BOUGHT. WITH THE INCOME FROM THE SAGE ENDOWMENT FUND THE GIFT OF Mtnv^ W. Sage 1891 A..M.?^Alr: U-d- 13.3.. Cornell University Library arviaese Telephones, their construction and fitti 3 1924 031 272 911 olln.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/cu31 924031 27291 1 TELEPHONES : THEIR CONSTRUCTION AND FITTINQ. BY THE SAME AUTHOR. In troum 8vo, Cloth, with 160 Illustrations, Price 3s. &d. PRACTICAL ELECTRIC-BELL PITTING. A PraotioBl Treatise on the fitting-up of Electric Bells and anziliary apparatus, PRACTICAL ELECTRIC-LIGHT FITTING. A Practical Treatise on the wiripg and fitting-up of buildings with the Electric Light, and laying down private installations, [Beady shortly. In Crown 8so, Cloth, with 177 Illustrations, drawn to scale. Price 3s. 6d, ELECTRIC-BELL CONSTRUCTION. A Trea- tise on the construction of Electric Bells, Indicators, and similar apparatus. TELEPHONE^ : THEIR CONSTEUCTION AND FITTING. A PRACTICAL TREATISE ON THE FITTING-UP AND MAINTENANCE OF TELEPHONES AND THE AUXILIARY APPARATUS. 4>0I,|;( LL F. C. ALLSOP, ADTHOS or 'PEAOTICAI. ELECIBIO BELL FmiHO,' 'SLECTBIC BILL COSSTBUCIIOH,' ■rBACIICAI. ELECTBIO LIGHT FITTISO,' ETC, 210 ILLUSTRATIONS. SECOND EDITION, SETI8SD AND ENLAROED. E. & P. N. SPON, 125, STRAND, LONDON. NEW YOBK: 12, COBTLANDT STREET. 1892. PREFACE TO FIRST EDITION. The breaking-up of the telephone monopoly throws open a vast field for development — that of erecting " private lines " between offices and works, residences and stables, different parts of large business establishments, and the thousand and one other places where telephonic communication proves not only an immense convenience, but also a means of saving both time and money. Many persons thus find themselves required to fit up for the first time an instrument with whose construc- tion and working they are totally unacquainted, and whose aptitude for developing " faults " if not properly erected, is oftentimes really marvellous. I have endeavoured, therefore, in the following pages, to give practical instruction on the working and fitting up of telephones, and also such hints as will enable an intelligent fitter with a little practice to readily detect and remove the different " faults " that are liable to appear. Like my former works, the greater portion of this book originally appeared as a series of articles in the ' English Mechanic' F. C. ALLSOP, OF F. C. ALLSOP & CO., Manufacturing Electbioians, 165, Qdfeh Ticiosia Stkbet, B.C. PREFACE TO SECOND EDITIOK. The very rapid exhaustion of the first edition necessitated the immediate production of the second, and advantage has been taken of the opportunity thus afibrded to thoroughly revise the whole of the matter and bring it up to date. The book has been greatly enlarged, both by the addition of new illus- trations as well as fresh matter, the more prominent of the former being some large folding plate diagrams. Throughout the entire revision I have endeavoured to keep to my original project, viz., to provide a complete and thoroughly practical instruction book for those engaged in the erection or maintenance of telephones. F. C. ALLSOP, 165, QCEEH YlCTOBIA STBEEI, £,C. CONTENTS. CHAPTER I. PAGE Eeoeivbrs .. .. .: .. .. ., .. 1 CHAPTER II. Tbansmitiebs ., .. .. .. .. .. 19 CHAPTER III. SWITOH-BBLLS .. .. .. .. .. .. 56 CHAPTER IV. Complete Instruments .. .. .. .. .. 73 . CHAPTER Y. The Magneto Genbbatob and Bell, Battebt Bells, AND Eblats .. .. .. ,, .. .. 99 CHAPTER VI. Switches and Switch-boaeds .. ., .. .. 118 CHAPTER VII. Battebies ., .. .. .. .. ., .. 127 X CONTENTS. CHAPTEE VIII. Eekcting Telephone Lutes, Overhead Wires, Ikstru- MENTS, Etc. ., ., ,. .. .. .. 137 CHAPTER IX. CONNEOTIKG-nP .. ,. .. .. .. .. 168 CHAPTER X. Private Exohanob Systems fob Hotels and other LARGE Buildings ,. .. .. .. .. 195 CHAPTER XL Pdblio Exchange Ststbms .. .. .. .. 209 CHAPTEE XII. Trsting fob and Bemovinq Faults .. .. .. 234 Index .. ,. .. ,. .. „ ., 251 LIST OF ILLUSTEATIONS. lie PAoa FROKTispiEOE. The Berlin Telephone Exchange 1 The Bell receiver (single pole) 3 2 Biagram of two Bell receivers - 4 3 Bell receiver (double pole) 5 4 External view of single-pole Bell receiver 6 5 „ donble-pole „ „ 6 6 The "Watch ''receiver 7 7 The Membrane receiver 9 8 The Gower receiver (plan) 10 9 » » „ (section) 10 10 The Ader receiver (section) 11 11 „ „ „ (external view) 12 12 » » .. (another form) 13 13 )> )» ?» fj >f ••• ••• ••• ••• 13 14 The D'Arsonval receiver 14 15 The Hickley receiver 15 16 The Siemens „ 16 17 The Spoon-shape receiver 17 18 Double receiver 17 19 The Collier receiver , 18 20 The Hughes microphone 20 21 The Blake transmitter (plan) 23 22 „ ,, » (section) 24 23 (plan) 25 2* The Gower transmitter (plan) 26 25 ., » .. (carbon pencil oQ 27 26 The Ader transmitter (plan) 27 27 „ » » (section) 28 28 The Crossley transmitter (plan) 28 29 „ ,, ., (section) 28 30 The Johnson transmitter 29 31 The Swinton „ 32 xu LIST OF ILLUSTRATIONS. FIO. 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48. 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 The Thompson transmitter The German post office transmitter (plan) „ „ „ (section) The Hunnings transmitter The Berthon „ (section).., » » 0>«spectiTe) The Berliner „ (section) Connections of microphone with receiver (without coil) „ „ „ (with coil) Transmitter induction coil „ „ „ with two primary circuits Two-pencil microphone case for Battery switch-bell The magneto switch-bell (perspective view) „ „ connections of ,,i Connections of automatic switch-hook » j» >t ...... Switch-hook Telephone instrument with lightning-arrester Lightning-arrester ,,, Telephone instrument with magnetic transmitter and receiver with special transmitter „ microphone Gower-Bell telephone The Bell-Blake telephone The Crossley telephone The Ader „ The Ader double „ The Johnson „ LIST OP ILLUSTRATIONS. XIU TIG. rAGS 75 The Johnson telephone ... ,.. ... ... 90 76 Outlying picket with telephone ... ... ... 91 77 Ship telephone 92 78 Divers „ 95 79 „ „ 96 80 The magneto generator ... ... ... ... ,,, ... 99 81 Diagram of magneto generator and bell ... 100 82 Armatare of generator ... ... ... ... 101 83 Magnets and carcass of generator ... ... ... 102 84 Armature cnt-ont ... 103 85 „ „ (another form) ... ... ... ,,, ,,, 104 86 „ „ „ „ 104 87 „ „ „ „ ... ... 105 88 The magneto hell 106 89 „ , 107 90 Battery bell 108 91 The vibrating electric bell 109 -92 The single-stroke , 110 93 The continuous-ringing electric bell ... ... ... ... Ill 94 The short-circnit electric bell ... ... ... 112 95 The differentially wound „ 113 96 CSrcular electric bell 114 97 „ „ (internal view) ... 114 98 The "Shield" electric beU 115 99 „ „ (internal view) 115 100 The church-bell shape electric bell ... ... 115 101 The relay 116 102 Electric bell switch 118 103 Telephone switch (three-point) ... 119 104 „ „ (four-point) 120 105 „ „ „ 120 106 „ „ „ 120 107 „ „ (six-point) 121 108 „ „ „ 122 109 „ „ „ 122 110 Plug switch - 122 111 , 122 112 Telephone switch-board 123 113 „ „ 124 114 Telephone plug 125 115 „ „ 125 116 „ switch-board 126 117 The Leclanchi battery (porous pot form) 128 XIT LIST OF ILLUSTRATIONS. no. ' ""A"" 118 Porons pot (external view) 128 119 „ (section) 129 120 Glass cell .'. ... 129 121 The Leclaiiche battery (agglomerate block form) 130 122 Agglomerate blocks and zinc rod 130 123 „ block 131 124 The six-block Leclanche battery 135 125 Agglomerate blocks and carbon ... ... ... 135 126 Four-cell battery in box 136 127 Battery box 136 128 Single-shed insulator 138 129 Double-shed „ 138 130 Kxternal view of insnlator ... ... 138 131 Insulator bolt 139 132 Single shackle 139 133 Double „ 140 134 Shackle strap 140 135 BobbiQ 140 136 Corner bracket for insulators ... 141 137 Bracket for insulators ... ... ... 141 138 , 141 139 142 140 Paying-out wire 144 Ul , 144 142 Kink in wire ,,, ... ... ,,, 145 143 145 144 Draw-vice ... ... ... ... 145 145 Key for draw-vice ... ,,. 145 146 " Vicing-up " a span 146 147 Shackle on chimney 147 148 Double shackle on building ... ... ,,, .,, ,,, 148 149 Finishing off a span ... ... , 148 150 Binding wire on insulator ... ,., 149 151 Chimney bracket I49 152 Pole on roof 150 153 „ chair I5I 154 Adjustable swivel I5I 155 Wood pole 152 156 Insulator on pole ,, ,,, 153 157 Pole clip 153 158 Arranging wires to prevent induction I57 159 „ „ „ „ 157 160 Leading-in the wire IgO LIST OF ILLUSTRATIONS. XV no. PASM 161 Insulator for leadiDg-in wire 161 162 Leading-in tube ... ... ... 161 163 Simple telephone circuit ... ... ... ... 168 164 Connections of instruments shown in Figs 59 and 60 ... ... 169 165 Two instruments with magnetic transmitters ... ... ... 170 166 Connections for two magneto switch-bell instruments 171 167 j> » )> » » 172 168 Two instruments with microphones, receivers, and battery switch-bells 173 169 M J, It jj it It 1*4 170 Connections for Gower-Bell telephone 176 171 „ Ader telephone 177 172 Two instruments with microphones, receivers, and magneto bells for signalling ... ... ... 178 1*3 „ „ „ „ „ I, ,, 179 174 Three telephones in series ... 182 175 Three telephone stations, one of which is able to communicate with the other two as desired ... 183 176 Four telephone stations connected to a central exchange ... 184 177 „ „ „ „ „ „ with local bell circuit ... 185 178 Three stations connected to a central one with indicator ... 187 179 Three telephone stations, arranged on the intercommunication system ... ... ... 188 180 Three telephone stations with three-point switch ... ... 189 181 Two telephone stations with extension bell ... ... ... 190 182 Three telephone stations with an extension bell at one station, and a four-point switch ... ... ... ... 190 183 Three telephone stations with a six-point switch and extension bell at the intermediate station ... ... 192 184 Three telephone stations with seven-point switch and extension bell, which is converted from vibrating to single-stroke ... 194 185 Single-cord switch-board 196 186 Bar switch-board 198 187 Telephone instrument 200 188 Switch-board 201 189 Private exchange system ... ... 202 190 Switch-board with automatic Index 205 191 Secret circuit inter-communication system 206 192 Sloper intercommunication switch 208 193 „ „ , 208 194 Western Electric Co.'s multiple switch-board ... 210 195 Standard board, diagram of 212 XVI LIST OF ILLUSTEATIONS. no. pagS 196 Multiple switch-board, diagram of 214 197 Spring-jack witli plug 216 198 Connections of spring-jacks ... ... ... ... ... 217 199 Connections of plugs in multiple board ... ... ... ... 218 200 Trunk wire between towns ... ... ... 221 201 British post office system ... ... ... ... ... ... 223 202 The French system 224 203 The Law system 228 204 The Mann system 229 205 Miller's returned call wire 231 206 Bennett's electrostatic call wire ... ... ... ... ... 232 207 Detector galvanometer ... ... ... ... 237 208 Linesman's testing set ,,, ... ... ... ... ••■ 238 TELEPHONES: THEIR CONSTRUCTION AND FITTING. CHAPTER I. RECEIVERS. A TELEPHONE instrument consists essentially of three parts : we have first the transmitter, second the receiver, and third the calling and switching apparatus, or switch-bell as it is commonly called. The transmitter transforms the vibrations produced by the sound-waves into undulating electric currents, which currents are transformed back by the receiver into sonorous vibrations. The switch-bell sends and receives the signal to call attention, and makes the necessary change of connections from signalling to speaking The whole combination of line wire, instruments, &c., is generally called a " telephone line," and a telephone line may be either "exchange" or "private." In an "exchange" telephone system one end of each subscriber's wire is taken to a central exchange or switch-room, where, by means of certain switching apparatus, each subscriber can be put into com- munication with any other subscriber on that exchange, while a " private " line is one erected merely for a person's own use between his office and works, office and residence, or other places between which communication may be desired. As most forms of receivers can be used also as transmitters, B 2 TELEPHONES : THEIR CONSTEUOTION AND FITTING. and are in fact for short lines often preferable to a microphone on account of their simplicity, receivers will be descnbed first. The Bell Eeceiver. To Prof. Graham Bell has been ascribed the honour of in- venting the first practical magnetic telephone, and Fig. 1 shows in section the most general form of this instrument in use at the present time. A laminated permanent magnet is used, as in this form it is less Kkely to lose its magnetism. This magnet a carries at each end two soft iron pole-pieces, the lower one of which holds the boxwood bobbin J, wound with No. 40 B.W.G. silk-covered copper wire, to a resistance of from 70 to 80 ohms. This magnet is contained in an ebonite case of the shape shown, and has opposite its lower end the thin ferrotype iron diaphragm c, the diaphragm being held in its position by the lid d, which screws on and off. The diaphragm is fixed only at the circumference, and in the centre is free to vibrate to and fro. Into the top pole-piece screws the screw e by means of which the distance of the oth6r end of the magnet off the diaphragm is adjusted. On either side of this screw are the terminals //, to which the ends of the bobbin S are connected. The action of the instrument is as follows : — Sound, as is well known, is the sensation produced in the ear by certain vibrations or undulations of the atmosphere. When we speak, air is forced out of the lungs through two delicate membranes situated in the upper part of the throat, called the vocal chords, which set the air as it passes over them in vibration, the number of these vibrations per second determining the pitch of the sound, while their amplitude determines the loudness. If we take two receivers (see Fig. 2), of the form shown in Fig. 1, and connect by means of two insulated wires the right-hand terminal of the one (A) to the right-hand of the other, and the left-hand of one to left-hand of the other (B), EEOEIVEES. we shall have a complete circuit right through the two receivers. If now we speak in front of one of these receivers, Fig. 1. Single-pole Bell Receiver. B 2 4 TELEPHONES : THEIR CONSTEUOTION AND FITTING. the best position being when the lips are about an inch from the mouthpiece, the sound-waves produced impinging on the Fig. 2. %- ^ f .1 « Two Eeoeivers connected. diaphragm c cause it to vibrate in unison with them. The diaphragm c, vibrating in front of the magnet, varies the number of lines of force that pass through the coil b, thus inducing in the coil electric currents which vary rapidly both in direction and electromotive force. These currents flow by means of the insulated wires to the second telephone, and, by passing through its coil, strengthen or weaken the per- manent magnet according to their direction, causing it to vary its attraction on the diaphragm in front, which thus vibrates in unison with the diaphragm in telephone No. 1. Words thus spoken to the one receiver are faithfully reproduced in the other, though very much reduced in loudness. Certain sounds are better reproduced than others, the sibilants being the most difficult to reproduce, this being dUe most probably to the com- plexity of their vibrations. The Bell receiver shown in the illustration is about three-quarter full size. A more powerful form of receiver can be obtained by employing a horseshoe magnet, and receivers thus made are known as " double-pole " as diifering from the " single-pole " just described. The double-pole Bell receiver is shown in section in Fig. 3. By employing a horseshoe form magnet, both the N and S poles of the magnet are presented to the iron diaphragm, thus bringing it into a more intense mag- netic field. The magnet consists of a flat steel rod a (bent to the shape shown), on the N and S poles of which are fastened the two oval-shaped bobbins 6 and e. The iron cores of the EEOEIVEBS. bobbins are screwed to the magnet ends, thus forming soft iron polar extensions of the magnet, the lower ends of the Fig. 3. Double-pole Bell Eeceiver. 6 TELEPHONES: THEIR CONSTEnOTION AND FITTING. cores coming close to the diaphragm d. The adjustment is effected as with the single-pole type by the screw e, which varies the distance of the two poles off the diaphragm. The two coils are connected in series, and arranged in the usual manner, i. e. so that a current in one direction would give a N to one and a S to the other, and not two N's or two S's. Thus when the rapidly alternating and undulating current from a transmitter passes through the coils it weakens or strengthens the N and S poles, as described for the single-pole type, which thus vary their attraction on the diaphragm. Fig. 4 shows the external appearance of the " single-pole" and Fig. 5 that of the " double-pole " Bell receiver. Fig. 4. Bell ReceiTers. Although by " Bell " receiver is more generally understood the form shown in Figs. 1, 3, 4, and 5, yet nearly every mag- netic receiver is a modification or re-arrangement of the original EECEIVEES. Bell instrument, certain modifications being introduced by tbe different inventors, with a view to increase the efficiency or render more compacfc A very compact form of receiver is that shown in Fig. 6, and known as the " watch," owing to its resemblance to that article. It is a double-pole receiver, and consists Fig. 6. of a flat horseshoe magnet, similar in shape to that in the Gower (see Fig. 8), with two oval-shaped bobbins on the soft iron polar extensions. The diaphragm, which is of thin ferrotype iron, is clamped between the lid and body of the case, the lid screwing on and off, as shown in the Bell. The receiver is suspended when not in use by the ring at the top, and the terminals are inside the case, the two metal-pointed ends of the receiver cord passing through two holes in the bottom of the case for the purpose of making connection with the terminals. It is not so powerful as the Bell receivers shown in Figs. 1 and 3, but is an exceed- ingly handy form, and gives very good results on short lines. Watot Reoeiyer. The Membrane Receivee. This receiver, which was also invented by BeU, was the one he adopted previous to his bringing out the improved form just described. It had an electro-magnet and goldbeater's skin diaphragm, in the centre of which was fixed a small steel plate. After experimenting with different forms of this instrument. Bell found that better results were obtained if he substituted' a thin sheet-iron diaphragm for the goldbeater's skin one, and that also by using a permanent instead of an electro-magnet, he could do away with the necessity of having a battery in 8 lELEPHONES; THEIR CONSTKUOTION AND FITTING. circuit. Owing to the details of this first form of Bell's receiver being published in the 'English Mechanic ' of August 1879, this form of the receiver is also known as the "English Mechanic" receiver. Some time after patenting his im- proved form, BeU filed a disclaimer repudiating all claim to his former instrument, so this form of receiver was free to be used and manufactiu-ed by any one while Bell's patent was in force, and was the form of transmitter and receiver used during that time by such telephone companies as were not licensed by the United Telephone Company. Fig. 7 shows, full size, partly in section, a form of the membrane receiver. It consists, as wiU be seen, of a box- wood, mahogany, or ebonite case a, fitted with a lid b, th« lid being fastened to it by the screws shown. Between the lid and the case is the diaphragm c, which may be of gold- beater's skin, parchment, or any similar material, and pre- ferably one not much afiected by atmospheric changes, the diaphragm being stretched on a brass or zinc ring or clamped between two, as shown in the illustration. In the centre of the diaphragm is the disc d, of tinned iron, which is affixed to the diaphragm by rubber solution or other similar cement- ing compound. The adjustment is effected by the screw g, which pulls against the spider wheel h. It is in making a diaphragm that will resist the at- mospheric changes that the difficult part of a membrane receiver comes in. The first forms introduced proved almost useless on account of their diaphragms, which would be taut one day, while the next perhaps they would be so slack as to quite prevent the transmission of speech. Swinton used a thin sheet of vulcanised fibre for the diaphragm of his receiver, but what seems to have given the best results is celluloid. With the Bell receiver, owing to the magnet being a permanent one, no battery is required when two receivers are joined up together for the purpose of speaking between two places; but with the "English Mechanic,'' or other EECEIVEKS. 9 receivers which have an electro-magnet, a battery is, of course, necessary. The expiration of the Bell patent on Dec. 9, 1890, proved Membrane Receiver. the death-stroke of the membrane receiver, since it was only employed as a means of avoiding this patent, and is not for a moment to be compared, both as regards conve- nience and speaking capabilities, to a properly constructed Bell receiver. The Gowbr Eeceivkr. Figs. 8 and 9 show the Gower receiver — the one used by the British Post Office. Fig. 8 is a view from the front with the 10 telephones: theie construction and fitting. diaphragm removed, while Fig. 9 is a side view, partly in section and partly in elevation. The permanent magnet ft, it Fig. 8. Fig. 9. will be seen, is semicircular in form, and has at each pole two bobbins of wire, the soft iron cores of which form extensions of the two poles. The dia- phragm c, which is generally of tinned iron, and somewhat larger than in the Bell, is carried by the front of the case, being fastened on to a brass ring by screws, as shown. In order to convey the sound from the dia- phragm to the ear, a flexible tube d is provided of the form used for speaking tubes. IntheGower-Bell combination the receiver is placed inside the switch-bell case, and the speech transmitted to the ears by two flexible tubes. Gower Receiver. EECEIVERS. 11 The Ader Eeceivee. Fig. 10 shows, partly in section and partly in elevation, the Ader receiver, which is the one employed by the Societe Gene- rale des Telephones in France, and which is also largely used in Belgium and Austria. It is undoubtedly entitled to take rank as one of the most powerfid and sensitive of receivers. It consists, like the Gower, of a semicircular magnet a, that Kg. 10. Ader Receiver, carries at its polar extremities two iron cores, on which are fixed the two bobbins h b. The diaphragm d, which is of thin ~tinned iron, is clamped between the Ud and body 'of the case, outside which case the magnet projects, thus serving also as a handle. The chief 'feature of the Ader receiver, how- ever, is the soft iron ring n n, fixed in the front of the case, which iatensifies the magnet field. This iron ring, which M, Ader caUs the " sur-excitateur," concentrates the lines of 12 telephones: theie consteuction and fitting. force, causing the variations in the magnetism of the magnet to have a greater effect on the diaphragm, thus increasing the sensitiveness of the receiver. In the smaller form of Ader receiver, which of late has been much used in this country, the magnet does not pro- ject through the back of the case, but is of small size and contained within it; this form is shown in Kg. 11. It is also Fig. H. Ader Receiver. to be obtained mounted as a Bell, as shown in Fig. 12, or as a spoon receiver, as shown in Fig. 13. The containing case of the Ader receiver is usually of metal, and the mouthpiece of ebonite, all external metal parts being plated. The D'Aksonval Eeceivee. In the receiver designed by M. D'Arsonval, and of which Fig. 14 is a section, the permanent magnet is bent into such a shape that one pole fastens to the iron core of the bobbin and the other to an iron tube that surrounds the bobbin. In the figure a is the permanent magnet, b the iron core of the EEOEIVEES. 13 coil of wire, and c the iron tube surrounding it. The iron core has a threaded part at the top, which part screws through the one pole, the other pole being attached to the iron tube by the screw shown. The diaphragm d, which is of thin ferro- Fig. 12. Kg. 13. Bell-pattem Ader Receivers. type iron, is clamped between the lid and body of the contain- ing case, as in the Ader. The novel feature of the D'Arsonval receiver is that the two poles of the magnet are exposed to the diaphragm, using only one coil instead of two, as in the pre- viously described forms of receivers having a horseshoe magnet. Thus there is no waste wire in the coil, the whole of it being subjected to induction. This receiver certainly gives very good results, and is, moreover, of comparatively light weight. 14 telephones: their oonsteuotion and fitting. The Hickley Ebcbiveb. Fig. 15 shows insection the Hickley receiver. This receiver, it will be seen, consists of the permanent magnet a, with one pole in the centre (which may be either N or S), and three other poles 6, of different polarity to the centre one. On the Fig. 14. D'Arsonval Receiver. centre pole is fixed the coil c, the two ends of which are con- nected to the flexible cord shown. The diaphragm d, which is of thin ferrotype iron, rests at its circumference on the outer poles, and by this means the resistance of the magnetic circuit is considerably reduced. Eeceivers made on this principle are capable of giving very excellent results. The Siemens Receiver. The receiver designed by Messrs. Siemens and Halske resembles internally the double-pole Bell shown in Fig. 2, and consists like the Bell, of a horseshoe magnet, having KECEIVEKS. 15 two Qval-shaped bobbins on its soft iron polar extensions. It is contained in a cylindrical case, the body of which is sheet iron, and the mouthpiece of polished hard wood, having the opening lined with brass. The regulation is effected by a small screw at the bottom of the telephone, by means of which the distance of the magnet off the diaphragm can be varied. Fig. 16 is an external view of this receiver. Fig. 15. Hiokley Eeoeiver. Spoon-shape and Double Receivers. Another very convenient form of receiver is that known as the "spoon," a form of which is illustrated in Fig. 17. In the form shown it consists of a Watch receiver mounted on a convenient handle, but in another common form the diaphragm and mouthpiece are applied sideways to the magnet, which is made to form the handle. The magnet is a permanent one of the horseshoe form, and the soft iron cores of the two oval- shaped bobbins are fastened on to the side of the poles. The body of the magnet is wound with leather or faced with wood, forming a convenient handle, and the connecting cord enters 16 telephones: theik construction and fitting. at the bottom, while at the top is the loop by which it is hung on the switch-hook of the telephone. In order to obviate the necessity of using two hands, the one to hold the transmitter and the other the receiver, what is known as a " double receiver " is often employed, a form of Fig. 16. ' Siemens Receiver. which is shown in Fig. 18. It consists of two receivers fastened to one handle and fixed in such a position, the one to the other that the act of holding the receiver to the ear places the trans- mitter in the proper position for the mouth, thus leaving one hand free. The watch form and the Ader are the receivers that lend themselves more readily for adaptation as double receivers. KECEIVEES. 17 The CoLtiEE Eeceiver. This receivier, which has only recently been introduced, was devised by Mr. A. T. Collier, of Sydney, New South Wales. It has several new features, and when well made constitutes a most powerful receiver. Its construction and action will be best understood by referring to Fig. 19, which is a section of the Kg. 17. Pig. 18. Spoon-shape Receiver. Double Receiver. complete receiver. In the figure H is the horseshoe magnet, of which N and S are the two poles. Between the ends of this magnet is fixed the coil C, the ends of the iron core of which come opposite the magnet poles. There are two diaphragms, D^ and D", which are fixed one in front of each pole of the 18 telephones: their constbtiction and fitting. Fig. 19. magnet. The mouthpiece M is not opposite the diaphragms, but immediately over them, and the diaphragms being com- pletely cased in the only exit for the sound waves, which are taken from the inner sides of the diaphragms, is through this common mouthpiece at the top. The coil is wound to a resis- tance of about 250 ohms. It will be seen that the two diaphragms are in a very intense magnetic iield and that their combined vibrations are projected through a specially shaped mouthpiece. In some tests made with the object of comparing -the efficiency of this in- strument with that of the double-pole Bell and Ader, it was found to give considerably better results, both as regards loudness and clear articula- tion, though it is perhaps only fair to state that the Collier had a very large number of turns on the magnet ap compared with the Bell and Ader, the resistance of the bobbins of the former being about 300 ohms as compared to 75 ohms of the two latter. Collier Receiver. ( 19 ) CHAPTER II. TEANSMITTERS. Any of the forms of receivers described in the last chapter can be used also as a transmitter, and such a combination, as was before stated, is sometimes to be preferred to a microphone for short distances, on account of their greater cheapness and simplicity. For long distances, however, the results obtained, from a pair of receivers, one of which is used as a trans- mitter, are in no way to be compared to those produced by using a microphone ; and it was the very poor results obtained from Bell's telephone, when used as a transmitter and receiver, that induced the diflferent inventors to turn their attention to devising a more efficient form of transmitter ; though it was not until the discovery, by Prof. Hughes in 1878, of the microphone, that the telephone became an efficient, long- distance instrument. Some months previous to this Edison had, it is true, brought out his carbon transmitter, an instru- ment that acts from a somewhat diflferent principle to the microphone, though it could scarcely be called an efficient transmitter, or at any rate one that was likely to have stood the test of everyday use. In as much, however, as Edison in his specification made mention of variable contacts and lamp- black (soft carbon), it was held that he had anticipated the discoveries of Hughes, and thus Edison's patent became the master patent for carbon transmitters. c 2 20 telephones: their construction and fitting. Hughes's Microphone. In Fig. 20 is shown, partly in section and partly in eleva- tion, Prof. Hughes's microphone, which forms the basis on which all the modem carbon transmitters are constructed. As aU receivers are more or less modifications or copies of the original Bell instrument, so are all the modem carbon trans- mitters modifications or rearrangements of Prof. Hughes s microphone. The instrument consists, as will be seen from Fig. 20. Hughes Microphone. the figure, of an upright pointed carbon pencil a, the points of which rest loosely in the two supports h h. These supports 6 6 are fastened to the thin sounding board c, which is fixed at the circumference by the wooden frame d. The whole apparatus is fixed on a suitable stand g. The apparatus is easily made, and the reader is advised to construct one, as a good idea of the action of carbon transmitters wiU readily be obtained by a little experimenting with it. For the carbon pencil a, a piece TRANSMITTEES. 21 of carbon rod, such as is used for arc lamps, ^ in. in diameter and 2 in. in length, should be procured, and the ends sharpened, as shown in Fig. 20. The two supports b b can be made out of a piece of old carbon battery plate, being filed to the shape shown, and drilled at the ends for the points of the carbon. A piece of ^ board, about 6 in. by 4 in,, is next procured, and mounted on a stand, as shown. To the centre of this board is supported the carbon pencil by means of the supports, as in Fig. 20, the carbon pencil being a loose fit in the holes in the carbon blocks. The carbon blocks are affixed to the board « by some elastic glue, or better still, by screwing, for which purpose the carbon blocks should be provided with a foot. Two pieces of thin silk-covered copper wire should be attached one to each carbon support, for the purpose of connections. If now we connect up this microphone to any of the forms of receivers just described, interposing in the circuit one or two smallest size Lecknche cells, we find that any words spoken to this carbon pencil will be faithfully reproduced in the receiver. If a watch is laid on the stand of the microphone, the ticking is distinctly heard in the receiver, being very loud and pro- nounced. The slightest touching of the stand or pencil is made manifest in the receiver by a loud sound, and if the microphone is in good order, the walking of a fly on the pencil can be readily detected. The action of the microphone is based on the principle that a loose contact, formed between two non-oxidisable substances, set into vibration, is subjected to great variations in resistance when traversed by an electric current, and that the greater or lesser intimacy of contact between these two surfaces is accompanied by a corresponding decrease or increase in its resistance. Thus, when words are spoken to the microphone described above, the carbon pencil partakes of the vibrations communicated to the air by the voice, and vibrates in unison with them. This causes the pencil to vary its pressure and intimacy of contact with the supporting blocks, which thus vary the resistance of 22 telephones: theib consteuotion and fittiho. the circuit, giving rise to undulations in the current -which are faithfully reproduced in the receiver. When it is understood that these variations amount at times to about 400,000 a minute, during which time the circuit is never once broken, the extreme beauty of the instrument -will be appreciated. Microphone transmitters can be classed under three dis- tinct headings, viz., the " platinum and carbon," the " carbon pencil," and the " granulated carbon " form. The first of these undoubtedly gives the most perfect and natural articulation, the second are the best for simple, reliable and aU-round trans- mitters, whilst the third are capable of giving the most power- ful results. The most important, and in fact the only one at present worthy of any note coming under heading No. 1, is the Blake, which will now be described. The Blake Teansmittek. It was in May 1878, that Prof. Hughes first introduced his microphone to the public, ajid it was as early as August in the same year that Mr. Francis Blake, assisted by several experts of the American Bell Telephone Company, produced the first prac- tical microphone transmitter. This instrument, which is known as the " Blake " transmitter, is the most widely used of any, there being over 100,000 in use at the present day. This is not due, as might be supposed, to any great superiority over other forms ; for, as a matter of fact, for long distances it is inferior to some, but chiefly owing to its being the first satisfactory one produced and having fallen into powerful hands. Figs. 21 and 22 show the form of Blake transmitter now in use, Fig. 21 being a plan, and Fig. 22 a section. It consists, as will be seen, of the cirdular iron frame a, with an upright post at the top and bottom. To the top post is screwed the spring 6, to which is fixed the iron lever c that is adjustable by the screw d in the bottom post. At the top of the lever c is TEANSMITTBES. 23 fixed ihe insulating block x, to which is fastened the thin spring s, carrying at its lower end the platinum point j". Against this platinum point presses the hard carbon button o, fastened to the brass carbon holder at the back, the carbon holder being carried by the spring p, which is fixed to the top part of the Fig. 21. Blake Transmitter. -lever c. The thin sheet-iron diaphragm/, is insulated from the iron frame a by the rubber ring g, and the vibrations of the diaphragm are damped by the steel spring Ic, the end of which is insulated by a rubber glove. The whole of the apparatus is contained in the polished walnut wood case t, into the front of which is cut the mouth-piece r. The spring s carrying the platinum point is called the " normal pressure " spring, and the one (p) which supports the carbon button the " carbon " spring. The circuit through the transmitter is as follows : 24 telephones: their consteuction and fitting. Fig. 22. The current entering, let us say, by the top -wire, passes from thereto the spring s and platinum pointy, thence to the carbon button 0, which presses lightly against it, then to the carbon holder, spring jj, lever e, spring 6, frame a, and leaving by the lower wire. • The following is the action of the instrument : — The sound- waves striking the diaphragm / cause it to vibrate in unison with them. The vibrations of the dia- phragm cause the platinum point j to vary its pressure on the carbon button 0, these variations in pressure causing changes in the resistance of the circuit, which give rise to undulations in the current. In adjusting a Blake transmitter, first, if the instrument is a new one, see that the paper padding is removed from between the carbon block and the frame. Next slack-back the adjusting- screw d, till the platinum point is just clear of the diaphragm,, then turn upwards two full turns., This will usually bring the instrument to the- right adjustment. Place the telephone to your ear, however, and tap the diaphragm of the transmitter, when, Blake Transmitter. if all is connected up properly, a sound vrill be heard in the telephone. If the sound is dull and short, slacken back the screw d ; but if it is inclined to be prolonged or make a humming noise, the screw must be tightened up a bit. When properly adjusted a clear musical sound should be heard, but leaving off sharp. Never at any time turn the screw more than a quarter of a turn at a time, as the best position is easily passed. If the carbon button be pulled back the platinum point should follow it nearly J in. TEANSMITTEES. 25 In adjusting a transmitter some allowance should always te made for the voice of the person who will usually use the instrument ; but the adjustment should never be left too loose or it will jar, and probably commence humming in an hour or two, as a newly set up battery becomes more active as the solution becomes saturated. In a well-adjusted Blake trans- mitter breathing against the diaphragm should be distinctly heard, and in a quiet place, persons talking some distance from the instrument should be heard at the other end of the line. In Fig. 21 it will be seen only half the transmitter case is shown, and the microphone is connected up to the two nickelled Fig. 23. Case of Blake Transmitter. Springs on the hinges m and n, which make the connections across to the other half of the case (see Fig. 23) that contains the induction coil. The induction coil, it will be seen, is at the bottom left-hand 26 telephones: theib construction and pitting. side of the case, and the ends of the two coils are connected up to the four terminals (1, 2, 3, 4) at the top. 1 and 2 are the ends of the primary, and 3 and 4 of the secondary, the lower end of the primary coil being connected to the hinge (w), and the circuit passes through the microphone before reaching terminal 1. The terminals 1, 2, 3, and 4 are connected up to similarly marked terminals in the switch-bell shown in Fig. 49. We now come to microphone transmitters of the second kind, viz. " carbon pencil " transmitters, one of the most familiar of which is the Gower. Fig. 2i. The Gower Transmitter. In Fig. 24 is shown Gower's transmitter, which is the form of transmitter adopted by the British Post Office. It consists, as will be seen from Fig. 24, which is a plan about quarter full size, of eight carbon pencils, connected together in two sets of four by means of the two copper strips m n. These carbon pencils are supported at one end by the separate carbon blocks c^ (?c' S' S^ Connections of Magneto Switoh-bell. TELEPHOKES: THEIB OONSTEtJCTION AND FITTING.. the weight of the receiver against the pull of the spiral spring Z. M and N are the two hinges that make connection across the Kg. 52. Magneto Switch-bell. SWITCH-BELLS. 67 Hi to the bell T ; L and E are the "line " and " earth " ter- minals, and E and E' those for the receiver. P and P' are the terminals for the primary circuit of the microphone, and Kg. 53. Magneto Switch-bell. S and S^ those for the secondary. The lightning-arrester at the top under the L and E terminals. The "ringing circuit consists of (when the receiver is on the hook), starting from the armature C : — Armature C, F 2 68 telephones: theie construction and pitting. contact spring G, hinge N, wire h, bell T, hinge M, spring K, switch-hook H, terminal L, "line" wire, other instrument, " earth," terminal E, frame of generator, and back to arma- ture C. Einging from the other end the circuit is just the same, except that when the current arrives at the frame of generator it passes through to the hinge N by means of the low re- sistance circuit formed by the armature cul^out (see p. 103). When the receiver is ofifthe hook the " speaking" circuit is, starting from the secondary of the induction coil : — Secondary of induction coil, terminal S, terminal E,^, receiver, terminal E, terminal E, " earth," other instrument, terminal L, switch- hook, spring J, wire e, terminal S', and back to secondary of coil. Fig. U. Switch-hook. The " local " circuit runs from the microphone to primary of induction coil, local battery, terminal P, switch-hook, spring I, wire/, terminal P^ and back to the microphone. The two other methods of connecting up the switch-hook are shown in Figs. 54 and 55. The same letters are used to denote the different parts as employed in Figs. 52 and 53. SWITCH-BELLS. 69 In Fig. 54, it will be seen, there is but little difference between this and the method shown in Fig. 52, an extra spring only being employed so as to have a separate spring for the secondary circuit. In Fig. 55 we have substantially the same arrangement as in Fig. 54, only that the two microphone springs are connected across by a metal piece that is insulated from the switch-hook, thus preventing the secondary and primary circuits of the induction coil being in connection at the switch-hook, which. Wu Kg. 55. TO TERMINAL "S" I J TO TERMINALS 'p'j.If'''" "^a \ K TO HINGE "jH" Switoh-hook. it will be seen, is the case in Figs. 52 and 54. The method shown in Fig. 55 is perhaps the best, though Fig. 52 is much used on account of its being the simpler. A special form of switch-hook, now much used, is shown in Fig. 56. In this form of switch-hook, which is of a very solid character and has an excellent rubbing action in the contacts, the bottom spring b, is arranged- so as *to supply the pressure necessary to keep the hook up when the receiver is removed, as well as form one of the contacts. 70 TELEPHONES: THEIE CONSTBUCTION AND FITTING. The different parts consist of the switch arm a, the three top springs e (only one of which is shown), and the bottom spring h. The switch arm is pivoted on the bracket d, and normally is weighted down by the receiver, causing it to make contact with the spring h. When released it flies up into the position shown, thus making contact with the springs c, the connec- tions for the different springs being exactly the same as shown in Fig. 55. It will be seen from Fig. 56 that the switch arm Fig. 56. '^=^ Switch-hook. is fitted with insulating studs, on to which studs the springs slide as they break contact with the arm. Thus both the top and bottom springs always maintain a firm pressure on the switch-hook, that of the bottom one preponderating, so as to throw the arm up when the receiver is removed. Lightning-arresters. The liability of overhead wires to be struck by lightning necessitates the employment of lightning-arresters in a tele- phone line where the wires are overhead, though the necessity for lightning-arresters is not so great in this country as abroad. LIGHTNING-AEEESTEES. 71 Fig. 57, When a telephone line without an arrester is struck, the dis- charge passes to. earth by means of one or both ends of the line, passing through and destroying the instrument, and might pass, if the conditions were favourable, to any person standing near the instrument, in all proba- bility with unpleasant, if not fatal, results. The duty of a lightning- arrester is to intercept the discharge and pass it directly to earth, thus protecting the instrument and the person who might be using it. The manner in which this is done will readily be understood by referring to Fig. 57, which shows the connections at one end of a telephone line with the telephone and lightning-arrester in circuit. The arrester consists of the two brass plates a and J, fixed on an insulating base so as to be perfectly insulated from one another. The two sides of the brass plate, where they come close together, are cut to a saw- (-i-. edge, as shown in the figure, and the ^""^ plates are so fixed that the project- Lightning-arreBter. ing points of the one plate come opposite those of the other plate, and as close as possible without touching. The tele- phone currents entering at line pass to the wire c, through the telephone instrument, to wire d, and thence to earth E. If the line,^ however, is struck by lightning, the discharge endeavours to pass to earth, and arriving at the plate a, jumps across to the plate 6, in preference to going round through the telephone, and passes directly to earth, the jumping across the two plates being assisted by the serrated edges. 72 TELEPHONES : THEIB CONSTETJOTION AND FITTING. As is pointed out on page 163, it is important that the earth wire does not pass too close to any pipes in connection with Pig. 58. the earth, or it might jump across to these in preference. Six inches is the least distance that should he allowed. The arrester is usually comhined with the switch-bell, being fixed by the " line " and " earth " terminals. Fig. 58 shows in detail a separate lightning-arrester for fixing at the point where the line wires enter the building, or for use in other places where it is not deemed advisable to have the arrester on the instrument. The two top plates are for the line wires, and the bottom one is con- nected to earth. Lightning-arrester. ( 73 ) CHAPTEE IV. COMPLETE INSTRUMENTS. The recent expiration of the whole of the master patents of Bell and Edison effected a break down of the great monopoly that had existed in telephones for the last ten or twelve years. That the cessation of this monopoly wQl prove a great stimulus to the erection of short private telephone lines is quite certain, though it is not likely to much affect the large telephone com- panies, whose exchanges in the various towns have gained too firm a footing to fear the advent of any rival. The patent rights in this country were originally acquired by the United Telephone Company, who worked the London and suburban districts and issued sub-licenses to various other companies, viz. the Western Counties, the Lancashire and Cheshire, and the South of England Telephone Company, for certain other districts. Subsequently, the majority of these companies amalgamated with the parent company, the combina- tion being now known as the National Telephone Company. The instruments are let out to the public on a rental system which, although admirable for "exchange" lines, has not met with much favour in regard to " private " ones, where purchasing outright is undoubtedly more satisfactory. The Bell patent expired on December the 9th, 1890, throw- ing open to the public the Bell receiver with its permanent magnet and metal diaphragm. Before the expiration of this patent, the form of telephone used by such persons as were not licensed by the United, was the " English Mechanic " receiver, with its membrane diaphragm and electro-magnets ; and although satisfactory results were obtained by these under 74 telephones: theib construction and fitting. favourable conditions, yet they were in no way to be compared to any forms of the Bell. The next patent to lapse was the Edison (No. 2909, 1877), which expired on July the 30th, 1891, throwing open to all the battery transmitter, by means of which only is long distance telephony practicable. It was on this patent, and not, as imagined by many, on that of the Blake transmitter, that the United Telephone Company took up their stand and held so successfully the sole right to use a battery transmitter in this country. The different forms of complete instruments may be classed under four distinct heads, viz. : — 1st, Those with battery" switch-bells and magnetic transmitters and receiv^ers ; 2nd, Those with magneto switch-bells and magnetic transmitters and receivers ; 3rd, Those with battery switch-bells, magnetic receiver, and microphone transmitter ; and, 4th, Those with magneto switch-bells, magnetic receiver, and microphone transmitter. Those of the 1st class are suitable for short lines, such as from room to room in large buildings, or for attaching tele- phones to existing electric bell circuits. The second class are suitable for somewhat longer lines, such as from house to stables, &c., or where it is desired to have no batteries. The 3rd class are suitable for all lines of moderate length, and are a favourite instrument. Those of the 4th are intended for very long lines, such as from 10 to 50 miles in length. Battery Switch-bells with Magnetic Transmitters. Two forms of this class of telephone instrument are shown in Figs. 59 and 60. The form shown in Fig. 59 consists of a Morse key-board, with two hooks at the bottom, these two hooks forming the automatic switch. A separate bell is re- quired with the instrument, which can be fixed above or at any other convenient place. The receiver, which in this instru- COMPLETE INSTRUMENTS. 75 ment is also the transmitter, hangs on the two hooks at the bottom, the metal suspension ring connecting them together, which' thus short circuits the receiver and obviates the neces- sity of ringing through the high resistance of its coil. Any form of receiver can be used with the instrument, a "watch" being show in the figure. The ringing is effected by pressing Fig. 59. Fig. 60. Telephone Instruments with Magnetic TransmittetB. the button of the key, and to speak the receiver is lifted off the hooks, thus throwing it into circuit. Another very con- venient form is shown in Fig. 60, the working and connections of which are similar. The external connections of both these instruments are shown in the diagrams of connections at the end 76 telephones: theie construction and fitting. Magneto Switch-bells with Magnetic Transmitters. Figs. 61 and 62 show two forms of this class of telephone instrument, which is perhaps the simplest and easiest fixed of any. The form shown in Fig. 61 has two double-pole Bell re- ceivers, which hang on two hooks on the front of the generator case, the right-hand side hook being the automatic switch. Fig. 61. Telephones with Magnetic Transmitters. To call attention, the handle on the right of the generator case is turned once or twice sharply, which causes both the bell at the other end of the line and also that at the sending end to ring. When the reply signal is received, the receivers are lifted ofif the hooks and held, the one firmly to the ear, and the other a convenient distance from the mouth, the speech COMPLETE INSTRUMENTS. 77 being directed into the mouthpiece. The form of instrument shown in Fig. 62 is similar to that just described, except that it has two " watch " receivers instead of double-pole Bell, and the automatic switch is at the left-hand side of the generator case. The two terminals " line " and " earth " are at the top of the case. As it is often desired to have the right hand free for the purpose of taking down messages, these instruments are fre- quently used with a fixed transmitter, a form of which is shown in Fig. 63. The " transmitter " in this case is an Ader receiver, to the back of which is fixed a wooden plug. This plug fits nicely into the metal tube seen to the right, and Special Transmitter. which is screwed on to the front of the generator case. Thus the receiver can be held in the hand while the speech, is directed to the fixed transmitter on the front of the case. Few people were probably aware, until they came to try them, of the really excellent results capable of being obtained from Bell receivers, one of which is used as a transmitter. Never- theless, for short distances the results obtained by using two double-pole Bell or Ader receivers are really very good, and from their simplicity they are in some instances to be pre- ferred to a microphone, as being less likely to get out of order, besides being cheaper both in the first cost and the subsequent expense of maintenance. It is necessary, however, to speak rather louder than when a microphone is used, and, moreover, the intonation of the 78 telephones: theik oonsteuotion and fitting. voice is not so well reproduced. In using these magnetic receivers they should be held firmly to the ear when listening, while for speaking the receiver should be held with the mouth- piece about three inches off the lips, and the speech should be clear, fairly loud, and directed well into the mouthpiece. The Ader receiver is, perhaps, the most powerful for use without a microphone, but it has not the soft tone of the double-pole Bell. Battery Switch-bells with Microphone. A form of telephone instrument coming under the third heading, and made by the writer's firm, is shown in Fig. 64. Fig. 64. Telephone Instrument with Microphone. It consists of a polished walnut-wood case, in the front of which is cut the circular aperture seen. Inside this lid is fixed the microphone (of the form shown in Fig. 46, p. 55), COMPLETE INSTEDMENTS. 79 which is connected directly to the induction coil in the body of the case. On the right-hand side is the automatic switch- hook, which is of a very solid character. At the bottom of the case is the gong of the bell, the movement of which is inside the case, and the ringing button can be seen on the top Fig. 65. Telephone Instrument with Microphone. left-hand side. The connections and interior construction of this instrument are shown in Fig. 47, the four terminals at the top being L, E Z, T Z, and C respectively, starting from the left-hand side. This class of telephone makes a very compact and loud-speaking instrument. Another form of the battery switch-bell instrument with microphone transmitter is shown in Fig. 65. It differs some- 80 telephones: their construction and fitting. Fig. 66. what from the preceding form, and is also fitted with a relay, being intended for long-dis- tance working. The bell gong is at the top, the automatic switch on the left-hand side, and the ringing key in the front of the case. The in- duction coil is in the bottom half of the body of the case, and on its right-hand side is the relay. Two " watch " re- ceivers are used with the in- strument, and the microphone is of the form shown in Fig. 46. A lightning-arrester is provided, being fixed just below the bell gong. Magneto Switch-bells with Microphone. A form of telephone instru- ment coming under the fourth heading is shown in Fig. 66. It consists of a polished wood backboard, on which are mounted a magneto switch- bell, a microphone transmit- ter and local cell for the micro- phone. The switch-bell is at the top, and has hanging on the automatic switch a double- pole Bell receiver. Below the switch-bell is the microphone, Telephone Instrument with *"*^ below this a box cOUr. Microphone. COMPLETE INSTEUMENTS. 81 taining the local cell. The top of this box is sloped for use as a ■writing-desk, should it be necessary to take down a mes- sage. The switch bell being very powerful, this instrument is eminently suited for long-distance working. Any other form of microphone can of course be substituted if desired. At the top are the three terminals, the right-hand side one the " line," on the left the " earth," and that in the middle is an extra one, for use where the instrument is not at a ter- minal station. If such is not the case, this terminal and the earth one must be joined with a piece of wire. Having described the different types of complete instru- ments, we will now pass on to one or two special forms that are in use or have been devised in the last six or seven years. One of the most prominent of these is the Gower-Bell, a very excellent instrument, and the one used by the British Post Office. The Gowee-Bell Telephone. Fig. 67 shows this instrument complete, it being a combina- tion- of the Gower microphone and the Gower-BeU receiver. The diaphragm, which is a thin pine board, is, it will be seen, exposed, and, in fact, forms the lid of the mahogany containing case. To the under side of the diaphragm is attached the Gower microphone, shown in Fig. 24, p. 26, connection being made to the body of the case by flexible wires. In the centre of the containing case is fixed the Gower receiver, the dia- phragm being placed downwards, and the sound-waves pro- duced are communicated to the ears by the two flexible speaking-tubes shown. On either side of the case are two movable supporting hooks, only one of which is visible, and on these hooks are hung. the receiving tubes when the instru- ment is not in use. These hooks form the automatic switch, the weight of the tubes moving them down against the action of a spring. The one hook opens and closes the local circuit through the primary of induction coil and microphone, and the G 82 telephones: their construction and fitting. other hook makes the change of connections from " ringing " to "speaking." The induction coil is fixed at the back part of Fig. 67. Gower-Bell Telephone. the inside of the case on the left-hand side, and on the right- hand side is the movement of the bell, the hammer projecting through a hole in the bottom of the case, and striking against COMPLETE INSTRUMENTS. 83 a gong fixed below. At the top of the back-hoard, of the instrument is the ringing key, which is an ordinary Morse-key push, the spring of which is attached to line, and its normal position rests against a brass plate let into the back-board of the instrument. The instrument can be obtained with a covered-in diaphragm and mouthpiece, so that the diaphragm is protected from injury. The Bell-Blake Telephone. These instruments, which are, perhaps, better known as the National Telephone Company's instruments, are the most widely used of any in this country. They are met with in three forms — the battery-bell instrument, the desk, and the magneto switch-bell instrument. Fig. 68. Bell-Blake Telephone. Fig. 68 shows the battery switch-bell type, which is not so much used now, it having given way to the magneto switch- bell form. It consists of a stained wood back-board, the front being covered with green baize, on which are mounted two G 2 8i TELEPHONES : THEIE CONSTEUCTION AND FITTING. polished walnut-wood cases. The case on the left-hand side contains the Blake transmitter, the diaphragm of which is visible through the mouthpiece. The other case contains the switch-bell, which bell is shown in detail in Fig. 48, p. 60. The connections from the one case to the other are made at the back of the board. A form of the portable or desk instrument is shown in Fig. 69. It consists of a magneto switch-bell mounted on a Fig. 69. Bell-Blake Telephone. special polished wood base so arranged that it will conveniently stand on the table. The transmitter, which is a special cir- cular-form Blake, is contained within the switch-bell, the mouthpiece being visible in front of the case. The receiver, a single-pole Bell, is to be seen hanging on the left, and from the back of the case springs the flexible wire that connects the instrument with the line wires. This form of instrument is very convenient for office use, as it can be stood on the desk and moved from one part of the room to the other as desired. The third form of the Bell-Blake combination, used by ,the National Telephone Company, has a magneto switch- bell, and a form of this instrument, now largely employed COMPLETE INSTRUMENTS. 85 Fig. 70. by them, is shown in Fig. 70. The switch-bell, Blake trans- mitter, and box containing the local cell, are mounted the one below the other on a long back-board of polished walnut-wood. The switch- bell is of the form shown in Fig. 50, and the receiver used is generally a single- or double-pole Bell. The Blake transmitter is placed directly beneath the switch-bell, and is fre- quently supported by rubber bands, so as to prevent vibration being trans- mitted to it through the medium of the back-board. The battery for working the micro- phone (a No. 2 agglomerate Leclanche) is placed inside the case at the bottom. The lid of this case is sloped so as to form a writing-desk, which lid, together with the front, is hinged, so that it can be let down when it is desired to inspect the battery. The internal connections of the switch-bell of this instrument are shown in Fig. 51, Bell-Blake Telephone. The Crossley Telephone. Fig. 71 shows the Crossley complete instrument, the lid of the case being open, thus showing the interior construction and the switching apparatus. As in the Gower-Bell telephone, the diaphragm consists, it will be seen, of a thin pine board, to the under side of which is fixed the Crossley microphone, described and illustrated on p. 28. The diaphragm is supported off the lid of the case for ^ in. by cork pads, and the sound-waves are directed on to it by a mouthpiece fitted in the front of the lid. On the left-hand side are the terminals of the instrument, and TELEPHONES: THEIR CONSTEUOTION AND FITTING. Fig. 71. Crossley Telephone. COMPLETE INSTRUMENTS. 87 On the right is the ringing key, consisting of a stout brass spring working between a front and back contact. Inside the case on the right-hand side is the switching apparatus, which con- sists of the brass hook H working on a pivot inside the case and kept in the position shown by a steel spring. In this position the back part of the arm H is resting against the bottom contact, and the " speaking " circuit is closed. When, however, the receiver is hung on the hook H, the hook moves down, and the back end of the arm moves up, making connec- tion with the top contact and closing the " ringing " circuit. On the left-hand side of the brass arm H is the ebonite block S, at the top of which is a brass plate, and when the arm is down, as is the ease when the receiver is off the hook, and conversation is being carried on, this plate connects across the two thin German silver springs shown, thus closing the local circuit of the transmitter. When the receiver is hung on the hook the arm moves up, and the springs slide from the brass plate to the ebonite block which opens the local circuit. At the bottom of the inside of the case is the induction coil, and outside, on the front of the case, the cord to the end of which the receiver is attached. The lid is fastened to the body of the case' by screws, and connection is made to the microphone by two flexible wires. The instrument is fixed with its back to the wall by means of the two brass brackets (one of which only is visible), thus leaving the diaphragm in a, jiosition slightly inclined from the horizontaL The Adee Telephone. The Ader complete instrument is shown in Fig. 72. The form shown has a battery switch-bell, microphone transmitter, and a pair of receivers. In general outline it will be seen it somewhat resembles the Gower-Bell instrument, though in the Ader there is only one switch-hook, and the ringing key is usually on the body of the case. The diaphragm is a thin 88 telephones: theie consteuction and fittiwo. pine board, which also forms the lid of the containing case, the lid being slightly inclined from the horizontal position. A separate bell is usually em- Fig. 72. ployed with this instrument, though if desired a circular bell can conveniently be mounted on the under side of the case. Another combination of the Ader telephone is shown in Fig. 73. It is intended for desk use, or for use in other places where a portable in- strument is desirable. The switch-bell is a magneto one, and arranged in a case that will conveniently stand on Ader Telephone. Fig. 73. 1 A"^m 3^%, „.^^M ^^hfTT Hn- ^3^^H n^^ ^^M^S ^^^^gr^ ^^"^^.^^p ^^^9 ka^ gs^m Ader Double Telephone, the table, as shown in Fig, 73. To this the combined receiver COMPLETE INSTRUMENTS. 89 and transmitter (which is of the form shown in Fig. 18) is attached by a long flexible cord. On the left-hand side of the switch bell is the handle of the generator, above which is the automatic switch-hook on which the telephone is hung when not in use. The Johnson TeIxEphonb. The Johnson instrument, complete with Bell receiver, is shown in Fig. 74. Externally this instrument very much resembles the Crossley, but difiers with regard to the microphone and switching apparatus. The microphone (which Kg. 74. was described and illustrated on p. 29) is provided with a shunt, and is fixed underneath a diaphragm of thin pine wood, supported after the manner of that shown in the Crossley in- strument. jgThe automatic hook switch is Haced at the side, and performs the same functions as the other automatic switches just described, though the various parts are somewhat differently arranged. Only one receiver is shown, which is sufficient for all ordinary purposes; but 90 TELEPHONES.: THEIR CONSTBUOTION AND FITTING. two can, of course, be employed with this or any other in- strument, and two are to be preferred if the instrument is fixed in a noisy position. Since the expiration of the microphone patents another form of the Johnson telephone has been introduced, which form is shown in Fig. 75. As it will be seen from the figure, the Fig. 75. Johnson Telephone. external appearance is somewhat difierent, the bell gong being above the body of the instrument and a wider mouthpiece being employed. The ringing button is in the centre of the case, and the switch-hook, on which is hanging an Ader receiver, is on the left. The resistance coil, used as a shunt to the microphone in the former instrument, has been discarded in the one shown above, because in actual practice it has been found to reduce the sensitiveness of the instrument. complete instruments. Special Applications of the Telephone. 91 There are various special uses to which the telephone is put, and in which it proves of great service. In the army it is rapidly finding favour, and there is no doubt that in future Fig. 76. Outlying Picket with Telephone. warfare it is likely to be extensively used. As a ready means of signalling between the camp and outposts it is eminently suited, since by its use the commanding officer in the camp can be placed in direct communication with the outlying picket. 92 telephones: their construction and fittiiTG. For reconnaissances, or when watching the movements of the enemy, it is likely to be of great service, as by its means the advanced or prospecting party can .keep in touch with the main body of the army, and this for the distances of even five or six miles. It has numerous advantages over flag signalling, which is so slow that much valu?,ble time might be lost, and which also is likely to attract the attention of the enemy. Where captive balloons are used to observe the movements of the enemy or survey the surrounding country, it forms an excellent means of communicating results to those below. The form of instrument generally used, and the method of operating it, is shown in Fig. 76. The telephone used is of some such form as shown in Fig. 18, with either two magnetic receivers, or, what is better, a receiver and Hunnings transmitter combined on one handle. The case containing the switch-bell (which is a magneto one) is slung by a strap over the shoulders, the handle of the generator projecting through a hole in the side of the case. Within the case, also, are two dry cells for working the microphone. The cable used is a specially flexible double wire, well insulated and strongly braided. This is best employed in lengths of about 500 yards, or even less, with special clip ends, so that one section can be rapidly connected or disconnected from the other. Thus lengths can be added as the party proceeds, or when necessary to retreat each man can be told ofif to disconnect and roll up his section as it is reached. Ship Telephones. As a means of establishing communication from one portion of a ship to another, the telephone is extensively employed. On men-of-war it forms an excellent method of communicating orders from the captain's quarters (where the oflScers may be assembled directing the attack) and the engine room, turrets, and torpedo room. On the first trials of telephones for this purpose it was found that the instruments required certain Fig. 77. Ship Telephone. 94 telephones: theib construction and fitting. modifications before they would be likely to be a success The firing of the heavy guns, if it did not break the carbon pencils of the microphone, so severely shook them as to render them utterly useless. The sea air also rapidly attacked all exposed and delicate metal work, necessitating very solid and specially treated parts. These difficulties were soon over- come, by using a magnetic transmitter as well as a receiver, making the different parts very soM, and soldering all con- nections. In the merchant service danger of damage to the microphone from firing of guns does not exist, and all we have to provide against is corrosion by the sea air. Kg. 77 shows a form of telephone instrument for use on board ship, the one shown being intended for use on deck. It consists of a circular metal case mounted on a pedestal in order to bring it to a convenient height. Inside this is the battery switch-bell, ringing key, &c., all of which are of an extremely solid character, with large surfaces of contact. The bell movement is entirely cased with metal, and above this beU wiU be seen the two hooks on which hang the receiver and transmitter. The transmitter is of the Berthon or Hunnings type, and is combined on the same handle as the receiver, there being also an additional receiver on the right hand which can be used in rough weather to keep out external noises. The case of the instrument has a tight- fitting lid to prevent wet penetrating in rough weather. Telephones for Mines and Diving Purposes. In mines, also, the telephone proves a great convenience, enabling more definite information to be conveyed than is possible with the ordinary electric bell signals. It can be used in conjunction with existing bell systems or separately by specially arranging the instruments. As the instruments are necessarily subjected to much rough usage, and are, moreover frequently situated in very damp places, they must be con- COMPLETE INSTRUMENTS. 95 Structed with a view to meet these requirements. The whole instrument must be contained in a metal case, and all connections should be made with brass strip, the joints being well soldered. The form of transmitter and receiver used also must be such as are not likely to get out of order by rough handling, or to be in any way affected by damp or gases. An individual to whom the telephone must certainly prove a great boon is the diver, forming as it does an excellent means of readily communicating his wishes to his assistants Fig. 78. Diver's Telephone. above. A small wire being the only connection necessary, the telephone adapts itself readily for diving purposes. A form of instrument designed by the Consolidated Telephone Com- pany for the use of divers is shown in Figs. 78 and 79, Fig. 78 being an external and Fig. 79 an internal view of the 96 TELEPHONES : THEIE CONSTRUCTION AND FITTING. apparatus. The transmitter and receiver are so fixed that the one comes conveniently to the mouth and the other to the ear, being fixed to a cap which the diver puts on his head previous to putting on the helmet. Fig. 79. Diver's Telephone. Telephones for Fire Brigades. Another use to which the telephone has been put with the most encouraging results is that of establishing a means of communicating from one portion of a fire brigade to another, thus allowing the central fire station to keep in touch with the difi'erent brigades who may be away at a fire. The fire stations can in this way be kept duly advised of the progress of the fire, more help can be readily summoned if required, and by being able to state definitely what is wanted much valuable time is saved. Quite recently the Glasgow Fire Brigade have been fitted COMPLETE INSTRUMENTS. 97 throughout with telephones, the ordinary fire alarm circuits being utilised Each brigade when it turns out carries on the engine a portable telephone, which on arrival at the fire is immediately plugged on to the fire-alarm box nearest to the scene of operations. Thus should a second alarm arrive at any of the fire-stations, intimation can at once be sent to the brigade at the first fire, from whence men could, if necessary, be sent direct to the second fire. Moreover, in case of need, these portable telephones can be tapped by the firemen on to any of the overhead wires that may be near for the purpose of communicating with the central exchange or private individuals. Long-distance Telephony. The distance to which the telephonic transmission of speech can be carried is rapidly increasing, and talking is now success- fully carried on between places that a few years ago were deemed much too far apart. Paris and Brussels have for some time been in communication, while in this country London and Brighton, London and Manchester, London and Birmingham, and numerous other towns are connected. One of the most recent and satisfactory long-distance lines is that between London and Paris, of which a short description is appended. The London and Paris Telephone Line. The route of the. wires from London to Paris is rid St. Margaret's Bay and Sangatte, the total distance being 311 miles, and the resistance 693 ohms. A complete metallic circuit is used, the wire passing from London to St. Margaret's overhead on poles, then across the channel by a special sub- marine cable to Sangatte, and from there to Paris by another length of overhead wires. H 98 TELEPHONES : THEIE CONSTBUCTION AND FITTING. The lengths and resistances of the different sections of the circuit are as follows : — Length. Kesistance. London to St. Margaret's Bay .. .. 84-5milea 183 ohms St. Margaret's Bay to Sangatte ..23 „ 143 „ Sangatte to Paris 199 „ 294 „ Paris 4-8 „ 70 „ 311-3 „ 693 „ On the completion of the line a trial was made with the Ader, Berliner, D'Arsonval, De Jongh, Gower-Bell, Eoulez, and Hunnings' transmitters in conjunction with double-pole Bell receivers, with a view to ascertain which was the most suitable instrument, those finally selected being the Gower- Bell (without hearing tubes) for the London, and the Eoulez for the Paris end. The Eoulez microphone is a modification of the Hunnings with broken incandescent lamp carbon fila- ments instead of the granules. The charge for the use of the London and Paris Une is 8s. for three minutes' conversation, and the average number of times it is used per day is about 86, the maximum being 108. At a special trial to test the capabilities of the combination, 150 words per minute were transmitted, being dictated in Paris and transcribed in London by shorthand. Paris being in communication with Brussels, speaking between London and Brussels was tried with satisfactory results, and also between London and Marseilles, a distance of over 900 miles. According to experiments made with the London and Paris line, long-distance speaking appears to be more a question of the circuit and its environs than the kind of transmitting or receiving apparatus used. CHAPTEE V. THE MAGNETO GENERATOR AND BELL, BATTERY BELLS, AND RELAYS. The apparatus required for signalling by magneto bells con- sists of two parts — the generator and the bell. In Fig. 80 is shown the most usual form of the magneto-generator divested of its outer wooden case. When the handle seen to the right of the generator is turned, it drives the armature by means of Fig. 80. Generator. cog gearing, causing it to rotate rapidly between the poles of the three permanent horseshoe magnets. The principle on which the generator acts is the same as that on which is based the action of all dynamos, and, in fact the generator finds in the dynamo almost its exact counterparts. The theory of the action of the magneto generator and bell will be best under- stood by referring to Fig. 81, where both the generator and the bell are shown diagrammatically. H 2 100 telephones: theie constetjction and fitting. In the figure the generator is on the right, and the bell on the left. The armature of the generator consists of an iron shuttle a, wound with fine silk-covered copper wire, which is caused to rotate rapidly between the soft iron polar extensions Fig. 81. cfhoiih jr F ■j"^ S IT Magneto Generator and BeU. ^^ of the permanent magnet 6. Faraday discovered that hy moving a wire or other conductor near the pole of a magnet in such a manner as to cut lines of force, a current of electricity is generated in that wire. Hence if the circuit of the armature coil is closed and the armature rotated, a rapidly alternating current is generated which flows by means of the two wires to the bell. This bell consists of an electro-magnet c d having before its poles the soft iron armature /, pivoted in the centre, from which centre springs the hammer h. Adjoining the electro-magnet is the permanent magnet e, so arranged that its south pole s' comes in close proximity to the armature /, and its lower or north pole W near to the yoke of the electro- magnet. The effect of this is, that the south pole of the per- manent magnet magnetises by induction the soft iron armature /, causing it to exhibit south polarity at its ends. The north pole of the permanent magnet similarly magnetises the iron THE MAGNETO 6ENEEAT0E, 101 cores of the electro-magnet, the poles of which thus exhibit north polarity. When, therefore, no current is flowing round the electro-magnet, both ends of the armature are attracted alike, and the hammer will remain against either gong if once placed there. If now a current from the generator flows round the electro-magnet in such a direction that the left-hand pole becomes north and the right-hand south, the north pole powerfully attracts one end of the armature and the south pole repels the other, throwing the armature over and causing the hammer h to strike the gong g. When at the half revolu- tion of the generator armature, the direction of the current is reversed, the right-hand pole becomes north and the left-hand south, throwing the armature over to the other side and causing the hammer to strike the gong ^. As the armature of the generator is rotated very quickly, the reversals of the current are very rapid, and the ringing becomes similar to that of the ordinary electric bell. In Fig. 82 is shown the wound armature of the generator, c and d being the bearings of the iron shuttle a on which is wound Kg. 82. Armature of Generator. the silk-covered wire 6. One end of this coil is fastened direct to the iron frame of the shuttle while the other is attached to the pin /, which is insulated from and passes through the inside of the bearing c, after the manner showi^ in Fig. 87. The pin / terminates on the point e, against which presses the spring G, see Fig. 52. One connection from the generator is taken from the frame, and the other from the spring G-. Fig. 83 shows the frg.TOework of the generator, m being one of the permanent 102 telephones: their constedction and fitting. F^. 83. magnets, and n n the two pole-pieces between which the armature revolves. The pole pieces are fixed together and kept at the proper distance from one another by the brass rods b and b', and the magnets are fastened to the pole-pieces by the clamping pieces and screws c c. The armature of the generator being wound with very fine wire, has necessarily a high resistance ; and since both the generator and ■beU are arranged in the same circuit it will be seen that the current from the generator at station No. 1 must, in passing through the bell at station No. 2, pass also through the armature of the generator No. 2, and if many stations are in the series the combined resistance of the gene- rator armatures becomes con- Magnete of Generator. siderable. Again, in the case of two stations a long distance apart, and an " earth " being used at each end, should a leak to earth occur anywhere along the line between the two stations, the resistance of the generator armature at station No. 2 would cause more current of the generator No. 1 to get to earth by the fault, than would other- wise take place if there was merely the resistance of the bell. Moreover when there are many generators and beUs in the series, should any disconnection occur in the armature of one generator, if an armature shunt is provided to the generators, the fault merely incapacitates that one generator from ringing, instead of causing a breakdown in the entire circuit, as would be the case were no armature shunts provided. In order, therefore, to do away with these disadvantages an "armature shunt" or "automatic cut-out" is provided, THE MAGNETO GENERATOE. 103 which when the armature is at rest, bridges across the high- resistance armature coil by a low-resistance circuit. If the generator is merely required for working a call-bell in buildings, &c., or for use on only short circuits, an armature shunt will be to a great extent superfluous ; but if for use on long circuits, or where there are many generators and bells in series, it will be found advantageous to employ one for the reasons stated above. Various forms of armature shunts or automatic cut-outs have from time to time been devised, some of which are fitted to the driving gear, while others are contained in the armature itself. The simplest method of shunting the armature of the generator when not in use is by an ordinary electric bell switch fixed on the wooden base or case of the generator ; but as the efficiency of this depends entirely on the memory of the operator, it is not to be compared with any of the automatic forms. In Figs. 84, 85, 87 are shown three forms of armature shunts, the forms shown in Figs. 84 and 85 being those most generally employed. Fig. 84. Armature Stunt. In the form shown in Fig. 84 the dri-ving wheel h fits nicely, but runs loose on the spindle d, which works in the two bearings e and/. In the right-hand side of the hub m of the 104 telephones: theie consteuction and fitting. wheel h is cut a V-shaped notch, in which works the pin n fixed to the spindle d. On the part of the spindle between the two bearings e and / is fixed the collar r, against which presses the spiral spring g in such a manner as to always keep the pin n (when the spindle is at rest) in the centre of the V-shaped notch. Against the end of the spindle d presses the stiff brass spring c, insulated from the framework by an ebonite block. The action of the shunt is as follows : — In its normal Fig. 85. Fig. 86. 1 Armature Shunt. position, the spring g pressing against the collar r forces the pin n into the V-shaped notch and causes the end of the spindle to make contact with the spring c. In this position, which is the one in which it is shown in the figure, it forms a low resistance shunt across the coil of the generator armature (see Fig. 52). When now an attempt is made to turn the handle t of the generator (the wheel h refusing to move until a certain pressure is put on) the pin n rides up in the V-shaped notch, drawing the spindle d, away from the spring c, against the pressure of the spring g. This breaks the shunt circuit, throwing the current of the generator to "line," the shunt being completed again as soon as the handle is released. THE MAGNETO 6ENEBAT0E. 105 In the fonn of armature shunt illustrated in Figs. 85 and 86, h is the cogged driving wheel, and n the 'spindle on which it runs, / the handle of the generator, and g the side of the wood case in which it is contained. This side is bushed with a brass bush in which the handle turns, and to this bush is connected one wire of the armature shunt, the other being connected to the frame of the generator. In a slot a of the wheel h projects the pin c, which is kept in the position shown in Fig. 85 by the spiral spring t fixed at one end to the pin c, and at the other to the ebonite block m fastened to the wheel h. The shunt works as follows : — In its normal position (which is that shown in Fig. 85) the pin c makes contact with the wheel A, and a low resistance shunt circuit is formed, but when the handle is turned the pin c moves forward and presses against the ebonite block h fixed in the groove a, thus opening the shunt circuit. When the handle is released the spiral spring t draws the pin c back against the uninsulated end of the groove a. The form of armature shunt shown in Fig. 87 (which is that employed in the Post magneto generator) is fitted on the Fig. 87. Armature Shuntj armature itself, and works by the action of centrifugal force on the bob d. In the illustration the armature, small cog wheel, and spindle only are shown, being part in section and part in elevation. The bob d is fixed to the end of the thin spring c, and in its 'normal position presses against the platinum-tipped pin / which is insulated from the armature, 106 telephones: theib constkuctipk and fitting. and in connection with the stud 6 «dso insulated, h represents the armature coil, one end ol which is fastened to the pin / and the other connected to the iron of the armature by the screw on the left. When at rest the bob d and the spring c form a low-resistance shunt across the armature coil J ; but when the armature is rapidly rotated, the bob flies out and breaks the shunt circuit, the bob being prevented from flying out too far by the stop h. There are three methods now employed of communicating the power from the big driving wheel to the small one on the armature : 1st cog-, 2nd friction-, and 3rd belt-gearing. Cog- gearing is the form most generally used, though friction- gearing has the advantage of silent and smooth running. Belt-gearing is now but rarely employed, on account of its not being diu'able enough. Fig. 88. Magneto Bell. Fig. 88 is a side elevation of the magneto bell with its wooden case removed, a, a are the two bobbins of the electro- magnet, the iron cores of which are riveted to the top bar n. THE MAGNETO BELL, 107 also of iron. This top bar n is fastened to the two hrass upright rods by nuts, the bottom brass bar m being also similarly fastened to the rods. This bottom bar carries the armature 6, from the centre of which springs the hammer d which works between the gongs e and /. c is the permanent magnet attached to the bottom bar m by the screw s. The ad- justment of the bell is effected by the screws g, by means o which the armature can be made to approach or recede from the poles of the electro-magnet. The gongs e and / are also adr instable towards or away from the hammer d. The first forms of the magneto bell were similar to thB Siemens polarised relay, the armature feeing a permanent magnet, and working between- two electro-magnets. It had many faults, however, the chief Mg. 89. Magneto Bell. of which were its sluggish action and the liability of the armature to lose its magnetism. The great improvement of the modern magneto bell over the old form consists in the substitution for the polarised steel armature of a soft iron one inductively magnetised by a permanent magnet placed in close proximity to it. Fig. 89 shows the magneto bell com- plete in polished wood case. 108 telephones: theib consteuotion and fitting. Fig. 90. Battery Bells. We will now pass on to a short description * of the various forms of battery or ordinary electric bells in use. Fig. 90 shows the external appearance of the ordinary islectric bell, and this is the form generally employed whether its movement be a vibrating, single- stroke, or short circuit one. There are five different kinds of move- ments that may be employed : 1st vibrating; 2nd single stroke; 3rd continuous ringing; 4th short cir- cuiting; and 5th differentially wound, these last two being best suited for working in series. The Vibrating Bell. In Fig. 91 is shown (with cover removed) the vibrating electric bell, which is the form in most general use. It is probably too well known to need much description, but con- _ ,^ „ „ sists of an electro-magnet fastened Battery Bell. , . , , - , . to an iron frame, which is screwed to a wooden back-board that forms the base of the bell. In front of the poles of the electro-magnet is a soft iron armature, one end of which is fitted with a hammer and the other fixed to the iron frame by a thin steel spring, the lower end of which carries a platinum contact. Fixed to the iron frame, but insulated therefrom, is a contact post fitted with a contact screw, the platinum pointed end of which comes opposite the end of the contact spring. The current entering at the terminal L passes through the coils of the electro- magnet to the iron frame and contact spring, contact screw, * For a detailed description see 'Practical Electric Bell Fitting.' BATTEKY BELLS. 109 Fig. 91. contact post, and thence to terminal Z. This causes the electro-magnet to attract the armature, bringing with it the hammer, which is impelled against the gong, and at the same time the contact spring is pulled away from the contact screw, thus breaking the circuit. As the cores of the electro-magnet are of soft iron, all magnetism now ceases, and the armature, impelled by the "spring, moves back into its former position, only to repeat the pre- vious operation so long as the cir- cuit is closed. To adjust a vibrating bell, first make sure all the connections are tight; then (holding the hammer against the gong) screw up the ad- justing screw till its point is just clear of the platinum contact on the spring. Then let go the hammer and see if the spring draws it back properly. See also that the arma- ^ ^^ ™^ ture when attracted does not touch the poles, or there will be a disagreeable tapping noise while ringing. The strength of the sound can be varied by means of the adjusting screw, since the further it is screwed back the less will be the force with which it reaches the gong. Sometimes a bell rings badly from the spring either setting the armature back too strongly, or from being so weak that it does not bring it back with sufficient rapidity. To find out which is the cause, take a piece of watch-spring, and whilst the bell is ringing, press the armature towards the poles; then if the ringing is im- proved the spring is too strong, and must be taken off and set a little inwards. If, on the contrary, the ringing improves when the armature is pressed away from the poles, the spring is too weak, and must be set a little outwards. Fig. 92. 110 telephones: theie constedction and pitting. The Single-stroke Bell. The single-stroke bell is shown in Fig. 92. It represents the electric bell in its simplest form, and has no contact breaker. The current entering at the terminal L passes through the magnet coUs to the terminal Z, so that when the circuit is closed the armature is attracted up to the poles, and remains there so long as the ringing key is kept pressed in. A stroke of the bell is thus obtained each time the ringing key is de- pressed, so that for signalling to a pre-arranged code the single-stroke bell is well adapted. To adjust a single-stroke bell so that a clear sound is obtained, push the armature up to the brass studs in the ends of the poles and bend the rod till the hammer is just clear of the gong. Then let go the hammer and adjust the stop-screw till the loudest stroke is obtained. The hammer should not touch the gong before the armature reaches the stops, or a harsh sound will be the re- sult, owing to the hammer stopping the vibrations of the gong. Single-stroke Bell. The Continuous-ringing Bell. The continuous-ringing bell is shown in Fig. 93, and when once started, continues to ring until stopped, which is generally done by pulling a cord at the side. The movement, it will be noticed, is similar to that of the vibrating bell (Fig. 91), with the addition of a lever and the extra contact post d. This lever is pivoted in the centre and supported at one end BATTERY BELLS. Ill Fig. 93... by the catch on the lower end of the armature. When the armature is attracted the lever slips off the catch, and, im- pelled by the spiral spring, makes contact with the contact post d. The lever is reset by pulling the cord at the side. The action of the bell, is as follows : — The current entering, let us say, by the terminal 0, passes through the magnet coils to the screw a, armature, contact spring, contact post, and thence to terminal L. This starts the bell, at the first stroke of which the lever is released and makes contact with the contact post d, the circuit now being from terminal C, to magnet coils, screw a, spring, contact' post J, lever c, contact post d, and thence to ter- minal Z. The bell ceases to ring when the cord at the side is pulled, ^hich resets the lever. In adjusting a continuous-ringing bell, the movement is first adjusted as was described (p. 109) for the vibrating bell. The lever c is then released and the tension of the spiral spring adjusted so that only such pressure is put on the lever as is suflBcient for good contact. The more the tension, the greater the pressure on the lever, and more battery power is thus required to release it. Coutinuous-ringing Bell. The Short-circuit Bell. It is very often necessary to place two or more bells in series on one circuit. This, if the bells are single-stroke, presents no difficulty, but on attempting to do this with the ordinary 112 TELEPHONES: THEIE CONSTKUCTION AND FITTING. Pig. 94. vibrating bell, the ringing becomes at the best very indifferent and spasmodic, arising from the fact that as the -bells are not exactly similar, they do not make and break the circuit in unison. One way of getting over this difficulty is to have one of the bells a vibrating and the rest single-stroke, the vibrating bell governing the vibrations of the single-stroke; but even when arranged thus, unless the bells are very much aUke, the ringing is rarely satisfactory. For bells in series, therefore, the best plan is to use those with movements either short-circuiting or else differentially wound. The shortcireuiting form of electric bell is shown in Fig. 94, and, as will be seen from the figure, governs its vibrations not by break- ing the circuit, but by shunting its coils. The current entering, let us suppose, at the terminal L, passes to the contact post b, from there through the magnet coils to the screw a, and from thence to terminal Z. This attracts the arma- ture, causing the spring on its .lower end to make contact with the contact post 5. There now exists a path across the magnet coils of practically no resistance ; the current, there- fore, is diverted from the magnet coils, and passes by the armature and contact post 6 to the next bell. Thus, no matter how many bells there may be in the series, the circuit is never broken. Short-circuit Bell. BATTEET BELLS. 113 Fig. 95. The Diffbkentially-wound Bell. Another form that works well in series is that known as the differentially-wound bell, a form of which is shown in Fig. 95. As regards its arrangement of parts, it is similar to the short- circuit form just described, but differs from it in respect to its mag- nets, which are wound with two coils, the one, c, in an opposite direction to the other, d. On the current entering at the terminal L the action of the bell is as fol- lows : — Starting from terminal L, it passes through the coil d to the screw a, and thence to terminal Z. The circuit of coil c being open, the iron cores are magnetised by the current in the coil d ; thus the armature is attracted, and makes contact with the contact post b. This closes the circuit through the coil c, which neutralises the mag- netism imparted by the coil d, and the armature falls back against the stop, only to repeat its previous operation. Besides being admirably adapted for series work- ing, this form is almost sparkless at its c6ntact, a matter of great importance in some cases. Speaking of this method of winding, Professor Sylvanus Thompson, in his excellent lectures on " The Electro-magnet," delivered recently before the Society of Arts, says : — " When equal currents flow in both circuits there is no magnetism. If you break the circuit of either of the two coils the core at once becomes magnetised. You get magnetism on breaking, you destroy magnetism on making, the circuit; it is just the I Differentially-wound Bell. 114 telephones: their consteuotion and fitting. inverse case to that of the ordinary electro-magnet. There the spark occurs when magnetism disappears ; but here, since the magnetism disappears when you make the circuit, you do not get any spark at make, because the circuit is abeady made. You do not get any at break, because at break there is no magnetism." CiRCULAK Bells. Bells with the movement contained within the gong are very suitable for mounting on telephone sets. The form most Fig. 96. Circular Bell. usually employed is shown in Figs. 96 and 97, Fig. 96 being a side view of the complete bell, while Fig. 97 is a plan with the upper part of the gong re- Fig. 97. moved. The movement can of course be vibrating, single-stroke, or short-circuiting, as desired, that shown in the figure being a vibrating one. The hammer, it will be seen, strikes on a lug oast on the gong, while the gong is supported on a projecting arm of the iron frame. In the figure the bell is shown mounted on a special wooden base, as is the case when the bell is used sepa- rate, but if for a telephone set, it is mounted directly on the wooden base-board. Circular Bell. RELAYS. 115 Fig. 98 shows another form of the circular bell, known as the " Shield," from the shape of its iron base. Fig. 99 shows Fig. 98. Fig.. 100. Circular Bell. the bell complete, while Fig. 99 is a plan with the gong re- moved. Only one bobbin is employed, and the hammer strikes, as is the case with the previously described form, on a lug on the inside of the gong. Another form of bell with the movement inside the gong is shown in Fig. 100. The gong is of the church-bell shape, by employing which shape it has been found the most agreeable tone is obtained. Eelays. Relays will often be necessary on loDg circuits where, from the ^^churoh-shape Bell, resistance of the line, the current has not strength enough to ring the bell, but ' quite sufficient to attract the delicately poised armature of a relay. The I 2 116 telephones: their consteuction and fitting. duty of a relay is to dose a local circuit when actuated by a current ciixulating through its coils. Formerly, when battery switch-bells were so much used, the relay was very frequently called into requisition, but with the change to magneto switch-bells they will not be so much required, owing to the ability of the magneto to ring through a high resistance. A form of the single-ciurent relay is shown in Mg. 101. It consists of an iron frame, similar to that used for the electric bell movements previously Fig. 101. Relay. described. Above the electro- magnet is fitted the armature, kept off the magnet poles by the spiral spring seen to the left, the tension of which can be adjusted by the milled nuts. The distance the armature moves back from the magnet poles can be regulated by means of the top set-screw. The magnet coils of the relay ai-e connected in the " main " or " line ' circuit, and one end of the local circuit is connected to the bottom contact post, while the other is connected to the frame of the relay. Thus when a current circulates in the main circuit, the armature of the relay is attracted, closing the local circuit. Much of the satisfactory working of a relay depends upon its proper adjustment, and the following is the right way to set about adjusting a relay :— First screw up the contact screw, so that when the contact spring makes firm contact with it there is just room to slip a piece of writing paper between the armature and poles of the electro-magnet. Then adjust the stop screw so that the contact spring only fairly leaves the contact screw. The tension of the armature spring should only be such as will just bring the armature back against the BATTEBY BELLS. 117 stop screw. A relay should be adjusted according to the pur- pose for which it is required. If for sensitiveness, as would be necessaify on long lines, it should be adjusted as described, but if for use with an indicator, a little more movement for the armature may be allowed. 118 TELEPHONES: THEIE CONSTRUCTION AND FITTING. CHAPTEE VI SWITCHES AND SWITCH-BOAKDS. Amongst the various auxiliary apparatus used in telephony, switches must certainly be placed in the foremost rank. Hardly a single instrument, whether private or exchange, can be erected without employing some form of switch, either automatic or worked by hand, and in the "switch-room" of an exchange system they may be reckoned up by thousands. They may be divided into two classes : 1st, those employed in the switch-room of an exchange, and 2nd, those used by the subscribers themselves, with which latter we shall confine ourselves in this chapter. Switches of the first class may be either the ordinary electric bell switch as shown in Fig. 102, or the telephone pattern as in Fig. 103. The form shown in Fig. 102 is the simplest form of switch, and is either one, two, three, or four-way, &c., accord- ing to the number of directions in which the current can be diverted. The other form of switch is the one most used in telephony. Two-way Switch. ^^^ consists of a wood base, the underneath side of which is hollowed out and contains the working parts. On the front are the terminals and the lever arm, by moving which from side to side the connections are changed. In some switches the terminals also are beneath Fig. 102. SWITCHES AND SWITCH-BOARDS. 119 the base ; but this form is very inconvenient, the whole switch having to be taken down should it be desired to alter the connections. The purposes to which these switches are applied are for connecting two or more instruments to the same line, or connecting an extra, or extension, bell, as it is called, to ring at some distance from the instrument, as the exigencies of the case demand. In an exchange system they are also employed to prevent subscribers making an illicit use of lines or instruments, as might be done in certain cases. These switches are designated by the number of terminals Fig. 103. Three-point Switch. or points, and the simplest form is the three-point shown in Fig. 103. It is used either for connecting one line to two different instruments, or for putting in an extension bell. For instance, take the case of an office in which there is a tele- phone in connection with the stores half a mile off, in which the telephone there is in a room on the ground floor, and the person who usually attends to the telephone calls is often at a distant part of the building. Then an extension bell would be placed in the distant part of the building, and a three-point switch fixed near the telephone below, and the attendant would before leaving the room switch on the extension bell, so that all signals would be communicated to him by the bell. 120 telephones: theib construction and fitting. Figs. 103 A and B are a key to the switch, showing which terminals are connected together when the handle of the switch is in the two different positions. When the handle is to the right-hand side, terminals 1 and 2 are connected together, but when to the left 2 and 3. Fig. 104 shows the circular pattern four-point switch. When the handle is to the right-hand side, terminals 1 and 2 Fig. 104. Fig. 105. Fig. 106. Four-point Switches. are connected together (see Fig. 182), and also terminals 3 and B. If the handle is moved to the right, terminals 1 and 3 are connected together, and also 2 and B. Fig. 105 shows the four-point switch from the back, showing the interior arrangement. SWITCHES AND SWITCH-BOAEUS. 121 Another form of the four-point switch is shown in Fig. 106, this being known as the square pattern. The switch is worked by moving the handle from one side to the other, the connections to the terminals being shown by the dotted lines. The connections in the form of switch shown in Fig. 104 are somewhat different to those in Fig. 105, but either switch can be connected to effect the' same object. The method of employing this switch is shown in Fig. 182. The six-point switch is shown in Fig. 107, with the key diagrams A, B, and C. When the handle of the switch is to the left, terminal 1 is in connection with terminal 3, terminal 2 with terminal i, and terminal 5 with 6. If the handle is put in the centre, as in B, terminal 1 is connected to terminal 2, and terminal 5 to 6. When the handle of the switch is put to the right, terminal 1 is connected to 2, 3 to. 6, and i to 5. Fig. 107. Six-point Switch. The square pattern six-point switch is shown in Figs. 108 and 109, Fig. 109 showing the connections. As with the circular pattern it has three positions in the centre, one of which is shown in Fig. 109. Another form of switch is shown in Figs. 110 and 111. These are known as plug switches, and form one of the cheapest and best means of' connecting up telephone instru- ments to meet special requirements, owing to the number 122 telephones: their construction and fitting. of different forms in which it can be made. The form shown in Fig. 110 is the simplest form, and often called an "interrupter," since it can only be used for making and Pig. 108. Fig. 109. ExTK. Bell Exxk. Bell. Line No. 2. Eabth. ■ "".■ll,:i:|:ili.iiNi||««lll ■;:. "li; .illll: Fig. 110. dj Cb -:0 > 1/ / ^' .'0 Q i-LZ] m Q Six-point Switch. Fig. 111. Plug Switches. breaking the circuit, and not for giving it a different direction. When the plug is inserted between the two blocks as in the figure, the circuit is closed, but on withdrawing it the circuit is opened. SWITCHES AND SWITCH-BOARDS. 123 The form shown in Fig. Ill is a three-block one, with a hole between each block, thus enabling any two of the blocks to be connected together. This form is very convenient for use vrith three telephone stations, as by inserting the plug in the proper hole any one telephone can be put into communi- cation with either of the remaining two. Fig. 112 (a front elevation) shows a small switch-board suitable for four stations, one of which is used as the 3-drop Annunciator. central station or switch-room. Fig. 113 is a view from the back, showing the connections. The switch-board consists of the three annunciator drops, 1, 2, and 3, contained in a polished mahogany case, a. At the bottom of the case are three brass springs, s\ s^ s^, the lower ends of which press firmly against the brass plate h. The annunciator drops are of a similar construction to those shown in Figs. 127 and 128 'Practical Electric Bell Fitting'*; the connections from the • Published by E. and F. N. Spon. 124 telephones: theib construction and fitting. coils pass through the back of the containing case by means of the two rods supporting each drop, and are marked respec- tively B}, R2^ E3 The connections to the terminals at the top of the case are shown by the dotted lines in Fig. 113. The method of operating the switch-board is as follows : — Supposing the switch-board to be situated at station No. 4, and station No. 2 wishes to speak with No. 3 ; then when the person at station No. 2 presses the ringing key of his instru- ment, the current enters the switch-board at terminal No. 2, passes through the annunciator No. 2, thence to spring s^, to Fig. 113. S-drop Annunciator. plate h, terminal E, and " earth." This causes the coUs of No. 2 annunciator to attract its armature, thus releasing the shutter and disclosing the number, as in Fig. 112. The person at No. 4 station hearing the bell ring (which is done by the shutter of the annunciator falling on to a contact and closing the local circuit of the bell), looks at the annunciator board, and sees that No. 2 station is ringing. He then takes what is called a "plug "(Figs. 114 and 115, Fig. 115 being a side SWITCHES AND SWITOH-BOAEDS. 125 view of Fig. 114), which consists of a brass piece 6, the bottom part being insulated, as shown, by the ebonite face a, and presses it under the spring 8\ the point of the plug pass- ing between the spring and the plate b, thus insulating the spring from earth, and putting it into connection with the Fig. 114. Fig. 115. Connecting Plug. telephone at No. 4 station by means of a flexible wire, one end of which is connected to the plug and the other to the telephone. The person at No. 4 station can then carry on conversation with the person at No. 2 station. No. 2 station now informs No. 4 that he wishes to be put into communica- tion with No. 3. The person at No. 4 station then takes two plugs, which are connected together by a short length of flexible wire, and, pulling out Ms own plug, slips one plug under No. 2, and the other under No. 3, spring, thus putting No. 2 station in connection with No. 3. If No. 2 station presses his ringing key now, he rings the bell at No. 3 station, and conversation can be carried on. By means of what is called a " knife plug " (which is like the plug shown in Figs. 114 and 115, but without the ebonite piece a) the person at station No. 4 can, by sliding this knife plug on top of the ordinary plug, ring or converse with either station No. 2 or No. 3 without breaking the connection between them. In a similar manner No. 2 station is put into communication with 126 TELEPHONES: THEIR CONSTEtJOTION AND FITTING. No. 1, or No. 1 -ivith No. 3. In an exchange worked on this system, which is called the "slipper-board system," every subscriber has an annunciator drop in the switch-board of the exchange, and is connected to any other by the attendant by means of the plugs. The outside connections for the switch- board are not shown in the Figs. 97 and 98, as these will be shown later on amongst the diagrams. Fig. 116. 4-drop AnnuDciator. Fig. 116 is a perspective view of a 4-drop annunciator board, similar to that just described. At the foot of the board are the plugs with which the connection between the different Unes is made. In this form of annunciator board it will be seen the plugs are circular in form. ( 127 ) CHAPTER VII. BATTERIES. The form of battery used in telephony is almost exclusively the Leclanche, and preferably the agglomerate block form. In exchange work a Gravity Daniell is often employed in con- nection with a pole changer at the switch-room in preference to a magneto generator. Before the introduction of the mag- neto switch-bell, a large number of batteries were necessary in an exchange system, there being generally four Leclanche cells at each subscriber's instrument, and a battery of ten or twelve gravity cells at the exchange. With the general adoption, however, of the magneto switch-bell, the ringing batteries were done away with at the subscribers' instruments, one cell only being retained for the transmitter. At the exchange, either the batteries were retained and a pole-changer employed for sending alternating currents, or else a small magneto gene- rator is employed, which is run continuously by a small water or gas motor. In private line work, the No. 2 size is the one generally employed, the number of cells at each end depending on the distance between the two stations. Except for short lines, it is better and cheaper to employ magneto switch-bells for ringing, one Leclanch^ cell being used for the transmitter. In the case where the transmitter and receiver are both of the magnetic type, the magneto bell for signalling only is required. The reason that the agglomerate block form is to be pre- - ferred for telephones, is because this kind has a lower resistance than the porous pot form. This is not, as a rule, of so much 128 telephones: their consteuction and fitting. importance on the ringing circuit as for the local circuit of the transmitter, since the ringing circuit itself has generally a high resistance, while the local circuit through the microphone is very low, and therefore it is important that the battery has also a low resistance. There are two kinds of the Leclanche cell, the " porous pot" and the " agglomerate block " form. The "porous pot" form is shown complete in Fig. 117, and •consists of a glass jar (Fig. 120) in which is contained the Fig. 117. Fig. 118. Porous Pot form Leclanche. amalgamated 2dnc rod forming the positive element. The negative element (which is shown in Fig. 118, and also in section in Fig. 119) consists of a carbon plate c, placed inside a porous pot^, and surrounded with a tightly packed mixture of carbon and peroxide of manganese, the top of the pot being run in with melted pitch. The Leclanche is a single-fluid cell the porous pot serving not to keep two fluids separate, but BATTERIES. 129 merely to contain the broken carbon and manganese, a,nd keep it in intimate contact with the carbon-plate. The exciting fluid is a solution of sal-ammoniac Fig. 120. Glass Cell. Porous Pot. This solution has no chemical effect, either on the zinc (pro- vided, it is pure) or the peroxide of manganese, so long as the circuit is broken and the cell not at work. On the circuit being completed a current flows from the carbon to the zinc .pole, the action in the cell being as follows : — The solution of chloride of ammonia (sal-ammoniac) is decomposed ; the chlo- rine, attacking the zinc, forms chloride of zinc, which is soluble in the surrounding Uquid ; while the ammonia, developing at the surface of the carbon, forms a soluble compound with the oxygen which it extracts from the manganese. While the cell is at work, then the zinc is consumed and chloride of zinc accumulates in the solution, the carbon remaining unaltered, and the peroxide of manganese loses some of , its oxygen. After a time, however, the supply of oxygen gets reduced and hydrogen accumulates on the surface of the carbon-plate, producing polarisation. If the circuit is broken, however, and 130 telephones: theie consteuction and fitting. ■the cell left to rest for a time, it will depolarise : the peroxide of manganese absorbing oxygen from the air. The terminal t is fixed to the carbon-plate by means of the lead cap n, which is cast on to the plate. Great care is necessary in fixing this lead cap to the carbon-plate, as if improperly done, the salts creep up and rapidly eat away the connection. Before the lead cap is iixed the carbon-plate is Fig. 121. Fig. 122. Agglomerate-block Form LeclancM. soaked for an hour or so in melted paraffin wax, at a tempera* ture of 110° C, to prevent the salts creeping. The " agglomerate block " form is shown complete in Fig. 121. In this form of the Leclanche cell a porous pot is not used, the depolarising mixture being applied to both sides of the carbon-plate in the form of a block. The materials used in the construction of these blocks are similar to those contained BATTEEIES. 131 Fig. 123. in the porous pot, with the addition of from 5 to 10 per cent, of some cementing compound, such as resin. In Fig. 122 are shown the carbon-plate, agglomerate blocks, and zinc rod removed from the glass cell, and in Fig. 123 the agglomerate block only ; a being a view of the block in a position at right angles to that of 6. In fitting up a cell of this form an agglomerate block a a (Fig. 122) is placed each side of the carbon-plate c, and two of the indiarubber bands 5 6 slipped over them. These bands have a,t d a, solid part, through which a hole has been stamped to receive the zinc rod. The zinc is thus kept fyom touching the nega- tive element, and both elements can (by Agglomerate Block, lifting at the positive terminal) be lifted bodily out of the glass jar. The following are the chief advantages claimed for the agglomerate block over the porous pot form : — That a better use is made of the depolarising power of the manganese, as its reduction is more complete, and that in consequence of the readier reduction of the manganese the carbon-plate is more rapidly depolarised, and consequently the E.M.F. is more sustained. That its resistance is extremely constant, whatever the electro chemical work done by the cell. That the battery is ready for use immediately on charging. That the renewal of an exhausted cell is exceedingly simple, new depolarising plates having only to be substituted for the exhausted ones. Their chief virtue is of course their low iniernal resistance, which makes them very suitable for a microphone cell, though in the author's opinion they are not equal to the porous pot form for ringing batteries where a low internal resistance is of no advantage. They are exceedingly dirty to handle, and subjected to an injurious local action, owing to impurities K-2 132 T-BLEPHONES: THEIE CONSTEUCTION AND FITTING. detached from the blocks settling on the tops of the rubber bands. A creeping of the salts up the inside and over the outside of the glass jar is a fault to -which the Leclanche cell is par- ticularly liable. This can, however, be somewhat prevented by rubbing the neck of the jar with grease, or by dipping it for an inch or so in melted paraffin wax. The strength of the solution has also some effect on the creeping. A good way to paraffin the top of the glass cells is to melt the wax in some vessel, the mouth of which is wide enough to admit of a ceU being inserted. A piece of glass tube, bent to the shape of the letter U, is placed inside the vessel that con- tains the wax, both ends of the tube being above the surface of the wax. The glass cells, having been previously warmed, are then dipped (mouth downwards) into the melted wax, one end of the glass tube passing inside the cell, and the other remaining outside exposed to the, air. This allows the wax inside the cell to rise at once to the level of that outside, instead of (if there was no tube) being prevented from entering by the pressure of the air. With a view also to prevent this creeping, the cells are sometimes sealed, i. e. the top is filled in with pitch, a hole being left for charging. The use of sealed cells, however, is not economical, as when exhausted they cannot well be recharged. The Leclanche cell is made in three sizes : No. 1, or three- pint ; No. 2, or quart ; No. 3, or pint, according to the amount of solution the glass cell will hold. Position of the Battery. The position of the battery is a matter of some importance as in warm or moist situations the creeping of the salts is greatly hastened. It should be placed, where possible on the floor, in a box, under the telephone instrument ; but if this is BATTEEIES. 133 olDjected to, it should be placed on a shelf in a cupboard or cellar, selecting as cool a place as possible. Setting up the Battery. In setting up a battery fill up the outer jar three-quarters full with solution, taking care not to splash the terminals or they vdll subsequently corrode. The best proportion of sal-acdmoniac to water is about 2 oz. to a pint, though often a saturated solution is used. A satiu^ated solution, however, greatly augments the creeping of the salts, so that if a saturated solution is used the battery should be inspected more frequently. The battery (unless an agglomerate block) will not start at once. If the battery is required immediately, a little solution should be made in a jug, and poured into the porous pot through the little hole in the top, or a small hole may be knocked in the bottom of the porous pot, so that the liquid rises at once to the same level as that in the jar. The battery, when once properly set up, requires but little attention, and will run without recharging for periods varying between six months to two or three years, according to the size of the battery and the amount of work it does. Inspecting a Batteky. When inspecting a Leclanche battery the following points ghould be looked to : — See that the salts are not creeping over the glass jar ; if so, the faulty jar must be taken out, well dried, and the neck rubbed with grease. See that the zincs are not eaten away, and scrape off any crystals that may have formed on them. Should the zincs be very black, while a strong smell of ammonia comes off from the porous pot, it indicates excessive working, probably a short circuit on some of the wires, which must be seen to. See that the solution is 134 telephones: their constkuction and fitting. not evaporated ; if so, fill up ■with water. If the solution is opaque or milky, add more crystals till it becomes clear again, Or substitute a new solution. See that none of the solution has got on the terminals, or it will rapidly eat them away. See that no white lead is forming between the lead cap and carbon plate ; if this is the case, exchange the porous pot for a new one, as owipg to the bad conducting power of the white lead increased resistance is thrown into the circuit. Kechaeging a Batteey. When recharging a Leclanche' battery it wiU. be necessary first to see if the zincs are stiU in good condition, and not eaten quite thin. If the zincs are in fair condition, renew the solution, and should this effect no improvement, new porous pots or agglomerate blocks must be substituted for the old ones. Owing to the slight cost of the new porous pots, it is never advisable to attempt to recharge the old ones, which at the best is a difficult and tedious operation. The following table shows the E.M.F. and internal resist- ances of the different sized Leclanche cells : — Size. Porous Pot Form. Agglomerate Block. E.M.F. Ees. E.M.F. Re>. No. 1 No. 2 No. 3 1-60 1-60 1-60 •75 l-IO, 1-50 1-55 1-55 1-55 •50 •60 •80 It will be noticed that the agglomerate block form has a slightly lower E.M.F., and a considerably lower resistance. A modification of the agglomerate block form of Leclanche BATTEEIES, 135 cells is shown in Fig. 124. It is known as the six-block agglomerate, and has a very low internal resistance. The negative element is shown in Fig. 125, and consists of a grooved carbon cylinder a, with the agglomerate rods b b h Fig. 124. Fig. 125. Agglomerate Block. Six-block Form. in each groove. The rods are kept in contact with the carbon cylinder by the wrapping of sackcloth c, outside which are two rubber bands. The positive element is in the form of a zinc cylinder (such as is used in the Bunsen cell), which completely surrounds the negative element, the sackcloth preventing its coming into contact. The containing jar is of glazed stoneware. For bells in parallel, or where a large current is required, this form of cell is very useful, as owing to its construction it has a very low resistance, its E.M.F. being 1'55, and its resistance •20 of an ohm. 136 telephones: THEIB COXSTBDCTION and FITTDia. Batteries are best placed in a battery box as shown in Fig. 126, which shows four of the porous pot Leclanches ready connected up in a box. A better form of box, however, is Fig. 126. Four^ell Battery in Box. Fig. 127. Battery Box. that shown in Fig. 127, which is so arranged that the front and lid when released fall forward outwards, thus allowing the condition of the battery to be inspected at a glance. ( 137 ) CHAPTER VIII. ERECTING TELEPHONE LINES, OVERHEAD WIRES, INSTRUMENTS, ETC. In a telephone line there are four different portions of the line to erect. There is, first, the " line " wire, which is the outside wire connecting the two instruments, and is run either over- head or underground ; second, the " leading-in " wire, which connects the outside wires with those inside ; third, the " joining up " or inside wires, which are those extending from the instrument to the " kading-in " wire and to the battery ; and, fourth, the " earth " wire, which runs from the instrument down to the earth connection. In places where a return wire is used, the earth wire is not, of course, required. Line Wires. For overhead purposes. No. 16 B.W.G. hard-drawn copper, silicium, or phosphor bronze wire should be employed, or, if a stronger wire is required, a stranded one, consisting of three strands of No. 18 copper or silicium bronze should be used. For private line work, however. No. 16 B.W.G. will be found the most suitable, and, in certain cases, where the spans are short, and not in an exposed position. No. 18 even may be erected. Formerly, iron wire. No. 8 or 11 B.W.G-., was much used : but very little is ever erected now, a No. 16 copper, phosphor, or silicium bronze having taken its place. Iron wire, when used, requires to be very well galvanised, or it soon rusts, and in towns is rapidly eaten away by the 138 TELEPHONES : THEIE CONSTBUCTION AND FITTING. sulphurous fumes from the chimneys. For this reason an iron wire, where it passes above a chimney, or even copper wire if it passes very close, should be wrapped with tape for a yard or two, and the tape served with a coating of varnish. In running the wires they must be fixed either on insulators or shackles, insulators for preference, as they give a higher insulation. Figs. 128 and 129 show in section the Cordeaux screw insulator. Fig. 128 being the single shed and Fig. 129 the Fig. 128. Fig. 129. Fig. 130. Insulators. double shed form. Fig. 130 shows the outside appearance of the insulator complete. The insulator is of glazed porcelain, supported by the galvanised iron bolt Fig. 131, the top end of which screws into the upper part of the insulator, as shown in Figs. 128 and 129. In the single shed insulator it will be seen there is only one recess, while in the double ghed there are two, thus giving better insulation. In Fig. 132 INSULATOES. 139 is shown the single shackle, while that in Fig. 133 is a double shackle. The part a in Fig. 132 is the shackle, made of glazed porcelain, and h is the shackle-strap of gal- vanised iron. In Fig. 134 is shown the shackle ^^' ^^^' strap complete with bolts. In some places, such as under sheds, &c., the small form of insulator shown in Fig. 135 may be used. This form is called a " bobbin," and wiU be found all that is necessary in dry places. The bobbin is fixed by a screw or bolt through the centre, and to fasten the wire a turn is taken right round the groove. White porcelain insulators or shackles are the best, but if they are placed in an exposed position where they are IJkely to be broken by stone-throwing, the brown porcelain should be used, as offering a less inviting appearance. Shackles are generally used at the ends of a line and the insulators as intermediate supports, as shackles can generally be fixed so as to withstand a bo^^ greater strain than insulators. The Telephone Com- panies use either insulators or double shackles, some having a preference for insulators, while others will use nothing but Fig. 132. Single Shackle. 'double shackles. The best insulation is undoubtedly ob- tained by using insulators, and if a very high insulation is desired, fluid insulators, such as the Johnson, should be 140 TELEPHONES: THEIB CONSTEUCTION AND FITTING. employed. Private line work, however, is different from exchange ; what is sufficient for the former being often quite inadmissible in the latter. In exchange work each wire, owing to its close proximity to others, and very often electric Fig. 133. ^ f ^^/ Double Shackle. light wires carrying high-tension currents, requires to be very well insulated, while a private line wire, which, in nine cases out of ten, is of no great length, is generally in private ground, and thus removed from external disturbances. For Fig. 134. Fig. 135. Bobbin. Shackle strap. short lines in towns, therefore, it will usually be found quite sufficient to fix the wire to single shackles, the shackles being fastened to the chimney stacks -by -^ galvanised iron wire taken once right round the stack, or, if the strain is great, twice, each turn being so arranged as to pull against a different course of bricks. When it is desired to fix to a chimney SHACKLES. 141 stack, a wrought-iron bracket, as shown in Fig. 136, should be used, and an insulator, or shackle, fixed at the end. The wire is then fixed to the insulator, and should be so arranged that Chimney Bracket. the only strain on the bracket is towards the chimney-stack. Wall brackets for supporting insulators take a variety of forms, and very often a bracket wiU have to be designed to meet special requirements. In Fig. 137 is shown a convenient form where there is only one wire to be carried. The end of Fig. 137 Fig. 138. /m Wall Brackets. wrought-iron rod has a wood-screw thread cut on it, by means of which it is fixed. Unless there is some suitable woodwork near, a brick must be taken out of the wall and a wood plug inserted. For nailing direct to the wall, a wall bracket of the form shown in Fig. 138 will be found more convenient. This 142 TELEPHONES : THEIR CONSTEUCTION AND FITTING. can be attached directly to the wall by stout nails, or else fixed to any suitable woodwork by screws. Another form of wall bracket is shown in Fig. 139. It is intended for carrying two wires, the bolts of the insulators being fixed to the two shoulders seen to the right of the figure. Mg. 139. Wall Bracket. Erecting Overhead Wires. In erecting overhead wires in towns, care must be taken to see that the wires are erected in a thoroughly substantial manner ; otherwise serious accidents may result. All streets should be crossed as nearly at right angles as circumstances will permit, and the wires kept oiF the main thoroughfares as much as possible. If a wire must be stretched across a street nearly parallel with the direction in which the street runs, extra precautions should be taken to see that the fixings are thoroughly sound and the wire properly erected. If a wire crosses a street in this direction and breaks, then the wire will fall right into the street, coiling up and twisting as it falls in a manner that cannot but cause the most serious results should there be much trafiic. In crossing electric-light wires, it is best, if there are only a few telephone wires, to cross under the electric-light wires, for electric-light wires are generally so much stouter than telephone ones, and more securely erected that they are not likely to break, whereas, if the telephone wires were to fall on to a naked electric-light wire, the annunciator at the exchange would get burnt out, or subscriber's instrument damaged. OVEBHEAD WIRES. 143 To fix overhead wires in a proper manner requires at least three men — four or five if in crowded thoroughfares. Before commencing to run the wires, the difierent points at which a fixing shall be taken must first he determined. This is best done by getting on the roof of the two buildings between which the wire is going to be run, and taking a survey, by which means it can generally be determined which are the most suit- able places. The next thing is to get permission to take a fixing on the houses, or a " way-leave '' as it is called, which must be obtained from the landlord. Very often this getting way-leaves is the most diflicult part of overhead wiring, many persons having (perhaps not unnaturally) a great dislike to wires on their roof. In private line work, however, the wires are generally erected on houses belonging to the owner of the tele- phones, and thus there are no way-leaves to be got ; but, never- theless, it frequently happens in towns that fixings have to be made on intermediate buildings where permission has to be obtained and very often a rental paid. Permission being obtained, the insulators or shackles should next be fixed at each place, and everything got ready for running the wire. The wire should be commenced running from one end and worked towards the other. In running each span, one man goes on top of the building from which a start is made, taking with him the coil of line wire and a ball of stout string. Another man goes on top of the building where the next fixing is to be made, also taking with him a ball of string. This string is first got through between these two points, which is done by working the string from each of the fixings, and then joining the two ends together and pulling the string up taut, when it will generally rise clear of everything ; if not it must be manipulated till it does. In crossing a street the ends of the string must first be brought to the house on each side, and the two ends thrown down at the same time into the street, one of the men remaining in the road to tie the ends together, when the string must be quickly pulled up taut. After the string has 144 TELEPHONES : THEIE CONSTEDOTION AND FITTING. been got through between two points, the man having the coil of -wire ties one end of the coil to the string and pays it out to the other man, who draws the wire across, and when he gets the end makes it fast to the insulator. The other man then proceeds to draw back the slack, after which he cuts the wire, draws it up tight with the draw-vice, and makes it fast to his insulator. In the same way the other spans are run until the line is complete. If the lines end at each insulator, a small piece of wire must be soldered to the end of each span, so as to bridge over the insulator and make a good connection right through. Each span should be erected, if possible, without joins, but if joining is necessary, the joint must be well soldered, which should be done at as low a heat as possible to' avoid softening the wire. Fig. 140. Fig. 141 Paying-out Wire. In " paying out " the wire as each span is run, a little care is requisite to prevent its going into " kinks." The coil of wire should either be let run oflf a reel or else it should be OVEEHEAD WIRES. 145 gripped firmly with both hands and turned round, as shown in Fig. 140, and not let slip one coil at a time, as shown in Fig. 14:1, which will assuredly cause it to go into kinks (see Fig. 142). These kinks, when pulled out, go into the form shown in Fig. 143, which weaken the wire, making it very liable to break at this point, besides giving the span a very unsightly appearance. Fig. 142. Fig. 143. Kink in wire. Fig. 144. Draw-yioe. Each span must be tightened up to the required degree by means of a draw-vice, a form of which is shown in Fig. 144, and the key in Fig. 145. The method of " vicing-up " a span is shown in Fig. 146. The end of the span a is gripped in the jaws b of the vice, while the cord c from the barrel d of Fig. 145. Draw- vice Key. the draw-vice is fastened to the pole or shackle strap as the case may be. When the barrel is turned by means of the key / the cord is wound round the barrel and the span thus tightened up. The span is afterwards fastened off when the required tension is obtained. A iirepot will be found very L 146 telephones: theib construction and fitting. useful for all outdoor work, as the soldering iron is con- stantly in requisition, or least should be, as all joints must be properly soldered. Fig. 146. a/ Vicing-up a Span. As regards the length of the spans, these should not, where it can be managed, exceed 75 or 80 yards, but No. 16 siUcium bronze may be safely run in 100 yard spans, though it is desirable to keep them shorter. This, however, cannot always be managed, as the shortest and best route may perhaps be debarred from use owing to inability to obtain wayleaves. However tight a span may be viced up, there will always be a certain drop in the centre, which drop is called the dip or sag of the span. The amount of this sag will of course vary considerably, according to the temperature of the atmosphere, owing to the expansion of metals by heat and contraction by cold. For an 80-yard span it is usual to allow a sag of about 3 feet in ordinary summer temperature, which may increase to 3 feet 9 inches on a very hot day, or decrease to 1 foot 8 inches in the depth of winter. For longer spans of course the sag will be greater, and in tightening up a span the amount of sag must be regulated by eye, care being taken, if there are more than one wire, to see that they all sag in the same pro- portion. The easiest and most common method of running a single telephone wire is by using single shackles, which are secured roimd the chimney stack by a -^inch galvanised iron OVESHEAD WIRES. 147 wire. This method is shown in Fig. 147, and though generally used for terminal supports, can also be used for intermediate ones. In fixing the shackle it must always be so arranged Fig. 147. Shakle fixed on Chimney. that the pull of the wire is away from the chimney stack, so that the shackle will swing clear of the brickwork. The illustration shows the shackle in use as an intermediate support ; if used at the end of a line the wire is terminated at the shackle and the "leading-in" wire attached to the pro- jecting end. Fig. 148 shows how the double shackle is used, it being chiefly employed for intermediate supports or else for terminating two lines where the telephone in the building is the intermediate instrument of three or more. In the illustra- tion it is shown fixed to a chimney or corner bracket, a method that will be found very suitable where the pull is towards the building ; if the puU is in the opposite direction the shackles should be slung round the chimney as shown in the preceeding figure. With double shackles the line is terminated at each shackle, and the break bridged across by a short length of wire as shown. The method of binding the line wire to the insulators and L 2 148 telephones: theie constkdction and fitting. shackles is shown in Figs. 149 and 150. In Fig. 149 it will be seen the wire is passed round the shackle and then wrapped round with some No. 18 B.W.G. ordinary copper wire. The Fig. 148. Double Shackle on Comer of Building. end of the " leading-in wire " is attached on to the short end of the line wire, and not on to the body of the wire, so that when Fig. 149. Finishing off a Span, the joint is soldered the span is not weakened, as would be the case were the heat applied to any part of the wire under strain This is very important, and care should be taken to OVERHEAD WIRES. 149 see that it is not done either in attaching the leading-in wire or bridging across the double shackles. The line wire is bound to the insulators, as shown in Fig. 150. The wire is first wrapped with the binding wire (No. ISB.W.Gr.) in order to prevent the line wire a being injured by chafing against the insulator. The binding wire is then bound round the line wire from 1 to 2 across the insulator to 3, from 3 to 4 and back again to 3, across the insulator to 2, from 2 to 1, and then finished off in a single layer from 1 to 5. Fig. 150. Fig. 151. Chimney Bracket. Binding Wire tb Insulator. In Fig. 151 is shown the application of the chimney bracket, the form shown being the double insulator one for two wires. The bracket is fastened to the chimney by stout nails, and must be so arranged that the pull of the wires is towards the chimney. Although it is best where there are only a few wires to avoid the use of poles or standards owing to the increased cost and additional dangers attached to such standards, never- theless there are cases in which it becomes imperative to use them. The form now in most common use is shown in 150 TELEPHONES : THEIE CONSTRUCTION AND FITTING. Fig. 152, the number of arms and insulators varying according to the number of wires. The poles, which vary from 15 to 20 feet in length, and from 3 to 4 inches in diameter, according Fig. 152. ^^/ ^ " / / / /7 Pole on Eoof . to the height and strength required, are hollow wrought-iron tubes, and the bottom end is forced into the socket of a cast iron chair (see Fig. 153), which chairs fit on to the ridge of the roof and form the base for the pole. The arms carrying the insulators are also of wrought iron, and bolted to the pole at the desired positions. In erecting the poles several wrappings of sheet lead are first put over the ridge at the place where the chair is to rest; on roofs where there are ridge tiles one must be removed to form room for the chair, care being taken to see the roof is afterwards made perfectly watertight. The pole is then erected on the chair and must OVERHEAD WIRES. 151 afterwards be securely stayed. These stays consist of stranded galvanised iron wire, fastened at a point about a foot below the top of the pole, the other ends being securely fastened to Fig. 153. Pole Chair. stout spikes driven into the brickwork, as shown, or else to stay-eye bolts, which are bolted right through the roof beams. An adjustable swivel (Fig. 154) is inserted in each stay so they Fig. 154. Adjustable Swivel. can be tightened independently of one another and the pole pulled into an upright position. The short iron cross-pieces on the poles are footholds for the linesmen when fastening up the wires. For running wires in the country, wooden poles are almost exclusively used, as being cheaper than iron, in addition to other advantages. The best poles are procured from "Norway and Sweden, and before being erected must be treated in some manner to prevent decay, which would rapidly take place, especially at the ground line. Numerous methods have been tried of treating the poles, but none are so effectual as creosot- ing, which consists in forcing creosote into the timber (which must first be thoroughly dried) till the quantity absorbed by the pole is about 8 lbs. per cubic foot. Wood poles vary in height from 30 to 60 feet, and are light or stout, according to 152 telephones: theik consteuction and fitting. the number of wires they have to cany. For four to six wires a pole 35 feet in length will be found ample. The arms for the insulators, which are also of wood, are bolted to the poles, and the insulators themselves fixed by bolting through the arms. Fig. 155. Wood Pole. In erecting the poles they must first have the arms and insulators attached, and also be prepared for the attachment of the stay wires. A hole is then dug about 5 feet long by 2 feet wide, upright at one end and sloped off towards the other, as shown by the dotted Hnes in Pig. 155, which represents the pole erected. The depth of the hole wiU vary according to the length of the pole, poles being usually buried one-fifth or one-sixth of their length. Thus a pole 35 feet high will require to be let into the ground about 6 feet. The hole OVBEHBAD WISES. 153 being ready a piece of plank is placed against the upright end of the hole, and the butt of the pole placed in the hole so that it rests against the plank, which prevents its penetrating the soil. Eopes are now tied to the top of the pole and the pole erected into a perpendicular position by means of ladders which are slipped underneath, and brought nearer and nearer to the base as the pole becomes more and more upright, the pole being steadied by means of the ropes. The hole must then be filled in and the earth rammed tightly down. The Fig. 156. Fig. 157. Pole Clip. Insulator on Pole, next operation is to fit the stay wires, for which purpose a hole of the shape shown in the figure is cut and a plate or balk of timber, to which the end of the stay rod is attached, buried in it. The object of under-cutting the hole for the stay plate is to enable the plate to pull against firm solid ground. The stay wires must afterwards be attached to these stay rods and the pole pulled into a perpendicular position. Where there is only one line wire a light pole, with the insulator fixed at the top, as shown in Kg. 156, can be employed. Fig. 157 is a pole clip to ena,ble extra wires to be added to a pole. The insulators are attached to the upright bolts and body of the clip clamped round the pole. 154 telephones: theib constbuction and fitting. The number of poles required per mile varies according to the number of wires and the course of the wire. On an average about twenty poles per mile will be found sufficient, more if there are a large number of wires or there are many curves. Humming of Wires. A great trouble that often arises with suspended wires is the humming produced in the wire near its supports. This is caused by the wind passing across the wire and setting it in vibration, the support acting as a sounding board. On wooden poles in the country, when the wind is strong, the sound is very loud, but it is in town chiefly where the greatest incon- venience arises. The noise is very disagreeable to the inhabi- tants of the house to which the wire happens to be attached, preventing many persons from sleeping at all on windy nights. Unfortunately, it is the bedrooms that are generally nearest to the wire, and this, coupled with the silence prevailing during the night, increases what is perhaps hardly heard in the day ten or twenty-fold at night. The trouble, however, can be con- siderably reduced by using a little judgment in selecting a fixing and by using special supports. Make your spans as short as possible, the noise is always worst on houses at the end of long spans, especially if the spans are in exposed positions. If the chimney, &c., is an intermediate support, terminate each span on the opposite side of the chimney, using separate bands (kept as far away from one another as possible) round the chimney for each support, and connect across with guttapercha covered wire. If this is not sufficient, bind round the insulator or shackle a piece of indianibber about half -an -inch thick, fastening the wire outside the rubber. The noise can often be stopped by clamping two strips of wood about 18 inches long, 2 inches wide, and 1 inch thick on the wire close by the insulator, the proper distance of this "damper" from the INDUCTION. 155 support being ascertained by sliding it along the wire. Sheet lead wrapped round the wire a short distance from the insulator will also frequently stop all humming. Induction and Leakage. Trouble will often arise in telephone lines that run side by side for any great distance from "induction" and "leakage from wire to wire." The latter can generally be remedied by a little attention to the insulation of the line, and the former by specially arranging the wires. The noises arising from induction are caused by the currents in a neighbouring wire inducing similar currents in the other wires. As we know from an ordinary induction coil, when we send a current in one direction in the primary, we get a current in the opposite direction in the secondary. In an induction coil, of course, the two circuits are coiled closely together, but the same result takes place in a less powerful manner when the circuits run straight side by side. Were the current in the primary of an induction coil perfectly continuous, there would be no result in the secondary ; hence the necessity for a make-and-break or else an alternating current. Likewise, if the telephone currents were continuous, there would be no trouble from induction ; but since the telephone depends for its action on tmdulating and varying currents, the currents given out by the microphone or the magnetic receiver are necessarily of a rapidly alternat- ing and undulating character. It may seem incredible that a wire perfectly insulated can have any very inconvenienc- ing effect on other wires, also well insulated, and some 3 feet or 4 feet away, but the currents required for working a telephone are of the most feeble strength. In a telephone exchange the inconveniences arising from induction are often very great; messages sent along one wire being heard dis- tinctly in a neighbouring wire, and thus a message intended 156 telephones: their constkuction and fitting. for a certain person might also reach the ears of persons from ■whom it was most desirable it should be kept. Although the induction from wire to wire is bad, yet that arising from neighbouring electric-light wires is very much worse, the electric-light currents being so powerful that they make their effects felt from a great distance. Nearly every- thing depends on the arrangement of the electric-light circuits as to their effect on the neighbouring 'telephone wires. For instance, if the electric-light circuit consists of arc lamps in series, with the lead leaving the central station in one direction, and after making a whole circuit of the town returning in another, then the telephones in that town will have a merry time of it at night. Happily, however, though this method of working electric lamps was much in vogue three or four years ago, it is now rapidly giving way to the transformer systems, and as the transformers are in parallel, the return lead must necessarily be run in close proximity to the feed, thus the effect of the one wire is neutralised by that of the other. When telephone wires run in close proximity to telegraph wires, we have noises in the telephones caused by the induc- tion from the telegraph wires, the quick make-and-break of the circuit by the telegraph instruments being distinctly audible. With the telegraph wires an earth return is used ; thus when towns are connected together for the purposes of telephonic communication, and the route along the- railroad is taken, if an earth return were used for the telephones also, it would be well nigh impossible to detect what was being said, owing to the noise arising from induction. A return wire is therefore used for the telephones ; though even this does not do away entirely with the induction, as one of the telephone wires is perhaps nearer to the telegraph wires than the other, and thus the neutralising effect of the two wires is lost. The telephone wires are therefore arranged so that they change position from pole to pole, first one wire and then the other being nearest the telegraph wires, as shown in Fig. 158, In INDTJOTION. 157 tte case of two telephone circuits, the wires are arranged as in Kg. 159, the one circuit heing represented by the continuous, and the other by the dotted, lines. In Fig. 158 a is the telegraph wire, and b and c are the two wires of the telephone line, while in Fig. 159 a a are the two wires of the one telephone line, and b b those of the other. Fig. 159. Arranging Wires to prevent Induction. Where telephone wires run for great distances together on the same poles or supports, another trouble that arises is that of leakage from one wire to another, causing noises in the telephone and "cross talk." This is caused by the current from one wire passing, by means of the pathway formed at every insulator by the dust and moisture that collect on the 158 telephones: theib construction and fitting. surface, to the neighbouring wires, all of which have a common return, viz. the earth. The greater the number of insulators on the lines, the more numerous the pathways from one wire to another, and the less the insulation resistance between the wires. Where trouble does arise from leakage and cross talk, it will generally be found that the insulation at some parts of the line has become defective. A film of dirt will often coat rapidly over the insulators, especially in smoky towns, and this when wet forms a path of leakage. It is best to expose the insulators of a line as much as possible, as then the heavy rains will from time to time wash them, and they will dry comparatively clean ; but if sheltered in any way, the dirt quickly accumulates. In the case of telegraph circuits, where the currents are more powerful, the chief inconvenience caused by the leakage is that it reduces the strength of the ciurrent at the sending station ; but in telephony, where the currents are so feeble, the trouble is rather to prevent these stray messages passing from one line to another than to provide against the reduction of the current strength. Underground Wires. Where the wires are run underground, No. 16 B. W.G., gutta- percha covered, and taped or braided, must be used. Braided wire is more expensive than taped, but is to be preferred, owing to its not unravelling so easily, and also because it will draw better into pipes. The wire should have been well served with Stockholm tar, which preserves it from decay, though it somewhat lowers its insulation. Bitumen-covered wires, either taped or braided, are also much used for underground purposes. It is considerably more expensive to place telephone wires underground than overhead; but the unsightliness and danger of overhead wires is done away with, and the expense of repairing them when broken by snow- storms, &c. Underground wires should be laid in iron pipes, TJNDEKGEOUND WIRES. 159 the pipes being laid about 12 in. below the surface of the ground. When the pipes are being laid, a naked wire is drawn through, by means of which the covered wires are afterwards drawn in. A method which allows of the wires being accessible at all parts is to lay the wires in small creo- soted wood troughing, fitted with a loose lid, the troughing being buried, like the iron pipes, 12 in. beneath the surface. Thus, if at any time the insulation of the wire should break down at any point, the earth can be removed from above the casing, and the wire inspected at the point where it is believed the fault lies. With iron pipes, nothing can be done save pulling out the faulty wire and drawing in a good one by means of it. The method adopted by the Post Office with their underground wires in towns is that of iron pipes, with junction-boxes at certain distances. These pipes are laid underneath the pavements and roads, and into them is drawn a cable containing a number of wires. If a fault occurs in one or two of the wires, the whole cable between the two junction- boxes is drawn out and a new cable drawn in by means of it, the old cable being sent to the works for repairs, and when repaired is used at some future time. If there are many wires in the same pipe or troughing, it will be found best to use a separate return-wire for each instrument, owing to the trouble arising from induction if an earth is used. The method adopted by the writer with underground wires is to lay them in wood troughing, and twist each pair of wires together throughout the entire distance. This method not only prevents trouble arising from induction, but also allows (if each pair is neatly laid side by side and one marked at intervals) each circuit being readily identified should it be necessary to test or repair the wires at any place. 160 telephones: theie consteuctiok and fitting. The Leabing-in Wires. For the leading-in wires No. 18 B.W.G. copper wire, gutta- percha covered, to No. 9 B.W.G., wound with tape and well covered with Stockholm tar, should be used. In places not much exposed to the weather No. 20 to 12 may be employed ; but in most cases No. 18 will be found the most durable, which should also be double taped if likely to be subjected to any mechanical strain. The leading-in wire is joined to the line wire close to the last shackle or insulator, the joint being carefully soldered. The wire is best brought into the building through the window frame, a hole being bored in the frame Fig. 160. ij TT ri ^S ^^^^^i^ ^Method of Leading-in the Wire, for this purpose, though if there is no window near, other means must be resorted to. The leading-in wire, before it enters the wall or window frame, should make a short dip below and then rise to the hole where it enters, as shown in Fig. 160, so that rain may run down and drip off at the bend LEADING-IN WIRES. 161 instead of running into the building. As there is in wet weather considerable leakage from the line-wire to earth by reason of the outside covering of the leading-in wire being wet and forming a conducting film, a porcelain cup (see Fig. 161) Kg. 161. LINE WIPE Leading-in Insulator. is " often fixed just above the joint between the line-wire and leading-in wire. This, by keeping the upper part of the leading wire dry for a space of 3 or 4 in., makes a break in Fig.'.162. Leading-in Tube, the conducting film, and preserves the insulation of the line. Porcelain "leading-in tubes," a form of which is shown in Fig. 162, are very convenient, and tend to increase the insula- M 162 TELEPHONES : 'JHEIE CONSTRUCTION AND FITTING. tion of, besides protecting, the wires. The tube is fitted at one end with a thread, which either screws into the hole in the woodwork, or is cemented into the wall. It is perhaps hardly necessary to mention that the mouth of the tube must be turned down and not upwards, so as to prevent any water entering. In bringing the wire down the side of a building, it should, if possible, be tied to the rain-water or other pipe; but if neither of these is procurable, the wire must be fixed by big staples, or tied to pipe hooks driven into the wall. Great care is necessary in driving these staples to see that the staple is not driven quite home, which would injure the insulation of the wire. Where the wire passes over the edge of the roof or the comer of a chimney stack, a short piece of the wire should be wound round where it touches the brickwork, to prevent the insulation being frayed off by the wind blowing the wire about. Inside or Joining-up Wires. If the telephone instrument is near the place where the " leading-in " wire enters the building, it is best to continue the guttapercha wire right to the instrument ; but if the distance is far, the leading-in wire should be stopped just inside the building, and the continuation made to the instrument with less expensive and more suitable wire. For inside wiring plain guttapercha-covered wires are unsuitable, as in dry situations the insulation cracks off in time. The best wire for inside wiring and joining up the battery is No. 20 B.W.G., served with a layer of rubber, then double cotton-covered and paraffined. This wire' can be obtained in almost any colour to suit the decoration; but a drab or neutral tint is the least noticeable. These wires should be run along the skirting- board and up the side of the wall, the wires being fastened by staples. Never, however, place two wires under one staple, or let two staples touch one another, as if this is done a short circuit is almost certain to be caused sooner or later. The EAETH WIRES. 163 different wires should be so arranged as always to retain the same position relative to one another, as this greatly facilitates tracing a fault. If the wires are likely to be interfered with they should be either stapled so as to be out of reach or else placed in wooden casing, such as is used for electric light wires. In passing from room to room the best plan is to bore a hole in one corner of the woodwork above the door ; if there are a number of wires the holes being bored so that the wires retain their relative position to one another. If there are electric- light wires in the same building, these must be kept as far away from as possible. If the telephone wires are obliged to be put near the electric-Ught wires, under no circumstances should they run parallel to them, owing to the disturbances arising from induction. It is best also to avoid passing too near gas- pipes, especially if they are only " compo," as in the case of lightning striking the outside wire, it is liable to "jump " from the inside wire to any neighbouring conductor in connection with the earth, and if this took place the discharge would probably fuse the pipe and set fire to the gas. If a joint has to be made it must be carefully soldered (rosin being used as a flux), after which the joint must be insulated with sheet guttapercha, or rubber strip, and wound with tape. ~ A little judgment is necessary in seeing that the joints do not come in inconvenient or bad positions, and also that the most suitable course for the wire is taken. Eaeth Wires and Earth Connections. The importance of a " good earth " is frequently underrated by many persons in erecting a telephone line, though they are ever so careful when a return wire is used in seeing that a good connection right through is obtained. Since, when an earth return is used, the ground takes the place of the retiu-n wire, it is obviously very important that a good connection to the ground is obtained at both ends of the line. M 2 164 TELEPHONES : THEIK OONSTEUOTION AND FITTING, A main water-pipe makes the best earth connection ; but if this is not obtainable, the earth wire may be attached to the gas-pipe. Care must be taken, however, to see that the water- pipe is really a main, and not a cistern pipe, as, if this latter is the case, there will be a " bad earth," caused by the break in continuity at the ball-cock in the cistern. With the gas-pipe also connectiMi must be made on the street side of the meter, owing to the red lead used in the joints being a bad conductor. If connection is made on the house side, the meter must be bridged over with a piece of wire ; but even this is liable to be interfered with by the gas inspector. The earth wire should never be connected to a composition gas-pipe, owing to its liability to being fused should the line be struck by lightning. Should neither a water nor gas-pipe be obtainable, a pump pipe leading to a well makes a good " earth " ; but if this is not to be had, an artificial earth must be resorted to. A good arti- ficial earth is made as follows : — Suspend 5 ft. or 6 ft. of sheet lead 6 in. wide in the centre of a hole about 4 ft. deep ; then ram in with ordinary gas-coke till within 6 in. of the surface, when fill in with soil. The earth wire must then be soldered to the projecting end of the lead. Care should be taken to obtain as moist a situation for the hole as possible. Never connect the earth wire on a gas-pipe at one end and a water-pipe at the other, as permanent currents are thereby often set up which may in certain cases give rise to noises in the telephone. In country places, where an artificial earth has often to be resorted to, care should be taken to see that the same material is used for the earth plate at each end of the same line. For instance, sheet lead should not be used at one end and an iron plate at the other, or permanent earth currents will be the result. For the earth wire. No. 18 B.W.G. copper wire, guttapercha- covered, taped, and tarred, such as is advised for the leading-in wires, should be used ; but if this is objected to on the score of economy. No. 18 naked copper or 3-18 galvanised iron can be employed. If a naked wire is used, No. 18 copper is to be FIXING THE INSTRUMENTS. 165 preferred, but it is never advisable to use the cotton-covered and paraflSned, such as advised for inside wires, as, in all probability, in getting to the water-main the wire has to pass through places where it will be liable to injury from dampness and other causes. If obliged to use paraffin wire, a short length of stout wire should be soldered to the water-pipe, and the other wire should be soldered to the projecting end. Care must be taken to see that a really good soldered connection is made to the pipe, otherwise the joint soon oxidises, and a bad " earth " is caused. If it can be managed, it is best to let the water out of the pipe while the joint is being soldered. In making the connection, the pipe must be scraped clean with a knife for the length of about 3 in., and the cleaned copper wire twisted tightly round it, the joint being soldered with resin as a fiux, though in the case of gas-pipes it will be necessary to use "spirits." It is generally sufficient if the stout earth wire starts from the zinc «f the battery, the connection from the zinc to the instrument being made with the small wire as used for inside wiring. Fixing the Instruments. The telephone line having been got through between the two places and the " earth '' wire run, the next thing is to fix the instruments, which should previously have been tested with a cell or two to see that they are in good condition. Having feet up the battery so that the sal-ammoniac can be dissolving while the instruments are being fixed, the first thing is to ascer- tain the best position in which to fix the telephone. In deciding on the position, care should be taken to see that the instrument is not placed on a partition or wall where there is much vibra- tion, such as is likely to be caused by machinery or the open- ing and shutting of doors, as this would cause noises in the telephone owing to the microphone being set in vibration. Noisy positions, such as near a window or door opening into the street, should also be avoided. The position being deter- 166 telephones: theib consteuction and fitting. mined, we next ascertain the nature of the wall, so that the fixing can be obtained accordingly. There are three diflferent kinds of fixings generally met with in buildings — 1, woodwork ; 2, laths and plaster ; and 3, brick, faced with plaster. The construction of the wall can usually be found out by tapping on it with a hammer or the end of a screwdriver. If the wall is woodwork, it will generally give out a loud sound y if laths and plaster, a hollow sound ; and if brick or stone a dull sound. In a lath and plaster partition the upright posts to which the laths are nailed can be found by probing with a bradawl or similar instrument. If the wall is wood, the fixing will be comparatively easy, as the instrument can be screwed to it with ordinary wood-screws ; but if laths and plaster, lath screws must be used, the proper length of which can be ascertained by probing for the laths with a bradawl. Should one of the screws pass between two laths, the position of the instrument should be altered uutU a lath is obtained for each screw. For a brick wall, the position for the screws must first be marked by holding the instrument against the wall and passing a bradawl through the screw-holes in the instrument, and, the position being marked, the wall must be plugged at these points. To plug the wall an inch cold chisel will be required, with which a hole must be cut in the wall about 3 in. deep and 1 J in. wide. The hole is cut square, the back part being slightly smaller in diameter than the opening. Wooden plugs must now be made, being cut square like the hole, but slightly thicker and shorter, and with a slight taper. It is better also to so cut the plugs as to give them a slight twist, as this form takes the best hold of a square hole. The plugs are afterwards driven into the plug holes flush with the surface of the wall, and the instrument fixed by means of wood-screws. In fixing the ends of the wires under the terminals of the instrument, the ends of the wire should be so placed under the terminal that when the terminal is screwed up it tends to twist the wire round the body of the screw, and not to FIXING THE INSTRUMENTS. 167 unwind it, as this would cause the wire to work out from under- neath the screwhead. In terminals where the wire passes into a hole, and the screw hears directly on it, the end of the wire should be neatly doubled back on itself before being passed into the hole. In finishing off the ends of the wire where they join the instrument, a short length of the wire should be spiralled round a pencil, as this gives the instrument a more finished appearance. 168 TELEPHONES : THEIR CONSTRDOTION AND FITTING. CHAPTER IX. CONNECTING-UP. In the diagrams of connections that will now be given, it has been the aim of the writer to include all the most important cases that are likely to be presented to the fitter ; but it must be borne in mind that special requirements are more the rule than the exception in telephony, and that to get at these special requirements one diagram requires to be read in conjunction with another. In the connections of the instruments also, the different parts of the telephones are arranged with a view to increase the clearness of the diagrams ; thus the relative position of one part to another must not be taken as a guide to the arrangement of parts that would be found in actual practice. The ringing key is in most instances shown as a separate Morse-key push, and the switch-hooks considerably simplified, nevertheless all the component parts are there and the con- Kg 163. I.INE KfToxn Two Receivers connected. nections can be easily traced. The main principle governing the connections of one instrument will be found to underlie the connections of all other instruments of the same class, the CONNEOTING-UP. 169 difiference being generally merely in the mechanical arrange- ment to effect certain operations. Simple Telephone Circuit. — Fig. 163 shows a simple circuit consisting of two magnetic receivers connected together, but without any arrangement for signalling between them. For E.M. or membrane receivers a battery of two or three cells requires to be interposed in the circuit. The earth, or return wire, is shown darker than the line-wire. Two Instruments with Battery Switch-hells an4 Magnetic Re- ceivers. — Fig. 164 shows the connections for the form of Connections for Instruments shown in Figs. 59 and 60. instruments illustrated in Figs. 59 and 60, page 75. The automatic switch is formed by the two hooks, which are short circuited by the ring of the receiver when hung on the hooks. Fig. 165 shows the connections for the same class of instru- 170 TELEPHONES : THEIB CONSTETTCTION AND FITTING. ment, except that it has a movable switch-hook of the ordinary kind. In the figure, a is the switch-bell, b the receiver, c the automatic switch, d the ringing key (shown for the sake of Fig. 165. Internal Connections of Instruments with Magnetic Transmitters. clearness as a separate key-push), and / the batteries for instrument No. 1; a', V, c', d', and /being the corresponding parts of instrument No. 2. When the receiver b is on the spring-hook of the automatic switch c, the hook is in contact with the bottom contact ; but when the weight of the receiver is taken off, the hook moves up, and is in connection with the CONNEOTING-UP. 17X top contact. Wien the push d of the current flows from the carbon bottom contact of the push, thence to the push-spring and bottom contact of the automatic switch c, from there to the spring-hook, line-wire, spring- hook of the automatic switch belonging to instrument No. 2, bottom contact of switch, spring of push d', top contact of push, right-hand terminal of bell a', through the beU to return wire, and from thence to zinc pole of battery /. This causes the beU of instrument No. 2 to ring, calling the attention of the person at that end, who presses' the button of his push, causing the bell at instrument No. 1 to ring in reply. The receivers are now taken off the switch-hooks, and conversation is carried on. The " speaking " circuit is, starting, let us say, from receiver b — re- ceiver 6, top contact of automatic switch c, spring-hook of switch (the circuit being now closed owing to the receiver being re- moved), line-wire, spring-hook of automatic switch of instrument No. 2, top contact of switch, receiver b' return wire, and from thence back to receiver b. Thus there is, when the receivers are off the hooks, a complete circuit instrument No. 1 is pressed, pole of the battery/ to the Fig. 166. Two Magneto Switch-bell Instnunents connected. 172 TELEPHONES: THEIR CONSTRUCTION AND PITTING. without the batteries, the batteries not being required owing to the receivers having permanent magnets. Two Instruments with Magneto Switch-hells and Magnetic Receivers. — ^Figs. 166 and 167 show the connections for the form of telephone instruments shown in Figs. 61 and 62, p. 76. Fig. 166 shows the external connections of the instru- Fig. 167. yKS/ M^^ A/tZ //\fSZ Internal Connections of Fig. 166. ment, and Fig. 167 the internal. The connecting-up of two of these instruments is, it will be seen from Fig. 166, a very simple matter ; the instruments having merely to be erected, and a wire run from one terminal (it is immaterial which of top two) of one instrument to that of the other. The re- maining terminal of each instrument is connected to " earth." In Fig. 167 a is the magneto bell, d the generator, c the automatic switch, and 6 the receiver of instrument No. 1 a', V, c', d' representing similar parts of instrument No. 2. CONNECTISG-aiP. 173 The " ringing " circuit is as follows : — When the handle of the generator d is turned, the current flows, let us say, from the right-hand terminal of the generator to bottom contact of automatic switch c, spring-hook of switch, line-wire, spring- hook of automatic switch c' (instrument No. 2), bottom con- tact, generator d', bell a', return wire, bell a (instrument No. 1), and thence to left-hand terminal of generator d. Ringing from the other end a similar action takes place. The " speaking " circuit, when the receivers are off the hooks, is as follows : — Starting from receiver b, the circuit runs to top contact of automatic switch c, spring-hook of switch, line- wire, spring-hook of switch c' (instrument No. 2), top contact of switch, receiver 6', return wire, and thence back to re- ceiver b. Fig. 168. ( = 1 krw — Aj Two Battery Switch-bell Instruments connected. Two Instruments with Battery Switch-bells, Microphones, and Receivers. — Figs. 168 and 169 show the connections for the form of instrument shown in Fig. 64, p. 78. Fig. 168 174 TELEPHONES : THEIR CONSTKTJOTIOtf AND FITTING. showing the external, and Kg. 169 the internal connections. It win be seen from figure there are four terminals at the top of the instrument, marked L, Z E, T Z, and C, being " line," " zinc " and " earth," " transmitter zdnc," and " carbon " respectively. Fig. 169. Diagrammatic View of Battery Switch-bell Instruments. CONNECTING-UP. 175 In Fig. 169 a is the bell, b the receiver, c the automatic switch, d the ringing key, m the microphone, n the induction coil, g the two contact springs (connected across by the back part of the automatic switch when the receiver is off the hook), by means of which the local circuit through the microphone is opened and closed, / the ringing battery, one cell h of which is the local cell for the microphone. The corresponding parts in instrument No. 2 are designated by a' V, c', d', &c., similar letters denoting similar parts. The " ringing " circuit, when the ringing key d of instru- ment No. 1 is pressed, is, starting from the carbon pole of battery/, bottom contact of key d, key-spring, bottom contact of automatic switch c, hook-lever of switch, pivot of switch, line-wire, pivot of switch c', instrument No. 2, hook-lever of switch, bottom contact key-spring, top contact, right-hand terminal of bell a', left-hand terminal, return wire, and zinc pole of battery /. "When the receivers are lifted oif the hooks, the hook-lever moves up and makes connection with the top contact, and at the same time connection is made between the two hooks g, thus closing the local circuit. The local circuit runs from the carbon pole of the cell h to the microphone m, from there through the primary of the induction coil n, springs g, and from thence to the zinc pole of the battery. The " speaking " circuit is (the receivers being off the hooks), starting from the secondary of the induction coil n, top contact of automatic switch c, hook-lever, pivot, line-wire, pivot of automatic switch c' (instrument No. 2), hook-lever, top contact, secondary winding of coil n', receiver h', return wire, receiver J, and from there back to secondary of induction coil n. The internal connections of two other instruments coming under this class will now be shown. Connections for the Oower-Bell Telephone. — ^Fig. 170 shows the connections for the Gower-Bell instrument. In the figure 176 TELEPHONES : THEIB CONSTEDOTION AND FITTING. a is the bell, h the receiver (the listening tubes of which are not shown), c and c' the automatic switches, d the ringing key, m, the microphone, n the induction coil, and / the battery, two cells of which are used for the microphone. It will be noticed there are two automatic switches, the one c making the changes from " ringing " to " speaking," and the other opening, and closing the local circuit through the microphone. The local circuit runs from the carbon pole of the two cells of the battery /, to back contact of automatic switch c', switch- Fig. 170. Internal Connections of Gower-bell. hook, primary of induction coU n, microphone m, and then to zinc pole of battery. The "ringing" circuit is from carbon pole of battery to bottom contact of ringing key a, key-spring, line-wire, instru- ment No. 2 (not shown in the figure), return wire, and zinc of the battery. The "speaking" circuit is from secondary windings of induction coil n, back contact of automatic switch c, switch- hook, back contact of ringing key, key-spring, line-wire, instrument No. 2, return wire, receiver, and from there back to secondary of induction coil. If a relay is required the bell CONNECTING-UP. 177 must he cut out, and the two wires going to the bell taken to the relay. Connections for the Ader Telephone. — Fig. 171 shows the con- nections for the Ader instrument. In the figure, A is the microphone, B and B' the two receiver cords, the coil, D the ,automatic switch, E the ringing key, and F the lightning- ' arrester. The receivers are not shown in the figure. The current entering at " line " passes through the bottom plate of Fig. 171. £ M[ ^S7t/^JV Internal Connections of Ader. the arrester to the spring a on the top of the automatic switch. From there it passes (if the receiver is on the hook) to bottom contact, ringing key-spring, back contact of key to bell, and from thence to top plate of arrester and " earth " or return line. If the receiver is off the hook, as shown in the figure, the current passes from spring a to top contact receiver B, secondary coil, receiver B', to " earth " or return line. N 178 TELEPHONES : THEIB CONSTEUCTION AND FITTING. The " local " circuit runs from the positive pole of one cell of the battery to primary of coil, microphone, spring b (closed by the brass pieces on the end of the switch-hook), and from there to the zinc of the battery. The " ringing " circuit is when the key E is pressed, from the positive pole of the battery to bottom contact of key, key- spring, switch-hook, spring a, bottom plate of lightning- arrester, to " line," other instrument, and back by " earth " or return line. Two Instrwnents with Magneto Switch-lells, Microphones, and Receivers. — Figs. 172 and 173 show the connections for instru- ments of the magneto switch-bell type, a form of which is shown in Fig. 66. It will be seen there are three terminals at the top of the instruments, that on the right, L, being the " line," and the other two, E, the " earth," which two terminals must be joined together and connected to earth as shown in the figure when the instrument is at a terminal station. As this centre terminal is therefore only required at intermediate stations, many forms of these instruments have only two terminals, the L and E. In connection with the instrument at the right- hand side station is shown an extension bell and two-way switch, so that if the operator wishes to leave the instrument, he can, by moving the lever of the switch, cause the calls from the other station to be received on the extension bell, which would be fixed in another part of the building. Another method of adding an extension bell is to connect it in the earth wire, though this method is objectionable in some cases, as the bell will always ring whether the operator is near the instrument or not. In Fig. 173, which is a diagrammatic view, showing the internal arrangement and connections, a is the microphone, h the receiver, c the automatic switch, d the generator, e the bell, g the two springs, by means of which the local circuit is opened and closed, / the battery for the microphone, and n the CONNBCTING-UI*. Fig. 172.. 179 Internal Connections of Kg. 172. N 2 180 TELEPHONES : THEIB CONSTRUCTION AND FITTING. induction coU; a', V, c', A', e', &c., being tte corresponding parts of instrument No. 2. Wien the handle of the generator d (instrument No. 1) is turned, and the receivers are on the switch-hooks c and c', the " ringing " circuit is, starting from the left-hand terminal of the generator d : — generator d, bottom contact of automatic s-witch c, switch-hook, pivot, "line" wire between the two instnmients, pivot of automatic switch d (instrument No. 2), switch-hook, bottom contact of switch, generator d', bell e', "earth," righ1>hand terminal of bell e (instrument No. 1), left-hand terminal, and from there back to generator d. When the handle of the generator d' is turned, a similar action takes place, and it will be noticed that both bells ring when the handle of either of the, generators d or d' is turned. When the two receivers, 6 and V, are off the switch-hooks, the circuits are as follows : — The " local " circuit runs from the carbon pole of the battery / to induction coil n, springs g, microphone a, and from there to the zinc pole of the battery. The "speaking" circuit is; starting, let us say, from the secondary windings of the coil n : coil n, top contact of auto- matic switch, switch-hook, pivot, line-wire between the two instruments, pivot of switch c' (instrument No. 2), switch- hook, top contact of switch, secondary of coU n', receiver 6', " earth " or return wire, if such is used, from " earth " to receiver 6, and back to secondary of coU n. Different Methods of Arranging Instruments. The diagrams that have so far been given relate chiefly to the internal connections of the instruments ; but those that now follow show the various ways of connecting up several instruments to meet certain requirements. The form of in- strument shown is chiefly of the magneto switch-bell kind the connections of which have just been given in detail in Fio'. 173. EHKTH Fig. 172. '-TJ "~T >- >■ l^' BCLL Two Stations with Magneto Switch-bell Instrument, and Microphone Transmitters. An Extension Bell and Two-way Switch are also shown at the Righthand Station CONNECTING-UP. 181 The " line " and " earth " terminals only are shown, as all the other connections are internal, and do not in any way affect the connection of one instrument with another. Every telephone has its "line" and "earth" terminals — i. e. a ter- minal to which the " line- wire " is connected, and another for the " earth " or " return-wire," irrespective of whether it has a battery or magneto switch-bell, microphone or no microphone. The form shown in the following figures con- tains a magneto generator and bell (the two gongs of which are visible at the top of the case), a microphone transmitter (the mouthpiece of which is shown at the bottom), with induction and local cell inside the case. The receiver is shown hanging on the hook at the left-hand side of- the case, and on the right-hand side is the handle of the generator. ^ If in any of the diagrams it is wished to follow the inside connections of any one of the instruments, it is only neces- sary to refer to Fig. 173, and follow the circuit througl^ the instrument shown there, from the "line" wire to the " return,-" or the " return " to " line," as the case may be. If it is wished to follow the connections, presuming the instru- ment has a battery switch-bell, the same process must be ^pursued, only with the insteument shown in Fig. 169. The form of instrument shown in the diagrams has been adopted, purely because, being compact, it adds to the clearness of the diagrams. Three Telephones in Series. — Fig. 174 shows how three or more telephone stations are connected in series, so that any one station can communicate with any other on that circuit. In order to be able to distinguish which station is wanted, a code of signals niust be arranged, such as one ring for No. 1, two for No. 2, and so on. Thus, if No. 2 station wishes to communicate with No. 1, he gives one ring ; with No. 3, three rings. When No. 2 receives a reply, he takes off his ' receiver, which cuts his bell out of circuit and puts the micro- phone and receiver in, enabling him to carry on conversation 182" TELEPHONES : THEIK CONSTEDCTION AND FITTING. with No. 1 or No. 3, as the case may be. Thus, when any one station riijgs, the bells at all the other stations ring also ; but only that station replies whose number corresponds to the signal given. If the instruments are of the battery switch- Fig. 174. tUSI AT- 2. //V«I HI2> Three Stations in Series. bell type, then a relay should be used for each instrument ; otherwise there will be difficulty in getting the bells to ring nicely, unless they are of the form (described on p. 112) which govern their vibrations, not by breaking the circuit, but by shunting their coils. Three Telephone Stations, One of which is able to communicate vnth the other Two as desired. — ^Fig. 175 shows an arrangement suitable for such places where it is desired for one station to be able to communicate with the other two, but not vice versa. As, for instance, where the head of the firm wishes to be able to communicate with the clerks' office, stores, or other part of a building, without allowing himself to be communicated with CONNEOTING-UP. 183 unless he desires. In order to accomplish this, a two-way plug, switch B, is required. This switch is fixed within easy reach of the person who uses instrument No. 1, and to the top blocks h and c are respectively attached the two line-wires from the Instruments No. 2 and No. 3. The bottom block a Pig. 175. N5.// One Station connected to Two others. is connected to instrument No. 1, and the return wires from all the instruments are joined together. Each of the brass blocks a, b, and c are fixed to a non-conducting base, and insulated from one another by an air space. When the brass plug is put in either of the two holes, the top plate above that hole is connected to the bottom plate. Thus, it will be understood that if the brass plug is inserted in the left-hand hole of the switch, No. 1 instrument will be connected to No. 2, and, if placed in the right-hand hole, to No. 3. When withdrawn altogether, communication is cut off from both instruments. A large number of stations can, of course, be connected into the system by employing a larger switch. Once the application and method of working the plug switch is understood, it will be seen that it is capable of great exten- 184 TELEPHONES : THEIB COSSTBUCTION AST) FITTING. sions, and, in fact, forms the siniplest and most ready means of connecting-up instruments to meet special requirements. Several Telephone Stations cowneeted to One Central Exchange. — Figs. 176 and 177 show how several stations are connected up to a central one by means of a switch-board designed for that purpose. Fig. 176 shows the connections for boards of the form shown in Figs. 112 and 113, but Fig. 177 for the "W. E. Co.'s patterns. In Fig. 176, No. 4 station is used as the " exchange," and contains, besides the instrument No. 4, the annunciator switch-board A, local beU B, and local battery C. The annunciator switch-board A is shown in detail in Figs. 112 and 113, thus allowing the connections to be followed right through. For the purpose of following the circuit right through, let us suppose that station No. 2 wishes to communicate with station No. 3. The person at Station No. 2 first turns the handle of his generator, or if the instrument has a battery switch-beU, presses the ringing key, thus sending the current to station No. 4. This causes the shutter of No. 2 drop to fall, closing the local circuit, and causing the bell B to ring, the circuits being as follows : — Left-hand terminal of No. 2 instrument, line-wire /, No. 2 terminal of annunciator, drop No. 2, spring s\ plate b, terminal E and earth, and from there back to instrument No. 2. The shutter of the annunciator falling, closes the local circuit which runs from the carbon pole of the battery C, to beU B, terminal B of annunciator, shutter, terminal B^, and thence to zinc pole of the battery. This causes the bell B to ring, calling the attention of the person at that station, who then pushes the "plug" J underneath the spring s^, thus putting his instrument in connection with that at No. 2 station. He then rings back and inquires of No. 2 which station he requires. Having obtained this information, he connects across the slipper spring s'^ of No. 2 annunciator with that s* of No. 3 by means of a piece of flexible cord with a " plug " at each end, thus putting No. 2 station in connection with No. 3. The circuit now runs from the left-hand terminal CONNEOTIKG-UP. 185 of instramenfc No. 2 to line-wire /, terminal No. 2 of annunciator, annunciator drop No. 2, spring s^, "plug" spring s^, drop No. 3, terminal No. 3, line-wire d, instrument No. 3 and earth, and from earth back to instrument No. 2. Fig. 176. Three Stations connected to One Central Exchange. When No. 2 and No. 3 stations have finished talking, they press the ringing key or turn the handle of the generator, as the case may be, which causes the annunciator shutter to fall, thus informing the operator at No. 4 station that they have finished talking", who then pulls out the connecting plugs. 186 TELEPHONES : THEIE CONSTEUCTION AND FITTING. In Fig. 177, the form of switch-board used differs somewhat from that just described. First, there is no local bell circuit, all the calls being received on the instrument bell ; and second, when two subscribers are connected through only one of the annunciator drops is in circuit. Suppose No. 1 station wishes to speak to No. 4, the ringing current from No. 1 station passes through No. 1 drop of the switch-board direct to earth, but, on the shutter falling, is diverted through the bell on the central station instrument. The operator at the central station, hearing the bell, inserts the plug connected to his instrument in No. 1 spring Jack, and, on learning the number required, immediately plugs the two stations through by means of the two plugs seen hanging below the switch-board. One of these plugs has, it will be seen, an insulated sleeve, so that when two stations are connected through only one of the drops is left in circuit for the " ring-off " signal. Four Telephone Stations, One of which has an Indicator and Switch, and is able to communicate with the other Three as desired. — Fig. 178 shows an arrangement very useful for connecting different parts of large buildings, such as asylums, &c. In the superintendent's office, or other part of the building which it is intended to make the chief station, is placed one of the instruments (No. 4), an indicator, bell,* and special switch. The other stations are connected to the switch and indicator as shown, either an earth or metallic return being used. When the switch is in its normal position, the circuits from telephones Nos. 1, 2, and 3 run directly through the switch, and respective indicator drops and bell to " earth." If a call is received (let us suppose from instrument No. 3), then person at No. 4 instrument moves the lever of his switch to No. 3 point, which transfers No. 3 line from the indicator to No. 1 instrument. No. 1 can thus converse with No. 3, and should any of the other stations ring up No. 1 (while so talking), these calls * This bell should be a low resistance one. ( Fig. 177. ^TftTION A/»2 STATION A/SS r T-r-! r SWITCHBBflRD \BnfiTHy ST/IT/ 0/V_ A-^-f "( r?n-Ei |^^wl==^-r Jj'our Telephone Stations ioonneoted to a central one with Switchboard. CONNEOTING-UP. 187 are received on the indicator and bell, and the number of the station ringing can at once be seen from the number of the V3,ne that falls. Either a mechanical replacement or pen- Fig. 178.° tNST N? I Three Stations connected to a Central one with Indicator. dulum indicator can be used for telephones arranged thus, the pendulum form being perhaps preferable, as they require no resetting. Three Telephone Stations, arranged on the Intercommunication System. — ^Fig. 179 shows a method of arranging telephones on the " intercommunication " system — a. system or method of connecting telephones that allows of any one station being put into communication with any other on that system by the operator himself. On comparing Fig. 176, which is an "ex- change " system, with Fig. 178, the difference between the two systems will be seen. In the " exchange " system it is necessary 188 TELEPHONES : THEIR CONSTEUCTION AND FITTING. for all the other stations to oommmiicate first with the central station before they can be put into communication with one another ; but in the " intercommunication " system, the operator at each station can, by inserting a plug or moving a Fig. 179. Intercommunication System, switch, place his instrument in connection with any other on that system. Them.ethod by which this is effected in Fig. 179 is by means of special plug switches. The instruments are marked No. 1, No. 2, No. 3, and the line- wires to each instru- ment are also likewise numbered. The plug switches to each instrument are marked A, B, C respectively. In their normal position, the brass plugs of each switch are always in the holes connecting the brass blocks 1 and a, 2 and 6, 3 and c together. Now, we- will suppose No. 1 wishes to communicate with No. 3 ; to do this, he takes the brass plug from between the blocks 1 and a of the switch A and places it between a and 3 ; he is then in connection with No. 3, and after ringing him up, can carry on conversation with him. When No. 1 has OONNECTING-UP. 189 finished talking, he withdraws the brass plug from between the blocks a and 3 and inserts it back into its original position between the blocks a and 1. A similar action takes place when any of the other stations wish to communicate, the only pre- caution to be taken being to see that the brass plug is returned to its original position when conversation is finished. It will be seen that any number of stations can be connected up on this system, the number of wires between each station being n + \, where n equals the number of stations. This system is especially adapted for communication in hotels and other large buildings, though, when the distance between each station is very great, the expense becomes high owing to the number of wires required. For long distances the exchange system is the most suitable, and an automatic switch-board might be used, a form of switch-board that does away with the necessity of an operator to make the connections at the central exchange, as this is done by the subscribers them- selves by means of contact discs so arranged as to work synchronously. Three Telephone Stations mth Three-point Switch. — .Pig. 180 shows one use of the three-point switch, there being three Pig. 180. Three Stations connected as in Fig. 175, but with Three-point Switch. telephone stations, one of which can communicate with either of the other two by means of the switch. The wire at the top runs to instrument No. 1, and is connected to the middle 190 TELEPHONES : THEIR CONSTBUCTION AND FITTING. terminal of the switch S. The left-hand terminal is connected to instrument No. 2, and the right-hand one to instrument No. 3, an earth return being used for all the instruments. The switch S would be fixed close to instrument No. 2 or No. 3. When the handle of the switch is to the left, No. 1 instrument is connected to No. 2, but when moved to the right No. 1 is connected to No. 3. This arrangement is very convenient where there are two offices at one end, of a line, and it is desired to be able to communicate from either of them. Thus, when the person leaves the one office he moves over the switch, which he again moves back when he returns. For a medical man also this is very useful, enabling him to have one instrument in his consulting room and' the other in his bedroom. In this case of course the wire to No. 1 instrument would be an exchange line. The small dia- grams a and 6 show which terminals of the switch are connected together when the handle is in the two different positions. Two Telephone Stations with an Extension Bell. — Fig. 181 is an arrangement similar to that just described, there being Fig. 181. Connections for adding an Extension Bell. what is called an " extension bell," instead of the third instru- ment. This enables the bell to be placed at such a place where it might not be convenient to fix the telephone, so that the signals can be better heard. It is convenient also where the r-±i_i STfilTION N92. J I EflRTH I Fig. 182. 5 QUfiaa P»TTER.N : i B 1 2 a B WW\ Q f.Hii TTEfiM NSI TO /V«2 /VS/ TO «»S H°l TO N'i. N9IT0 V83 DIFFFHe NT POSITIONS OF 4WITCH -K I STfJTfON mi r jQl; El J \E/iRTH I t-POIMT S\NITCH Three Telephone Stations, No. 1 of which is able to communicate with No. 2 or No. 3, but not The Station not speaking to No. 1 rings up on the Extension Bell. eXTENSIOAf BELL \E^kTH I No. 2 with No. S. STATION /V22l \ef>RTH I CONNECTING-UP. 191 person who uses the instrument wishes at times to leave his oflBce for another part of the building where the bell would be fixed. 'W'hen the handle of the switch (which is a three-point one, as shown in Fig. 91) is to the left, the extension bell is connected to instrument No. 1 ; but when to the right, No. 1 is connected to No. 2. The handle of the switch must be put to the right during conversation, but returned to the left when finished. The extension bell shown is a magneto one, but the connections are similar for the battery form. Three Telephone Stations, mth Extension Bell at One Station and a Four-point Smtch.— Fig. 182 shows how three telephone stations can be arranged by means of a four-point switch, so that No. 1 can speak with No. 2 or No. 3 ; but No. 2 and No. 3 cannot communicate with one another, an extension bell being used so that the station not in connection with No. 1 can give notice of their desire to communicate. In the key diagrams at the top of the figure the connections of both the- square and circular pattern switches are shown. These switches will be found described and illustrated on page 120. It will be seen, on referring to Fig. 182, that when the handle of the switch is to the right, No. 1 instrument is con- nected to No. 2, and instrument No. 3 is in connection with the extension bell. When the handle is to the left. No. 1 instru- ment is connected to No. 3, and No. 2 instrument is on the extension bell. Both the switch and extension bell would be in the same room as instrument No. 1, and the normal position of the switch would be that shown in the figure — that is, instrument No. 2 connected to No. 1, and instrument No. 3 on the extension bell. If instrument No. 3 wishes to communicate with No. 1, he rings the extension bell, and the person at station No. 1 puts over the switch. This arrangement is some- times used in connection with a public exchange system, in order to prevent the subscriber making an illicit use of his instruments. Thus it will be seen that if No. 2 instrument is the exchange, the subscriber is enabled to communicate from 192 telephones: their construction and pitting. No. 1 instrument with the exchange, and can use No. 1 and No. 3 as a private line, but not speak from No. 3 to the exchange, which he would not be entitled to do unless he previously arranged to that effect with the Company. The form of instruments shown both in this and the following diagram will be found described and illustrated on page 78. Three Telephone Stations with a Six-point Switch and Extension Bell at the Intermediate Station. — Fig. 183 shows a very favourite way of connecting up three telephone sta- tions so that all can communicate. An extension bell and six-point switch are required at the intermediate station, as shown in the figure. Of the six-point switch there are two kinds now in general use, viz., the square and the circular pattern, the former being that most often employed. The circular pattern is described and illustrated on page 121, and the square pattern on page 122, the difference being merely in the shape, as both effect the same operations. The square pattern is shown in the diagram (Fig. 183), the terminals being "marked 1 (line No. 1), B B (two terminals for extension bell), 2 (line No. 2), E (earth), 3 (line No. 3), respectively. On page 121 the terminals of the circular pattern are marked 1, 2, 3, 4, 5, 6, passing from left to right, these being 1 (one terminal of extension bell), 2 (line No. 2), 3 (earth), 4 (line No. 1),- 5 (line No. 3), and 6 (other terminal of extension bell). Of the three telephone stations, one may be the exchange, or they may be wholly private lines. As shown in Fig. 183, the stations are represented as being all private ones and No. 2 is speaking to No. 3, the switch being in the central position. When the handle of the switch is to the left-hand side. No. 2 station is in connection with No. 1, while No. 3 station is con- nected to the extension bell, the left-hand terminal of which is put to " earth." If the switch handle is moved over to the right-hand side. No. 1 station is connected to No. 3, and station Fig. 183. Base ■|@:® Co t^ fl^ ® c ® 3® ® 1^ ^ OIPfEHef^T POSITIONS OF SWITCH U/ME N?Z L/A/S A«/ (iNTERMEOIflTE) C/A/e A/£3 I Three Telephone Stations all of which can communicate. The Station not speaking to No. 1 rings up on the Extersion Bell, by means of which Bell also Nob. 2 and 3, when connected together, can call the attention of No. 1. ' CONNECTING-UP. 193 No. 2 is unconnected with the extension bell, the right-hand terminal of which is put to "earth." When the handle of the switch is in the centre instrument, No. 2 is connected to No. 3, and instrument Na 1 is cut out of the circuit, the extension bell being looped in so that No. 1 station can be signalled to disconnect. As an illustration of the use of this arrangement when No. 2 instrument is an exchange line, we will take the case of a large , suite of offices. No. 1 instrument with the switch and extension bell would then be placed in the clerk's office, and No. 3 in that of the principal. All calls are then received and answered by the clerk, who,' if it is important, places the handle of the switch over to the right, and asks the principal if he will speak with the person calling. Should he wish to do so, the clerk moves the handle of the switch to the central position, and the clerk's office is cut out. When the conversation is finished, the clerk's office is signalled to put back the switch into its normal position, which is that shown in the figure. Fig. 184. Connections for Three Stations as in Fig. 183, but with Seven-point Switch. Three Telephone Stations with ^even-point Switch and Extension Bell, which is converted from Vibrating into Single 19i TELEPHONES : THEIB CONSTBUCTION AND PITTINa. Stroke. — Fig. 184 shows how three stations are connected up, using a battery extension bell, which is converted from vibrating into single-stroke, when the intermediate station is cut out, so as to avoid a possible break of the circuit when speaking through the contact-breaker of the extension bell. The arrangement, it will be noticed, is very similar to the one just described. A seven-point switch, however, is used, the key diagrams of which are shown in a, b, and c. A wire is taken from the frame of bell, so that when the switch is in the central position, and the intermediate station is cut out, the bell becomes a single stroke ; but when the handle of the switch is to the left or right, the bell is a vibrating one. This prevents the conversation being interrupted when station No. 1 is speaking to station No. 3 by any one accidentally touching the hammer of the bell, which would cause the spring to break contact with the contact-screw, and thus break the circuit. ( 195 ) CHAPTER X. PRIVATE EXCHANGE SYSTEMS FOE HOTELS AND OTHER LARGE BUILDINGS. As a means of establishing a ready method of communicating between the different departments of large buildings, the telephone is admirably adapted, and it is the intention in this chapter to describe one or two systems of telephonic com- munication suitable for hotels, large business houses, asylums, &c., which enable the stations in the different portions of the building to communicate the one with the other surely and with absolute despatch. For stations up to six in number the "intercommunication system," as shown in Fig. 178, is un- doubtedly the most convenient, and the one that allows of the "calling" being most quickly put into communication with the " wanted " station. It requires a large amount of M'iring, however, so that for buildings with more than six or seven Stations some other system is best employed, especially if the stations are far apart. ' In aU buildings where there are more than twelve stations there is no doubt that the most satisfactory method is to make one of the stations the central exchange, to which all the lines are brought and from which all the desired connections can be made. The station selected for the central exchange should be that one to which calls will be most often sent, as this will considerably reduce the switching. A convenient switch-board for private exchanges, up to about 50 or 60 stations, is the single-cord form, a five-station one, on which system, made by the Telegraph Manufacturing Company, 2 196 telephones: their constetjction and mtting. is shown in Fig. 185. It diflfers from the ordinary exchange system, as shown in Fig. 176, merely in the form and arrange- Fig. 185. Single-oord Switch-board, EXCHANGE SYSTEM FOR HOTELS, ETC. 197 ment of the exchange switch-board, in which one or two modifications are introduced. By referring to Fig. 176 it will be seen that when one station rings up, the operator at the exchange, after ascertaining the number, has two " plugs " to insert— one for the "calling," and the other for the "wanted" station. This, although it only requires one or two double plugs, necessitates two operations and a consequent loss of time. With the single-cord switch-board there are an equal number of connecting plugs and plug-cords as there are annunciator drops or subscribers' lines, and on the operator at the exchange receiving the number required, she at once inserts the plug of the "calling" in the "wanted" station spring-jack, and the two stations are " through." Referring to Fig. 185, it will be seen there are five annun- ciator drops at the top of the board, below this a similar number of spring-jacks, and at the bottom and supported on a small projection the connecting plugs. The plug-cords have a weighted pulle}' attached, so that when released they fall back into the convenient upright position shown. The mode of operating is as follows : — Suppose No. 2 station rings, No. 2 annunciator falls and the operator inserts her plug in No. 2 spring-jack. She then ascertains what number is required, which, let us say, is No. 5, and the operator on hearing this inserts No. 2 plug in No. 5 jack, presses her ringing key (thus ringing the beUs at both No. 2 and No. 5 station), and the two stations are in communication. It will be seen from this that the connections and disconnections are made in a very short time, allowing a better service, while at the same time the operator's work is considerably reduced. Moreover, should one plug-cord fail the other is available ; for instance, if Nos. 2 and 5 wish to communicate, either No. 2 plug can be inserted in No. 5 jack, or No. 5 plug in No. 2 jack ; in both cases Nos. 2 and 5 would be connected together. Another form of switch-board, much used for small private 198 TELEPHONES : THEIE C0K8TBUCTI0N AND FITTING, exchanges, is shown in Fig. 186, this form of board being also very suitable for stations arranged on the intercommunication system, in which case there is a switch-board at each station. Beneath the annunciator drops are, it will be seen from the Fig. 186. Bar Switch-board. figure, five horizontal strips of metal, which are crossed at the back by six vertical ones, one from each drop. All these metal bars are perfectly insulated from one another, and are bored with a hole at each point where they cross. Thus it will be seen that by inserting a metal plug in any of the holes the corresponding horizontal and vertical bars are connected, and by inserting the plug in the correct hole any one station can be connected to any other. EXCHANGE SYSTEM FOR HOTELS, ETC. 199 The SooifeTE GfeNiiRALE des TliLifiPHONES System. This system, which is somewhat extensively used for hotels, &o., on the Continent, is one of the few in which absolute secrecy between the stations in communication is obtained. One of the most common objections urged against the exchange system of communication is that you can never be sure that part or even the whole of the conversation is not overheard either by the operator at the exchange, or in the intercommunication system by some inquisitive person at any of the other stations. For it will be seen, by referring to Fig. 176 and Fig. 178, that the operator at the exchange can, by sliding in the plug, place his instrument in circuit with the other two, and this without either of the speakers being aware of it. Similarly, on the intercommunication system, any one at either of the remaining stations can, by inserting the plug or moving the handle of the intercommuni- cation switch, throw his instrument into circuit with any of the others. Thus the speaker is afraid to trust to the telephone matters of importance, and must either go to or summon the person to his presence, a proceeding likely very often to cause considerable inconvenience. In the system about to be described, however, there are none of these objections, and each station can, moreover, when put through, signal to the other station direct, as well as to the central station. In Fig. 189 are shown four stations connected on this system, though any number can of course be similarly arranged. In the figure, Nos. 1, 2, 3, and 4 are the instru- ments at the different stations, A the switch-board at the central or switch-room, B the local bell, and D the battery, which can be located anywhere in the building, but should be preferably near the switch-board. The telephone instrument is shown, with its inside connec- tion, in Fig. 187, and the switch-board in Fig. 188. 200 telephones: theib constbuction and fitting. The telephone instrument, it will be seen from Figs. 187 and 189, is of a similar form to that shown in Kg. 60, p. 75, except that it has two ringing buttons, a black and a white one. The telephone is not shown in Pig. 187, but hangs Interna,! Connectioiis of Instrument. when not in use on the two switch-hooks a and a' at the bottom. A separate bell is required with each instrument, though in some forms a buzzer is placed inside the wooden case. The switch-board (Fig. 188) consists of a polished wood case, in which are contained the annunciator drops m\ n\ «*, and n*, the connecting plugs m', m^, m^, and m*, the ringing keys k\ k\ 1any is mainly that of single wires with "earth" return and Western Electric multiple switch- boards, except in the small exchanges, where standard boards, either double or single cord, are used. The wires from the subscribers to the exchange are run overhead, and the sub- scribers are provided with magneto switch-beU instruments of the form shown in Fig. 70. The different towns in each district are rapidly being connected one to the other, so that a subscriber in one town can speak with another in a town 50 or 60 miles away. For instance, London is in tele- phonic communication with Brighton, Birmingham, and Manchester, as well as Paris ; while the neighbouring towns around these first three centres are also connected, so that in a few seconds one subscriber can be switched on to another in any of these towns. These lines connecting the different towns or different exchanges in a town are called " tmnk " lines, to distinguish them from the subscribers' lines. Complete metallic circuits are always employed for trunk lines to get rid of inductive noises, and as a further pre- vention the wires are run on some twist system after the manner shown in Kgs. 158 and 159. The exchange system PUBLIC EXCHANGE SYSTEMS. 211 most widely used is that of the Western Electric Company, a description of which will now be given. The Western Electric Company's Multiple System. This system is specially adapted for coping with very large numbers of subscribers, and as the number increases, so fresh sections can easily be added to the board. It can be employed with either single or double wires, though in this country, as used by the National Telephone Company, single wires and earth returns are almost always used. The frontispiece shows a part of the Berlin exchSinge, which is fitted throughout on the Western Electric Company's system, and Fig. 194 shows a portion of the multiple switch board (also made by the same company) at the National Telephone Company's Brighton exchange, with which exchange the writer was formerly connected. The Berlin board differs slightly from the Brighton one, the former being a single and the latter a double cord. Before the invention of multiple switch-boards, public telephone exchanges in this country were worked similar to the method shown in Fig. 176, all the subscribers' lines being terminated at a large board, having an annunciator and spring- jack for each line. One or two of the operators sat at tables provided with instruments by means of which they answered the calls of the subscribers, and on learning the numbers required called them out to other operators at the board, who then made the necessary connections. This method answered very well when there were only a few subscribers, but as the number increased, the noise and confusion arising from such a mode of operating necessitated other means being adopted. The first improvement was to allot to each operator fifty or one hundred lines which terminated at her board, and to which number she had to attend, answering the calls of the subscribers and making all the necessary connections. This arrangement P 2 212 telephones: theik consteuction and fitting. is illustrated in Fig. 195, which shows nine subscribers con- nected to the central exchange to two standard boards, five to one board, and four to the other, the boards for simplicity being shown diagranunatically and without drop-or operators' instruments. Fig. 195. s e 7 e 9 CI ibi:rs BOARD N° I. EXCHANGE Standard Switch-board. BOARD N? 2. It will be seen that No. 4 on Board 1 is connected to No. 8 on Board 2, connection being made by means of the separate spring-jacks M and N, and the wire T. The great disadvantage in this method is that any sub- scriber not on one operator's board had to be asked for from another, and connection made between the two boards by PDBLIO EXCHANGE SYSTEMS. 213 means of a special wire, an arrangement that means consider- able loss of time ; and it was not until tie introduction of the multiple switch-board that a quick and comparatively silent service was obtained. The principle of the multiple switch-board will best be under- stood by referring to Fig. 196, which shows nine subscribers connected up to the central exchange on this system ; though it must be borne in mind that this figure does not show the actual method of connecting up the spring-jacks. The board is divided into sections, and a certain number of subscribers' lines (generally about 200) are allotted to each section, these lines being terminated in the diagram at the local spring-jacks. In addition to this the line of every subscriber whose wire runs into the exchange passes at the back of all the sections and is connected to the "ordinary " spring-jacks as shown in Fig. 196. Thus the operator at each section can connect any one of the subscribers allotted to her to any other subscriber on the exchange without moving from her place. In Fig. 196 the nine subscribers are allotted three to each section. Section No. 1 takes wires 1, 2, and 3, section No. 2 wires 3, 4, and 5, and .section No. 3 wires 7, 8, and 9, these wires being marked with the letter m'to distinguish them from the wires running to the ordinary jacks. In section No. 2 it will be noticed No. 6 subscriber is connected to No. 4, and in section 3 No. 8 subscriber to No. 9. We will now proceed to a more detailed description of the multiple switch-board, which derives its name from the fact that the points at which connection can be made to any one line are multiplied. Eeferring to the Brighton board, shown in Fig. 194, it will be seen that it is divided into sections or tables, only two of which sections are shown. Strictly speaking, the build of this board differs slightly from the usual pattern, being put together in half instead of whole sections, which ha;lf sectix)ns can be seen by the joins in the woodwork. This, however, does not affect the general construction or working 214 telephones: theib constbuction and fitting. of the board. Each section is divided into four panels, and in the panels of each section are fixed the ordinary spring- jacks, the circular openings of which only are visible, these jacks being arranged in five rows of 20 in each panel, making Fig. 196. ' SUBSCRIBERS 3 4 5 6 SECTION K'.l. SECTION N? 2. SECTION N?3. EXCHANGE Multiple Switch-hoard. 400 altogether. Beneath these jacks are the 200 local spring- jacks, to which are connected the wires of those subscribers that terminate in that section. Immediately below the local jacks and on a ledge about 6 inches wide can be seen 40 pairs of connecting plugs, the cords of which pass down behind the PUBLIC EXCHANGE SYSTEMS. 215 board and are visible underneath. These cords are weighted with pulley weights, which cause the plugs to stand in a vertical position and prevent the cords from twisting. Under- neath the plugs will be seen in each section of the board 200 annunciator drops, one for each subscriber's line that terminates in that section, and immediately below these 40 smaller annun- ciators, one of which is in circuit with each pair of plugs. These 40 annunciators are called the " clearing-out " or " ring- off " drops. On a projecting ledge below these drops are 40 switches, in front of which are 80 ringing keys, two to each switch, these switches and ringing keys being also in circuit with the plugs. When the lever of a switch is depressed it puts the operator's instrument in connection with that pair of cords corresponding to the lever depressed. The operator's receivers can be seen hanging up by the annunciators, and the transmitters (Blake's) are supported by brass standards from the ledge carrying the plugs. It will be noticed that there is ample room above the ordinary spring-jacks for more to be added, and as the number of subscribers increases a strip of the woodwork is taken out of each panel, and 200 additional spring-jacks added to each section. Another section is also added at the end of the board to take the terminating wires of these new subscribers, so that the length of the board continually in- creases, and this fact should be kept in view when selecting a room for exchange purposes. The size of the space for the ordinary spring-jacks determines the ultimate number of subscribers the board will carry, or, what is called its " ultimate capacity." The ultimate capacity of the Brighton board is 2000 subscribers. An enlarged ^n.ew of the spring-jack with the connecting plug in place is shown in Fig. 197, the plug being indicated by the dotted lines. The jack consists of the metal body B, to which is attached the spring m and pin n, both of which are perfectly insulated from the metal body. A hole is bored 216 telephones: theie constbuction akd fitting. in the shank g, of the jack, through which passes the point of the plug when inserted for the purpose of making a connection. In its normal position the spring m presses firmly against and makes contact with the pin n, but when the plug A is Fig. 197. Spring- jack with Plug. inserted it is moved into the position shown by the dotted lines. This causes the spring to make contact with the end of the plug and break contact with the pin n, the spring m also making connection with the metal body of the jack through the point of the plug. The jack is inserted in the woodwork of the switch-board till the flange t comes flush with the surface, leaving only the opening exposed as in Fig. 1 94. The connections of the spring-jacks on difiierent sections of the board will best be understood by referring to Fig. 198, where the wire of No. 6 (see Fig. 196) subscriber can be followed through the spring-jacks of three sections of the board. The wire of No. 6 subscriber passes first though the ordinary jack No. 6 of section No. 1, next to ordinary jack No. 6 of section 2, then to ordinary jack No. 6 of section 3, and lastly to local spring-jack and annunciator, No. 6 in section 2, and thence to "earth." No. 6 being one of the wires allotted to section No. 2. If the operator at any of the sections has a subscriber who wishes to speak to No. 6 she inserts the plug on one end of the connecting cord into the local jack of the "calling" subscriber and the other into spring-jack No. 6. The effect of this is to raise the spring m PUBLIC EXCHANGE SYSTEMS. 217 (see section 1, Fig. 198) off the contact n and connect it to the plug, and the two subscribers are through, the spring m also being connected to the metal body of the jack as before described. Fig. 198.' SECTION N»t SECTION NO 2 SECTION N9 3 Connections of Spring-jacks. This brings us to one of the most ingenious points of the board, that is the " engaged test." It is obvious that as there are numerous places in the switch-room where a line may be connected, some means of readily ascertaining whether the " wanted " line is already in use becomes indispensable. The way in which this is done in the Western Electric Company's board is simple, ingenious, and eflScient. On referring to Fig. 198 it will be seen that all the spring-jacks on every section of the board are connected by a separate insulated wire as showii by the dotted lines, and this wire is called the " test wire." So long as all the spring-jacks of the one number are without a plug in them this wire is perfectly insulated, but on inserting a plug (as shown in section, 1 Fig. 198) the test wire, it will be seen, gets " earthed " through the subscriber's line. In the line circuit of the operator's instrument is an 218 telephones: their constktjction and fitting. extra cell called the test cell (see Fig. 199), so arranged that if the operator touches the metal body of the " wanted " line spring-jack with the end of the cord to which she has previously connected her instrument by pressing down one of the switches, a "click" will be heard in her receiver Fig. 199. CLEARINfi OUT DROP Connections of Plugs in Multiple Switch-board. should the line be engaged. This click is caused by the test ceU getting a complete circuit in one direction through the " caUing " subscriber's, and in the other through the " wanted " subscriber's instrument, by way of the metal frame of the spring-jack and test wire. The clearing-out drops, ringing keys, &c., are in circuit between the two plugs of each connecting cord as in Fig. 199, which shows how the different parts are generally connected up in the multiple board. The table switch has two positions. In its normal position, the top and bottom springs make contact with the centre plate, but when the lever is moved, the springs make contact as in the figure. With the switch in the position PUBLIC EXCHANGE BTSTEMS. 219 shown, it will be seen, the circuit runs from one plug to the other through the ringing keys, switch, and operator's instru- ment, but with the switch in the other position, both plugs are connected to earth through the clearing-out drop.* The back ends of the plugs when they are not in use make coptact with metal plates in connection with " earth." The method of operating the board is as follows : — ^Let us suppose subscriber No. 75 wishes to speak to No. 120. Sub- scriber No. 75 turns the handle of his generator and drops the shutter of No. 75 annunciator at the exchange. The operator (in whose section No. 75 happens to be) at once inserts one of the plugs in No. 75 local jack, and pressing down the switch corresponding to the number of the connecting cord she is using takes off the receiver and asks the number required, in this case No. 120. She then takes the plug on the other end of the cord, and touches it momentarily on the hole of No. 120 subscriber's spring-jack, thus getting connection on to the metal body of the jack. Should she hear a click she knows the line is in use, and informs No. 75 that the line is at present engaged. If no sound is heard on touching the spring-jack she at once pushes the plug home, and pressing down one of the ringing keys rings the bell of subscriber No. 120, and the two subscribers are through. The operator listens until she hears the conversation commence, when she pulls over the switch lever and cuts off her instrument from those two subscribers. When the conversation is finished, the subscribers turn the handles of their generators, thus dropping the shutter of the " clearing-out " drop corresponding to the connecting cord in use, and the operator at once withdraws the two plugs. It will be seen from Fig. 199, that when either of the ringing keys is pressed a current is sent to that subscriber's line to * The clearing-out drop when connected as in F^. 199 ia in a branch circuit to " earth," the drop being of a, special form called .a " retardation drop." In the older forms of boards the clearing-out drop ia in series with the two plugs. 220 telephones: their constbuction and fitting. which the plug happens to be connected. This ringing current is furnished either by a magneto generator kept running continuously by a water motor, or by a battery of ten or twelve gravity cells in conjunction with a pole-changer. A pole- changer is a piece of apparatus so arranged that the current from the battery as it passes through it is sent first in one direction and then the other, one moment the positive pole of the battery being to " line " and then the negative. The unidirection current of the battery is thus transformed into an alternating one suitable for ringing the magneto bells of the subscribers. For the trunk lines between the different towns, double wires without " earth " are, as was before mentioned, always employed, chiefly because were an " earth " return used on these long lines, the noise arising from induction from neigh- bouring wires would quite overpower the speech. On the London and Brighton trunk line, for instance, the line runs for about 50 miles in close proximity to the telegraph wires on the railway, and when a trial was made of a single wire with earth return, the inductive noises were very loud, a rapid " click, click " being the predominating sounds. Double wires, however, run on some cross-over system, as shown in Fig. 158 completely do away with the trouble from induction, as the effect on the " line " wire is neutralised by that on the " return." A difficulty that presented itself first connec- ting up the different towns was how to connect the sub- scribers' Hues to the trunk wires without putting "earth'' on to the trunk wires and thus destroy their freedom from induction. For instance, the subscribers in London and Brighton have single exchange wires with earth returns, while the tinink line is a complete metallic circuit, and it is evident that to connect the subscribers direct to the trunk line is to at once put it to " earth." This difficulty is overcome by employing at each end of the trunk line a translator, the connections being as shown in Fig. 200 PUBLIC EXCHANGE SYSTEMS. 221 The translator consists of an induction coil, the two circuits of which are wound with an equal number of turns, and have about the same resistance. The one circuit is connected to the trunk wires, and the other to the subscriber's line as shown, the currents in the one coil being reproduced in the other by induction, with of course a slight loss. Thus the trunk line, it Fig. 200. SU3SCRIBER TOWN N? 1 TRANStATOB EXCHANGE TRUNK LINE b TRANSLATOR ~ EXCHANGE TOWN N? 2- SUBSCRIBI.Ri cti Trunk Wires between Towns, will be seen, consists of a complete loop and is not affected by the earth return of the subscribers while the subscribers' Knes do not require to be altered in the least. In some of the later forms of translators the efficiency of conversion between the two coils is so good that the subscribers are enabled to ring as well as speak through them. 222 telephones : their constkuction and fitting. The British Post Office System. This system, which is in successful operation in Newcastle, Sunderland, and numerous other towns, has several novel features, the most prominent of which is the employment of a permanent current that retains the shutter of the annun- ciator at the exchange in position, and keeps the needle of a special indicator deflected. This current is utilised in con- junction with the annunciator and indicator, 1st, to enable the different subscribers to call the exchange ; 2nd, for the " ring-off " signal ; and 3rd, it forms a permanent indication of the condition of each subscriber's line. MetaUic circuits are used exclusively, and the instruments employed are the Gower-Bell (as described on page 82) with Daniell batteries for ringing. The system wiU best be understood by referring to Fig. 201, which shows diagrammatically three stations and a portion of the switch-board at the exchange. The two lines of each subscriber terminate at the spring-jacks S', S", and S'", in the switch-board, and the indicators N', N", and N"', with an annunciator (not shown in the figure), are included in each circuit. The indicators consist of a pivoted needle that is deflected by a current, and the annunciators are so arranged that the shutter is only held up so long as a current is passing through it. Normally the two spring-jacks are in contact with each other as shown by those of line No. 1, but when the operator wishes to join any two subscribers together, he slides in the special connecting plugs P and P', thus separating the two springs which make contact with the top and bottom plates of the plug respectively. The method of working is as follows : — A Daniell battery is placed at each subscriber's instrument and the switch-hooks so arranged that so long as the hearing tubes are hung up the batteries are in circuit, and a current passes continually from the subscribers' instruments through the annunciator, spring- jacks, and indicators at the exchange, deflecting the needles PUBLIC EXCHANGE SYSTEMS. 223 of the. indicators N. When any station wishes to call the exchange, all that it is necessary to do is to lift up the hearing N? I Fig. 201. .SUBSCRIBEK N? 2 N°3 British Post Office System. tubes, which cuts off the permanent current, thus causing the shutter of the annunciator to drop, and the needle of the 224 TELEPHONES : THEIH CONSTRUCTION AND FITTING. indicator to go back to its central position. The operator then plugs in his instrument and ascertains the number required, on hearing which he calls the wanted station and puts the two stations through as shown in Fig. 201, where No. 2 is talking to No. 3 while No. 1 is inactive. This calling of a subscriber is effected by sending a powerful ciurent from the exchange, which actuates the relay in the subscriber's instru- ment, and rings his bell, the armature of the relay being kept off by a stiff spring so as not to be affected by the permanent current. No: 2 and No. 3 stations being talking the tubes of the instruments are off their hooks and the permanent current cut off, which state of affairs is disclosed to the operator at the exchange by the needle of the indicator not. being deflected. When the two stations have finished they replace the hearing tubes, switching on the permanent current, and the operator seeing the needles deflect, at once withdraws the connecting plugs from the spring-jacks. The connecting plugs are flat^shaped, and so arranged that they can only be placed in the spring-jacks the right way, that is, top plate to top spring, and also so connected up that when two plugs are put in, as P and P', the top spring S" is connected to the bottom one S'", and the bottom spring S" to the top one S "', otherwise the permanent ciurrents of the two instruments would, when the two subscribers hang up their tubes, oppose one another. This system is an excellent one for small exchanges, and one that is capable of giving great satisfaction to the subscribers, though the expense of keeping up so many DanieU cells makes it somewhat costly to maintain. The Fkench System. In the exchange system used in Paris, like in the one just described, metallic circuit and battery switch-beUs are used. All the wires are placed underground, being made up into con- venient cables and run in the excellent and capacious sewers PUBLIC EXCHANGE SYSTEMS. 225 for which the city is noted. Special hooks are fastened into the roofs of the sewers on which hooks the cables are hung. Each subscriber's instrument is provided with two ringing buttons, with the one of which he calls the exchange and with the other he can (when put through at the exchange) signal direct to any other subscriber, similar to the private exchange system shown in Figs. 188 and 189. In signalling and talking to the exchange, or when talking to any other subscriber, the metallic circuit is used, but when one subscriber signals to another by means of the direct call key the two wires are connected together so as to form one, and an earth return is used. The manner in which this is effected is shown in Fig. 202, which shows diagrammatically two subscribers' instruments with their annunciators and jacks at the exchange. Only the ringing keys of No. 1 subscriber's instrument are shown, and the jack at the exchange is illustrated as two separate holes for the sake of clearness. In reality the two contacts are com- bined in one hole, the plugs having two insulated parts that make contact with them in the ordinary manner. The method of operating is as follows : — No. 1 subscriber, to call the exchange, presses the button A of his exchange call key, which puts the top spring to one pole of the battery, and the .bottom one to the other. This sends a current through the metallic circuit and drops the shutter of the annunciator at the exchange. The operator at exchange then inquires the number wanted, and on learning this plugs No. 1 and No, 2 through as shown in the figure. Nos. 1 and 2 can now signal direct to one another without affecting the exchange. For if No. 1 presses the button B of his direct call key he depresses the three springs, putting one pole of his battery to " earth " and the other to both of his lines, the current passing through the two lines as one, through the exchange, and to earth through the relay of No. 2 subscriber's instrument, thus ringing his bell. The annunciators at the exchange are, it will Q 226 telephones: theie constbuotion and pitting. be seen, in a shunt circuit to the jacks (when two subscribers are connected through), and their resistance is so proportioned that the subscribers after having finished can, by pressing their ANNUNICIATOtt Fig. 202. EXCHANGE N?l JACK EXCHANGE CALL KEY a 1 n rOt^ n DIRECT CALL KEY 'im i SUBSCRIBER N'\ N?2 NUNICIATOR The French System. N?2 I "ST m ^ SUBSCRIBER N° 2 exchange keys, drop the shutters of both their annunciators as a "ring-off" signal. When no plugs are in, each subscriber's aunnnciator forms part of his metallic circuit. PUBLIC EXCHANGE SYSTEMS. 227 This being able to signal direct from one subscriber to another without affecting the exchange is a great convenience, since one knows that any delay after having been informed by the exchange that you are " through " can only be occasioned by want of attention on the part of the other subscriber. The speaking between two subscribers is of course on the metallic circuit, all earth being cut off by the ringing keys and the switch-hooks. The Law System. This system was devised by Mr. F. Shaw, of the Law Tele- graph Company, New York, the object of the inventor being to simplify the exchange apparatus, and by enabling the sub- scribers to put themselves at once into communication with the operator at the exchange to secure a more rapid service. This is effected by providing in addition to the subscriber's direct wire to the exchange a " call " or " service " wire, which after leaving the exchange passes from one subscriber to another, thus joining them aU in series as in Fig. 203. Twelve subscribers are shown connected to the central exchange, and are numbered 1, 2, 3, 4, 5, 6, &c., the call wire being indicated by the heavy black line and the direct wires by the thin lines. The method of operating is as follows : — At the exchange the operator sits with a special form of telephone clasped to her head, this telephone being in circuit with the call wire on which she listens continually for calls. Every subscriber is provided with a special switch, by means of which he can connect his instrument to his own direct exchange line or loop it into the call wire. Each subscriber, therefore, when he wants to speak to another, moves his switch so that his instrument is looped in the call wire, and on taking off his receiver finds himself in direct communication with the operator at the exchange. He then makes known his requirements by saying (presuming No. 20 wishes to speak to No. 75) " 20 to 75," which numbers the operator repeats to Q 2 228 TELEPHONES : THEIK CONSTRUCTION AND FITTING. show that she has heard, and having rung the bell of No. 75 by sending a current from the exchange, immediately plugs the direct wires of Nos. 20 and 75 through. No. 20 then moves back his switch, putting his instrument on to his direct exchange wire, and speaks with No. 75. At the close of the conversation one of the subscribers switches his instrument on Fig. 203. EXCHANGE artial break or disconnection somewhere in the circuit. A trans- mitter will often speak through a high resistance contact or partial disconnection where a battery-bell would not ring, since a very small current is required to work the receiver, and the fault might be of too high a resistance to let sufficient pass for the bell, but quite enough for the receiver, the current for which is of a higher E.M.F. If the switch-bell is of the magneto form, it is probable that the generator, if a good one, would ring through any resistance that the transmitter would speak through. Signalling! good in both directions, hit cannot make Distant Station hear. — ^The fault here is probably in the local circuit of the home-station instrument. Examine transmitter ceU and test with galvanometer (thick wire coil), to see if it is in good condition. If this is so, inspect microphone, and also local circuit switch, which may not be making good contact. Should this be all right, the fault is probably in the primary of induction coil, which should be tested with galvano- meter for continuity. Should all be found in good order at home station, inspect receiver at distant station, where iron filings or dust may probably have got between the pole-piece and the diaphragm. SignalUng good in both directions, but cannot hear at Some TESTING FOR PAXTLTS. 247 Station. — This fault is similar to the one just described, and is probably due to some disarrangement in the local circuit in the instrument at distant station. Test as described for the previous fault. To ascertain whether the fault is at the home or distant station, join terminals L and E (that is " line " and " earth "), take receiver off the hook and holding it to your ear, gently tap with your finger the diaphragm of the transmitter, which should produce a loud sound in the receiver. If this is so, the fault is probably at the distant station ; but if the tapping produces no noise, examine receiver, where the fault will most probably be found. Signalling good in both directions, hut cannot hear at either Station. — The fault in this case may be either in the primary or microphone circuit of both instruments, or in the primary circuit and receiver of one instrument. It would also be caused by a break in the secondary circuit of the coil and its connections at either station, or the automatic switch may be at fault. To ascertain at which station the fault is, join terminals L and E with a short length of wire, take receiver off the hook, and holding it to your ear, tap the diaphragm of the microphone. If this produces a loud sound in the receiver the fault is at the other station ; but if no noise can be heard the fault is at your own station. Proceed to locate the fault as follows : Take the receiver oif the hook, and place to your ear. Next momentarily connect terminals C and L with a short length of wire, and if you get a sound at the moment of connecting, the trouble is in the microphone or primary of induction coil and its connec- tions. If you get no sound, inspect the automatic switch, and see that it makes good connection with the top, or telephone circuit contact. If you find no fault here, take away the receiver cord and replace it with two wires, and if you get a sound now the trouble is in the cord, which ' must be replaced by a new one. If the receiver still appears dumb, connect across the two ends of the secondary of the coil, and then 248 TELBEHOKES: THEIB CONSTEUCTION AND FITTING. join C and L as before. If you get a soiind in the receiver now, the fault is in the secondary windings of the coil. If you get no sound, the fault is in the primary of coil or micro- phone and its connections. Having traced the fault to the primary or local circuit, we have now to find out the exact spot. To do this first inspect the local transmitter cell to see that it is in good condition, and also inspect the local contact breaker of automatic switch, and note that it makes good connection. These being aU right, take your galvanometer (using the thick wire coils and stiU keeping the receiver off the hook), fasten one wire on to the terminal C, and with the other touch in succession difiierent points of the local circuit, noting the deflection. Should at one place no deflection be obtained, the fault will be found between that point and the one last touched. Presum- ing there is a fault found in the local or primary circuit at one instrument^ there must still be another in the secondary or receiver circuit to account for the speech not being received from the other end ; unless, of course, there is a fault in local circuit of both instruments. When looking for faults in the local circuit of the Blake transmitter, it should be, noted that the spring carrying the carbon button and the one with the platinum point do not touch one another except at the platinum point. It is advisable also to test with a galvano- meter and battery to see that the iron frame and diaphragm are insulated from one another, as contact between these would prevent the microphone working properly. While testing a piece of paper must be placed between the carbon button and platinum point. Partial BreaMown. Ringing and Speaking in both directions faint. — The most probable cause of this woidd be a partial break or high resistance connection in the circuit. Join ter- minals L and C to test yoiu' bell, and afterwards join terminals L and E, and take off receiver, tap diaphragm of transmitter while listening in receiver. If the sound is loud and your TESTING FOE FAULTS. 24.9 bell rings all right, the fault is at the other station or in the "line."' Test similariy at other station, and if that instru- ment is in good order the line or earth-wires are at fault. If the bell did not ring when terminals C and L were joined, and the instrument seemed dumb when you joined terminals L and E, go carefully over the connections of the instrument, looking more particularly to all moving contacts. Dust or film of dirt in the contacts of automatic switch may be the cause of the trouble. Total Breakdown. Cannot ring or speak in either direction. — The most probable cause of this is either a broken line or earth-wire. It would also be caused by " full earth " on the line-wire — i. e.the line- wire has got into direct communication with earth. Join terminals L and C to test the bell, and also terminals L and E, as described for the previous fault. If the instrument is in good order disconnect the " line " and " earth " (L and E) terminals, and test with the battery and galvano- meter both wires in succession, using a temporary earth-wire for the purpose. If no deflection is obtained with the earth- wire the wire is probably broken or corroded at some point, and this n^ust be found and repaired. If the fault is in the line-wire, this must be located by testing, as follows : — Locating a " Break " in an Underground Wire. — When locating a break or disconnection in an underground wire where an " earth " return is used, the wire at one end of the line must be disconnected from the instrument while the other is left connected up. One end of the line thus makes earth though the other is perfectly insulated. Now taking the portable testing set, and starting from the end of the line that is put to earth, proceed to the most accessible point and dig up the wire. Next put one of the poles of the battery to earth, which can be done by driving an iron rod into the moist ground, and connect the other to one terminal of the detector, using the fine wire coils. A short length of wire must also be joined to the other terminal of the detector. 250 TELEPHONES : THElK COKSTfiTJCTlON AND FITTINCt. Now with a knife remove the covering of the wire (taking care not to nick the wire or remove more covering than is necessary to expose the copper), and touch the wire from the detector on the exposed place. If (when the wire is touched on) a movement of the detector needle is obtained the wire is intact between the place tested and the end of the Una put to earth, but if no deflection is obtained the wire is broken in this part. Care must be taken to see that a good earth con^ nection is made by the iron rod. If the circuit is complete so far proceed to the next convenient place ; having first well insulated the bared place on the wire with rubber solution and tape. Here we go through the same operation, and if the circuit is complete proceed to the next, and so on imtil no deflection of the detector needle is obtained, when the break will be between this place and the one last tried at which detector showed a deflection. From this place we then work backwards till the fault is found. It must be borne in mind, however, that this test is no good if the insulation of the line is faulty, and it makes earth anywhere, which should be pre- viously ascertained. Locating a Leak to " Earth." — If the fault is a leak to earth instead of a break, disconnect the line wires from the instru- ments at both ends of the line before commencing to test. Then proceed to the most accessible point in the wire (prefer- ably where there is known to be a joint), and having arranged the detector as described for the previous fault, cut the line wire, and touch one end of the wire from the detector first on one end of the Hne and then on the other ; the part which gives a deflection being the faulty wire. Difierent places must then be tried in the faulty part till the fault is localised. Always make perfectly swre, however, before proceeding to pull yoiu: line-wires to pieces that the fault is really in the Une- wires and not in either of the telephone instruments, as cutting and re-insulating the wires is not particularly beneficial to the insulation of the line. ( 251 ) INDEX. A. Action of Blake transmitter, 24 eleotrio bell, continuous ringing, 111 , differentially wound, 113 ' , short circuiting, 112 , single stroke, 110 , vibrating, 109 — — Leclanohe battery, 129 lightning-arrester, 71 magneto bell, 100 magneto generator, 100 microphone, 20 receiver, 2 Ader receiver, 11 transmitter, 27 Armature shunts, 103 Automatic switch-hooks, 69 Batteries, 127 Battery, Leolanche (porous pot form), 128 , (agglomerate block form), 130 , (6-block agglomerate form), 135 , position of, 132 , inspecting, 133 Battery, recharging, 134 , setting up, 133 Battery, table of B.M.F. and resistances of, 134 bells bell, church bell shape, 115 , circular, 114 , continuous ringing, 111 , differentially wound, 113 ."Shield," 115 , short circuiting, 112 , single stroke, 110 , vibrating, 109 boxes, 136 faults, 132 switch-bells, 56 Bell receiver (single pole), 3 (double pole), 5 Bennett's electrostatic call wire, 232 Berliners transmitter, 37 Berthon transmitter, 37 Binding wire on insulator, 149 Blake transmitter, 23 Brackets for insulators, 141 Biitish Post Office system, 222 Buzzing noise in transmitter, 239 C. Call wire systems, 227 Charging batteries, 133 Chimney brackets, 149 Clearing-out drops, 218 252 INDEX. Collier receiver, 17 Complete telephone instrument, 73 , Ader, the, 88 . , Bell-Blake, the, 84 , Crosisley, the, 86 Complete telephone instrument, dif- ferent forms of, 74 , Gower-Bell, the, 82 — , for divers, 95 , for fire-brigades, 96 , for military use, 91 , for naval purposes, 92 , Johnson, the, 89 Connections of plugs in multiple board, 218 , spring-jacks, 217 Continuous ringing bell, 111 Cross-talk, 157 Crossley transmitter, 86 D. D'Arsonval receiver, 14 Detector galvanometer, 207 Diagrams of the different ways of con- necting up telephones, 168 Simple telephone circuit, 169 Two instrumenfs, with battery switch - bells and magnetic receivers, 169 Two instruments, with magneto switch - bells and magnetic receivers, 172 Two instruments, with battery switch-bells, microphones, and receivers, 173 Connections of Gower-Bell tele- phone, 176 Connections of Ader telephone, 177 Two instruments, with magneto switch-bells, microphones, and receivers, 178 Diagrams — continued. Three telephone stations in series, 181 Three telephone stations, one of which is able to communicate with the other two, as desired, 183 Several telephone stations connected to one central exchange, 184 Four telephone stations, one of which has an indicator, and is able to communicate with the other three, as desired, 187 Three telephone stations, arranged on the intercommunication system, 188 Three telephone stations, with three- point switch, 189 Two telephone stations, with an extension bell at one of them, 190 Three telephone stations, with an extension bell, and four-point switch at one station, 191 Three telephone stations, all of which can communicate, there being an extension bell and six- point switch at the intermediate station, 192 Three telephone stations, arranged as above, but with seven-point switch, which converts extension bell from vibrating to single stroke, 194 Diagrams of different exchange systems, 214 The standard switch-board, 213 The multiple, 214 The Law system and its modi- fications, 227 The French system, 224 The British Post OfBce system, 222 The "Secret Circuit" intercom- munication system, 206 Dip of spans, 146 INDEX. 253 Double reoeivera, 15 shackles, 140 Draw-vice, 145 B. Earth connections, 163 wires, 163 ' English Mechanic ' receiver, 8 Erecting poles, 152 telephone lines, 137 Exchange systems, private, 195 , public, 209 F. "Faults," 235 in batteries, 243 in receivers, 241 in switch-bells, 242 in transmitters, 239 in the " line," 243 Bell at "home" station does not ring, ringing at " distant " station good, and speaking good in both directions, 244 Bell at "home" station rings, but cannot reply, speaking good in both directions, 245 Bell at "home" station does not ring, and no call can be sent to "distant" station, speaking good, 246 Signalling good in both directions, but cannot make "distant" station hear, 246 Signalling good in both directions, but cannot hear at "home" sta- tion, 246 Signalling good in both directions, but cannot hear at either station, 247 Partial breakdown. Kinging and " Faults " — oontinued. speaking in both directions faint, 248 Total breakdown. Cannot ring or speak in either direction, 249 Locating a "break" in an under- ground wire, 249 Locating a leak to " earth," 250 Fire pot, 145 Fixing overhead wires, 144 poles, 152 Fixing shackles, 148 Four-point switch, 120 G. Galvanometer for testing, 237 German Post Office transmitter, 33 Gower-Bell telephone, 83 receiver, 10 transmitter, 26 Granulated carbon transmitters, 34 Hickley receiver, 14 Hughes microphone, 20 Humming of wires, 154 Hunnings transmitter, 35 I. Induction, 155 Induction coils, 39 Inside wires, 162 Insulators (single slied), 138 (double shed), 138 binding wire on, 149 Intercommunication systems, 205 Johnson transmitter, 29 , complete instrument, 8 Joining up instruments, 166 254 INDEX. K. KinkB in wires, 145 Leading-in wrreB, 160 , insulator for, 161 Leading-in tube, 161 Leakage, 155 Leolanche battery, 127 , porous pot form, 128 , agglomerate block form, 130 , six block form, 135 , inspecting, 133 Leolanche battery, position of, 132 , setting up, 183 , recharging, 134 — , box for, 136 Length of spans, 146 Lightning-arresters, 71 Line-wires, 137 Liverpool switch-bell, 60 Locating faults, 244 Long-distance telephony, 97 London and Paris telephone line, 97 M. Magneto bell, 107 , construction of, 108 Magneto generator, 99 , action of, 100 , automatic cut-out of, 103 , construction of, 102 Magneto switch-bells, 64 Membrane receiver, 7 Microphone, the, 20 , action of, 21 , two-pencil forms, 53 , patents, the, 43 Military telephones, 91 Miller's returned call wire, 231 Multiple switch-boards, 211 method of operating, 219 , principle of, 214 N. National Telephone Company, 75 . , switch-bell, 60 ' — , instruments used by, 83 O. Overhead wires, 137 , crossing streets with, 143 , dip of, 146 , paying out, 144 , vicing-up, 146 , way-leaves for, 143 Patent, the Bell receiver, 73 , the carbon transmitter, 19 Patents, the different microphone, 43 , Blake's, 48 , Crossley's, 51 , Edison's, 43 , Hunnings', 47 Paying-out wire, 144 Plugs, 218 Plug switches, 122 Pole-chairs, 151 Pole-clips, 153 Poles, wood, 152 , iron, 150 , erecting, 152 , on roofs, 150 , in the country, 152 Portable testing set, 238 Private exchange systems for hotels,&c., 195 Private telephone line, 1 Proper way to pay out wire, 144 INDEX. 255 Public exchange systems, 209 , WeBtern Electric Com. pany's, 211 , British Post Office,222 , the French, 224 , the Law, 227 , the Mann, 229 R. Receiver, Ader, 11 , Bell, (single pole), 3 (double pole), 5 , Collier, 12 , D'Arsonval, 12 , ' English Mechanic,' 9 , double, 16 , Gower, 10 , Hickley, 14 , Siemens, 16 , " ■Watch," 7 Receivers, 1 , action of, 2 Relays, 116 Sag of spans, 146 Searching for a fault, 235 Secret circuit systems, 206 Shackle straps, 140 Shackles, 139 , fixing, 148 Ship telephones, 92 Short-circuit electric bell, 112 Single cord switch-boards, 196 Single-stroke bell, 110 Sloper intercommunication switch, 208 Spans finishing oflf, 148 Special applications of the telephone, 91 Spoon-shape receivers, 15 Spring-jacks, 216 Standard switch-boards, 212 Swinton's transmitter, 32 Switch, ordinary form, 118 , three-point, 119 , four-point (extension bell), 120 , six-point (intermediate), 121 , plug form, 121 Switch-bells, 56 Switch-boards, 196-211 Switch-hooks, different forms of, 68 Switches, 118 Swivels, 151 T. Telephones for army use, 91 diving purposes, 95 fire brigades, 96 mines, 94 ship use, 92 Testing for " faults," 234 Thompson's transmitter, 33 1'hree-number switch-board, 123 Three-point switch, 119 Translator, 221 Transmitter, Ader, 27 , Berthon, 37 , Berliner, 37 , Blake, 24 , Crossley, 28 , Gower, 28 , Johnson, 29 , German Post OflSce, 34 , Hunnings, 85 , Swinton, 32 , Thompson, 33 Transmitter induction coils, 39 Transmitters, 19 Trunk lines, 221 U. Underground wires, 158 , testing for faults io, 234 Undulating currents from microphone, 22 256 INDEX. Valve miciophone, 33 Vibrating electric bell, 109 , adjusting, 109 , construction of, 109 Vicing-up a span, 145 W Wall brackets, 141 " Watch " receiver, 7 Wayleaves, 143 Western Electric Company's Hunnings, 36 — multiple system, 211 Wires, earth, 163 , inside, 162 , leading-in, 160 , overhead, 137 , underground, 158 LO:iDOH : PEIKTED BT WUilAM CLOWES AND SONS, LIMITED, 6TAUF0BD STBEBT AMD CBABINQ CBO^.