22, 19, choosing either to
+forge the horse-shoe magnet, Fig. 20, or to turn up the two cores, as
+shown at Fig. 21 (A), to screw into the metal base, Fig. 21 B, or to be
+fastened by nuts, as shown at Fig. 19. The result will be the same in
+the end, if good workmanship is employed, and the proper care taken in
+fixing and adjusting the parts. A tin-plate worker may even cut his
+base-plate out of stout block tin, and get as good results as if the
+bell were made by an engineer. In some makes, the base-plate is cut or
+stamped out of thick sheet-iron, in the form shown by the dotted lines
+on Fig. 18, and when thus made, the part A is turned up at right angles
+to form a bracket for the magnet cores, the opposite projection is cut
+off, and a turned brass pillar is inserted at B to hold the contact
+screw, or contact breaker (§ 41).
+
+[Illustration: Fig. 19.]
+
+[Illustration: Fig. 20.]
+
+[Illustration: Fig. 20 A.]
+
+The _Magnet_ may be formed as shown at Fig. 20, or at Fig. 20^A. Its
+essential parts are: 1st. Two soft iron cores (in some forms a single
+core is now employed); 2nd. An iron base, or yoke, to hold the cores
+together; 3rd. Two bobbins wound with wire. The old form of magnet is
+shown at Fig. 20. In this form the cores and yoke are made out of one
+piece of metal. A length of round Swedish iron is bent round in the
+shape of a horseshoe; this is rendered thoroughly soft by annealing, as
+explained further on. It is absolutely essential that the iron be very
+soft and well annealed, otherwise the iron cores retain a considerable
+amount of magnetism when the current is not passing, which makes the
+bell sluggish in action, and necessitates a higher battery power to make
+it work (see § 14). Two bobbins of insulated wire are fitted on the
+cores, and the magnet is held in its place by a transverse strip of
+brass or iron secured by a wood screw passing between the two bobbins.
+The size of the iron, the wire, the bobbins, and the method of winding
+is the same as in the form next described, the only difference being
+that the length of the iron core, before bending to the horse-shoe
+form, must be such as to allow of the two straight portions of the legs
+to be 2 in. in length, and stand 1-3/8 apart when bent. We may now
+consider the construction of a magnet of the form shown at Fig. 20^A. To
+make the cores of such a magnet, to ring a 2-1/2 in. bell, get two 2
+inch lengths of 5/16 in. best Swedish round iron, straighten them,
+smooth them in a lathe, and reduce 1/4 in. of one end of each to 4/16 of
+an in., leaving a sharp shoulder, as shown at Fig. 21 A. Next, get a
+2-in. length of angle iron, drill in it two holes 1-3/8 apart, of the
+exact diameter of the turned ends of the cores, and rivet these securely
+in their places; this may be done by fastening the cores or legs in a
+vice whilst they are being rivetted. Two holes should be also bored in
+the other flange to receive the two screws, which are to hold the magnet
+to the base, as shown at Fig. 21 B. The magnet is now quite equal to the
+horse-shoe form, and must be made quite soft by annealing. This is done
+by heating it in a clear coal fire to a bright red heat, then burying it
+in hot ashes, and allowing it to cool gradually for a period of from 12
+to 24 hours; or perhaps a better guide to the process will be to say,
+bury the iron in the hot ashes and leave it there until both it and they
+are quite cold. The iron must be brought to a bright cherry red heat
+before allowing it to cool, to soften it properly, and on no account
+must the cooling be hurried, or the metal will be _hard_. Iron is
+rendered hard by hammering, by being rapidly cooled, either in cold air
+or water, and hard iron retains magnetism for a longer time than soft
+iron. As we wish to have a magnet that will only act as such when a
+current of electricity is passing around it, and shall return to the
+state of a simple piece of unmagnetised iron when the current is broken,
+we take the precaution of having it of soft iron. Many bells have failed
+to act properly, because this precaution has been neglected, the
+"residual" (or remaining) magnetism holding down the armature after
+contact has been broken. When the magnet has been annealed, its legs
+should be polished with a piece of emery cloth, and the ends filed up
+level and smooth. If it is intended to fasten the cores into the
+base-plate, this also should be annealed, unless it be made of brass, in
+which case a thin strip of soft iron should connect the back ends of the
+two legs before they are attached to the brass base (an iron yoke is
+preferable, as it certainly is conducive to better effects to have a
+massive iron yoke, than to have a mere strip as the connecting piece).
+It will also be readily understood and conceded that the cores should be
+cut longer when they are to be fastened by nuts, to allow a sufficient
+length for screwing the ends to receive the nuts. The length and size of
+the legs given above are suitable for a 2-1/2 in. bell only; for larger
+bells the size increases 1/16 of an inch, and the length 1/4 of an inch,
+for every 1/2 in. increase in the diameter of the bell.
+
+[Illustration: Fig. 21.]
+
+The _Bobbins_, on which the wire that serves to carry the magnetising
+current is to be wound, next demand our attention. They may be turned
+out of boxwood, ebony, or ebonite, or out of any hard wood strong enough
+and dense enough to allow of being turned down thin in the body, a very
+necessary requirement to bring the convolutions of wire as near the coil
+as possible without touching it. Some amateurs use the turned ends of
+cotton reels or spools, and glue them on to a tube of paper formed on
+the cores themselves. If this tube be afterwards well covered with
+melted paraffin wax, the plan answers admirably, but of course the
+bobbins become fixtures on the magnets. There are some persons who are
+clever enough to make firm bobbins out of brown paper (like rocket
+cases), with reel ends, that can be slipped off and on the magnet cores.
+To these I would say, "by all means at your command, do so if you can."
+The size of the bobbins for a 2-1/2 in. bell should be: length 1-3/4
+in., diameter of heads 3/4 of an in., the length increasing 1/4 of an
+in. and the diameter 1/8 of an in. for every additional 1/2 in. in the
+diameter of the bell. The holes throughout the bobbins should be of a
+size to fit the iron cores exactly, and the cores should project 1/8 of
+an inch above the end of the bobbins when these are fitted on. The wire
+to be wound on the bobbins is sold by all dealers in electrical
+apparatus. It is copper wire, covered with cotton or with silk, to
+ensure insulation. Mention has already been made of what is meant by
+insulation at § 3, but, in order to refresh the reader's memory, Mr. G.
+Edwinson's words are quoted here. "To insulate, as understood by
+electricians, means to protect from leakage of the electric current, by
+interposing a bad conductor of electricity between two good conductors,
+thus insulating[11] or detaching them from electric contact."
+
+[Footnote 11: _Insula_ in Latin means an island, hence an electrified
+body is said to be insulated when surrounded by non-conductors, as an
+island by the sea.]
+
+The following list will enable my readers to see at a glance the value
+of the substances mentioned here as conductors or insulators, the best
+conductors being arranged from the top downwards, and the bad conductors
+or insulators opposed to them in similar order, viz., the worst
+conductors or best insulators being at the top:--
+
+ _Conductors._ _Insulators._
+ Silver. Paraffin Wax.
+ Copper. Guttapercha.
+ Iron. Indiarubber.
+ Brass. Shellac.
+ All Other Metals. Varnishes.
+ Metallic Solutions. Sealing Wax.
+ Metallic Salts. Silk and Cotton.
+ Wet Stone. Dry Clothing.
+ Wet Wood. Dry Wood.
+ Oil, Dirt and Rust.
+
+See also the more extended list given at § 5 for a more complete and
+exact classification.
+
+It will be seen, on reference to the above, that copper is a good
+conductor, being excelled by silver alone in this respect; and that silk
+and cotton are bad conductors. When, therefore, a copper wire is bound
+round with silk or with cotton, even if two or more strands of such a
+covered wire be superimposed, since these are electrically separated by
+the non-conducting covering, no escape of electricity from one strand to
+the other can take place, and the strands are said to be insulated. If
+the copper wire had been coiled _naked_ round a bobbin, each convolution
+touching its neighbour, the current would not have circled round the
+whole length of the coils of wire, but would have leapt across from one
+coil to the other, and thus the desired effect would not have been
+obtained. A similar result, differing only in degree, would occur if a
+badly insulating wire were used, say one in which the covering had been
+worn in places, or had been badly wound, so as to expose patches of bare
+copper wire. If the insulation of a wire be suspected, it should be
+immersed in hot melted paraffin wax, and then hung up to drain and cool.
+The size of wire to be used on a 2-1/2 in. bell should be No. 24 B. W.
+G., the size falling two numbers for each 1/2 in. increase in the
+diameter of the bell. In these wires the higher the number, the finer
+the size, No. 6 being 1/5 and No. 40 being 1/200 of an inch in diameter.
+Silk-covered wire has an advantage over cotton-covered wire, inasmuch as
+the insulating material occupies less space, hence the convolutions of
+wire lie closer together. This is important, as the current has less
+effect on the iron if removed further from it, the decrease being as
+the _square_ of the distance that the current is removed from the wire.
+Magnets coiled with silk-covered wire admit also of better finish, but
+for most purposes cotton-covered wire will give satisfaction, especially
+if well paraffined. This wire must be wound on the bobbins, from end to
+end regularly, with the coils side by side, as a reel of cotton is
+wound. This may be done on a lathe, but a little practice will be
+necessary before the inexperienced hand can guide the wire in a regular
+manner. If, however, the spool of wire have a metal rod passed up its
+centre, and this be held in the hand at a distance of a foot or more
+from the bobbin on the lathe, the wire will almost guide itself on,
+providing the guiding hand be allowed to follow its course. With a
+little care, the wire for these little magnets may be wound entirely by
+hand. Before commencing to wind on the bobbins, just measure off 8 in.
+of the wire (not cutting it off) and coil this length around a pencil,
+to form a small coil or helix. The pencil may then be withdrawn from the
+helix thus formed, which serves to connect the wire with one of the
+points of contact. This free end is to be fastened outside the bobbin by
+a nick in the head; or the 1/8 in. length, before being formed into a
+helix, may be pushed through a small hole made on the head of the
+bobbin, so that 8 in. project _outside_ the bobbin, which projecting
+piece may be coiled into a helix as above described. The wire should now
+be wound exactly as a reel of cotton is wound, in close coils from end
+to end, and then back again, until three layers of wire have been laid
+on, so that the coiling finishes at the opposite end to that at which it
+began. To prevent this uncoiling, it should be fastened by tying down
+tightly with a turn or two of strong silk. The wire should now be cut
+from the hank, leaving about 2 in. of free wire projecting at the
+finishing end of each bobbin. In cases where many bobbins have to be
+wound, either for bells, for relays, or for indicator coils, a device
+similar to that illustrated at Fig. 21 A may be employed. This _electric
+bobbin winder_ consists in a table which can be stood on a lathe or near
+any other driving wheel. Two carriers, C C, somewhat similar to the back
+centre and poppet head of a lathe, hollow inside, and furnished with a
+spring and sliding piston spindle, stand one at each end of this table.
+The sliding spindle of the one carries at its extremity a pulley, A, by
+means of which motion can be transmitted from the band of the driving
+wheel. The sliding spindles, B B, are fitted with recesses and screws, H
+H H H, by means of which the temporary wooden cores, or the permanent
+iron cores, of the bobbins can be held while the bobbins are being
+wound. The bobbin is placed as shown at D; a flat piece of metal, E,
+hinged at G, presses against the bobbin, owing to the spring F. The
+centre figure shows details of the carrier, C, in section. At the bottom
+is shown the spool of wire on a standard L. The wire passes from this
+spot between the two indiarubber rollers, M M, on to the bobbin D.
+
+[Illustration: Fig. 21 A.]
+
+When the bobbins have been wound, they may be slipped over the magnet
+cores. They should fit pretty tightly; if they do not, a roll of paper
+may be put round the magnet cores, to ensure their not slipping when
+the bell is at work. The helix ends of the bobbins should stand
+uppermost, as shown at Fig. 22 A. A short length of the lower free ends
+of wire (near the base or yoke) should now be bared of their covering,
+cleaned with emery paper, twisted together tightly, as shown at Fig. 22
+B, soldered together, and any excess of wire cut off with a sharp pair
+of pliers. To prevent any chance electrical leakage between this bared
+portion of the wire and the iron, it should be carefully coated with a
+little melted guttapercha, or Prout's electric glue.
+
+[Illustration: Fig. 22.]
+
+Of course, if the operator has any skill at winding, he may wind both
+bobbins with one continuous length of wire, thus avoiding joins, taking
+care that the direction of the winding in the finished coils be as shown
+at Fig. 22 B; that is to say, that the wire from the _under_ side of one
+bobbin, should pass _over_ to the next in the same way as the curls of
+the letter [rotated S].
+
+[Illustration: Fig. 23.]
+
+[Illustration: Fig. 24.]
+
+[Illustration: Fig. 25.]
+
+[Illustration: Fig. 26.]
+
+[Illustration: Fig. 27.]
+
+The part that next claims our consideration is the _armature_, with its
+fittings. The armature is made out of 5/16 square bar iron, of the best
+quality, soft, and well annealed, and filed up smooth and true. The
+proportionate length is shown at Figs. 23 and 24; and the size of the
+iron for other bells is regulated in the same ratio as that of the
+cores. Two methods of making and attaching the springs and hammers are
+shown. Fig. 24 shows the section of an armature fitted with back spring
+and contact spring in one piece. This is cut out of hard sheet-brass, as
+wide as the armature, filed or hammered down to the desired degree of
+springiness, then filed up true on the edges. It may be attached to the
+iron of the armature, either by soldering, by rivetting, or by means of
+two small screws. Rivetting is, perhaps, the best mode, as it is not
+liable to shake loose by the vibration of the hammer. The spring at its
+shank end may be screwed or rivetted to the bracket. Mr. Edwinson
+considers this the better form of contact spring. The other form is made
+in two pieces, as shown at Fig. 23, where two strips of hard brass are
+cut off, of the width of the armature, and the edges filed. A slot is
+then cut in the back end of the armature to receive the two brass
+strips, and these are soldered into it. The top strip is then bent back
+over the armature to form the contact-spring, the other strip being
+soldered or rivetted to a small bracket of angle brass. In either case a
+short rod of stout hard brass wire is rivetted or screwed into the free
+end of the armature, and to the end of this rod is screwed or soldered
+the metal bead, or bob, which forms the hammer or "clapper" of the bell.
+The next portion to be made is the contact pillar, or bracket, with its
+screw, as shown at Fig. 25. This may either be a short stout pillar of
+1/4 in. brass rod, about 1 in. high, tapped on one side to receive the
+screw, which should be fitted with a back nut; or it may, as shown in
+the figure, be made out of a stout piece of angle brass. The exact size
+and length of the screw is immaterial; it must, however, be long enough
+to reach (when put in its place behind the contact spring) the spring
+itself, and still have a few threads behind the back nut to spare. The
+screw should be nicely fitted to the pillar, and the lock nut should
+clench it well, as when once the adjustment of the parts is found which
+gives good ringing, it is advisable that no motion should take place,
+lest the perfection of ringing be interfered with. Some makers use a
+"set screw" at the side of the pillar wherewith to hold the contact
+screw; others split the pillar and "spring" it against the contact
+screw; but, all things considered, the back nut gives the greatest
+satisfaction. When the bell is in action, a tiny spark is produced at
+every make and break of contact between the contact spring and this
+screw. This spark soon corrodes the end of the screw and the back of the
+spring if brass alone is used, as this latter rusts under the influence
+of the spark. To prevent this, a piece of platinum must be soldered or
+rivetted to the spring, at the point where the screw touches, as shown
+at Fig. 26, and also at the extremity of the contact screw itself. It is
+better to rivet the platinum than to solder it, as the platinum is very
+apt to absorb the solder, in which case it rusts quickly, and the
+goodness of the contact is soon spoiled, when the bell ceases to ring.
+To rivet the platinum piece on to the spring, as shown at Fig. 26, it is
+only needful to procure a short length of No. 16 platinum wire, say 1/8
+in., then, having drilled a corresponding hole at the desired spot in
+the contact spring, put the platinum wire half way through the hole, and
+give it one or two sharp blows on an anvil, with a smooth (pened)
+hammer.
+
+[Illustration: Fig. 28.]
+
+[Illustration: Fig. 29.]
+
+This will at once rivet it in its place, and spread it sufficiently to
+make a good surface for contact. The screw must likewise be tipped with
+platinum, by having a small hole bored in the centre of its extremity,
+of the same diameter as the platinum wire, which must then be pushed in,
+and rivetted by hammering the end, and burring the sides of the screw.
+Whichever method be adopted, care must be taken that the platinum tip on
+the screw and the speck on the contact spring are adjusted so as to
+touch exactly in their centres. It will be hardly worth while for the
+amateur to cast or even turn up his own bells (which are generally of
+the class known as clock gongs), as these can now be procured so cheaply
+already nickelled (see Fig. 28). The bell must be adjusted on its pillar
+(see Fig. 29^A), which is itself screwed into a hole in the base-plate,
+where it is held by a nut. The adjustment of the bell is effected by
+placing it over the shoulder of the pillar, and then clenching it down
+by screwing over it one or other of the nuts shown at Fig. 29. The bell
+should clear the base, and should be at such a height as to be struck on
+its edge by the hammer or clapper attached to the armature, Figs. 23 and
+24. We still need, to complete our bell, two binding screws, which may
+take either of the forms shown at Fig. 27; and an insulating washer, or
+collar, made of ebonite or boxwood, soaked in melted paraffin, to
+prevent the contact pillar (Fig. 25) making electrical contact with the
+metal base. The best shape to be given to these washers is shown at Fig.
+30. They consist in two thin circlets of wood or ebonite, that will just
+not meet when dropped, one on the one side, and one on the other of the
+hole through which the shank of the contact pillar passes when set up on
+the base-plate. If a wooden base be used below the metal base-plate,
+then only one washer, or collar, need be used--that is, the one
+_above_--since the screw of the pillar will pass into the wood, and this
+is not a conductor. If the metal base alone be used, both washers must
+be employed, and a small nut (not so large as the washer) used to
+tighten up and hold the pillar firm and immovable in its place opposite
+the contact spring.
+
+[Illustration: Fig. 30.]
+
+Having now all the parts at hand, we can proceed to fit them together,
+which is done as follows:--The bell pillar, with its bell attached, is
+fastened by its shank into the hole shown near B, Fig. 17, where it is
+screwed up tight by the square nut shown at Fig. 29 _c_. In the same
+manner, we must fasten the contact pillar, or bracket, shown at Fig. 24
+A. Whichever form be used, we must take great care that it be insulated
+from metallic contact with the metal base-plate by washers, as shown at
+Fig. 30 (similar washers must be used for the two binding screws if the
+_whole_ base-plate be made in metal). This being done, the metal frame,
+Fig. 18, is put in position on the wooden base, as shown at Fig. 17, and
+screwed down thereto by the screws indicated at _s s s_. The magnet may
+then be screwed down to the metal frame as shown. The small bracket of
+angle brass marked B, in Figs. 23 and 24, is next screwed into its
+place; that is, in such a position that the armature stands squarely
+facing the poles of the electro-magnet, but not quite touching them (say
+1/16 of an inch for a 2-1/2 in. bell). In setting up this and the
+contact pillar, the greatest care must be taken that the platinum tip of
+the contact screw, Fig. 25, should touch lightly the centre of the
+platinum speck at the back of the spring, Figs. 23 and 24, shown full
+size at Fig. 26.
+
+The free ends of the helically coiled electro-magnet wires should now be
+inserted into short lengths of small indiarubber tubing (same as used
+for feeding bottles), the extremities being drawn through and 1 in. of
+the copper wire bared of its covering for the purpose of making good
+metallic contact with the connections. One of these ends is to be
+soldered, or otherwise metallically connected, to the angle brass
+carrying the armature, spring and clapper, the other being similarly
+connected with the left-hand binding-screw, shown at Fig. 17. Another
+short length of wire (also enclosed in rubber tubing) must be arranged
+to connect the contact screw pillar Fig. 17, with the right-hand
+binding-screw. When this has been done, we may proceed to test the
+working of the bell by connecting up the binding screws with the wires
+proceeding from a freshly-charged Leclanché cell. If all have been
+properly done, and the connections duly made, the armature should begin
+to vibrate at once, causing the "bob," or hammer, to strike the bell
+rapidly; that is, provided the platinum tipped screw touches the
+platinum speck on the contact spring. Should this not be the case, the
+screw must be turned until the platinum tip touches the platinum speck.
+The armature will now begin to vibrate. It may be that the clapper runs
+too near the bell, so that it gives a harsh, thuddy buzz instead of a
+clear, ringing sound; or, possibly, the clapper is "set" too far from
+the bell to strike it. In either case a little bending of the brass wire
+carrying the clapper (either from or towards the bell, as the case may
+dictate) will remedy the defect. It is also possible that the armature
+itself may have been set too near, or too far from the electro-magnet.
+In the latter case, the clapper will not vibrate strongly enough, in the
+former the vibration will be too short, and the clapper may even stick
+to the poles of the electros, especially if these have not been
+carefully annealed. A little bending of the spring, to or from the
+magnets, will remedy these deficiencies, unless the distance be very
+much too great, in which case the bending of the spring would take the
+platinum tip out of the centre of the platinum speck.
+
+[Illustration: Fig. 31.]
+
+
+§ 43. Having thus constructed an efficient electric bell we may proceed
+to study its action and notice some of the defects to which it may be
+subject. In the first place, if we connect up the bell with the battery
+as shown in Fig. 17, viz., the left-hand binding-screw with the wire
+proceeding from the carbon of the Leclanché, and the right-hand screw
+with the wire from the zinc, then, if the platinum tipped screw touches
+the platinum speck, at the back of the contact spring, a current of
+electricity flows from the left-hand binding-screw all round the coils
+of the electro-magnets, passes along the contact spring and platinum
+speck, thence to the platinum tipped screw along the short length of
+wire to the right-hand binding-screw, whence it returns to the zinc
+element of the battery, thus completing the circuit. The current, in
+thus passing around the electro-magnet cores, converts them, _pro tem._,
+into a powerful magnet (see § 13); consequently, the armature, with its
+contact spring and hammer, is pulled towards the electro-magnets and at
+the same time gives a blow to the bell. Now, if instead of having the
+platinum speck attached to a flexible spring, it had been attached
+bodily to the rigid iron armature, directly the electro-magnets felt the
+influence of the current, the platinum speck would have also been pulled
+out of contact with the platinum screw, therefore the electro-magnet
+cores would have _immediately_ lost their magnetism (see § 13, last five
+lines). This would have been disadvantageous, for two reasons: 1st,
+because the _stroke_ of the hammer would have been very short, and
+consequently the ring of the bell very weak; and, 2nd, because, as even
+the softest iron requires some appreciable time for the electric current
+to flow round it to magnetise it to its full capacity, it would need a
+much greater battery power to produce a given stroke, if the contact
+were so very short. The use of an elastic contact spring is, therefore,
+just to lengthen the time of contact. But the electro-magnets, even when
+the flexible spring is used, do actually pull the platinum speck out of
+contact with the platinum screw. When this takes place, the circuit is
+broken, and no more current can flow round the electro-magnets, the
+spring reasserts its power, and the contact is again made between the
+contact screw and contact spring, to be again rapidly broken, each break
+and make contact being accompanied by a correspondingly rapid vibration
+of the armature, with its attendant clapper, which thus sets up that
+characteristic rapid ringing which has earned for these bells the name
+of trembling, chattering, or vibrating bells.
+
+
+§ 44. From a careful consideration of the last two sections it will be
+evident that the possible defects of electric bells may be classed under
+four heads: viz., 1st, Bad contacts; 2nd, Bad adjustment of the parts;
+3rd, Defective insulation; 4th, Warpage or shrinkage of base. We will
+consider these in the above order. Firstly, then, as to bad contacts.
+Many operators are content with simply turning the terminal wires round
+the base of the binding-screws. Unless the binding-screws are firmly
+held down on to the wires by means of a back nut, a great loss is sure
+to occur at these points, as the wires may have been put on with sweaty
+hands, when a film of oxide soon forms, which greatly lowers the
+conductivity of the junction. Again, at the junction points of the wires
+with the contact angle brass and contact pillar, some workmen solder the
+junctions, using "killed spirits" as a flux. A soldered contact is
+certainly the best, electrically speaking, but "killed spirits," or
+chloride of zinc, should never be used as a flux in any apparatus or at
+any point that cannot be washed in abundance of water, as chloride of
+zinc is very _deliquescent_ (runs to water), rottens the wire, and
+spoils the insulation of the adjacent parts. If solder be used at any
+parts, let _resin_ be used as a flux. Even if any excess of resin remain
+on the work, it does no harm and does not destroy the insulation of any
+of the other portions. Another point where bad contact may arise is at
+the platinum contacts. Platinum is a metal which does not rust easily,
+even under the influence of the electric spark given at the point of
+contact. Therefore, it is preferred to every other metal (except,
+perhaps, iridium) for contact breakers. Platinum is an expensive metal,
+the retail price being about 30s. an ounce, and as it is nearly twice as
+heavy as lead (Lead 11. Platinum 21·5) very little goes to an ounce. For
+cheap bells, therefore, there is a great temptation to use some other
+white metal, such as silver, german silver, platinoid, etc.
+
+The tip of the platinum screw may be tested for its being veritably
+platinum in the following mode: Touch the tip with the stopper of a
+bottle containing aquafortis, so as to leave a tiny drop on the extreme
+point of the suspected platinum. If it boils up green, or turns black,
+it is _not_ platinum; if it remains unaltered, it may be silver or
+platinum. After it has stood on the tip for a minute, draw it along a
+piece of white paper, so as to produce a streak of the acid. Expose the
+paper for a few minutes to sunlight. If the streak turns violet or pinky
+violet, the metal is _silver_; if the paper simply shows a slightly
+yellowish streak, the metal is platinum. The tip of the platinum screw
+must be carefully dried and cleaned after this trial before being
+replaced.
+
+Secondly, as to bad adjustment. It is evident that the magnets and the
+armature must stand at a certain distance apart to give the best effects
+with a given battery power. The distance varies from 1/24 in. in the
+very smallest, to 1/8 in. in large bells. Sometimes (but only in very
+badly made instruments) the armature adheres to the poles of the
+electro-magnet. This is due to _residual_ _magnetism_ (see § 14), and
+points to hard or unannealed iron in the cores or armature. As a
+make-shift, this defect may be partially remedied by pasting a thin
+piece of paper over that surface of the armature which faces the poles
+of the electro-magnets. Another bad adjustment is when the platinum
+screw does not touch fairly on the centre of the platinum speck, but
+touches the spring or the solder. Rust is then sure to form, which
+destroys the goodness of the contact. To adjust the contact spring at
+the right distance from the platinum screw, hold the hammer against the
+bell or gong. The armature should now _just not touch_ the poles of the
+electro-magnet. Now screw up the platinum screw until it _clears_ the
+contact spring by about the thickness of a sheet of brown paper (say
+1/50 of an inch). Let the hammer go, and notice whether the contact
+spring makes good contact with the platinum screw. This may be tried by
+the Leclanché cell as well, so as to make sure of the character of the
+_ringing_. When this has been satisfactorily adjusted the back-nut or
+set screw may be tightened, to insure that the vibration of the hammer
+shall not alter the adjustment. It sometimes happens that the spring
+that bears the armature is itself either too strong (or set back too
+far) or too weak. In the former case, the electro-magnet cannot pull the
+armature with sufficient force to give a good blow; in the latter, the
+spring cannot return the armature, with its attendant contact spring,
+back to its place against the platinum screw. To ascertain which of
+these two defects obtains, it is only necessary, while the bell is in
+action, to press the spring lightly with a bit of wire, first _towards_
+and then _away_ from the electro-magnets. If the ringing is improved in
+the first case, the spring is too strong; if improvement takes place in
+the latter case, the spring is too weak. The third source of inefficient
+action, defective insulation, is not likely to occur in a newly-made
+bell, except by gross carelessness. Still, it may be well to point out
+where electrical leakage is likely to occur, and how its presence may be
+ascertained, localized, and remedied. If the wire used to wind the
+electro-magnet be old, badly covered, or bared in several places in
+winding, it probably will allow the current to "short circuit," instead
+of traversing the whole length of the coils. If this be the case, the
+magnet will be very weak: the magnet of a 2-1/2-in. bell should be able
+to sustain easily a 1 lb. weight attached by a piece of string to a
+smooth piece of 1/2-in. square iron placed across its poles, when
+energized by a single pint Leclanché cell. If it will not do this, the
+insulation may be suspected. If the wire has been wound on the bare
+cores (without bobbins), as is sometimes done, bared places in the wire
+may be touching the iron. This may be ascertained by connecting one pole
+of a bottle bichromate, or other powerful battery, with one of the wires
+of the electro-magnet coils, and drawing the other pole of the battery
+across the clean iron faces of the electro-magnet poles. If there is any
+leakage, sparks will appear on making and breaking contact. Nothing but
+unwinding and rewinding with a well covered wire can remedy these
+defects. The other points where the insulation may be defective are
+between the binding screws and the base, if this be all of metal; or
+between the contact spring block and the base, and the contact pillar.
+It is also probable (if the connecting wires have not been covered with
+indiarubber tubing, as recommended) that leakage may be taking place
+between these wires and some portion of the metal work of the base or
+frame. This must be carefully examined, and if any point of contact be
+observed, a little piece of Prout's elastic glue, previously heated,
+must be inserted at the suspected places. With regard to the binding
+screws, if they stand on the wooden base, their insulation (unless the
+base be very damp indeed) will be sufficiently good; but if the base is
+entirely metallic, then ebonite or boxwood washers must be used to
+insulate them from contact with the base-plate. With regard to the
+contact spring block and the platinum screw pillar, it is _permissible_
+that one or the other should not be insulated from the base or frame;
+but one or the other _must_ be insulated by means of ebonite or other
+insulating washers. Personally, I prefer to insulate both; but in many
+really good bells only the platinum screw pillar is thus insulated. Any
+such leakage can be immediately detected by holding one pole of a
+powerful battery against the suspected binding-screw, or block, or
+pillar, and while in this position, drawing the other pole across some
+bare iron portion of the frame or metal base. Sparks will appear if
+there is any leakage.
+
+The fourth defect--that is, warpage or shrinkage of the base--can only
+occur in badly-made bells, in which the entire base is of wood. A
+cursory examination will show whether the board is warped or swollen, or
+whether it has shrunk. Warping or swelling will throw the electro-magnet
+too far from the armature, or "set" the pillar out of place; shrinkage,
+on the contrary, will bring the parts too close together and jamb the
+magnets, the armature, and the contact pillar into an unworkable
+position.
+
+
+§ 45. Before quitting the subject of the defects of bells, it may not be
+out of place to mention that no bell that is set to do real work should
+be fitted up without a cover or case. The dust which is sure to
+accumulate, not to speak of damp and fumes, etc., will certainly
+militate against good contacts and good action if this important point
+be neglected. The cover or case generally takes the form of a shallow
+box, as shown at Fig. 32, and may be made from 1/4-in. teak, mahogany,
+or walnut, dovetailed together and well polished. It is fastened to the
+base in the same manner as the sides of a Dutch clock, by means of
+studs, hooks and eyes. At the bottom of the box is cut a slot, of
+sufficient width and length to admit the play of the hammer shank.
+
+[Illustration: Fig. 32.]
+
+In the annexed table is given a general idea of the proportion which
+should be observed in the construction of bells of different sizes. It
+must be noted that if the bells are to be used at long distances from
+the battery, rather more of a finer gauge of wire must be employed to
+wind the magnets than that herein recommended, unless, indeed, _relays_
+be used in conjunction with the bells.
+
+
+§ 46.--
+
+TABLE
+
+Showing proportions to be observed in the different parts of electric
+bells.
+
+ ---------+---------+----------+--------+---------+----------
+ Diameter |Length of|Diameter |Length |Diameter | B. W. G.
+ of | Magnet |of Magnet | of |of Bobbin| of Wire
+ Bell. | Cores. | Cores. |Bobbin. | Head. |on Bobbin.
+ ---------+---------+----------+--------+---------+----------
+ 2-1/2" | 2" | 5/16" | 1-3/4" | 3/4" | 24
+ 3 | 2-1/4 | 3/8 | 2 | 7/8 | 24
+ 3-1/2 | 2-1/2 | 7/16 | 2-1/4 | 1 | 22
+ 4 | 2-3/4 | 1/2 | 2-1/2 | 1-1/8 | 22
+ 4-1/2 | 3 | 9/16 | 2-3/4 | 1-1/4 | 20
+ 5 | 3-1/4 | 5/8 | 3 | 1-3/8 | 18
+ 5-1/2 | 3-1/2 | 11/16 | 3-1/4 | 1-1/2 | 16
+ 6 | 3-3/4 | 3/4 | 3-1/2 | 1-5/8 | 16
+ 6-1/2 | 4 | 13/16 | 3-3/4 | 1-3/4 | 16
+ 7 | 4-1/4 | 7/8 | 4 | 1-7/8 | 16
+ 7-1/2 | 4-1/2 | 15/16 | 4-1/4 | 2 | 14
+ 8 | 4-3/4 | 1 | 4-1/2 | 2-1/8 | 14
+ 8-1/2 | 5 | 1-1/16 | 4-3/4 | 2-1/4 | 14
+ 9 | 5-1/4 | 1-1/8 | 5 | 2-3/8 | 14
+ 9-1/2 | 5-1/2 | 1-3/16 | 5-1/4 | 2-1/2 | 14
+ 10 | 5-3/4 | 1-1/4 | 5-1/2 | 2-5/8 | 14
+ 10-1/2 | 6 | 1-5/16 | 5-3/4 | 2-3/4 | 12
+ 11 | 6-1/4 | 1-3/8 | 6 | 2-7/8 | 12
+ 11-1/2 | 6-1/2 | 1-7/16 | 6-1/4 | 3 | 10
+ 12 | 6-3/4 | 1-1/2 | 6-1/2 | 3-1/8 | 10
+ ---------+---------+----------+--------+---------+----------
+
+[Illustration: Fig. 33 A.]
+
+[Illustration: Fig. 33 B.]
+
+[Illustration: Fig. 34.]
+
+
+§ 47. We can now glance at several modifications in the shape and mode
+of action of electric bells and their congeners. Taking Figs. 33 A and B
+as our typical forms of trembling bell, the first notable modification
+is one by means of which the bell is made to give a single stroke only,
+for each contact with the battery. This form, which is known as the
+"single stroke bell," lends itself to those cases in which it may be
+required to transmit preconcerted signals; as also where it is desired
+to place many bells in one circuit. Fig. 34 illustrates the construction
+of the single stroke bell. It differs from the trembling bell in the
+mode in which the electro-magnet is connected up to the binding screws.
+In the trembling bell, Fig. 33, the circuit is completed through the
+platinum screw pillar, to the binding screw marked Z, hence the circuit
+is rapidly made and broken as long as by any means contact is made with
+the battery, and the binding screws L and Z. But in the single stroke
+bell, Fig. 34, the wires from the electro-magnet are connected directly
+to the two binding screws L and Z, so that when contact is made with the
+battery, the armature is drawn to the poles of the electro-magnet, and
+kept there so long as the battery current passes. By this means, only
+one stroke or blow is given to the bell for each contact of the battery.
+Of course, directly the connection with the battery is broken, the
+spring which carries the armature and clapper flies back ready to be
+again attracted, should connection again be made with the battery. To
+regulate the distance of the armature from the poles of the
+electro-magnets, a set screw Q takes the place of the platinum screw in
+the ordinary form, while to prevent the hammer remaining in contact with
+the bell (which would produce a dull thud and stop the clear ring of the
+bell), a stop (_g_) is set near the end of the armature, or two studs
+are fixed on the tips of the poles of the electro-magnets. The mode of
+adjusting this kind of bell, so as to obtain the best effect, differs a
+little from that employed in the case of the trembling bell. The
+armature must be pressed towards the poles of the electro-magnets, until
+it rests against the stop or studs. A piece of wood or cork may be
+placed between the armature and the set screw Q, to retain the armature
+in this position, while the rod carrying the hammer or clapper is being
+bent (if required) until the hammer just clears the bell. If it touches
+the bell, a thud instead of a ring is the result; if it is set off too
+far, the ring will be too weak. The armature can now be released, by
+removing the wood or cork, and the set screw Q driven forwards or
+backwards until the best effect is produced when tested with the
+battery. The tension of the armature spring must be carefully looked to
+in these single stroke bells. If it is too strong, the blow will be
+weak; if too weak, the hammer trembles, so that a clear single stroke is
+not obtainable, as the spring _chatters_.
+
+
+§ 48. _The continuous ringing bell_ is the modification which next
+demands our attention. In this, the ringing action, when once started by
+the push,[12] or other contact maker, having been touched, continues
+either until the battery is exhausted, or until it is stopped by the
+person in charge. The great use of this arrangement is self-evident in
+cases of burglar alarms, watchman's alarms, etc., as the continuous
+ringing gives notice that the "call" has not received attention. The
+continuous ringing bell differs but little from the ordinary trembling
+bell. The chief difference lies in the addition of an automatic device
+whereby contact is kept up with the battery, even after the "push"
+contact has ceased. As it is desirable for the person in charge to be
+able to stop the ringing at will, without proceeding to the place where
+the "push" stands, so it is not usual to make the continuous ringing
+arrangement dependent on the "push," though, of course, this could be
+done, by causing it to engage in a catch, which would keep up the
+contact, when once made. Continuous ringing bells may be conveniently
+divided into two classes; viz., 1st, those in which a device is attached
+to the framework of the bell; which device, when once upset by the first
+stroke of the bell, places the bell in direct communication with the
+battery independent of the "push" or usual contact; and 2ndly, those in
+which a separate device is used, for the same purpose. This latter
+arrangement admits of the use of an ordinary trembling bell.
+
+[Footnote 12: A "push," of which several forms will hereafter be
+described and figured, consists essentially in a spring carrying a stud,
+standing directly over, but not touching, another stud, fixed to a base.
+The lower stud is connected to one terminal of battery, the spring is
+connected to the bell. When the spring is pressed down, the two studs
+come into contact, the current flows, and the bell rings.]
+
+[Illustration: Fig. 35.]
+
+[Illustration: Fig. 36.]
+
+Fig. 35 illustrates the action of bells of the first class. In the first
+place it will be noticed that there are three binding screws instead of
+two, as in the ordinary pattern, one marked C connected as usual with
+the carbon element of the battery; another marked L, which connects with
+line wire, and a third, Z, connected by means of a branch wire (shunt
+wire), proceeding from the zinc of the battery. It will be seen, that
+if the battery current is by means of the push caused to flow through
+the coils of the electro-magnets, the armature is attracted as usual by
+them, and in moving towards them, releases and lets fall the lever
+contact, which, resting on the contact screw, completes the circuit
+between Z and C, so that the bell is in direct communication with its
+battery, independently of the push. Hence the bell continues ringing,
+until the lever is replaced. This can be done, either by pulling a
+check string (like a bell-pull) attached to an eye in the lever, or by
+means of a press-button and counter-spring; as shown in Fig. 36, A and
+B.
+
+[Illustration: Fig. 37.]
+
+[Illustration: Fig. 38.]
+
+[Illustration: Fig. 39.]
+
+In continuous ringing bells of the second class, a detent similar to
+that shown at Fig. 35 D is used, but this, instead of being actuated by
+the electro-magnet belonging to the bell itself, is controlled by a
+separate and entirely independent electro-magnet, which, as it may be
+wound with many coils of fine wire, and have a specially light spring
+for the armature, can be made very sensitive. This second
+electro-magnet, which serves only to make contact with a battery, is
+known as a _Relay_, and is extensively employed in many cases where it
+is desired to put one or more batteries into, or out of circuit, from a
+distance. The relay may be looked upon as an automatic hand, which can
+be made to repeat at a distant point contacts made or broken by hand at
+a nearer one. Fig. 37 shows this arrangement, attached to the same base
+board as the bell itself. On contact being made with the push, the
+current enters at C, circulates round the cores of the relay, thus
+converting it into a magnet. The armature _a_ is thereby pulled to the
+magnet, and in so doing releases the detent lever, which falls on the
+contact screw, thus at one and the same time breaking the circuit
+through the relay, and making the circuit through the bell magnets B B´,
+back to the battery by Z. A second modification of this mode of causing
+an ordinary bell to ring continuously is shown at Fig. 38, the peculiar
+form of relay used therewith being illustrated at Fig. 39. Here, the
+relay is placed on a separate base board of its own, and could, if
+necessary, be thrown out of circuit altogether, by means of a
+_switch_,[13] so that the bell can be used as an ordinary bell or
+continuous action at will. It will be noticed that the relay has in this
+sketch only one core. But the delicacy of the action is not impaired
+thereby, as the armature, by means of the steel spring _s_, is made to
+form part and parcel of the magnet, so that it becomes magnetised as
+well as the core, and is attracted with more force than it would be, if
+it were magnetically insulated. The battery current enters by the wires
+C and W, passes round the coils of the electro-magnet, and returns by Z.
+In so doing it energises the electro-magnet E, which immediately
+attracts its armature A. The forward movement of the armature A,
+releases the pivoted arm L, to which is attached a platinum-tipped
+contact prong P. This, it will be noticed, is in metallic connection
+with the pillar P', and with the base, and, therefore, through the wire
+W, with the battery. When the arm L falls, the contact prong completes
+the circuit to the bell, through the insulated pillar X. The relay is
+thus thrown out of the circuit at the same time that the bell is thrown
+in. A device similar to those illustrated at Fig. 36 can be employed to
+reset the arm L.
+
+[Footnote 13: Described at § 61.]
+
+[Illustration: Fig. 40.]
+
+A rather more complicated arrangement for continuous bell ringing is
+shown at Fig. 40. It is known as Callow's, and is peculiarly adapted to
+ringing several bells from one attachment, etc. Owing to the relay in
+this form being wound with two sets of wires, it takes a little more
+battery power; but this disadvantage is compensated by its many good
+points. The following description, taken from F. C. Allsop's papers in
+the _English Mechanic_, will render the working of Callow's attachment
+perfectly clear. "When the button of the push P is pressed, the current
+in the main circuit flows from the positive pole C of the battery D
+through the relay coil _a_, and thence by the wire _d_ and push P, to
+the zinc of the battery. This attracts the armature A of the relay R,
+closing the local bell circuit, the current flowing from C of the
+battery to armature A of the relay R, through contact post _p_, terminal
+L of the bell, through bell to terminal Z, and thence by the wire _g_ to
+the zinc of the battery. Part of the current also flows along the wire
+from the bell terminal L through the relay coil _b_ and switch W, to
+terminal Z of the bell, thus keeping the armature of the relay down,
+after the main circuit (through the push) has been broken; the bell
+continuing to ring until the shunt circuit is broken by moving the arm
+of the switch W over to the opposite (or non-contact) side. The bell can
+also be stopped by short circuiting the relay, which can be effected by
+an ordinary push. It will be seen that more than one bell can be rung
+from the same attachment, and the bell can, by moving the arm of the
+switch W, be made continuous ringing or not, at will. If the arm of the
+switch is moved over to the opposite side to which it is shown in the
+figure, the shunt circuit of the bell through the relay is broken, and
+the bell will ring only so long as the button of the push is kept in.
+This continuous arrangement is very convenient for front doors, etc.,
+where trouble is experienced in securing immediate attention to the
+summons. Instead of being taken to the switch, as in Fig. 40, the two
+wires are taken to a contact piece fixed on the side of the door frame,
+and so arranged that when the door is opened, it either short circuits
+or breaks the shunt circuit: thus when the push is pressed, the bell
+rings until the door is opened, the continual ringing of the bell
+insuring prompt attention."
+
+Mr. H. Thorpe, of 59, Theobald's Road, London, has devised a very
+ingenious arrangement for the continuous ringing of one or more bells
+for a stated period of time. This is shown at Fig. 40 A. It is set in
+action by pulling the ring outside the bottom of the core. The bell or
+bells then start ringing, as contact is established and kept up. The
+novelty lies in the fact that the duration of the contact, and
+consequently of the ringing, can be accurately timed from 5 seconds to
+30 seconds, by merely inserting a pin at different holes in the rod, as
+shown. After the bells have rung the required time the instrument
+automatically resets itself.
+
+[Illustration: Fig. 40 A.]
+
+
+§ 49. The modifications we are now about to consider, differ from the
+ordinary bell, either in the shape or material of the bell itself, the
+relative disposition of the parts, or some structural detail; but not
+upon the introduction of any new principle. The most striking is
+certainly the Jensen bell, which is shown in section at Fig. 41.
+
+[Illustration: Fig. 41.]
+
+According to Mr. Jensen's system of electric bells, the bell may take
+any desired form, that of the ordinary church bell being preferred, and
+the electro-magnetic apparatus is placed entirely inside the bell
+itself. To attain this end the electro-magnetic apparatus must be
+compact in form. A single electro-magnet has pole pieces at each end
+opposite to which an armature is suspended from a pivot and balanced by
+the hammer of the bell. At the back of the armature there may be a make
+and break arrangement, whereby a continuous succession of strokes is
+effected, or this may be omitted, in which case a single stroke is
+given when the contact with the battery is made, or both may be effected
+by separate wires, make contact with one wire, and a single stroke is
+struck; make it with the other and the current passes through the make
+and break and a succession of strokes is heard. When the contact-breaker
+is used, it is so arranged that a slight rub is caused at every stroke,
+so keeping the contact clean. The flexible break, with the ingenious
+wiping contact, is a great improvement over the ordinary screw, which
+often becomes disarranged.
+
+The form of the magnet is such that a considerable degree of magnetic
+force is caused by a comparatively small battery power. The
+electro-magnetic apparatus being within the bell the latter forms a very
+effective and handsome shield for the former. Not only can the bell
+shield the electro-magnet from wet but the whole of the conducting wires
+as well.
+
+The bell may be screwed to a tube through which passes the conducting
+wire, which makes contact with an insulated metallic piece in the centre
+of the top of the bell. Both the wire and the contact piece are as
+completely shielded from the weather as if within the bell itself.
+
+[Illustration: Fig. 42.]
+
+The great point of departure is the discarding of the unsightly magnet
+box, and the hemispherical bell (_see_ Fig. 32), and substituting a bell
+of the Church type (see Fig. 42), and placing inside it an
+electro-magnet specially arranged. The inventors use a single solenoidal
+magnet of a peculiar construction, by which the armature is attracted by
+both poles simultaneously. By this means less than half the usual
+quantity of wire is required, thus reducing the external resistance of
+the circuit one half. Moreover the armature, besides being magnetised by
+induction, as acted on in the ordinary method of making electric bells,
+is by Messrs. Jensen's plan directly polarised by being in actual
+magnetic contact by the connection of the gimbal (which is one piece
+with the armature) with the core iron of their magnet. It is thus
+induced to perform the largest amount of work with the smallest
+electro-motive force. Instead of the armature and clapper being in a
+straight line attached to a rigid spring, which necessitates a
+considerable attractive power to primarily give it momentum, in the
+Jensen Bell the armature and hammer are in the form of an inverted [U],
+and being perfectly balanced from the point of suspension, the lines of
+force from a comparatively small magnetic field suffice to set this
+improved form of armature into instant regular vibration. By using a
+flexible break and make arrangement instead of the usual armature spring
+and set screw (at best of most uncertain action), it is found that a
+much better result is attained, and by this device the armature can be
+set much nearer the poles of the magnet with sufficient traverse of the
+hammer. This is in strict accordance with the law of inverse squares,
+which holds that the force exerted between two magnetic poles is
+inversely proportionate to the square of the distance between them, or,
+in other words, that magnets increase proportionately in their power of
+attraction as they decrease in the square of the distance. It will now
+be seen why these bells require so little battery power to ring them:
+firstly, the armature and hammer are so perfectly balanced as to offer
+but little resistance; secondly, the external resistance to the current
+is reduced; and thirdly, the best possible use is made of the
+electro-magnetic force at disposal.
+
+
+§ 50. The next modification which demands attention is the so-called
+"Circular bell." This differs from the ordinary form only in having the
+action entirely covered by the dome. Except, perhaps, in point of
+appearance, this presents no advantages to that. The bells known as
+"Mining bells" resemble somewhat in outward appearance the circular
+bell; but in these mining bells the action is all enclosed in strong,
+square teak cases, to protect the movement, as far as possible, from the
+effects of the damp. All the parts are, for the same reason, made very
+large and strong; the armature is pivoted instead of being supported on
+a spring, the hammer shank being long, and furnished with a heavy bob.
+The domes or bells are from 6 inches to 12 inches in diameter, and are
+generally fitted with _single stroke_ movement, so as to enable them to
+be used for signalling. The hammer shank, with its bob, and the dome,
+which stands in the centre of the case, are the only parts left
+uncovered, as may be seen on reference to Figs. 43 A and B, where the
+exterior and interior of such a bell are shown.
+
+[Illustration: Fig. 43 A.]
+
+[Illustration: Fig. 43 B.]
+
+[Illustration: Fig 44.]
+
+
+§ 51. In the "Electric Trumpet," introduced by Messrs. Binswanger, of
+the General Electric Company, we have a very novel and effective
+arrangement of the parts of an electric bell and telephone together.
+This instrument, along with its battery, line and push, is illustrated
+at Fig. 44, where A is a hollow brass cylinder, in which is placed an
+ordinary electro-magnet similar to Figs. 20 or 20 A. At the front end,
+near B, is affixed by its edges a thin disc of sheet iron, precisely as
+in the Bell telephone,[14] and over against it, at B, is an insulated
+contact screw, as in the ordinary trembling bell. On the disc of sheet
+iron, at the spot where the screw touches, is soldered a speck of
+platinum. The wires from the electro-magnet are connected, one to the
+upper binding screw, the other to the brass case of the instrument
+itself, which is in metallic communication with the sheet iron disc.
+The return wire from the contact screw is shown attached to the
+insulated piece, and is fastened to another binding screw (not visible)
+on the base board. When contact is made with the battery, through the
+press or push, the magnet becomes energised, and pulls the iron disc or
+diaphragm towards it, causing it to buckle inwards. In doing this,
+contact is broken with the screw B; consequently the diaphragm again
+straightens out, as the magnet no longer pulls it. Again contact is
+made; when of course the same round of performances is continuously
+repeated. As the plate or diaphragm vibrates many hundreds of times per
+second, it sets up a distinctly musical and loud sound wave, not unlike
+the note of a cornet-a-piston, or a loud harmonium reed. With a number
+of these "trumpets," each diaphragm being duly tuned to its proper
+pitch, it would be possible to construct a novel musical instrument,
+working solely by electricity. The "pushes" need only take the form of
+pianoforte keys to render the instrument within the grasp of any
+pianoforte or organ player.
+
+[Footnote 14: See "Electrical Instrument Making for Amateurs." Whittaker
+& Co. Second edition.]
+
+
+§ 52. Sometimes the gong or "dome" of the ordinary bell is replaced by a
+coil spring, as in the American clocks; sometimes quaint forms are given
+to the parts covering the "movement," so as to imitate the head of an
+owl, etc. But bells with these changes in outward form will not present
+any difficulty, either in fixing or in management, to those who have
+mastered the structural and working details given in this chapter.
+
+
+
+
+CHAPTER IV.
+
+ON CONTACTS, PUSHES, SWITCHES, KEYS, ALARMS, AND RELAYS.
+
+
+§ 53. All the appliances which have hitherto been described, would be
+utterly useless for the purposes intended, had we not at hand some means
+of easily, certainly and rapidly completing and breaking the circuit
+between the bell or bells, on the one hand, and the battery on the
+other. This necessary piece of apparatus, which is simply a contact
+maker, receives different names, dependent on its application. When it
+is intended to be actuated directly by hand, it is known as a "push," a
+"pressel," or "pull," according to the mode in which the contact is
+made. At Fig. 45, A, B, C, D, and E, show the outward forms of various
+"pushes," in wood and china, as sent out by the leading makers. (The
+ones figured are from Messrs. Binswanger & Co.) At F is a sectional view
+of one of these pushes, and G shows the interior when the cover has been
+removed. From these two latter illustrations it will be easily
+understood that the "push" consists essentially in two pieces of metal
+one or both of which are springs, and one of which is connected with one
+of the wires from the battery, while the other is attached to the wire
+proceeding to the bell. When the button is pressed the upper spring
+comes into contact with the lower metal spring or plate. The circuit is
+now complete; hence the bell rings. But as soon as the finger is removed
+from the stud or button of the "push," the spring returns to its old
+place, contact being thereby broken when the bell ceases to ring, unless
+it be fitted with a continuous ringing arrangement (see § 48). In
+fastening the leading wires to these pushes, care must be taken that
+the ends of the wires be scraped, and sand papered quite clean and
+bright, bent into a loop which must be inserted under the head of the
+screw that holds the wire to the spring pieces; the screws being then
+tightened up carefully to ensure a good grip and contact with the wires.
+
+[Illustration: Fig. 45.]
+
+[Illustration: Fig. 46.]
+
+
+§ 54. A "pressel" (Fig. 46) is simply a push which instead of being made
+a fixture by being fastened in the wall or door, is attached to a
+metallic wired line, so that it is generally made to resemble somewhat
+in outward appearance the knob or tassel of the bell-pull of the last
+generation, the interior arrangement is precisely similar to that of the
+push; that is to say, the pressel consists in a pear-shaped or
+acorn-shaped hollow wooden box, with a projecting knob or button below.
+This button is attached to a spring, the tension of which keeps the knob
+protruding from the end of the box, and at the same time prevents
+contacts with the second spring at the bottom of the box. Two insulated
+wires, one from the battery, the other from the bell, are connected to
+separate screws at the top of the pressel. One of these screws connects
+with the lower spring, the other with the upper.
+
+[Illustration: Fig. 47.]
+
+
+§ 55. The "pull" (Fig. 47), as its name implies, makes contact and rings
+the bell on being pulled. The knob has a rather long shank bar, around
+which is coiled a pretty stiff spring. At the farther extremity is an
+ebonite or boxwood collar ending in a rather wider metal ring. The wires
+from the bell and battery are connected respectively to two flat
+springs, _a a'_, by the screws _b b'_. When the knob is pulled, the
+metal collar touches both springs, and the circuit is completed. Closely
+allied to the "pull" is a form of bedroom contact, which combines
+pear-push or pressel and pull in one device. This will be readily
+understood on reference to Fig. 48. Another form of bedroom pull, with
+ordinary rope and tassel, consists in a box containing a jointed metal
+lever, standing over a stud, from which it is kept out of contact by a
+counter spring. To the projecting end of the lever is attached the bell
+rope. When this is pulled the lever touches the stud, contact is made,
+and the bell rings. This is clearly shown in Fig. 49 A. In all these
+contacts, except the door pull (Fig. 47) where the friction of the
+action of pulling keeps the surfaces bright, the points of contact
+should be tipped with platinum. Another form of contact to be let in the
+floor of the dining-room, within easy reach of the foot of the carver,
+or other persons at the head of the table, is shown at Fig. 49 B.
+
+[Illustration: Fig. 48.]
+
+[Illustration: Fig. 49 A.]
+
+[Illustration: Fig. 49 B.]
+
+Mr. Mackenzie has introduced a very ingenious contrivance whereby the
+ringer may know whether the bell at the distant end has rung. This is
+effected by inclosing in the push a device similar to that shown at Fig.
+43 A. That is to say, an electro-magnet wound with wire, and surmounted
+by a thin iron disc, is placed in circuit with the line wires. The
+ringing of the bell rapidly magnetises and demagnetises the
+electro-magnet, and causes a humming sound, which clearly indicates
+whether the bell is ringing or not. As this device can be made very
+small, compact, and not liable to derangement, it is of easy
+application.
+
+
+§ 56. The next form of contact to which our attention must be directed,
+is that known as the _burglar alarm_, with its variant of door-contacts,
+sash-contacts, till-contacts, etc.
+
+The "burglar's pest" (as the contrivance we illustrate is called) is one
+of the most useful applications of electricity for the protection of
+property against thieves. It consists usually, first, of a brass plate
+(Fig. 50), upon which a platinum contact piece is fixed, and second, of
+a spring made of hardened brass or steel insulated from the plate; or of
+a cylindrical box with a spiral spring inside (see Fig. 51). It is so
+arranged that as long as the stud is kept pressed in, the platinum
+points of contact are kept apart; this is the position when fixed in the
+rebate of a closed door or window; but as soon as opened, the stud
+passes outward through the hole, and the points of contact come together
+and complete the circuit of the wires in connection with the bell. The
+bell is best to be a continuous ringing one. It may be fixed in the
+master's bedroom, or outside the premises in the street.
+
+[Illustration: Fig. 50.]
+
+[Illustration: Fig. 51.]
+
+Legge's Window Blind contact is an arrangement by which the blind is
+secured at the bottom by attaching it to a hook or button. A slight
+pressure against the blind (caused by anyone trying to enter after
+having broken a window) sets the electric bell in motion unknown to the
+intruder.
+
+[Illustration: Fig. 52.]
+
+[Illustration: Fig. 53.]
+
+A form of floor contact, which may be placed under a light mat or
+carpet, illustrated at Fig. 52, serves to give notice if anyone be
+waiting at the door, or stepping into places which are desired to be
+kept private. All these arrangements, to be serviceable, should be
+connected with continuous ringing bells (see § 48). Wherever it is
+likely that these arrangements may stand a long time without being
+called into play, it is better to employ some form of contact in which a
+_rubbing_ action (which tends to clean the surfaces and then make a good
+contact) is brought into play, rather than a merely _dotting_ action.
+For this reason, spring contacts in which the springs connected with the
+wires are kept apart by an insulating wedge (shown at Fig. 53) as long
+as the door or window are kept closed, are preferred. In the case of
+windows, strips of brass let into the frame on each side of the sash,
+are thrown into contact by the springs _a_ and _a'_ in the sash itself,
+as shown at Fig. 54. For shop doors and others, where a short contact
+only is required, and this only when the door is opened, a contact such
+as shown at Fig. 55 is well adapted. It consists, as will be seen, in a
+peculiarly shaped pivoted trigger _a_, which is lifted forwards when the
+door is opened, so that it makes contact with the spring _b_. Owing to
+the curved shape of the arm of the trigger, the contact is not repeated
+when the door is closed.
+
+[Illustration: Fig. 54.]
+
+[Illustration: Fig. 55.]
+
+
+§ 57. In all forms of burglar or thief alarms, the ordinary system of
+having the circuit broken, until contact is made by the intruder
+involuntarily making contact at some point, presents one great
+disadvantage; and that is, that if "_notre ami l'ennemi_," viz., the
+thief or burglar, be anything of an electrician (and alas! to what base
+uses may not even science be perverted) he will begin by cutting all
+suspicious-looking wires before he attempts to set about any serious
+work. This disadvantage may be entirely overcome by the adoption of a
+simple modification, known as the "closed circuit system" of bell
+ringing. For this the bells, etc., are continuously in contact with the
+batteries, but owing to the peculiar connections, do not ring unless the
+circuit is broken. To render the working of such a system clear to my
+readers, I quote the description given in the _English Mechanic_, by one
+of our leading electricians:--
+
+Writing on the subject of Closed Circuit Bell-ringing, Mr. Perren
+Maycock says:--"This is principally adopted for alarm purposes. Its
+superiority over the open circuit system lies in the fact that notice is
+given on opening (breaking) the circuit, which is the reverse to the
+usual practice. In the ordinary method it becomes necessary to have a
+contact maker, differing in form for various purposes and situations,
+which, along with the leading wires, must be artfully concealed. All
+this entails great expense; besides which one can never be sure that the
+contacts and wires are in proper order without actually trying each one.
+On the other hand, with the "closed circuit" system, one has merely to
+place the wire in any convenient position, it being better _seen_ than
+_hidden_. The very fact that alarm is given on breaking the contact
+renders the method applicable in circumstances and under conditions
+which would render the "open" method difficult and expensive, if not
+impossible. One can always be certain that everything is in order. The
+modern burglar, electrically educated as regards common practise in
+such matters, would naturally make a point of cutting all wires that
+fall in his path. From these and other obvious considerations, it is
+evident how simple and yet how perfect a means of protection such a
+system provides. I will now proceed to explain the manner of
+application. The bell used differs from the ordinary, only in the
+arrangement of its external connections.
+
+[Illustration: Fig. 56 A.]
+
+Fig. 56 A represents a single-alarm circuit. When contact is broken
+externally, there is a closed circuit in which are the battery and bell
+magnet coils. Consequently the armature is drawn away from the contact
+stud, close up to the electro-magnet, and is held so. When a break
+occurs, the armature flies back, completes the local circuit, and rings
+so long as the external circuit remains broken. There is a switch for
+use when the alarm is not required.
+
+[Illustration: Fig. 56 B.]
+
+[Illustration: Fig. 57.]
+
+Fig. 56 B represents a case in which notice is given at two places. By
+insulating a key as shown, reply signalling can be carried on between
+the points at which the bells are placed. A special gravity Daniell
+modification (§ 25) is used for this class of work (Fig. 57): a narrow
+lead cylinder, about 2" in diameter, watertight except at the bottom,
+where it opens out into an inverted cone, the surface of which is
+pierced with holes. This stands immersed in dilute sulphuric acid. A
+saturated solution of copper sulphate is next carefully introduced, so
+as to displace the acid upwards. Crystals of sulphate of copper are
+introduced into the open end at the top of cylinder, to fill the
+perforated portion at the bottom. From the wooden cover of cell a thick
+flat ring of amalgamated zinc hangs suspended in the dilute acid. Care
+should be taken not to introduce the zinc till the two solutions have
+become well separated. During action this becomes coppered, while in
+contact with the sulphate of copper, but it is not attacked by the acid.
+It is, however, preferable to _paint_ that portion of the lead, which is
+surrounded by the acid. The height of the cell is about 14.''
+
+It will be readily understood that if this latter system be employed,
+special contacts, which break contact when the pressure is removed, must
+be employed for the door or window contacts. A simple form is shown at
+Fig. 58.
+
+[Illustration: Fig. 58.]
+
+Contacts similar to Figs. 50, 53 and 54, may be fitted on tills or
+drawers.
+
+
+§ 58. Another useful application of "contact" is for the notification of
+any rise or fall of temperature beyond certain fixed limits. The devices
+used for this purpose are known as "fire alarms," "frost alarms," and
+"thermometer alarms." The thermometer alarm is at once the most
+effective and trustworthy of the forms known, as, besides its delicacy,
+it has the advantage of being able to give notice of low, as well as of
+abnormally high temperature. The form usually given to the electric
+alarm thermometer, is well shown at Fig. 59. It consists in an ordinary
+thermometer with a wire projecting into the tube to a certain point, say
+100 degrees. The mercury in the bulb being also connected with another
+wire. When the temperature is within the usual climatic range, the
+mercury does not reach the upper wire. If by reason of fire or any other
+abnormal heat, the temperature rises beyond that to which the instrument
+is set, the mercury rises and touches the upper wire, contact is thus
+established, and the bell rings.
+
+[Illustration: Fig. 59.]
+
+By giving the thermometer the shape of a letter [U], it is possible to
+notify also a fall below a certain degree, as well as a rise beyond a
+certain fixed point. These thermometers are specially used by nurserymen
+and others, to warn them of the too great lowering of temperature, or
+_vice versâ_, in the houses under their charge.
+
+Other forms of fire alarms are shown at Fig. 60 and 61. If a strip be
+built up of two thin layers of dissimilar metals riveted together, as
+the two metals do not expand at the same rate, the strip will bend to
+the _right_ if heated, and to the _left_ if cooled. In the instrument
+shown at Fig. 60, the application of heat causes the flexible strip
+carrying the contact screw, to bend over till it touches the lower stop,
+when, of course, the bell rings. If two stops are employed instead of
+the lower one only, the bell will ring when a low temperature is
+reached, which causes the strip to bend in the opposite direction.
+
+[Illustration: Fig. 60.]
+
+[Illustration: Fig. 61.]
+
+At Fig. 61 is illustrated a novel form, in which the expansion of air
+causes contact to be made. It consists in an air chamber hermetically
+closed by a corrugated metal plate I, similar to that used in the
+aneroid barometers. When the temperature rises to a certain point, the
+expansion of the air in the chamber brings the metallic plate into
+contact with the screw, as shown below. This closes the circuit and
+rings the bell in the usual manner. In all these fire or thermometer
+alarms, the exact degree of heat at which the bell shall ring, can be
+pretty accurately adjusted by means of the contact screws.
+
+
+§ 59. Closely allied to these forms of contacts are the devices whereby
+an ordinary clock or watch can be made to arouse the over-drowsy sleeper
+by the ringing of an electric bell, which in this case should be of the
+continuous type. All these depend in their action upon some arrangement
+whereby when the hour hand of the clock or watch arrives at a certain
+given point in its travel, it makes contact between the battery and
+bell. In general the contact piece is attached bodily to the clock, but
+in the very ingenious arrangement illustrated at Fig. 62 (devised by
+Messrs. Binswanger) the contacts are attached to an outer case, and as
+the case of the watch itself forms one point of contact, any watch that
+will slip in the case, may be set to ring the bell.
+
+[Illustration: Fig. 62.]
+
+[Illustration: Fig. 63.]
+
+Messrs. Gent, of Leicester, have also perfected an electric watchman's
+clock, which records the number of places the watchman in charge has
+visited or missed on his rounds. This we illustrate at Fig. 63. We quote
+Messrs. Gent's own words, in the following description:--
+
+"It consists of an eight-day clock, to which is attached a disc or table
+revolving upon a vertical axis and driven by the mechanism of the clock.
+The disc is covered with a sheet of paper, attached to it by a binding
+screw so that it can be removed when used and a clean sheet substituted
+for it. Each sheet of paper is divided longitudinally into hours and, if
+necessary, parts of hours, and crosswise into as many divisions as there
+are places to be visited by the watchman--any number from one to twenty.
+Each division has a corresponding marker, which indicates, by the
+impression it makes upon the paper, the time the watchman visits the
+place connected with that marker. Wires are carried from the terminals
+of the clock, one to the battery, and one to each press-button fixed at
+the points intended to be visited by the watchman; another wire is
+carried from each press-button to the other end of the battery. The
+action is very simple: when the button is pressed in the current passes
+through a coil carrying an armature and contact breaker with a point at
+the end of a long arm; a hammer-like motion is given to the pointer, and
+a distinct perforation made in the card. It is usual to have the
+press-button in a box locked up, of which the watchman only has the key.
+
+"The clock may be in the office or bedroom of the manager or head of
+the establishment, who can thus, from time to time, satisfy himself of
+the watchman's vigilance. The record should be examined in the morning,
+and replaced by a clean sheet of card.
+
+"This clock received the special mention of Her Majesty's Commissioners
+in Lunacy, and has been adopted by some of the largest asylums in the
+country.
+
+"We have recently made an important improvement by adding a relay for
+every marker, thus enabling a local battery of greater power to be used
+for actuating the markers. This has made no alteration in the appearance
+of the clock, as the relays are contained within the cornice at the top
+of the clock case."
+
+
+§ 60. By means of a float, it is possible to give notice of the height
+of water in a tank, a reservoir, or even of the state of the tide. In
+these cases all that is needed is a float with an arm, having a suitable
+contact attached, so that when the water rises to the level of the float
+and lifts it, it causes the contact piece to complete the circuit
+through a set screw. Or the float may be attached to an arm having a
+certain play in both directions, _i.e._, up and down, within which no
+contact is made, as the arm has a contact piece on either side, which
+can touch either an upper or a lower contact screw, according to whether
+the tide is low or high, or whether the lock or tank is nearly empty or
+too full.
+
+[Illustration: Fig. 64.]
+
+
+§ 61. Sometimes it is convenient to be able to ring an ordinary
+trembling bell continuously, as when a master wishes to wake a member of
+his family or a servant; or again, to cut a given bell or bells out of
+circuit altogether. The arrangements by which this can be effected, are
+known as "switches." Of switches there are two kinds, namely,
+_plugswitches_ or _interruptors_, and _lever switches_. The former
+consists essentially in two stout plates of brass affixed to a base
+board of any insulating material. These brass plates are set parallel to
+each other, a short distance apart, and the centre of the facing edge is
+hollowed out to take a brass taper plug. A binding or other screw is
+fixed to each brass plate, to connect up to the leading wires. When the
+plug is in its socket, the circuit between the two plates (and
+consequently between the battery and bell, etc.) is complete; when the
+plug is out, the contact is broken. This form of switch is subject to
+work out of order, owing to the fact that the taper plug gradually
+widens the hole, so that the contact becomes uncertain or defective
+altogether. By far the better form of switch is the lever switch, as
+shown at Fig. 64. This consists in a movable metal lever or arm, which
+is held by a strong spring in contact with the upper binding screw. It
+can be made to slide over to the right or left of the centre, at its
+lower or free end, as far as the binding screws or studs shown, which
+act at once as stops and point of connection to wires. When the arm or
+lever is in the centre no contact is made but if it be pushed over to
+the right, it slides on a brass strip let into and lying flush with the
+base. Contact is thus made between the upper binding screw and the
+left-hand screw. If there is another brass strip on the left-hand side
+(as shown in the figure), contact may be made with another bell, etc.,
+by sliding the arm to the left; or again, if no metal strip be placed on
+the left side the contact may be broken by pushing the arm towards the
+left-hand stud.
+
+
+§ 62. A _key_ is another form of contact, by means of which a long or
+short completion of circuit can be made by simply tapping on the knob.
+It is particularly useful when it is desired to transmit signals, either
+by ringing or otherwise. It consists, as may be seen at Fig. 65, of a
+lever or arm of brass, pivoted at its centre, furnished with a spring
+which keeps the portion under the knob out of contact with the stud in
+the front of the base-board. As both the stud and the lever are
+connected to binding screws communicating with the battery and bell,
+etc., it is evident that on depressing the key the circuit with the bell
+will be completed for a longer or shorter period, varying with the
+duration of the depression. Hence, either by using preconcerted signals
+of short and long rings to signify certain common words, such as a long
+ring for _No_, and a short one for _Yes_, or by an adaptation of the
+ordinary Morse code, intelligible conversation can be kept up between
+house and stable, etc., etc., by means of a key and a bell. As Mr.
+Edwinson has given much time to the elucidation of this system of bell
+signalling, I cannot do better than quote his instructions, as given in
+_Amateur Work_:--
+
+"For this purpose preconcerted signals have been agreed upon or invented
+as required, and these have been found to be irksome and difficult to
+remember, because constructed without any reference to a definite plan.
+We may, however, reduce bell signals to a definite system, and use this
+system or code as a means to carry on conversation at a distance as
+intelligently as it can be done by a pair of telegraph instruments. In
+fact, the Morse telegraph code can be easily adopted for use with
+electric bells of the vibrating or trembling type, and its alphabet, as
+appended below, easily learnt. The letters of the alphabet are
+represented by long strokes and short strokes on the bell, as here
+shown.--
+
+ A ·-
+ B -···
+ C -·-·
+ D -··
+ E ·
+ F ··-·
+ G --·
+ H ····
+ I ··
+ J ·---
+ K -·-
+ L ·-··
+ M --
+ N -·
+ O ---
+ P ·--·
+ Q --···
+ R ·-·
+ S ···
+ T -
+ U ··-
+ V ···-
+ W ·--
+ X -··-
+ Y -·--
+ Z --··
+ Ch ----
+ Ä (æ) ·-·-
+ Ö ([oe]) ---·
+ Ü (ue) ··--
+ 1 ·----
+ 2 ··---
+ 3 ···--
+ 4 ····-
+ 5 ·····
+ 6 -····
+ 7 --···
+ 8 ---··
+ 9 ----·
+ 0 -----
+
+"It will be noticed that the strokes to represent a letter do not in any
+case exceed four, and that all the figures are represented by five
+strokes of varying length to each figure. Stops, and other marks of
+punctuation, are represented by six strokes, which are in their
+combination representations of two or three letters respectively, as
+shown below:--
+
+ Comma (,) by A A A or ·-·-·-
+ Full stop (.) " I I I " ······
+ Interrogation (?) " U D " ··--··
+ Hyphen (-) " B A " -····-
+ Apostrophe (') " W G " ·----·
+ Inverted commas (") " A F " ·-··-·
+ Parenthesis () " K K " -·--·-
+ Semi-colon (;) " K Ch " ·-----
+ Surprise (!) " N Ch " -·----
+ Colon (:) " I Ch " ··----
+
+"In sending signals to indicate stops, no regard must be had to the
+letters which they represent; these are only given as aids to memory,
+and are not to be represented separately on the bell. Bell signals must
+be given with a certain amount of regularity as to time; indeed, to
+carry on a conversation in this way it is necessary to be as punctilious
+in time as when playing a piece of music on a piano, if the signals are
+to be understood. The dots of the signal should therefore be represented
+in time by _one_, and the dashes by _two_, whilst the spaces between
+words and figures where a stop does not intervene should be represented
+by a pause equal to that taken by a person counting _three_, the space
+between a word and a stop being of the same duration. To make this more
+clear I give an example. The mistress signals to her coachman:--
+
+ G | E | T | | T | H | E |
+ --· | · | - | | - | ···· | ·
+ 221 | 1 | 2 |3| 2 | 1111 | 1 | 3
+
+ C | A | R | R | I | A | G | E |
+ -·-· | ·- | ·-· | ·-· | ·· | ·- | --· | · |
+ 2121 | 12 | 121 | 121 | 11 | 12 | 221 | 1 | 3
+
+ R | E | A | D | Y
+ ·-· | · | ·- | -·· | -·--
+ 121 | 1 | 12 | 211 | 2122
+
+"The coachman replies:--
+
+ R | E | A | D | Y
+ ·-· | · | ·- | -·· | -·--
+ 121 | 1 | 12 | 211 | 2122
+
+"When the mistress is ready she signals:--
+
+ B | R | I | N | G | | T | H | E |
+ -··· | ·-· | ·· | -· | --· | | - | ···· | · |
+ 2111 | 121 | 11 | 21 | 221 | 3| 2 | 1111 | 1 | 3
+
+ C | A | R | R | I | A | G | E
+ -·-· | ·- | ·-· | ·-· | ·· | ·- | --· | ·
+ 2121 | 12 | 121 | 121 | 11 | 12 | 221 | 1
+
+"And the coachman replies with a single long ring to signify that he
+understands. It will be found convenient to have an answering signal
+from the receiving end of the line to each word separately. This must be
+sent in the pause after each word, and consists of the short signal E ·
+when the word is understood, or the double short signal I ·· when the
+word is not understood. A negative reply to a question may be given by
+the signal for N -·, and an affirmative by the signal for Æ ·-·-; other
+abbreviations may be devised and used where desired. The code having
+been committed to memory, it will be quite easy to transpose the words
+and send messages in cypher when we wish to make a confidential
+communication; or the bells may be muffled under a thick cloak, and
+thus, whilst the measured beats are heard by the person for whom the
+signal is intended, others outside the room will not be annoyed by
+them."
+
+[Illustration: Fig. 65.]
+
+
+§ 63. At § 48, we noticed that a device known as a _Relay_ is a
+convenient, if not an essential mode of working continuous ringing
+bells. Here we will direct our attention to its structural arrangement,
+and to its adaptations. Let us suppose that we had to ring a bell at a
+considerable distance, so far indeed that a single battery would not
+energise the electro-magnets of an ordinary bell, sufficiently to
+produce a distinct ring. It is evident that if we could signal, ever so
+feebly, to an attendant at the other end of the line to make contact
+with another battery at the distant end of the line to _his_ bell, by
+means, say, of a key similar to that shown at Fig. 65, we should get a
+clear ring, since this second battery, being close to the bell, would
+send plenty of current to energise the bell's magnets. But this would
+require a person constantly in attendance. Now the _relay_ does this
+automatically; it _relays_ another battery in the circuit. The manner in
+which it effects this will be rendered clear, on examination of Fig. 66.
+Here we have an armature A attached to a light spring, which can play
+between an insulated stop C, and a contact screw B. The play of this
+armature can be regulated to a nicety by turning the screws B or C.
+These two screws are both borne by a double bent arm (of metal) affixed
+to the pillar D. This pillar is separated from the rest of the frame by
+an insulating collar or washer of ebonite, so that no current can pass
+from E to D, unless the armature be pulled down so as to make contact
+with the contact screw B. Just under the armature, stands the
+electro-magnet G, which when energised can and does pull down the
+armature A. It will be readily understood that if we connect the wires
+from the electro-magnet G, to the wires proceeding from the battery and
+push (or other form of contact) at the distant station, the
+electro-magnet, being wound with a large quantity of fine wire, will
+become sufficiently magnetized to pull the armature down through the
+small space intervening between C and B; so that if the screws D and E
+are connected respectively to the free terminals of a battery and bell
+coupled together at the nearer station, this second battery will be
+thrown into circuit with the bell, and cause it to ring as well and as
+exactly as if the most skilful and most trustworthy assistant were in
+communication with the distant signaller. Every tap, every release of
+the contact, (be it push, key, or switch) made at the distant end, will
+be faithfully reproduced at the nearer end, by the motion of the
+armature A. For this reason we may use a comparatively weak battery to
+work the relay, which in its turn brings a more powerful and _local_
+battery into play, for doing whatever work is required. In cases where a
+number of calls are required to be made simultaneously from one centre,
+as in the case of calling assistance from several fire engine stations
+at once, a relay is fixed at each station, each connected with its own
+local battery and bell. The current from the sending station passes
+direct through all the relays, connecting all the local batteries and
+bells at the same time. This is perhaps the best way of ringing any
+number of bells from one push or contact, at a distant point. Ordinary
+trembling bells, unless fitted with an appropriate contrivance, cannot
+well be rung if connected up in _series_. This is owing to the fact that
+the clappers of the bells do not all break or make contact at the same
+time, so that intermittent ringing and interruptions take place. With
+single stroke bells, this is not the case, as the pulling down of the
+armature does not break the contact.
+
+[Illustration: Fig. 66.]
+
+[Illustration: Fig. 67.]
+
+[Illustration: Fig. 68.]
+
+
+§ 64. We now have to consider those contrivances by means of which it is
+possible for an attendant to know when a single bell is actuated by a
+number of pushes in different rooms, etc., from whence the signal
+emanates. These contrivances are known as _indicators_. Indicators may
+be conveniently divided into 3 classes, viz.:--1st, indicators with
+_mechanical_ replacements; 2nd, those with electrical replacements; and
+3rdly, those which are self replacing. Of the former class we may
+mention two typical forms, namely, the ordinary "fall back" indicator,
+and the drop indicator. All indicators depend in their action on the
+sudden magnetisation of an electro-magnet by the same current that works
+the electric bell at the time the call is sent. To understand the way in
+which this may be effected, let the reader turn to the illustration of
+the Relay (Fig. 66), and let him suppose that the pillar D, with its
+accompanying rectangle B C, were removed, leaving only the
+electro-magnet G, with its frame and armature A. If this armature holds
+up a light tablet or card, on which is marked the number of the room, it
+is evident that any downward motion of the armature, such as would occur
+if the electro-magnet were energised by a current passing around it,
+would let the tablet fall, so as to become visible through a hole cut in
+the frame containing this contrivance. It is also equally evident that
+the card or tablet would require replacing by hand, after having once
+fallen, to render it capable of again notifying a call. Fig. 67 shows
+the working parts of one of these "drop" indicators, as sent out by
+Messrs. Binswanger. In another modification, known as Thorpe's
+"Semaphore Indicator," we have a most ingenious application of the same
+principle in a very compact form. In this (Fig. 68), the electro-magnet
+is placed directly behind a disc-shaped iron armature, on which is
+painted or marked the number of the room etc. (in this case 4); this
+armature is attached by a springy shank to the drop bar, shown to the
+left of the electro-magnet. In front of the armature is a light metal
+disc, also pivoted on the drop bar. This engages in a catch above, when
+pushed up so as to cover the number. When pushed up, the spring of the
+armature retains it in its place so that the number is hidden. When the
+current passes around the electro-magnet, the armature is pulled toward
+it, and thus frees the covering disc, which therefore falls, and
+displays the number. The ordinary form of "fall back" indicator (a
+misnomer, by the way, since the indicator falls forwards) is well
+illustrated at Fig 69. Here we have an ordinary electro-magnet A, with
+its wires _w_ _w'_ standing over an armature B attached to a spring C,
+which bears on its lower extremity, a toothed projection which serves to
+hold up the short arm of the bent lever D, which supports the number
+plate E. When the electro-magnet A is energised by the current, it pulls
+up the armature B, which releases the detent D from the tooth C; the
+number plate therefore falls forwards, as shown by the dotted lines,
+and shows itself at the aperture E´, which is in front of the indicator
+frame. To replace the number out of sight, the attendant pushes back the
+plate E, till it again engages the bent lever D in the tooth C. This
+replacement of the number plate, which the attendant in charge is
+obliged to perform, gives rise to confusion, if through carelessness it
+is not effected at once, as two or more numbers may be left showing at
+one time. For this reason, indicators which require no extraneous
+assistance to replace them, are preferred by many. Indicators with
+electrical replacements meet in part the necessities of the case. This
+form of indicator consists usually of a permanent bar magnet pivoted
+near its centre, so that it can hang vertically between the two poles of
+an electro-magnet placed at its lower extremity. The upper extremity
+carries the number plate, which shows through the aperture in the frame.
+This bar magnet is made a trifle heavier at the upper end, so that it
+must rest against either the one or other pole of the electro-magnet
+below. If the _north_ pole of the bar magnet rests against the _right_
+hand pole of the electro-magnet when the number does not show, we can
+cause the bar magnet to cross over to the other pole, and display the
+number by sending a current through the electro-magnet in such a
+direction as to make its right hand pole a north pole, and its left hand
+a south pole. This is because the two north poles will repel each other,
+while the south will attract the north. On being once tilted over, the
+bar magnet cannot return to its former position, until the person who
+used the bell sends a current in the opposite direction (which he can do
+by means of a reversing switch), when the poles of the electro-magnet
+being reversed, the bar magnet will be pulled back into its original
+position. Indicators of this class, owing to the fact that their
+replacement depends on the _polarity_ of the bar magnet, are also known
+as "polarised indicators."
+
+[Illustration: Fig. 69.]
+
+
+§ 65. For general efficiency and trustworthiness, the _pendulum
+indicator_; as shown at Fig. 70, is unsurpassed. It consists of an
+electro-magnet with prolongation at the free end on which is delicately
+pivoted a soft iron armature. From the centre of this armature hangs,
+pendulum fashion, a light brass rod carrying a vane of fluted silver
+glass, or a card with a number on it, as may be found most convenient.
+This vane or card hangs just before the aperture in the indicator frame.
+Stops are usually placed on each side of the pendulum rod to limit the
+swing. When the electro-magnet is magnetised by the passage of the
+current, the armature is pulled suddenly on one side, and then the
+pendulum swings backwards and forwards in front of the aperture for some
+minutes before it comes to rest. When fitted with silver fluted glass,
+the motion of the vane is clearly visible even in badly lighted places.
+As the pendulum, after performing several oscillations, comes to rest by
+itself in front of the aperture, this indicator requires no setting.
+Messrs. Binswanger fit these indicators with double core magnets, and
+have a patented adjustment for regulating the duration of the swings of
+the pendulum, which may be made to swing for two or three minutes when
+the circuit is completed by pressing the push; it then returns to its
+normal position, thus saving the servant the trouble of replacing the
+"drop."
+
+[Illustration: Fig. 70.]
+
+Messrs. Gent, of Leicester, have also patented a device in connection
+with this form of indicator, which we give in the patentee's own
+words:--"The objection so frequently urged against the use of Electric
+Bells, that the servants cannot be depended upon to perform the
+operation of replacing the signals, cannot any longer apply, for the
+pendulum signals require no attention whatever. It consists of an
+electro-magnet having forks standing up in which [V] openings are made. An
+armature of soft iron, with a piece of thin steel projecting at each end
+lies suspended at the bottom of the [V] opening, a brass stem carrying the
+signal card is screwed into the armature, the action being, that when a
+current is allowed to pass through the electro-magnet the armature with
+the pendulum is drawn towards it and held there until the current ceases
+to pass, when it instantly looses its hold of the armature, which swings
+away and continues to oscillate for two or three minutes, so that if the
+servant happens to be out of the way, it may be seen on her return which
+pendulum has been set in motion. The Pendulum Indicator we have recently
+patented is entirely self-contained. The magnet has its projecting poles
+riveted into the brass base which carries the flag. The flag is
+constructed as Fig. 70, but swings in closed bearings, which prevents
+its jerking out of its place, and enables us to send it out in position
+ready for use. It will be seen this _patented_ improvement makes all
+screws and plates as formerly used for securing the parts unnecessary.
+It will be seen at once that this is simplicity itself, and has nothing
+about it which may by any possibility be put out of order, either by
+warping or shrinking of the case or carelessness of attendants."
+
+[Illustration: Fig. 71.]
+
+There is only one point that needs further notice with regard to these
+pendulum indicators, and that is, that since the rapid break and make
+contact of the ringing bell interferes somewhat with the proper action
+of the indicator magnet, it is always advisable to work the indicator by
+means of a relay (fixed in the same frame) and a _local_ battery. This
+is shown in Fig. 71, where a second pair of wires attached to C and C,
+to the extreme right of the indicator frame, are brought from the same
+battery to work the indicator and contained relay. It is not advisable,
+however, with the pendulum indicator, to use the same battery for the
+indicator; the relay should throw a local battery into the indicator
+circuit. In Fig. 71 six pushes are shown to the left of the indicator
+frame. These, of course, are supposed to be in as many different rooms.
+
+[Illustration: Fig. 72.]
+
+We close this chapter with an engraving of a very compact and neat form
+of drop indicator devised by Messrs. Gent, and called by them a
+"Tripolar Indicator." It consists, as the name implies, of a single
+magnet, having one end of the iron core as one pole, the other end
+extending on each side like a [V], forming, as it were, three poles.
+Though but one bobbin is used, the effect is very powerful. There are no
+springs or other complications, so that the arrangement is adapted for
+ship use, as are also those represented at Figs. 67 and 68. Pendulum and
+fall-back indicators, as well as polarised indicators, owing to the
+delicacy of the adjustments, are unfitted for use on board ship, or in
+the cabs of lifts, where the sudden jolts and jerks are sure to move the
+indicators, and falsify the indications. The tripolar indicator is
+illustrated at Fig. 72.
+
+
+
+
+CHAPTER V.
+
+ON WIRING, CONNECTING UP, AND LOCALISING FAULTS.
+
+
+§ 66. However good may be the bells, indicators, batteries, etc., used
+in an electric bell installation, if the _wiring_ be in any wise faulty,
+the system will surely be continually breaking down, and giving rise to
+dissatisfaction. It is therefore of the highest importance that the
+workman, if he value his good name, should pay the greatest attention to
+ensure that this part of his work be well and thoroughly done. This is
+all the more necessary, since while the bells, batteries, relays,
+pushes, etc., are easily got at for examination and repair, the wires,
+when once laid, are not so easily examined, and it entails a great deal
+of trouble to pull up floor boards, to remove skirtings etc., in order
+to be able to overhaul and replace defective wires or joints. The first
+consideration of course, is the kind and size of wire fitted to carry
+the current for indoor and outdoor work. Now this must evidently depend
+on three points. 1st, The amount of current (in ampères) required to
+ring the bell. 2nd, The battery power it is intended to employ. 3rd, The
+distance to which the lines are to be carried. From practical
+experience I have found that it is just possible to ring a 2-1/2" bell
+with 1/2 an ampère of current. Let us consider what this would allow us
+to use, in the way of batteries and wire, to ring such a bell. The
+electro-motive force of a single Leclanchè cell is, as we have seen at §
+38, about 1·6 volt, and the internal resistance of the quart size, about
+1·1 ohm. No. 20 gauge copper wire has a resistance of about 1·2 ohm to
+the pound, and in a pound (of the cotton covered wire) there are about
+60 yards. Supposing we were to use 60 yards of this wire, we should have
+a wire resistance of 1·2 ohm, an internal resistance of 1·1 ohm, and a
+bell resistance of about 0·1 of an ohm, altogether about 2·4 ohms. Since
+the E.M.F. of the cell is 1·6 volt, we must divide this by the total
+resistance to get the amount of current passing. That is to say:--
+
+ Ohms. Volts. Ampères.
+ 2·4) 1·60 (0·66,
+
+or about 2/3 of an ampère; just a little over what is absolutely
+necessary to ring the bell. Now this would allow nothing for the
+deterioration in the battery, and the increased resistance in the
+pushes, joints, etc. We may safely say, therefore, that no copper wire,
+of less diameter than No. 18 gauge (48/1000 of an inch diameter) should
+be used in wiring up house bells, except only in very short circuits of
+two or three yards, with one single bell in circuit; and as the
+difference in price between No. 18 and No. 20 is very trifling, I
+should strongly recommend the bell-fitter to adhere to No. 18, as his
+smallest standard size. It would also be well to so proportion the size
+and arrangement of the batteries and wires, that, at the time of setting
+up, a current of at least one ampère should flow through the entire
+circuit. This will allow margin for the weakening of the battery, which
+takes place after it has been for some months in use. As a guide as to
+what resistance a given length of copper wire introduces into any
+circuit in which it may be employed, I subjoin the following table of
+the Birmingham wire gauge, diameter in 1,000ths of an inch, yards per
+lb., and resistance in ohms per lb. or 100 yards, of the wires which the
+fitter is likely to be called upon to employ:--
+
+ ------------------------------------------------------------
+ Table of Resistance and lengths per lbs.
+ & 100 yards of cotton covered copper wires.
+ ------------------------------------------------------------
+ Birmingham | Diameter in | Yards | Ohms. | Ohms. per
+ Wire Gauge. | 1000th of | per lb. | per lb. | 100 yards.
+ | an inch. | |
+ ------------+-------------+----------+----------+-----------
+ No. 12 | 100 | 9 | 0·0342 | 0·0038
+ 14 | 80 | 15 | 0·0850 | 0·0094
+ 16 | 62 | 24 | 0·2239 | 0·0249
+ 18 | 48 | 41 | 0·6900 | 0·0766
+ 20 | 41 | 59 | 1·2100 | 0·1333
+ 22 | 32 | 109 | 3·1000 | 0·3444
+ ------------------------------------------------------------
+
+
+§ 67. Whatever gauge wire be selected, it must be carefully insulated,
+to avoid all chance contact with nails, staples, metal pipes or other
+wires. The best insulation for wires employed indoors is gutta-percha,
+surrounded with a coating of cotton wound over it, except only in cases
+when the atmosphere is excessively dry. In these, as the gutta-percha
+is apt to crack, india-rubber as the inner coating is preferable. If No.
+18 wire be used, the thickness of the entire insulating coating should
+be thick enough to bring it up to No. 10 gauge, say a little over 1/10th
+inch in diameter. There is one point that will be found very important
+in practice, and that is to have the cotton covering on the wires
+_leading_ to the bells of a different colour from that on the _return_
+wires; in other words, the wires starting from the zinc poles of the
+battery to the bells, indicators, relays, etc., should be of a different
+colour from that leading from the carbon poles to the bells, etc.
+Attention to this apparently trifling matter, will save an infinite
+amount of trouble in connecting up, repairing, or adding on fresh branch
+circuits. For outdoor work, wire of the same gauge (No. 18) may
+generally be used, but it must be covered to the thickness of 1/10" with
+pure gutta-percha, and over this must be wound tape served with
+Stockholm tar. Wires of this description, either with or without the
+tarred tape covering, may be obtained from all the leading electricians'
+sundriesmen. Many firms use copper wire _tinned_ previous to being
+insulated. This tinning serves two good purposes, 1st, the copper wire
+does not verdigris so easily; 2ndly, it is more easily soldered. On the
+other hand, a tinned wire is always a little harder, and presents a
+little higher resistance. Whenever wires are to be joined together, the
+ends to be joined must be carefully divested of their covering for a
+length of about three inches, the copper carefully cleaned by scraping
+and sand-papering, twisted tightly and evenly together, as shown in
+Fig. 73 A, and soldered with ordinary soft solder (without spirits), and
+a little resin or composite candle as a flux. A heavy plumber's
+soldering iron, or even a tinman's bit, is not well adapted for this
+purpose, and the blowpipe is even worse, as the great heat melts and
+spoils the gutta-percha covering. The best form of bit, is one made out
+of a stout piece of round copper wire 1/4" thick with a nick filed in
+its upper surface for the wire to lie in (see Fig. 73 B). This may be
+fastened into a wooden handle, and when required heated over the flame
+of a spirit lamp. When the soldering has been neatly effected, the waste
+ends _a_ and _b_ of the wire should be cut off flush. The wire must then
+be carefully covered with warm Prout's elastic or softened gutta-percha,
+heated and kneaded round the wire with the fingers (moistened so as not
+to stick) until the joint is of the same size as the rest of the covered
+wire. As a further precaution, the joints should be wrapped with a layer
+of tarred tape. Let me strongly dissuade the fitter from ever being
+contented with a simply twisted joint. Although this may and does act
+while the surfaces are still clean, yet the copper soon oxidises, and a
+poor non-conducting joint is the final result.
+
+"That'll do" will not do for electric bell-fitting.
+
+[Illustration: Fig. 73.]
+
+
+§ 68. Whenever possible, the wiring of a house, etc., for bell work,
+should be done as soon as the walls are up and the roof is on. The
+shortest and straightest convenient route from bell to battery, etc.,
+should always be chosen where practicable to facilitate drawing the wire
+through and to avoid the loss of current which the resistance of long
+lengths of wire inevitably entails. The wires should be run in light
+zinc tubes nailed to the wall.
+
+In joining up several lengths of tubing, the end of one piece of tube
+should be opened out _considerably_ of a trumpet shape for the other
+piece to slip in; and the end of this latter should also be _slightly_
+opened out, so as not to catch in the covering of any wire drawn through
+it. The greatest care must be exercised in drawing the wires through the
+tubes or otherwise, that the covering be not abraded, or else leakage at
+this point may take place. In cases where tubes already exist, as in
+replacing old crank bells by the electric bells, the new wires can be
+drawn through the tubes, by tying the ends of the new wire to the old
+wire, and carefully pulling this out, when it brings the new wire with
+it. Or if the tubes are already empty, some straight stout wire may be
+run through the tubes, to which the new wires may be attached, and then
+drawn through, using, of course, every possible precaution to avoid the
+abrasion of the insulating covering of the wire, which would surely
+entail leakage and loss of current. All the old fittings, cranks,
+levers, etc., must be removed, and the holes left, carefully filled with
+dowels or plaster. In those cases where it is quite impossible to lay
+the wires in zinc or wooden tubes (as in putting up wires in furnished
+rooms already papered, etc.), the wires may be run along the walls, and
+suspended by staples driven in the least noticeable places; but in no
+case should the two wires (go and return) lie under the same staple, for
+fear of a short circuit. It must be borne in mind that each complete
+circuit will require at least two wires, viz., the one leading from the
+battery to the bell, and the other back from the bell to the battery;
+and these until connection is made between them by means of the
+"contact" (pull, push, or key) must be perfectly insulated from each
+other. In these cases, as far as possible, the wires should be laid in
+slots cut in the joists under the floor boards, or, better still, as
+tending to weaken the joists less, small holes may be bored in the
+joists and the wires passed through them; or again, the wires may be led
+along the skirting board, along the side of the doorpost, etc., and when
+the sight of the wires is objectionable, covered with a light ornamental
+wood casing. When the wires have been laid and the position of the
+"pushes," etc., decided upon, the _blocks_ to which these are to be
+fastened must be bedded in the plaster. These blocks may be either
+square or circular pieces of elm, about 3 inches across, and 1 inch
+thick, bevelled off smaller above, so as to be easily and firmly set in
+the plaster. They may be fastened to the brickwork by two or three
+brads, at such a height to lie level with the finished plaster. There
+must of course be a hole in the centre of the block, through which the
+wires can pass to the push. When the block has been fixed in place, the
+zinc tube, if it does not come quite up to the block, should have its
+orifice stopped with a little paper, to prevent any plaster, etc.,
+getting into the tube. A little care in setting the block will avoid the
+necessity of this makeshift. A long nail or screw driven into the block
+will serve to mark its place, and save time in hunting for it after the
+plastering has been done. When the blocks have been put in their places,
+and the plastering, papering, etc., done, the wires are drawn through
+the bottom hole of the push (after the lid or cover has been taken off),
+Fig. 74, and a very small piece of the covering of the wire having been
+removed from each wire, and brightened by sand papering, one piece is
+passed round the shank of the screw connected with the lower spring,
+shown to the _right_ in Fig. 74, and the other round the shank of the
+screw connected to the upper spring, shown to the _left_ in the Fig. The
+screws must be loosened to enable the operator to pass the wire under
+their heads. The screws must then be tightened up to clench the wire
+quite firmly. In doing this, we must guard against three things.
+Firstly, in pulling the wire through the block, not to pull so tightly
+as to cut the covering against the edge of the zinc tube. Secondly, not
+to uncover too much of the wire, so as to make contact between the wires
+themselves either at the back of the push, or at any other part of the
+push itself. Thirdly, to secure good contact under the screws, by having
+the ends of the wires quite clean, and tightly screwed down.
+
+[Illustration: Fig. 74.]
+
+
+§ 69. In all cases where the wires have to be taken out of doors, such
+as is necessitated by communication from house to outhouses, stables,
+greenhouses, etc., over head lines (No. 18 gauge, gutta-percha tape and
+tar covering) should be used. Where overhead lines are not admissible,
+either as being eyesores, or otherwise, the wires may be laid in square
+wooden casings of this section [box open up], the open part of
+which must be covered by a strip of wood laid over it. The wood must
+have been previously creosoted, in the same manner as railway sleepers.
+This mode admits of easy examination. Iron pipes must, however, be used
+if the lines have to pass under roads, etc., where there is any heavy
+traffic. And it must be borne in mind that however carefully the iron
+pipes, etc., be cemented at the joints, to make them watertight, there
+will always be more electrical leakage in underground lines than in
+overhead ones. In certain rare cases it may be needful to use _iron_
+wires for this purpose instead of copper; in this case, as iron is six
+or seven times a worse conductor than copper, a much heavier wire must
+be employed to get the same effect. In other words, where iron wire is
+used, its section must be not less than seven times that of the copper
+wire which it replaces.
+
+
+§ 70. It is always preferable, where great distance (and, consequently,
+greater expense) do not preclude it, to use wire for the leading as well
+as for the returning circuit. Still, where for any reason this is not
+practicable, it is perfectly admissible and possible to make a good
+return circuit through the _earth_, that is to make the damp soil carry
+the return current (see § 37). As recommended at the section just
+quoted, this earth circuit must have at each extremity a mass of some
+good conductor plunged into the moist ground. In _towns_, where there
+are plenty of water mains and gas mains, this is a matter of no
+difficulty, the only point being to ensure _good_ contact with these
+masses of metal. In other places a hole must be dug into the ground
+until the point of constant moisture is reached; in this must be placed
+a sheet of lead or copper, not less than five square feet surface, to
+which the _earth_ wires are soldered, the hole then filled in with
+ordinary coke, well rammed down to within about six inches of the
+surface, and then covered up with soil well trodden down. In making
+contact with water or gas pipes, care must be taken to see that these
+are _main_ pipes, so that they _do_ lead to earth, and not to a cistern
+or meter only, as, if there are any white or red lead joints the circuit
+will be defective. To secure a good contact with an iron pipe, bare it,
+file its surface clean, rub it over with a bit of blue stone (sulphate
+of copper) dipped in water; wipe it quite dry, bind it tightly and
+evenly round with some bare copper wire (also well cleaned), No. 16
+gauge. Bring the two ends of the wire together, and twist them up
+tightly for a length of three or four inches. Now heat a large soldering
+bit, put some resin on the copper wire, and solder the wire, binding
+firmly down to the iron pipe. Do likewise to the projecting twist of
+wire, and to this twist solder the end of the _return_ wire. On no
+account should the two opposite _earth_ wires be soldered to water mains
+and gas mains at the same time, since it has been found that the
+different conditions in which these pipes find themselves is sufficient
+to set up a current which might seriously interfere with the working of
+the battery proper. Sometimes there is no means of getting a good
+_earth_ except through the gas main: in this case we must be careful to
+get to the street side of the meter, for the red lead joints will
+prevent good conductivity being obtained. In out of the way country
+places, if it is possible to get at the metal pipe leading to the well
+of a pump, a very good "earth" can be obtained by soldering the wires to
+that pipe, in the same manner as directed in the case of the water main.
+The operator should in no case be contented with a merely twisted joint,
+for the mere contact of the two metals (copper and iron) sets up in the
+moist earth or air a little electric circuit of its own, and this
+speedily rusts through and destroys the wires. The following
+suggestions, by Messrs. Gent, on the subject of wiring, are so good,
+that we feel that we shall be doing real service to the reader to quote
+them here in full:--
+
+"1st.--The description of wire to be used. It is of the utmost
+importance that all wires used for electric bell purposes be of pure
+copper and thoroughly well insulated. The materials mostly employed for
+insulating purposes are indiarubber, gutta-percha, or cotton saturated
+with paraffin. For ordinary indoor work, in dry places, and for
+connecting doors and windows with burglar alarms, or for signalling in
+case of fire, indiarubber and cotton covered wires answer well; but for
+connecting long distances, part or all underground, or along walls, or
+in damp cellars or buildings, gutta-percha covered wire is required, but
+it should be fixed where it will not be exposed to heat or the sun, or
+in very dry places, as the covering so exposed will perish, crack, and
+in time fall off. This may be, to some extent, prevented by its being
+covered with cotton; but we recommend for warm or exposed positions a
+specially-prepared wire, in which rubber and compound form the
+insulating materials, the outside being braided or taped.
+
+"For ordinary house work, we refer to lay a wire of No. 18 or 20 copper,
+covered to No. 14 or 11 with gutta-percha, and an outer covering of
+cotton, which we called the 'battery' wire, this being the wire which
+conveys the current from the battery to every push, etc., no matter how
+many or in what position. The reason for selecting this kind is, that
+with the gutta-percha wires the joints may be more perfectly covered and
+made secure against damp. This is of the utmost importance in the case
+of '_battery wires_,' as the current is always present and ready to
+take advantage of any defect in the insulation to escape to an adjoining
+wire, or to '_earth_,' and so cause a continuous waste of current. The
+wires leading from the pushes to the signalling apparatus or bell we
+call the 'line' wires. In these, and the rest of the house wires, the
+perfect covering of the joints is important. For _line wires_ we usually
+prefer No. 18 or 20 copper, covered with indiarubber, and an outer
+coating of cotton, well varnished. In joining the '_battery wires_,' the
+place where the junction is to be made must be carefully uncovered for
+the distance of about an inch; the ends of the wire to be joined, well
+cleaned, and tightly twisted together; with the flame of a spirit lamp
+or candle the joint must be then heated sufficiently to melt fine solder
+in strips when held upon it, having first put a little powdered resin on
+the joint as a flux; the solder should be seen to run well and adhere
+firmly to the copper wire. A piece of gutta-percha should then be taken
+and placed upon the joint while warm, and with the aid of the spirit
+lamp and wet fingers, moulded round until a firm and perfect covering
+has been formed. _On no account use spirits_ in soldering. With the
+_line wire_, it is best, as far as possible, to convey it all the way
+from the push to the signal box or bell in _one continuous_ length. Of
+course, when two or more pushes are required to the same wire, a
+junction is unavoidable. The same process of joining and covering, as
+given for the battery wire, applies to the line wire. Where many wires
+are to be brought down to one position, a large tube may be buried in
+the wall, or a wood casing fixed flush with the plaster, with a
+removable front. The latter plan is easiest for fixing and for making
+alterations and additions. For stapling the wires, in no case should the
+wires be left naked. When they pass along a damp wall, it is best to fix
+a board and _loosely_ staple them. _In no case allow more than one wire
+to lie under the same staple_, and do not let the staples touch one
+another. In many cases, electric bells have been an incessant annoyance
+and complete failure, through driving the staples _tight up to the
+wires_, and several wires to the same staple,--this must not be done on
+any account. A number of wires may be twisted into a cable, and run
+through a short piece of gutta-percha tube, and fastened with ordinary
+gas hooks where it is an advantage to do so. In running the wires, avoid
+hot water pipes, and do not take them along the same way as plumber
+pipes. Underground wires must be laid between pieces of wood, or in a
+gas or drain pipe, and not exposed in the bare earth without protection,
+as sharp pieces of stone are apt to penetrate the covering and cause a
+loss; in fact, in this, as in every part of fixing wires, the best wire
+and the best protection is by far the cheapest in the end. The copper
+wire in this case should not be less than No. 16 B.W.G., covered with
+gutta-percha, to No. 9 or 10 B.W.G., and preferably an outer covering of
+tape or braid well tarred. Outside wire, when run along walls and
+exposed to the weather, should be covered with rubber and compound, and
+varnished or tarred on an outer covering of tape or braid. Hooks or
+staples must be well galvanised to prevent rusting, and fixed loosely.
+If the wire is contained within an iron pipe, a lighter insulation may
+be used: _but the pipe must be watertight_. In a new building, wires
+must be contained within zinc or copper bell tubes. A 3/8 inch tube will
+hold two wires comfortably. The tubes should be fixed to terminate in
+the same positions in the rooms as ordinary crank bell levers,--that is,
+about three feet from the floor. At the side of the fireplace a block of
+wood should be fixed in the wall before any plaster is put on, and the
+end of the tube should terminate in the centre of the same. A large nail
+or screw may be put in to mark the place, so that the end of the tube
+may be found easily when the plastering is finished. Bend the tube
+slightly forward at the end, and insert a short peg of wood to prevent
+dirt getting into the tube. Do the same at the side of, or over the bed
+in bedroom. If the tubes are kept clean, the wires may be easily drawn
+up or down as the case may require. The best way is to get a length of
+ordinary copper bell wire, No. 16, sufficient to pass through the tube,
+and having stretched it, pass it through and out at the other end. Here
+have your coils of insulated wire, viz., one battery wire, which is
+branched off to every push, and one line wire, which has to go direct to
+the indicator or bells, and having removed a short portion of the
+insulation from the end of each, they are tied to the bare copper wire
+and drawn through. This is repeated wherever a push is to be fixed
+throughout the building. In making connection with binding screws or
+metal of any kind, it is of the utmost importance that everything should
+be _perfectly clean_. _Joints_ in wire, whether tinned or untinned,
+_must be soldered and covered_. We cannot impress this too earnestly on
+fixers. Never bury wires in plaster unprotected, and in houses in course
+of erection, the _tubes_ only should be fixed until the plastering is
+finished, the wires to be run in at the same time that the other work is
+completed."
+
+[Illustration: Fig. 75.]
+
+
+§ 71. The wires having been laid by any of the methods indicated in the
+preceding five sections, the fixer is now in a position to _connect up_.
+No two houses or offices will admit of this being done in _exactly_ the
+same way; but in the following sections most of the possible cases are
+described and illustrated, and the intelligent fixer will find no
+difficulty, when he has once grasped the principle, in making those
+trifling modifications which the particular requirements may render
+necessary. The first and simplest form, which engages our attention, is
+that of a _single bell, battery, and push_, connected by wire only. This
+is illustrated at Fig. 75. Here we see that the bell is connected by
+means of one of the wires to the zinc pole of the battery, the push or
+other contact being connected to the carbon pole of the same battery. A
+second wire unites the other screw of the push or contact with the
+second binding screw of the bell. There is no complete circuit until the
+push is pressed, when the current circulates from the carbon or positive
+pole of the battery, through the contact springs of the push, along the
+wire to the bell, and then back again through the under wire to the zinc
+or negative pole of the battery.[15] It must be clearly understood that
+the exact position of battery, bell, and push is quite immaterial. What
+is essential is, that the relative connections between battery, bell,
+and push be maintained unaltered. Fig. 76 shows the next simplest case,
+viz., that in which a single bell and push are worked by a single cell
+through an "earth" return (see § 70). Here the current is made to pass
+from the carbon pole of the battery to the push, thence along the line
+wire to the bell. After passing through the bell, it goes to the
+right-hand earth-plate E, passing through the soil till it reaches the
+left-hand earth-plate E, thence back to the zinc pole of the battery. It
+is of no consequence to the working of the bell whether the battery be
+placed between the push and the left-hand earth-plate, or between the
+bell and the right-hand earth-plate; indeed, some operators prefer to
+keep the battery as near to the bell as possible. At Fig. 77 is shown
+the mode by which a single battery and single bell can be made to ring
+from two (or more) pushes situated in different rooms. Here it is
+evident that, whichever of the two pushes be pressed, the current finds
+its way to the bell by the upper wire, and back home again through the
+lower wire; and, even if both pushes are down at once, the bell rings
+just the same, for both pushes lead from the same pole of the battery
+(the carbon) to the same wire (the line wire).
+
+[Footnote 15: It must be borne in mind that the negative element is that
+to which the positive pole is attached, and _vice versâ_ (see ss. 8 and
+9).]
+
+[Illustration: Fig. 76.]
+
+[Illustration: Fig. 77.]
+
+In Fig. 78, we have a slight modification of the same arrangement, a
+front-door _pull_ contact being inserted in the circuit; and here, in
+view of the probably increased resistance of longer distance, _two_
+cells are supposed to be employed instead of _one_, and these are
+coupled up in series (§ 40), in order to overcome this increased
+resistance.
+
+[Illustration: Fig. 78.]
+
+The next case which may occur is where it is desired to ring two or more
+bells from one push. There are two manners of doing this. The first mode
+is to make the current divide itself between the two bells, which are
+then said to be "_in parallel_." This mode is well illustrated both at
+Figs. 79 and 80. As in these cases the current has to divide itself
+among the bells, larger cells must be used, to provide for the larger
+demand; or several cells may be coupled up in parallel (§ 40). At Fig.
+79 is shown the arrangement for two adjoining rooms; at Fig. 80, that to
+be adopted when the rooms are at some distance apart. If, as shown at
+Fig. 81, a switch similar to that figured in the cut Fig. 64 be inserted
+at the point where the line wires converge to meet the push, it is
+possible for the person using the push to ring both bells at once, or to
+ring either the right-hand or the left-hand bell at will, according to
+whether he turns the arm of the switch-lever on to the right-hand or
+left-hand contact plate.
+
+[Illustration: Fig. 79.]
+
+[Illustration: Fig. 80.]
+
+[Illustration: Fig. 81.]
+
+The second mode of ringing two or more bells from one push is that of
+connecting one bell to the other, the right-hand binding screw of the
+one to the left-hand binding screw of the next, and so on, and then
+connecting up the whole series of bells to the push and battery, as if
+they were a single bell. This mode of disposing the bells is called the
+_series_ arrangement. As we have already noticed at § 63, owing to the
+difference in the times at which the different contact springs of the
+various bells make contact, this mode is not very satisfactory. If the
+bells are single stroke bells, they work very well in series; but, to
+get trembling bells to work in series, it is best to adopt the form of
+bell recommended by Mr. F. C. Allsop. He says: "Perhaps the best plan is
+to use the form of bell shown at Fig. 82, which, as will be seen from
+the figure, governs its vibrations, not by breaking the circuit, but by
+shunting its coils. On the current flowing round the electro-magnet, the
+armature is attracted, and the spring makes contact with the lower
+screw. There now exists a path of practically no resistance from end to
+end. The current is therefore diverted from the magnet coils, and passes
+by the armature and lower screw to the next bell, the armature falling
+back against the top screw, and repeating the previous operation so long
+as the circuit is closed. Thus, no matter how many bells there be in the
+series, the circuit is never broken. This form of bell, however, does
+not ring so energetically as the ordinary form, with a corresponding
+amount of battery power."
+
+[Illustration: Fig. 82.]
+
+[Illustration: Fig. 83.]
+
+Fig. 83 illustrates the mode in which a bell, at a long distance, must
+be coupled up to work with a local battery and relay. The relay is not
+shown separately, but is supposed to be enclosed in the bell case. Here,
+on pressing the push at the external left-hand corner, the battery
+current passes into the relay at the distant station, and out at the
+right-hand earth-plate E returning to the left-hand earth-plate E. In
+doing this, it throws in circuit (just as long as the push is held down)
+the right-hand local battery, so that the bell rings by the current sent
+by the local battery, the more delicate relay working by the current
+sent from the distant battery.
+
+[Illustration: Fig. 84.]
+
+[Illustration: Fig. 85.]
+
+At Fig. 84, we have illustrated the mode of connecting up a continuous
+ringing bell, with a wire return. Of course, if the distance is great,
+or a roadway, etc., intervene, an overhead line and an earth plate may
+replace the lines shown therein, or both lines may be buried. It is
+possible, by using a Morse key (Fig. 65) constructed so as to make
+contact in one direction when _not_ pressed down, and in the other
+_when_ pressed down, to signal from either end of a circuit, using only
+one line wire and one return. The mode of connecting up for this purpose
+is shown at Fig. 85. At each end we have a battery and bell, with a
+double contact Morse key as shown, the Morse key at each end being
+connected through the intervention of the line wire through the central
+stud. The batteries and bells at each station are connected to earth
+plates, as shown. Suppose now we depress the Morse key at the right-hand
+station. Since by so doing, we lift the back end of the lever, we throw
+our own bell out of circuit, but make contact between our battery and
+the line wire. Therefore the current traverses the line wire, enters in
+the left-hand Morse key, and, since this is not depressed, can, and
+does, pass into the bell, which therefore rings, then descends to the
+left-hand earth-plate, returning along the ground to the battery from
+whence it started at the right-hand E. If, on the contrary, the
+_left_-hand Morse key be depressed, while the right-hand key is not
+being manipulated, the current traverses in the opposite direction, and
+the right-hand bell rings. Instead of Morse keys, _double contact_
+pushes (that is, pushes making contact in one direction when _not_
+pressed, and in the opposite _when_ pressed) may advantageously be
+employed. This latter arrangement is shown at Fig. 86.
+
+[Illustration: Fig. 86.]
+
+It is also possible, as shown at Fig. 87, to send signals from two
+stations, using but one battery (which, if the distance is great, should
+be of a proportionate number of cells), two bells, and two ordinary
+pushes. Three wires, besides the earth-plate or return wire, are
+required in this case. The whole of the wires, except the _return_, must
+be carefully insulated. Suppose in this case we press the right-hand
+button. The current flows from the battery along the lower wire through
+this right-hand push and returns to the distant bell along the top wire,
+down the left-hand dotted wire back to the battery, since it cannot
+enter by the left-hand press, which, not being pushed, makes no contact.
+The left-hand bell therefore rings. If, on the other hand, the left-hand
+push be pressed, the current from the carbon of the battery passes
+through the left-hand push, traverses the central line wire, passes into
+the bell, rings it, and descends to the right-hand earth plate E,
+traverses the earth circuit till it reaches the left-hand earth plate E,
+whence it returns to the zinc pole of the battery by the lower dotted
+line.
+
+[Illustration: Fig. 87.]
+
+Fig. 88 shows how the same result (signalling in both directions) may be
+attained, using only two wires, with earth return, and two Morse keys.
+The direction of the current is shown by the arrows. Both wires must be
+insulated and either carried overhead or underground, buried in tubes.
+Fig. 89 shows the proper mode of connecting the entire system of bells,
+pushes, etc., running through a building. The dotted lines are the wires
+starting from the two poles of the battery (which should consist of more
+cells in proportion as there is more work to do), the plain lines being
+the wires between the pushes and the bell and signalling box. In this
+illustration a door-pull is shown to the extreme left. Pendulum
+indicators are usually connected up as shown in this figure, except that
+the bell is generally enclosed in the indicator case. The wire,
+therefore, has to be carried from the left-hand screw of the indicator
+case direct to the upper dotted line, which is the wire returning to the
+zinc pole of the battery. N.B.--When the wires from the press-buttons
+are connected with the binding-screw, of the top of or inside of the
+indicator case, the insulating material of the wires, at the point where
+connection is to be made, must be removed, and the wires _carefully
+cleaned_ and _tightly clamped down_.
+
+[Illustration: Fig. 88.]
+
+[Illustration: Fig. 89.]
+
+When it is desired to connect separate bells to ring in other parts of
+the building, the quickest way is to take a branch wire out of the
+nearest _battery wire_ (the wire coming from the carbon pole), and carry
+it to the push or pull, from thence to the bell, and from the bell back
+to the zinc of the battery.
+
+
+§ 72. We should advise the fixer always to draw out a little sketch of
+the arrangement he intends to adopt in carrying out any plan, as any
+means of saving useless lengths of wire, etc., will then easily be seen.
+In doing this, instead of making full sketches of batteries, he may use
+the conventional signs [battery] for each cell of the battery, the thick
+stroke meaning the carbon, the thin one the zinc. Pushes may be
+represented by (·), earth-plates by [E] and pulls, switches, &c., as
+shown in the annexed cut, Fig. 90, which illustrates a mode of
+connecting up a lodge with a house, continuous bells being used, in such
+a way that the lodge bell can be made to ring from the lodge pull, the
+house bell ringing or not, according to the way the switch (shown at top
+left-hand corner) is set. As it is set in the engraving, only the lodge
+bell rings.
+
+[Illustration: Fig. 90.]
+
+
+§ 73. There are still two cases of electric bell and signal fitting, to
+which attention must be directed. The first is in the case of _ships_.
+Here all the connections can be made exactly as in a house, the only
+exception to be made being that the indicators must not be of the
+_pendulum_, or other easily displaced type; but either of the form shown
+at Fig. 67 or 68, in which the electro-magnet has to lift a latch to
+release the fall or drop, against a pretty stiff spring. Besides being
+thus firmly locking, so as not to be affected by the ship's motion, all
+the wood work should be soaked in melted paraffin wax, the iron work
+japanned, and the brass work well lacquered, to protect all parts from
+damp. The second case requiring notice is that of _lifts_. Every
+well-appointed lift should be fitted with electric bells and
+indicators. In the cab of the lift itself should be placed an electric
+bell, with as many double contact pushes and indicators as there are
+floors to be communicated with. At the top and at the bottom of the left
+shaft, as near to the landing side as possible, must be set two stout
+wooden blocks (oak, elm, or other non-perishable wood). From top to
+bottom of the shaft must then be stretched, in the same manner as a
+pianoforte is strung, on stout metal pins, with threading holes and
+square heads, as many No. 12 or 14 bare copper wires as there are floors
+or landings, and two more for the battery and return wire respectively.
+Care must be taken that these wires are strung perfectly parallel, and
+that they are stretched quite taut, but not strained, otherwise they
+will surely break. To the top of the cab, and in connection in the usual
+manner by wires with the bell and indicator (which, as in the case of
+ships, must be of the locking type, lest the jolts of the cab disturb
+their action) must be attached a number of spoonbill springs, which
+press against the naked wires running down the shaft. The shape of these
+springs (which should be of brass) at the part where they press against
+the bare wires, is similar to that of the spoon break of a bicycle. Some
+operators use rollers at the end of the spring instead of spoonbills,
+but these latter _rub_ the wires and keep up good contact, while the
+rollers slip over the wires and do not keep them clean. By means of
+these springs, the current from the batteries, which are best placed
+either at the top of the lift itself, or in one of the adjacent rooms
+(never at the bottom of the shaft, owing to the damp which always reigns
+there), can be taken off and directed where it is desired, precisely as
+if the batteries were in the cab itself. It is usual (though not
+obligatory) to use the two wires _furthest_ from the landing as the go
+and return battery wires, and from these, through the other wires, all
+desired communication with the landings can be effected. To obtain this
+end, it will be necessary to furnish every landing with a double contact
+push and bell, and each bell and push must be connected up to the shaft
+wires in the following mode:--
+
+A wire must be led from the _lower_ contact spring of the double contact
+push, to the _main battery carbon wire_ in the shaft. A second wire is
+led from the _upper contact stop_ of the double contact push to the
+bell, and thence to the _main battery zinc wire_ on the shaft. Lastly, a
+third wire is taken from the _upper contact spring_ of the push and
+connected to that particular wire in the shaft which by means of the
+spoonbill springs connects the particular push and indicator in the cab,
+destined to correspond with it. It will be seen that with the exception
+of using the rubbing spoonbill springs and return wires in the shaft,
+this arrangement is similar to that illustrated at Fig. 87.
+
+[Illustration: Fig. 91.]
+
+A glance at Fig. 91 will render the whole system of wiring and
+connecting up with lifts and landing, perfectly clear. In connecting the
+branch lines to the main bare copper wires in the shaft, in order that
+the spoonbill springs should not interfere with them, they (the ends of
+the branch wires) must be bent at right angles, like a letter [L], and the
+upright portion soldered neatly to the _back_ of the shaft wire. Any
+solder which may flow over to the _front_ of the wire must be carefully
+scraped off to prevent any bumps affecting the smooth working of the
+contact springs. It will be evident on examination of Fig. 91, that if
+any of the pushes on the landings be pressed, the circuit is completed
+between the battery at the top, through the two battery wires to the
+bell and one of the indicators to the cab, and, on the other hand, that
+if a push be pressed in the cab, a corresponding bell on the landing
+will be rung, precisely as in Fig. 87.
+
+Some fitters employ a many-stranded cable to convey the current to and
+from the battery to the cab and landing, instead of the system of
+stretched wires herein recommended; but this practice cannot be
+advocated, as the continual bending and unbending of this cable,
+repeated so frequently every day, soon breaks the leading wires
+contained in the cable.
+
+
+§ 74. In many cases where a "call" bell alone is required, the battery
+may be entirely dispensed with, and a small dynamo (§ 15) employed
+instead. The entire apparatus is then known as the "magneto-bell," and
+consists essentially of two parts, viz., the generator, Fig. 92, and the
+bell, Fig. 93. The _generator_ or _inductor_ consists of an armature,
+which by means of a projecting handle and train of wheels can be
+revolved rapidly between the poles of a powerful magnet; the whole being
+enclosed in a box. The current produced by the revolution of the
+armature is led to the two binding screws at the top of the box. By
+means of two wires, or one wire and an earth circuit, the current is led
+to the receiver or bell case, Fig. 93. Here, there are usually two
+bells, placed very near one another, and the armature attached to the
+bell clapper is so arranged between the poles of the double-bell
+magnets, that it strikes alternately the one and the other, so that a
+clear ringing is kept up as long as the handle is being turned at the
+generator.
+
+[Illustration: Fig. 92.]
+
+[Illustration: Fig. 93.]
+
+[Illustration: Fig. 94.]
+
+If a _combined_ generator and bell be fitted at each end of a line, it
+becomes possible to communicate both ways; one terminal of each
+instrument must be connected to the line, and the other terminal on each
+to earth. A combined generator and bell is shown at Fig. 94. These
+instruments are always ready for use, require no battery or
+press-buttons. The generator, Fig. 92, will ring seven bells
+simultaneously, if required, so powerful is the current set up; and by
+using a switch any number of bells, placed in different positions, can
+be rung, by carrying a separate wire from the switch to the bell.
+
+[Illustration: Fig. 95.]
+
+
+§ 75. Our work would not be complete unless we pointed out the means
+necessary to detect faults in our work. In order to localise faults, two
+things are requisite: first, a means of knowing whether the battery
+itself is working properly, that is to say, giving the due _amount_ of
+current of the right _pressure_, or E.M.F.; secondly, a means of
+detecting whether there is leakage, or loss of current, or break of
+circuit in our lines. Fortunately, the means of ascertaining these data
+can be all combined in one instrument, known as a linesman's
+galvanometer or detector, of which we give an illustration at Fig. 95.
+It will be remembered (§ 10) that if a current be passed over or under a
+poised magnetic needle, parallel to it, the needle is immediately
+deflected out of the parallel line, and swings round to the right or
+left of the current, according to the _direction_ of the current;
+likewise that the needle is deflected farther from the original position
+as the current becomes stronger. The deflections, however, are not
+proportionate to the strength of the current, being fairly so up to
+about 25 to 30 degrees of arc out of the original position, but being
+very much less than proportionate to the current strength as the needle
+gets farther from the line of current; so that a current of infinite
+strength would be required to send the needle up to 90°. On this
+principle the detector is constructed. It consists of a lozenge-shaped
+magnetic needle, suspended vertically on a light spindle, carrying at
+one end a pointer, which indicates on a card, or metal dial, the
+deflection of the needle. Behind the dial is arranged a flat upright
+coil of wire (or two coils in many cases) parallel to the needle, along
+which the current to be tested can be sent. The needle lies between the
+front and back of the flat coil. The whole is enclosed in a neat wooden
+box, with glazed front to show the dial, and binding screws to connect
+up to the enclosed coil or coils. If the coil surrounding the needle be
+of a few turns of coarse wire, since it opposes little resistance to the
+passage of the current, it will serve to detect the presence of large
+_quantities_ of electricity (many ampères) at a low pressure; this is
+called a _quantity_ coil. If, on the other hand, the coil be one of fine
+wire, in many convolutions, as it requires more _pressure_, or E.M.F.,
+or "intensity" to force the current through the fine high-resistance
+wire, the instrument becomes one fitted to measure the voltage or
+_pressure_ of the current, and the coil is known as the "intensity." If
+both coils are inserted in the case, so that either can be used at will,
+the instrument is capable of measuring either the quantity of
+electricity passing, or the pressure at which it is sent, and is then
+known as a quantity and intensity detector. No two galvanometers give
+exactly the same deflection for the same amount of current, or the same
+pressure; the fitter will therefore do well to run out a little table
+(which he will soon learn by heart) of the deflection _his_ instrument
+gives with 1, 2, 3, 4, 5 and 6 Leclanché's _coupled in parallel_, when
+connected with the quantity coil. He will find the smaller sizes give
+less current than the larger ones. In testing the deflections given by
+the intensity coil, he must remember to couple his cells _in series_, as
+he will get no increase in _tension_ or _pressure_ by coupling up in
+parallel. In either case the cells should be new, and freshly set up,
+say, within 24 hours. As some of my readers may like to try their skill
+at constructing such a detector, I transcribe the directions given in
+"Amateur work" by Mr. Edwinson:--
+
+
+§ 76. "Such an instrument, suitable for detecting the currents in an
+electric bell circuit, may be made up at the cost of a few shillings for
+material, and by the exercise of a little constructive ability. We shall
+need, first of all, a magnetised needle; this can be made out of a piece
+of watch spring. Procure a piece of watch spring two inches long, soften
+it by heating it to redness, and allowing it to cool gradually in a bed
+of hot ashes; then file it up to the form of a long lozenge, drill a
+small hole in the centre to receive the spindle or pivot, see that the
+needle is quite straight, then harden it by heating it again to a bright
+red and plunging it at once into cold water. It now has to be
+magnetised. To do this, rub it on a permanent horse-shoe, or other
+magnet, until it will attract an ordinary sewing needle strongly, or
+wrap it up in several turns of insulated line wire, and send many jerky
+charges of electricity from a strong battery through the wire. When it
+has been well magnetised, mount it on a spindle of fine hard wire, and
+secure it by a drop of solder. We will next turn our attention to the
+case, bobbin, or chamber in which the needle has to work. This may be
+made out of cardboard entirely, or the end pieces may be made of ivory
+or ebonite, or it may be made out of thin sheet brass; for our purpose
+we will choose cardboard. Procure a piece of stout cardboard 4-3/4
+inches long by 2 inches wide, double it to the form of a Tãndstickor
+match-box, and pierce it in exactly opposite sides, and in the centre of
+those sides with holes for the needle spindle. Now cut another piece of
+stout, stiff cardboard 2-3/4 inches long by 3/4 inch wide, and cut a
+slit with a sharp knife to exactly fit the ends of the case or body
+already prepared. The spindle holes must now be bushed with short
+lengths of hard brass or glass bugles, or tubing, made to allow the
+spindle free movement, and these secured in position by a little melted
+shellac, sealing-wax, or glue. The needle must now be placed in the
+case, the long end of the spindle first, then the short end in its
+bearing; then, whilst the case with the needle enclosed is held between
+the finger and thumb of the left hand, we secure the joint with a little
+glue or with melted sealing-wax. The end-pieces are now to be put on,
+glued, or sealed in position, and set aside to get firm, whilst we turn
+our attention to other parts. The case, 5 inches by 4 inches by 2 inches
+in depth, may be improvised out of an old cigar-box, but is best made of
+thin mahogany or teak, nicely polished on the outside, and fitted with a
+cover sliding in a groove, or hinged to form the back of the instrument.
+The binding screws should be of the pattern known as the telegraph
+pattern, fitted with nuts, shown at Fig. 27. A small brass handle to be
+fitted to the top of the instrument, will also be handy. A circular
+piece of smooth cardboard 3-1/4 inches in diameter, with a graduated
+arc, marked as shown in Fig. 95, will serve the purpose of a dial, and a
+piece of thin brass, bent to the form of [box open down], will be
+required as a needle guard. The face of the dial may be a circular piece
+of glass, held in a brass ogee, or a hole the size of the dial may be
+cut in a piece of thin wood; this, glazed on the inside with a square of
+glass, may be made to form the front of the instrument over the dial. An
+indicating needle will also be required for an outside needle; this is
+usually made of watch spring, and nicely blued; but it may be made of
+brass or any other metal, one made of aluminium being probably the best
+on account of its lightness. It must be pierced with a hole exactly in
+the centre, so as to balance it as the beam of scales should be
+balanced, and should one end be heavier than the other it must be filed
+until they are equal.
+
+We will now turn our attention to the coil.
+
+Procure sixpennyworth of No. 36 silk-covered copper wire and wind three
+layers of it very evenly on the coil case or bobbin, being careful in
+passing the needle spindle not to pinch it or throw it out of truth.
+When this has been wound on, it will be found that one end of the wire
+points to the left and the other end to the right. These are destined to
+be connected to the under side of the binding screws shown on the top of
+Fig. 95. We therefore secure them to their respective sides with a touch
+of sealing wax, and leave enough wire free at the ends to reach the
+binding screws--say, about 6 inches. It is handy to have an additional
+coil for testing strong currents, and as this may be combined in one
+instrument at a trifle additional cost, we will get some line wire (No.
+22) and wind six or eight turns of it around the coil outside the other
+wire; one end of this wire will be attached to an additional binding
+screw placed between the others, and the other end to left binding screw
+shown. The coil thus prepared may now be mounted in position. Pierce the
+board dial and the wood at its back with a hole large enough for the
+needle spindle to pass through from the back to the centre of the dial.
+See that the thick end of the inside needle hangs downwards, then place
+the coil in the position it is intended to occupy, and note how far the
+needle spindle protrudes on the face of the dial. If this is too long,
+nip off the end and file it up taper and smooth until it will work
+freely in a hole in the needle guard, with all parts in their proper
+places. This being satisfactory, secure the coil in its place by sealing
+wax, or, better still, by two thin straps of brass, held by screws at
+each end, placed across the coil. Now clean the free ends of the coil
+wires, insert them under the nuts of the binding screws, fix the
+indicating needle on the end of the spindle outside, and see that it
+hangs in a vertical position with the inside needle when the instrument
+is standing on a level surface. Secure it in this position, screw on the
+needle guard, fasten on the glass face, and the instrument will be
+complete.
+
+
+§ 77. Provided thus with an efficient detector, the fitter may proceed
+to test his work. In cases of _new installations_, take the wire off
+the carbon binding screw of the battery and attach it to one screw of
+the galvanometer (on the intensity coil side), next attach a piece of
+wire from the other binding screw of the galvanometer (the central one)
+so as to place the galvanometer in circuit. _There should be no movement
+of the needle_, and in proportion to the deflection of the needle, so
+will the loss or waste be. If loss is going on, every means must be used
+to remedy it. It is of the utmost importance to the effective working of
+the battery and bells that not the _slightest leakage_ or _local action_
+should be allowed to remain. However slight such loss may be, it will
+eventually ruin the battery. Let damp places be sought out, and the
+wires removed from near them. Bad or injured coverings must also be
+looked for, such as may have been caused by roughly drawing the wires
+across angular walls, treading on them, or driving staples too tightly
+over them. Two or more staples may be touching, or two or more wires
+carelessly allowed to lie under one staple. The wire may have been bared
+in some places in passing over the sharp edges of the zinc tube. The
+backs of the pushes should be examined to see if too much wire has been
+bared, and is touching another wire at the back of the push-case itself.
+Or the same thing may be taking place at the junction with the relays or
+at the indicator cases. Should the defect not be at any of these places,
+the indicator should next be examined, and wire by wire detached (not
+cut) until the particular wire in which the loss is going on has been
+found. This wire should then be traced until the defect has been
+discovered. In testing underground wires for a loss or break, it will be
+necessary first to uncouple the _distant_ end, then to disconnect the
+other end from the instruments, and attach the wire going underground to
+the screw of the galvanometer. A piece of wire must then be taken from
+the other screw of the detector to the carbon end of the battery, and a
+second wire from the zinc end of the battery to the earth plate or other
+connection. Proceeding to that part of the wire where the injury is
+suspected, the wire is taken up, and a temporary earth connection having
+been made (water main, gas pipe, etc.), and by means of a sharp knife
+connected with this latter, the covering of the suspected wire
+penetrated through to the wire, so as to make a good connection between
+this suspected wire and the temporary earth plates. If, when this is
+done, the needle is deflected fully, the injury is farther away from the
+testing end, and other trials must be made farther on, until the spot is
+discovered. Wherever the covering of the wire has been pierced for
+testing, it must be carefully recovered, finished off with Prout's
+elastic glue, or gutta-percha, and made quite sound. The connections
+with the earth plates very frequently give trouble, the wires corrode or
+become detached from the iron pipes etc., and then the circuit is
+broken.
+
+
+§ 78. When the fitter is called to localise defects which may have
+occurred in an installation which has been put up some time, before
+proceeding to work let him ask questions as to what kind of defect there
+is, and when and where it evinces itself. If all the bells have broken
+down, and will not ring, either the battery or the main go and return
+wires are at fault. Let him proceed to the battery, examine the binding
+screws and connected wires for corrosion. If they are all right, let the
+batteries themselves be tested to see if they are giving the right
+amount of current. This should be done with the quantity coil of the
+detector. Should the battery be faulty, it will be well to renew the
+zincs and recharge the battery, if the porous cell be still in good
+condition; if not, new cells should be substituted for the old ones.
+Should the battery be all right, and still none of the bells ring, a
+break or bad contact, or short circuit in the main wires near the
+battery may be the cause of the mischief. If some bell rings
+continuously, there must be a short circuit in the push or pushes
+somewhere; the upper spring of one of the pushes may have got bent, or
+have otherwise caught in the lower spring. _Pulls_ are very subject to
+this defect. By violent manipulations on the part of mischievous butcher
+or baker boys, the return spring may be broken, or so far weakened as
+not to return the pull into the "off" position. If, the batteries being
+in good order, any bell rings feebly, there is either leakage along its
+line, or else bad contact in the push or in the connections of the wires
+to and from the push. There should be platinum contacts at the ends of
+the push springs; if there are not, the springs may have worked dirty at
+the points of contact, hence the poor current and poor ringing. It is
+seldom that the bells themselves, unless, indeed, of the lowest
+quality, give any serious trouble. Still the set screw may have shaken
+loose (which must then be adjusted and tightened up), or the platinum
+speck has got solder on its face and therefore got oxidised. This may be
+scraped carefully with a penknife until bright. Or, purposely or
+inadvertently, no platinum is on the speck at all, only the solder. A
+piece of platinum foil should be soldered on the spot, if this is so. Or
+again (and this only in very bad bells), the electro-magnets being of
+hard iron, may have retained a certain amount of _permanent magnetism_,
+and pull the armature into permanent contact with itself. This can be
+remedied by sticking a thin piece of paper (stamp paper will do) over
+the poles of the magnet, between them and the armature. In no case
+should the fitter _cut_ or _draw up_ out of tubes, etc., any wire or
+wires, without having first ascertained that the fault is in that wire;
+for, however carefully joints are made, it is rare that the jointed
+places are so thoroughly insulated as they were before the cutting and
+subsequent joining were undertaken. To avoid as much as possible cutting
+uselessly, let every binding screw be examined and tightened up, and
+every length of wire, which it is possible to get at, be tested for
+continuity before any "slashing" at the wires, or furious onslaughts on
+the indicator be consummated.
+
+In conclusion, I beg to record my thanks for the very generous
+assistance which I have received in the compilation of the foregoing
+pages from the electrical firms of Messrs. Blakey Emmot, Binswanger,
+Gent, Judson, Jensen, and Thorpe.
+
+
+
+
+ADDENDUM.
+
+THE GASSNER BATTERY.
+
+
+Since the compilation of the foregoing pages, a _dry battery_, known by
+the above name, has found great favour with electric-bell fitters. Its
+peculiarity consists in the zinc element forming the outside cell. In
+this is placed the carbon, which is separated from the zinc by a thick
+paste or jelly made of gypsum and oxide of zinc. The cell can be placed
+in any position, works as well on its side as upright, is not subject to
+creeping, has an E.M.F. of about 1·5 volt, with an internal resistance
+of only 0·25 ohm in the round form, and 0·6 in the flat form. The
+Gassner dry battery polarizes much less quickly than the ordinary
+Leclanché. The only defects at present noticeable, are the flimsy
+connections, and the fact that the outer cases being _metal_ must be
+carefully guarded from touching one another. This can be effected by
+enclosing in a partitioned _wooden box_.
+
+
+
+
+INDEX.
+
+
+ A.
+
+ Acid, Chromic, 33, 46
+
+ ---- Hydrobromic, 20
+
+ ---- Hydrochloric, 20
+
+ ---- Hydriodic, 20
+
+ ---- Nitric, 20
+
+ ---- Sulphuric, 20
+
+ Action in Bichromate, 47
+
+ ---- Dotting, 116
+
+ ---- of electric bell, 81
+
+ ---- Leclanché, 35
+
+ ---- Relay, 134
+
+ ---- Rubbing, 116
+
+ ---- of zinc on acids, 21
+
+ Agglomerate block, 38
+
+ ---- Cell, 38
+
+ ---- Compo, 38
+
+ Alarms, Burglar, 113
+
+ ---- Fire, 123
+
+ ---- Frost, 121
+
+ ---- Thermometer, 122
+
+ ---- Thief, 113
+
+ ---- Watch, 124
+
+ Amber, 1
+
+ Ampère, 55
+
+ Ampère's law, 11
+
+ Annealing iron, 13
+
+ Arrangement of bells for lifts, 171
+
+ ---- Ships, 170
+
+ Attraction, 3
+
+
+ B.
+
+ Batteries, 18
+
+ Battery agglomerate, 39
+
+ Battery, Bichromate, 48
+
+ ---- Bunsen, 33
+
+ ---- Chromic acid, 46
+
+ ---- Daniell's, 29
+
+ ---- Gassner (addendum), 186
+
+ ---- Gent's, 44
+
+ ---- Gravity, 31
+
+ ---- Modified, 120
+
+ ---- Grenet, 46
+
+ ---- Grove, 33
+
+ ---- Judson's, 41
+
+ ---- Leclanché, 33
+
+ ---- Reversed, 46
+
+ ---- Minotto, 31
+
+ ---- Smee's, 27
+
+ ---- Walker's, 27
+
+ Bell action, case for, 88
+
+ Blocks, wooden, 150
+
+ Bobbins, electric bell, 67
+
+ Box for batteries, 43
+
+ Brushes, dynamo, 17
+
+
+ C.
+
+ Cable, many stranded, 174
+
+ Case for bell action, 88
+
+ Cells in parallel, 57
+
+ ---- series, 53
+
+ Charging fluid, recipes, 48
+
+ ---- Fuller, 49
+
+ Circuits, closed, 52, 118
+
+ ---- Of bells complete in house, 168
+
+ ---- For signalling, 167
+
+ ---- In both directions, 168
+
+ Circuits of bells with Morse key, 165
+ In parallel, 161
+ Series, 162
+ With relay, 164
+ Single bell and wire, 159
+ Earth, 160
+ Two pushes, 161
+ Push and pull, 161
+ Open, 52
+
+ Closed circuit system, 118
+
+ Code for signalling, 130
+
+ Coil spring, 108
+
+ Conductors, 3
+
+ Connecting up, 144, 159
+
+ Contacts, burglar alarm, 113
+ Door, 116
+ Drawer, 121
+ Floor, 113
+ For closed circuits, 121
+ Mackenzie's humming, 113
+ Shop door, 116
+ Till, 121
+ Watch alarm, 124
+ Window sash, 116
+
+ Corrugated carbons, 41
+
+ Creeping in cells, 43
+ To remedy, 44
+
+ Callow's attachment, 99
+
+ Current, 54
+ To ring bell, 145
+
+
+ D.
+
+ Daniell's cell, 29
+ Action in, 29
+
+ Deflection of needle, 9, 11
+
+ Detector or galvanometer, to make, 178
+
+ Detent lever, 94
+
+ Door contact, 116
+
+ Dotting action, 116
+
+ Drawing out plans, 169
+
+ Dynamo, 15
+ Armature, 16
+ Brushes, 17
+ Commutator, 17
+
+ Dynamo, Cumulative effects, 17
+ Field magnets, 16
+
+
+ E.
+
+ Earth, 52
+ Plate, 53
+ Return, 153
+
+ Electric bell, action of, 81
+ Armature, 74
+ Base, 61
+ Bobbins, 67
+ Contact screw, 75
+ Continuous, 92
+ Circular bell, 106
+ Gong, 77
+ How to make, 60
+ In lifts, 171
+ Ships, 170
+ Jensen's, 101
+ Joining E. M. wire, 73
+ Magnets, 63
+ Magneto, 174
+ Mining, 106
+ Paraffining, 69
+ Platinum tip, 76
+ Putting together, 78
+ Single stroke, 91
+ Spring, 74
+ Thorpe's, 100
+ Trembling, 81, 90
+ Winding wire on, 71
+ Wire for, 69
+ Trumpet, 107
+
+ Electricity, sources of, 2
+
+ Electrodes, 26
+
+ Electro-motive force, 51
+
+ Electron, 1
+
+ E.M.F., 51
+
+ Excitation, 6
+
+
+ F.
+
+ Faults to detect, 182
+
+ Fire alarms, 123
+
+ Floor contacts, 113
+
+ Frost alarms, 121
+
+ Fuller charging, 49
+
+
+ G.
+
+ Galvanometer, 176
+
+ Gas evolved, 18
+
+ Gassner battery (addendum), 186
+
+ Generator (magneto), 174
+
+ Gent's battery, 44
+
+ Glue, Prout's elastic, 148
+
+ Graphite, 27
+
+ Gravity battery, 31
+ Daniell battery, 31
+ Modified, 120
+
+ Grenet battery, 46
+
+ Grove battery, 33
+
+ Gutta-percha, 148
+
+
+ I.
+
+ Indicator, 135
+ Automatic, 138
+ Drop, 136
+ Electric replacement, 136
+ Gent's, 140
+ Tripolar, 143
+ Mechanical replacement, 136
+ Mode of coupling up, 142
+ Pendulum, 139
+ Polarised, 139
+ Self replacing, 136
+ Semaphore, 136
+
+ Inductor, 174
+
+ Insulation, 68
+
+ Insulators, 4
+
+ Internal resistance, 56
+
+ Interior of push, 151
+
+ Iron, importance of soft, 65
+ Yoke, 66
+
+
+ J.
+
+ Jensen's bell, 101
+
+ Joining wires to push, 151
+
+ Judson's cell, 41
+
+
+ K.
+
+ Key, Morse, 129
+
+
+ L.
+
+ Leakage, 52
+
+ Leclanché cell, 33
+ reversed, 46
+
+ Legge's contact, 115
+
+ Lever switches, 128
+
+ Lifts, bells for, 171
+
+ Localising faults, 144, 175
+
+ Lodge bell, 169
+
+
+ M.
+
+ Magnetic field, 14
+
+ Magneto bells, 175
+ Electric machines, 14, 15
+
+ Magnets, 13
+
+ Magnets producing electricity, 14
+
+ Magnetisation of iron, 12
+ Steel, 13
+
+ Manganese oxide, 33
+
+ Minotto cell, 31
+
+ Modified gravity battery, 120
+
+ Morse key, 129
+
+ Musical instrument, novel, 108
+
+
+ N.
+
+ Negative electricity, 7
+
+ Non-conductors, 3
+
+ Novel musical instrument, 108
+
+
+ O.
+
+ Ohm, 55
+
+ Ohm's law, 55
+
+ Open circuit, 52
+
+ Overhead lines, 152
+
+
+ P.
+
+ Paraffin, 69, 170
+
+ Percha, gutta, 148
+
+ Plans, drawing out, 169
+
+ Platinum, riveting, 76
+
+ Platinum, use of, 76
+
+ Plug switches, 128
+
+ Polarisation, 26
+
+ Positive electricity, 7
+
+ Proportions of bell parts, table of, 89
+
+ Pressels, 111
+
+ Prout's elastic glue, 148
+
+ Pulls, 111
+
+ Push, 92, 151, 109
+ Interior of, 151
+ Joining wires to, 151
+
+
+ R.
+
+ Relay, 96, 133
+ Action of, 134
+
+ Repulsion, 3
+
+ Resinous electricity, 7
+
+ Resistance of wire, table of, 146
+
+ Return current, 153
+
+ Riveting platinum, 76
+
+ Rubbing action, 116
+
+
+ S.
+
+ Ships, bells for, 170
+
+ Shop door contact, 116
+
+ Signalling by bells, 130
+ Code, 130
+
+ Silver platinised, 27
+
+ Single cell, 9
+
+ Sizes of Leclanché's, 42
+
+ Smee's cell, 27
+
+ Spring coil, 108
+
+ Standard size of wires, 146
+
+ Switches, lever, 128
+ Plug, 128
+
+
+ T.
+
+ Table of batteries, E.M.F. and R., 58
+ Conductors and insulators, 4, 68
+ Metals in acid, 8
+
+ Table of Proportions of bell parts, 89
+ Wire resistance, etc., 146
+
+ Testing new work, 182
+ Old, 183
+
+ Thermometer alarms, 122
+
+ Thorpe's Ball, 100
+
+
+ U.
+
+ Use of platinum, 76
+
+
+ V.
+
+ Vitreous electricity, 7
+
+ Volt, 53
+
+
+ W.
+
+ Walker's cell, 27
+
+ Watchman's clock, 124
+
+ Water level indicator, 127
+
+ Washer, insulating, 77
+
+ Window sash contact, 116
+
+ Wiping contact, 102
+
+ Wire covering, 147
+ In iron pipes, 152
+ In wooden boxes, 152
+ Iron, 152
+ Joining, 148
+ To push, 151
+ Laying in tubes, 149
+ Leading, 147, 150
+ Overhead, 152
+ Resistance, table of, 146
+ Return, 147, 150
+ Soldering iron, 148
+ Tinned, 147
+ Underground, 152
+
+ Wiring, general instructions, 155
+ Up, 144
+
+
+ Z.
+
+ Zinc, amalgamated, 22
+ Blacking, 45
+ Consumption, 21
+ Commercial, 19
+ Pure, 19
+
+
+WILLIAM RIDER AND SON, PRINTERS, LONDON.
+
+ * * * * *
+
+ _Small crown 8vo, cloth._ _With many Illustrations._
+
+
+ WHITTAKER'S LIBRARY OF ARTS, SCIENCES,
+ MANUFACTURES AND INDUSTRIES.
+
+ MANAGEMENT OF ACCUMULATORS AND PRIVATE ELECTRIC LIGHT INSTALLATIONS.
+
+ A Practical Handbook by Sir DAVID SALOMONS, Bart., M. A.
+
+ 4th Edition, Revised and Enlarged, with 32 Illustrations. Cloth 3s.
+
+ "To say that this book is the best of its kind would be a poor
+ compliment, as it is practically the only work on accumulators that
+ has been written."--_Electrical Review._
+
+ ELECTRICAL INSTRUMENT-MAKING FOR AMATEURS. A Practical Handbook. By
+ S. R. BOTTONE, Author of "The Dynamo," &c. With 60 Illustrations.
+ Second Edition. Cloth 3s.
+
+ ELECTRIC BELLS. By S. R. BOTTONE. With numerous Illustrations.
+
+
+IN PREPARATION.
+
+ THE PROTECTION OF BUILDINGS FROM LIGHTNING. A Treatise on the Theory
+ of Lightning Conductors from a Modern Point of View. Being the
+ substance of two lectures delivered before the Society of Arts in
+ March, 1888. By OLIVER J. LODGE, LL.D., D.Sc, F.R.S., Professor of
+ Physics in University College, Liverpool.
+
+ Published with various amplifications and additions, with the
+ approval of the Society of Arts.
+
+ ELECTRICAL INFLUENCE MACHINES: Containing a full account of their
+ historical development, their modern Forms, and their Practical
+ Construction. By J. GRAY, B.Sc.
+
+ ELECTRICAL ENGINEERING IN OUR WORKSHOPS. A Practical Handbook. By
+ SYDNEY F. WALKER.
+
+ [_Ready Shortly_
+
+ * * * * *
+
+
+Transcriber's Note
+
+Page 12: changed "guage" to "gauge" (... cotton-covered copper wire,
+say No. 20 gauge ...)
+
+Page 35: changed "change" to "charge" (... losing at the same time its
+electrical charge ...)
+
+Page 55: changed "guage" to "gauge" (... 1 foot of No. 41 gauge pure
+copper wire ...)
+
+Page 64: changed "exaet" to "exact" (... of the exact diameter of the
+turned ends of the cores ...)
+
+Page 73: moved comma "Rivetting, is" to "Rivetting is," (Rivetting, is
+perhaps, the best mode ...)
+
+Page 81: added hyphen (... along the short length of wire to the
+right-hand binding-screw ...)
+
+Page 83: changed "head" to "heads" (... the possible defects of
+electric bells may be classed under four heads: ...)
+
+Page 92: changed "its" to "it" (... until it rests against the stop or
+studs.)
+
+Page 102: changed "contract-breaker" to "contact-breaker" (When the
+contact-breaker is used, ...)
+
+Page 103: changed "instead" to "Instead" (Instead of the armature and
+clapper ...)
+
+Page 132: in the Morse code for "BRING THE", the code for "H" has been
+corrected from two dots to four dots.
+
+Page 136: changed "eletro-magnet" to "electro-magnet" (... if the
+electro-magnet were energised ...)
+
+Page 137: changed "idicator" to "indicator" (since the indicator falls
+forwards)
+
+Page 146: changed "arrangment" to "arrangement" (the size and
+arrangement of the batteries and wires)
+
+Page 146: added comma "nails," (... chance contact with nails,
+staples, metal pipes or other wires ...)
+
+Page 179: changed "carboard" to "cardboard" (... for our purpose we
+will choose cardboard.)
+
+Page 179: changed "Tanstickor" to "Tãndstickor" (... double it to the
+form of a Tãndstickor match-box, ...)
+
+Page 185: suspected typo (unchanged) "Emmot" should perhaps be
+"Emmott" (... the electrical firms of Messrs. Blakey Emmot, ...)
+
+Page 186: changed "Leclanchè" to "Leclanché" (... polarizes much less
+quickly than the ordinary Leclanché.)
+
+Page 187: changed two instances of "Ampére" to "Ampère" in the index
+(Ampère, 55 / Ampère's law, 11)
+
+
+
+
+
+End of Project Gutenberg's Electric Bells and All About Them, by S. R. Bottone
+
+*** END OF THIS PROJECT GUTENBERG EBOOK ELECTRIC BELLS AND ALL ABOUT THEM ***
+
+***** This file should be named 39053-8.txt or 39053-8.zip *****
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