fyxull Wimvmxi^^xiixM^ BOUGHT WITH THE INCOME FROM THE . SAGE ENDOWMENT FUND THE GIFT OF 1891 imestic 3 1924 031 265 543 olin.anx The original of tliis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924031265543 A POPULAR GUIDE TO COMMERCIAL AND DOMESTIC TELEPHONY KEV. H. RUNNINGS, INVENTOR OF THE GRANULAR TRANSMITTER. (From ail Original Photogra-ph in possession of the General Electric Co.) A POPULAR GUIDE TO COMMERCIAL & DOMESTIC TELEPHONY BY M. 8YNG, M.I.E.E. AND F. G. BELL FIRST EDITION 1898 THE GENERAL ELECTRIC CO., LIMITED, LONDON, MANCHESTER, GLASGOW, NEWCASTLE, BIRMINGHAM & DUBLIN ; ALSO WHITTAKER & CO., 2, White Hart Street, Paternoster Square, E.C. {Copyright in America) Sr CONTENTS CHAPTER I. PAGE BELL TELEPHONE RECEIVERS. The Magnetic Field — Its effect upon moving conductors — Solenoid — Application of principle to the " Bell " telephone — Electro- magnet — Its properties which have a bearing upon the " Bell " telephone used as a receiver — The Double Pole " Bell " receiver^-The Manchester watch receiver . . . 1-13 CHAPTER II. MICROPHONE TRANSMITTERS. Resistance — Effect of a variable resistance in an electrical circuit —Hughes' microphone — The " Hunnings " microphone — In- duction coil — The " Byng" microphone — The " Hunningscone Deckert" microphone . 14-25 CHAPTER III. BATTERIES AND ELECTRIC BELLS. Simple form of battery — "Element" and "Pole" — ^The Car- porous battery — The E C C dry battery — Methods of con- necting batteries — The Electric Bell — Testing for fault in Electric Bell . . . .... 26-36 CHAPTER IV. THE "STANLEY" DIRECT WORKING TELEPHONE. Calling apparatus — " Stanley " wall pattern telephone and its construction — Method of connecting — Adaptation of "Stanley" telephone to existing bell circuits — "Stanley" table pattern telephone—" Stanley " hand combination — " Stanley " portable telephone ... . 37-63 CHAPTER V. INDUCTION COIL TELEPHONES. " Hunningscone Deckert " domestic telephone ; wall pattern with attached bell ; with separate bell—" Hunningscone Deckert " table pattern telephones 64-73 vi CONTENTS CHAPTER VI. PAGE SWITCHES AND ANNUNCIATORS. Imaginary examples of systems required — Simple switch — Four- point commutator switch ; five-point ditto ; six-point ditto — Domestic indicator plug board — Switch board for private exchanges — Old method of plug board intercommunication . 74-91 CHAPTER VII. THE "general" INTERCOMMUNICATION SYSTEM. The wall pattern instrument— Multiple cable— Connecting boxes — Mixed intercommunication — Wood casing — Flexible cables —Multiple rosettes— Insulated staples— Table pattern instru- ments—Reply and call system-^" Byng " intercommunication instrument . 92-106 CHAPTER VIII. MAGNETO RINGING APPARATUS. Magneto generators — Magneto bells — Complete wall telephone, with magneto ringing apparatus for long distances — Table pattern instruments 107-122 CHAPTER IX. METALLIC CIRCUIT OR DOUBLE LINE SYSTEMS. Intermediate switch — Annunciator switch board . . 123-128 CHAPTER X. CHOICE OF INSTRUMENTS .... 129 CHAPTER XI. CONSTRUCTION. Indoor wiring — Stapling wires — Indoor joint — Outside wiring — Insulators and fittings — Joint for overhead wires — Paying out wire — Leading-in wires — Lightning arresters . . 130-140 CHAPTER XII. FAULTS. Testing for instrument faults — Examples : Method of adapting " Hunningscone Dfickert " transmitter to obsolete pattern instruments . .... 141-152 INDEX TO ILLUSTRATIONS AND DIAGRAMS The Rev. H. Hunnings, Inventor of the Granular Transmitter Frontispiece Fig. P.4GE 1. Illustrating the Magnetic Field 2 2. A closed conductor in the Magnetic Field 2 3. The Solenoid 3 4. The Theory of the " Bell " Telephone 3 5. The " Bell " Receiver 5 6. The Electro Magnet 9 7. Two " Bell " Receivers connected for conversation ... ... 10 8. The " Double Pole " Bell Receiver 12 9. The " Manchester Watch " Receiver 13 10. Hughes' Original Experiment 16 11. Hughes' Perfected Microphone 17 12. The Hunnings Microphone 18 13. The Induction Coil 20 14. The " Byng " Transmitter 21 15. The " Byng " Transmitter connected to Watch Receiver ... 21 16. Two " Byng " Transmitters connected to two Watch Receivers 21 17.) 18. (-The " Hunningscone Deckert" Transmitter 22 19.) 20. Two " Hunningscone Deckert " Transmitter and two Double Pole " Bell " Receivers connected together ... 25 21. Simple Form of Battery Cell 26 22. Carporous Leclanche Battery Cell 28 23. The E C C Dry Cell 30 24. Connecting Cells in series 31 25. Connecting Cells in parallel 32 26. Connecting Cells in series-parallel 32 27. The Electric Bell 33 28. The " Stanley " Telephone Combination 38 ^' L Construction of the " Stanley " Telephone 39 31. Diagrammatic Connections of two " Stanleys " 40 32. Back of " Stanley " Telephone 44 33. Simple Connections of two " Stanleys " 44 34. Simple Electric Bell Circuit, A to B 45 34A. " Stanley" Telephone adapted to Simple Electric Bell Circuit 46 35. Simple Domestic Bell and Indicator Circuit 47 viii INDEX TO ILLUSTRATIONS AND DIAGRAMS Fig. 36. 37- 38. 39- 40. 41- 42. 43- 44- 45-' 46. 47-, 48. 49- 50. 51- 52- 53. 54- SS- 56. 57- 58. 59- 60. 61. 62. 63. 64. 65- 66. 67. 68. 69. 70. 71- 72. 73- 74- 75- 76. 77- 78. 79- 80. 8i. 82. " Stanley " Telephones adapted to Simple Domestic Indicator Circuit " Stanley'' Telephone adapted to Simple Domestic Indicator Circuit, but with ringing either way Plug Board Switch Office Call Bell System, A to B, C, D, E, F, and G "Stanley" Telephone connected so that A can call and con- verse with B, C, D, E, F, and G " Stanley " Telephone connected so that A can call and con- verse with B, C, D, E, F, and G, but to call either way ... B, C, D, E, F, and G, to call to A and speak " Stanley " Combined "Wall Set " Stanley " "Wall Set connected to Table Set -" Stanley " Table Sets 47 49 50 52 52 52 54 55 55 56,57 " Stanley " Hand Combination ... 58 „ „ „ Diagrammatic 58 ,, „ „ connected to "Wall Set ... 60 Two " Stanleys " connected together, with only one Battery 61 " Stanley " Portable Telephone 62 „ „ „ Diagrammatic ... ... 62 Special Plug for " Stanley " Portable Telephone 63 " Hunningscone Deckert " Domestic Wall Set 65 ,, „ „ „ Diagrammatic 66 Two ' Hunningscone Deckert " Sets connected 67 " Hunningscone Deckert " Set without Bell 68 Two „ „ connected 69 Superior quality "Wall Telephone without Bell ... ... 70 „ „ „ with Bell 70 Two „ „ „ connected 70 h " Hunningscone Deckert " Table Telephones ... 71,72 "W^all Set with Hand Combination 73 "Wall Set connected to Table Set 73 " Byng " Telephone Set with Induction Coil 73 Simple Two Way Switch 75 A to speak to B and C with Simple Two Way Switch ... 75 Two 'Way Switch with back contacts 76 Four-point Commutator Switch ... 76 A to call and speak to B and C, and OTcc j;crsa 77 Back connections of Four-point Commutator Switch ... 77 Five-point Commutator Switch 78 Back connections of Five-point Commutator Switch ... 78 Six-point Commutator Switch 79 A to call and speak to B and C, and vice versa ; and B and C speak to each other through A 80 Back Connections of Six-point Commutator Switch 80 Domestic Indicator Plug Board 81 Diagrammatic Connections of one movement 82 Connections from a Central Station to any number of Sub- stations 83 INDEX TO ILLUSTRATIONS AND DIAGRAMS ix Fig. page 83. Annunciator Switch Board 85 84. Single movement shown diagrammatically 86 85. Connections of Sub-stations to Annunciator Switch Board ... 87 86. Two Sub-stations plugged through 88 87. Plug Board Intercommunication System 90 88. Intercommunication Plug Board 91 89. The " General " Intercommunication Wall Set ... «... 93 go. Internal connections of the " General " Intercommunication Wall Set 93 gi. The " General " Intercommunication System facing g^ 92. Multiple Cable 94 93. Connecting Box closed 95 94- >, ■, open 95 95. Method of using Connecting Box 96 96. Back view of Connecting Box 97 97. " General " System with Mixed Stations facing g8 98. Single Groove Casing 100 99. Insulated Staples 100 ■[ Table Intercommunication Sets loi 102. Multiple Flexible Cable 102 103. Multiple Rosette 102 104. Method of using Multiple Rosette 103 105. " General " Wall Set with Hand Combination 104 106. The " Byng " Intercommunication Telephone 105 107. The " Reply " and " Call " Telephone 105 108. A to call or be called by any number of Sub-stations on the " Reply " and " Call " System 106 109. Magnets and Pole Pieces of a Magneto Generator 108 no. Illustration of Armature of Magneto Generator 108 111. Section of Armature 109 112. Armature ; showing method of connecting Armature Wires 109 II3.^ "4- 1 The Magneto Bell 110,111 lie!) 117. Two Generators and two Bells connected for Signalling ... 113 118. System of cutting out Armature when Generator is at rest 114 119. Magneto Telephone Combination for Long Distance Work 115 120. „ „ on Backboard 116 121. Two Magneto Telephone Sets connected together 117 122. Internal Connections of Magneto Wall Set 118 ^^M Magneto Combination Table Telephones 119 125. A to call and speak to B and C, and vice versa ; and B to speak to C through A with Magneto Combinations 120 126. A to call and speak to any number of Sub-stations and vice versa. Also Sub-stations to be plugged through to each other, using Magneto Combinations 120 127. Short Distance Magneto 121 128. Internal Connections of Short Distance Magneto 122 129. Double Line Intermediate Switch 124 X INDEX TO ILLUSTRATIONS AND DIAGRAMS Fig. page 130. Connections of Double Line Intermediate Switch 125 131. Movement of Double Line Switch Board 126 132. Showing two Sub-stations plugged through to each other using Double Lines 127 133. Connection of Annunciator Switch Board with Double Lines 128 134. How Wires should be stapled 131 135. Indoor Joint for Telephone Wire 131 136. 137- 138. 139- 140. Pole Roof 141. " Sinclair " Insulator 142. Binding Line to Insulators 143. Britannia Joint for Overhead Wire 144. Correct Method of paying out Wire 145. Incorrect Method 146. Leading-in Insulator 147. Method of using Leading-in Insulator 148. Toothed Plate Lightning Arrester 149. Method of connecting same 150. Circular Plate Lightning Arrester 151. B'use Lightning Cut-out 152. Pair of Lines protected by Circular Plate Arrester and Cut outs 153. Internal Connections of Domestic Telephone 154. Linesman's Galvanometer 156. Illustrative of Method of Testing Instruments 157. Ditto ditto 158. Testing for Short Circuit on Lines ... 159. Testing Battery for Short Leak 160. The " Hunningscone Deckert," Front View 161. „ „ „ Back View 162. Method of cutting Woodwork for fitting "Hunningscone Deckert" 163. " Hunningscone Deckert " fixed 164. Blake Converter Type of " Hunningscone Deckert 165. Method of fitting same 150 151 151 151 PREFACE WE have frequently brought to our notice the difficulties which present themselves to those unaccustomed to telephone work — difficulties trifling in themselves to the experienced tele- phone hand, but which, to those to whom the work is new, offer a great drawback to the introduction of the telephone in many instances where it is at present unthought of. The object of these pages, therefore, is to assist the fitter to obtain some knowledge of the telephone, both theoretically and practically, and also to give diagrammatic connections of most of the systems that are likely to be required under ordinary conditions. The remarks throughout will have special reference to the various types of instruments manufactured by the "General Electric Company," and we shall en- deavour, by showing internal as well as external con- nections of the instruments, to render the matter of locating instrument faults as simple as possible. xii PREFACE We do not wish it to be inferred that this is a general treatise on the telephone. It is intended to be handled by the trade with a view to saving them the time and trouble so often expended in puzzling over an ap- parently faulty instrument and finally returning same to be repaired, whilst in 99 per cent, of the cases the faults exist quite outside the instrument, or if an in- strument fault, is such as could be easily remedied by one conversant with the details of consti"uction. In order that this may prove of service to those absolutely ignorant of Electrical Science, we find it necessary to explain some of the very elementary laws of Electricity and Magnetism, without knowledge of which it would not be possible to understand the technical expressions necessarily used. We trust that the effect of our efforts will be to enable those who have hitherto looked upon telephone work as some- thing complicated and difficult, to lay themselves out for this class of work with confidence. For further and more detailed information we would recommend our readers to study the excellent works by Preece & Stubbs, Sinclair & Raphael, A. R. Bennett, F. C. Allsop, Poole, &c., in which collectively will be found exhaustive information, including descriptions of the most complicated exchange systems. CHAPTER I "BELL" TELEPHONE RECEIVERS PROFESSOR FARADAY formulated the rule, " That a conductor of electricity moved in a magnetic field so as to cut the lines of force constituting same, has, generated within it, currents of electricity which circulate throughout its length and which vary in direction according as the movement is to or from the magnetic field." In order to intelligently understand this rule, it is necessary to have some idea as to what is meant by the "magnetic field." Suppose we take a steel permanent magnet (with which the reader is doubtless familiar), lay it on a flat surface and place over it a sheet of white paper. Now sift some iron filings over the paper, and it will be observed that they arrange themselves in a series of symmetrical curves along the sides and ends of the magnet (Fig. i). These curves are known as "Lines of Force," and the 2 COMMERCIAL AND DOMESTIC TELEPHONY whole of the space permeated thereby is termed the " Magnetic Field." It will be observed that the " Lines of Force " are most numerous at the ends or " Poles " of the magnet, consequently it is at these points that the " Magnetic Field " is most intense. If a ring of metal such as copper is introduced into the magnetic field (F'ig. 2), the act of such introduction N Fiy2. causes an electric current to be generated in the ring which circulates around its circumference in a given direction. If the ring is now withdrawn a current is again generated therein, the direction of which is opposite to that which was generated by the first movement. Replace this ring by a coil of wire having several turns called a "solenoid" (Fig. 3). "BELL" TELEPHONE RECEIVERS 3 Introduce into the centre of this solenoid a steel magnet (as shown by dotted Hnes). A current is generated in exactly the same manner as in the first instance. Withdraw the magnet and again we have a current generated in the opposite direction to the first. If now we take a bar magnet, and on one of the ends wind a coil of fine insulated wire, i.e., covered with some non-conducting material such as silk, and having a great number of turns, we have a conductor permanently fixed within the magnetic field (Fig. 4), in such a manner that the lines of force cut through many turns of the coil. So long as no disturbing influence is brought to bear upon them no currents are generated therein. But now supposing a piece of iron be introduced within the magnetic field as 4 COMMERCIAL AND DOMESTIC TELEPHONY shown by the dotted lines. For simpHcity's sake we will examine two lines only, a a. The firm lines in Fig. 4 show the magnet with coil of wire wound on the end and the two lines of force intersecting, one over and one under. The dotted lines, h b, show the same lines of force when a -bar of iron is placed in the magnetic field. The dot and dash lines, c c, show the same lines again when the iron is approached nearer to the magnet. It will thus be observed that the position of the lines of force is, by the movement of the iron bar, caused to be altered, and that in effecting the alteration they have traversed through and across a great many of the turns of wire. This movement has practically the same effect on the wire as takes place in the closed conductor moved in a magnetic field. In both cases a current is generated by the lines of force cutting the coils of the conductor, the only distinction being that in the first case the conductor was caused to move in the magnetic field, whereas in the second case the magnetic field (represented by the lines of force) is caused to move through or across the conductor. The effect is in each case the same. If the bar of iron is now removed a current is set up in the opposite direction, the reason being that the lines of force in regaining their normal position move in exactly the opposite direction to that in which they moved when first disturbed. This gives rise to a modification of the rule laid down, namely — "That if both conductor and magnetic field be "BELL TELEPHONE RECEIVERS 5 stationary-, any medium which causes a disturbance of the magnetic field will also cause currents to be generated within the conductor, the direction of which is governed by the direction in which the disturbance is exercised." To Professor Graham Bell is due the credit of first turning these phenomena to account in the invention of the telephone. Bell's perfected telephone was constructed as shown at Fig. 5. In this figure, a re- presents a wooden containing case, b the bar magnet, c the coil of fine wire having many turns, d is a circular diaphragm of thfn sheet iron, held firmly in position by the cap e; f f represent two binding screws lor making connections. If the foregoing remarks have been clearly compre- hended it will readily be seen that any disturbance of the diaphragm d will have the effect of causing a cor- responding disturbance in the magnetic field of b, in which coil c is fixed, and that any such disturbance will have the effect of causing currents of electricity to be generated in c, the direction of which will be con- 6 COMMERCIAL A\D DOMESTIC TELEPHONY trolled by the direction in which the disturbance takes place J that is, whether d approaches or recedes from the end of the magnet b. So that if the diaphragm be made to vibrate rapidly, the movements will consist of an alternation of approaches to and recessions from the end of the magnet. The consequence will be that so long as this vibration continues alternating currents of electricity will be generated in the coil c, the rapidity and strength of which will be governed by the rapidity and amplitude of the vibrations of diaphragm =^ h "mm A In the induction coil the thick lines represent the "primary" coil, and the thin lines the "secondary" coil. If A speaks to B, the secondary currents induced in A's induction coil are conveyed through his own receiver to the line through B's receiver, " secondary " coil, along the return wire and back to A's secondary coil. The respective resistances of the induction coils finally adopted by the G.P.O. are — Primary', i ohm. Secondary, 25 ohms. CHAPTER III B BATTERIES AND ELECTRIC BELLS EFORE proceeding with a description of the various types of instruments, a few remarks relative to Electric Bells and Batteries may very conveniently be inserted, since they play an uii- portant part in telephony. The Electric Battery in its simplest form consists of a copper plate and a zinc plate immersed in acidulated water contained in a convenient vessel for the purpose (Fig. 2i). If the plates are metallically connected to BATTERIES AND ELECTRIC BELLS 27 each other by a piece of wire to binding-screws provided for the purpose (see dotted line), an electric current is set up which circulates through the battery and connecting wire in the direction shown by the arrows ; that is, it passes from zinc to copper inside the battery, and from copper to zinc outside the battery. If the connecting wire is severed, the passage of the current is checked. The zinc and copper plates are known as the "Elements" of the battery, and the binding-screws to which the wire is connected are known as the " Poles." The zinc is the positive element, as the current inside the battery passes from it to the copper which is the negative element. The connecting point on the copper is the positive " Pole," as the current outside the battery passes from it to the zinc which is the negative " Pole." Care must be taken not to confuse these two terms " Pole " and " Element." Whenever the positive " Pole " of a battery is mentioned it refers to the copper, and negative " Pole " refers to the zinc, although if spoken of as elements the copper would be negative and the zinc positive. The sign -\- is used to indicate the positive pole, and — to indicate the negative pole. Although above we have only mentioned copper and zinc, it must not be supposed that only these two metals will set up an electric current. As a matter of fact, any two dissimilar metals immersed in acidulated water will behave in the same manner more or less efficiently. The quantity of current obtained is in direct pro- portion to the size of the plates, and the pressure of the current depends upon the materials used for the 28 COMMERCIAL AND DOMESTIC TELEPHONY elements. The unit of current is the "Ampere," and the unit of pressure (generally termed E M F, or electro- motive force) is the Volt. An analogy may be useful. Suppose a stream of water is being forced through a pipe by a pi-essure of 50 lbs. behind it. This pressure is analogous to the E M F of our battery, and the quantity of water is analogous to the quantity of current. For instance, we say that Fig. 12. the discharge of water is, say, 50 gallons with a pressure of 50 lbs. ; so we say that a battery is discharging, say, 4 amperes of current at 2 volts. As stated above, the zinc and copper elements form the simplest form of battery, but the modifications and improvements in batteries have been simply too numerous for the present work, and we would refer our readers to more extensive treatises on the subject, and come at once to the two forms with which we are most BATTERIES AXD ELECTRIC BELLS 29 nearly concerned, and which are best for use with any of the telephones hereafter described. The first of these is the " Leclanche Carporous" battery, the appearance of which is shown at Fig. 22. This battery consists of — 1. An outer containing glass jar. 2. A carbon cylindrical inner vessel which contains a mixture of crushed carbon and per oxide of manganese, and forms the negative element. 3. A rod of zinc forming the positive element, which is placed down the centre of the negative element inside a tube of porous earthenware. 4. A saturated solution of salammoniac forming the exciting medium. There are three sizes of this battery, namely, No. i (3-pint), No. 2 (2-pint), and No. 3 (i-pint). The second form of battery referred to above is the E C C Dry Cell. This is constructed as shown in Fig. 23, which also shows a section of the cell. Index to parts. T (+) represents terminal positive. C „ carbon. S C „ cotton. M „ manganese dioxide, &c. L „ lime and salammoniac, &c. Z „ zinc containing vessel. T (-) „ negative terminal wire. P „ pitch (top covering). I „ insulating base. W T „ waste tube. 30 COMMERCIAL AND DOMESTIC TELEPHONY The dry cell has great advantages over the wet cell in the way of cleanliness, but has not so long a life. In many cases, however, it is very convenient, as it does not freeze, neither is there any solution to evaporate. The E M F of either of these cells is approximately 1*50 volts. It is obvious that this would only be sufficient to overcome a limited Fig. 23.— Vertical Cross Section.— K.C.C. Cell. resistance, and it therefore often becomes necessary to increase the E M F. This is done by con- necting a number of cells together, as shown at Fig. -'4, with the zinc of the first cell connected to the carbon of the second and so on. If we take, say, two cells and connect them in this manner, the E M F becomes twice that of one cell, and so on in direct BATTERIES AND ELECTRIC BELLS 31 piroportion as the number of cells is increased. This is called connecting in series, and the end zinc and the end carbon form the poles of the battery. It will therefore be seen that if the ciixuit is one of high resistance the battery cells should be connected in series. In speaking of batteries it is usual to speak of a single set of elements as one cell, whilst a number of cells connected together is called a "battery" of so many cells. FigZ4 The symbol i| is used in diagrams to denote one cell of battery. The short line represents " zinc," and the long line represents " carbon." For the " Stanley " telephone the battery required will depend on the length of line ; but for all ordinary purposes, two cells connected in series at each station, where a separate battery to each is used, or four cells where a battery common to the whole is used, will be found sufficient. For the " Hunningscone Deckert" microphone circuit two cells in series are sufficient for all purposes. 32 COMMERCIAL AND DOMESTIC TELEPHONY Besides being able to increase the E M P" of a battery as above shown, it is sometimes necessary to increase the quantity of current given out, particularly in very low resistance circuits. In Fig, 24 the E M F only is increased, the quantity of current remaining the same. We have stated above that if we increase the size of the elements the current is increased in proportion ; but since the battery cells sold commercially are of a yig25 Fig.&6 standard size, it would be inconvenient to do this literally. The expedient resorted to, therefore, is that shown at Fig. 25, wherein it will be seen that the cells are connected with all the carbons and all the zincs together. If we take two cells so connected, the current obtained is double that obtained from one cell, and in fact the two cells really represent one cell with elements double the size of a single cell, and the same rule holds good if fifty cells were connected in this manner. This is known as connecting in parallel BATTERIES AND ELECTRIC BELLS 33 (or multiple), and the E M F is not increased at all by this method, but remains the same as for one cell. A further method of connecting batteries is shown at Fig. 26, in which six cells are shown connected in what is called parallel-series — that is, to obtain the E M F of three cells but the current of two cells. First of all two sets of three cells are connected in series, and then the end carbons and the end zincs respectively are connected together. The Electric Bell is constructed as shown at Fig. 27. al a" represent two coils wound upon iron cores, constituting an electro-magnet ; h is the framework which carries the electro-magnet, spring c, and iron armature d; e is an extension of ai'mature, and / is the hammer which strikes on bell gong, g. It will be observed that one end of spring c is set outwards from the iron armature and rests against a pointed screw, h. This screw is carried upon a brass pillar, i, called a contact pillar, so that it can be adjusted forwards or 4 34 COMMERCIAL AND DOMESTIC TELEPHONY backwards and fixed in position by set screw /'. The contact pillar is mounted upon the same iron frame as the rest of the apparatus, but is carefully insulated from it by ebonite bushings. Two binding-screws, /' /", form a convenient means of connecting the battery wires. If now the poles of a battery are connected to the two binding-screws, /' j", the hammer / immediately com- mences vibrating, which is brought about by the follo\\'- ing process : — Supposing the carbon is connected to binding-screw /", the current passes round the two coils, ((' a", on to the contact pillar, // /, through the spring, c, and on to terminal, j' , and so to zinc of battery. The consequence is that the iron armature, d, is attracted by the electro-magnet to a sufficient extent to draw the spring, c, away from point /;, with the result that the circuit becomes broken, the electro- magnet loses its magnetism, and the armature falls back to its former position only to be attracted again and again so long as the battery is connected to terminals, / and /"- The electric bell is applied to telephones for the purpose of signifying to the person at the distant end that his attention is required at the telephone. Electric bells are often liable to faults due, it may be, to faulty manufacture, or, as is often the case, to inexperienced handling. Suppose on closing the circuit the armature becomes attracted but does not vibrate. First see that the spring leaves the contact point, h, when attracted. If it does not do so, draw the screw backwards until it does. If this does not remedy the defect, the evidence BATTERIES AND ELECTRIC BELLS 35 points to a short circuit between the contact breaker and the metal frame, b. Examine well the end of coil connected to contact breaker and see that it does not touch the frame. If it is all right in this respect, then the insulation between the contact breaker and the frame must be deficient and should be attended to. Suppose on closing the circuit the armature does not move at all, and, in fact, shows no sign of the presence of a current passing round the coils, a' a", this points to a disconnection somewhere and should be localised as follows : — 1 . Connect one pole of battery to terminal, /'. 2. Lay bare the joint, k, which connects the two coils together, and touch it with a wire connected to the other pole of battery. If circuit between /' and joint k is good the armature will be attracted. 3. If the armature is not attracted, scrape the insula- tion of the wire, /, passing from coil through base, hold one battery wire thereon and the other battery wire on joint as before. If the armature is now attracted, the fault is in the wire which is connected on to the terminal /' / if it does not attract, then the fault is in the coil a' . Suppose, however, that at the second test it was found that the armature became attracted, pro- ceed further. ' 4. Touch battery wire on the contact pillar, h. If the armature does not now become attracted the fault is in coil a". If it does attract, touch battery wire on iron framework. If the armature is now attracted it will vibrate, but if it is not attracted the probability is that the contact points of h and c are dirty, and not 36 COMMERCIAL AND DOMESTIC TELEPHONY in electrical contact with each other. If, however, the armature vibrates, then the fault must be between the terminal /' and connection on the metal frame- work, b. It sometimes happens that the armature is attracted and does not fall away when the circuit is broken. This is generally due to residual magnetism in the magnet cores, which, if of too hard iron, will retain their magnetism even after the circuit is broken. Most bells have brass pins in the ends of cores which prevent the armature from sticking. The defect is also some- times temporarily remedied by sticking a strip of paper on the face of armature. CHAPTER IV THE "STANLEY" DIRECT WORKING TELEPHONE IT is evident that for ordinary commercial purposes, the Telephone simply as previously described would be practically useless. • In the first place, if the "Byng" or "Hunningscpne Deckert" mid^ophones with their receivers and batteries were left connected as shown at Figs. i6 and 20 respectively, the batteries would very soon get exhausted and new required. In the second place, the telephone would be useless with- out some loud signal to call the attention of the person required. It is therefore necessary to introduce into the instrument an arrangement of switches and calling apparatus whereby, under normal conditions, the lines are left connected to an electric call bell at each end, and the act of lifting the receiver causes the electric bell to be automatically switched off and the telephone with its battery to be switched into circuit. These calling apparatus are divided into two classes, namely — 37 38 COMMERCIAL AND DOMESTIC TELEPHONY (a) Battery call apparatus. (6) .Magneto call apparatus. The Battery call apparatus is that in which an ordinary electric bell in combination with the tele- phone, as above explained, is caused to ring by pressing the push button provided for the purpose on each instrument. The Magneto call apparatus is that in which a magneto-electric generator is used for ringing the bell Fig. 28. at the respective ends, particulars of which will be found in Chapter VII. Dealing first with the battery call apparatus, we come at once to the " Byng" combination, which is made up in the form shown at Fig. 28 and called the "Stanley" Telephone. Fig. 29 shows a section of this instrument in its complete form. Fig. 30 shows plan of same with receiver and front plates removed, and Fig. 31 shows THE STANLEY DIRECT WORKING TELEPHONE 39 rr'r-r'^n\\y^ FicfS^g Ti^ZO. 40 COMMERCIAL AND DOMESTIC TELElPHONY a o ja tn G ^ en -2 ^ u M ".S S « c o o a, O en en -ri H 5 g« a, "u o THE STANLEY DIRECT WORKING TELEPHONE 41 the practical connections of the various parts of two instruments connected together for communication. For the sake of clearness, this last is made purely diagrammatic, without any regard for the exact shape or position of the various parts. The same reference letters denote the same parts in all these diagrams. a is an ebonite base, shaped to accommodate the various parts. h The transmitter, c Push button of ringing key. d Line spring of ringing key. e Battery contact of ringing key. / Switch lever. g Flexible steel extension of switch lever. h Bell contact of switch. { Microphone contact of switch. j Spiral spring having the inside end fixed to spindle of switch, and the other end clamped under brass plate. k Spindle carrying switch lever. I Brass front plate, which has a filigree opening so that it can be spoken through. m Semi-circular yoke of brass in which receiver n rests when not in use. German-silver spring which holds the transmitter in position and also forms electrical contact therewith. p Tinfoil ring to make contact with diaphragm of transmitter. The swdtch lever, /, when receiver is out of yoke projects upwards through the plate I (see Fig. 31), 42 COMMERCIAL AND DOMESTIC TELEPHONY being maintained in that position by the tension of spiral springy, which also causes extension g of switch lever to make electrical contact with contact stud i. When receiver is placed in the yoke, in, the lever, /, is depressed as shown at Fig. 29, the result being that the extension, g, is caused to make contact with bell contact, h. Thus it will be seen that the parts /, g, h, i, I, con- stitute an automatic switch, which is actuated by raising the receiver or replacing it. The ringing key consists of the parts c, d, e and plate /. Normally the spring d rests by its upward set against the plate /, but when button c is pressed, d leaves plate / and makes contact with e. The symbols R, R indicate the receiver terminals or connecting plates. B. Bell. Batt. Battery. L.. Line. As the first action in using a telephone is to give the call signal, we will examine what takes place when the push button, say at " B," is pressed, the receivers being at rest in their respective yokes. Starting at the carbon of B's battery, we find that the only possible circuit is from carbon to battery terminal, stud c, key spring d, line terminal, through line to line terminal at A, spring d, plate /, springy, lever /^, bell contact h, terminal B, one terminal of electric bell, through same to each terminal, return wire, and so back to zinc of B's battery. It will be observed that a battery is fixed at each station, and that the battery of B, as just shown, rings the bell THE STANLEY DIRECT WORKING TELEPHONE 43 at A. When A presses his ringing key, the same effect is produced but in the reverse direction ; A's battery being brought into use to ring bell at B. If now a signal has been given and answered, each person takes receiver from yoke, places it to the ear and commences conversing. The speaking circuit is now as follows : — Commencing at carbon of B's battery to batt. termi- nal, back electrode b of transmitter, through carbon granules to diaphragm, tinfoil ring p, receiver terminal R, receiver, terminal R', contact stud i, switch^/, spring 7, plate /, spring of ringing key d, line terminal L, through line to terminal L at A, spring of ringing key d, plate /, spring j, lever /, g, contact stud /, receiver terminal R', receiver, terminal R, tinfoil ring p, diaphragm of transmitter, carbon granules, back electrode, battery terminal to zinc of A's battery, through battery to carbon which is connected on to the return wire and finally gets back to zinc of battery at B. An important point to be observed is that at one station the carbon of battery is connected to instrument, whilst at the other station the zinc of battery is connected to instrument. This is very essential, as when, speaking, both batteries are in use, and are in fact working in series, so that if carbon were connected to instrument in each case, the currents from the respective batteries would be opposing each other, and no practical result would follow. A careful perusal of the above will also show that although accessory apparatus has been intro- duced, when speaking, the conditions are precisely the same as in Fig. 16. This point should be borne in 44 COMMERCIAL AND DOMESTIC TELEPHONY mind, as these conditions are always necessary, no matter in what combination the instruments are used. KiG. Fig. 32 shows the exact arrangement of the terminals at the back of the instrument, and Fig. 33 shows two instruments as supplied, and are connected for working purposes, establishing perfect telephonic communication between A and B. In future diagrams where a simple instrument is required to be shown it will be represented THE STANLEY DIRECT WORKING TELEPHONE 45 as at Fig 33 ; the internal connections can always be followed by referring to Fig. 31. The great feature of the "Stanley" Telephone' is its adaptability to ordinary existing electric bell circuits. Thus if we have a simple electric bell, say from drawing-room A to kitchen B {see Fig. 34), it might be considered, and undoubtedly would be, advantageous to have verbal communication, instead of simply a call bell, which necessitates the servant coming to the drawing-room to get her instructions. This com- munication can be very easily effected by using the LINE -^n PUSH o Hill RETURN > Fig. 34.^Simple Electric Call-Bell Circuit. " Stanley " telephone in connection with the existing wires, battery, and bell. All that is required is simply to remove the push at A, substitute the telephone, and add a telephone at B exactly as shown at Fig. 34a. The mistress in drawing-room A can now, by pressing the ringing key, ring to the servant in the kitchen B ; they then each take a receiver from the yoke, hold it to the ear, and converse in the ordinary manner. This is the ' ' Stanley " adapted to a simple electric bell circuit, and it is just as easily adapted to bell circuits where a number of rooms ring to the kitchen. 46 COMMERCIAL AND DOMESTIC TELEPHONY on an indicator, indicating from which room the bell has rung. Fig. 35 shows the existing bell circuits with pushes in rooms Nos. i to 4. Fig. 36 shows that all that is required to establish telephonic communication between any of the rooms and kitchen is — I. Cut wire between Z of battery and bell, say at A. Then connect the free end from zinc to line terminal of telephone. Connect the other free end which comes from the bell on to the bell terminal. Connect terminal marked Bat. to the return terminal of indicator (Fig. 36). i-IA/E /y34^ fJETURU/ W/K£ " Stanley " Telephone adapted to Simple Electric Bell Circuit. 2. Remove pushes from their position in rooms, leaving the two push wires free. Connect one of these wires on to line terminal and the other on to the battery terminal of telephone. It does not matter much which is connected to line or which to battery, but it is advisable to let the wire which is connected to the battery terminal be the main carbon wire as shown in Fig. 36. The above simple operation establishes verbal com- munication between any of the rooms so connected THE STANLEY DIRECT WORKING TELEPHONE 47 $ (#) (^ ^ Fig 35- o o- If 9 ® m a Simple Domestic Bell and Indicator Circuit. 'Stanley" Telephones adapted to Electric Bell and Indicator Circuit. 48 COMMERCIAL AND DOMESTIC TELEPHONY and the kitchens, and the method of using is as follows : — To call attention from any room to kitchen — 1. Press small button at the bottom of instrument. This rings the bell and operates indicator in kitchen. 2. Take receiver from yoke in which it normally rests, place it to the ear and wait the servant's reply. When answering speak against the filagree plate, keep- ing the receiver held to the ear. The servant on receiving a call immediately takes her receiver from yoke and replies in the usual way. The servant must be taught to always answer the telephone immediately the bell rings. From the above it will be seen that the only articles required are the telephones themselves, no accessories whatever other than those already in use for the electric bells, that is, assuming that they are in fair condition. It is sometimes thought to be irksome for a mistress to be under the necessity of holding the telephone to the ear until the servant replies. In suph cases, there- fore, the system shown in Fig. 37 can be easily used, but necessitates the running of one extra wire all round the system. The following accessories would also be required ; — One 4-cell battery B. One bell for each room. One plug-boai-d with spring contact. It will be observed from Fig. 32 that the terminal marked Bat. really consists of two terminals joined together by a strip of metal. For the above system this connecting piece must be removed from all the THE STANLEY t)IRECT WORKING TELEPHONE 49 telephones, except the one in the kitchen, and the terminal bearing contact spring {see Fig. 29) must be connected to the extra or Return wire as shown. This system allows the mistress to ring the servants y ^^LJ^'RcTjiw FlG. 37. and wait until they ring back in reply before taking the receiver from the yoke of telephone. Supposing now that one of the rooms wishes to call the kitchen. By pressing the ringing key the carbon of battery A is connected to line. The current passes 5 So COMMERCIAL ANt) DOMESTIC TELEPHONY through the line to screw g, g to barrel of plug-hole //, (see Fig. 38), contact spring /, and to indicator move- ment of that particular apartment through bell to zinc of battery, thus ringing and at the same time indicating from which room the call has been given. Suppose room No. 2 has rung up. The servant takes the plug hanging from plug-board and inserts it into No. 2 plug- hole, asy. Fig. 38. The end of this plug is insulated with an ebonite extension (see Fig. 38). J This ebonite end is pushed into contact with the spring and raises it from the barrel portion of plug- hole, thus breaking connection between the line of telephone and the indicator. At the same time the brass portion of the plug forms contact with plug-hole, thus connecting the line of kitchen instrument to the line of No. 2 instrument. Dotted lines show position when plug is inserted. If now the servant presses ringing key of her instrument, the carbon of battery B is connected to line of No. 2, and the current passes vid No. 2's line terminal, ringing key, and switch to THE STANLEY DIRECT WORKING TELEPHONE 51 bell, through bell to return wire, and so back to zinc of battery B, thus giving a reply ring to the call. If now the receivers are taken from their yokes, the current would pass from battery B to kitchen instrument, throiigh same, through plug j, barrel of plug-hole h, line terminal g, and so on to No. 2, leaving No. 2 instrument by the return terminal, and so back to zinc of battery B. In each of these last two systems it may be borne in mind that it is not essentiar ihat all the rooms be connected unless required ; only those which require to speak to the kitchen need be so connected ; the other rooms need not be interfered with. The Electric Bell systems above assumed are those generally met with in private establishments, but in business houses somewhat different systems are fre- quently found. For instance, the principal (A) of a large firm very frequently has a push-board on his table with, say, half a dozen pushes on it which ring to various offices, B, C, D, E, F, G, for the purpose of summoning attention of any individual whose presence is required. In the ordinary course of events the pushes, battery, and bells would be connected as shown in Fig. 39. If it is required to introduce telephonic communica- tion into these offices, the same wires, batteries, and bells can be used ; and in fact all that is required is seven instruments and a six-way line selector. The connections to instruments must be made as at Fig. 40. By inserting plug of line selector in the hole which is connected to the line of office required and 52 COMMERCIAL AND DOMESTIC TELEPHONY FyS9 Office Call-Bell system. W W -i "Stanley" Telephone adapted to Office Call- Bell system. Ring one way only— A to B, C, D, E, F, and G. SJW 'm iW m iw Fi^tl A ji A A ji." ii---- -"-.- " Stanley " Telephone adapted to Office Call-Bell system to rini' both wavs. THE STANLEY DIRECT WORKING TELEPHONE 53 pressing the ringing key, a call on the bell can be given and replied to in the ordinary manner. Thus it will be seen that with very little accessory apparatus besides the actual telephone instruments, the existing bells, batteries, &c., are utilised with but slight alteration. This system simply allows the principal to call the different offices and receive a I'eply, but does not allow the offices to call up the principal. Where this is required, the simplest method is to alloW the Bell System to remain unaltered, and run an extra wire round to all the stations, as shown in Fig. 41. The principal calls by using the existing bells and pushes, and any of the offices can call principal by pressing the push-button on their respective instru- ments. In Fig. 41 the dotted lines show the existing bell system, and the firm lines show the addition of the extra wire and telephones. It will be observed that the instruments are all connected aci^oss the line and return wires, but it is only the instrument which has its receiver out of yoke that is in circuit. The foregoing deals with the application of the telephone to most of the electric bell systems in ordinary use, but it is of course obvious that the diagrams given are equally applicable where new installations are proposed. Many of the following examples, for instance, refer to the foregoing diagrams : Example i. A wishes to call and speak to B, but does not want B to call him {see Fig. 34a). 54 COMMERCIAL AND DOMESTIC TELEPHONY Example 2. A wishes to call up and converse with B, C, D, E, F, 01- G, but does not want B, C, D, E, F or G to call him {see Fig. 40). Example 3. A wishes to call up, or be called by, B, C, D, E, F and G {see Fig. 41). Example 4. B, C, D, E and F wish to call, but not to be called by, A {see Fig. 42). Example 5. A wishes to call up, or to be called by, three or more stations, and requires indication of the person who is calling {see Fig. 37). In examples 3 and 4 it will be seen that the bell Fig 42 x_ " Stanley " Telephone connected so, that B, C, D, E, K, and G can call A. terminal of the telephone is left disconnected, except at A, as it is not used in these systems. These two examples are open to one objection, viz., that if A is talking to one station, any one at the other stations could, by holding the receiver to their ear, overhear the conversation ; but since for ordinary business purposes secrecy is not always of great importance, they will be found useful and cheaply in- stalled systems. Where, however, secrecy /.<; required, the system in example 5 should be used. Fig. 43 illustrates a wall pattern "Stanley" Telephone, THE STANLEY DIRECT WORKING TELEPHONE 55 Fig. 43. Fiji 4 4". RETURN WIRE ' Stanley " Table Telephone fitted to a Wall Pattern instrument. 56 COMMERCIAL AND DOMESTIC TELEPHONV with circular bell attached. This bell is made very compactly, with the movement underneath the gong. The terminals marked L, BAT, and BL indicate Fig. 45. Fl(i, 46. respectively "Line," "Battery," and "Battery- Line." They are to be connected as shown in Fig. 44. THE STANLEY DIRECT WORKING TELEPHONE 57 The " Stanley " Telephone, owing to the neatness of its design, is readily adapted foi" table use, and Figs. 45, 46, and 47 show three very neat patterns, each of which is made up with call bell. The instrument is connected to the battery and line wires through a flexible cord having three conductors, which terminate on a terminal board, having terminals marked L, Bat, Bl. Fig. 44 shows a table instrument connected to a wall instrument. In many cases it is convenient to have the tele- phone arranged with the transmitter and receiver in one piece, so that no effort is required to speak sufficiently close to the transmitter. Fig. 48 illustrates an arrangement of the " Stanley " Telephone for this purpose, which contains in the handle the necessary arrangement for ringing and also for switching out the bell and switching in the 58 COMMERCIAL AND DOMESTIC TELEPHONY Fig. 48. Interna) connection of Stanley Hand Combination. THE STANLEY DIRECT WORKING TELEPHONE 59 telephone, thus dispensing with the automatic switch before described. The instrument is shown diagrammatically at Fig. 49. The following is an index to the vai^ious parts : — a is an ebonite rocking lever, pivoted at its centre. 6 is a metal plate, fixed on the under side of a. c is a flat spring, which makes contact with b, and also with d, which is a metal cock for purpose described hereafter. e is the ringing contact of battery. ^ is a spiral spring, which forms connection between plate b and screw h, off which line connection is taken. / is an ebonite base, carrying the above parts. j is the receiver. /; is the transmitter. /, m, are the two connecting screws of k. n is wire connecting receiver to transmitter. is wire connecting receiver to switch. p is the telephone contact of switch. q, r, and s are " line," " battery," and " bell " wires re- spectively, which terminate in terminal board marked Line, Batt, Bell {see Fig. 48.) These terminals should be connected as at Fig. 50, which shows the hand combination used in conjunc- tion with an ordinary wall-set. From examination of Fig. 49 it will be seen that, on A (Fig. 50) giving a call, the current enters B by the line terminal to screw h, spring g, plate b, spring c, cock d, wire s, to bell terminal of connecting block, 6o COMMERCIAL AND DOMESTIC TELEPHONY thence to bell, through bell to return wire, and so back to A's battery. When, in reply, B depresses the end of rocking lever marked Ring, the current enters by battery terminal and wire r to screw e, plate 6, spring g, screw /;, and so to line, and through A's bell as usual. When he de- presses the end of lever marked Speak, the spring c is caused to leave cock d and make contact with p, Line P'iSSO fiETuRN wme B W/r J Stanley Hand Combination connected to Wall Set. thus cutting out the bell and switching in thereceiver and transmitter. The circuit is as follows : — Line to screw h, spring g, plate b, spring c, contact p, wire o, receiver j, wire u, transmitter screw /, transmitter k, screw m, and by wire r to battery, through battery to return wire, and so through A's battery and instrument as usual. This combination is very useful, as it can be hung up anywhere, laid down, or, in fact, can be fixed in any position that may be required. In this, as in all THE STANLEY DIRECT WORKING TELEPHONE 6i instruments with detached call bells, the bell can be fixed anywhere out of the way, so as not to be un- sightly. Fig. 51 illustrates a method of connecting two Stanley Telephones, using only one battery. This necessitates the running of a third wire, marked Battery Wire in diagram ; also, in B's instrument, Two Stanleys to ring and speak either way, using only one Battery. the removal of metal connecting strip referred to in connection with Fig. 37. As will be seen, the screw marked Return at B is connected to the return wire, whilst the battery wire is connected to terminal marked Bat. at both stations. Fig. 52 shows a special arrangement of the "Stanley" Telephone for portable purposes. This arrangement contains the "Stanley" Telephone, Call Buzzer and two 62 COMMERCIAL AND DOMESTIC TELEPHONY Fiu. 52. Method of connecting "Stanley" Portable Set. THE STANLEY DIRECT WORKING TELEPHONE 63 small E. C. C. cells. Each instrument is fitted with six yards of flexible cord, terminating in a special form of plug, so that when two instruments are plugged together they have twelve yards of wire between them. Fig. 53 shows the internal arrangement of the connections. It will be observed that each instrument has the carbon of battery connected to it, which would at first sight appear to be contrary to what we have hitherto said. But the question of opposing batteries is overcome by the special arrangement of the con- necting plug. Figure 54 illustrates this plug, and it will be seen Fig. 54. that each portion consists of a plug and socket, side by side, and that the plug of each fits into the socket of the other. Consequently, by connecting the line of instrument to the plug in each case, when they are joined together, the line of one is connected to the return of the other, so that the carbon of one battery, passing through the instrument to line, meets the zinc of the other's battery at the plug. It will thus be seen that they work in series with each other. This is a very useful combination for establishing communication from one room to another, particularly where it is desired to hold communication with a room in which an infectious disease exists. CHAPTER V INDUCTION COIL TELEPHONES THE "Stanley" Telephone, being a direct working instrument, is only recommended for short lines indoors, and for such simple systems as shown in the last chapter. Where the points to be connected are any distance apart, say more than loo yards, and also for more com- plicated systems, it is advisable to use the "Hunning- scone Deckert " or " Byng " induction coil instruments ; and, in fact, where a little additional initial expense is not important, these instruments are recommended for any system. Being much more substantially made than the " Stanley," they should always be used where likely to be subjected to rough usage. Fig. 55 shows the outward appearance of the " Hunningscone Deckert " Domestic Telephone with a double pole " watch " receiver ; V'lg. 56 shows the internal connections of this instrument. In induction coil instruments the automatic switch 64 INDUCTION COIL TELEPHONES 6S has to perform a double function when the receiver is Hfted from the hook. It has to disconnect the bell, switch on the telephone, and, at the same time, close the primary circuit of the induction coil, battery and transmitter. The symbols used with this instrument are as follows : — L, which denotes the " line " terminal. ZE C MC L Fig. 55 M C, which denotes the " microphone carbon " terminal. C, which denotes the " ringing carbon " terminal. ' ZE, which denotes the "zinc" and "earth" terminal. In Fig. 56, it will be noticed that the automatic switch of this instrument consists of a switch lever, a, having a bar, b, projecting from its side. This bar works up and down with the lever. When down, it 6 66 COMMERCIAL AND DOMESTIC TPXEPHONY makes contact with spring c, and when up it makes contact with springs d and e. Fig. 57 shows two of these instruments connected for use, and examination of this in conjunction with Fig. 56 will make the manipulation and working of the telephone quite clear. Supposing A presses his ringing key, the spring /is ZE C MC U "' 1 i J. pushed in, and is caused to leave contact point g, and to make contact with point e. The carbon of his battery is thereby connected to the line, the current passes along the line, to Hne terminal of B, to key/ of instrument, back contact of key g, enters bell, passes through bell coils and contact breaker h, out by the iron INDUCTION COIL TELEPHONES 67 frame i of bell movement and on to the spring c, switch hook a, terminal Z E, along the return wire to zinc of A's battery, thus giving the call on B's bell. If now the receiver is lifted off the hook, the bell is switched out of circuit and the telephone switched in, and further, the microphone circuit is established. The telephone circuit runs as follows : — Line terminal of A to ringing key, receiver, secondaiy -41] Fig. 57. coil, switch spring d, switch hook, and Z E terminal, thence by way of return wire to Z E terminal of B, and through the various parts of instrument to terminal L, and back to terminal L of A. The "Primary" or microphone circuit is merely local ; that is, it does not touch the lines at all, but runs as follows: — Battery to terminal M C, through hinge j to trans- mitter, hinge k to primary coil, spring e, switch hook 68 COMMERCIAL AND DOMESTIC TELEPHONY a, and terminal ZE, which, being connected to the zinc of battery, completes the microphone circuit. For all ordinary purposes three battery cells of the No. 2 " Carporous " or " E C C " type {see Fig. 57) will be found sufficient. Reference to Fig. 57 will show that three cells connected in series are used in giving a call, but that for the microphone circuit only two of the cells are used. It will be readily seen how this is brought about. In special cases, the call bell on this instrument Fig. 58. may not be powerful enough to meet the requirements of intending users ; in which case it is advisable to use the instrument shown at Fig. 58. This instrument is not provided with a bell, but has two binding-screws for the purpose of allowing the fitter to connect any sized bell that may be required. These terminals are always marked B B, and when connected to the bell, the circuits run exactly the same as Fig. 56. Fig. 59 shows two such instruments connected together. INDUCTION COIL TELEPHONES 69 Figui-es 60 and 61 show two instruments, which, in effect, are exactly the same as Figs. 58 and 55, the only difference being that they are much more substantially made, and more suited for public institutions and Admiralty work. OR RETURN Fig. 59. Fig. 59 shows the connection of instrument shown at Fig. 60, and Fig. 62 shows connections of instrument shown at Fig. 61. Figures 63, 64, and 65 show three forms of table telephones, either of which will work perfectly with the instruments illustrated in Figs. 55, 58, 60, and 61. 70 COMMERCIAL AND DOMESTIC TELEPHONY Fig. 6o. Fig. 6i. =11 ecc 0f vc $ ^ ^ ti 1 |0\ (J - r^->->->- r-V>->-!>->- ?^Wt\k- r^^^^h^^^- r-)V>- — r)m- — r-)7'7'->- -r->->W- -r:>7->->-)->- -T->-;>- -;>— r->:>->-;'-i'j.- "GENERAL" INTERCOMMUNICATION SYSTEM 95 for " lines," one for " return," and one for " carbon " wire, making twelve conductors in all, that is — two more than the number of stations. The conductor of this cable is of No. 20 standard wire gauge, tinned copper, covered with indiarubber, two lappings of cotton, and then soaked in paraffin wax. Each conductor is covered with a different colour to any other in the same cable and is consequently easily identified. The whole are braided together under one fancy coloured covering. The next item for consideration is the method of Fig. 93. Fig. 94. making the Tee joints. The old method of scraping the conductors and soldering the Tee pieces on, although safe, is very clumsy, and by the time each joint is separately insulated and the whole bound together a very unsightly job is made. It is therefore much neater and quicker to use the special connecting box shown at Fig. 93 for the purpose. These connecting boxes are supplied with the requisite number of brass plates to suit the cable, each having three special pattern binding-screws. Fig. 94 shows the box with cover removed and cable connected. For the purpose 96 COMMERCIAL AND DOMESTIC TELEPHONY of description we will refer to Fig. 95, where a single conductor only is dealt with. At the point where -a Tee joint requires to be made, cut- the cable and pass the two ends from the back through round hole in the connecting box. In Fig. 95, A and B represent the two wires coming through the box. Now connect the two ends to the terminal plate on the screws a and b as shown. It will be observed that they now form a continuous conductor through the box. To take ofif a Tee joint, the wire to be joined, C, should be passed Fi(j95 from back of box through the hole between connecting plates and connected on to the remaining screw of plate as at c. In dealing with a number of conductors the cable to be joined on has its outside covering stripped off for a few inches and the conductors are passed through the hole between plates in pairs from the back (see Fig. 96). Great care should be taken that wires with the same coloured coverings are connected to each plate, otherwise a great amount of confusion will follow. "GENERAL" INTERCOMMUNICATION SYSTEM 97 The fitter, when connecting an installation on this system, should first settle in his own mind the station which each coloured conductor is to represent. For instance, Red shall represent No. i Blue „ „ No. 2 Green „ ,, No. 4 White „ „ No. 5 and so on. Fig. 96. If each plate has the same colours connected to it, then wherever a Ted, greien, or blue, or any other colour is met with, the station it represents is instantly understood. There should then be no difficulty in connecting up according to the diagram shown at Fig. 91. The connecting box has been designed so as to prevent 98 COMMERCIAL AND DOMESTIC TELEPHONY as much as possible the crossing of wires, and to facihtate the disconnection of any one section of the system. Thus cable A, Fig. 95, should have its conductors all connected to the corresponding screws (a) of their respective plates. Cable B the same. Then by disconnecting all the wires from screws a the whole of system to left of box is cut off. By disconnecting all the wires from screws b the whole of system to the right of box is cut off ; and by disconnecting all the wires from screws c the instrument only for which the tapping is made is cut off, and this without any uncovering wire or unsoldering joints. The advantage of these connecting boxes is therefore very clearly demonstrated. In some cases it may happen that there are fifteen stations in a warehouse, but that it is not necessary for all the stations to intercommunicate. Suppose that five of these fifteen wish to speak to each other and all the rest, but ten of them only wish to speak to nine out of the fifteen. The instruments of the first five are provided with fifteen-way line selectors, and the instruments of the other ten are provided with ten- way line selectors. Take a 17- wire cable and run it through the whole route as a main. Now carefully decide the most convenient point at which the Tee joints connecting the instruments should be made, and insert the connecting boxes in circuit with cable. Take a i2-wire cable and connect to the boxes, one con- ductor to the "carbon," one to the "return," one to the "home line" in the main cable, and the other nine to the lines with whom it is required to converse (see Fig. 97, "GENERAL" INTERCOMMUNICATION SYSTEM 99 2> 3) S)' At the same time those stations requiring connection with the whole system can be tee-d off as usual (see Fig. 97, Nos. i and 4). The cables can be lain either in zinc tubing or in wood casing. In the latter case, a casing with single groove is provided (see Fig. 98). Where the cable is not considered unsightly it can be stapled to the wall, but insulated staples must be used. These staples are provided with a lining of vulcanised fibre, which allows them to be driven hard home without cutting the cable or short circuiting the conductors (see Fig. 99). Figs. 100 and loi represent two forms of general instruments designed for table use. In this case the instrument has connected to it a flexible cable (see Fig. 102), which must have four conductors more than the number of lines ; that is, in the case of a ten-line instrument fourteen conductors altogether. Thus— ten lines, one return, one carbon, one microphone zinc, and one microphone carbon. This flexible cable should be connected to the ordinary cable through the medium of a connecting rosette, shown with cover removed at Fig. 103. It will be seen that this rosette is provided with the requisite number of connecting plates each with two connecting screws, and that there are two holes drilled in the wood base for each plate, one at its inside end and one at its outside end. The inside screws are intended for the flexible cable and the outside screws for the ordinary cable. Before connecting the flexible, the ends of the conductors should be prepared for the purpose by laying bare about i" of each conductor loo COMMERCIAL AND DOMESTIC TELEPHONY and twisting the strands of each tightly together, the ends should then be bent round to form a loop and held in that position .by cotton or silk binding. See Fig. 104, which shows each conductor so prepared Fig. 98. and the outside covering neatly bound round in .1 similar manner. Having prepared the flexible so far, pass the end through the cover of rosette a, V\g. 104, then through hole b in base; turn each conductor and push each through hole c at the inside end of its respective Fig. 99. connecting plate. Take the binding-screw out of its plate, push it through the loop in conductor and replace it, seeing that it is screwed well home on to the conductor. The ends of the flexible to be 'GENERAL" INTERCOMMUNICATION SYSTEM loi Fig. ioo. Fig. ioi. I02 COMMERCIAL AND DOMESTIC TELEPHONY connected to the instrument should be prepared with loops as above, and connected to the binding-screws in the same manner. mmmmm Fig. 102. Too much importance cannot be attached to the observance of the above details, as unless carefully carried out the flexible very frequently causes a great Fig. iv^^jj. deal of trouble by stray strands of a conductor connecting two or three terminals together. If neatly carried out, however, no trouble need be feared. "GENERAL" IXTERCOMMUXICATION SYSTEM 103 Fig. 105 illustrates a Wall Pattern Instrument with Microphone Combination, a form in some cases found very useful. This General System is also made up with a " Byng " Transmitter (see Fig. 106) for the purpose of meeting a demand for a cheap instrument, and will be found very reliable. All the instructions and accessories pertaining to the " General " System are also applicable to the Byng System. A modification of " the General " System is used for enabling one station. A, to call or be called by any number of stations, say B, C, D, and E. In this case A's telephone would consist of an instru- ment as at Fig. 89. It is as well that a ten-line switch 104 COMMERCIAL AND DOMESTIC TELEPHONY should be used at A, so as to allow of additions if occasion arises. The sub-stations B, C, D, and E have similar instru- ments, but provided only with two-way switch (see Fig. 105. Fig. 107). The connections are as shown at Fig. 108. The two switch studs of B, C, D and E are marked " Call" and " Reply " respectively. To call up A the switch arm must be resting on "Call"; but when a "GENERAL" INTERCOMMUNICATION SYSTEM 105 call is received from A, the switch arm must rest on " Reply " before a reply can be given. Fig. 106. Fig. 107. This system is especially useful where A requires to use a table instrument, as it dispenses with an indicator board which is not readily adaptable to the purpose. io6 COMMERCIAL AND DOMESTIC TELEPHONY CHAPTER VIII COMBINATIONS WITH MAGNETO RINGING APPARATUS WE now come to the consideration of magneto ringing apparatus, as mentioned in the early part of Chapter IV. In this apparatus, a generator of electricity is con- structed on the principle laid down in the first chapter, viz. : — "That a conductor of electricity moved in a magnetic field has generated within itself electric currents which vary in direction according as the movement is to or from the magnetic field." For this purpose, one or more horseshoe-shaped magnets are used, and the conductor is caused to revolve between its poles. Fig. 109 shows three mag- nets having the three north and the three south poles yoked together by iron pole pieces, a, a, which are io8 COMMERCIAL AND DOMESTIC TELEPHONY Fig. 109. Fig. iio. MAGNETO RIXGIXG APPARATUS lOQ hollowed out to receive the conductor. This arrange- ment concentrates the magnetic field at the point where most needed. The conductor (technically termed the armature) represented at Fig. no consists of an iron core, having a quantity of very fine insulated wire wound longi- tudinally upon it. Fig. in shows a cross section of this armature, which is fitted in position between the iron pole pieces of the magnets, resting in suitably Fig. h2. arranged bearings so as to be free to revolve easily on its axis. The spindle on which the armature revolves requires to be specially prepared, so that, when revolving, the electrical connections between the ends of armature no COMMERCIAL AND DOMESTIC TELEPHONY wire and other portions of the apparatus may be sustained intact. This is accomplished as follows : — One end of the spindle has a fairly large hole drilled up its centre for a distance of about one inch, and a vulcanite lining inserted (see a, Fig. 112). Inside this lining is fixed a steel pin, b. A hole is drilled from the outside of spindle through lining, and into pin, b. This hole has also a vulcanite lining, so that a second pin, c, can be thrust through it into b, with which it is required Fig. 113. Fig. 114. to make contact. The two pins b and c now represent electrically one piece passing up the centre and through the side of the armature spindle, but well insulated therefrom. One end of the armature is permanently soldered on to pin c, and the other end is permanently connected to the spindle at d. When fixed in position the pin b presses against a contact spring k (see Fig. 117), so that if one connection is made to the metal of generator, and the other to contact spring k, the latter makes connection via pins b and c to one end of MAGNETO RINGING APPARATUS in armature wire, and the former through the bearings of armature makes connection with the other end of armature wire. If the armature is now revolved, the electrical connections are still maintained. The rapid revolution of the armature causes alter- nating currents of electricity to be generated in the fine wire which have a very high E M F, capable of over- coming a great amount of resistance. In order to utilise these currents for signalling purposes, a special Fig. 115. Fig. 116. form of bell is devised, as illustrated at Figs. 113 and 114, which show its diagrammatic construction, a, a are the two coils wound on iron cores, yoked together by iron yoke 6 ; c is an iron armature pivoted at d, and carrying a long stem e, terminating in knob /. This knob nominally rests between two gongs, g, h. i is a permanent magnet, of shape shown in Fig. 1 14, so that the top end bends round over the top of armature c, and its bottom end is fixed by a screw to iron yoke b. In order to explain the working of bell, Fig. 113 must be regarded in connection with one or two outline figures {see Figs. 115, 116). 112 COMMERCIAL AND DOMESTIC TELEPHONY The effect of this arrangement is as follows : If magnet i has north pole at its lower end, and south pole at its upper end, the two cores N and N' of the electro-magnet, by contact with north pole of i, become magnetised with a north polarity. The armature, by virtue of its situation in the magnetic field of i, becomes magnetised with a south polarity at each end. If a current of electricity is passed round the coils a, a in such a direction as to produce a south pole at N, and a north pole at N', as shown by dotted letters {see Fig. 115), the south pole of electro-magnet will repel that end of armature c opposite which it is fixed, and the north pole of electro-magnet will attract the opposite end. This movement has the result of throwing hammer / from one side to the other, and causing it to strike one of the bell gongs ^^ (Fig. 115). If the current is now passed through the coils in the opposite direction, the polarity of a becomes re- versed, consequently the action of the armature is also reversed, and the hammer is moved back again to its former position, striking bell gong h (Fig. 1 16), so that rapid alternations of current passed round a, a result in a rapid vibration of the hammer knob between bell gongs g and h, which it strikes alternately. For signalling purposes two bells and two generators are connected together, as at Fig. 117. When handle of generator at A is turned, the currents generated pass from A's armature through bell coils to line, through line to B, through B's bell and armature to the return wire, and so back to A's generator. MAGNETO RINGING APPARATUS "3 The bells both at A and B are caused to ring. It would appear to be some objection that the bell of the person calling should ring as well as that of the person called, but it really is not so, as it serves to signify to the person calling that the circuit is complete. If the line were broken, neither bell would ring. In connect- ing as above, when A is ringing, it will be observed that the armature of B's generator is in circuit, offering a considerable amount of useless resistance. ^:^,^^ ,c:^ -% Fig nj. ] As it should be the object to reduce the resistance of circuits as much as possible, a small device is attached to the generator, which causes the armature to be cut out when in a position of rest. This device is shown at Fig. ii8. which for clearness i-epresents the generator without the magnets. It. will be seen that the hub, c, of the driving-wheel has a v-shaped notch, a, cut in it. The shaft 6 passes through the hub c and through bearing d, being extended through a second bearing, e. 9 114 COMMERCIAL AND DOMESTIC TELEPHONY The end of this shaft at / carries an ivory tip, g. A hole is tapped through the shaft, which carries a screw, h, having its ends projecting through each side in the crutch of V-shaped notch, a, in hub, c. The object of this arrangement is as follows : — When the handle is turned, the first part of the movement causes screw h to slide on the side of the V-shaped groove, so that the whole shaft is thrown Fig. 1 1 8. forward slightly, the driving-wheel being prevented from moving by clutch /. To make use of this arrangement, the generator is provided with a spring, j, connected with contact spring k. In a state of rest, y rests against contact point /, so that the armature is short circuited, and does not pre- sent a resistance in circuit when a call is received ; but when handle of generator is turned to ring up, the inward movement of driving-shaft causes spring j to be MAGNETO RIXGIXG APPARATUS 115 pushed out of contact with point / (see dotted line), thus opening the armature, and allowing the currents generated to pass through the circuit. Fig. 119 shows the external appearance of a magneto generator and call bell, mounted with Deckert trans- mitter induction coil, bell receiver, and automatic switch hook, in the form generally adopted. Fig. 120 shows a similar instrument mounted on Fig. 119. back board with battery box. Fig. 121 shows two of these latter instruments connected for use. It will be observed that there are four terminals on the top of magneto, and that two of them, viz., that marked B and that marked R (return), are connected together. The object of this arrangement is as follows : — It is sometimes required that, besides the telephone bell ringing, a further bell shall also ring, probably in some distant part of the building. If the wire con- ii6 COMMERCIAL AND DOMESTIC TELEPHONY necting piece between B and R is removed, and the extra bell inserted as shown in Fig. 122, it will ring whenever the telephone is called up, and will be cut Fig. J20. out of circuit when the receiver is raised in the same manner as the ordinary telephone bell. Diagrams shown in Figs. 121, 125 and 126 assume that "Earth" MAGNETO RINGING APPARATUS 117 is used as a return, so that terminals R and E are taken to Earth by one wire. If a wire return is used, E should be taken to " Earth " by itself for the purposes of lightning arrester, as at F^ig. 133. See Chapter XL, which gives particulars of establishing " Earth " connection, and also explains working of lightning arrester. Fig. 122 shows the internal con- nections of magneto combination, shown at Fig. 1-19 with receiver off hook. Careful examination will show that, when receiver is on the hook, the ringing current ii8 COMMERCIAL AND DOMESTIC TELEPHONY enters by the line terminal L, and passes to switch hook a, contact spring b, hinge c, bell coils d, hinge e, spring /, contact point g, through framework of gene- rator to h and on to terminal B, through connecting wire, or extension bell to R, whence it gets to the return wire, and so back to generator of person calling. EARTH '£ J-- LINE -^ ir-f ""^^J^ Fig. 122. When speaking, the line circuit runs as follows : — Terminal L, switch hook a, contact spring i, secondary of induction coil, and out at j, receiver ter- minal k, through receiver (or if there are two, it passes through the two in parallel) to terminal /, and thence to terminal R. MAGNETO RINGING APPARATUS 119 Fig. 123. Fig. 124. I20 COMMERCIAL AND DOMESTIC TELEPHONY MAGNETO RINGING APPARATUS 121 The microphone circuit runs as follows : — Carbon of battery to terminal in, hinge n, trans- mitter 0, hinge p, spring q, end of switch hook, to spring i, primary of induction coil, and out at r, direct to terminal s, and back to zinc of battery. At Figs. 123 and 124 are shown two forms of mag- neto ringing apparatus for table use, and although the Fig. 127. parts are somewhat differently disposed, the connec- tions internally are the same as in Fig. 122. Fig. 125 shows three magneto .stations, connected to an extension bell and switch, enabling A to call B or C, and vice versa, and enabling A to connect B and C together. Fig. 126 shows the method of connecting to an annunciator switch board of the description used with 122 COMMERCIAL AND DOMESTIC TELEPHONY the battery ringing instruments. In this case, the coils of movements have to be wound to a high resistance, otherwise they would not be actuated by the magneto current. Fig. 127 shows a smaller form of magneto ringing ..J ! Z. C station, which can be used with advantage, as regards economy, on lines up to one mile in length. The connections internally are somewhat different to the system shown at Fig. 122. They are shown in detail at Fig. 128. CHAPTER IX "METALLIC CIRCUIT" OR "DOUBLE LINE" SYSTEMS WHERE a number of lines run parallel to each other for any great distance, con- siderable trouble is sometimes caused by cross talk on the lines, due to induction. To minimise this trouble, double lines are run — that is, a line and return wire to each station, instead of simply a line to each station and a common return for the whole. It is obvious that, in order to keep all the returns separate, the switching arrangements must be specially constructed. Dealing first, therefore, with the intermediate switch, we illustrate at Fig. 129 a switch for double lines which fulfils exactly the same purpose as the switch in Fig. 78, in that it enables A to call B or C, and vice versd, and also enables A to switch B and C through to each- other, leaving the extension bell in circuit, so that, when they 124 COMMERCIAL AND DOMESTIC TELEPHONY have finished conversing, they can ring off by the extension bell. This extension bell should be wound to 1,000 ohms resistance, as it is connected on the lines in shunt when B and C are through to each other. Fig. 130 shows the diagrammatic condition of the connections with the switch in its three various posi- tions. When pointer of switch is to the right as Fig. 129. at I, A is on to C and B is on the extension bell. When switch pointer is to the left as at 2, A is on to B and C is on to the extension bell. When switch pointer is in the middle position as at 3, B is connected to C with the extension bell across the lines. When conversation is finished they ring off by turning the generator handle. This causes extension bell at A to ring, signifying to A that conversation is finished. We now have to consider the connections of the annunciator switch board for double lines. In speak- ■METALLIC CIRCUIT" 125 ing of the single-line board, we showed that the bell was thrown into shunt with the indicator coils when the shutter dropped. In the case of double-line board, this system is not possible, as the returns could not be kept separate. The bell is therefore so arranged that when the shutter drops it causes a local battery circuit to be closed, and bell rings until the shutter is replaced. Fig. 131 shows the connection of one movement of iGp B jpOOO 6 do 6^ »- ©„°3 ■ '^ 6 06 6 A\ c\ i 1 fiy J 30. switch board with its spring-jack, and also shows the two forms of plugs used. L, L' are the line terminals ; B, B' the local bell circuit terminals. The latter should be connected as at Fig. 133. The spring-jack and plugs are different to those used in single-line boards, as will be observed. The dark portions of plugs and jacks represent vulcanite insu- lating collars. 126 COMMERCIAL AND DOMESTIC TELEPHONY If a current passes along the line and enters L', il passes through the indicator as follows : — L' to q, q to p, through indicator coil to o, o to spring b, b to c, c to to c', and out at L, back to the calling station. The shutter drops and closes local bell circuit as follows : — Carbon of battery to B, B to screw /, / to spring m, framework k of movement which is connected to B', B' to bell, through bell to zinc of battery. In replying to the call, the operator takes plug of form A, which is connected to the line and return terminal of his telephone, and inserts it into the plug socket d. Reference to Fig. 132, No. 2 will show that the plug A makes two connections — one with spring d and one with frame a of spring-jack, and also disconnects "METALLIC CIRCUIT" 127 b from c, so that the -two line terminals L, L' are con- nected direct to the two conductors of the flexible coi-d, and through these to operator's telephone. At the same time, by causing the spring b to break contact with c, the indicator circuit is broken. Fig. 132 shows two stations plugged through to each other with the two plugs A and B shown at Fig. 131 with No. I's movement left in circuit for ringing off. Fig. 133 shows the external connection of a double- line switch board to operator's telephone and five pairs of lines. The terminals T, T are not connected inside the board, but are only for convenience in connecting operator's plug to his telephone lines. In speaking of a double-line system it is frequently referred to as a " metallic circuit" system, but this term is misleading, in that, a common return wire used to all the stations, would be only a " single-wire " system, but would also literally constitute a "metallic circuit," 128 COMMERCIAL AND DOMESTIC TELEPHONY although it would not answer the same purpose as if a line and return wire were run to each station. It is therefore preferable, to prevent confusion, to speak of the two systems as a "double-line" or " single-line " system, as the case may be. CHAPTER X CHOICE OF INSTRUMENTS IN deciding upon the installation of telephones, the most important, and by no means the most simple, matter is the choice of instruments, and the following advice on this point may be of service to many. If the telephone is to be used in private houses with all inside wiring, the " Stanley " telephone will be found suitable. If the telephone is to be used in offices or ware- houses for any distance up to a quarter of a mile, the Hunningscone (Fig. 55) or Byng (Fig. 68) combi- nation should be used. If the lines do not exceed one mile, the small magneto (Fig. 127) can be used. For any distance over one mile the magneto instru- ment, illustrated in Fig. 120, should be used. 10 I2S CHAPTER XI CONSTRUCTION AS many exhaustive works have been written deaHng with the construction of Telephone Lines, notably those mentioned in our Preface, we propose only to convey a few hints as to the method of wiring and the most suitable materials to use. INDOOR WIRING The most suitable wire to be used for indoor work consists of a conductor of No. 20 S.W.G. tinned copper wire, covered with indiarubber, two coverings of cotton, and the whole served with paraffin wax. This wire can be run in wood casing or tube, or it can be simply stapled in position. In the latter case care should be taken that no two wires are fastened under the same staple, and that no two staples touch each other. Each should be stapled alternately. CONSTRUCTION 131 Figure 134 shows what is meant by this. If the wires are not run in casing, advantage should be taken of all cornices and skirtings to keep them well out of sight. Where it is necessary to make a joint, this should be done as shown at Fig. 135, from which it will be seen that each wire is lapped round the other. They should be carefully nipped round each other by use of pliers, so as to ensure a good contact. The joint should then be covered with gutta- percha, which is supplied in thin sheets and can easily be torn in strips about half an inch wide. This strip should be lapped round the joint and softened by application of heat. It can then be moulded round the joint by the fingers, which, however, should be moistened, so as to prevent sticking. OUTSIDE WIRING For outdoor wiring, overhead, a bare mangan copper wire (No. x6 S.W.G.) is used, and must be run on suitable insulators supported at convenient points. These supports should be about a hundred yards apart ; but of course, where a number of sharp turns have to be taken, they must often be considerably closer. In open country it will be necessary to fix 132 COMMERCIAL AND DOMESTIC TELEPHONY poles for attaching the wires to ; but in towns, chimney-stacks, corners of buildings, &c., are fre- quently made use of. The form of support to be used for the insulators will of course depend upon the position in which they have to be fixed. For instance, where corners of buildings or chimney-stacks are available, the bracket shown in Fig, 136 is useful. In some cases, where a wall only is available, the wall bracket (Fig. 137) can be used, but the line must have a pull at right angles to the direction in which the ■111^103 Fig. 136. Fig. 137. bracket is driven into the wall. For the top of poles, the bracket (Fig. 138) is well adapted, and for sides of poles Fig. 139. The tops of poles should be protected by pole caps, as shown at Fig. 140. There are many types of insulators, but that shown in Fig. 141, known as the " Sinclair " insulator, is one that can well be used for all-round purposes, and is therefore to be recommended. The line wire should be bound to the insulator with No. 18 soft copper wire. The method is shown in Fig. 142. The wire is first lapped with the binding wire in order to pre- vent the line wire being injured by chafing against CONSTRUCTION 133 the insulator. The binding wire is then bound round the line wire from i to 2, round the groove in insulator to 3, from 3 to 4, and back again to 3, round insulator to 2, from 2 to i, and then finished off in a single layer fi-om i to 5. Joints should, as Fig. 138. Fig. 139, far as possible, be avoided ; but where necessary, the form known as the "Britannia" joint, shown in Fig. 143, should be used. When the wire has been bound round as shown, it should be well soldered, Fig. 140. although the soldering requires to be done quickly, as too much heat causes a softening of the wire, which would be considerably weakened thereby. Care should also be taken in paying out the wire to avoid kinks, as when tightening up the wire it is sure 134 COMMERCIAL AND DOMESTIC TELEPHONY to break. Figs. 144 and 145 illustrate clearly the correct and incorrect methods respectively. At the terminal point, the wire must be finished off round the insulator, and must be connected to the Fig. 142. Fig. 141. Fig. 143. interior of building by means of a special leading-in wire. This leading-in wire should consist of No. 18 S.W.G., covered with pure and vulcanised india- rubber, with an outside covering of cotton braid, CONSTRUCTION 135 well served with preservative compound. It is not sufficient to simply solder this wire on to the line and lead it down the side of building, but a special form of leading-in insulator must be used at the terminal point, otherwise in wet weather a great amount of leakage will ensue. This leading-in insu- lator is constructed as at Fig. 146. a is an ebonite insulator ; 6 is a metal screw, passing right through the top and projecting inside the insulator. This screw has a hole right through it, c. The line is Fig. 144. Fig. 145. made off round the terminal insulator, and has con- nected to it the leading -off wire as at Fig. 147. This is passed through the hole c in screw b, and the leading-in wire soldered to it on the under side of the insulator. To prevent wet running in from the top, the space round wire must be filled in with solder. Fig. 147 shows the terminal insulator with leading-in wire, taken off in the above manner. It will be readily seen that by this means a portion of the leading-in wire is ensured against wet, so that this source of danger is disposed of. The other end 136 COMMERCIAL AND DOMESTIC TELEPHONY of leading - in wire should be carried down the brickwork of building (to which it can be fixed c Fig. 146. by galvanised iron staples) to the nearest window. It can be taken into the house through a hole in the Fig. 147. ■ sash. If the telephone is to be fixed near the window it is best to continue the leading-in wire right up to CONSTRUCTION 137 the instrument, but if it has far to run it should be joined inside the window to the indoor wire, which can then be run to any part of the house required. On long lines, an economy is often effected by using the earth as the return conductor. In this case it is usual to connect the return terminal of telephone at each end to the water service pipes, which form a sufficient connection with the earth for the purpose. This connection should be made on the main side of the cistern. Where a water service is not available, a hole must be dug in the earth at each end about six feet deep, and into this must be sunk a copper plate, not less than two feet square, having a strip of copper tape riveted or welded to it. This earth plate must be filled round with fine coke dust, well rammed in. In establishing a connection with the earth, the damper the soil in which the plate can be sunk the better for the purpose. Most instruments intended for long lines, such as that shown at Fig. 120, are provided with lightning arresters — that is, a means of arresting the progress of a charge of electricity which may be given to the lines by the discharge lightning. Without such pro- tection the instruments would be more liable to become fused by the heavy charge that would be passed through them. These lightning arresters are made of various forms. That shown at Fig. 148 is the form fitted to the magneto instrument. Fig. 120. Fig. 149 shows this arrester connected to a pair of lines when used separately from the telephone. It will be seen that it consists of three plates. A, B, 138 COMMERCIAL AND DOMESTIC TELEPHONY Fig. 148. L //V£ J TO/NSTKU jitrvjiN J \ /I \ ( i 5 Q ) 1 V wl) fi I Fig. 149. CONSTRUCTION 139 and C. A forms the line, B the return, and C the earth connection. Where earth is used for return, B and C can be joined together and taken to earth by the same wire ; but where a wire return is used, plate B is connected to earth by itself, and serves Fig. ISO. to protect both line and return. This arrester depends for its efficiency upon the affinity which electricity possesses of discharging itself across points, and so escaping the instrument. In situations where thunder- storms are exceptionally heavy, it is as well not to Fig. 151. trust implicitly to the arresters supplied with the in- struments, but to supplement them by separate arresters. Fig. 150 shows a different type, known as a plate arrester, which consists of three circular discs of brass separated from each other by thin sheets of mica, which have several holes punched in them. By this means the plates are brought as near as possible I40 COMMERCIAL AND DOMESTIC TELEPHONY to each other without touching, and the Hghtning charge can readily jump across the thin air space through the holes in mica. Fig. 151 shows a lightning cut-out, which consists of a glass tube, containing a thin fusible wire connected to a metal cap at each end. These caps fit into a clip at each end. The cut-out is inserted in the line circuit, u/ve KETUKn Fig. 152. and a heavy charge of electricity causes the wire in glass tube to fuse, thus severing the connection with instrument. The tube can be readily removed, and a new one fitted. A line would be well protected with fuse cut-out in conjunction with plate arresters. Fig. 152 shows the method of connecting with double lines. CHAPTER XII FAULTS IF a telephone installation is carefully erected, the question of faults is not likely to prove a very serious one; but, as the instruments are some- times fitted under adverse conditions, faults are very liable to develop themselves, no matter how well the work may have been carried out. It would, of course, take far too much space to deal with all possible faults that may occur. We shall therefore, by taking one or two examples, endeavour to indicate a simple method of reasoning as to the cause of a fault, and also the method of localising same. To do this we shall deal only with one type of instrument, that shown in Fig. 55, and have no doubt that the reader will be able, by these examples, to test any of the other forms of .instru- ments described, as the general method should be the same. 141 142 COMMERCIAL AND DOMESTIC TELEPHONY Example i. A cannot call B, but B can call A, and speaking can take place either way. The fault in this case would, in all probability, be either of the following : — A severed connection somewhere between carbon 1 r, RECEIVER of A's battery and C terminal of instrument, or — Key / (Fig. 153) at B may not be making good contact on point g. To ascertain this, proceed as follows, leaving the instruments connected up, as at Fig. 57. Take a small piece of wire and connect terminal C of A to terminal L. If on making this FAULTS 143 connection A's bell rings, it follows that the con- nection between carbon of battery and terminal C is quite intact, thus disposing of fault A. It would be well, however, before leaving this instrument, to see that the wire connecting C with contact e is in perfect order. Now go to station B, and connect C L together, as in the case of A. If the bell at B does not ring, then the contact of key / with g is likely to be defective, or the bell itself may be de- fective, and should be tested as explained in Chapter III. To do this, the line and return should be dis- connected, and the terminals L and Z E treated as the bell terminals. Example 2. Can ring both ways, but cannot speak either way. This is probably due to a disconnection of some of the instrument parts internally. To localise this, leave the instruments connected, take a short piece of wire as before, and on one of the instruments connect terminal L to terminal Z E. Now hold the receiver to the ear and slightly tap the transmitter mouthpiece with the knuckle. If the tapping is heard in the receiver it can be taken for granted that the instrument is all right and the fault must be in the other. If, however, the tapping cannot be heard in the instrument, then proceed to localise the fault as follows : Disconnect the instrument, take a galvanometer of the form shown at Fig. 154, and connect one side to terminal L of instrument and the other side to the carbon of a small testing battery, which may consist of two or three cells. Connect a 144 COMMERCIAL AND DOMESTIC TELEPHONY Fig. 154. FAULTS 145 piece of wire on to zinc of battery, leaving the end free, as at a, Fig. 156. Now, with the receiver off the hook, touch the free end of zinc on to spring /, and watch the galvanometer needle. If it is deflected, all is right, and you can proceed to touch the various parts of the instruments as follows : — First terminal of receiver ; second ditto, point at which wire from latter is connected to secondary of induction coil ; switch spring d ; hook a ; terminal Z E. By this method of procedure a point is reached at which the galvanometer needle is not deflected, and the conclusion is that the fault exists between this point and that which was last touched, and it should then be easily detected. Example 3. Can ring both ways, but can only hear one way. This fault would probably exist in the microphone circuit or the wire connecting the M C terminal to the battery. It is well to test the instrument first, and the best method of doing so is to use the telephone receiver as a detector in the following manner : — Connect one of the receiver tags to carbon of testing battery, and the other tag to terminal M C of instrument (Fig. 157). Connect the zinc of battery to a piece of wire as before, hold the receiver to the ear, and proceed to touch the various parts of the instrument as follows : — Terminal M C, hinge J, hinge K, switch spring e, hook a, terminal Z E. The continuity of circuit will make itself apparent by a clicking in the telephone II 146 COMMERCIAL AND DOMESTIC TELEPHONY receiver, and when a point is reached at which no cHck is heard, the fault is between this point and that last touched. In this test, however, it is possible to obtain a click in receiver right through from M C to Z E, and still the fault exist. This would point to the fact that the transmitter is faulty. This can be ascer- ZE. CMC L- Td o 6 o wr:^. m ^ a Fig. 157. tained by tapping the mouthpiece of transmitter, when the zinc wire used in the above test reaches terminal K. If the tapping is not heard in the receiver, then the probability is that the transmitter has its diaphragm and back electrode in solid contact with each other. Example 4. Can neither ring or speak either way. l^eave the instruments connected, take the receiver FAULTS 147 from hook, hold it to the ear, and tap the transmitter mouthpiece. If the tapping is not heard, the Hne or return is disconnected or broken, and should be care- fully examined. If, however, the tapping is heard, then the line and return are probably short circuited somewhere in their course. This can be readily ascer- tained by disconnecting the line and return at each end, and inserting a galvanometer and testing battery /5 y fSB. as shown at Fig. 158. If a deflection is shown, the proof of short circuit is conclusive. In addition to the above examples, the following additional remarks are recommended to be borne in mind. Always see that the wires are carefully cleaned before fixing to the terminals, and see that the binding-screws are screwed firmly down. In some cases, the speaking can only be heard very faintly, due to the diaphragm of receiver resting solidly against the poles of the 148 COMMERCIAL AND DOMESTIC TELEPHONY magnet. This is often brought about by mischievous persons poking the diaphragm with pencils, &c. All installations when finished should be tested by connecting a galvanometer between the zinc of battery and the wire to be connected to it {see Fig. 159), for the purpose of ascertaining if there is any leakage between the wires, as such leakage would not always interfere with the working of the telephone when first fitted, but would cause the battery to give out in a few days. A great source of leakage is found in fitters using only cotton-covered wire on damp walls. The wire for such purpose should be the same as advised for leading-in, see p. 134. In magneto instruments, trouble is sometimes caused by small grains of metal dust getting between the teeth of lightning arrester, which would have the effect of preventing ringing or speaking either way. Where a central station system is used, very fre- quently it is found that when one sub-station rings up, several, or all, of the shutters drop. This is in- variably due to a bad earth connection, and to test this a temporary wire may be run if the distance is not too great. In the "General" Intercommunication system, com- plaints are sometimes made that two persons are called at once. This will generally be found to be caused by some careless person leaving his switch-arm mid- way between two of the switch-studs ; and, in fact, not infrequently it will be found that a great deal of trouble can be obviated by the users taking the ti^ouble to use the instrument exactly as intended. FAULTS 149 In the course of a fitter's experience, it frequently happens that he is called to repair instruments of an obsolete pattern which have defective transmitters. In this case, the best thing to be done is to fit new transmitters of the " Deckert " pattern, and, as stated in an earlier chapter, they should be fitted so that they can receive a half turn occasionally. The method of accomplishing this is as follows : — If the transmitter can be mounted on the front of Fig. 160. Fig. i6i. the case, the form shown in Fig. 160 should be used. Fig. 161 shows a view of the back in perspective. First make a hole in the front of the case, of sufficient size to allow shoulder a to enter and turn freely ; then cut a horse-shoe shaped slot, extending somewhat beyond the limit of a semicircle, see Fig. 162. The object of this slot is (i) to allow the stop-pins h to move in, (2) to pass the flexible conductors through, and (3) to limit the play of the transmitter to half a turn. Fig. 162 is an exact template of this hole and slot. The ISO COMMERCIAL AND DOMESTIC TELEPHONY transmitter is now placed in position, and fixed from the back of the case by two screws, which first pass through a spring-washer, a {see Fig. 163). The screws should not be screwed right home, as it is intended that the spring-washer should hold the transmitter firmly, but, by virtue of its springiness to allow it to revolve freely. The transmitter should always be turned to the extreme right or left. Fig. 162. In cases where the mouthpiece of transmitter is formed by a counter-sunk hole in the front of case (as in the type known as the " Blake "), the form of trans- mitter shown at Fig. 164 should be used. In this, the revolution is limited by means of stop-pins in the back of transmitter, which stop against the fixing bracket. Fig. 165 shows clearly the method of fixing this trans- mitter. FAULTS 151 Fig. 164 152 COMMERCIAL AND DOMESTIC TELEPHONY The fixing bracket forms one connection, and a screw on case of transmitter forms the other. The latter is connected with the rest of the apparatus by a flexible conductor, so that, when transmitter is turned, the connection is not strained. On the back of transmitter will be found a straight line through its centre. When fixed and turned to the extreme right or left, this line should be perfectly horizontal. In concluding this work, we would strongly impress upon the fitter the great importance of paying attention to the minor matters connected with installing tele- phones, as neglect of even the most minute detail will often cause a great amount of loss and trouble. Also bear in mind that no matter what amount of competi- tion may be met with, it is only a thoroughly good job that will recommend itself for future work, and it therefore pays to let everything used be of the highest standard of quality obtainable. UNWIN BROTHERS, THE GRESHAM PRESS, -nOKIXO AXD LOXDOX.