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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)
+
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+
+
+
+
+
+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 ***
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+<pre>
+
+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: UTF-8
+
+*** 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)
+
+
+
+
+
+
+</pre>
+
+
+<div class="trans-note">
+<h4>Transcriber's Notes</h4>
+
+<p>Inconsistent spellings (e.g. depolariser &amp; depolarizer) and hyphenation
+(e.g. guttapercha &amp; 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 <a href="#Transcribers_Notes">the end of the book</a>.</p>
+
+<p class="center"><a href="images/i_cover.png">[cover image]</a></p>
+<p class="center"><a href="#CONTENTS">Table of Contents</a>.</p>
+<p class="center"><a href="#LIST_OF_ILLUSTRATIONS">List of Illustrations</a>.</p>
+<p class="center"><a href="#INDEX">Index</a>.</p>
+
+</div>
+<p><!-- Page i --><span class="pagenum"><a name="Page_i" id="Page_i">[Pg i]</a></span></p>
+
+
+
+<h1>                         ELECTRIC BELLS AND<br />
+                           ALL ABOUT THEM.</h1>
+
+<p class="center">                 A Practical Book for Practical Men.</p>
+
+<p class="center">                <i>WITH MORE THAN 100 ILLUSTRATIONS.</i></p>
+
+<p class="center">                                  BY
+                            S. R. BOTTONE,</p>
+
+<p class="center">        CERTIFICATED BY SOUTH KENSINGTON (LATE OF THE COLLEGIO
+               DEL CARMINE, TURIN, AND OF THE ISTITUTO
+                          BELLINO, NOVARA);</p>
+
+<p class="center">          <i>Author of "The Dynamo," "Electrical Instruments for
+                            Amateurs," &amp;c.</i></p>
+
+<p class="center">                               LONDON:
+              <span class="smcap">WHITTAKER &amp; CO., Paternoster Square, E.C.</span></p>
+
+<p class="center">                                1889.</p>
+
+<p class="center">                      (<i>All rights reserved.</i>)</p>
+<p><!-- Page iii --><span class="pagenum"><a name="Page_iii" id="Page_iii">[Pg iii]</a></span></p>
+
+
+
+<h2>PREFACE.</h2>
+
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>
+<span class="smcap">Carshalton, Surrey</span>,<br />
+<i>November, 1888</i>.</p>
+
+
+
+<hr class="long" />
+<p><!-- Page v --><span class="pagenum"><a name="Page_v" id="Page_v">[Pg v]</a></span></p>
+<h2><a name="CONTENTS" id="CONTENTS"></a>CONTENTS.</h2>
+
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="right"><span class="smcap">chap.</span></td><td align="right" colspan="3"><span class="smcap">page</span></td></tr>
+<tr><td align="right">I.</td><td align="left">Preliminary Considerations</td><td align="right"><a href="#Page_1">1</a></td></tr>
+<tr><td align="right"> II.</td><td align="left">On the Choice of Batteries for Electric Bell Work</td><td align="right"><a href="#Page_18">18</a></td></tr>
+<tr><td align="right">III.</td><td align="left">On Electric Bells and other Signalling Appliances</td><td align="right"><a href="#Page_59">59</a></td></tr>
+<tr><td align="right"> IV.</td><td align="left">On Contacts, Pushes, Switches, Keys, Alarms, and Relays</td><td align="right"><a href="#Page_109">109</a></td></tr>
+<tr><td align="right">V.</td><td align="left">On Wiring, Connecting up, and Localising Faults</td><td align="right"><a href="#Page_144">144</a></td></tr>
+</table></div>
+
+<p><!-- Page vii --><span class="pagenum"><a name="Page_vii" id="Page_vii">[Pg vii]</a></span></p>
+
+
+
+<hr class="long" />
+<h2><a name="LIST_OF_ILLUSTRATIONS" id="LIST_OF_ILLUSTRATIONS"></a>LIST OF ILLUSTRATIONS.</h2>
+
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="list of illustrations">
+<tr><td align="left"><span class="smcap">Fig.</span></td><td align="right" colspan="3"><span class="smcap">Page</span></td></tr>
+<tr><td align="left" class="in1"> <a href="#FIG_1">1</a>.</td><td align="left">Direction of current in cell</td><td align="right">9</td></tr>
+<tr><td align="left" class="in1"> <a href="#FIG_2">2</a>.</td><td align="left">Direction of current out of cell</td><td align="right">10</td></tr>
+<tr><td align="left" class="in1"> <a href="#FIG_3">3</a>.</td><td align="left">Bar and horse-shoe magnets</td><td align="right">14</td></tr>
+<tr><td align="left" class="in1"> <a href="#FIG_4">4</a>.</td><td align="left">The Dynamo</td><td align="right">16</td></tr>
+<tr><td align="left" class="in1"> <a href="#FIG_5">5</a>.</td><td align="left">The Smee cell</td><td align="right">28</td></tr>
+<tr><td align="left" class="in1"> <a href="#FIG_6">6</a>.</td><td align="left">The Daniell cell</td><td align="right">30</td></tr>
+<tr><td align="left" class="in1"> <a href="#FIG_7">7</a>.</td><td align="left">The Gravity cell</td><td align="right">32</td></tr>
+<tr><td align="left" class="in1"> <a href="#FIG_8">8</a>.</td><td align="left">The Leclanché cell and parts</td><td align="right">34</td></tr>
+<tr><td align="left" class="in1"> <a href="#FIG_9">9</a>.</td><td align="left">The Agglomerate cell</td><td align="right">40</td></tr>
+<tr><td align="left"><a href="#FIG_10">10</a>.</td><td align="left">The Judson cell</td><td align="right">42</td></tr>
+<tr><td align="left"><a href="#FIG_11">11</a>.</td><td align="left">The Battery in box</td><td align="right">43</td></tr>
+<tr><td align="left"><a href="#FIG_12">12</a>.</td><td align="left">The Gent cell</td><td align="right">44</td></tr>
+<tr><td align="left"><a href="#FIG_13">13</a>.</td><td align="left">The Bichromate cell</td><td align="right">48</td></tr>
+<tr><td align="left"><a href="#FIG_14">14</a>.</td><td align="left">The Fuller cell</td><td align="right">50</td></tr>
+<tr><td align="left"><a href="#FIG_15">15</a>.</td><td align="left">The Cells coupled in series</td><td align="right">54</td></tr>
+<tr><td align="left"><a href="#FIG_16">16</a>.</td><td align="left">The Cells coupled in Parallel</td><td align="right">57</td></tr>
+<tr><td align="left"><a href="#FIG_17">17</a>.</td><td align="left">Outline of electric bell</td><td align="right">61</td></tr>
+<tr><td align="left"><a href="#FIG_18">18</a>.</td><td align="left">Frame of bell</td><td align="right">62</td></tr>
+<tr><td align="left"><a href="#FIG_19">19</a>.</td><td align="left">E-shaped frame</td><td align="right">63</td></tr>
+<tr><td align="left"><a href="#FIG_20">20</a>.</td><td align="left">Electro-magnet, old form</td><td align="right">64</td></tr>
+<tr><td align="left"><a href="#FIG_20A">20<span class="smcap">A</span></a>.</td><td align="left">Electro-magnet, modern form</td><td align="right">65</td></tr>
+<tr><td align="left"><a href="#FIG_21">21</a>.</td><td align="left">Magnet frame</td><td align="right">66</td></tr>
+<tr><td align="left"><a href="#FIG_21A">21<span class="smcap">A</span></a>.</td><td align="left">Winder</td><td align="right">72</td></tr>
+<tr><td align="left"><a href="#FIG_22">22</a>.</td><td align="left">Mode of joining electromagnet wires</td><td align="right">73</td></tr>
+<tr><td align="left"><a href="#FIG_23">23</a>.</td><td align="left">Armature spring</td><td align="right">74</td></tr>
+<tr><td align="left"><a href="#FIG_24">24</a>.</td><td align="left">Armature spring Another form</td><td align="right">74</td></tr>
+<tr><td align="left"><a href="#FIG_25">25</a>.</td><td align="left">Platinum tipped screw</td><td align="right">75</td></tr>
+<tr><td align="left"><a href="#FIG_26">26</a>.</td><td align="left">Platinum tipped spring</td><td align="right">76</td></tr>
+<tr><td align="left"><a href="#FIG_27">27</a>.</td><td align="left">Binding screws</td><td align="right">77</td></tr>
+<tr><td align="left"><a href="#FIG_28">28</a>.</td><td align="left">Bell or gong</td><td align="right">78</td></tr>
+<tr><td align="left"><a href="#FIG_29">29</a>.</td><td align="left">Pillar and nuts</td><td align="right">78</td></tr>
+<tr><td align="left"><a href="#FIG_30">30</a>.</td><td align="left">Washers</td><td align="right">78</td></tr>
+<tr><td align="left"><a href="#FIG_31">31</a>.</td><td align="left">Trembling bell</td><td align="right">81</td></tr>
+<tr><td align="left"><a href="#FIG_32">32</a>.</td><td align="left">Bell action enclosed in case</td><td align="right">88</td></tr>
+<tr><td align="left"><a href="#FIG_33A">33</a>.</td><td align="left">Ordinary trembling bells</td><td align="right">90</td></tr>
+<tr><td align="left"><a href="#FIG_34">34</a>.</td><td align="left">Single stroke bell</td><td align="right">91</td></tr>
+<tr><td align="left"><a href="#FIG_35">35</a>.</td><td align="left">Continuous ring bell</td><td align="right">94</td></tr>
+<tr><td align="left"><a href="#FIG_36">36</a>.</td><td align="left">Release action</td><td align="right">95</td></tr>
+<tr><td align="left"><a href="#FIG_37">37</a>.</td><td align="left">Continuous ringing with relay</td><td align="right">96</td></tr>
+<tr><td align="left"><a href="#FIG_38">38</a>.</td><td align="left">Continuous ringing action with indicator</td><td align="right">97</td></tr>
+<tr><td align="left"><a href="#FIG_39">39</a>.</td><td align="left">Relay and detent lever for indicator</td><td align="right">97</td></tr>
+<tr><td align="left"><a href="#FIG_40">40</a>.</td><td align="left">Callow's attachment</td><td align="right">99</td></tr>
+<tr><td align="left"><a href="#FIG_40A">40<span class="smcap">A</span></a>.</td><td align="left">Thorpe's arrangement</td><td align="right">101</td></tr>
+<tr><td align="left"><a href="#FIG_41">41</a>.</td><td align="left">Jensen bell, <i>section</i></td><td align="right">102</td></tr>
+<tr><td align="left"><a href="#FIG_42">42</a>.</td><td align="left">Jensen bell, <i>exterior</i></td><td align="right">104</td></tr>
+<tr><td align="left"><a href="#FIG_43A">43<span class="smcap">A</span></a>.</td><td align="left">Circular bell</td><td align="right">106</td></tr>
+<tr><td align="left"><a href="#FIG_43B">43<span class="smcap">B</span></a>.</td><td align="left">Mining bell</td><td align="right">106</td></tr>
+<tr><td align="left"><a href="#FIG_44">44</a>.</td><td align="left">Electric trumpet (Binswanger's)</td><td align="right">107</td></tr>
+<tr><td align="left"><a href="#FIG_45">45</a>.</td><td align="left">Various forms of pushes</td><td align="right">110</td></tr>
+<tr><td align="left"><a href="#FIG_46">46</a>.</td><td align="left">Pressel</td><td align="right">111</td></tr>
+<tr><td align="left"><a href="#FIG_47">47</a>.</td><td align="left">Pull</td><td align="right">112</td></tr>
+<tr><td align="left"><a href="#FIG_48">48</a>.</td><td align="left">Bedroom pull</td><td align="right">113</td></tr>
+<tr><td align="left"><a href="#FIG_49A">49<span class="smcap">A</span></a>.</td><td align="left">Bedroom pull Another form</td><td align="right">114<!-- Page viii --><span class="pagenum"><a name="Page_viii" id="Page_viii">[Pg viii]</a></span></td></tr>
+<tr><td align="left"><a href="#FIG_49B">49<span class="smcap">B</span></a>.</td><td align="left">Floor contact, ball form</td><td align="right">114</td></tr>
+<tr><td align="left"><a href="#FIG_50">50</a>.</td><td align="left">Burglar alarm</td><td align="right">115</td></tr>
+<tr><td align="left"><a href="#FIG_51">51</a>.</td><td align="left">Burglar alarm <i>Another form</i></td><td align="right">115</td></tr>
+<tr><td align="left"><a href="#FIG_52">52</a>.</td><td align="left">Floor contact</td><td align="right">115</td></tr>
+<tr><td align="left"><a href="#FIG_53">53</a>.</td><td align="left">Door contact</td><td align="right">116</td></tr>
+<tr><td align="left"><a href="#FIG_54">54</a>.</td><td align="left">Sash contact</td><td align="right">117</td></tr>
+<tr><td align="left"><a href="#FIG_55">55</a>.</td><td align="left">Shop door contact</td><td align="right">117</td></tr>
+<tr><td align="left"><a href="#FIG_56A">56<span class="smcap">A</span></a>.</td><td align="left">Closed circuit system, <i>single</i></td><td align="right">119</td></tr>
+<tr><td align="left"><a href="#FIG_56B">56<span class="smcap">B</span></a>.</td><td align="left">Closed circuit system, <i>double</i></td><td align="right">119</td></tr>
+<tr><td align="left"><a href="#FIG_57">57</a>.</td><td align="left">Modified gravity, Daniell</td><td align="right">120</td></tr>
+<tr><td align="left"><a href="#FIG_58">58</a>.</td><td align="left">Contact for closed circuit</td><td align="right">121</td></tr>
+<tr><td align="left"><a href="#FIG_59">59</a>.</td><td align="left">Thermometer alarm</td><td align="right">122</td></tr>
+<tr><td align="left"><a href="#FIG_60">60</a>.</td><td align="left">Fire alarm</td><td align="right">123</td></tr>
+<tr><td align="left"><a href="#FIG_61">61<span class="smcap">A</span></a>.</td><td align="left">Fire alarm Another form</td><td align="right">123</td></tr>
+<tr><td align="left"><a href="#FIG_61">61<span class="smcap">B</span></a>.</td><td align="left">Fire alarm Another form in action</td><td align="right">123</td></tr>
+<tr><td align="left"><a href="#FIG_62">62</a>.</td><td align="left">Binswanger's "watch alarm" contact</td><td align="right">125</td></tr>
+<tr><td align="left"><a href="#FIG_63">63</a>.</td><td align="left">Watchman's electric tell-tale clock</td><td align="right">126</td></tr>
+<tr><td align="left"><a href="#FIG_64">64</a>.</td><td align="left">Lever switch, <i>two-way</i></td><td align="right">128</td></tr>
+<tr><td align="left"><a href="#FIG_65">65</a>.</td><td align="left">Morse key, <i>double contact</i></td><td align="right">133</td></tr>
+<tr><td align="left"><a href="#FIG_66">66</a>.</td><td align="left">Relay</td><td align="right">134</td></tr>
+<tr><td align="left"><a href="#FIG_67">67</a>.</td><td align="left">Indicator, drop</td><td align="right">137</td></tr>
+<tr><td align="left"><a href="#FIG_68">68</a>.</td><td align="left">Indicator, Semaphore</td><td align="right">138</td></tr>
+<tr><td align="left"><a href="#FIG_69">69</a>.</td><td align="left">Indicator, Fall back</td><td align="right">139</td></tr>
+<tr><td align="left"><a href="#FIG_70">70</a>.</td><td align="left">Indicator, Pendulum</td><td align="right">140</td></tr>
+<tr><td align="left"><a href="#FIG_71">71</a>.</td><td align="left">Indicator, Coupled up</td><td align="right">142</td></tr>
+<tr><td align="left"><a href="#FIG_72">72</a>.</td><td align="left">Indicator, Gent's tripolar</td><td align="right">143</td></tr>
+<tr><td align="left"><a href="#FIG_73">73</a>.</td><td align="left">Soldering iron and wires</td><td align="right">148</td></tr>
+<tr><td align="left"><a href="#FIG_74">74</a>.</td><td align="left">Push, interior of</td><td align="right">151</td></tr>
+<tr><td align="left"><a href="#FIG_75">75</a>.</td><td align="left">Bell, battery and push</td><td align="right">159</td></tr>
+<tr><td align="left"><a href="#FIG_76">76</a>.</td><td align="left">Bell, battery and push And earth return</td><td align="right">160</td></tr>
+<tr><td align="left"><a href="#FIG_77">77</a>.</td><td align="left">Bell, and two pushes</td><td align="right">161</td></tr>
+<tr><td align="left"><a href="#FIG_78">78</a>.</td><td align="left">Bell, two pushes and one pull</td><td align="right">161</td></tr>
+<tr><td align="left"><a href="#FIG_79">79</a>.</td><td align="left">Two bells in parallel</td><td align="right">162</td></tr>
+<tr><td align="left"><a href="#FIG_80">80</a>.</td><td align="left">Two bells in parallel Another mode</td><td align="right">162</td></tr>
+<tr><td align="left"><a href="#FIG_81">81</a>.</td><td align="left">Two bells in parallel with two-way switch</td><td align="right">163</td></tr>
+<tr><td align="left"><a href="#FIG_82">82</a>.</td><td align="left">Series coupler</td><td align="right">163</td></tr>
+<tr><td align="left"><a href="#FIG_83">83</a>.</td><td align="left">Bell with local battery and relay</td><td align="right">164</td></tr>
+<tr><td align="left"><a href="#FIG_84">84</a>.</td><td align="left">Continuous ringing bell with wire return</td><td align="right">165</td></tr>
+<tr><td align="left"><a href="#FIG_85">85</a>.</td><td align="left">Bells with Morse keys for signalling</td><td align="right">165</td></tr>
+<tr><td align="left"><a href="#FIG_86">86</a>.</td><td align="left">Bells with double contact pushes for signalling</td><td align="right">166</td></tr>
+<tr><td align="left"><a href="#FIG_87">87</a>.</td><td align="left">Bells with double contact with one battery only</td><td align="right">167</td></tr>
+<tr><td align="left"><a href="#FIG_88">88</a>.</td><td align="left">Two-way signalling with one battery only</td><td align="right">168</td></tr>
+<tr><td align="left"><a href="#FIG_89">89</a>.</td><td align="left">Complete installation of bells, batteries, pushes, etc.</td><td align="right">169</td></tr>
+<tr><td align="left"><a href="#FIG_90">90</a>.</td><td align="left">Mode of getting out plan or design</td><td align="right">170</td></tr>
+<tr><td align="left"><a href="#FIG_91">91</a>.</td><td align="left">Lift fitted with bells</td><td align="right">173</td></tr>
+<tr><td align="left"><a href="#FIG_92">92</a>.</td><td align="left">Magneto bell: generator</td><td align="right">174</td></tr>
+<tr><td align="left"><a href="#FIG_93">93</a>.</td><td align="left">Magneto bell: Receiver</td><td align="right">175</td></tr>
+<tr><td align="left"><a href="#FIG_94">94</a>.</td><td align="left">Magneto bell: Combined</td><td align="right">176</td></tr>
+<tr><td align="left"><a href="#FIG_95">95</a>.</td><td align="left">Detector or galvanometer</td><td align="right">176</td></tr>
+</table></div>
+
+
+
+<hr />
+
+<p><!-- Page 1 --><span class="pagenum"><a name="Page_1" id="Page_1">[Pg 1]</a></span></p>
+<h1><a name="ELECTRIC_BELLS" id="ELECTRIC_BELLS"></a>ELECTRIC BELLS.</h1>
+
+
+
+<h2><a name="CHAPTER_I" id="CHAPTER_I"></a>CHAPTER I.</h2>
+
+<h3>PRELIMINARY CONSIDERATIONS.</h3>
+
+
+<p><a name="SEC_1" id="SEC_1"></a>§ 1. <span class="smcap">Electricity.</span>&mdash;The primary cause of all the
+effects which we are about to consider resides in a force
+known as <i>electricity</i>, 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 <span class="smcap">B.C.</span>, observed the former
+of these facts, but nearly twenty centuries elapsed
+before it was suspected that any connection existed
+between these phenomena.</p>
+
+
+<p><a name="SEC_2" id="SEC_2"></a>§ 2. According to the present state of our knowledge,<!-- Page 2 --><span class="pagenum"><a name="Page_2" id="Page_2">[Pg 2]</a></span>
+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, <i>heat</i> and <i>light</i>. These,
+like <i>sound</i>, are known to be dependent on undulatory
+motion; but, whilst <i>sound</i> is elicited by the vibration of
+a body <i>as a whole</i>, electricity appears to depend, in its
+manifestations, upon some motion (whether rotary,
+oscillatory, or undulatory, it is not known) of the atoms
+themselves.</p>
+
+<p>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.:&mdash;1st,
+mechanical; 2nd, chemical; 3rd, changes of temperature.
+Among the <i>mechanical</i> may be ranged friction,
+percussion, vibration, trituration, cleavage, etc. Among
+the <i>chemical</i> 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. <i>Changes of temperature</i>,
+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.</p>
+
+
+<p><a name="SEC_3" id="SEC_3"></a>§ 3. We may now proceed to study a few of these
+methods of evoking electricity, so as to familiarise ourselves
+with the leading properties.</p>
+
+<p>If we rub any resinous substance (such as amber,
+copal, resin, sealing-wax, ebonite, etc.) with a piece of<!-- Page 3 --><span class="pagenum"><a name="Page_3" id="Page_3">[Pg 3]</a></span>
+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 <i>attracted</i> and then
+<i>repelled</i>. This is owing to the fact that the damp
+cotton allows the electricity to escape along it: <i>id est</i>,
+damp cotton is a <span class="smcap">CONDUCTOR</span> of electricity, while silk
+does not permit its dissipation; or, in other words, silk
+is a <span class="smcap">NON-CONDUCTOR</span>. All bodies with which we are
+acquainted are found, on trial, to fall under one or other
+of the two heads&mdash;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.</p>
+
+
+<p><a name="SEC_4" id="SEC_4"></a>§ 4. As a knowledge of which bodies are, and which
+are not, conductors of electricity is absolutely essential<!-- Page 4 --><span class="pagenum"><a name="Page_4" id="Page_4">[Pg 4]</a></span>
+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 <i>good</i> conductors,
+and ending with those which oppose the highest
+resistance to its passage, or are insulators, or non-conductors:&mdash;</p>
+
+
+<p class="center"><a name="SEC_5" id="SEC_5"></a>§ 5. TABLE OF CONDUCTORS AND INSULATORS.
+<!-- Page 5 --><span class="pagenum"><a name="Page_5" id="Page_5">[Pg 5]</a></span></p>
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="Table of conductors and insulators">
+<tr><th align="center" class="bt">Quality.</th><th align="center" class="bt" colspan="3">Name of Substance.</th><th align="center" class="bt">Relative Resistance.</th></tr>
+<tr><td align="left" class="bt" rowspan="24" valign="middle">Good Conductors</td><td align="left" class="bt" colspan="3">Silver, annealed</td><td align="right" class="bt">1.</td></tr>
+<tr><td align="left" colspan="3">Copper, annealed</td><td align="right">1.063</td></tr>
+<tr><td align="left" colspan="3">Silver, hard drawn</td><td align="right">1.086</td></tr>
+<tr><td align="left" colspan="3">Copper, hard drawn</td><td align="right">1.086</td></tr>
+<tr><td align="left" colspan="3">Gold, annealed</td><td align="right">1.369</td></tr>
+<tr><td align="left" colspan="3">Gold, hard drawn</td><td align="right">1.393</td></tr>
+<tr><td align="left" colspan="3">Aluminium, annealed</td><td align="right">1.935</td></tr>
+<tr><td align="left" colspan="3">Zinc, pressed</td><td align="right">3.741</td></tr>
+<tr><td align="left" colspan="3">Brass (variable)</td><td align="right">5.000</td></tr>
+<tr><td align="left" colspan="3">Platinum, annealed</td><td align="right">6.022</td></tr>
+<tr><td align="left" colspan="3">Iron</td><td align="right">6.450</td></tr>
+<tr><td align="left" colspan="3">Steel, soft</td><td align="right">6.500</td></tr>
+<tr><td align="left" colspan="3">Gold and silver alloy, 2 to 1</td><td align="right">7.228</td></tr>
+<tr><td align="left" colspan="3">Nickel, annealed</td><td align="right">8.285</td></tr>
+<tr><td align="left" colspan="3">Tin, pressed</td><td align="right">8.784</td></tr>
+<tr><td align="left" colspan="3">Lead, pressed</td><td align="right">13.050</td></tr>
+<tr><td align="left" colspan="3">German silver (variable)</td><td align="right">13.920</td></tr>
+<tr><td align="left" colspan="3">Platinum-silver alloy, 1 to 2</td><td align="right">16.210</td></tr>
+<tr><td align="left" colspan="3">Steel, hard</td><td align="right">25.000</td></tr>
+<tr><td align="left" colspan="3">Antimony, pressed</td><td align="right">23.600</td></tr>
+<tr><td align="left" colspan="3">Mercury</td><td align="right">62.730</td></tr>
+<tr><td align="left" colspan="3">Bismuth</td><td align="right">87.230</td></tr>
+<tr><td align="left" colspan="3">Graphite</td><td align="right">145.000</td></tr>
+<tr><td align="left" colspan="3">Nitric Acid</td><td align="right">976000.000</td></tr>
+<tr><td align="left" class="bt" rowspan="5" valign="middle">Imperfect Conductors</td><td align="left" class="bt" colspan="3">Hydrochloric acid</td><td align="left" class="bt"><a name="FNanchor_1_1" id="FNanchor_1_1"></a><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr>
+<tr><td align="left" colspan="3">Sulphuriacid</td><td align="right">1032020.000</td></tr>
+<tr><td align="left" colspan="3">Solutions of metallic salts</td><td align="right">varies with strength</td></tr>
+<tr><td align="left" colspan="3">Metallic sulphides</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr>
+<tr><td align="left" colspan="3">Distilled water</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a> 6754208.000</td></tr>
+<tr><td align="left" class="bt" rowspan="10" valign="middle">Inferior Conductors.</td><td align="left" class="bt" colspan="3">Metallic salts, solid</td><td align="left" class="bt"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr>
+<tr><td align="left">Linen</td><td align="left" rowspan="4"><span class="bigbrace">}</span></td><td align="left" rowspan="4" valign="middle">and other forms of cellulose</td><td align="left" valign="middle" rowspan="4"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr>
+<tr><td align="left">Cotton</td></tr>
+<tr><td align="left">Hemp</td></tr>
+<tr><td align="left">Paper</td></tr>
+<tr><td align="left" colspan="3">Alcohol</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr>
+<tr><td align="left" colspan="3">Ether</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr>
+<tr><td align="left" colspan="3">Dry Wood</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr>
+<tr><td align="left" colspan="3">Dry Ice</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr>
+<tr><td align="left" colspan="3">Metallic Oxides</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr>
+<tr><td align="left" class="bt" rowspan="15" valign="middle">Non-conductors,<br /> or Insulators.</td><td align="left" class="bt" colspan="3">Ice, at 25 c.</td><td align="left" class="bt"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr>
+<tr><td align="left" colspan="3">Fats and oils</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr>
+<tr><td align="left" colspan="3">Caoutchouc</td><td align="right">1000000000000.</td></tr>
+<tr><td align="left" colspan="3">Guttapercha</td><td align="right">1000000000000.</td></tr>
+<tr><td align="left" colspan="3">Dry air, gases, and vapours</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr>
+<tr><td align="left" colspan="3">Wool</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr>
+<tr><td align="left" colspan="3">Ebonite</td><td align="right">1300000000000.</td></tr>
+<tr><td align="left" colspan="3">Diamond</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr>
+<tr><td align="left" colspan="3">Silk</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr>
+<tr><td align="left" colspan="3">Glass</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr>
+<tr><td align="left" colspan="3">Wax</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr>
+<tr><td align="left" colspan="3">Sulphur</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr>
+<tr><td align="left" colspan="3">Resin</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr>
+<tr><td align="left" colspan="3">Amber</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr>
+<tr><td align="left" colspan="3">Shellac</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr>
+<tr><td align="left" class="bb"></td><td align="left" class="bb" colspan="3">Paraffin</td><td align="right" class="bb">1500000000000.</td></tr>
+</table></div>
+
+
+<div class="footnote"><p><a name="Footnote_1_1" id="Footnote_1_1"></a><a href="#FNanchor_1_1"><span class="label">[1]</span></a> These have not been accurately measured.</p></div>
+
+<p>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.</p>
+
+<p>It must be borne in mind that <i>dry air</i> is one of the<!-- Page 6 --><span class="pagenum"><a name="Page_6" id="Page_6">[Pg 6]</a></span>
+<i>best insulators</i>, or worst <i>conductors</i>, with which we are
+acquainted; while damp air, on the contrary, owing to
+the facility with which it deposits <i>water</i> on the surface
+of bodies, is highly conducive to the escape of electricity.</p>
+
+
+<p><a name="SEC_6" id="SEC_6"></a>§ 6. If the experiment described at <a href="#SEC_3">§ 3</a> 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 <i>rubber</i> 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<!-- Page 7 --><span class="pagenum"><a name="Page_7" id="Page_7">[Pg 7]</a></span>
+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
+<i>vitreous</i> and <i>resinous</i>, 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 <i>positive</i> and
+<i>negative</i>; 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.</p>
+
+
+<p><a name="SEC_7" id="SEC_7"></a>§ 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, <i>that
+body, the particles of which are more easily displaced,
+becomes negatively electrified</i>.</p>
+
+
+<p><a name="SEC_8" id="SEC_8"></a>§ 8. As, however, the electricity set up by friction<!-- Page 8 --><span class="pagenum"><a name="Page_8" id="Page_8">[Pg 8]</a></span>
+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.</p>
+
+<p>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.<a name="FNanchor_2_2" id="FNanchor_2_2"></a><a href="#Footnote_2_2" class="fnanchor">[2]</a> 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:&mdash;</p>
+
+<div class="center">
+<table border="0" cellpadding="0" cellspacing="0" summary="">
+<tr>
+<td rowspan="13" valign="middle">The portion immersed in the acid fluid.</td>
+<td align="center">&#9127;</td><td align="center">&#8595;</td><td align="left" class="padlr">Zinc.</td><td align="center">&#8593;</td><td align="center">&#9131;</td>
+<td rowspan="13" valign="middle">The portion out of the acid fluid.</td>
+</tr>
+<tr><td align="center">&#9130;</td><td align="center">&#8595;</td><td align="left" class="padlr">Cadmium.</td><td align="center">&#8593;</td><td align="center">&#9130;</td></tr>
+<tr><td align="center">&#9130;</td><td align="center">&#8595;</td><td align="left" class="padlr">Tin.</td><td align="center">&#8593;</td><td align="center">&#9130;</td></tr>
+<tr><td align="center">&#9130;</td><td align="center">&#8595;</td><td align="left" class="padlr">Lead.</td><td align="center">&#8593;</td><td align="center">&#9130;</td></tr>
+<tr><td align="center">&#9130;</td><td align="center">&#8595;</td><td align="left" class="padlr">Iron.</td><td align="center">&#8593;</td><td align="center">&#9130;</td></tr>
+<tr><td align="center">&#9130;</td><td align="center">&#8595;</td><td align="left" class="padlr">Nickel.</td><td align="center">&#8593;</td><td align="center">&#9130;</td></tr>
+<tr><td align="center">&#9130;</td><td align="center">&#8595;</td><td align="left" class="padlr">Bismuth.</td><td align="center">&#8593;</td><td align="center">&#9130;</td></tr>
+<tr><td align="center">&#9130;</td><td align="center">&#8595;</td><td align="left" class="padlr">Antimony.</td><td align="center">&#8593;</td><td align="center">&#9130;</td></tr>
+<tr><td align="center">&#9130;</td><td align="center">&#8595;</td><td align="left" class="padlr">Copper.</td><td align="center">&#8593;</td><td align="center">&#9130;</td></tr>
+<tr><td align="center">&#9130;</td><td align="center">&#8595;</td><td align="left" class="padlr">Silver.</td><td align="center">&#8593;</td><td align="center">&#9130;</td></tr>
+<tr><td align="center">&#9130;</td><td align="center">&#8595;</td><td align="left" class="padlr">Gold.</td><td align="center">&#8593;</td><td align="center">&#9130;</td></tr>
+<tr><td align="center">&#9130;</td><td align="center">&#8595;</td><td align="left" class="padlr">Platinum.</td><td align="center">&#8593;</td><td align="center">&#9130;</td></tr>
+<tr><td align="center">&#9129;</td><td align="center">&#8595;</td><td align="left" class="padlr">Graphite.</td><td align="center">&#8593;</td><td align="center">&#9133;</td></tr>
+</table></div>
+
+
+<p>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 <i>positive</i> to those below them, but
+negative to those above them, if the test have reference
+to the condition of the parts <i>within</i> the fluid. On the<!-- Page 9 --><span class="pagenum"><a name="Page_9" id="Page_9">[Pg 9]</a></span>
+contrary, we shall find that any member of the list will
+be found to be <i>negative</i> to any one below it, or <i>positive</i>
+to any above it, if tested from the portion <span class="smcap">NOT</span> immersed
+in the acid fluid.</p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_1" id="FIG_1"></a>
+<img src="images/i_018.png" width="400" height="293" alt="" title="Direction of current in cell" />
+<p class="caption">Fig. 1.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 278px;">
+<a name="FIG_2" id="FIG_2"></a>
+<img src="images/i_019.png" width="278" height="400" alt="" title="Direction of current out of cell" />
+<p class="caption">Fig. 2.</p>
+</div>
+
+
+<p><a name="SEC_9" id="SEC_9"></a>§ 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<!-- Page 10 --><span class="pagenum"><a name="Page_10" id="Page_10">[Pg 10]</a></span>
+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
+<a href="#FIG_1">Fig. 1</a>, the needle will be impelled out of its normal
+position, and be deflected more or less out of the line of<!-- Page 11 --><span class="pagenum"><a name="Page_11" id="Page_11">[Pg 11]</a></span>
+the wire. If the needle be again allowed to come to
+rest <span class="smcap">N.</span> and <span class="smcap">S.</span> (the battery or couple having been
+removed), and then the tumbler be held close over the
+needle, as in <a href="#FIG_2">Fig. 2</a>, 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.</p>
+
+
+<p><a name="SEC_10" id="SEC_10"></a>§ 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:&mdash;</p>
+
+
+<p><a name="SEC_11" id="SEC_11"></a>§ 11. "If a current be caused to flow <i>over</i> and parallel
+to a freely suspended magnetic needle, previously
+pointing north and south, the north pole will be
+impelled to the <span class="smcap">LEFT</span> of the <i>entering</i> current. If, on
+the contrary, the wire, or conductor, be placed
+<i>below</i> the needle, the deflection will, under similar
+circumstances, be in the opposite direction, viz.: the<!-- Page 12 --><span class="pagenum"><a name="Page_12" id="Page_12">[Pg 12]</a></span>
+north pole will be impelled to the <span class="smcap">RIGHT</span> of the
+<i>entering</i> current." In both these cases the observer is
+supposed to be looking along the needle, with its <span class="smcap">N.</span>
+seeking pole pointing at him.</p>
+
+
+<p><a name="SEC_12" id="SEC_12"></a>§ 12. From a consideration of the above law, in
+connection with the experiments performed at <a href="#SEC_9">§ 9</a>,
+it will be evident that inside the tumbler the zinc is
+<i>positive</i> to the copper strip; while, viewed from the
+outside conductor, the copper is positive to the zinc
+strip.<a name="FNanchor_3_3" id="FNanchor_3_3"></a><a href="#Footnote_3_3" class="fnanchor">[3]</a></p>
+
+
+<p><a name="SEC_13" id="SEC_13"></a>§ 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 &frac12;" 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 <a href="#SEC_9">§ 9</a>, 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, "<i>the soft iron is a
+magnet, so long as an electric current flows round it</i>."
+If contact between the battery wires and the coiled wires<!-- Page 13 --><span class="pagenum"><a name="Page_13" id="Page_13">[Pg 13]</a></span>
+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.</p>
+
+
+<p><a name="SEC_14" id="SEC_14"></a>§ 14. If, instead of using a <i>soft</i> iron bar in the above
+experiment, we had substituted one of <i>hard</i> 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 <i>cores</i> of the electro-magnets should be of the very
+softest iron. Long annealing and gradual cooling
+conduce greatly to the softness of iron.</p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_3" id="FIG_3"></a>
+<img src="images/i_023.png" width="400" height="322" alt="" title="Bar and horse-shoe magnets" />
+<p class="caption">Fig. 3.
+<br />
+<span class="smcap">Magnets</span>, showing Lines of Force.</p>
+</div>
+
+
+<p><a name="SEC_15" id="SEC_15"></a>§ 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<!-- Page 14 --><span class="pagenum"><a name="Page_14" id="Page_14">[Pg 14]</a></span>
+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." <a href="#FIG_3">Fig. 3</a> 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<!-- Page 15 --><span class="pagenum"><a name="Page_15" id="Page_15">[Pg 15]</a></span>
+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
+<span class="smcap">Dynamo</span>.</p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_4" id="FIG_4"></a>
+<img src="images/i_025.png" width="400" height="249" alt="" title="The Dynamo" />
+<p class="caption">Fig. 4.
+<br />
+<span class="smcap">Typical Dynamo</span>, showing essential portions.</p>
+</div>
+
+
+<p><a name="SEC_16" id="SEC_16"></a>§ 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<!-- Page 16 --><span class="pagenum"><a name="Page_16" id="Page_16">[Pg 16]</a></span>
+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 (<a href="#FIG_4">Fig. 4</a>) will assist the student in getting a clear
+idea of the essential portions in a dynamo:&mdash;<span class="smcap">E</span> is the
+mass of wrought iron wound with insulated wire, and
+known as the <i>field-magnet</i>. <span class="smcap">N</span> and <span class="smcap">S</span> are cast-iron
+prolongations of the same, and are usually bolted to the
+field-magnet. When current is passing these become
+powerfully magnetic. <span class="smcap">A</span> is the rotating iron ring, or
+cylinder, known as the <i>armature</i>, which is also wound
+with insulated wire, <span class="smcap">B</span>, the ends of which are brought
+out and connected to the insulated brass segments<!-- Page 17 --><span class="pagenum"><a name="Page_17" id="Page_17">[Pg 17]</a></span>
+known as the <i>commutator</i>, <span class="smcap">C</span>. Upon this commutator
+press the two springs <span class="smcap">D</span> and <span class="smcap">D'</span>, known as the <i>brushes</i>,
+which serve to collect the electricity set up by the
+rotation of the armature. These <i>brushes</i> are in electrical
+connection with the two terminals of the machine <span class="smcap">F F'</span>,
+whence the electric current is transmitted where required;
+the latter being also connected with the wire encircling
+the field-magnet, <span class="smcap">E</span>.</p>
+
+<p>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 (<a href="#SEC_13">§ 13</a>), and, being more magnetically active, sets
+up a more powerful electrical disturbance in the armature.</p>
+
+<p>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.</p>
+
+<div class="footnote"><p><a name="Footnote_2_2" id="Footnote_2_2"></a><a href="#FNanchor_2_2"><span class="label">[2]</span></a> 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.</p></div>
+
+<div class="footnote"><p><a name="Footnote_3_3" id="Footnote_3_3"></a><a href="#FNanchor_3_3"><span class="label">[3]</span></a> 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.</p></div>
+
+
+
+<hr class="long" />
+<p><!-- Page 18 --><span class="pagenum"><a name="Page_18" id="Page_18">[Pg 18]</a></span></p>
+<h2><a name="CHAPTER_II" id="CHAPTER_II"></a>CHAPTER II.</h2>
+
+<h3>ON THE CHOICE OF BATTERIES FOR ELECTRIC BELL
+WORK.</h3>
+
+
+<p><a name="SEC_17" id="SEC_17"></a>§ 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<a name="FNanchor_4_4" id="FNanchor_4_4"></a><a href="#Footnote_4_4" class="fnanchor">[4]</a>), 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 <i>heat</i> and <i>electricity</i>.
+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 <i>does not</i> take place between the two
+elements, no perceptible change takes place in the<!-- Page 19 --><span class="pagenum"><a name="Page_19" id="Page_19">[Pg 19]</a></span>
+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 &#923;, 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.</p>
+
+<p>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.</p>
+
+
+<p><a name="SEC_18" id="SEC_18"></a>§ 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 <i>chlorine</i>, <i>iodine</i>, <i>bromine</i>, etc.,
+or a compound radical, such as <i>cyanogen</i>; secondly,
+the strongly electro-positive body <i>hydrogen</i>.<!-- Page 20 --><span class="pagenum"><a name="Page_20" id="Page_20">[Pg 20]</a></span></p>
+
+<p>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:&mdash;</p>
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="representation of acids">
+<tr><td align="center">H Cl</td><td align="center">H Br</td><td align="center">H I</td></tr>
+<tr><td align="center">&#9495;&#9473;&#9473;&#9499;</td><td align="center">&#9495;&#9473;&#9473;&#9499;</td><td align="center">&#9495;&#9473;&#9473;&#9499;</td></tr>
+<tr><td align="center">Hydrochloric<br /> Acid<a name="FNanchor_5_5" id="FNanchor_5_5"></a><a href="#Footnote_5_5" class="fnanchor">[5]</a>.</td><td align="center">Hydrobromic<br /> Acid.</td><td align="center">Hydriodic<br /> Acid.</td></tr>
+</table></div>
+
+
+
+<p>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:&mdash;</p>
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="center">H<sub>2</sub>SO<sub>4</sub></td><td align="center">&nbsp;</td><td align="center">HNO<sub>6</sub></td></tr>
+<tr><td align="center">&#9495;&#9473;&#9473;&#9473;&#9499;</td><td align="center">&nbsp;</td><td align="center">&#9495;&#9473;&#9473;&#9499;</td></tr>
+<tr><td align="center">Sulphuric<br /> Acid<a name="FNanchor_6_6" id="FNanchor_6_6"></a><a href="#Footnote_6_6" class="fnanchor">[6]</a>.</td><td align="center">and</td><td align="center">Nitric<br /> Acid<a name="FNanchor_7_7" id="FNanchor_7_7"></a><a href="#Footnote_7_7" class="fnanchor">[7]</a>.</td></tr>
+</table></div>
+
+
+
+
+<p>When zinc <i>does</i> 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, <i>neutralized</i>.
+<i>One</i> atom of zinc can replace <i>two</i> 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.</p>
+
+<p>This power of displacement and replacement possessed
+by zinc is not peculiar to this metal, but is<!-- Page 21 --><span class="pagenum"><a name="Page_21" id="Page_21">[Pg 21]</a></span>
+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.</p>
+
+<p>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:&mdash;</p>
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="center">Hydrochloric Acid</td><td align="center">and</td><td align="center">Zinc,</td><td align="center">equal</td><td align="center">Zinc Chloride</td><td align="center">and</td><td align="center">Hydrogen Gas.</td></tr>
+<tr><td align="center">2HCl</td><td align="center">+</td><td align="center">Zn</td><td align="center">=</td><td align="center">ZnCl<sub>2</sub></td><td align="center">+</td><td align="center">H<sub>2</sub></td></tr>
+</table></div>
+
+
+<p>or:&mdash;</p>
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="center">Sulphuric Acid</td><td align="center">and</td><td align="center">Zinc,</td><td align="center">equal</td><td align="center">Zinc Sulphate</td><td align="center">and</td><td align="center">Hydrogen Gas.</td></tr>
+<tr><td align="center">H<sub>2</sub>SO<sub>4</sub></td><td align="center">+</td><td align="center">Zn</td><td align="center">=</td><td align="center">ZnSO<sub>4</sub></td><td align="center">+</td><td align="center">H<sub>2</sub></td></tr>
+</table></div>
+
+
+<p>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:&mdash;</p>
+
+<p class="center">
+Zn + H<sub>2</sub>X = ZnX + H<sub>2</sub><br />
+</p>
+
+<p>the final result being in every case the corrosion and
+solution of the zinc, and the extrication of the hydrogen
+gas displaced.</p>
+
+
+<p><a name="SEC_19" id="SEC_19"></a>§ 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 <i>useful</i> consumption
+of zinc takes place, the greater will be the electrical
+effects produced. But here it must be borne in mind<!-- Page 22 --><span class="pagenum"><a name="Page_22" id="Page_22">[Pg 22]</a></span>
+that if the zinc is being consumed when we are <i>not</i>
+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 <i>amalgamating the zinc</i>, 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:&mdash;</p>
+
+
+<p><a name="SEC_20" id="SEC_20"></a>§ 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 (<a href="#SEC_17">§ 17</a>), and as soon as<!-- Page 23 --><span class="pagenum"><a name="Page_23" id="Page_23">[Pg 23]</a></span>
+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:&mdash;"Whenever the zinc shows
+a grey granular surface (or rather before this), brush it<!-- Page 24 --><span class="pagenum"><a name="Page_24" id="Page_24">[Pg 24]</a></span>
+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<a name="FNanchor_8_8" id="FNanchor_8_8"></a><a href="#Footnote_8_8" class="fnanchor">[8]</a>; 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."</p>
+
+
+<p><a name="SEC_21" id="SEC_21"></a>§ 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.</p>
+
+
+<p><a name="SEC_22" id="SEC_22"></a>§ 22. Some operators recommend the use of mercurial
+salts (such as mercury nitrate, etc.) as advan<!-- Page 25 --><span class="pagenum"><a name="Page_25" id="Page_25">[Pg 25]</a></span>tageous
+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 <i>salts</i> 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.</p>
+
+
+<p><a name="SEC_23" id="SEC_23"></a>§ 23. If, having thus amalgamated the zinc plate of
+the little battery described and figured at <a href="#SEC_9">§ 9</a>, 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 <i>that</i>
+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<!-- Page 26 --><span class="pagenum"><a name="Page_26" id="Page_26">[Pg 26]</a></span>
+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 <i>polarisation of the negative plate</i>, 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
+<i>electrodes</i>. Again, the <i>copper</i> 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, <span class="smcap">Z<!-- Page 27 --><span class="pagenum"><a name="Page_27" id="Page_27">[Pg 27]</a></span></span>
+and <span class="smcap">C</span>, connected by a straight piece of tubing. If <span class="smcap">Z</span> be
+full and <span class="smcap">C</span> have an outlet, it is very evident that <span class="smcap">Z</span> can
+and will discharge itself into <span class="smcap">C</span> until exhausted; but if <span class="smcap">C</span>
+be allowed to fill up to the same level as <span class="smcap">Z</span>, then no
+farther flow can take place between the two.</p>
+
+<p>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:&mdash;</p>
+
+
+<p><a name="SEC_24" id="SEC_24"></a>§ 24. <i>Roughening the surface of the negative plate</i>,
+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 <a href="#FIG_5">Fig. 5</a>.</p>
+
+<div class="figcenter" style="width: 328px;">
+<a name="FIG_5" id="FIG_5"></a>
+<img src="images/i_037.png" width="328" height="400" alt="" title="The Smee cell" />
+<p class="caption">Fig. 5.</p>
+</div>
+
+<p>The silver sheet, before being placed in position, is
+<i>platinised</i>; 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<!-- Page 28 --><span class="pagenum"><a name="Page_28" id="Page_28">[Pg 28]</a></span>
+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.</p>
+
+<p>Other <i>mechanical</i> 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
+<i>chemical</i> 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<!-- Page 29 --><span class="pagenum"><a name="Page_29" id="Page_29">[Pg 29]</a></span>
+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<sub>4</sub>. When the dilute sulphuric acid acts on the
+zinc plate or rod (<a href="#SEC_18">§ 18</a>), sulphate of zinc is formed, which
+dissolves in the water, and hydrogen is given off:&mdash;</p>
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="center">Zn</td><td align="center">+</td><td align="center">H<sub>2</sub>SO<sub>4</sub></td><td align="center">=</td><td align="center">ZnSO<sub>4</sub></td><td align="center">+</td><td align="center">H<sub>2</sub>.</td></tr>
+<tr><td align="center">Zinc</td><td align="center">and</td><td align="center">sulphuric acid</td><td align="center">produce</td><td align="center">zinc sulphate</td><td align="center">and</td><td align="center">free hydrogen.</td></tr>
+</table></div>
+
+
+<p>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<sub>4</sub>,
+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<!-- Page 30 --><span class="pagenum"><a name="Page_30" id="Page_30">[Pg 30]</a></span>
+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:&mdash;</p>
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="center">H<sub>2</sub></td><td align="center">+</td><td align="center">CuSO<sub>4</sub></td><td align="center">=</td><td align="center">H<sub>2</sub>SO<sub>4</sub></td><td align="center">+</td><td align="center">Cu.</td></tr>
+<tr><td align="center">Free hydrogen</td><td align="center">and</td><td align="center">copper sulphate</td><td align="center">produce</td><td align="center">sulphuric acid</td><td align="center">and</td><td align="center">free copper.</td></tr>
+</table></div>
+
+
+<div class="figcenter" style="width: 330px;">
+<a name="FIG_6" id="FIG_6"></a>
+<img src="images/i_039.png" width="330" height="400" alt="Fig. 6. Daniell Cell." title="" />
+<p class="caption">Fig. 6. Daniell Cell.</p>
+</div>
+
+
+<p><a name="SEC_25" id="SEC_25"></a>§ 25. The original form given to this, the Daniell
+cell, is shown at <a href="#FIG_6">Fig. 6</a>, in which <span class="smcap">Z</span> is the zinc rod standing
+in the porous pot <span class="smcap">P</span>, in which is placed the dilute
+sulphuric acid. A containing vessel, <span class="smcap">V</span>, of glazed earthenware,
+provided with a perforated shelf, <span class="smcap">S</span>, on which
+are placed the crystals of sulphate of copper, serves<!-- Page 31 --><span class="pagenum"><a name="Page_31" id="Page_31">[Pg 31]</a></span>
+to hold the copper sheet, <span class="smcap">C</span>, and the solution of sulphate
+of copper. <span class="smcap">T</span> and <span class="smcap">T'</span> are the terminals from which the
+electricity is led where desired.</p>
+
+<p>In another form, the copper sheet itself takes the form
+and replaces the containing vessel <span class="smcap">V</span>; 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
+<i>sand</i> or by <i>sawdust</i>, 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 (<i>weight, bulk for bulk</i>) 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. <a href="#FIG_7">Fig. 7</a> illustrates the construction of
+one of these, known as "Gravity Daniells."</p>
+
+<div class="figcenter" style="width: 376px;">
+<a name="FIG_7" id="FIG_7"></a>
+<img src="images/i_041.png" width="376" height="400" alt="Fig. 7. Gravity Cell." title="" />
+<p class="caption">Fig. 7. Gravity Cell.</p>
+</div>
+
+<p>In this we have a plate, disc, or spiral of copper, <span class="smcap">C</span>,
+connected by an insulated copper wire to the terminal <span class="smcap">T'</span>.
+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, <span class="smcap">T</span>, is allowed to rest
+a thick disc of zinc, <span class="smcap">Z</span>. Speaking of these cells, Professor
+Ayrton, in his invaluable "Practical Electricity,"
+says:&mdash;"All gravity cells have the disadvantage that<!-- Page 32 --><span class="pagenum"><a name="Page_32" id="Page_32">[Pg 32]</a></span>
+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.</p>
+
+
+<p><a name="SEC_26" id="SEC_26"></a>§ 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<!-- Page 33 --><span class="pagenum"><a name="Page_33" id="Page_33">[Pg 33]</a></span>
+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 (<a href="#SEC_18">§ 18</a>) and
+reconverts the free hydrogen into water. This acid is
+used as the "depolarizer"<a name="FNanchor_9_9" id="FNanchor_9_9"></a><a href="#Footnote_9_9" class="fnanchor">[9]</a> 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.</p>
+
+<p>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.</p>
+
+
+<p><a name="SEC_27" id="SEC_27"></a>§ 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,<!-- Page 34 --><span class="pagenum"><a name="Page_34" id="Page_34">[Pg 34]</a></span>
+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 <a href="#FIG_8">Fig. 8</a>.</p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_8" id="FIG_8"></a>
+<img src="images/i_043.png" width="400" height="289" alt="Fig. 8." title="The Leclanché cell and parts" />
+<p class="caption">Fig. 8.</p>
+</div>
+
+<p>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<!-- Page 35 --><span class="pagenum"><a name="Page_35" id="Page_35">[Pg 35]</a></span>
+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:&mdash;</p>
+
+<p>When the zinc, Zn, is acted on by the ammonium
+chloride, 2NH<sub>4</sub>Cl, the zinc seizes the chlorine and forms
+with it zinc chloride, ZnCl<sub>2</sub>, while the ammonium, 2NH<sub>4</sub>,
+is liberated. But this ammonium, 2NH<sub>4</sub>, 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<sub>4</sub> + 2NH<sub>4</sub>Cl = 2NH<sub>4</sub>Cl
++ 2NH<sub>4</sub>; 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, <a href="#SEC_24">§ 24</a>)
+until the surface of the carbon is reached. Here, as
+there is no more ammonium chloride to decompose, the
+ammonium 2NH<sub>4</sub> immediately splits up into ammonia
+<!-- Page 36 --><span class="pagenum"><a name="Page_36" id="Page_36">[Pg 36]</a></span>2NH<sub>3</sub> and free hydrogen H<sub>2</sub>. The ammonia escapes,
+and may be detected by its smell; while the hydrogen
+H<sub>2</sub>, finding itself in contact with the oxide of manganese,
+2MnO<sub>2</sub>, seizes one atom of its oxygen, O, becoming
+thereby converted into water H<sub>2</sub>O; while the manganese
+dioxide, 2MnO<sub>2</sub>, by losing one atom of oxygen, is
+reduced to the form of a lower oxide of manganese,
+known as manganese sesquioxide, Mn<sub>2</sub>O<sub>3</sub>. Expressed
+in symbols, this action may be formulated as below:&mdash;</p>
+
+<p>In the zinc compartment&mdash;</p>
+
+<p class="center">
+Zn + 2NH<sub>4</sub>Cl  =  ZnCl<sub>2</sub> + 2NH<sub>3</sub> + H<sub>2</sub><br />
+</p>
+
+<p>In the peroxide of manganese compartment&mdash;</p>
+
+<p class="center">
+H<sub>2</sub> + 2MnO<sub>2</sub>  =  Mn<sub>2</sub>O<sub>3</sub> + H<sub>2</sub>O.<br />
+</p>
+
+<p>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<!-- Page 37 --><span class="pagenum"><a name="Page_37" id="Page_37">[Pg 37]</a></span>
+"needle" form, and both this and the carbon should be
+sifted to remove dust.</p>
+
+
+<p><a name="SEC_28" id="SEC_28"></a>§ 28. In the admirable series of papers on electric bell
+fitting which was published in the <i>English Mechanic</i>,
+Mr. F. C. Allsop, speaking of the Leclanché cell, says:&mdash;"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."</p>
+
+
+<p><a name="SEC_29" id="SEC_29"></a>§ 29. Another form of Leclanché, from which great<!-- Page 38 --><span class="pagenum"><a name="Page_38" id="Page_38">[Pg 38]</a></span>
+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:&mdash;</p>
+
+<p class="center">No. 1.</p>
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="left">Manganese dioxide</td><td align="right">40</td><td align="left">parts.</td></tr>
+<tr><td align="left">Powdered gas carbon</td><td align="right">55</td><td align="left">parts.</td></tr>
+<tr><td align="left">Gum lac resin</td><td align="right">5</td><td align="left">parts.</td></tr>
+</table></div>
+
+
+<p class="center">No. 2.</p>
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="left">Manganese dioxide (pyrolusite)</td><td align="right">40</td><td align="left">parts.</td></tr>
+<tr><td align="left">Gas carbon (powdered)</td><td align="right">52</td><td align="left">parts.</td></tr>
+<tr><td align="left">Gum lac resin</td><td align="right">5</td><td align="left">parts.</td></tr>
+<tr><td align="left">Potassium bisulphate</td><td align="right">3</td><td align="left">parts.</td></tr>
+</table></div>
+
+
+<p>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.</p>
+
+<p class="center">No. 3.</p>
+
+<p class="center">
+<i>Barbier and Leclanché's Patent.</i></p>
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="left">Manganese dioxide</td><td align="right">49</td><td align="left">parts.</td></tr>
+<tr><td align="left">Graphite</td><td align="right">44</td><td align="left">parts.</td></tr>
+<tr><td align="left">Pitch ("brai gras")</td><td align="right">9</td><td align="left">parts.</td></tr>
+<tr><td align="left">Sulphur</td><td align="right">&#8535;</td><td align="left">parts.</td></tr>
+<tr><td align="left">Water</td><td align="right">&#8534;</td><td align="left">parts.</td></tr>
+</table></div>
+
+<p><!-- Page 39 --><span class="pagenum"><a name="Page_39" id="Page_39">[Pg 39]</a></span></p>
+
+<p>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<!-- Page 40 --><span class="pagenum"><a name="Page_40" id="Page_40">[Pg 40]</a></span>
+action on caoutchouc (which is likewise a hydro-carbon)
+during the process of vulcanisation.</p>
+
+<div class="figleft" style="width: 183px;">
+<a name="FIG_9" id="FIG_9"></a>
+<img src="images/i_049.png" width="183" height="400" alt="Fig. 9." title="The Agglomerate cell" />
+<p class="caption">Fig. 9.</p>
+</div>
+
+<p>These agglomerate blocks, however prepared, are
+placed in glass or porcelain containing vessels, as shown
+in <a href="#FIG_9">Fig. 9</a>, 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.</p>
+
+<p>Among the various advantages claimed
+for the agglomerate form of Leclanché over
+the ordinary type, may be mentioned the
+following:&mdash;</p>
+
+<p>1st.&mdash;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.</p>
+
+<p>2nd.&mdash;That, owing to the absence of the
+porous cell, there is less internal resistance
+in the battery and therefore more available current.</p>
+
+<p>3rd.&mdash;That the resistance of the battery remains pretty
+constant, whatever work be put upon it.</p>
+
+<p>4th.&mdash;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.</p>
+
+<p>5th.&mdash;That the renewal or recharging is exceedingly
+easy, since the elements can be removed together, fresh
+solution added, or new depolarising blocks substituted.<!-- Page 41 --><span class="pagenum"><a name="Page_41" id="Page_41">[Pg 41]</a></span></p>
+
+<p>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 <i>in parallel</i>, 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.</p>
+
+<p>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.</p>
+
+
+<div class="figleft" style="width: 199px;">
+<a name="FIG_10" id="FIG_10"></a>
+<img src="images/i_051.png" width="199" height="420" alt="Fig. 10." title="The Judson cell" />
+<p class="caption">Fig. 10.</p>
+</div>
+
+<p><a name="SEC_30" id="SEC_30"></a>§ 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 <a href="#FIG_10">Fig.
+10</a>, 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<!-- Page 42 --><span class="pagenum"><a name="Page_42" id="Page_42">[Pg 42]</a></span>
+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.</p>
+
+
+<p><a name="SEC_31" id="SEC_31"></a>§ 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
+<i>pint</i> size, No. 1, others give this name to the
+largest, or <i>three-pint</i>, 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 <a href="#FIG_11">Fig. 11</a>.<!-- Page 43 --><span class="pagenum"><a name="Page_43" id="Page_43">[Pg 43]</a></span></p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_11" id="FIG_11"></a>
+<img src="images/i_052.png" width="400" height="292" alt="Fig. 11. Battery in Box." title="" />
+<p class="caption">Fig. 11. Battery in Box.</p>
+</div>
+
+
+<p><a name="SEC_32" id="SEC_32"></a>§ 32. There are certain ills to which the Leclanché
+cells are liable that require notice here. The first is
+<i>creeping</i>. 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<!-- Page 44 --><span class="pagenum"><a name="Page_44" id="Page_44">[Pg 44]</a></span>
+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.</p>
+
+<div class="figleft" style="width: 254px;">
+<a name="FIG_12" id="FIG_12"></a>
+<img src="images/i_053.png" width="254" height="400" alt="Fig. 12." title="The Gent cell" />
+<p class="caption">Fig. 12.</p>
+</div>
+
+<p>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 <a href="#FIG_12">Fig.
+12</a>, and the following is the
+description supplied by the
+patentees:&mdash;"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<!-- Page 45 --><span class="pagenum"><a name="Page_45" id="Page_45">[Pg 45]</a></span>
+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.</p>
+
+<p>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 <i>local action</i> 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 <i>testing wires</i>),
+to replace the old zincs by new ones, which are not
+costly.</p>
+
+
+<p><a name="SEC_33" id="SEC_33"></a>§ 33. There is yet a modification of the Leclanché<!-- Page 46 --><span class="pagenum"><a name="Page_46" id="Page_46">[Pg 46]</a></span>
+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.</p>
+
+
+<p><a name="SEC_34" id="SEC_34"></a>§ 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<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub>, 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<!-- Page 47 --><span class="pagenum"><a name="Page_47" id="Page_47">[Pg 47]</a></span>
+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:&mdash;</p>
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="center">K<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub></td><td align="center">+</td><td align="center">H<sub>2</sub>SO<sub>4</sub></td><td align="center">+</td><td align="center">H<sub>2</sub>O</td><td align="center">=</td><td align="center">K<sub>2</sub>SO<sub>4</sub></td><td align="center">+</td><td align="center">2H<sub>2</sub>CrO<sub>4</sub></td></tr>
+<tr><td align="center">&#9495;&#9473;&#9473;&#9473;&#9499;</td><td align="center">&nbsp;</td><td align="center">&#9495;&#9473;&#9473;&#9499;</td><td align="center">&nbsp;</td><td align="center">&#9495;&#9473;&#9499;</td><td align="center">&nbsp;</td><td align="center">&#9495;&#9473;&#9473;&#9499;</td><td align="center">&nbsp;</td><td align="center">&#9495;&#9473;&#9473;&#9473;&#9499;</td></tr>
+<tr><td align="center">1 molecule of bichrome.</td><td align="center">&amp;</td><td align="center">1 molecule of sulphuric acid.</td><td align="center">&amp;</td><td align="center">1 molecule of water.</td><td align="center">give</td><td align="center">1 molecule of sulphate of potash.</td><td align="center">&amp;</td><td align="center">2 molecules of chromic acid.</td></tr>
+</table></div>
+
+
+<p>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
+(<a href="#SEC_18">§ 18</a>) chromic acid parts with a portion of its oxygen,
+forming water and sesquioxide of chromium, Cr<sub>2</sub>O<sub>3</sub>, 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:&mdash;</p>
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="center">2H<sub>2</sub>CrO<sub>4</sub></td><td align="center">+</td><td align="center">3H<sub>2</sub></td><td align="center">=</td><td align="center">5H<sub>2</sub>O</td><td align="center">+</td><td align="center">Cr<sub>2</sub>O<sub>3</sub></td></tr>
+<tr><td align="center">&#9495;&#9473;&#9473;&#9473;&#9499;</td><td align="center">&nbsp;</td><td align="center">&#9495;&#9473;&#9499;</td><td align="center">&nbsp;</td><td align="center">&#9495;&#9473;&#9473;&#9499;</td><td align="center">&nbsp;</td><td align="center">&#9495;&#9473;&#9473;&#9499;</td></tr>
+<tr><td align="center">2 molecules of chromic acid.</td><td align="center">&amp;</td><td align="center">3 molecules of hydrogen.</td><td align="center">give</td><td align="center">5 molecules of water.</td><td align="center">&amp;</td><td align="center">1 molecule of chromium sesquioxide.</td></tr>
+</table></div>
+<p><!-- Page 48 --><span class="pagenum"><a name="Page_48" id="Page_48">[Pg 48]</a></span></p>
+
+<div class="figright" style="width: 222px;">
+<a name="FIG_13" id="FIG_13"></a>
+<img src="images/i_057.png" width="222" height="400" alt="Fig. 13." title="The Bichromate cell" />
+<p class="caption">Fig. 13.</p>
+</div>
+
+
+<p><a name="SEC_35" id="SEC_35"></a>§ 35. The "bottle" form of the bichromate or chromic
+acid battery (as illustrated at <a href="#FIG_13">Fig. 13</a>) 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:&mdash;</p>
+
+<p class="center"><span class="smcap">First Recipe.</span></p>
+
+<p class="center"><i>Bichromate Solution.</i></p>
+
+<p>
+Bichromate of potash (finely powdered)     <span class="recipe_amount">3 oz.</span><br />
+Boiling water                              <span class="recipe_amount">1 pint.</span><br />
+</p>
+
+<p>Stir with a glass rod, allow to cool, then add, in a fine
+stream, with constant stirring,</p>
+
+<p>
+Strong sulphuric acid (oil of vitriol)     <span class="recipe_amount">3 fluid oz.</span><br />
+</p>
+
+<p>The mixture should be made in a glazed earthern
+vessel, and allowed to cool before using.<!-- Page 49 --><span class="pagenum"><a name="Page_49" id="Page_49">[Pg 49]</a></span></p>
+
+<p class="center"><span class="smcap">Second Recipe.</span></p>
+
+<p class="center"><i>Chromic Acid Solution.</i></p>
+
+<p>
+Chromic acid (chromic trioxide)      <span class="recipe_amount">3 oz.</span><br />
+Water                                <span class="recipe_amount">1 pint.</span><br />
+</p>
+
+<p>Stir together till dissolved, then add gradually, with
+stirring,</p>
+
+<p>
+Sulphuric acid                       <span class="recipe_amount">3 oz.</span><br />
+</p>
+
+<p>This also must not be used till cold.</p>
+
+<p>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.</p>
+
+
+<p><a name="SEC_36" id="SEC_36"></a>§ 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,<!-- Page 50 --><span class="pagenum"><a name="Page_50" id="Page_50">[Pg 50]</a></span>
+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:&mdash;"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."<!-- Page 51 --><span class="pagenum"><a name="Page_51" id="Page_51">[Pg 51]</a></span></p>
+
+<div class="figcenter" style="width: 216px;">
+<a name="FIG_14" id="FIG_14"></a>
+<img src="images/i_059.png" width="216" height="400" alt="Fig. 14." title="The Fuller cell" />
+<p class="caption">Fig. 14.</p>
+</div>
+
+<p><a href="#FIG_14">Fig. 14</a> illustrates the form usually given to the
+modification of the Fuller cell as used for bell and
+signalling work.</p>
+
+
+<p><a name="SEC_37" id="SEC_37"></a>§ 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 <i>electromotive force</i>, 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 <i>current</i>,
+or evidence of electric flow, unless there is some means
+provided to allow the <i>tension</i>, 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,<!-- Page 52 --><span class="pagenum"><a name="Page_52" id="Page_52">[Pg 52]</a></span>
+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 "<i>closed circuit</i>." 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 <i>broken</i>. 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 <i>wet</i>, 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<!-- Page 53 --><span class="pagenum"><a name="Page_53" id="Page_53">[Pg 53]</a></span>
+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."</p>
+
+
+<p><a name="SEC_38" id="SEC_38"></a>§ 38. The next point to be remembered in connection
+with batteries is, that the electromotive force
+(E.M.F.) depends on the <i>nature</i> 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 <i>size</i>. 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 <i>series</i>; 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<!-- Page 54 --><span class="pagenum"><a name="Page_54" id="Page_54">[Pg 54]</a></span>
+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 <a href="#FIG_15">Fig. 15</a>, which illustrates
+3 Leclanché cells set up in series, we should get</p>
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="center">1·6</td><td align="center">volt</td></tr>
+<tr><td align="center">1·6</td><td align="center">"</td></tr>
+<tr><td align="center">1·6</td><td align="center">"</td></tr>
+<tr><td align="center" class="bt">4·8</td><td align="center" class="bt">volts</td></tr>
+</table></div>
+
+
+<p>as the total electromotive force of the combination.</p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_15" id="FIG_15"></a>
+<img src="images/i_063.png" width="400" height="196" alt="Fig. 15." title="The Cells coupled in series" />
+<p class="caption">Fig. 15.</p>
+</div>
+
+
+<p><a name="SEC_39" id="SEC_39"></a>§ 39. The <i>current</i>, 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<!-- Page 55 --><span class="pagenum"><a name="Page_55" id="Page_55">[Pg 55]</a></span>
+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 <span class="smcap">Ampère</span>; 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 <span class="smcap">Ohm</span>.
+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&frac14; 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.</p>
+
+
+<p><a name="SEC_40" id="SEC_40"></a>§ 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 "<span class="smcap">Ohm's Law</span>." It is that if we divide the number
+of electromotive force units (volts) employed by<!-- Page 56 --><span class="pagenum"><a name="Page_56" id="Page_56">[Pg 56]</a></span>
+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:</p>
+
+<p class="center">E/R = C or Electromotive force/Resistance = Current.</p>
+
+<p>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.</p>
+
+<p>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 &frac14; of an
+ohm, since 1 divided by &frac14; 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 "<i>internal resistance</i>," and must always be reckoned
+in these calculations. We can <i>halve</i> the internal resistance
+by <i>doubling</i> the size of the negative plate, or what
+amounts to the same thing by connecting two similar
+cells "<i>in parallel</i>;" 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<!-- Page 57 --><span class="pagenum"><a name="Page_57" id="Page_57">[Pg 57]</a></span>
+of cells thus coupled together "<i>in parallel</i>" 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 <i>in parallel</i> would have a
+joint resistance of &#8539; ohm only. The E.M.F. would
+remain the same, since this does not depend on the size
+of the plate (see <a href="#SEC_38">§ 38</a>). The arrangement of cells in
+parallel is shown at <a href="#FIG_16">Fig. 16</a>, 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<!-- Page 58 --><span class="pagenum"><a name="Page_58" id="Page_58">[Pg 58]</a></span>
+resistance in ohms, of the cells mostly used in electric
+bell work.</p>
+
+<div class="figcenter" style="width: 357px;">
+<a name="FIG_16" id="FIG_16"></a>
+<img src="images/i_066.png" width="357" height="400" alt="Fig. 16." title="The Cells coupled in Parallel" />
+<p class="caption">Fig. 16.</p>
+</div>
+
+<hr />
+
+<p class="center">TABLE SHOWING E.M.F. AND R. OF BATTERIES.</p>
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><th align="left">Name of Cell.</th><th align="left">Capacity of Cell.</th><th align="left">Electromotive <br />force in Volts.</th><th align="left">Resistance <br />in Ohms.</th></tr>
+<tr><td align="left">Daniell</td><td align="left">2 quarts</td><td align="left">1·079</td><td align="left" class="in1">1</td></tr>
+<tr><td align="left">Daniell Gravity</td><td align="left">2 quarts</td><td align="left">1·079</td><td align="left">10</td></tr>
+<tr><td align="left">Leclanché</td><td align="left">1 pint</td><td align="left">1·60</td><td align="left" class="in1">1·13</td></tr>
+<tr><td align="left">Leclanché</td><td align="left">2 pints</td><td align="left">1·60</td><td align="left" class="in1">1·10</td></tr>
+<tr><td align="left">Leclanché</td><td align="left">3 pints</td><td align="left">1·60</td><td align="left" class="in1">0·87</td></tr>
+<tr><td align="left">Agglomerate</td><td align="left">1 pint</td><td align="left">1·55</td><td align="left" class="in1">0·70</td></tr>
+<tr><td align="left">Agglomerate</td><td align="left">2 pints</td><td align="left">1·55</td><td align="left" class="in1">0·60</td></tr>
+<tr><td align="left">Agglomerate</td><td align="left">3 pints</td><td align="left">1·55</td><td align="left" class="in1">0·50</td></tr>
+<tr><td align="left">Fuller</td><td align="left">1 quart</td><td align="left">1·80</td><td align="left" class="in1">0·50</td></tr>
+</table></div>
+
+
+<p>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 <i>some</i> 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.</p>
+
+<div class="footnote"><p><a name="Footnote_4_4" id="Footnote_4_4"></a><a href="#FNanchor_4_4"><span class="label">[4]</span></a> 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.</p></div>
+
+<div class="footnote"><p><a name="Footnote_5_5" id="Footnote_5_5"></a><a href="#FNanchor_5_5"><span class="label">[5]</span></a> Spirits of salt.</p></div>
+
+<div class="footnote"><p><a name="Footnote_6_6" id="Footnote_6_6"></a><a href="#FNanchor_6_6"><span class="label">[6]</span></a> Oil of vitriol.</p></div>
+
+<div class="footnote"><p><a name="Footnote_7_7" id="Footnote_7_7"></a><a href="#FNanchor_7_7"><span class="label">[7]</span></a> Aquafortis.</p></div>
+
+<div class="footnote"><p><a name="Footnote_8_8" id="Footnote_8_8"></a><a href="#FNanchor_8_8"><span class="label">[8]</span></a> Power to set up a current of electricity.</p></div>
+
+<div class="footnote"><p><a name="Footnote_9_9" id="Footnote_9_9"></a><a href="#FNanchor_9_9"><span class="label">[9]</span></a> Depolarizer is the technical name given to any body which, by absorbing
+the free hydrogen, removes the false polarity of the negative plate.</p></div>
+
+
+
+<hr class="long" />
+<p><!-- Page 59 --><span class="pagenum"><a name="Page_59" id="Page_59">[Pg 59]</a></span></p>
+<h2><a name="CHAPTER_III" id="CHAPTER_III"></a>CHAPTER III.
+<br />
+ON ELECTRIC BELLS AND OTHER SIGNALLING
+APPLIANCES.</h2>
+
+
+<p><a name="SEC_41" id="SEC_41"></a>§ 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, <i>for
+the time being</i>, powerfully magnetic (see <a href="#SEC_13">§ 13</a>). A piece
+of soft iron (known as the <i>armature</i>), 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 <i>trembling</i>, the <i>single stroke</i>, or the
+<i>continuous ringing</i> class.</p>
+
+
+<p><a name="SEC_42" id="SEC_42"></a>§ 42. In order that the electric bell-fitter may have an<!-- Page 60 --><span class="pagenum"><a name="Page_60" id="Page_60">[Pg 60]</a></span>
+intelligent conception of his work, he should <i>make</i> 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:&mdash;<a name="FNanchor_10_10" id="FNanchor_10_10"></a><a href="#Footnote_10_10" class="fnanchor">[10]</a></p>
+
+<p><i>How to make a bell.</i>&mdash;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:&mdash;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<!-- Page 61 --><span class="pagenum"><a name="Page_61" id="Page_61">[Pg 61]</a></span>
+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.</p>
+
+<div class="figright" style="width: 222px;">
+<a name="FIG_17" id="FIG_17"></a>
+<img src="images/i_070.png" width="222" height="400" alt="Fig. 17." title="Outline of electric bell" />
+<p class="caption">Fig. 17.</p>
+</div>
+
+<div class="figright" style="width: 243px;">
+<a name="FIG_18" id="FIG_18"></a>
+<img src="images/i_071.png" width="243" height="400" alt="Fig. 18." title="Frame of bell" />
+<p class="caption">Fig. 18.</p>
+</div>
+
+<div class="figright" style="width: 258px;">
+<a name="FIG_19" id="FIG_19"></a>
+<img src="images/i_072.png" width="258" height="400" alt="Fig. 19." title="E-shaped frame" />
+<p class="caption">Fig. 19.</p>
+</div>
+
+<p><i>The Base</i>, to which all the
+other parts are fastened, is
+made of &frac34; in. mahogany or
+teak, 6 in. by 4 in., shaped
+as shown at <a href="#FIG_17">Fig. 17</a>, 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 <a href="#FIG_18">Fig. 18</a>;
+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 <a href="#FIG_19">Fig. 19</a>. 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<!-- Page 62 --><span class="pagenum"><a name="Page_62" id="Page_62">[Pg 62]</a></span>
+manufacture his bell out of the parts sketched in Figs.
+<a href="#FIG_17">17</a>, <a href="#FIG_18">18</a>, <a href="#FIG_20A">20<sup>A</sup></a>, <a href="#FIG_21">21</a>, <a href="#FIG_23">23</a>, <a href="#FIG_24">24<sup>A</sup></a>, and <a href="#FIG_25">25</a>; but, on the other hand,
+a smith or engineer might prefer the improved form
+shown at <a href="#FIG_31">Fig. 31</a>, and select the parts shown at Figs. <a href="#FIG_20A">20<sup>A</sup></a>,
+<a href="#Page_22">22</a>, <a href="#FIG_19">19</a>, choosing either to forge the horse-shoe magnet,
+<a href="#FIG_20">Fig. 20</a>, or to turn up the
+two cores, as shown at
+<a href="#FIG_21">Fig. 21</a> (<span class="smcap">A</span>), to screw into
+the metal base, <a href="#FIG_21">Fig. 21</a> <span class="smcap">B</span>,
+or to be fastened by nuts,
+as shown at <a href="#FIG_19">Fig. 19</a>. 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 <a href="#FIG_18">Fig. 18</a>, and
+when thus made, the part <span class="smcap">A</span> 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 <span class="smcap">B</span> to hold the contact screw, or contact breaker (<a href="#SEC_41">§ 41</a>).<!-- Page 63 --><span class="pagenum"><a name="Page_63" id="Page_63">[Pg 63]</a></span></p>
+
+<p>The <i>Magnet</i> may be formed as shown at <a href="#FIG_20">Fig. 20</a>, or at
+<a href="#FIG_20A">Fig. 20<sup>A</sup></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 <a href="#FIG_20">Fig. 20</a>. 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 <a href="#SEC_14">§ 14</a>). 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<!-- Page 64 --><span class="pagenum"><a name="Page_64" id="Page_64">[Pg 64]</a></span>
+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&#8540; apart when bent.
+We may now consider the construction of a magnet of
+the form shown at <a href="#FIG_20A">Fig. 20<sup>A</sup></a>. To make the cores of
+such a magnet, to ring a 2&frac12; in. bell, get two 2 inch
+lengths of 5/16 in. best Swedish round iron, straighten
+them, smooth them in a lathe, and reduce &frac14; in. of one
+end of each to 4/16 of an in., leaving a sharp shoulder,
+as shown at <a href="#FIG_21">Fig. 21</a> <span class="smcap">A</span>. Next, get a 2-in. length of
+angle iron, drill in it two holes 1&#8540; 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.<!-- Page 65 --><span class="pagenum"><a name="Page_65" id="Page_65">[Pg 65]</a></span>
+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 <a href="#FIG_21">Fig. 21</a> <span class="smcap">B</span>. 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 <i>hard</i>. Iron is rendered hard by hammering,
+by being rapidly cooled, either in cold air or water,<!-- Page 66 --><span class="pagenum"><a name="Page_66" id="Page_66">[Pg 66]</a></span>
+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&frac12; in. bell only;<!-- Page 67 --><span class="pagenum"><a name="Page_67" id="Page_67">[Pg 67]</a></span>
+for larger bells the size increases 1/16 of an inch, and the
+length &frac14; of an inch, for every &frac12; in. increase in the
+diameter of the bell.</p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_20" id="FIG_20"></a>
+<img src="images/i_073.png" width="400" height="331" alt="Fig. 20." title="Electro-magnet, old form" />
+<p class="caption">Fig. 20.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_20A" id="FIG_20A"></a>
+<img src="images/i_074.png" width="400" height="336" alt="Fig. 20 A." title="Electro-magnet, modern form" />
+<p class="caption">Fig. 20 A.</p>
+</div>
+
+<div class="figright" style="width: 339px;">
+<a name="FIG_21" id="FIG_21"></a>
+<img src="images/i_075.png" width="339" height="400" alt="Fig. 21." title="Magnet frame" />
+<p class="caption">Fig. 21.</p>
+</div>
+
+<p>The <i>Bobbins</i>, 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&frac12; in.
+bell should be: length 1&frac34; in., diameter of heads &frac34; of an
+in., the length increasing &frac14; of an in. and the diameter &#8539; of
+an in. for every additional &frac12; 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 &#8539; 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<!-- Page 68 --><span class="pagenum"><a name="Page_68" id="Page_68">[Pg 68]</a></span>
+with silk, to ensure insulation. Mention has already
+been made of what is meant by insulation at <a href="#SEC_3">§ 3</a>, 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<a name="FNanchor_11_11" id="FNanchor_11_11"></a><a href="#Footnote_11_11" class="fnanchor">[11]</a>
+or detaching them from electric contact."</p>
+
+<p>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:&mdash;</p>
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><th align="center"><i>Conductors.</i></th><th align="center"><i>Insulators.</i></th></tr>
+<tr><td align="left">Silver.</td><td align="left">Paraffin Wax.</td></tr>
+<tr><td align="left">Copper.</td><td align="left">Guttapercha.</td></tr>
+<tr><td align="left">Iron.</td><td align="left">Indiarubber.</td></tr>
+<tr><td align="left">Brass.</td><td align="left">Shellac.</td></tr>
+<tr><td align="left">All Other Metals.</td><td align="left">Varnishes.</td></tr>
+<tr><td align="left">Metallic Solutions.</td><td align="left">Sealing Wax.</td></tr>
+<tr><td align="left">Metallic Salts.</td><td align="left">Silk and Cotton.</td></tr>
+<tr><td align="left">Wet Stone.</td><td align="left">Dry Clothing.</td></tr>
+<tr><td align="left">Wet Wood.</td><td align="left">Dry Wood.</td></tr>
+<tr><td align="left"></td><td align="left">Oil, Dirt and Rust.</td></tr>
+</table></div>
+
+
+<p>See also the more extended list given at <a href="#SEC_5">§ 5</a> for a more
+complete and exact classification.<!-- Page 69 --><span class="pagenum"><a name="Page_69" id="Page_69">[Pg 69]</a></span></p>
+
+<p>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 <i>naked</i> 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&frac12; in. bell should be No. 24 B. W. G., the size falling two
+numbers for each &frac12; 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<!-- Page 70 --><span class="pagenum"><a name="Page_70" id="Page_70">[Pg 70]</a></span>
+from it, the decrease being as the <i>square</i> 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 &#8539; 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 <i>outside</i> 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<!-- Page 71 --><span class="pagenum"><a name="Page_71" id="Page_71">[Pg 71]</a></span>
+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 <a href="#FIG_21A">Fig. 21 <span class="smcap">A</span></a> may be employed. This
+<i>electric bobbin winder</i> consists in a table which can be
+stood on a lathe or near any other driving wheel. Two
+carriers, <span class="smcap">C C</span>, 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, <span class="smcap">A</span>, by means of which
+motion can be transmitted from the band of the driving
+wheel. The sliding spindles, <span class="smcap">B B</span>, are fitted with recesses
+and screws, <span class="smcap">H H H H</span>, 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 <span class="smcap">D</span>; a flat piece of metal, <span class="smcap">E</span>,
+hinged at <span class="smcap">G</span>, presses against the bobbin, owing to the
+spring <span class="smcap">F</span>. The centre figure shows details of the carrier,
+<span class="smcap">C</span>, in section. At the bottom is shown the spool of wire
+on a standard <span class="smcap">L</span>. The wire passes from this spot between
+the two indiarubber rollers, <span class="smcap">M M</span>, on to the bobbin <span class="smcap">D</span>.</p>
+
+<div class="figcenter" style="width: 594px;">
+<a name="FIG_21A" id="FIG_21A"></a>
+<img src="images/i_081.png" width="594" height="600" alt="Fig. 21 A." title="Winder" />
+<p class="caption">Fig. 21 A.</p>
+</div>
+
+<p>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<!-- Page 72 --><span class="pagenum"><a name="Page_72" id="Page_72">[Pg 72]</a></span>
+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 <a href="#FIG_22">Fig. 22 <span class="smcap">A</span></a>. A short
+length of the lower free ends of wire (near the base or
+yoke) should now be bared of their covering, cleaned<!-- Page 73 --><span class="pagenum"><a name="Page_73" id="Page_73">[Pg 73]</a></span>
+with emery paper, twisted together tightly, as shown at
+<a href="#FIG_22">Fig. 22 <span class="smcap">B</span></a>, 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.</p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_22" id="FIG_22"></a>
+<img src="images/i_082a.png" width="400" height="332" alt="Fig. 22." title="Mode of joining electromagnet wires" />
+<p class="caption">Fig. 22.</p>
+</div>
+
+<p>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
+<a href="#FIG_22">Fig. 22 <span class="smcap">B</span></a>; that is to say, that the wire from the <i>under</i>
+side of one bobbin, should pass <i>over</i> to the next in the
+same way as the curls of the letter <span title="[rotated S in original text]">S</span>.</p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_23" id="FIG_23"></a>
+<img src="images/i_083a.png" width="400" height="134" alt="Fig. 23." title="Armature spring" />
+<p class="caption">Fig. 23.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_24" id="FIG_24"></a>
+<img src="images/i_083b.png" width="400" height="140" alt="Fig. 24." title="Armature spring Another form" />
+<p class="caption">Fig. 24.</p>
+</div>
+
+<div class="figright" style="width: 300px;">
+<a name="FIG_25" id="FIG_25"></a>
+<img src="images/i_084.png" width="300" height="352" alt="Fig. 25." title="Platinum tipped screw" />
+<p class="caption">Fig. 25.</p>
+</div>
+
+<div class="figright" style="width: 300px;">
+<a name="FIG_26" id="FIG_26"></a>
+<img src="images/i_085.png" width="300" height="72" alt="Fig. 26." title="Platinum tipped spring" />
+<p class="caption">Fig. 26.</p>
+</div>
+
+<div class="figright" style="width: 300px;">
+<a name="FIG_27" id="FIG_27"></a>
+<img src="images/i_086.png" width="300" height="348" alt="Fig. 27." title="Binding screws" />
+<p class="caption">Fig. 27.</p>
+</div>
+
+<p>The part that next claims our consideration is the<!-- Page 74 --><span class="pagenum"><a name="Page_74" id="Page_74">[Pg 74]</a></span>
+<i>armature</i>, 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. <a href="#FIG_23">23</a> and <a href="#FIG_24">24</a>; 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. <a href="#FIG_24">Fig. 24</a>
+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<!-- Page 75 --><span class="pagenum"><a name="Page_75" id="Page_75">[Pg 75]</a></span>
+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 <a href="#FIG_23">Fig. 23</a>, 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 <a href="#FIG_25">Fig. 25</a>. This may either be a
+short stout pillar of &frac14; 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<!-- Page 76 --><span class="pagenum"><a name="Page_76" id="Page_76">[Pg 76]</a></span>
+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 <a href="#FIG_26">Fig. 26</a>, 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 <a href="#FIG_26">Fig. 26</a>, it is only needful to procure
+a short length of No. 16 platinum wire, say &#8539; 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.<!-- Page 77 --><span class="pagenum"><a name="Page_77" id="Page_77">[Pg 77]</a></span></p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_28" id="FIG_28"></a>
+<img src="images/i_087a1.png" width="400" height="400" alt="Fig. 28." title="Bell or gong" />
+<p class="caption">Fig. 28.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 385px;">
+<a name="FIG_29" id="FIG_29"></a>
+<img src="images/i_087a2.png" width="385" height="400" alt="Fig. 29." title="Pillar and nuts" />
+<p class="caption">Fig. 29.</p>
+</div>
+
+<p>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
+(<a href="#FIG_28">see Fig. 28</a>). The bell must be
+adjusted on its pillar (<a href="#FIG_29">see Fig. 29<sup>A</sup></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 <a href="#FIG_29">Fig. 29</a>. 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. <a href="#FIG_23">23</a>
+and <a href="#FIG_24">24</a>. We still need, to complete our bell, two
+binding screws, which may take either of the forms shown
+at <a href="#FIG_27">Fig. 27</a>; and an insulating washer, or collar, made
+of ebonite or boxwood, soaked in melted paraffin, to
+prevent the contact pillar (<a href="#FIG_25">Fig. 25</a>) making electrical<!-- Page 78 --><span class="pagenum"><a name="Page_78" id="Page_78">[Pg 78]</a></span>
+contact with the metal base. The best shape to be given
+to these washers is shown at <a href="#FIG_30">Fig. 30</a>. 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&mdash;that is, the one <i>above</i>&mdash;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.</p>
+
+<div class="figcenter" style="width: 322px;">
+<a name="FIG_30" id="FIG_30"></a>
+<img src="images/i_087b.png" width="322" height="247" alt="Fig. 30." title="Washers" />
+<p class="caption">Fig. 30.</p>
+</div>
+
+<p>Having now all the parts at hand, we can proceed to
+fit them together, which is done as follows:&mdash;The bell
+pillar, with its bell attached, is fastened by its shank<!-- Page 79 --><span class="pagenum"><a name="Page_79" id="Page_79">[Pg 79]</a></span>
+into the hole shown near <span class="smcap">B</span>, <a href="#FIG_17">Fig. 17</a>, where it is screwed
+up tight by the square nut shown at <a href="#FIG_29">Fig. 29 <i>c</i></a>. In the
+same manner, we must fasten the contact pillar, or bracket,
+shown at <a href="#FIG_24">Fig. 24 <span class="smcap">A</span></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
+<a href="#FIG_30">Fig. 30</a> (similar washers must be used for the two binding
+screws if the <i>whole</i> base-plate be made in metal).
+This being done, the metal frame, <a href="#FIG_18">Fig. 18</a>, is put in
+position on the wooden base, as shown at <a href="#FIG_17">Fig. 17</a>, and
+screwed down thereto by the screws indicated at <i>s s s</i>.
+The magnet may then be screwed down to the metal
+frame as shown. The small bracket of angle brass
+marked <span class="smcap">B</span>, in Figs. <a href="#FIG_23">23</a> and <a href="#FIG_24">24</a>, 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&frac12; in.
+bell). In setting up this and the contact pillar, the
+greatest care must be taken that the platinum tip of the
+contact screw, <a href="#FIG_25">Fig. 25</a>, should touch lightly the centre
+of the platinum speck at the back of the spring, Figs.
+<a href="#FIG_23">23</a> and <a href="#FIG_24">24</a>, shown full size at <a href="#FIG_26">Fig. 26</a>.</p>
+
+<p>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<!-- Page 80 --><span class="pagenum"><a name="Page_80" id="Page_80">[Pg 80]</a></span>
+and clapper, the other being similarly connected with
+the left-hand binding-screw, shown at <a href="#FIG_17">Fig. 17</a>. Another
+short length of wire (also enclosed in rubber tubing)
+must be arranged to connect the contact screw pillar
+<a href="#FIG_17">Fig. 17</a>, 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 dis<!-- Page 81 --><span class="pagenum"><a name="Page_81" id="Page_81">[Pg 81]</a></span>tance
+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.</p>
+
+<div class="figright" style="width: 209px;">
+<a name="FIG_31" id="FIG_31"></a>
+<img src="images/i_090.png" width="209" height="400" alt="Fig. 31." title="Trembling bell" />
+<p class="caption">Fig. 31.</p>
+</div>
+
+
+<p><a name="SEC_43" id="SEC_43"></a>§ 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 <a href="#FIG_17">Fig. 17</a>,
+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, <i>pro tem.</i>, into a powerful magnet (see <a href="#SEC_13">§ 13</a>); con<!-- Page 82 --><span class="pagenum"><a name="Page_82" id="Page_82">[Pg 82]</a></span>sequently,
+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 <i>immediately</i> lost
+their magnetism (see <a href="#SEC_13">§ 13</a>, last five lines). This would
+have been disadvantageous, for two reasons: 1st, because
+the <i>stroke</i> 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<!-- Page 83 --><span class="pagenum"><a name="Page_83" id="Page_83">[Pg 83]</a></span>
+bells the name of trembling, chattering, or vibrating
+bells.</p>
+
+
+<p><a name="SEC_44" id="SEC_44"></a>§ 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
+<i>deliquescent</i> (runs to water), rottens the wire, and spoils
+the insulation of the adjacent parts. If solder be used
+at any parts, let <i>resin</i> 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<!-- Page 84 --><span class="pagenum"><a name="Page_84" id="Page_84">[Pg 84]</a></span>
+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.</p>
+
+<p>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 <i>not</i> 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 <i>silver</i>; 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.</p>
+
+<p>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 &#8539; 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 <i>residual</i><!-- Page 85 --><span class="pagenum"><a name="Page_85" id="Page_85">[Pg 85]</a></span>
+<i>magnetism</i> (see <a href="#SEC_14">§ 14</a>), 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 <i>just not touch</i> the poles of the
+electro-magnet. Now screw up the platinum screw
+until it <i>clears</i> 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 <i>ringing</i>. 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<!-- Page 86 --><span class="pagenum"><a name="Page_86" id="Page_86">[Pg 86]</a></span>
+the spring lightly with a bit of wire, first <i>towards</i> and
+then <i>away</i> 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&frac12;-in. bell should be able to sustain
+easily a 1 lb. weight attached by a piece of string to a
+smooth piece of &frac12;-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<!-- Page 87 --><span class="pagenum"><a name="Page_87" id="Page_87">[Pg 87]</a></span>
+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 <i>permissible</i>
+that one or the other should not be insulated
+from the base or frame; but one or the other <i>must</i> 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.</p>
+
+<div class="figright" style="width: 192px;">
+<a name="FIG_32" id="FIG_32"></a>
+<img src="images/i_097.png" width="192" height="400" alt="Fig. 32." title="Bell action enclosed in case" />
+<p class="caption">Fig. 32.</p>
+</div>
+
+<p>The fourth defect&mdash;that is, warpage or shrinkage of the
+base&mdash;can only occur in badly-made bells, in which the<!-- Page 88 --><span class="pagenum"><a name="Page_88" id="Page_88">[Pg 88]</a></span>
+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.</p>
+
+
+<p><a name="SEC_45" id="SEC_45"></a>§ 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 <a href="#FIG_32">Fig. 32</a>, and may be made from &frac14;-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.</p>
+
+<p>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<!-- Page 89 --><span class="pagenum"><a name="Page_89" id="Page_89">[Pg 89]</a></span>
+battery, rather more of a finer gauge of wire must be
+employed to wind the magnets than that herein recommended,
+unless, indeed, <i>relays</i> be used in conjunction
+with the bells.</p>
+
+
+<p><a name="SEC_46" id="SEC_46"></a>§ 46.&mdash;</p>
+
+<p class="center"><span class="smcap">Table</span></p>
+
+<p class="center">Showing proportions to be observed in the different
+parts of electric bells.</p>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><th align="left">Diameter of Bell.</th><th align="left">Length of Magnet Cores.</th><th align="left">Diameter of Magnet Cores.</th><th align="left">Length of Bobbin.</th><th align="left">Diameter of Bobbin Head.</th><th align="center">B. W. G. of Wire on Bobbin.</th></tr>
+<tr><td align="left" class="in1">2&frac12;''</td><td align="left">2''</td><td align="left" class="in1">5/16''</td><td align="left">1&frac34;''</td><td align="left" class="in1">&frac34;''</td><td align="center">24</td></tr>
+<tr><td align="left" class="in1">3</td><td align="left">2&frac14;</td><td align="left" class="in1">&#8540;</td><td align="left">2</td><td align="left" class="in1">&#8542;</td><td align="center">24</td></tr>
+<tr><td align="left" class="in1">3&frac12;</td><td align="left">2&frac12;</td><td align="left" class="in1">7/16</td><td align="left">2&frac14;</td><td align="left">1</td><td align="center">22</td></tr>
+<tr><td align="left" class="in1">4</td><td align="left">2&frac34;</td><td align="left" class="in1">&frac12;</td><td align="left">2&frac12;</td><td align="left">1&#8539;</td><td align="center">22</td></tr>
+<tr><td align="left" class="in1">4&frac12;</td><td align="left">3</td><td align="left" class="in1">9/16</td><td align="left">2&frac34;</td><td align="left">1&frac14;</td><td align="center">20</td></tr>
+<tr><td align="left" class="in1">5</td><td align="left">3&frac14;</td><td align="left" class="in1">&#8541;</td><td align="left">3</td><td align="left">1&#8540;</td><td align="center">18</td></tr>
+<tr><td align="left" class="in1">5&frac12;</td><td align="left">3&frac12;</td><td align="left" class="in1">11/16</td><td align="left">3&frac14;</td><td align="left">1&frac12;</td><td align="center">16</td></tr>
+<tr><td align="left" class="in1">6</td><td align="left">3&frac34;</td><td align="left" class="in1">&frac34;</td><td align="left">3&frac12;</td><td align="left">1&#8541;</td><td align="center">16</td></tr>
+<tr><td align="left" class="in1">6&frac12;</td><td align="left">4</td><td align="left" class="in1">13/16</td><td align="left">3&frac34;</td><td align="left">1&frac34;</td><td align="center">16</td></tr>
+<tr><td align="left" class="in1">7</td><td align="left">4&frac14;</td><td align="left" class="in1">&#8542;</td><td align="left">4</td><td align="left">1&#8542;</td><td align="center">16</td></tr>
+<tr><td align="left" class="in1">7&frac12;</td><td align="left">4&frac12;</td><td align="left" class="in1">15/16</td><td align="left">4&frac14;</td><td align="left">2</td><td align="center">14</td></tr>
+<tr><td align="left" class="in1">8</td><td align="left">4&frac34;</td><td align="left">1</td><td align="left">4&frac12;</td><td align="left">2&#8539;</td><td align="center">14</td></tr>
+<tr><td align="left" class="in1">8&frac12;</td><td align="left">5</td><td align="left">1-1/16</td><td align="left">4&frac34;</td><td align="left">2&frac14;</td><td align="center">14</td></tr>
+<tr><td align="left" class="in1">9</td><td align="left">5&frac14;</td><td align="left">1&#8539;</td><td align="left">5</td><td align="left">2&#8540;</td><td align="center">14</td></tr>
+<tr><td align="left" class="in1">9&frac12;</td><td align="left">5&frac12;</td><td align="left">1-3/16</td><td align="left">5&frac14;</td><td align="left">2&frac12;</td><td align="center">14</td></tr>
+<tr><td align="left">10</td><td align="left">5&frac34;</td><td align="left">1&frac14;</td><td align="left">5&frac12;</td><td align="left">2&#8541;</td><td align="center">14</td></tr>
+<tr><td align="left">10&frac12;</td><td align="left">6</td><td align="left">1-5/16</td><td align="left">5&frac34;</td><td align="left">2&frac34;</td><td align="center">12</td></tr>
+<tr><td align="left">11</td><td align="left">6&frac14;</td><td align="left">1&#8540;</td><td align="left">6</td><td align="left">2&#8542;</td><td align="center">12</td></tr>
+<tr><td align="left">11&frac12;</td><td align="left">6&frac12;</td><td align="left">1-7/16</td><td align="left">6&frac14;</td><td align="left">3</td><td align="center">10</td></tr>
+<tr><td align="left">12</td><td align="left">6&frac34;</td><td align="left">1&frac12;</td><td align="left">6&frac12;</td><td align="left">3&#8539;</td><td align="center">10</td></tr>
+</table></div>
+
+<hr />
+
+<p><!-- Page 90 --><span class="pagenum"><a name="Page_90" id="Page_90">[Pg 90]</a></span></p>
+
+<div class="figright" style="width: 339px;">
+<a name="FIG_33A" id="FIG_33A"></a>
+<img src="images/i_099a.png" width="339" height="400" alt="Fig. 33 A." title="Ordinary trembling bell (A)" />
+<p class="caption">Fig. 33 A.</p>
+</div>
+
+
+<p><a name="SEC_47" id="SEC_47"></a>§ 47. We can now glance at several modifications in
+the shape and mode of action of electric bells and their
+congeners. Taking Figs. <a href="#FIG_33A">33 <span class="smcap">A</span></a> and <a href="#FIG_33B"><span class="smcap">B</span></a> 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. <a href="#FIG_34">Fig. 34</a>
+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, <a href="#FIG_33A">Fig. 33</a>, the circuit is
+completed through the platinum screw pillar, to the
+binding screw marked <span class="smcap">Z</span>, hence the circuit is rapidly made<!-- Page 91 --><span class="pagenum"><a name="Page_91" id="Page_91">[Pg 91]</a></span>
+and broken as long as by any means contact is made
+with the battery, and the binding screws <span class="smcap">L</span> and <span class="smcap">Z</span>. But
+in the single stroke bell, <a href="#FIG_34">Fig. 34</a>, the wires from the
+electro-magnet are connected directly to the two binding
+screws <span class="smcap">L</span> and <span class="smcap">Z</span>, 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 <span class="smcap">Q</span> 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 (<i>g</i>) 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<!-- Page 92 --><span class="pagenum"><a name="Page_92" id="Page_92">[Pg 92]</a></span>
+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 <span class="smcap">Q</span>, 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 <span class="smcap">Q</span> 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 <i>chatters</i>.</p>
+
+<div class="figcenter" style="width: 284px;">
+<a name="FIG_33B" id="FIG_33B"></a>
+<img src="images/i_099b.png" width="284" height="400" alt="Fig. 34." title="Ordinary trembling bell (B)" />
+<p class="caption">Fig. 33 B.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 209px;">
+<a name="FIG_34" id="FIG_34"></a>
+<img src="images/i_100.png" width="209" height="400" alt="Fig. 34." title="Single stroke bell" />
+<p class="caption">Fig. 34.</p>
+</div>
+
+
+<p><a name="SEC_48" id="SEC_48"></a>§ 48. <i>The continuous ringing bell</i> is the modification
+which next demands our attention. In this, the ringing
+action, when once started by the push,<a name="FNanchor_12_12" id="FNanchor_12_12"></a><a href="#Footnote_12_12" class="fnanchor">[12]</a> 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<!-- Page 93 --><span class="pagenum"><a name="Page_93" id="Page_93">[Pg 93]</a></span>
+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.</p>
+
+<div class="figcenter" style="width: 230px;">
+<a name="FIG_35" id="FIG_35"></a>
+<img src="images/i_103.png" width="230" height="400" alt="Fig. 35." title="Continuous ringing bell" />
+<p class="caption">Fig. 35.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 328px;">
+<a name="FIG_36" id="FIG_36"></a>
+<img src="images/i_104.png" width="328" height="400" alt="Fig. 36." title="Release action" />
+<p class="caption">Fig. 36.</p>
+</div>
+
+<p><a href="#FIG_35">Fig. 35</a> 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 <span class="smcap">C</span> connected as usual
+with the carbon element of the battery; another
+marked <span class="smcap">L</span>, which connects with line wire, and a third,
+<span class="smcap">Z</span>, connected by means of a branch wire (shunt wire),<!-- Page 94 --><span class="pagenum"><a name="Page_94" id="Page_94">[Pg 94]</a></span>
+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 <span class="smcap">Z</span> and <span class="smcap">C</span>, 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<!-- Page 95 --><span class="pagenum"><a name="Page_95" id="Page_95">[Pg 95]</a></span>
+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 <a href="#FIG_36">Fig. 36</a>,
+<span class="smcap">A</span> and <span class="smcap">B</span>.</p>
+
+<div class="figright" style="width: 170px;">
+<a name="FIG_37" id="FIG_37"></a>
+<img src="images/i_105.png" width="170" height="400" alt="Fig. 37." title="Continuous ringing with relay" />
+<p class="caption">Fig. 37.</p>
+</div>
+
+<p>In continuous ringing bells of the second class, a
+detent similar to that shown at <a href="#FIG_35">Fig. 35</a> <span class="smcap">D</span> 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<!-- Page 96 --><span class="pagenum"><a name="Page_96" id="Page_96">[Pg 96]</a></span>
+serves only to make contact with a battery, is known
+as a <i>Relay</i>, 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. <a href="#FIG_37">Fig. 37</a> shows this arrange<!-- Page 97 --><span class="pagenum"><a name="Page_97" id="Page_97">[Pg 97]</a></span>ment,
+attached to the same base board as the bell itself.
+On contact being made with the push, the current
+enters at <span class="smcap">C</span>, circulates round the cores of the relay, thus
+converting it into a magnet. The armature <i>a</i> 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
+<span class="smcap">B B´</span>, back to the battery by <span class="smcap">Z</span>. A second modification
+of this mode of causing an ordinary bell to ring continuously
+is shown at <a href="#FIG_38">Fig. 38</a>, the peculiar form of<!-- Page 98 --><span class="pagenum"><a name="Page_98" id="Page_98">[Pg 98]</a></span>
+relay used therewith being illustrated at <a href="#FIG_39">Fig. 39</a>.
+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 <i>switch</i>,<a name="FNanchor_13_13" id="FNanchor_13_13"></a><a href="#Footnote_13_13" class="fnanchor">[13]</a> 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 <i>s</i>, 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 <span class="smcap">C</span> and <span class="smcap">W</span>, passes
+round the coils of the electro-magnet, and returns by <span class="smcap">Z</span>.
+In so doing it energises the electro-magnet <span class="smcap">E</span>, which
+immediately attracts its armature <span class="smcap">A</span>. The forward
+movement of the armature <span class="smcap">A</span>, releases the pivoted
+arm <span class="smcap">L</span>, to which is attached a platinum-tipped contact
+prong <span class="smcap">P</span>. This, it will be noticed, is in metallic connection
+with the pillar <span class="smcap">P'</span>, and with the base, and,
+therefore, through the wire <span class="smcap">W</span>, with the battery. When
+the arm <span class="smcap">L</span> falls, the contact prong completes the circuit
+to the bell, through the insulated pillar <span class="smcap">X</span>. 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 <a href="#FIG_36">Fig. 36</a> can be employed to reset the
+arm <span class="smcap">L</span>.</p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_38" id="FIG_38"></a>
+<img src="images/i_106a.png" width="400" height="146" alt="Fig. 38." title="Continuous ringing action with indicator" />
+<p class="caption">Fig. 38.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_39" id="FIG_39"></a>
+<img src="images/i_106b.png" width="400" height="226" alt="Fig. 39." title="Relay and detent lever for indicator" />
+<p class="caption">Fig. 39.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 600px;">
+<a name="FIG_40" id="FIG_40"></a>
+<img src="images/i_108.png" width="600" height="214" alt="Fig. 40." title="Callow's attachment" />
+<p class="caption">Fig. 40.</p>
+</div>
+
+<p>A rather more complicated arrangement for continuous
+bell ringing is shown at <a href="#FIG_40">Fig. 40</a>. It is known<!-- Page 99 --><span class="pagenum"><a name="Page_99" id="Page_99">[Pg 99]</a></span>
+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 <i>English Mechanic</i>, will render the working
+of Callow's attachment perfectly clear. "When the
+button of the push <span class="smcap">P</span> is pressed, the current in
+the main circuit flows from the positive pole <span class="smcap">C</span> of the
+battery <span class="smcap">D</span> through the relay coil <i>a</i>, and thence by
+the wire <i>d</i> and push <span class="smcap">P</span>, to the zinc of the battery.
+This attracts the armature <span class="smcap">A</span> of the relay <span class="smcap">R</span>, closing the
+local bell circuit, the current flowing from <span class="smcap">C</span> of the
+battery to armature <span class="smcap">A</span> of the relay <span class="smcap">R</span>, through contact
+post <i>p</i>, terminal <span class="smcap">L</span> of the bell, through bell to terminal
+<span class="smcap">Z</span>, and thence by the wire <i>g</i> to the zinc of the battery.
+Part of the current also flows along the wire from the
+bell terminal <span class="smcap">L</span> through the relay coil <i>b</i> and switch <span class="smcap">W</span>,
+to terminal <span class="smcap">Z</span> of the bell, thus keeping the armature<!-- Page 100 --><span class="pagenum"><a name="Page_100" id="Page_100">[Pg 100]</a></span>
+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 <span class="smcap">W</span> 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 <span class="smcap">W</span>, 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 <a href="#FIG_40">Fig. 40</a>, 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."</p>
+
+<div class="figright" style="width: 220px;">
+<a name="FIG_40A" id="FIG_40A"></a>
+<img src="images/i_110.png" width="220" height="400" alt="Fig. 40 A." title="Thorpe's arrangement" />
+<p class="caption">Fig. 40 A.</p>
+</div>
+
+<p>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 <a href="#FIG_40A">Fig. 40 <span class="smcap">A</span></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<!-- Page 101 --><span class="pagenum"><a name="Page_101" id="Page_101">[Pg 101]</a></span>
+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.</p>
+
+
+<p><a name="SEC_49" id="SEC_49"></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 <a href="#FIG_41">Fig. 41</a>.</p>
+
+<hr />
+
+<div class="figcenter" style="width: 332px;">
+<a name="FIG_41" id="FIG_41"></a>
+<img src="images/i_111.png" width="332" height="400" alt="Fig. 41." title="Jensen bell, section" />
+<p class="caption">Fig. 41.</p>
+</div>
+
+<p>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,<!-- Page 102 --><span class="pagenum"><a name="Page_102" id="Page_102">[Pg 102]</a></span>
+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.</p>
+
+<p>The form of the magnet is such that a considerable<!-- Page 103 --><span class="pagenum"><a name="Page_103" id="Page_103">[Pg 103]</a></span>
+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.</p>
+
+<p>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.</p>
+
+<div class="figcenter" style="width: 327px;">
+<a name="FIG_42" id="FIG_42"></a>
+<img src="images/i_113.png" width="327" height="400" alt="Fig. 42." title="Jensen bell, exterior" />
+<p class="caption">Fig. 42.</p>
+</div>
+
+<p>The great point of departure is the discarding of
+the unsightly magnet box, and the hemispherical bell
+(<i>see</i> <a href="#FIG_32">Fig. 32</a>), and substituting a bell of the Church
+type (see <a href="#FIG_42">Fig. 42</a>), 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<!-- Page 105 --><span class="pagenum"><a name="Page_105" id="Page_105">[Pg 105]</a></span><!-- Page 104 --><span class="pagenum"><a name="Page_104" id="Page_104">[Pg 104]</a></span>
+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.</p>
+
+
+<p><a name="SEC_50" id="SEC_50"></a>§ 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,<!-- Page 106 --><span class="pagenum"><a name="Page_106" id="Page_106">[Pg 106]</a></span>
+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 <i>single stroke</i>
+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. <a href="#FIG_43A">43 <span class="smcap">A</span></a> and <a href="#FIG_43B"><span class="smcap">B</span></a>, where the exterior and interior of
+such a bell are shown.</p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_43A" id="FIG_43A"></a>
+<img src="images/i_115a.png" width="400" height="299" alt="Fig. 43 A." title="Circular bell" />
+<p class="caption">Fig. 43 A.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_43B" id="FIG_43B"></a>
+<img src="images/i_115b.png" width="400" height="345" alt="Fig. 43 B." title="Mining bell" />
+<p class="caption">Fig. 43 B.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_44" id="FIG_44"></a>
+<img src="images/i_116.png" width="400" height="362" alt="Fig. 44." title="Electric trumpet (Binswanger's)" />
+<p class="caption">Fig. 44.</p>
+</div>
+
+
+<p><a name="SEC_51" id="SEC_51"></a>§ 51. In the "Electric Trumpet," introduced by
+Messrs. Binswanger, of the General Electric Company,
+we have a very novel and effective arrangement of<!-- Page 107 --><span class="pagenum"><a name="Page_107" id="Page_107">[Pg 107]</a></span>
+the parts of an electric bell and telephone together.
+This instrument, along with its battery, line and push,
+is illustrated at <a href="#FIG_44">Fig. 44</a>, where <span class="smcap">A</span> is a hollow brass
+cylinder, in which is placed an ordinary electro-magnet
+similar to <a href="#FIG_20">Figs. 20</a> or <a href="#FIG_20A">20 <span class="smcap">A</span></a>. At the front end, near <span class="smcap">B</span>, is
+affixed by its edges a thin disc of sheet iron, precisely
+as in the Bell telephone,<a name="FNanchor_14_14" id="FNanchor_14_14"></a><a href="#Footnote_14_14" class="fnanchor">[14]</a> and over against it, at <span class="smcap">B</span>, 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<!-- Page 108 --><span class="pagenum"><a name="Page_108" id="Page_108">[Pg 108]</a></span>
+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 <span class="smcap">B</span>; 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.</p>
+
+
+<p><a name="SEC_52" id="SEC_52"></a>§ 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.</p>
+
+<div class="footnote"><p><a name="Footnote_10_10" id="Footnote_10_10"></a><a href="#FNanchor_10_10"><span class="label">[10]</span></a> "Amateur Work."</p></div>
+
+<div class="footnote"><p><a name="Footnote_11_11" id="Footnote_11_11"></a><a href="#FNanchor_11_11"><span class="label">[11]</span></a> <i>Insula</i> 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.</p></div>
+
+<div class="footnote"><p><a name="Footnote_12_12" id="Footnote_12_12"></a><a href="#FNanchor_12_12"><span class="label">[12]</span></a> 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.</p></div>
+
+<div class="footnote"><p><a name="Footnote_13_13" id="Footnote_13_13"></a><a href="#FNanchor_13_13"><span class="label">[13]</span></a> Described at <a href="#SEC_61">§ 61</a>.</p></div>
+
+<div class="footnote"><p><a name="Footnote_14_14" id="Footnote_14_14"></a><a href="#FNanchor_14_14"><span class="label">[14]</span></a> See "Electrical Instrument Making for Amateurs." Whittaker &amp; Co.
+Second edition.</p></div>
+
+
+
+<hr class="long" />
+<p><!-- Page 109 --><span class="pagenum"><a name="Page_109" id="Page_109">[Pg 109]</a></span></p>
+<h2><a name="CHAPTER_IV" id="CHAPTER_IV"></a>CHAPTER IV.
+<br />
+ON CONTACTS, PUSHES, SWITCHES, KEYS, ALARMS,
+AND RELAYS.</h2>
+
+
+<p><a name="SEC_53" id="SEC_53"></a>§ 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 <a href="#FIG_45">Fig. 45</a>, <span class="smcap">A</span>, <span class="smcap">B</span>, <span class="smcap">C</span>,
+<span class="smcap">D</span>, and <span class="smcap">E</span>, 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 &amp; Co.)
+At <span class="smcap">F</span> is a sectional view of one of these pushes, and <span class="smcap">G</span>
+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<!-- Page 110 --><span class="pagenum"><a name="Page_110" id="Page_110">[Pg 110]</a></span>
+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 <a href="#SEC_48">§ 48</a>). In fastening the leading wires to these<!-- Page 111 --><span class="pagenum"><a name="Page_111" id="Page_111">[Pg 111]</a></span>
+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.</p>
+
+<div class="figcenter" style="width: 600px;">
+<a name="FIG_45" id="FIG_45"></a>
+<img src="images/i_119.png" width="600" height="501" alt="Fig. 45." title="Various forms of pushes" />
+<p class="caption">Fig. 45.</p>
+</div>
+
+<hr />
+
+<div class="figright" style="width: 250px;">
+<a name="FIG_46" id="FIG_46"></a>
+<img src="images/i_120.png" width="250" height="400" alt="Fig. 46." title="Pressel" />
+<p class="caption">Fig. 46.</p>
+</div>
+
+
+<p><a name="SEC_54" id="SEC_54"></a>§ 54. A "pressel" (<a href="#FIG_46">Fig. 46</a>) 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.</p>
+
+<hr />
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_47" id="FIG_47"></a>
+<img src="images/i_121.png" width="400" height="293" alt="Fig. 47." title="Pull" />
+<p class="caption">Fig. 47.</p>
+</div>
+
+<hr />
+
+<div class="figright" style="width: 127px;">
+<a name="FIG_48" id="FIG_48"></a>
+<img src="images/i_122.png" width="127" height="400" alt="Fig. 48." title="Bedroom pull" />
+<p class="caption">Fig. 48.</p>
+</div>
+
+<p><a name="SEC_55" id="SEC_55"></a>§ 55. The "pull" (<a href="#FIG_47">Fig. 47</a>), as its name implies,
+makes contact and rings the bell on being pulled. The<!-- Page 112 --><span class="pagenum"><a name="Page_112" id="Page_112">[Pg 112]</a></span>
+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, <i>a a'</i>, by
+the screws <i>b b'</i>. 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 <a href="#FIG_48">Fig. 48</a>. 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 <a href="#FIG_49A">Fig. 49 <span class="smcap">A</span></a>. In
+all these contacts, except the door pull (<a href="#FIG_47">Fig. 47</a>) where
+the friction of the action of pulling keeps the surfaces<!-- Page 113 --><span class="pagenum"><a name="Page_113" id="Page_113">[Pg 113]</a></span>
+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 <a href="#FIG_49B">Fig. 49 <span class="smcap">B</span></a>.</p>
+
+<div class="figcenter" style="width: 395px;">
+<a name="FIG_49A" id="FIG_49A"></a>
+<img src="images/i_123a.png" width="395" height="400" alt="Fig. 49 A." title="Bedroom pull Another form" />
+<p class="caption">Fig. 49 A.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_49B" id="FIG_49B"></a>
+<img src="images/i_123b.png" width="400" height="76" alt="Fig. 49 B." title="Floor contact, ball form" />
+<p class="caption">Fig. 49 B.</p>
+</div>
+
+<p>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 <a href="#FIG_43A">Fig.
+43 <span class="smcap">A</span></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.</p>
+
+
+<div class="figright" style="width: 120px;">
+<a name="FIG_50" id="FIG_50"></a>
+<img src="images/i_124a.png" width="120" height="400" alt="Fig. 50." title="Burglar alarm" />
+<p class="caption">Fig. 50.</p>
+</div>
+
+<p><a name="SEC_56" id="SEC_56"></a>§ 56. The next form of contact
+to which our attention must be
+directed, is that known as the <i>burglar alarm</i>, with
+its variant of door-contacts, sash-contacts, till-contacts,
+etc.</p>
+
+<p>The "burglar's pest" (as the contrivance we illustrate
+is called) is one of the most useful applications of<!-- Page 114 --><span class="pagenum"><a name="Page_114" id="Page_114">[Pg 114]</a></span>
+electricity for the protection of property against thieves.
+It consists usually, first, of a brass plate (<a href="#FIG_50">Fig. 50</a>), 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 <a href="#FIG_51">Fig. 51</a>). 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<!-- Page 115 --><span class="pagenum"><a name="Page_115" id="Page_115">[Pg 115]</a></span>
+fixed in the master's bedroom, or outside the premises
+in the street.</p>
+
+<div class="figcenter" style="width: 376px;">
+<a name="FIG_51" id="FIG_51"></a>
+<img src="images/i_124b.png" width="376" height="400" alt="Fig. 51." title="Burglar alarm Another form" />
+<p class="caption">Fig. 51.</p>
+</div>
+
+<div class="figright" style="width: 223px;">
+<a name="FIG_52" id="FIG_52"></a>
+<img src="images/i_124c.png" width="223" height="400" alt="Fig. 52." title="Floor contact" />
+<p class="caption">Fig. 52.</p>
+</div>
+
+<p>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.</p>
+
+<p>A form of floor contact, which may be placed under a
+light mat or carpet, illustrated at <a href="#FIG_52">Fig. 52</a>, 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 <a href="#SEC_48">§ 48</a>). Wherever it
+is likely that these arrangements may stand a long time<!-- Page 116 --><span class="pagenum"><a name="Page_116" id="Page_116">[Pg 116]</a></span>
+without being called into play, it is better to employ
+some form of contact in which a <i>rubbing</i> action (which
+tends to clean the surfaces and then make a good contact)
+is brought into play, rather than a merely <i>dotting</i>
+action. For this reason, spring contacts in which the
+springs connected with the wires are kept apart by an
+insulating wedge (shown at <a href="#FIG_53">Fig. 53</a>) 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 <i>a</i> and <i>a'</i> in the sash itself, as shown at <a href="#FIG_54">Fig. 54</a>.
+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 <a href="#FIG_55">Fig. 55</a> is well adapted. It
+consists, as will be seen, in a peculiarly shaped pivoted
+trigger <i>a</i>, which is lifted forwards when the door is
+opened, so that it makes contact with the spring <i>b</i>.
+Owing to the curved shape of the arm of the<!-- Page 117 --><span class="pagenum"><a name="Page_117" id="Page_117">[Pg 117]</a></span>
+trigger, the contact is not repeated when the door is
+closed.</p>
+
+<div class="figcenter" style="width: 260px;">
+<a name="FIG_53" id="FIG_53"></a>
+<img src="images/i_125.png" width="260" height="400" alt="Fig. 53." title="Door contact" />
+<p class="caption">Fig. 53.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 365px;">
+<a name="FIG_54" id="FIG_54"></a>
+<img src="images/i_126a.png" width="365" height="400" alt="Fig. 54." title="Sash contact" />
+<p class="caption">Fig. 54.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_55" id="FIG_55"></a>
+<img src="images/i_126b.png" width="400" height="119" alt="Fig. 55." title="Shop door contact" />
+<p class="caption">Fig. 55.</p>
+</div>
+
+
+<p><a name="SEC_57" id="SEC_57"></a>§ 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 "<i>notre ami l'ennemi</i>," 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<!-- Page 118 --><span class="pagenum"><a name="Page_118" id="Page_118">[Pg 118]</a></span>
+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 <i>English Mechanic</i>, by one of our leading
+electricians:&mdash;</p>
+
+<p>Writing on the subject of Closed Circuit Bell-ringing,
+Mr. Perren Maycock says:&mdash;"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
+<i>seen</i> than <i>hidden</i>. 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<!-- Page 119 --><span class="pagenum"><a name="Page_119" id="Page_119">[Pg 119]</a></span>
+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.</p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_56A" id="FIG_56A"></a>
+<img src="images/i_128a.png" width="400" height="367" alt="Fig. 56 A." title="Closed circuit system, single" />
+<p class="caption">Fig. 56 A.</p>
+</div>
+
+<p><a href="#FIG_56A">Fig. 56 <span class="smcap">A</span></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.<!-- Page 120 --><span class="pagenum"><a name="Page_120" id="Page_120">[Pg 120]</a></span>
+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.</p>
+
+<div class="figcenter" style="width: 600px;">
+<a name="FIG_56B" id="FIG_56B"></a>
+<img src="images/i_128b.png" width="600" height="229" alt="Fig. 56 B." title="Closed circuit system, double" />
+<p class="caption">Fig. 56 B.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 600px;">
+<a name="FIG_57" id="FIG_57"></a>
+<img src="images/i_129.png" width="600" height="395" alt="Fig. 57." title="Modified gravity, Daniell" />
+<p class="caption">Fig. 57.</p>
+</div>
+
+<p><a href="#FIG_56B">Fig. 56 <span class="smcap">B</span></a> 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
+(<a href="#SEC_25">§ 25</a>) is used for this class of work (<a href="#FIG_57">Fig. 57</a>): 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<!-- Page 121 --><span class="pagenum"><a name="Page_121" id="Page_121">[Pg 121]</a></span>
+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 <i>paint</i> that portion of the lead,
+which is surrounded by the acid. The height of the
+cell is about 14."</p>
+
+<p>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 <a href="#FIG_58">Fig. 58</a>.</p>
+
+<p>Contacts similar to Figs. <a href="#FIG_50">50</a>, <a href="#FIG_53">53</a> and <a href="#FIG_54">54</a>, may be fitted
+on tills or drawers.</p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_58" id="FIG_58"></a>
+<img src="images/i_130.png" width="400" height="227" alt="Fig. 58." title="Contact for closed circuit" />
+<p class="caption">Fig. 58.</p>
+</div>
+
+
+<div class="figright" style="width: 124px;">
+<a name="FIG_59" id="FIG_59"></a>
+<img src="images/i_131.png" width="124" height="400" alt="Fig. 59." title="Thermometer alarm" />
+<p class="caption">Fig. 59.</p>
+</div>
+
+<p><a name="SEC_58" id="SEC_58"></a>§ 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 <a href="#FIG_59">Fig. 59</a>. It consists in an<!-- Page 122 --><span class="pagenum"><a name="Page_122" id="Page_122">[Pg 122]</a></span>
+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.</p>
+
+<p>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 <i>vice versâ</i>, in the
+houses under their charge.</p>
+
+<p>Other forms of fire alarms are shown
+at Fig. <a href="#FIG_60">60</a> and <a href="#FIG_61">61</a>. 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 <i>right</i>
+if heated, and to the <i>left</i> if cooled.
+In the instrument shown at <a href="#FIG_60">Fig. 60</a>, the application of
+heat causes the flexible strip carrying the contact screw,
+to bend over till it touches the lower stop, when, of<!-- Page 123 --><span class="pagenum"><a name="Page_123" id="Page_123">[Pg 123]</a></span>
+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.</p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_60" id="FIG_60"></a>
+<img src="images/i_132a.png" width="400" height="84" alt="Fig. 60." title="Fire alarm" />
+<p class="caption">Fig. 60.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 394px;">
+<a name="FIG_61" id="FIG_61"></a>
+<img src="images/i_132b.png" width="394" height="400" alt="Fig. 61." title="Fire alarm Another form and (below) in action" />
+<p class="caption">Fig. 61.</p>
+</div>
+
+<p>At <a href="#FIG_61">Fig. 61</a> 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<!-- Page 124 --><span class="pagenum"><a name="Page_124" id="Page_124">[Pg 124]</a></span>
+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.</p>
+
+
+<p><a name="SEC_59" id="SEC_59"></a>§ 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 <a href="#FIG_62">Fig. 62</a> (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.</p>
+
+<div class="figcenter" style="width: 317px;">
+<a name="FIG_62" id="FIG_62"></a>
+<img src="images/i_134.png" width="317" height="400" alt="Fig. 62." title="Binswanger's &quot;watch alarm&quot; contact" />
+<p class="caption">Fig. 62.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 278px;">
+<a name="FIG_63" id="FIG_63"></a>
+<img src="images/i_135.png" width="278" height="400" alt="Fig. 63." title="Watchman's electric tell-tale clock" />
+<p class="caption">Fig. 63.</p>
+</div>
+
+<p>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 <a href="#FIG_63">Fig. 63</a>. We quote
+Messrs. Gent's own words, in the following description:&mdash;</p>
+
+<p>"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<!-- Page 125 --><span class="pagenum"><a name="Page_125" id="Page_125">[Pg 125]</a></span>
+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&mdash;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<!-- Page 126 --><span class="pagenum"><a name="Page_126" id="Page_126">[Pg 126]</a></span>
+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.</p>
+
+<p>"The clock may be in the office or bedroom of the<!-- Page 127 --><span class="pagenum"><a name="Page_127" id="Page_127">[Pg 127]</a></span>
+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.</p>
+
+<p>"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.</p>
+
+<p>"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."</p>
+
+
+<p><a name="SEC_60" id="SEC_60"></a>§ 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>i.e.</i>, 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.</p>
+
+<div class="figcenter" style="width: 373px;">
+<a name="FIG_64" id="FIG_64"></a>
+<img src="images/i_137.png" width="373" height="400" alt="Fig. 64." title="Lever switch, two-way" />
+<p class="caption">Fig. 64.</p>
+</div>
+
+
+<p><a name="SEC_61" id="SEC_61"></a>§ 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<!-- Page 128 --><span class="pagenum"><a name="Page_128" id="Page_128">[Pg 128]</a></span>
+circuit altogether. The arrangements by which this can
+be effected, are known as "switches." Of switches there
+are two kinds, namely, <i>plugswitches</i> or <i>interruptors</i>, and
+<i>lever switches</i>. 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 <a href="#FIG_64">Fig. 64</a>. 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<!-- Page 129 --><span class="pagenum"><a name="Page_129" id="Page_129">[Pg 129]</a></span>
+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.</p>
+
+
+<p><a name="SEC_62" id="SEC_62"></a>§ 62. A <i>key</i> 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
+<a href="#FIG_65">Fig. 65</a>, 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 <i>No</i>, and a short one for
+<i>Yes</i>, 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<!-- Page 130 --><span class="pagenum"><a name="Page_130" id="Page_130">[Pg 130]</a></span>
+than quote his instructions, as given in <i>Amateur
+Work</i>:&mdash;</p>
+
+<p>"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.&mdash;</p>
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="Morse telegraph code">
+<tr><td align="left">A</td><td align="left">&ndash;&nbsp;&mdash;&nbsp;</td></tr>
+<tr><td align="left">B</td><td align="left">&mdash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;</td></tr>
+<tr><td align="left">C</td><td align="left">&mdash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;&ndash;&nbsp;</td></tr>
+<tr><td align="left">D</td><td align="left">&mdash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;</td></tr>
+<tr><td align="left">E</td><td align="left">&ndash;&nbsp;</td></tr>
+<tr><td align="left">F</td><td align="left">&ndash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;&ndash;&nbsp;</td></tr>
+<tr><td align="left">G</td><td align="left">&mdash;&nbsp;&mdash;&nbsp;&ndash;&nbsp;</td></tr>
+<tr><td align="left">H</td><td align="left">&ndash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;</td></tr>
+<tr><td align="left">I</td><td align="left">&ndash;&nbsp;&ndash;&nbsp;</td></tr>
+<tr><td align="left">J</td><td align="left">&ndash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;</td></tr>
+<tr><td align="left">K</td><td align="left">&mdash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;</td></tr>
+<tr><td align="left">L</td><td align="left">&ndash;&nbsp;&mdash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;</td></tr>
+<tr><td align="left">M</td><td align="left">&mdash;&nbsp;&mdash;</td></tr>
+<tr><td align="left">N</td><td align="left">&mdash;&nbsp;&ndash;&nbsp;</td></tr>
+<tr><td align="left">O</td><td align="left">&mdash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;</td></tr>
+<tr><td align="left">P</td><td align="left">&ndash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;&ndash;&nbsp;</td></tr>
+<tr><td align="left">Q</td><td align="left">&mdash;&nbsp;&mdash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;</td></tr>
+<tr><td align="left">R</td><td align="left">&ndash;&nbsp;&mdash;&nbsp;&ndash;&nbsp;</td></tr>
+<tr><td align="left">S</td><td align="left">&ndash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;</td></tr>
+<tr><td align="left">T</td><td align="left">&mdash;&nbsp;</td></tr>
+<tr><td align="left">U</td><td align="left">&ndash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;</td></tr>
+<tr><td align="left">V</td><td align="left">&ndash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;</td></tr>
+<tr><td align="left">W</td><td align="left">&ndash;&nbsp;&mdash;&nbsp;&mdash;</td></tr>
+<tr><td align="left">X</td><td align="left">&mdash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;</td></tr>
+<tr><td align="left">Y</td><td align="left">&mdash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;&mdash;</td></tr>
+<tr><td align="left">Z</td><td align="left">&mdash;&nbsp;&mdash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;</td></tr>
+<tr><td align="left">Ch</td><td align="left">&mdash;&nbsp;&mdash;&nbsp;&mdash;</td></tr>
+<tr><td align="left">Ä (æ)</td><td align="left">&ndash;&nbsp;&mdash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;</td></tr>
+<tr><td align="left">Ö (œ)</td><td align="left">&mdash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;&ndash;&nbsp;</td></tr>
+<tr><td align="left">Ü (ue)</td><td align="left">&ndash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;&mdash;</td></tr>
+<tr><td align="left">1</td><td align="left">&ndash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;&mdash;</td></tr>
+<tr><td align="left">2</td><td align="left">&ndash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;</td></tr>
+<tr><td align="left">3</td><td align="left">&ndash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;&mdash;</td></tr>
+<tr><td align="left">4</td><td align="left">&ndash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;</td></tr>
+<tr><td align="left">5</td><td align="left">&ndash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;</td></tr>
+<tr><td align="left">6</td><td align="left">&mdash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;</td></tr>
+<tr><td align="left">7</td><td align="left">&mdash;&nbsp;&mdash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;</td></tr>
+<tr><td align="left">8</td><td align="left">&mdash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;</td></tr>
+<tr><td align="left">9</td><td align="left">&mdash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;&ndash;&nbsp;</td></tr>
+<tr><td align="left">0</td><td align="left">&mdash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;</td></tr>
+</table></div>
+
+
+<p>"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<!-- Page 131 --><span class="pagenum"><a name="Page_131" id="Page_131">[Pg 131]</a></span>
+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:&mdash;</p>
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="Morse telegraph punctuation marks">
+<tr><td align="left">Comma</td><td align="left">(,)</td><td align="center">by</td><td align="left">A A A</td><td align="center">or</td><td align="left">&ndash;&nbsp;&mdash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;&ndash;&nbsp;&mdash;</td></tr>
+<tr><td align="left">Full stop</td><td align="left">(.)</td><td align="center">"</td><td align="left">I I I</td><td align="center">"</td><td align="left">&ndash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&ndash;</td></tr>
+<tr><td align="left">Interrogation</td><td align="left">(?)</td><td align="center">"</td><td align="left">U D</td><td align="center">"</td><td align="left">&ndash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;</td></tr>
+<tr><td align="left">Hyphen</td><td align="left">(-)</td><td align="center">"</td><td align="left">B A</td><td align="center">"</td><td align="left">&mdash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;</td></tr>
+<tr><td align="left">Apostrophe</td><td align="left">(')</td><td align="center">"</td><td align="left">W G</td><td align="center">"</td><td align="left">&ndash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;&ndash;&nbsp;</td></tr>
+<tr><td align="left">Inverted commas</td><td align="left">(")</td><td align="center">"</td><td align="left">A F</td><td align="center">"</td><td align="left">&ndash;&nbsp;&mdash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;&ndash;</td></tr>
+<tr><td align="left">Parenthesis</td><td align="left">(&nbsp;)</td><td align="center">"</td><td align="left">K K</td><td align="center">"</td><td align="left">&mdash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;&ndash;&nbsp;&mdash;</td></tr>
+<tr><td align="left">Semi-colon</td><td align="left">(;)</td><td align="center">"</td><td align="left">K Ch</td><td align="center">"</td><td align="left">&ndash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;&mdash;</td></tr>
+<tr><td align="left">Surprise</td><td align="left">(!)</td><td align="center">"</td><td align="left">N Ch</td><td align="center">"</td><td align="left">&mdash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;&mdash;</td></tr>
+<tr><td align="left">Colon</td><td align="left">(:)</td><td align="center">"</td><td align="left">I Ch</td><td align="center">"</td><td align="left">&ndash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;&mdash;&nbsp;</td></tr>
+</table></div>
+
+
+<p>"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
+<i>one</i>, and the dashes by <i>two</i>, 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 <i>three</i>, the space between a word and a stop
+being of the same duration. To make this more clear<!-- Page 132 --><span class="pagenum"><a name="Page_132" id="Page_132">[Pg 132]</a></span>
+I give an example. The mistress signals to her coachman:&mdash;</p>
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="display of Morse code message">
+<tr><td align="center" class="br">G</td><td align="center" class="br">E</td><td align="center" class="br">T</td><td align="center" class="br">&nbsp;</td><td align="center" class="br">T</td><td align="center" class="br">H</td><td align="center" class="br">E</td></tr>
+<tr><td align="center" class="br">&mdash;&nbsp;&mdash;&nbsp;&ndash;</td><td align="center" class="br">&ndash;</td><td align="center" class="br">&mdash;</td><td align="center" class="br">&nbsp;</td><td align="center" class="br">&mdash;</td><td align="center" class="br">&ndash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&ndash;</td><td align="center" class="br">&ndash;</td></tr>
+<tr><td align="center" class="br">2&nbsp;2&nbsp;1</td><td align="center" class="br">1</td><td align="center" class="br">2</td><td align="center" class="br">3</td><td align="center" class="br">2</td><td align="center" class="br">1&nbsp;1&nbsp;1&nbsp;1</td><td align="center" class="br">1</td><td align="center">3</td></tr>
+</table></div>
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td>&nbsp;</td></tr>
+<tr><td align="center" class="br">C</td><td align="center" class="br">A</td><td align="center" class="br">R</td><td align="center" class="br">R</td><td align="center" class="br">I</td><td align="center" class="br">A</td><td align="center" class="br">G</td><td align="center" class="br">E</td></tr>
+<tr><td align="center" class="br">&mdash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;&ndash;</td><td align="center" class="br">&ndash;&nbsp;&mdash;</td><td align="center" class="br">&ndash;&nbsp;&mdash;&nbsp;&ndash;</td><td align="center" class="br">&ndash;&nbsp;&mdash;&nbsp;&ndash;</td><td align="center" class="br">&ndash;&nbsp;&ndash;</td><td align="center" class="br">&ndash;&nbsp;&mdash;</td><td align="center" class="br">&mdash;&nbsp;&mdash;&nbsp;&ndash;</td><td align="center" class="br">&ndash;</td></tr>
+<tr><td align="center" class="br">2&nbsp;1&nbsp;2&nbsp;1</td><td align="center" class="br">1&nbsp;2</td><td align="center" class="br">1&nbsp;2&nbsp;1</td><td align="center" class="br">1&nbsp;2&nbsp;1</td><td align="center" class="br">1&nbsp;1</td><td align="center" class="br">1&nbsp;2</td><td align="center" class="br">2&nbsp;2&nbsp;1</td><td align="center" class="br">1</td><td align="center">3</td></tr>
+</table></div>
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td>&nbsp;</td></tr>
+<tr><td align="center" class="br">R</td><td align="center" class="br">E</td><td align="center" class="br">A</td><td align="center" class="br">D</td><td align="center">Y</td></tr>
+<tr><td align="center" class="br">&ndash;&nbsp;&mdash;&nbsp;&ndash;</td><td align="center" class="br">&ndash;</td><td align="center" class="br">&ndash;&nbsp;&mdash;</td><td align="center" class="br">&mdash;&nbsp;&ndash;&nbsp;&ndash;</td><td align="center">&mdash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;&mdash;</td></tr>
+<tr><td align="center" class="br">1&nbsp;2&nbsp;1</td><td align="center" class="br">1</td><td align="center" class="br">1&nbsp;2</td><td align="center" class="br">2&nbsp;1&nbsp;1</td><td align="center">2&nbsp;1&nbsp;2&nbsp;2</td></tr>
+</table></div>
+
+
+<p>"The coachman replies:&mdash;</p>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td>&nbsp;</td></tr>
+<tr><td align="center" class="br">R</td><td align="center" class="br">E</td><td align="center" class="br">A</td><td align="center" class="br">D</td><td align="center">Y</td></tr>
+<tr><td align="center" class="br">&ndash;&nbsp;&mdash;&nbsp;&ndash;</td><td align="center" class="br">&ndash;</td><td align="center" class="br">&ndash;&nbsp;&mdash;</td><td align="center" class="br">&mdash;&nbsp;&ndash;&nbsp;&ndash;</td><td align="center">&mdash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;&mdash;</td></tr>
+<tr><td align="center" class="br">1&nbsp;2&nbsp;1</td><td align="center" class="br">1</td><td align="center" class="br">1&nbsp;2</td><td align="center" class="br">2&nbsp;1&nbsp;1</td><td align="center">2&nbsp;1&nbsp;2&nbsp;2</td></tr>
+</table></div>
+
+<p>"When the mistress is ready she signals:&mdash;</p>
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="center" class="br">B</td><td align="center" class="br">R</td><td align="center" class="br">I</td><td align="center" class="br">N</td><td align="center" class="br">G</td><td align="center" class="br">&nbsp;</td><td align="center" class="br">T</td><td align="center" class="br">H</td><td align="center" class="br">E</td></tr>
+<tr><td align="center" class="br">&mdash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&ndash;</td><td align="center" class="br">&ndash;&nbsp;&mdash;&nbsp;&ndash;</td><td align="center" class="br">&ndash;&nbsp;&ndash;</td><td align="center" class="br">&mdash;&nbsp;&ndash;</td><td align="center" class="br">&mdash;&nbsp;&mdash;&nbsp;&ndash;</td><td align="center" class="br">&nbsp;</td><td align="center" class="br">&mdash;</td><td align="center" class="br">&ndash;&nbsp;&ndash;&nbsp;&ndash;&nbsp;&ndash;</td><td align="center" class="br">&ndash;</td></tr>
+<tr><td align="center" class="br">2&nbsp;1&nbsp;1&nbsp;1</td><td align="center" class="br">1&nbsp;2&nbsp;1</td><td align="center" class="br">1&nbsp;1</td><td align="center" class="br">2&nbsp;1</td><td align="center" class="br">2&nbsp;2&nbsp;1</td><td align="center" class="br">3</td><td align="center" class="br">2</td><td align="center" class="br">1&nbsp;1&nbsp;1&nbsp;1</td><td align="center" class="br">1</td><td align="center">3</td></tr>
+</table></div>
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td>&nbsp;</td></tr>
+<tr><td align="center" class="br">C</td><td align="center" class="br">A</td><td align="center" class="br">R</td><td align="center" class="br">R</td><td align="center" class="br">I</td><td align="center" class="br">A</td><td align="center" class="br">G</td><td align="center" class="br">E</td></tr>
+<tr><td align="center" class="br">&mdash;&nbsp;&ndash;&nbsp;&mdash;&nbsp;&ndash;</td><td align="center" class="br">&ndash;&nbsp;&mdash;</td><td align="center" class="br">&ndash;&nbsp;&mdash;&nbsp;&ndash;</td><td align="center" class="br">&ndash;&nbsp;&mdash;&nbsp;&ndash;</td><td align="center" class="br">&ndash;&nbsp;&ndash;</td><td align="center" class="br">&ndash;&nbsp;&mdash;</td><td align="center" class="br">&mdash;&nbsp;&mdash;&nbsp;&ndash;</td><td align="center" class="br">&ndash;</td></tr>
+<tr><td align="center" class="br">2&nbsp;1&nbsp;2&nbsp;1</td><td align="center" class="br">1&nbsp;2</td><td align="center" class="br">1&nbsp;2&nbsp;1</td><td align="center" class="br">1&nbsp;2&nbsp;1</td><td align="center" class="br">1&nbsp;1</td><td align="center" class="br">1&nbsp;2</td><td align="center" class="br">2&nbsp;2&nbsp;1</td><td align="center" class="br">1</td></tr>
+</table></div>
+
+<p>"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 &ndash; when the word is understood, or the
+double short signal I &ndash;&nbsp;&ndash; when the word is not understood.
+A negative reply to a question may be given by the<!-- Page 133 --><span class="pagenum"><a name="Page_133" id="Page_133">[Pg 133]</a></span>
+signal for N &mdash;&nbsp;&ndash;, and an affirmative by the signal for
+Æ &ndash;&nbsp;&mdash;&nbsp;&ndash;&nbsp;&mdash;; 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."</p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_65" id="FIG_65"></a>
+<img src="images/i_142.png" width="400" height="240" alt="Fig. 65." title="Morse key, double contact" />
+<p class="caption">Fig. 65.</p>
+</div>
+
+
+<p><a name="SEC_63" id="SEC_63"></a>§ 63. At <a href="#SEC_48">§ 48</a>, we
+noticed that a device
+known as a <i>Relay</i> 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 <i>his</i> bell, by means, say, of a key similar
+to that shown at <a href="#FIG_65">Fig. 65</a>, 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.<!-- Page 134 --><span class="pagenum"><a name="Page_134" id="Page_134">[Pg 134]</a></span>
+But this would require a person constantly in attendance.
+Now the <i>relay</i> does this automatically; it <i>relays</i>
+another battery in the circuit. The manner in which
+it effects this will be rendered clear, on examination of
+<a href="#FIG_66">Fig. 66</a>. Here we have an armature <span class="smcap">A</span> attached to a
+light spring, which can play between an insulated stop
+<span class="smcap">C</span>, and a contact screw <span class="smcap">B</span>. The play of this armature
+can be regulated to a nicety by turning the screws
+<span class="smcap">B</span> or <span class="smcap">C</span>. These two screws are both borne by a double
+bent arm (of metal) affixed
+to the pillar <span class="smcap">D</span>. 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 <span class="smcap">E</span> to <span class="smcap">D</span>, unless the
+armature be pulled down
+so as to make contact with
+the contact screw <span class="smcap">B</span>. Just
+under the armature, stands
+the electro-magnet <span class="smcap">G</span>, which when energised can and does
+pull down the armature <span class="smcap">A</span>. It will be readily understood
+that if we connect the wires from the electro-magnet <span class="smcap">G</span>,
+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 <span class="smcap">C</span> and <span class="smcap">B</span>; so that if the screws <span class="smcap">D</span> and <span class="smcap">E</span> are
+connected respectively to the free terminals of a<!-- Page 135 --><span class="pagenum"><a name="Page_135" id="Page_135">[Pg 135]</a></span>
+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 <i>local</i> 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 <i>series</i>. 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.</p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_66" id="FIG_66"></a>
+<img src="images/i_143.png" width="400" height="352" alt="Fig. 66." title="Relay" />
+<p class="caption">Fig. 66.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 370px;">
+<a name="FIG_67" id="FIG_67"></a>
+<img src="images/i_146.png" width="370" height="400" alt="Fig. 67." title="Indicator, drop" />
+<p class="caption">Fig. 67.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 367px;">
+<a name="FIG_68" id="FIG_68"></a>
+<img src="images/i_147.png" width="367" height="400" alt="Fig. 68." title="Indicator, Semaphore" />
+<p class="caption">Fig. 68.</p>
+</div>
+
+
+<p><a name="SEC_64" id="SEC_64"></a>§ 64. We now have to consider those contrivances
+by means of which it is possible for an attendant to<!-- Page 136 --><span class="pagenum"><a name="Page_136" id="Page_136">[Pg 136]</a></span>
+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 <i>indicators</i>.
+Indicators may be conveniently divided into 3 classes,
+viz.:&mdash;1st, indicators with <i>mechanical</i> 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 (<a href="#FIG_66">Fig. 66</a>),
+and let him suppose that the pillar <span class="smcap">D</span>, with its accompanying
+rectangle <span class="smcap">B C</span>, were removed, leaving only
+the electro-magnet <span class="smcap">G</span>, with its frame and armature <span class="smcap">A</span>.
+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. <a href="#FIG_67">Fig. 67</a> 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<!-- Page 137 --><span class="pagenum"><a name="Page_137" id="Page_137">[Pg 137]</a></span>
+ingenious application of the same principle in a very
+compact form. In this (<a href="#FIG_68">Fig. 68</a>), 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 <a href="#FIG_69">Fig 69</a>. Here we have an
+ordinary electro-magnet <span class="smcap">A</span>, with its wires <i>w</i> <i>w'</i> standing
+over an armature <span class="smcap">B</span> attached to a spring <span class="smcap">C</span>, which bears
+on its lower extremity, a toothed projection which
+serves to hold up the short arm of the bent lever <span class="smcap">D</span>,
+which supports the number plate <span class="smcap">E</span>. When the electro-magnet
+<span class="smcap">A</span> is energised by the current, it pulls up the
+armature <span class="smcap">B</span>, which releases the detent <span class="smcap">D</span> from the
+tooth <span class="smcap">C</span>; the number plate therefore falls forwards, as<!-- Page 138 --><span class="pagenum"><a name="Page_138" id="Page_138">[Pg 138]</a></span>
+shown by the dotted lines, and shows itself at the
+aperture <span class="smcap">E´</span>, which is in front of the indicator frame.
+To replace the number out of sight, the attendant
+pushes back the plate <span class="smcap">E</span>, till it again engages the
+bent lever <span class="smcap">D</span> in the tooth <span class="smcap">C</span>. 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<!-- Page 139 --><span class="pagenum"><a name="Page_139" id="Page_139">[Pg 139]</a></span>
+that it must rest against either the one or other pole
+of the electro-magnet below. If the <i>north</i> pole of the
+bar magnet rests against the <i>right</i> 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
+<i>polarity</i> of the bar magnet, are also known as "polarised
+indicators."</p>
+
+<div class="figcenter" style="width: 293px;">
+<a name="FIG_69" id="FIG_69"></a>
+<img src="images/i_148.png" width="293" height="400" alt="Fig. 69." title="Indicator, Fall back" />
+<p class="caption">Fig. 69.</p>
+</div>
+
+<hr />
+
+
+<div class="figright" style="width: 297px;">
+<a name="FIG_70" id="FIG_70"></a>
+<img src="images/i_149.png" width="297" height="400" alt="Fig. 70." title="Indicator, Pendulum" />
+<p class="caption">Fig. 70.</p>
+</div>
+
+<p><a name="SEC_65" id="SEC_65"></a>§ 65. For general efficiency and trustworthiness, the
+<i>pendulum indicator</i>; as shown at <a href="#FIG_70">Fig. 70</a>, is unsurpassed.
+It consists of an electro-magnet with prolongation<!-- Page 140 --><span class="pagenum"><a name="Page_140" id="Page_140">[Pg 140]</a></span>
+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."</p>
+
+<p>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:&mdash;"The objection so<!-- Page 141 --><span class="pagenum"><a name="Page_141" id="Page_141">[Pg 141]</a></span>
+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 <a href="#FIG_70">Fig. 70</a>, 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 <i>patented</i> 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."</p>
+
+<div class="figcenter" style="width: 600px;">
+<a name="FIG_71" id="FIG_71"></a>
+<img src="images/i_151.png" width="600" height="409" alt="Fig. 71." title="Indicator, Coupled up" />
+<p class="caption">Fig. 71.</p>
+</div>
+
+<p>There is only one point that needs further notice<!-- Page 142 --><span class="pagenum"><a name="Page_142" id="Page_142">[Pg 142]</a></span>
+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 <i>local</i> battery. This is shown in <a href="#FIG_71">Fig. 71</a>,
+where a second pair of wires attached to <span class="smcap">C</span> and <span class="smcap">C</span>, 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 <a href="#FIG_71">Fig. 71</a> six pushes are shown to the left of
+the indicator frame. These, of course, are supposed to
+be in as many different rooms.<!-- Page 143 --><span class="pagenum"><a name="Page_143" id="Page_143">[Pg 143]</a></span></p>
+
+<div class="figright" style="width: 336px;">
+<a name="FIG_72" id="FIG_72"></a>
+<img src="images/i_152.png" width="336" height="400" alt="Fig. 72." title="Indicator, Gent's tripolar" />
+<p class="caption">Fig. 72.</p>
+</div>
+
+<p>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. <a href="#FIG_67">67</a> and <a href="#FIG_68">68</a>. 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 <a href="#FIG_72">Fig. 72</a>.</p>
+
+
+
+<hr class="long" />
+<p><!-- Page 144 --><span class="pagenum"><a name="Page_144" id="Page_144">[Pg 144]</a></span></p>
+<h2><a name="CHAPTER_V" id="CHAPTER_V"></a>CHAPTER V.
+<br />
+ON WIRING, CONNECTING UP, AND LOCALISING FAULTS.</h2>
+
+
+<p><a name="SEC_66" id="SEC_66"></a>§ 66. However good may be the bells, indicators,
+batteries, etc., used in an electric bell installation, if the
+<i>wiring</i> 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<!-- Page 145 --><span class="pagenum"><a name="Page_145" id="Page_145">[Pg 145]</a></span>
+practical experience I have found that it is just possible
+to ring a 2&frac12;" bell with &frac12; 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 <a href="#SEC_38">§ 38</a>, 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:&mdash;</p>
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="center">Ohms.</td><td align="center">Volts.</td><td align="center">Ampères.</td></tr>
+<tr><td align="center">2·4)</td><td align="center">1·60</td><td align="center">(0·66,</td></tr>
+</table></div>
+
+
+<p>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<!-- Page 146 --><span class="pagenum"><a name="Page_146" id="Page_146">[Pg 146]</a></span>
+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:&mdash;</p>
+
+<p>Table of Resistance and lengths per lbs.
+        &amp; 100 yards of cotton covered copper wires.</p>
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><th align="right">Birmingham <br />Wire Gauge.</th><th align="right">Diameter in <br />1000th of an inch.</th><th align="center">Yards per lb.</th><th align="center">Ohms. per lb.</th><th align="center">Ohms. per 100 yards.</th></tr>
+<tr><td align="right">No. 12</td><td align="right">100</td><td align="right">9</td><td align="center">0·0342</td><td align="center">0·0038</td></tr>
+<tr><td align="right">14</td><td align="right">80</td><td align="right">15</td><td align="center">0·0850</td><td align="center">0·0094</td></tr>
+<tr><td align="right">16</td><td align="right">62</td><td align="right">24</td><td align="center">0·2239</td><td align="center">0·0249</td></tr>
+<tr><td align="right">18</td><td align="right">48</td><td align="right">41</td><td align="center">0·6900</td><td align="center">0·0766</td></tr>
+<tr><td align="right">20</td><td align="right">41</td><td align="right">59</td><td align="center">1·2100</td><td align="center">0·1333</td></tr>
+<tr><td align="right">22</td><td align="right">32</td><td align="right">109</td><td align="center">3·1000</td><td align="center">0·3444</td></tr>
+</table></div>
+
+
+<p><a name="SEC_67" id="SEC_67"></a>§ 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,<!-- Page 147 --><span class="pagenum"><a name="Page_147" id="Page_147">[Pg 147]</a></span>
+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 <i>leading</i> to
+the bells of a different colour from that on the <i>return</i>
+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 <i>tinned</i> 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<!-- Page 148 --><span class="pagenum"><a name="Page_148" id="Page_148">[Pg 148]</a></span>
+and evenly together, as shown in <a href="#FIG_73">Fig. 73 A</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 &frac14;" thick with a nick filed in its
+upper surface for the wire to lie in (see <a href="#FIG_73">Fig. 73 <span class="smcap">B</span></a>). 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 <i>a</i> and <i>b</i> 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<!-- Page 149 --><span class="pagenum"><a name="Page_149" id="Page_149">[Pg 149]</a></span>
+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.</p>
+
+<p>"That'll do" will not do for electric bell-fitting.</p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_73" id="FIG_73"></a>
+<img src="images/i_157.png" width="400" height="128" alt="Fig. 73." title="Soldering iron and wires" />
+<p class="caption">Fig. 73.</p>
+</div>
+
+
+<p><a name="SEC_68" id="SEC_68"></a>§ 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.</p>
+
+<div class="figright" style="width: 279px;">
+<a name="FIG_74" id="FIG_74"></a>
+<img src="images/i_160.png" width="279" height="400" alt="Fig. 74." title="Push, interior of" />
+<p class="caption">Fig. 74.</p>
+</div>
+
+
+<p>In joining up several lengths of tubing, the end of
+one piece of tube should be opened out <i>considerably</i> of
+a trumpet shape for the other piece to slip in; and the
+end of this latter should also be <i>slightly</i> 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<!-- Page 150 --><span class="pagenum"><a name="Page_150" id="Page_150">[Pg 150]</a></span>
+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 <i>blocks</i>
+to which these are to be fastened must be bedded in
+the plaster. These blocks may be either square or circular<!-- Page 151 --><span class="pagenum"><a name="Page_151" id="Page_151">[Pg 151]</a></span>
+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), <a href="#FIG_74">Fig. 74</a>, 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 <i>right</i> in <a href="#FIG_74">Fig. 74</a>, and the other round the
+shank of the screw connected to the upper spring, shown
+to the <i>left</i> 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<!-- Page 152 --><span class="pagenum"><a name="Page_152" id="Page_152">[Pg 152]</a></span>
+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.</p>
+
+<p><a name="SEC_69" id="SEC_69"></a>§ 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 <span title="box section with opening to above">&#9495;&#9473;&#9499;</span>, 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 <i>iron</i> 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<!-- Page 153 --><span class="pagenum"><a name="Page_153" id="Page_153">[Pg 153]</a></span>
+words, where iron wire is used, its section must be not
+less than seven times that of the copper wire which it
+replaces.</p>
+
+
+<p><a name="SEC_70" id="SEC_70"></a>§ 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 <i>earth</i>, that is to make
+the damp soil carry the return current (see <a href="#SEC_37">§ 37</a>). 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 <i>towns</i>,
+where there are plenty of water mains and gas mains, this
+is a matter of no difficulty, the only point being to
+ensure <i>good</i> 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 <i>earth</i> 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 <i>main</i> pipes, so that they <i>do</i> 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<!-- Page 154 --><span class="pagenum"><a name="Page_154" id="Page_154">[Pg 154]</a></span>
+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 <i>return</i> wire. On no
+account should the two opposite <i>earth</i> 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 <i>earth</i> 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:<!-- Page 155 --><span class="pagenum"><a name="Page_155" id="Page_155">[Pg 155]</a></span>&mdash;</p>
+
+<p>"1st.&mdash;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.</p>
+
+<p>"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 '<i>battery wires</i>,' as the current is always<!-- Page 156 --><span class="pagenum"><a name="Page_156" id="Page_156">[Pg 156]</a></span>
+present and ready to take advantage of any defect
+in the insulation to escape to an adjoining wire, or to
+'<i>earth</i>,' 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 <i>line wires</i> we usually prefer
+No. 18 or 20 copper, covered with indiarubber, and an
+outer coating of cotton, well varnished. In joining the
+'<i>battery wires</i>,' 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. <i>On no account use spirits</i> in soldering.
+With the <i>line wire</i>, it is best, as far as possible, to convey
+it all the way from the push to the signal box or bell in
+<i>one continuous</i> 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<!-- Page 157 --><span class="pagenum"><a name="Page_157" id="Page_157">[Pg 157]</a></span>
+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 <i>loosely</i>
+staple them. <i>In no case allow more than one wire to lie
+under the same staple</i>, 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 <i>tight up to the wires</i>, and several wires to
+the same staple,&mdash;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 <span class="smcap">B.W.G.</span>, covered with gutta-percha,
+to No. 9 or 10 <span class="smcap">B.W.G.</span>, 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<!-- Page 158 --><span class="pagenum"><a name="Page_158" id="Page_158">[Pg 158]</a></span>
+rusting, and fixed loosely. If the wire is contained
+within an iron pipe, a lighter insulation may be used:
+<i>but the pipe must be watertight</i>. In a new building,
+wires must be contained within zinc or copper bell tubes.
+A &#8540; 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,&mdash;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 <i>perfectly clean</i><!-- Page 159 --><span class="pagenum"><a name="Page_159" id="Page_159">[Pg 159]</a></span>.
+<i>Joints</i> in wire, whether tinned or untinned, <i>must be
+soldered and covered</i>. We cannot impress this too earnestly
+on fixers. Never bury wires in plaster unprotected,
+and in houses in course of erection, the <i>tubes</i> 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."</p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_75" id="FIG_75"></a>
+<img src="images/i_168.png" width="400" height="116" alt="Fig. 75." title="Bell, battery and push" />
+<p class="caption">Fig. 75.</p>
+</div>
+
+
+<p><a name="SEC_71" id="SEC_71"></a>§ 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 <i>connect up</i>. No two houses
+or offices will admit of this being done in <i>exactly</i> 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 <i>single bell, battery, and push</i>,
+connected by wire only. This is illustrated at <a href="#FIG_75">Fig. 75</a>.
+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<!-- Page 160 --><span class="pagenum"><a name="Page_160" id="Page_160">[Pg 160]</a></span>
+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.<a name="FNanchor_15_15" id="FNanchor_15_15"></a><a href="#Footnote_15_15" class="fnanchor">[15]</a> 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. <a href="#FIG_76">Fig. 76</a> 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 <a href="#SEC_70">§ 70</a>).
+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
+<span class="smcap">E</span>, passing through the
+soil till it reaches the
+left-hand earth-plate <span class="smcap">E</span>, 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 <a href="#FIG_77">Fig. 77</a> 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<!-- Page 161 --><span class="pagenum"><a name="Page_161" id="Page_161">[Pg 161]</a></span>
+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).</p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_76" id="FIG_76"></a>
+<img src="images/i_169.png" width="400" height="228" alt="Fig. 76." title="Bell, battery and push And earth return" />
+<p class="caption">Fig. 76.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_77" id="FIG_77"></a>
+<img src="images/i_170a.png" width="400" height="113" alt="Fig. 77." title="Bell, and two pushes" />
+<p class="caption">Fig. 77.</p>
+</div>
+
+<p>In <a href="#FIG_78">Fig. 78</a>, we
+have a slight modification
+of the same arrangement, a front-door <i>pull</i>
+contact being inserted in the circuit; and here, in view
+of the probably increased resistance of longer distance,
+<i>two</i> cells are supposed to be employed instead of <i>one</i>,
+and these are coupled up in series (<a href="#SEC_40">§ 40</a>), in order
+to overcome this
+increased resistance.</p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_78" id="FIG_78"></a>
+<img src="images/i_170b.png" width="400" height="268" alt="Fig. 78." title="Bell, two pushes and one pull" />
+<p class="caption">Fig. 78.</p>
+</div>
+
+<p>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 "<i>in parallel</i>." This mode is well
+illustrated both at Figs. <a href="#FIG_79">79</a> and <a href="#FIG_80">80</a>. 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<!-- Page 162 --><span class="pagenum"><a name="Page_162" id="Page_162">[Pg 162]</a></span>
+several cells may be coupled up in parallel (<a href="#SEC_40">§ 40</a>). At
+<a href="#FIG_79">Fig. 79</a> is shown the arrangement for two adjoining
+rooms; at <a href="#FIG_80">Fig. 80</a>, that to be adopted when the rooms
+are at some distance apart. If, as shown at <a href="#FIG_81">Fig. 81</a>, a
+switch similar to that figured in the cut <a href="#FIG_64">Fig. 64</a> 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.</p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_79" id="FIG_79"></a>
+<img src="images/i_171a.png" width="400" height="115" alt="Fig. 79." title="Two bells in parallel" />
+<p class="caption">Fig. 79.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_80" id="FIG_80"></a>
+<img src="images/i_171b.png" width="400" height="259" alt="Fig. 80." title="Two bells in parallel Another mode" />
+<p class="caption">Fig. 80.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_81" id="FIG_81"></a>
+<img src="images/i_172a.png" width="400" height="270" alt="Fig. 81." title="Two bells in parallel with two-way switch" />
+<p class="caption">Fig. 81.</p>
+</div>
+
+<p>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
+<i>series</i> arrangement. As we have already noticed
+at <a href="#SEC_63">§ 63</a>, owing to the difference in the times at which<!-- Page 163 --><span class="pagenum"><a name="Page_163" id="Page_163">[Pg 163]</a></span>
+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 <a href="#FIG_82">Fig. 82</a>, 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.<!-- Page 164 --><span class="pagenum"><a name="Page_164" id="Page_164">[Pg 164]</a></span>
+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."</p>
+
+<div class="figcenter" style="width: 329px;">
+<a name="FIG_82" id="FIG_82"></a>
+<img src="images/i_172b.png" width="329" height="400" alt="Fig. 82." title="Series coupler" />
+<p class="caption">Fig. 82.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 600px;">
+<a name="FIG_83" id="FIG_83"></a>
+<img src="images/i_173.png" width="600" height="157" alt="Fig. 83." title="Bell with local battery and relay" />
+<p class="caption">Fig. 83.</p>
+</div>
+
+<p><a href="#FIG_83">Fig. 83</a> 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 <span class="smcap">E</span> returning to the left-hand
+earth-plate <span class="smcap">E</span>. 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.<!-- Page 165 --><span class="pagenum"><a name="Page_165" id="Page_165">[Pg 165]</a></span></p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_84" id="FIG_84"></a>
+<img src="images/i_174a.png" width="400" height="269" alt="Fig. 84." title="Continuous ringing bell with wire return" />
+<p class="caption">Fig. 84.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 600px;">
+<a name="FIG_85" id="FIG_85"></a>
+<img src="images/i_174b.png" width="600" height="170" alt="Fig. 85." title="Bells with Morse keys for signalling" />
+<p class="caption">Fig. 85.</p>
+</div>
+
+	<p>At <a href="#FIG_84">Fig. 84</a>, 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 (<a href="#FIG_65">Fig. 65</a>) constructed
+so as to make contact in one
+direction when <i>not</i> pressed down,
+and in the other <i>when</i> 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 <a href="#FIG_85">Fig. 85</a>.
+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<!-- Page 166 --><span class="pagenum"><a name="Page_166" id="Page_166">[Pg 166]</a></span>
+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 <span class="smcap">E</span>. If, on
+the contrary, the <i>left</i>-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, <i>double contact</i> pushes (that is, pushes
+making contact in one direction when <i>not</i> pressed, and
+in the opposite <i>when</i> pressed) may advantageously
+be employed. This latter arrangement is shown at
+<a href="#FIG_86">Fig. 86</a>.</p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_86" id="FIG_86"></a>
+<img src="images/i_175.png" width="400" height="267" alt="Fig. 86." title="Bells with double contact pushes for signalling" />
+<p class="caption">Fig. 86.</p>
+</div>
+
+<p>It is also possible, as shown at <a href="#FIG_87">Fig. 87</a>, 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<!-- Page 167 --><span class="pagenum"><a name="Page_167" id="Page_167">[Pg 167]</a></span>
+wires, besides the earth-plate or return wire, are required
+in this case. The whole of the wires,
+except the <i>return</i>, 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 <span class="smcap">E</span>, traverses the earth
+circuit till it reaches the left-hand
+earth plate <span class="smcap">E</span>, whence it returns to
+the zinc pole of the battery by the
+lower dotted line.</p>
+
+<div class="figcenter" style="width: 600px;">
+<a name="FIG_87" id="FIG_87"></a>
+<img src="images/i_176.png" width="600" height="153" alt="Fig. 87." title="Bells with double contact with one battery only" />
+<p class="caption">Fig. 87.</p>
+</div>
+
+<p><a href="#FIG_88">Fig. 88</a> 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<!-- Page 168 --><span class="pagenum"><a name="Page_168" id="Page_168">[Pg 168]</a></span>
+either carried overhead or underground, buried in
+tubes. <a href="#FIG_89">Fig. 89</a> 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.&mdash;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 <i>carefully cleaned</i> and <i>tightly clamped down</i>.</p>
+
+<div class="figcenter" style="width: 600px;">
+<a name="FIG_88" id="FIG_88"></a>
+<img src="images/i_177.png" width="600" height="162" alt="Fig. 88." title="Two-way signalling with one battery only" />
+<p class="caption">Fig. 88.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 600px;">
+<a name="FIG_89" id="FIG_89"></a>
+<img src="images/i_178.png" width="600" height="204" alt="Fig. 89." title="Complete installation of bells, batteries, pushes, etc." />
+<p class="caption">Fig. 89.</p>
+</div>
+
+<p>When it is desired to connect separate bells to ring<!-- Page 169 --><span class="pagenum"><a name="Page_169" id="Page_169">[Pg 169]</a></span>
+in other parts of the building, the quickest way is to
+take a branch wire out of the nearest <i>battery wire</i> (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.</p>
+
+
+<p><a name="SEC_72" id="SEC_72"></a>§ 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 <span title="battery symbol (thick and thin vertical lines)">&#9613;&#9615;</span> 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 [<span class="smcap">E</span>] and pulls, switches,
+&amp;c., as shown in the annexed
+cut, <a href="#FIG_90">Fig. 90</a>, 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<!-- Page 170 --><span class="pagenum"><a name="Page_170" id="Page_170">[Pg 170]</a></span>
+corner) is set. As it is set in the engraving, only the
+lodge bell rings.</p>
+
+<div class="figcenter" style="width: 600px;">
+<a name="FIG_90" id="FIG_90"></a>
+<img src="images/i_179.png" width="600" height="348" alt="Fig. 90." title="Mode of getting out plan or design" />
+<p class="caption">Fig. 90.</p>
+</div>
+
+
+<p><a name="SEC_73" id="SEC_73"></a>§ 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 <i>ships</i>. 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 <i>pendulum</i>, or other easily displaced type; but either
+of the form shown at <a href="#FIG_67">Fig. 67</a> or <a href="#FIG_68">68</a>, 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 <i>lifts</i>. Every well-appointed
+lift should be fitted with electric bells and<!-- Page 171 --><span class="pagenum"><a name="Page_171" id="Page_171">[Pg 171]</a></span>
+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
+<i>rub</i> 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),<!-- Page 172 --><span class="pagenum"><a name="Page_172" id="Page_172">[Pg 172]</a></span>
+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 <i>furthest</i>
+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:&mdash;</p>
+
+<p>A wire must be led from the <i>lower</i> contact spring of
+the double contact push, to the <i>main battery carbon wire</i>
+in the shaft. A second wire is led from the <i>upper contact
+stop</i> of the double contact push to the bell, and thence
+to the <i>main battery zinc wire</i> on the shaft. Lastly, a
+third wire is taken from the <i>upper contact spring</i> 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 <a href="#FIG_87">Fig. 87</a>.</p>
+
+<div class="figcenter" style="width: 267px;">
+<a name="FIG_91" id="FIG_91"></a>
+<img src="images/i_182.png" width="267" height="400" alt="Fig. 91." title="Lift fitted with bells" />
+<p class="caption">Fig. 91.</p>
+</div>
+
+<p>A glance at <a href="#FIG_91">Fig. 91</a> 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<!-- Page 173 --><span class="pagenum"><a name="Page_173" id="Page_173">[Pg 173]</a></span>
+to the <i>back</i> of the shaft wire. Any solder which may
+flow over to the <i>front</i> 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 <a href="#FIG_91">Fig. 91</a>, 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<!-- Page 174 --><span class="pagenum"><a name="Page_174" id="Page_174">[Pg 174]</a></span>
+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 <a href="#FIG_87">Fig. 87</a>.</p>
+
+<p>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.</p>
+
+
+<div class="figright" style="width: 319px;">
+<a name="FIG_92" id="FIG_92"></a>
+<img src="images/i_183.png" width="319" height="400" alt="Fig. 92." title="Magneto bell: generator" />
+<p class="caption">Fig. 92.</p>
+</div>
+
+<p><a name="SEC_74" id="SEC_74"></a>§ 74. In many cases where
+a "call" bell alone is required,
+the battery may be entirely
+dispensed with, and a small
+dynamo (<a href="#SEC_15">§ 15</a>) employed instead.
+The entire apparatus
+is then known as the
+"magneto-bell," and consists
+essentially of two parts, viz., the generator, <a href="#FIG_92">Fig. 92</a>,
+and the bell, <a href="#FIG_93">Fig. 93</a>. The <i>generator</i> or <i>inductor</i> 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<!-- Page 175 --><span class="pagenum"><a name="Page_175" id="Page_175">[Pg 175]</a></span>
+receiver or bell case, <a href="#FIG_93">Fig. 93</a>. 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.</p>
+
+<div class="figcenter" style="width: 400px;">
+<a name="FIG_93" id="FIG_93"></a>
+<img src="images/i_184.png" width="400" height="391" alt="Fig. 93." title="Magneto bell: Receiver" />
+<p class="caption">Fig. 93.</p>
+</div>
+
+<hr />
+
+<div class="figcenter" style="width: 340px;">
+<a name="FIG_94" id="FIG_94"></a>
+<img src="images/i_185a.png" width="340" height="400" alt="Fig. 94." title="Magneto bell: Combined" />
+<p class="caption">Fig. 94.</p>
+</div>
+
+<p>If a <i>combined</i> 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
+<a href="#FIG_94">Fig. 94</a>. These instruments are
+always ready for use, require no
+battery or press-buttons. The
+generator, <a href="#FIG_92">Fig. 92</a>, 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.</p>
+
+<div class="figcenter" style="width: 309px;">
+<a name="FIG_95" id="FIG_95"></a>
+<img src="images/i_185b.png" width="309" height="400" alt="Fig. 95." title="Detector or galvanometer" />
+<p class="caption">Fig. 95.</p>
+</div>
+
+
+<p><a name="SEC_75" id="SEC_75"></a>§ 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 <i>amount</i>
+of current of the right <i>pressure</i>, or E.M.F.; secondly, a
+means of detecting whether there is leakage, or loss of<!-- Page 176 --><span class="pagenum"><a name="Page_176" id="Page_176">[Pg 176]</a></span>
+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 <a href="#FIG_95">Fig. 95</a>. It will be remembered
+(<a href="#SEC_10">§ 10</a>) 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 <i>direction</i> 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,<!-- Page 177 --><span class="pagenum"><a name="Page_177" id="Page_177">[Pg 177]</a></span>
+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 <i>quantities</i> of electricity (many ampères)
+at a low pressure; this is called a <i>quantity</i> coil. If, on
+the other hand, the coil be one of fine wire, in many
+convolutions, as it requires more <i>pressure</i>, 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 <i>pressure</i> 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 <i>his</i> instrument gives with 1, 2, 3, 4, 5
+and 6 Leclanché's <i>coupled in parallel</i>, when connected
+with the quantity coil. He will find the smaller sizes
+give less current than the larger ones. In testing the<!-- Page 178 --><span class="pagenum"><a name="Page_178" id="Page_178">[Pg 178]</a></span>
+deflections given by the intensity coil, he must remember
+to couple his cells <i>in series</i>, as he will get no increase
+in <i>tension</i> or <i>pressure</i> 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:&mdash;</p>
+
+
+<p><a name="SEC_76" id="SEC_76"></a>§ 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 card<!-- Page 179 --><span class="pagenum"><a name="Page_179" id="Page_179">[Pg 179]</a></span>board
+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&frac34; 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&frac34; inches
+long by &frac34; 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 <a href="#FIG_27">Fig. 27</a>. A small brass
+handle to be fitted to the top of the instrument,<!-- Page 180 --><span class="pagenum"><a name="Page_180" id="Page_180">[Pg 180]</a></span>
+will also be handy. A circular piece of smooth
+cardboard 3&frac14; inches in diameter, with a graduated
+arc, marked as shown in <a href="#FIG_95">Fig. 95</a>, will serve the purpose
+of a dial, and a piece of thin brass, bent to the form of
+&#9487;&#9473;&#9491;, 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.</p>
+
+<p>We will now turn our attention to the coil.</p>
+
+<p>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 <a href="#FIG_95">Fig. 95</a>. 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&mdash;say, about 6 inches.<!-- Page 181 --><span class="pagenum"><a name="Page_181" id="Page_181">[Pg 181]</a></span>
+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.</p>
+
+
+<p><a name="SEC_77" id="SEC_77"></a>§ 77. Provided thus with an efficient detector, the
+fitter may proceed to test his work. In cases of <!-- Page 182 --><span class="pagenum"><a name="Page_182" id="Page_182">[Pg 182]</a></span>
+<i>new installations</i>, 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. <i>There should be no movement of the needle</i>,
+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 <i>slightest leakage</i> or <i>local action</i> 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<!-- Page 183 --><span class="pagenum"><a name="Page_183" id="Page_183">[Pg 183]</a></span>
+has been discovered. In testing underground wires for
+a loss or break, it will be necessary first to uncouple the
+<i>distant</i> 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.</p>
+
+
+<p><a name="SEC_78" id="SEC_78"></a>§ 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<!-- Page 184 --><span class="pagenum"><a name="Page_184" id="Page_184">[Pg 184]</a></span>
+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. <i>Pulls</i> 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,<!-- Page 185 --><span class="pagenum"><a name="Page_185" id="Page_185">[Pg 185]</a></span>
+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 <i>permanent magnetism</i>, 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 <i>cut</i> or <i>draw up</i>
+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.</p>
+
+<p>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.</p>
+
+
+<div class="footnote"><p><a name="Footnote_15_15" id="Footnote_15_15"></a><a href="#FNanchor_15_15"><span class="label">[15]</span></a> It must be borne in mind that the negative element is that to which
+the positive pole is attached, and <i>vice versâ</i> (see ss. 8 and 9).</p></div>
+
+
+
+<hr class="long" />
+<p><!-- Page 186 --><span class="pagenum"><a name="Page_186" id="Page_186">[Pg 186]</a></span></p>
+<h2><a name="ADDENDUM" id="ADDENDUM"></a>ADDENDUM.
+<br />
+<span class="smcap">The Gassner Battery.</span></h2>
+
+
+<p>Since the compilation of the foregoing pages, a <i>dry
+battery</i>, 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 <i>metal</i> must be
+carefully guarded from touching one another. This
+can be effected by enclosing in a partitioned <i>wooden box</i>.<!-- Page 187 --><span class="pagenum"><a name="Page_187" id="Page_187">[Pg 187]</a></span></p>
+
+
+
+<hr class="long" />
+<h2><a name="INDEX" id="INDEX"></a>INDEX.</h2>
+
+
+
+<p>A.</p>
+<ul>
+<li>Acid, Chromic, <a href="#Page_33">33</a>, <a href="#Page_46">46</a></li>
+<li class="indent1">Hydrobromic, <a href="#Page_20">20</a></li>
+<li class="indent1">Hydrochloric, <a href="#Page_20">20</a></li>
+<li class="indent1">Hydriodic, <a href="#Page_20">20</a></li>
+<li class="indent1">Nitric, <a href="#Page_20">20</a></li>
+<li class="indent1">Sulphuric, <a href="#Page_20">20</a></li>
+<li>Action in Bichromate, <a href="#Page_47">47</a></li>
+<li class="indent1">Dotting, <a href="#Page_116">116</a></li>
+<li class="indent1">of electric bell, <a href="#Page_81">81</a></li>
+<li class="indent1">Leclanché, <a href="#Page_35">35</a></li>
+<li class="indent1">Relay, <a href="#Page_134">134</a></li>
+<li class="indent1">Rubbing, <a href="#Page_116">116</a></li>
+<li class="indent1">of zinc on acids, <a href="#Page_21">21</a></li>
+<li>Agglomerate block, <a href="#Page_38">38</a></li>
+<li class="indent1">Cell, <a href="#Page_38">38</a></li>
+<li class="indent1">Compo, <a href="#Page_38">38</a></li>
+<li>Alarms, Burglar, <a href="#Page_113">113</a></li>
+<li class="indent1">Fire, <a href="#Page_123">123</a></li>
+<li class="indent1">Frost, <a href="#Page_121">121</a></li>
+<li class="indent1">Thermometer, <a href="#Page_122">122</a></li>
+<li class="indent1">Thief, <a href="#Page_113">113</a></li>
+<li class="indent1">Watch, <a href="#Page_124">124</a></li>
+<li>Amber, <a href="#Page_1">1</a></li>
+<li>Ampère, <a href="#Page_55">55</a></li>
+<li>Ampère's law, <a href="#Page_11">11</a></li>
+<li>Annealing iron, <a href="#Page_13">13</a></li>
+<li>Arrangement of bells for lifts, <a href="#Page_171">171</a></li>
+<li class="indent1">Ships, <a href="#Page_170">170</a></li>
+<li>Attraction, <a href="#Page_3">3</a></li>
+</ul>
+
+<p>B.</p>
+<ul>
+<li>Batteries, <a href="#Page_18">18</a></li>
+<li>Battery agglomerate, <a href="#Page_39">39</a></li>
+<li>Battery, Bichromate, <a href="#Page_48">48</a></li>
+<li class="indent1">Bunsen, <a href="#Page_33">33</a></li>
+<li class="indent1">Chromic acid, <a href="#Page_46">46</a></li>
+<li class="indent1">Daniell's, <a href="#Page_29">29</a></li>
+<li class="indent1">Gassner (addendum), <a href="#Page_186">186</a></li>
+<li class="indent1">Gent's, <a href="#Page_44">44</a></li>
+<li class="indent1">Gravity, <a href="#Page_31">31</a></li>
+<li class="indent1">Modified, <a href="#Page_120">120</a></li>
+<li class="indent1">Grenet, <a href="#Page_46">46</a></li>
+<li class="indent1">Grove, <a href="#Page_33">33</a></li>
+<li class="indent1">Judson's, <a href="#Page_41">41</a></li>
+<li class="indent1">Leclanché, <a href="#Page_33">33</a></li>
+<li class="indent1">Reversed, <a href="#Page_46">46</a></li>
+<li class="indent1">Minotto, <a href="#Page_31">31</a></li>
+<li class="indent1">Smee's, <a href="#Page_27">27</a></li>
+<li class="indent1">Walker's, <a href="#Page_27">27</a></li>
+<li>Bell action, case for, <a href="#Page_88">88</a></li>
+<li>Blocks, wooden, <a href="#Page_150">150</a></li>
+<li>Bobbins, electric bell, <a href="#Page_67">67</a></li>
+<li>Box for batteries, <a href="#Page_43">43</a></li>
+<li>Brushes, dynamo, <a href="#Page_17">17</a></li>
+</ul>
+
+
+<p>C.</p>
+<ul>
+<li>Cable, many stranded, <a href="#Page_174">174</a></li>
+<li>Case for bell action, <a href="#Page_88">88</a></li>
+<li>Cells in parallel, <a href="#Page_57">57</a></li>
+<li class="indent1">series, <a href="#Page_53">53</a></li>
+<li>Charging fluid, recipes, <a href="#Page_48">48</a></li>
+<li class="indent1">Fuller, <a href="#Page_49">49</a></li>
+<li>Circuits, closed, <a href="#Page_52">52</a>, <a href="#Page_118">118</a></li>
+<li class="indent1">Of bells complete in house, <a href="#Page_168">168</a></li>
+<li class="indent1">For signalling, <a href="#Page_167">167</a></li>
+<li class="indent1">In both directions, <a href="#Page_168">168</a><!-- Page 188 --><span class="pagenum"><a name="Page_188" id="Page_188">[Pg 188]</a></span></li>
+<li>Circuits of bells with Morse key, <a href="#Page_165">165</a></li>
+<li class="indent1">In parallel, <a href="#Page_161">161</a></li>
+<li class="indent1">Series, <a href="#Page_162">162</a></li>
+<li class="indent1">With relay, <a href="#Page_164">164</a></li>
+<li class="indent1">Single bell and wire, <a href="#Page_159">159</a></li>
+<li class="indent1">Earth, <a href="#Page_160">160</a></li>
+<li class="indent1">Two pushes, <a href="#Page_161">161</a></li>
+<li class="indent1">Push and pull, <a href="#Page_161">161</a></li>
+<li class="indent1">Open, <a href="#Page_52">52</a></li>
+<li>Closed circuit system, <a href="#Page_118">118</a></li>
+<li>Code for signalling, <a href="#Page_130">130</a></li>
+<li>Coil spring, <a href="#Page_108">108</a></li>
+<li>Conductors, <a href="#Page_3">3</a></li>
+<li>Connecting up, <a href="#Page_144">144</a>, <a href="#Page_159">159</a></li>
+<li>Contacts, burglar alarm, <a href="#Page_113">113</a></li>
+<li class="indent1">Door, <a href="#Page_116">116</a></li>
+<li class="indent1">Drawer, <a href="#Page_121">121</a></li>
+<li class="indent1">Floor, <a href="#Page_113">113</a></li>
+<li class="indent1">For closed circuits, <a href="#Page_121">121</a></li>
+<li class="indent1">Mackenzie's humming, <a href="#Page_113">113</a></li>
+<li class="indent1">Shop door, <a href="#Page_116">116</a></li>
+<li class="indent1">Till, <a href="#Page_121">121</a></li>
+<li class="indent1">Watch alarm, <a href="#Page_124">124</a></li>
+<li class="indent1">Window sash, <a href="#Page_116">116</a></li>
+<li>Corrugated carbons, <a href="#Page_41">41</a></li>
+<li>Creeping in cells, <a href="#Page_43">43</a></li>
+<li class="indent1">To remedy, <a href="#Page_44">44</a></li>
+<li>Callow's attachment, <a href="#Page_99">99</a></li>
+<li>Current, <a href="#Page_54">54</a></li>
+<li class="indent1">To ring bell, <a href="#Page_145">145</a></li>
+</ul>
+
+
+<p>D.</p>
+<ul>
+<li>Daniell's cell, <a href="#Page_29">29</a></li>
+<li class="indent1">Action in, <a href="#Page_29">29</a></li>
+<li>Deflection of needle, <a href="#Page_9">9</a>, <a href="#Page_11">11</a></li>
+<li>Detector or galvanometer, to make, <a href="#Page_178">178</a></li>
+<li>Detent lever, <a href="#Page_94">94</a></li>
+<li>Door contact, <a href="#Page_116">116</a></li>
+<li>Dotting action, <a href="#Page_116">116</a></li>
+<li>Drawing out plans, <a href="#Page_169">169</a></li>
+<li>Dynamo, <a href="#Page_15">15</a></li>
+<li class="indent1">Armature, <a href="#Page_16">16</a></li>
+<li class="indent1">Brushes, <a href="#Page_17">17</a></li>
+<li class="indent1">Commutator, <a href="#Page_17">17</a></li>
+<li>Dynamo, Cumulative effects, <a href="#Page_7">17</a></li>
+<li class="indent1">Field magnets, <a href="#Page_16">16</a></li>
+</ul>
+
+<p>E.</p>
+<ul>
+<li>Earth, <a href="#Page_52">52</a></li>
+<li class="indent1">Plate, <a href="#Page_53">53</a></li>
+<li class="indent1">Return, <a href="#Page_153">153</a></li>
+<li>Electric bell, action of, <a href="#Page_81">81</a></li>
+<li class="indent1">Armature, <a href="#Page_74">74</a></li>
+<li class="indent1">Base, <a href="#Page_61">61</a></li>
+<li class="indent1">Bobbins, <a href="#Page_67">67</a></li>
+<li class="indent1">Contact screw, <a href="#Page_75">75</a></li>
+<li class="indent1">Continuous, <a href="#Page_92">92</a></li>
+<li class="indent1">Circular bell, <a href="#Page_106">106</a></li>
+<li class="indent1">Gong, <a href="#Page_77">77</a></li>
+<li class="indent1">How to make, <a href="#Page_60">60</a></li>
+<li class="indent1">In lifts, <a href="#Page_171">171</a></li>
+<li class="indent1">Ships, <a href="#Page_170">170</a></li>
+<li class="indent1">Jensen's, <a href="#Page_101">101</a></li>
+<li class="indent1">Joining E. M. wire, <a href="#Page_73">73</a></li>
+<li class="indent1">Magnets, <a href="#Page_63">63</a></li>
+<li class="indent1">Magneto, <a href="#Page_174">174</a></li>
+<li class="indent1">Mining, <a href="#Page_106">106</a></li>
+<li class="indent1">Paraffining, <a href="#Page_69">69</a></li>
+<li class="indent1">Platinum tip, <a href="#Page_76">76</a></li>
+<li class="indent1">Putting together, <a href="#Page_78">78</a></li>
+<li class="indent1">Single stroke, <a href="#Page_91">91</a></li>
+<li class="indent1">Spring, <a href="#Page_74">74</a></li>
+<li class="indent1">Thorpe's, <a href="#Page_100">100</a></li>
+<li class="indent1">Trembling, <a href="#Page_81">81</a>, <a href="#Page_90">90</a></li>
+<li class="indent1">Winding wire on, <a href="#Page_71">71</a></li>
+<li class="indent1">Wire for, <a href="#Page_69">69</a></li>
+<li class="indent1">Trumpet, <a href="#Page_107">107</a></li>
+<li>Electricity, sources of, <a href="#Page_2">2</a></li>
+<li>Electrodes, <a href="#Page_26">26</a></li>
+<li>Electro-motive force, <a href="#Page_51">51</a></li>
+<li>Electron, <a href="#Page_1">1</a></li>
+<li>E.M.F., <a href="#Page_51">51</a></li>
+<li>Excitation, <a href="#Page_6">6</a></li>
+</ul>
+
+<p>F.</p>
+<ul>
+<li>Faults to detect, <a href="#Page_182">182</a></li>
+<li>Fire alarms, <a href="#Page_123">123</a></li>
+<li>Floor contacts, <a href="#Page_113">113</a><!-- Page 189 --><span class="pagenum"><a name="Page_189" id="Page_189">[Pg 189]</a></span></li>
+<li>Frost alarms, <a href="#Page_121">121</a></li>
+<li>Fuller charging, <a href="#Page_49">49</a></li>
+</ul>
+
+<p>G.</p>
+<ul>
+<li>Galvanometer, <a href="#Page_176">176</a></li>
+<li>Gas evolved, <a href="#Page_18">18</a></li>
+<li>Gassner battery (addendum), <a href="#Page_186">186</a></li>
+<li>Generator (magneto), <a href="#Page_174">174</a></li>
+<li>Gent's battery, <a href="#Page_44">44</a></li>
+<li>Glue, Prout's elastic, <a href="#Page_148">148</a></li>
+<li>Graphite, <a href="#Page_27">27</a></li>
+<li>Gravity battery, <a href="#Page_31">31</a></li>
+<li class="indent1">Daniell battery, <a href="#Page_31">31</a></li>
+<li class="indent1">Modified, <a href="#Page_120">120</a></li>
+<li>Grenet battery, <a href="#Page_46">46</a></li>
+<li>Grove battery, <a href="#Page_33">33</a></li>
+<li>Gutta-percha, <a href="#Page_148">148</a></li>
+</ul>
+
+<p>I.</p>
+<ul>
+<li>Indicator, <a href="#Page_135">135</a></li>
+<li class="indent1">Automatic, <a href="#Page_138">138</a></li>
+<li class="indent1">Drop, <a href="#Page_136">136</a></li>
+<li class="indent1">Electric replacement, <a href="#Page_136">136</a></li>
+<li class="indent1">Gent's, <a href="#Page_140">140</a></li>
+<li class="indent1">Tripolar, <a href="#Page_143">143</a></li>
+<li class="indent1">Mechanical  replacement, <a href="#Page_136">136</a></li>
+<li class="indent1">Mode of coupling up, <a href="#Page_142">142</a></li>
+<li class="indent1">Pendulum, <a href="#Page_139">139</a></li>
+<li class="indent1">Polarised, <a href="#Page_139">139</a></li>
+<li class="indent1">Self replacing, <a href="#Page_136">136</a></li>
+<li class="indent1">Semaphore, <a href="#Page_136">136</a></li>
+<li>Inductor, <a href="#Page_174">174</a></li>
+<li>Insulation, <a href="#Page_68">68</a></li>
+<li>Insulators, <a href="#Page_4">4</a></li>
+<li>Internal resistance, <a href="#Page_56">56</a></li>
+<li>Interior of push, <a href="#Page_151">151</a></li>
+<li>Iron, importance of soft, <a href="#Page_65">65</a></li>
+<li class="indent1">Yoke, <a href="#Page_66">66</a></li>
+</ul>
+
+<p>J.</p>
+<ul>
+<li>Jensen's bell, <a href="#Page_101">101</a></li>
+<li>Joining wires to push, <a href="#Page_151">151</a></li>
+<li>Judson's cell, <a href="#Page_41">41</a></li>
+</ul>
+
+<p>K.</p>
+<ul>
+<li>Key, Morse, <a href="#Page_129">129</a></li>
+</ul>
+
+<p>L.</p>
+<ul>
+<li>Leakage, <a href="#Page_52">52</a></li>
+<li>Leclanché cell, <a href="#Page_33">33</a></li>
+<li class="indent1">reversed, <a href="#Page_46">46</a></li>
+<li>Legge's contact, <a href="#Page_115">115</a></li>
+<li>Lever switches, <a href="#Page_128">128</a></li>
+<li>Lifts, bells for, <a href="#Page_171">171</a></li>
+<li>Localising faults, <a href="#Page_144">144</a>, <a href="#Page_175">175</a></li>
+<li>Lodge bell, <a href="#Page_169">169</a></li>
+</ul>
+
+<p>M.</p>
+<ul>
+<li>Magnetic field, <a href="#Page_14">14</a></li>
+<li>Magneto bells, <a href="#Page_175">175</a></li>
+<li class="indent1">Electric machines, <a href="#Page_14">14</a>, <a href="#Page_15">15</a></li>
+<li>Magnets, <a href="#Page_13">13</a></li>
+<li>Magnets producing electricity, <a href="#Page_14">14</a></li>
+<li>Magnetisation of iron, <a href="#Page_12">12</a></li>
+<li class="indent1">Steel, <a href="#Page_13">13</a></li>
+<li>Manganese oxide, <a href="#Page_33">33</a></li>
+<li>Minotto cell, <a href="#Page_31">31</a></li>
+<li>Modified gravity battery, <a href="#Page_120">120</a></li>
+<li>Morse key, <a href="#Page_129">129</a></li>
+<li>Musical instrument, novel, <a href="#Page_108">108</a></li>
+</ul>
+
+<p>N.</p>
+<ul>
+<li>Negative electricity, <a href="#Page_7">7</a></li>
+<li>Non-conductors, <a href="#Page_3">3</a></li>
+<li>Novel musical instrument, <a href="#Page_108">108</a></li>
+</ul>
+
+<p>O.</p>
+<ul>
+<li>Ohm, <a href="#Page_55">55</a></li>
+<li>Ohm's law, <a href="#Page_55">55</a></li>
+<li>Open circuit, <a href="#Page_52">52</a></li>
+<li>Overhead lines, <a href="#Page_152">152</a></li>
+</ul>
+
+<p>P.</p>
+<ul>
+<li>Paraffin, <a href="#Page_69">69</a>, <a href="#Page_170">170</a></li>
+<li>Percha, gutta, <a href="#Page_148">148</a></li>
+<li>Plans, drawing out, <a href="#Page_169">169</a></li>
+<li><!-- Page 190 --><span class="pagenum"><a name="Page_190" id="Page_190">[Pg 190]</a></span>
+Platinum, riveting, <a href="#Page_76">76</a></li>
+<li>Platinum, use of, <a href="#Page_76">76</a></li>
+<li>Plug switches, <a href="#Page_128">128</a></li>
+<li>Polarisation, <a href="#Page_26">26</a></li>
+<li>Positive electricity, <a href="#Page_7">7</a></li>
+<li>Proportions of bell parts, table of, <a href="#Page_89">89</a></li>
+<li>Pressels, <a href="#Page_111">111</a></li>
+<li>Prout's elastic glue, <a href="#Page_148">148</a></li>
+<li>Pulls, <a href="#Page_111">111</a></li>
+<li>Push, <a href="#Page_92">92</a>, <a href="#Page_151">151</a>, <a href="#Page_109">109</a></li>
+<li class="indent1">Interior of, <a href="#Page_151">151</a></li>
+<li class="indent1">Joining wires to, <a href="#Page_151">151</a></li>
+</ul>
+
+<p>R.</p>
+<ul>
+<li>Relay, <a href="#Page_96">96</a>, <a href="#Page_133">133</a></li>
+<li class="indent1">Action of, <a href="#Page_134">134</a></li>
+<li>Repulsion, <a href="#Page_3">3</a></li>
+<li>Resinous electricity, <a href="#Page_7">7</a></li>
+<li>Resistance of wire, table of, <a href="#Page_146">146</a></li>
+<li>Return current, <a href="#Page_153">153</a></li>
+<li>Riveting platinum, <a href="#Page_76">76</a></li>
+<li>Rubbing action, <a href="#Page_116">116</a></li>
+</ul>
+
+<p>S.</p>
+<ul>
+<li>Ships, bells for, <a href="#Page_170">170</a></li>
+<li>Shop door contact, <a href="#Page_116">116</a></li>
+<li>Signalling by bells, <a href="#Page_130">130</a></li>
+<li class="indent1">Code, <a href="#Page_130">130</a></li>
+<li>Silver platinised, <a href="#Page_27">27</a></li>
+<li>Single cell, <a href="#Page_9">9</a></li>
+<li>Sizes of Leclanché's, <a href="#Page_42">42</a></li>
+<li>Smee's cell, <a href="#Page_27">27</a></li>
+<li>Spring coil, <a href="#Page_108">108</a></li>
+<li>Standard size of wires, <a href="#Page_146">146</a></li>
+<li>Switches, lever, <a href="#Page_128">128</a></li>
+<li class="indent1">Plug, <a href="#Page_128">128</a></li>
+</ul>
+
+<p>T.</p>
+<ul>
+<li>Table of batteries, E.M.F. and R., <a href="#Page_58">58</a></li>
+<li class="indent1">Conductors and insulators, <a href="#Page_4">4</a>, <a href="#Page_68">68</a></li>
+<li class="indent1">Metals in acid, <a href="#Page_8">8</a></li>
+<li>Table of Proportions of bell parts, <a href="#Page_89">89</a></li>
+<li class="indent1">Wire resistance, etc., <a href="#Page_146">146</a></li>
+<li>Testing new work, <a href="#Page_182">182</a></li>
+<li class="indent1">Old, <a href="#Page_183">183</a></li>
+<li>Thermometer alarms, <a href="#Page_122">122</a></li>
+<li>Thorpe's Ball, <a href="#Page_100">100</a></li>
+</ul>
+
+<p>U.</p>
+<ul>
+<li>Use of platinum, <a href="#Page_76">76</a></li>
+</ul>
+
+<p>V.</p>
+<ul>
+<li>Vitreous electricity, <a href="#Page_7">7</a></li>
+<li>Volt, <a href="#Page_53">53</a></li>
+</ul>
+
+<p>W.</p>
+<ul>
+<li>Walker's cell, <a href="#Page_27">27</a></li>
+<li>Watchman's clock, <a href="#Page_124">124</a></li>
+<li>Water level indicator, <a href="#Page_127">127</a></li>
+<li>Washer, insulating, <a href="#Page_77">77</a></li>
+<li>Window sash contact, <a href="#Page_116">116</a></li>
+<li>Wiping contact, <a href="#Page_102">102</a></li>
+<li>Wire covering, <a href="#Page_147">147</a></li>
+<li class="indent1">In iron pipes, <a href="#Page_152">152</a></li>
+<li class="indent1">In wooden boxes, <a href="#Page_152">152</a></li>
+<li class="indent1">Iron, <a href="#Page_152">152</a></li>
+<li class="indent1">Joining, <a href="#Page_148">148</a></li>
+<li class="indent1">To push, <a href="#Page_151">151</a></li>
+<li class="indent1">Laying in tubes, <a href="#Page_149">149</a></li>
+<li class="indent1">Leading, <a href="#Page_147">147</a>, <a href="#Page_150">150</a></li>
+<li class="indent1">Overhead, <a href="#Page_152">152</a></li>
+<li class="indent1">Resistance, table of, <a href="#Page_146">146</a></li>
+<li class="indent1">Return, <a href="#Page_147">147</a>, <a href="#Page_150">150</a></li>
+<li class="indent1">Soldering iron, <a href="#Page_148">148</a></li>
+<li class="indent1">Tinned, <a href="#Page_147">147</a></li>
+<li class="indent1">Underground, <a href="#Page_152">152</a></li>
+<li>Wiring, general instructions, <a href="#Page_155">155</a></li>
+<li class="indent1">Up, <a href="#Page_144">144</a></li>
+</ul>
+
+<p>Z.</p>
+<ul>
+<li>Zinc, amalgamated, <a href="#Page_22">22</a></li>
+<li class="indent1">Blacking, <a href="#Page_45">45</a></li>
+<li class="indent1">Consumption, <a href="#Page_21">21</a></li>
+<li class="indent1">Commercial, <a href="#Page_19">19</a></li>
+<li class="indent1">Pure, <a href="#Page_19">19</a></li>
+</ul>
+
+
+<p class="center">WILLIAM RIDER AND SON, PRINTERS, LONDON.</p>
+
+<hr style="width: 45%;" />
+
+<p class="center">
+<i>Small crown 8vo, cloth.</i>&emsp;&emsp;&emsp;&emsp;&emsp;<i>With many Illustrations.</i><br />
+</p>
+
+<h3>WHITTAKER'S LIBRARY OF ARTS, SCIENCES,
+MANUFACTURES AND INDUSTRIES.</h3>
+
+
+<div class="blockquot"><p>MANAGEMENT OF ACCUMULATORS AND
+PRIVATE ELECTRIC LIGHT INSTALLATIONS.</p>
+
+<p>A Practical Handbook by Sir <span class="smcap">David Salomons</span>, Bart., M. A.</p>
+
+<p>4th Edition, Revised and Enlarged, with 32 Illustrations. Cloth 3s.</p>
+
+<p>"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."&mdash;<i>Electrical
+Review.</i></p></div>
+
+<div class="blockquot"><p>ELECTRICAL INSTRUMENT-MAKING FOR
+AMATEURS. A Practical Handbook. By <span class="smcap">S. R. Bottone</span>,
+Author of "The Dynamo," &amp;c. With 60 Illustrations. Second
+Edition. Cloth 3s.</p></div>
+
+<div class="blockquot"><p>ELECTRIC BELLS. By <span class="smcap">S. R. Bottone</span>. With
+numerous Illustrations.</p></div>
+
+
+<p class="center"><span class="smcap">In Preparation.</span></p>
+
+<div class="blockquot"><p>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 <span class="smcap">Oliver J. Lodge</span>, LL.D., D.Sc, F.R.S., Professor of Physics
+in University College, Liverpool.</p>
+
+<p>Published with various amplifications and additions, with the
+approval of the Society of Arts.</p></div>
+
+<div class="blockquot"><p>ELECTRICAL INFLUENCE MACHINES:
+Containing a full account of their historical development, their
+modern Forms, and their Practical Construction. By <span class="smcap">J. Gray</span>,
+B.Sc.</p></div>
+
+<div class="blockquot"><p>ELECTRICAL ENGINEERING IN OUR
+WORKSHOPS. A Practical Handbook. By <span class="smcap">Sydney F.
+Walker</span>.</p></div>
+
+<p>
+<span style="margin-left: 30em;">[<i>Ready Shortly</i></span><br />
+</p>
+
+
+<div class="trans-note">
+<h4><a name="Transcribers_Notes" id="Transcribers_Notes"></a>Transcriber's Notes</h4>
+
+<p>Page <a href="#Page_12">12</a>: changed "guage" to "gauge" ( ... cotton-covered copper
+wire, say No. 20 gauge ...)</p>
+
+<p>Page <a href="#Page_35">35</a>: changed "change" to "charge" ( ... losing at the same
+time its electrical charge ...)</p>
+
+<p>Page <a href="#Page_55">55</a>: changed "guage" to "gauge" ( ... 1 foot of No.
+41 gauge pure copper wire ...)</p>
+
+<p>Page <a href="#Page_64">64</a>: changed "exaet" to "exact" ( ... of the exact
+diameter of the turned ends of the cores ...)</p>
+
+<p>Page <a href="#Page_73">73</a>: moved comma "Rivetting, is" to "Rivetting is,"
+(Rivetting, is perhaps, the best mode ...)</p>
+
+<p>Page <a href="#Page_81">81</a>: added hyphen ( ... along the short
+length of wire to the right-hand binding-screw ...)</p>
+
+<p>Page <a href="#Page_83">83</a>: changed "head" to "heads" ( ... the possible defects of
+electric bells may be classed under four heads: ...)</p>
+
+<p>Page <a href="#Page_92">92</a>: changed "its" to "it" ( ... until it rests against the stop
+or studs.)</p>
+
+<p>Page <a href="#Page_102">102</a>: changed "contract-breaker" to "contact-breaker"
+(When the contact-breaker is used, ...)</p>
+
+<p>Page <a href="#Page_103">103</a>: changed "instead" to "Instead" (Instead of the armature and clapper ...)</p>
+
+<p>Page <a href="#Page_132">132</a>: in the Morse code for "BRING THE", the code for "H" has been
+corrected from two dots to four dots.</p>
+
+<p>Page <a href="#Page_136">136</a>: changed "eletro-magnet" to "electro-magnet" ( ... if the electro-magnet were energised ...)</p>
+
+<p>Page <a href="#Page_137">137</a>: changed "idicator" to "indicator" (since the indicator falls forwards)</p>
+
+<p>Page <a href="#Page_146">146</a>: changed "arrangment" to "arrangement" (the size and arrangement
+of the batteries and wires)</p>
+
+<p>Page <a href="#Page_146">146</a>: added comma "nails," ( ... chance contact with nails,
+staples, metal pipes or other wires ...)</p>
+
+<p>Page <a href="#Page_179">179</a>: changed "carboard" to "cardboard" ( ... for our purpose we will choose cardboard.)</p>
+
+<p>Page <a href="#Page_179">179</a>: changed "Tanstickor" to "Tãndstickor" ( ... double it to the form of a Tãndstickor match-box, ...)</p>
+
+<p>Page <a href="#Page_185">185</a>: suspected typo (unchanged) "Emmot" should perhaps be
+"Emmott" (... the electrical firms of Messrs. Blakey Emmot, ...)</p>
+
+<p>Page <a href="#Page_186">186</a>: changed "Leclanchè" to "Leclanché" ( ... polarizes much
+less quickly than the ordinary Leclanché.)</p>
+
+<p>Page <a href="#Page_187">187</a>: changed two instances of "Ampére" to "Ampère" in the index (Ampère, 55 / Ampère's law, 11)</p>
+</div>
+
+
+
+
+
+
+
+<pre>
+
+
+
+
+
+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-h.htm or 39053-h.zip *****
+This and all associated files of various formats will be found in:
+        http://www.gutenberg.org/3/9/0/5/39053/
+
+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
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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: ASCII
+
+*** 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 Plain Text version uses symbols from the ASCII character set
+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 accented and special symbols:
+
+  [:A], [:O], [:U]  A-umlaut, O-umlaut, U-umlaut
+  [^a]              a-curcumflex
+  [AE], [ae]        upper and lower case ae-ligature
+  ['e], [e'], [^e]  e-acute, e-grave, e-circumflex
+  [oe]              oe-ligature
+  [battery]         vertical lines (thick and thin)
+  [box open up]     3 sides of rectangular (open side up)
+  [box open down]   3 sides of rectangular (open side down)
+  deg.              degree symbol
+  [Lambda]          sans-serif capital Lambda
+  [rotated S]       S-like symbol rotated 90 deg.
+  [L], [U], [V]     sans-serif letter shapes
+  [S]               section symbol
+
+       *       *       *       *       *
+
+                         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.  "  Leclanch['e] 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.
+
+
+[S] 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.
+
+
+[S] 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.
+
+
+[S] 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.
+
+
+[S] 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:--
+
+
+[S] 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.
+
+
+[S] 6. If the experiment described at [S] 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.
+
+
+[S] 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_.
+
+
+[S] 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.]
+
+
+[S] 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.
+
+
+[S] 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 Amp[e']re's law, is briefly as follows:--
+
+
+[S] 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.
+
+
+[S] 12. From a consideration of the above law, in connection with the
+experiments performed at [S] 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.]
+
+
+[S] 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 [S] 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.
+
+
+[S] 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.]
+
+
+[S] 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.]
+
+
+[S] 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 ([S] 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.
+
+
+[S] 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.
+
+
+[S] 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.
+
+
+[S] 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:--
+
+
+[S] 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 ([S] 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.]
+
+
+[S] 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.
+
+
+[S] 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.
+
+
+[S] 23. If, having thus amalgamated the zinc plate of the little battery
+described and figured at [S] 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:--
+
+
+[S] 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 ([S] 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.]
+
+
+[S] 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.
+
+
+[S] 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 ([S] 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 "Leclanch['e]." As the battery has been,
+and will probably remain, long a favourite, the next paragraph will be
+devoted to its consideration.
+
+
+[S] 27. The Leclanch['e] 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 Leclanch['e] 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 deg. 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 Leclanch['e] 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, [S] 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.
+
+
+[S] 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 Leclanch['e] cell, says:--"A severe and prolonged test, extending over
+many years, has proved that for general electric bell work the Leclanch['e]
+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."
+
+
+[S] 29. Another form of Leclanch['e], 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 deg. C.
+(212 deg. Fahr.), under a pressure of 300 atmospheres, say 4,500 lbs. to
+the square inch.
+
+No. 3.
+
+      _Barbier and Leclanch['e]'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 deg. C. (about 662
+deg. 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
+Leclanch['e] consists in a solution of ammonium chloride.
+
+[Illustration: Fig. 9.]
+
+Among the various advantages claimed for the agglomerate form of
+Leclanch['e] 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.
+
+
+[S] 30. A third form of Leclanch['e], 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.]
+
+
+[S] 31. The ordinary form of Leclanch['e] 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.]
+
+
+[S] 32. There are certain ills to which the Leclanch['e] 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 Leclanch['e] 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 Leclanch['e]." 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.
+
+
+[S] 33. There is yet a modification of the Leclanch['e] which is sometimes
+used to ring the large bells in hotels, etc., known as the Leclanch['e]
+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.
+
+
+[S] 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 ([S] 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.]
+
+
+[S] 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.
+
+
+[S] 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.
+
+
+[S] 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."
+
+
+[S] 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 deg.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 deg.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 Leclanch['e] is very nearly 1.6 volt,
+or nearly 1 volt and 2/3. Thus in Fig. 15, which illustrates 3 Leclanch['e]
+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.]
+
+
+[S] 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 AMP[E']RE; and 1
+amp[e']re 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 millim[e']tre (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 deg.
+Fahr., or 0 deg. Centigrade.
+
+
+[S] 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
+(amp[e']res) 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, amp[e']res, and ohms, instead
+of the general terms, E, R, and C, we may write V/R = A, or Volts/Ohms =
+Amp[e']res.
+
+From this it appears that 1 volt will send a current of 1 amp[e']re through
+a total resistance of 1 ohm, since 1 divided by 1 equals 1. So also 1
+volt can send a current of 4 amp[e']res 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 [S] 38). The arrangement of cells in parallel is shown at Fig.
+16, where three Leclanch['e] 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
+  Leclanch['e]    |     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 amp[e']res 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 amp[e']re, 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.
+
+
+[S] 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 [S] 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.
+
+
+[S] 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 ([S] 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 [S] 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 [S] 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 [S] 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 Leclanch['e] 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.]
+
+
+[S] 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 Leclanch['e], 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 [S] 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 [S] 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.
+
+
+[S] 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 [S] 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 Leclanch['e] 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 Leclanch['e] 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.
+
+
+[S] 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.
+
+
+[S] 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.]
+
+
+[S] 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_.
+
+
+[S] 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 [S] 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.]
+
+
+[S] 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.
+
+
+[S] 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.]
+
+
+[S] 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.]
+
+
+[S] 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.
+
+
+[S] 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 [S] 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.]
+
+
+[S] 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.]
+
+
+[S] 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.
+
+
+[S] 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 [S] 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.]
+
+
+[S] 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 ([S] 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.
+
+
+[S] 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 vers[^a]_, 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.
+
+
+[S] 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."
+
+
+[S] 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.]
+
+
+[S] 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.
+
+
+[S] 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          ----
+  [:A] ([ae]) .-.-
+  [:O] ([oe]) ---.
+  [:U] (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 [AE] .-.-; 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.]
+
+
+[S] 63. At [S] 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.]
+
+
+[S] 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.]
+
+
+[S] 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.
+
+
+[S] 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 amp[e']res) 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 amp[e']re 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 Leclanch[e'] cell is, as we have seen
+at [S] 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. Amp[e']res.
+  2.4)  1.60   (0.66,
+
+or about 2/3 of an amp[e']re; 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 amp[e']re 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
+  ------------------------------------------------------------
+
+
+[S] 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.]
+
+
+[S] 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.]
+
+
+[S] 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.
+
+
+[S] 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 [S] 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.]
+
+
+[S] 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 [S] 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 vers[^a]_ (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 ([S] 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 ([S] 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 [S] 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.
+
+
+[S] 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.]
+
+
+[S] 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.
+
+
+[S] 74. In many cases where a "call" bell alone is required, the battery
+may be entirely dispensed with, and a small dynamo ([S] 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.]
+
+
+[S] 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 ([S] 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 deg. 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 amp[e']res) 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 Leclanch['e]'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:--
+
+
+[S] 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 T[:a]ndstickor
+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.
+
+
+[S] 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.
+
+
+[S] 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
+Leclanch['e]. 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
+
+  ---- Leclanch['e], 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
+
+  Amp[e']re, 55
+
+  Amp[e']re'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
+
+  ---- Leclanch['e], 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
+
+  Leclanch['e] 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 Leclanch['e]'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 "T[:a]ndstickor" (... double it to the
+form of a T[:a]ndstickor match-box, ...)
+
+Page 185: suspected typo (unchanged) "Emmot" should perhaps be
+"Emmott" (... the electrical firms of Messrs. Blakey Emmot, ...)
+
+Page 186: changed "Leclanch[e']" to "Leclanch['e]" (... polarizes much
+less quickly than the ordinary Leclanch['e].)
+
+Page 187: changed two instances of "Amp['e]re" to "Amp[e']re" in the
+index (Amp[e']re, 55 / Amp[e']re'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 ***
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