The Practical Telephone Handbook J.POOLE. BOUGHT WITH THE INCOME PROM THE SAGE ENDOWMENT FUND THE GIFT OF Henir|9 W. Sage Z891 ..A...^i72/....: ?/.2:/i.L The date shows when this volume was taken. Cranes and LiflE^iacnineryf^^™^^ 2s. 6d. Crellin's Bookkeeping, \s.6d. Key,zr. Crests, Fairbairn, 3/. 3^-. Crosby and Bell's The Electric Rail- way, los. dd. Cunarders (New), ds. Canning's Cabinet Making, 5^. Designing, Leland, is. Dictionaries, Technological. Discount Tables, is. Dissections Illustrated, Brodie. Part I., %s. dd. Part II., \Qs. Part III., los. Part IV., \os. In One Volume, 2/. 2.s. Drainage, Beardmore, 5j-. Nadieine, \s. Drawing and Designing, is. Dredge's Electric Illumination, Vol. II., 30J. Mod. Fr. Artillery, 50J. Pennsylvania Rlwy., 52^. dd. Drum Armatures, "js. 6d. Dynamo, Hawkins and Wallis, los.dd. Bottone, 2s. 6d. How to Manage, Bottone, l^. Building, Walker, 2s. Machinery, Hopkinson, 5^. &c., Kapp, 10s. dd. Dynamos, Continuous Current, £5. Education, Practical, ds. Eglestcn's Metallurgy, 2 vols., 31 J. dd. each. [others, 30J. Electric Illumination, by Dredge and Influence Machines, 4J-. dd. ■ Lamps, Fleming, Is. dd. Light Cables, Russell, "js. dd. Light Carbons, is. dd. Light Distribution,Russell,7j.672 46 Gower , 73 47 D'Arsonval , 73 LIST OF ILLUSTRATIONS. 48 D'Arsonval Transmitter, 74 49;De Jongh , 74 50 Mix c& Genest • , 75 Si' , 75 52 Hunnings , 76 53 Marr , 78 54 Brass Frame of, 78 55 Berthon Transmitter, 79 56 Roulez , 79 57 Berliner Universal , 80 58 Thornberry Long-distance, 81 59 Electric Bell, 85 60 " Silvertown " Switch-bell, 87 6l , 88 62 — Switch Bells joined to Line, 89 63 " Liverpool " Switch-bell, 90 64 Pedestal or Desk Instrument, 91 65 Connections of Relay, 92 66 Post Office Pattern Relay, 93 67 Magnets and Pole-pieces of Magneto Switch-bell, 95 68 . , 95 69 Armature of Magneto Bell, 96 70 End View, 96 71 Post Pattern, 98 72 Driving Gear of W. E. Co.'s Magneto, 99 73 Polarised Bell, 101 74 , loi 75 Automatic Switch, 103 76 , 103 77 Another Form, 104 78 , 104 79 Lightning Arrester, 105 80 ■ — : Another Form, 105 81 Post -Office Pattern, 106 82 Connections of Magneto-bell, 106 83 Magneto Switch-bell Complete, 107 84 Interior View, 108 85 Magneto Desk Set, 108 86 Carty's Magneto-bell, Connec- tions of, 109 87 Wall Drill for Plugging, 113 88 Three Magneto Stations on One Line in Series, 114 89 in Shunt, 115 90 Poole's Intermediate Switch, 116 91 Simplified, 117 92 Miller's Intermediate Switch, 118 93 ."9 94 Connections of, 119 95 Double-bar Switch, 120 96 Two-way Switch, 121 97 , 121 98 , 121 99 Bennett'sTwo-way Switch, 121 100 Drop Indicator, 122 loi V/. E. Co.'s, 123 102 Ironclad, 124 103 Poole's Small Switchboard, 125 104 W. E. Co.'s- 126 105 Spring-jack for above, 127 106 Switchboard Plug, 127 107 Connections of W. E. Co.'s Switchboard, 128 loS Crossbar Switchboard, 130 109 William's Slide Switchboard, 131 Section, 131 no III 112 113 114 Ii5 Dewar Table-switch, 136 117 . 137 118 .New Double-contact Spring Gilliland Switchboard, 132 ■ — Full View, 133 "Standard" Switchboard, 134. Connections of, 135 13s 119 jack, 138 . 138 of Single-cord 120 Connections Switchboard, 139 121 Subscribers' PJug for Single- cord Switchboard, 140 LIST OF ILLUSTRATIONS, 122 Operators'Double-plugSwitch- board, 140 123 Connections of Operators' Set, 140 124 Ericsson's Operators' Set, 142 125 Poole's Contact Breaker for Switchboard, 143 126 Gray's , 143 127 Domestic Switchboard, 144 128 Connections for above, 145 129 Another form of Domestic Switchboard^ 146 130 One Section of Manchester Multiple Switchboard, (to face) 149 131 Werner Table-switch, 150 132 : . 151 133 Connections of Subscribers' Line to Multiple Switch- board, 152 ■ Operators' Set, 153 134 .. , . 13s Set of Spring-jacks, 154 136 ,iSS 137 Forming Block for above, 157 138 Section of Cables in Position, 158 139 Plan of Cables in Position, 159 140 Connections of Single-cord Multiple-board, 160 141 Post-Office Gower Bell. Tele- phone Set, 162 142 Interior View, 163 143 Connections, 164 144 Drop Indicator, 165 14s , 16S 146 — : Spring-jack and Plug, 165 147 Connections of Post - Office Switchboard, 166 148 Poole's Ring-off Button, 168 149 , 168 150 View of Manchester Switch- room, (to face) 169 151 Connections of Call-Wire for Law System, 171 - 152 Mann's—- , 172 FIG, 153 Carbon- Lightning Arrester and Test-plate, 173 . 154 Subscribers' Connections, New Telephone Company, 174 155 Part Section of a Switchboard Square , 175 156 Cross Section of Complete Switchboard , 176 157 Connecting Plug New Tele- phone Company, 177 158 Connections for Engaged Test, , 178 159 . : 179 160 Call-wire Connections - at Exchange, 180 161 Connections for "Bolton' System, 181 162 Poole's Test-board, 184 163 , 184 164 , 184 165 Lightning Arrester Board, 185 166 Single Test-shoe for Use on Test-board, 186 167 Double ■ , 186 168 Distributing-board, 187 169 r , 187 170 Arrangements for Running Cross-connecting Wires, 188 171 General View of Test-board, (to face) 190, 172 Coleman-Jackson 'sTest-board, 191 173 , 191 174 Another Form of Test-board, 191 175 , 191 176 Magneto-generator for Power- driving, 192 177 W. E. Co.'s Pole-changer, 193 178 , 194 179 Another Form of Pole-changer, 194 180 Galvanometer with Polarised Needle, 195 LIST OF ILLUSTRATIONS. FIG. 181 Connections for Testing In- struments, 196 182 Cordeaux's Screw Insulator, 203 183 Binding Wire to Insulator, 1!04 184 Langdon's Insulator, 205 185 Bennett's Insulator, 205 186 Double Shackle Insulator, 206 187 Erection of Pole, 208 188 View of Top of Pole with Arms, etc., 210 189 , 210 190 Pole with Stay Attached, 211 191 Trussed Pole, 212 192 Chimney Bracket, 213 193 Bennett s Iron Standard, 214 194 Arm of Above, 216 195 Section, 216 196 Bennett's Methoa of Trussing Iron Standard, 217 197 Details of Above, 218 198 , 218 199 Clayton Standard, 218 200 Plan, 219 201 Bennett's Arm Extender, 219 202 Draw-vice for Erection of Lines, 220 203 Britannia joint, 221 2C4 Method of Suspending Cable, 224 205 Twist System for Metallic Circuits, 229 206 , 229 207 for Four Circuits, 230 208 Cross System for Metallic Circuits,Bennett'sMethod, 231 209 Diagrams for Cross System, 232 210 Bennett's Translator, Diagram of Connections, 233 211 Coleman- Jackson's Translator, 212 Connections for Working Single-wire Trunks, 236 FIG. 213 Connections for Working Single - wire Trunks, Coleman-Jackson's Trans- lator, 237 214 Section of Submarine Cable for London and Paris Tele- phone Line, 240 215 Man-hole for the Underground Conduits, 258 216 Man-hole for Underground Work, National Tele- phone Company, 261 217 Connections for Mixed System Switchboard, 264 218 Metallic-circuit Spring-jacks, 265 219 Operators' Connection for Mixed System, 266 220 Engaged Test, W. E. Co.'s Multiple Switchboard, 267 221 Spring-jack Connections of National Telephone Co.'s Multiple Switchboard,269 222 Operators' Connections for ,270 223 W. E. Co.'s Self-restoring Drop, 271 Showing Call, 272 224 — 225 Section of Spring-jack for W. E. Co.'s Branching System, 272 226 Connecting Plug 273 227 Connections for Self-restoring Drop, 273 228 Operators' Connections for Branching System, 274 229 Testing , 275 230 Junction Line Connections of National Telephone Com- pany, 277 231 277 232 Loop arranged for Multiplex Working, 278 233 Two Loops ,279 234 Somerville & McLean's Call- wire Plan, 279 LIST OF ILLUSTRATIONS. FIG. 235 Bennett's Ring-off System, 281 236 Poole & Maclver's Call-office Apparatus, 284 237 Interior, 285 23$ Smith & Sinclair's Apparatus, 286 239 Mix & Genest's - -, 288 240 Theatre Arrangements, Paris, 290 241 Man- chester, 292 242 Diagram of Fall of Potential, 296 243 Connections of Wheatstone- Bridge, 297 244 Post-Office Pattern of ,297 245 ■ , Plan, 298 246 Battery Reverser, 300 247 , Plan of, 301 248 Loop-test for Fault, 301 249 .Another 250 Plan, 302 ■ Contact, 303 251 Insulation Test byWheatstone- Bridge, 304 252 Kelvin Reflecting Galvano- meter, 305 253 Lamp and Screen for 306 254 View of Shunt-box, 307 255 Plan of 308 256 Connections for Galvanometer Constant, 308 257 Insulation Resistance, 310 Diagram No. 1. — Connections for Three Sets of Instruments. No. 2. — Six Sets with Central Switch, No. 3. Four Sets by Domestic Switchboard. No. 4.— Ten Stations by "General" Domestic Switchboard. Note. — The above Diagrams will be found at end of book. FIG. 258 Standard Condenser 259 Kempe's Discharge Key, Side Vie 260 /lew, 313 Plan, 313 for Capacity 261 Connections Constant, 314 262 Test, 315 263 Connections for Battery Re- sistance, 317 264 Munroe's Method, 318 265 , 318 266 Running's "Cone" Trans- mitter, 322 267 Section, 322 268 Skeleton Form, 323 269 323 270 " Solid-back " Transmitter, 324 271 Marr's , 325 272 The " lol " , 325 273 Johnson's with Con- nections, 326 274 Collier's Receiver, 328 275 . 328 276 , 328 277 Mercadier's Bitelephone Sec- tion, 329 278 . , as used, 330 279 Microtelephone, 331 280 Table Set, Con. Tel. Co.'s, 331 281 , Ericsson's, 332 282 Post-Office " Universal " Set, 333 283 Connections, 334 284 Railway Set, 335 285 Trotter's Wire Gauge, 336 286 , 336 287 Poole's : , 337 288 , 337 PRACTICAL TELEPHONE HANDBOOK. CHAPTER I. PRELIMINARY. Before proceeding to the subject proper, it will be advisable to define the various terms used by tele- phonists, so that no misunderstanding may afterwards arise as to their correct meaning. Electric Current. — When electricity is in motion, or is propagated from one point to another, certain effects are produced upon adjacent bodies. These effects — magnetism, motion, heat, chemical changes, etc. — are said to be due to an electric current. As electric currents are the only currents that will be dealt with in this book, no misunderstanding should arise if the term electric is dropped. Strength of a Current. — This is measured by the magnitude of the effects produced in a certain time. 10 PRACTICAL TELEPHONE HANDBOOK. Resistance. — An infinite variety of strengths of current may be obtained by including different substances and different masses of these substances in the path of a current. The cause of the various strengths is due to the different resistances which these materials oppose to electricity in motion. All bodies offer some resistance, which is found to be in direct proportion to the length of any material of uniform section and quality, and inversely proportional to the area of section or to the square of its diameter. Resistance also varies with the temperature of the material, that of metallic bodies increasing with a rise of temperature, and that of non-metallic bodies decreasing, of some, such as carbon, very markedly. Conductivity. — Substances, such as the metals, which offer the least resistance are called good conductors, or are said to have a good conductivity. This term is there- fore the converse of resistance. Of the metals, pure silver and copper offer the least resistance. If that offered by a piece of pure silver is taken as the unit, the resistance of the more common metals and other substances will be approximately as follows : — Pure Silver i „ Copper I -04 „ Platinum 574 „ Iron 6-04 „ Lead i2"8 „ Mercury 59 „ Carbon 1,450 to 40,000 pRELiMmARY. a Liquids, Dilute Sulphuric Acid {i^ acid) 2,062,000 Pure Water 44,000,000 Glass 14,000,000,000,000 Gutta-percha 2 1 o,ooo,ooo,coo,ooo,ooo,ooo Insulators. — From this list it will be seen that glass and gutta-percha offer an immense resistance to the passage of the current, therefore these, and substances such as porcelain, india-rubber, and ebonite, are selected to confine the current to a certain path by acting as supports to the conducting materials. They are there- fore called insulators, and are of great importance in practical electrical matters. Potential. — The strength of the current which can pass through a path of a certain resistance depends upon the difference between two points of that path, in regard to what is called the potential of the electricity. This is a property of electricity analogous to the pressure of steam or level of water in regard to their power of doing work. The greater the difference in level of two reservoirs of water, the stronger will be the flow of the water through a certain sized pipe from one to the .other, and the more work could be done by this flow. So with electrical currents, the greater the difference of potential between any two points of a con- ducting path, the stronger will be the current along that path. Potential is sometimes called electrical pressure. Electro-motive Force. — Any arrangement which can produce a difference of potential is said to have an electro-motive force, which term is usually abbreviated to E.M.F, There are many methods of causing a 12 PRACTICAL TELEPHONE: HANDBOOK. difference of potential, such as by means of voltaic batteries, magneto-electric machines, and dynamo machines. Volt. — Difference of potential, or E.M.F., is compared by reference to a practical unit called the volt, a little less than the E.M.F, of a Daniell cell, which is ro65 volts. The Leclanch4 cell has an E.M.F. of i'46 volts. The Ohm is the unit in which all measurements of resistance are expressed. It is the resistance of a column of mercury io6'25 centimetres long, and one square millimetre in section at a temperature of o° centigrade. A better idea of this I'esistance will be obtained by giving the length of some common materials offering I ohm resistance, such as — 2*48 feet of copper wire sJo-inch in diameter. This is the size of wire used for winding most telephone receiver bobbins. 430 feet or 143 yards of copper wire xVinch diameter, which is the wire used for the lines of telephone exchange subcribers. 71 feet of iron wire ^ inch diameter. Very high resistances are measured in Megohms. One megohm = one million ohms. Ampere. — The unit strength of current is called the ampere, and is such a current as would be sent through a resistance of i ohm by an E.M.F. of i volt. The Milliampire, equal to the lAiith part of an ampere, is often used as a unit in telephony. PnEUMINAkY. 13 The Circuit. — The whole path through which a generator of electricity sends a current is called a circuit. It always forms a closed loop. When a current is passing the circuit is said to be closed, or complete. When the continuity of the conductors is broken by interposing an insulating body, the current ceases, and the circuit is said to be open, or broken. Some current, however, passes through substances of the highest resistance, so that the above only applies to the useful current. Earth. — The circuit may be made up of different substances. In most cases it is made up of wires, but even bad conductors, such as earth or water, may form part of a useful circuit when in large masses. For economy, the earth is often used to complete a circuit for a telephone connection, in order to save a second wire between the places connected. In making such a connection it is of the utmost importance that a con- ductor having a large surface in contact with the earth or water should be used as a medium of connection between the wire and the earth. For this purpose the water pipes of a town's water supply are always chosen. If they are not available, large iron or copper plates are buried in damp ground, and the circuit wires connected to them. By a metallic circuit is meant one of which the earth does not form a part, being made wholly of metal. -Metallic circuits are becoming more extensively employed, because the use of the earth for telephonic working brings many disadvantages with it. 14 , PRACTICAL TELEPHONE HANDBOOK. If in an ordinary circuit different conductors follow one after the other, these conductors are said to be joined up in series. The resistance of a circuit is the sum of the resistances of its different parts joined up in series, and includes the resistance of the generator itself, called its iiiternal resistance. A circuit may be divided into several branches, which must all come together again at some point. These branches are called derived, divided, branch, or shunt circuits. A current flov/s through a divided circuit in proportion to the conductivity, or inversely proportional to the resistance of each branch. Resistance of Divided Circuits. — If each branch of a divided circuit is equal, the combined resistance of them all will be equal to that of one branch divided by the number of branches. If they are unequal, their combined resistance will be equal to the reciprocal of the sum of the reciprocals of the resistances of the several branches. The reciprocal of a number is unity, or one, divided by that number. The reciprocal of 20= i^ror 'OS, that of 30=3^ or -033, and the reciprocals of '05 and "033 = 20 and .30 respectively. Suppose a divided circuit made up of two wires whose resistance are 20 and 30 ohms. The combined resistance of the two wires would be equal to the reciprocal of A + aV. ^+^=2^^o and the reciprocal of this = .?^P-° =12; 20x30 A 20+30 ' or, working by decimals, •05+"033 = -o83, the reciprocal of which = 1 2 as before. Short Circuit.— K derived circuit of very low resist- PRELIMINARY. 15 ance compared to the resistance of the other branch or branches, is called a short circuit. It robs the other circuits of nearly all current. Ohm's Law. — This law is the most important one in electrical matters, and states : — That if the resistance of a circuit be expressed in ohms and the total E.M.F. in volts, then the strength of the current produced will be given in amperes by dividing the latter by the former. If R represents resistance in ohms, E the volts, and C amperes, the relation between the three will be expressed by C = ^ or E=CR or R = g so that, given any two of these quantities, the third may be easily obtained. Ohm's law applies to any portion of a circuit, as well as to a whole circuit. Magnetism. — Magnetic Lines of Force. — The reader will be familiar with the beautiful curves in which iron filings sprinkled over a card covering a magnet set themselves, as shown in Fig. i . At the poles or strongest points the lines are clustered together, and spread out from these points in symmetrical curves. These curves are only sections of the magnetic field surrounding the magnet, and show the direction in which the magnetic action extends, and in which small magnetic needles free to move would set themselves. A piece of soft iron in the neighbourhood of the magnet modifies the magnetic field, and the curves are altered in shape, appearing to be attracted to the iron, so that a greater number of the lines pass through the space occupied by I6 PRACTICAL TELEPHONE HANDBOOK the iron than there did formerly. In passing through the iron the lines of force convert it into a magnet. These lines of force have become of the greatest corir sequence to electricians, and the idea of them is much employed in magnetic measurements. The intensity of magnetism at any part is proportional to the number of Unes of force which pass through a certain unit space. Fig. 1. Magnets. — The simplest form of magnet is the straight bar magnet. Horse-skoe ones are, however', much stronger, the poles being close together and the lines of force clustered together between them. They have about three or four times the attractive power on a piece of soft iron near their poles that a bar magnet of the same size would exert. FRELlMlMARV, \1 Thin bars or plates of steel can be more powerfully magnetised in proportion to their weight, therefore when a strong permanent magnet is required it is generally- made up of several thin plates, producing what is called a compound or laminated magnet. The plates are usually bound together by pieces of soft iron, which form the pole-pieces. Some compound magnets have been made which would carry a load equal to 25 times their own weight. The best cast steel, with an addition of 3 per cent, of tungsten, makes the best magnet steel, the value of which depends upon what is called its coercive force, or its resistance to cha,nge in its magnetic state. This coercive force is the greater the harder the steel is tempered. By a process, however, of subjecting the steel to very great pressure, M. Clemandot has given a high coercive force to it, with the advantage that the metal can be filed, turned, etc, without impair- ing its magnetic value. Magnetising. — The best method of magnetising is by means of a strong electro-magnet furnished with a large pole-piece. The steel is drawn over the pole, always in the same direction, some 20 or 30 times. Small magnets, such as the needles of galvanometers, are liable to lose their magnetism from various causes, such as lightning discharges or strong currents. For such purposes it is much better to use a soft iron needle polarized by means of comparatively large magnets fixed near. Currents Induced by Magnets.— Fa.rada.y's discovery that electric currents could be caused to flow through a C i8 PRACTICAL TELEPHONE HANDBOOK. coil of wire by the approach or recession of a magnet is of the greatest service in telephony, Bell's original telephone being based upon it. These induced currents are only momentary ones, lasting as long as the move- ment. They are in strength proportional to the strength of the magnet, the speed of its movement, and the number of turns of wire in the coil. The direction of the currents is dependent on which pole of the magnet is used, one producing opposite currents to the other. Also the currents produced by approach are opposite in direction to those produced by recession of the same pole. Relative motion is all that is necessary, so that the same effects are produced by moving the coil to or from the magnet. Faraday showed that to produce the currents it was necessary that the number of lines of force passing through the coil should vary with the movement, and that the strength of the induced currents was proportional to this variation. Lenz's Law is applicable to all electrical induced effects, and states : — That " the induced currents have such a direction that their reaction tends to stop the motion or current which produces them." Current Induction. — Wires conveying electric currents also exhibit magnetic properties, and are surrounded with a magnetic field and lines of force. A section of this field may be shown by passing a wire conveying a strong current vertically through a horizontal card and sprink- ling iron filings over the card, the filings will arrange PREUMtNARY. tg Ihemselves in concentric circles round the wire, as in Fig. 2, which gives a plan of the card and section of the wire. Each filing is really made into a magnet by the lines of force passing through it, and a small freely suspended magnetic needle would set itself as a tangent to one of the circles. When the wire is bent into a circle, a large number of these lines of force come together in the interior, and the magnetic action there is consequently more intense than in the case of a straight wire, and is still further increased when the wire makes a number of turns and forms a coil. The Electro-magnet is constructed on this prin- ciple, the lines of force passing through the soft iron core inside the coil or coils, rendering it power- fully magnetic. The practical points in connection with electro- magnets are as follows : — The cores, armature, and other ironwork should be made of the softest iron, well ■annealed, and should not afterwards be turned or filed, so that it may be rendered strongly magnetic by the current, or, in other words, have a high degree of .permeability, and may lose as much as possible of its •magnetism on the current ceasing. To attain the latter s V Fig. 2. 26 Practical telephone handbook. object it is necessary that the armature be prevented from coming into actual contact with the iron of the cores, which would allow the magnetic circuit to be completed if a horse-shoe magnet, and would give rise to the sticking of the armature, due to the residual magnetism which would exist after the current ceased. To prevent this sticking it is usual to drill small holes in the ends of the cores, in which are inserted core pins of brass wire, projecting very slightly past the ends of the core. The number of turns of wire on the coils should be large when the magnet has to form part of a circuit of high resistance. This entails the use of thin wire for winding. When for a circuit of low resistance it is best to use thick wire, but the number of turns should be as large as the bobbin will allow. The wire in the coils (if there are two) must be con- nected up in such a manner that the windings would be continuous in one direction if the magnet were straightened out. In the Galvanometer a small magnetic needle takes the place of the core of the electro-magnet. It is so pivoted inside the coil that by gravity, or the earth's magnetic action, it tends to set itself in a line with the direction of the wire forming the coils. When a current passes through the coils, its magnetic action tends to set the needle at right angles or along the axis of the coil. The galvanometer mostly used in telephonic work for testing batteries, tracing faults, etc., is shown in Fig. 3, PRELIMINARY. 21 and is called a lineman's detector. The magnetic needle is inside, that outside being merely a pointer attached to the same pivot. It is generally furnished with two coils of wire : one, consisting of a few turns of thick wire, used for roughly measuring low resistances, such as the internal resistance of a battery; the other coil is made up of a large number of turns of thin wire, having a resistance of lOO or 200 ohms. The latter coil is used for testing circuits of a high re- sistance, and for roughly measur- ing the E.M.F. of batteries. The Induction Coil is made by winding over an electro-magnet coil another coil, usually of fine wire, with a large number of turns. Whenever the current in the electro-magnet ox primary "' coil of wire is started or stopped, or its strength varied, induced currents are produced in the other or secondary coil if the circuit of the latter is complete. The starting or strengthening of a current has the same effect as bringing up a magnet to the coil, and the stopping or weakening, the same effect as taking away the, magnet from the coil. The strengths of the induced currents depend upon the number of turns of wire on both coils, and the rate o variation in the strength of the magnetising or primary current. The cores of induction coils are usually made up of a bundle of thin iron wires, in order to reduce the Fig' 3. 22 PRACTICAL TELEPHONE HANDBOOIC, reactive effect on the primary current, and because it has been found that such cores gain and lose magnetism more quickly than solid ones, and a greater rate of variation in the magnetism can therefore be obtained. Induction of Straight Wires. — Owing to its magnetic action, a current passing through a straight wire will induce currents in another wire running parallel, when the current is varied in strength. The current induced on starting or strengthening the primary one is in the opposite direction, that on stopping or weakening in the same direction. The reaction of the induced currents weakens and opposes the primary ones, according to Lenz's law. The strength of the induced currents depends upon the rate of variation of the primary cur- rent, the distance apart of the wires, the lengths they run together, and the insulating substance or dielectric between them. The induction through dry air is less than when any other substance intervenes between the wires. What is called the inductive capacity of air being unity, that of resin=i7, glass i'9, paraffin vgZ, india-rubber 2"8, and gutta-percha 4*2. It is important to consider these values in connection with cables for telephone wires, and, if otherwise possible, to choose a substance which has the least inductive capacity, and so keep down the inducing action between the wires. Self-induction. — Any wire conveying a current may be looked upon as made up of a multitude of small wires connected together, each conveying a portion PRELIMINARY. 23 of the current. Each of these small currents reacts momentarily on the others whenever its strength is varied, tending to oppose them. This is called the self-induction of a current, and its power depends upon the shape of the conductor. Anything which tends to separate the contiguous portions, such as flattening the wire or stranding the conductor — that is, making it up of several small wires — reduces the self- induction. Electro-magnetic Inertia, — The magnetic property of iron wires has a harmful influence on currents rapidly varying in strength which pass through them. Such are the currents which pass through the telephone ' wires in conveying speech. A part of the energy of such cur- rents is wasted in magnetising the material of the wire. The weakening is said to be due to the electro-magnetic inertia of the wire. Both self-induction and electro-magnetic inertia are met with in a high degree in connection with electro- magnets. Each turn of the coil acts on the other turns as though it were an independent circuit, and thereby produces intense self-induction, which is much increased by the magnetisation of the core. The magnetising of the core also robs the current of much of its energy v/hen it rapidly varies in strength. In consequence of the above action of electro-magnets much attention has lately been drawn to the injurious effects of introducing them into a telephone circuit. Their action is said to be due to an impedance in the path of the currents, which weakens the transmitted 24 PRACTICAL TELEPHONE HANDBOOK. speech very materially. The more iron there is in connection with the electro-magnets, the more marked is the evil. Making up the cores of soft iron wires reduces to some extent the impedance of the electro- magnets. Static Induction. — The inducing effects hitherto mentioned have been due to dynamical or magnetic action, but somewhat similar results are produced by the statical electric action of one conductor on another. This action has considerable importance in telephonic matters. Every current passing through a wire charges it with static or frictional electricity, the charge depend- ing upon the potential of the current, the surface of the conductor charged, the proximity of other conductors, and the specific inductive capacity of the substances intervening between the conductors. This charging weakens the original current, especially when very rapid variations of potential are concerned, its effect being especially marked in cables where the conductors are close together. It is principally this which prevents telephonic speaking through any long length of sub- marine cable. On overhead land lines its effect is comparatively small, as the conductors are wide apart and are separated by air, which has the least inductive capacity. It seems very likely, however, that most of the overhearing on land lines is due to static induction. Microfarad.— The unit of capacity is the Farad, but the practical unit is the one-millionth part of this, called the microfarad. About three miles of submarine cable will have one microfarad capacity. PRELIMINARY. 25 Wire Gauges. — Wires were formerly compared in size by the Birmingham wire gauge, but its unreliability — from the fact that several different gauges existed, all professing to be the B. W. G. — led to the British Board of Trade issuing what is called the British Imperial Standard Wire Gauge, a list of some of the sizes of which, compared with the most reliable B. W. G., is given at the end of the book. The Mil. — A better way of comparing wires is to give their diameter in thousandths of an inch, which are called mils. ^_^^ This mil must not be I (2) . confounded with the French millimetre, which is equal to about 40 mils. A micrometer gauge is necessary to measure in mils, and a very convenient one for the purpose is shown full size in Fig. 4. It is worked by a fine screw, and easily measures to half a mil. Another convenient way of designating the size ol uncovered wire is by its Weight per mile. This method is adopted to a large extent in the telegraph and telephone service. Ohm-mile. — Multiplying the weight of one mile of wire of a certain material by its resistance a number is obtained which is constant for that material, and is known as the Ohm-mile, as it represents the weight of one mile of a wire of that material measuring one ohm Fig. 4. 26 PRACTICAL TELEPHONE HANDBOOK. resistance. The resistance of a mile of any other wire of the same material can be at once found by dividing the constant by its weight per mile, or its weight per mile is obtained by dividing by its resistance per mile. The constant for the hard-drawn copper wire used for telephone lines is 892, or, roughly, 900. That for the silicium bronze wire generally used for telephone lines may be taken at 1950. Copper Wire. — The following are very useful formulae for the calculation of resistance, etc., of pure copper wires, the diameters being given in mils : — 1. The resistance per mile of a wire d mils in diameter = ^'^^"^ "^ legal ohms. 2. The weight per mile = -r-, — lbs. 3. The dia. of a wire weighing n lbs. per mile = -/« X 7'9i mils. 4. From (i) the resistance of a wire one foot long and one mil dia. = iO'2 ohms ; from which is obtained : — 5. The resistance of a wire / feet in length and d mils in dia. = ^°^J^ legal ohms. If the wire is of any other metal than copper its resistance may be obtained by multiplying the resist- ance obtained for a copper wire of equal size (by No.i or No. 4 formula), by the number giving the com- parative resistance of the metal on page 10. The above formulae only hold good for wire at a temperature of 60" F. or 15" C, but are sufficiently accurate for rough purposes. PRELIMTN-ARY. VJ TJte Percentage Conductivity of any wire is the con- ductivity of that wire compared with one of the same dimensions of pure copper, at the same temperature, taken as lOO. It is obtained by multiplying the calcu- lated resistance of the pure copper wire by lOO, and dividing the product by the actual measured resistance of the wire in question. For such calculations as the above the Wiring Tables of W. T. Glover & Co. are very useful, as they give a large amount of information in regard to pure copper wires of the various gauge sizes, such as the relation between their diameteri, weights, resistances, lengths, etc., of the greatest value to telephonists. Attention may also be called to the special and useful forms of wire gauges sold by the same firm. These are illustrated . in the Appendix, CHAPTER n. BATTERIES USED IN TELEPHONY. The elementary facts in regard to voltaic cells, it is pre- sumed, will be known t9 the reader, therefore practical points will be mostly referred to in connection with t lem. The qualities which it is desirable a cell should possess may be summed up as follows : — 1. It should have a large E.M.F. 2. This should remain constant in working. 3. Its internal resistance should be small. 4. This also should be constant. 5. The materials it consumes should be cheap. 6. There should be no waste of these materials when the cell is not in use, that is, no local action. 7. Its condition should be capable of being easily inspected. 8. It should be easily refreshed. 9. It should not emit offensive fumes. 10. Its first cost should be smaU. No one cell is known which unites in itself all the BATTERIES USED IN TELEPHONY. 29 above qualities. Each cell has its special advantages ; so it becomes a practical question to decide which are the most important conditions necessary for any particular purpose. For ordinary telephone work the most important qualities are Nos. 5, 6, and 9; but Nos. i, 7, 8, and 10 are also of tra- portance. No cell has yet been found which unites these qualities so well as the Leclanche, which, therefore, is almost universally used for tele- phonic purposes. Its only fault is that it is deficient in constancy when heavily worked. Polarization. — The dif- ferent kinds of cells .in use represent so many methods of preventing polarization, caused by a deposit of hydrogen Fig. 5. gas on the electro-negative plate, which increases the resistance of the cell, and opposes the original current, by tending to send one in the opposite direction. The Leclanche, Cell. — The ordinary form is made up of a glass vessel of the shape shown in Fig. 5. Into this a zinc rod, provided with a connecting wire, is 30 PRACTICAL TELEPHONE HANDBOOK. placed. Inside the glass vessel is a cylindrical pot of porous earthenware containing a carbon plate, round which is packed a mixture of about equal parts of carbon and needle binoxide of manganese broken into pieces of about the size of peas, care being taken to prevent dust being included. The carbon plate is provided with a lead cap and terminal. To set in action, the glass is nearly filled with a saturated solution of sal-ammoniac or chloride of ammonium. This gradually percolates through the porous pot, until the whole is left about three-fourths full. The action which takes place, under favourable con- ditions, is as follows : — The zinc combines with the chlorine of the sal-ammoniac to form zinc chloride, which is dissolved in the solution, whilst the hydrogen set free from the sal-ammoniac robs the binoxide of manganese of some of its oxygen to form water ; ammonia being also given off, as shown in the chemical formula : — Zn-f2NH^CH-2MnO,=ZnCl2-l-H,0-f2NH34-Mn203 If the cell is hard worked the action becomes more complicated, substances, such as oxy-chlorides of zinc, being formed which are with difficulty dissolved in the solution, and soon impair the working and lead to the polarization of the cell. On allowing it to rest, how- ever, it quickly regains its power. One of the best features of the Leclanche cell is that no local action or waste of materials takes place when not in use, unless impure zinc is used. The ammonia gas given off during action is not offensive and is seldom noticed, unless the cell is very hard worked. BATTERIES USED m TELEPHONY. 31 There are many practical points in connection with the cell to which attention should be paid. Carbon Plate. — The attachment of the lead pap to the carbon is one of the most important points, and much trouble was at one time experienced by the solution creeping up through the pores of the carbon and acting upon the lead and the terminal. This quickly corroded and destroyed the connection. To prevent this action, about two inches of the top of the carbon should be soaked for some time in hot paraffin wax. This plugs up the pores so that the creeping cannot take place. To ensure a good connection between the terminal and the carbon, the latter should have two or three holes of about \ dia. drilled at about A in. from its top edge, and the shank of the terminal should be tinned before the lead is cast round it and the head of the carbon. The terminals, if made of brass, are apt to be corroded by the- ammonia fumes and by solution dropped on them accidentally. No such corrosion takes place if the terminals are made of Britannia metal or pewter. The top of the porous pot should also be soaked in paraffin, and the carbon block and mixture kept in place by a covering of marine glue about J in. thick, in which two small ventilating holes are made. The holes are useful also for pouring a little of the solution in the pot when the cell is required to work at once. The porous pots should be rather soft, as hard ones offer too great a resistance to give sufficient current for a transmitter, but will do for a ringing battery. Only the best needle manganese should be used, or 32 PRACTICAL TELEPHONE HANDBOOK. the cells will soon give out. It is desirable, therefore, to get the cells from the best makers, who only use first-class materials. The same applies to the sal- ammoniac used, as impurities in this give rise to local action. The zinc rod is best made of rolled metal, and care should be taken that its wire connection is well soldered. The glass cell should be coated at its top for a distance of about 2 inches inside and out with black Japan varnish, to prevent the solution from creeping over the edge of the jar and down the outside by- capillary action. The cell is often drained dry in this way to the detriment of wall-paper, etc., in the offices where it is fixed. The solution will not wet the varnish, and so the creeping is prevented. Paraffin wax is sometimes used for the purpose, but is not nearly so effective. The lead cap and top of carbon should also be varnished. The cells are made in three sizes. The No. 2, or medium, is the one mostly used ; but the No. i, or largest size, is frequently employed for the working of trans- mitters with much advantage, as they are heavily worked, and a greater body of depolarizing material is desirable and more solution to keep up its strength. A stronger current is also obtained, as the internal resistance is only about I to 2 ohms as compared with that of the No, 2, which is from 2 to 4 ohms. The E.M.F. of the Leclanche = v\6 volts at starting. The Agglomerate Leclanche. — In order to get rid of the porous pot and its resistance, a mixture of carbon and BATTERIES USED IN TELEPHONY. 33 binoxide of manganese is solidified by being crushed and mixed with a proportion of gum-lac resin, and the resulting compound put into moulds, and subjected to a great pressure after being heated to 212° F. The solid blocks thus formed are fastened round the carbon-plate by india-rubber bands, usually provided with small Fig. 6. Fig. 7. holes for the zinc rods to keep the latter from touching the blocks. For the same purpose, and also to prevent the cell running down too quickly, small porous pots are sometimes provided for the zincs, as shown in Fig. 6. Fig. 7 shows a later form, called the six-block agglo- merate cell. A fluted carbon block is used, to 34 PRACTICAL TELEPHONE HANDBOOK: which are bound six cylindrical agglomerate blocks, completely protecting the carbon from direct action. With it may be used a cylindrical zinc surrounding the blocks, and very materially reducing the internal resistance of the cell. The expectation that these agglomerate cells would altogether supplant the porous pot form has not been realised, as they have not proved so reliable. They are, however, used in preference when specially strong currents are required. The Daniell Cell. — In the matter of constancy no working cell is superior to the Daniell. Except by the British Post Office, it is not used for the general working of telephones, but is frequently used for the special purpose of working the transmitters in very busy telephonic exchanges, especially where the multiple switch-board is employed. The ordinary Daniell is made up of a copper-plate or cylinder immersed in a saturated solution of .sulphate of copper, which is separated by porous earthenware from a vessel containing a zinc plate or cylinder immersed in a weak solution of sulphate of zinc. The hydrogen, instead of polarizing the cell, acts upon the sulphate of copper, and metallic copper from this is deposited on the copper-plate. The defects of the Daniell are that its internal resistance is high, and that the fluids get mixed through the division. Much local action results, and it is nc advantage to disconnect the cell from its work to recuperate. B/l TTERIES USED IN TELEPHONY. 3S To remedy these defects to some extent, advantage has been taken of the fact that the specific gravity of a saturated solution of sulphate of copper is greater than that of a weak solution of sulphate of zinc, to form what are called Gravity Cells. Two of what are called the Crowfoot gravity cells are shown in Fig. 8. The glass cells are 6\ in. dia. and 8^ in. deep. Three copper strips, about 2 in. wide, are rivetted together by a copper Fig. 8. rivet, and then opened out into the shape shown af the bottom, a gutta-percha covered wire being attached for connection. The jar is next filled three-parts full of water, and crystals of sulphate of copper are dropped in until the copper is nearly covered, and then a solution of sulphate of zinc is carefully put in the top of the jar. Lastly, the crowfoot-shaped zinc is hung on the side of the jar, as shown. Another form of gravity cell is shown in Fig. 9. 36 PRACTICAL TELEPHONE HANDBOOK. Much attention needs to be paid to these cells, for if the solution of sulphate of zinc gets too strong, it becomes heavier than the sulphate of copper solution, and sinks to the bottom, and the displaced copper solution deposits copper on the zinc. Some of the top. liquid should therefore be taken out every few days by means of a syringe, and water put in to take its place. A hydrometer is a very useful instrument to indicate the degree of saturation of the upper solution. More copper crystals should be dropped through the liquid as the others are dissolved. The cells must be kept very still, or the solutions will mix. The E.M.F. being only — I '065 volts, two cells joined up in series are required to work a Blake transmitter. Other batteries are used occasionally in telephony, such as Fuller's Bichromate of Potash, for very strong currents; Bennett's Iron-borings, and Clark's Silver Chloride. Dry Cells. — Some form.s of dry cells, such as the Silvertown, Gassner and the Hellesen, are extending in Fig. 9. BA Tl^ERIES USED IN TELEPHONY. 37 use for special purposes, such as for use with portable telephone sets for testing lines. The last-named cell appears to be the best of the class, giving very satis- factory results, and is comparatively cheap. Its E.M.F. = i"4 volts, and the internal resistance of a cell about the size of a No. 2 Leclanche is only about Ath of an ohm, so that a powerful current can be obtained from it through a low resistance. Battery Boxes. — These should be made so that both the front and top will open, in order that inspection of the cells may be easy. The cells should be prevented + rlh h hhh , - .+ V Fi". 10. Fig. II. from touching each other, or the sides of the box, by a light wooden framework fitting between them. In diagrams a cell is usually represented by two parallel lines, a short thick one for the zinc, and a longer thin one for the copper or carbon, as shown in Fig. 10. Batteries are represented by combinations of these, as Fig. ii, which shows a battery of four cells joined up in series. The E.M.F. and internal resistance of such a com- bination will be four times that of a single cell. When a low internal resistance is required cells are joined 38 PRACTICAL TELEPHONE HANDBOOKi up SO that all the zincs are connected together, and all the carbons together, as in Fig. 12, which shows three cells so connected abreast, or for quantity, as it is called. The internal resistance of such a combination will be ^rd that of a single cell, but the E.M.F. will only be equal to that of a single cell, the combination being only equiva- 1 "" lent to a single . ~ _^_^ cell having plates lI _i_ _] three times the ^^~* size. It is much ^'S' 12. better to use large- sized cells, when they can be obtained, than to resort to the above arrangement. Much valuable information in regard to batteries is given in Walker's " Electricity in our Homes and Workshops," published in the same series as this book. Secondary Cells"*' are now much used for the working of operators' transmitters in large exchanges. As the internal resistance of these is very small, a number of transmitters may be worked from a single cell. The cells are charged from direct current electric light mains. As these are usually at a pressure of about 100 volts, it becomes necessary to provide about 50 cells for charging, or to reduce the electrical pressure by means of motor- transformers.* From ten to twenty transmitters may be worked by a single cell. * For descriptions of these see Sir D. Salomons' book on " Tlie Manage- ment of Accumulators." CHAPTER III, HISTORY. The first electrical appliance to which the name tele- p/wne was attached was that invented by Philip Reis, in 1 86 1. This, however, was only intended for the trans- mission of musical sounds, although it appears that on some occasions it was successful in transmitting spoken words, but in an accidental manner, the principles involved not being adequately known. These principles were first clearly explained by Prof. Graham Bell, in 1876, and, as he produced the first practical instrument he is generally credited with the invention of the telephone. Reis's Telephone. — Although of little practical use, Reis's instrument is important from a historical point of view. Its working depends upon the fact that an iron rod, when magnetised by a current, gives out a ticking sound. If the current be interrupted very frequently and regularly, and the rod attached by its two ends to a sounding-board or box, a musical note will be produced of a pitch depending upon the 46 Practical telephone handbook. frequency of the breaks in the current. Fig. 13 shows one of Reis's arrangements of this kind, which serves as the receiver. The cover D fitted over the coil g and rod d d serves to intensify the result. The transmitter, Fig. 14, was more complicated. It was so arranged that the voice or a musical instrument sounded into the mouthpiece T should cause interrup- tions in the current in unison with the vibrations of the sound produced. To accomplish this a large circular opening on the top of the box K is closed in with a Fig- 13- stretched membrane, m. On the upper surface of this is a strip of platinum, i, connected to the terminal 2. On the part of this in the centre of the membrane, one corner of a platinum point attached at b to an angle-shaped metal piece, a b c, just touches it under normal conditions. If the contact forms part of a circuit which includes a battery and the receiver. Fig. 13, and the membrane be set in vibration by a musical sound, the circuit will be interrupted at every vibration. Each interruption produces a sound in the receiver, and a musical sound similar in pitch to the one sounded in HISTORY. 41 the mouthpiece of the transmitter will be given out by the receiver, no matter how distant it may be. The apparatus shown on the sides of the instruments are battery keys for signalling purposes. By such means the pitch of any sound may be reproduced at a distance, but this was not enough for the transmission of speech. Pitch is only one of the characteristics of sound, for besides it, sound has quality -ig< Fig. 14. or timbre, and degrees of loudness or intensity, which it was necessary to transmit before human speech could bs perfectly transmitted. This cannot be done by an apparatus which employs interrupted currents for its working. Sound is conveyed through air by a wave motion. The wave motion of water is caused by an up-and-down motion of the particles of water. Wave motion in air is caused by a movement of the particles of air back- 42 PRACTICAL TELEPHONE HANDBOOK. wards and forwards in a line with the direction in which the wave progresses. Every different sound needs a different motion of the air particles for its conveyance, and if the characteristic motion of any sound can be im- pressed upon the air particles at any place, that sound will be reproduced. This v/as the problem attacked by Prof. Bell. Bell's Telephone, the instrument with which Prof. Bell first succeeded, is shown in Fig. 15, where E is an electro- magnet mounted so as to be adjustable near the centre of a mem- brane, M, of gold-beater's skin, stretched over the end of a hollow cylinder. ' "'""" ' "'' ' ' ' ' ^A small piece of clock- ^'g- 'S- spring is cemented to the centre of the membrane. Two of these instru- ments, some distance apart, were joined in a circuit, including a battery, one used as transmitter and the other as receiver. The action was as follows : — On speaking into the cylinder the membrane moved in" unison with the movements of the air particles. These movements of a magnetic substance in front of the magnet produced alterations in the magnet field in which the coils were situated. The effect was to cause electrical pulsations or waves to pass through the coils, the connecting wires and the coils of the receiving instrument at the distant end, of such a nature that they so affected the attraction between the magnet and hisTORy. 43 the steel spring of the receiver as to set up exactly corresponding movements in its diaphragm to those impressed upon that of the transmitter. These move- ments being impressed upon the air, a person listening at the end of the cylinder would hear the original sound lTntfll:illillll!!IM!inlnilllilill!iliffilll!iiililililliniinH^ Fig. 17. reproduced, but in a much fainter degree. All the characteristics of any sound could thus be transmitted and reproduced. Gradually improvements were made by Prof. Bell, until he arrived at the instrument shown in Figs. 16 and 17 where a compound horse-shoe permanent magnet, A, 44 PRACTICAL TELEPHONE HANDBOOK. took the place of the original electro-magnet, two small coils of wire, B b', being fixed on soft iron pieces attached to its poles. It had been found that no battery was required, its only use being to produce a magnetic field by means of the electro-magnet. The gold-beater's skin membrane had also been discarded, one of thin sheet-iron being substituted. With this instrument much louder effects were pro- duced, but it lacked portability, to attain which the 7////y/i;^///////////////77777777?^^ Fig. 18. Scile \. form shown in Fig. 18 was adopted, and may be con- sidered the final form. It was made up of a wooden case in the handle part of which was fitted a bar magnet, N s. On one end of this magnet was fixed a bobbin of wire, the ends of the coil being connected to the terminals at the end of the handle. The diaphragm D, of ferrotype iron clamped close in front of the end of the magnet by a cap in which was turned a funnel- shaped mouth or ear piece with a small opening in the centre. The action of the later forms is similar to that of the HISTORY. 45 original form, except that the pulsatory currents are wholly developed by the movements of the diaphragm, instead of the movement simply varying a current already existing. The instruments served both as transmitters and receivers, and came extensively into use in this form. Lines were joined up, as shown in Fig. 19, but two instruments were generally used at each end to save the constant changing from mouth to ear, and vice versd. The received sounds, although very clear, were rather Fig. 19. faint, so much so that the telephone would have come but slowly into general use, if an instrument to serve as a transmitter, based on a different principle and giving much louder sounds, had not shortly after been invented. It had been pointed out by Prof. Bell that the necessary waves of electricity might be produced in another way than the one employed in his magneto- telephone, in which the waves were produced by a vary- ing E.M.F. caused in the transmitter by the movement of the diaphragm. The second method of producing the waves was by varying the resistance in the circuit 46 PRACTICAL TELEPHONE LIANDBOOK in proportion to the movements of the air-particles whilst the E.M.F. remained constant. Bell had shown a method of doing this by means of a platinum- wire attached to the centre of a horizontal stretched membrane, and just dipping under the surface of acidulated water. The wire and the water formed part of a circuit containing a receiver and a battery. On speaking to the membrane its vibrations would cause the extent of contact of the wire and water to be varied, and so produce corresponding variations and pulsations in the current circulating through the receiver, which latter would reproduce the sound in the manner already described. On the same day that Bell filed his patent, Prof. E. Gray also filed one with similar suggestions for pro- ducing variations in the resistance of an electric circuit. The apparatus employed by the two inventors for this purpose were almost identical. Edison s Carbon Transmitter.— F^dison, in 1878, was the first to produce a successful instiument based on the variation of resistance principle. He took advantage of the fact discovered by Du Moncel, " that the increase of pressure between two conductors in contact produces a diminution in their electrical resistance." This is eminently the case with carbon, and this v/as the sub- stance chosen by Edison, its great variation of resistance under pressure having been independently discovered by him. The instrument he finally adopted after many were tried is shown in Fig. 20, where D is a vibrating disc HISTORY. 47 of mica clamped to the iron case by the iron cap, in which is screwed the ebonite mouthpiece E. Pressing against the 'centre of D is the ivory button b, attached to a small disc of platinum, B B. This forms the loose cover of a chamber, with ebonite sides, in which is placed a quantity of lamp black, I. The amount of initial pressure on the lamp-black can be regulated by the screw V. The terminals of the instrument are connected one to B B and the other to Fig. 20. the metal case, the lamp-black thus forming part of the circuit. Speaking on to the diaphragm causes it to vary its pressure on the carbon, producing corresponding variations in the resistance of a circuit containing also a Bell receiver and a battery. The pulsatory currents thus set up, passing through the receiver, give rise to a reproduction of words spoken into the transmitter. The received sounds are much louder with this instru- ment than when a magneto transmitter is used. ^S PRACTICAL TELEPHONE HANDBOOK. Induction Coil. — Edison still further augmented the power of the instrument, especially when used over long distances, by using an induction coil m conjunc- tion with his transmitter. The carbon and battery were included in the primary wire circuit, and the line and receivers in the secondary circuit of fine wire. This subject will be referred to again in Chapter V. Fig. 21. Microphones. — The next step in the direction of improvement was the discovery by Prof Hughes, of London, in 1878, of the fact that any loose contact between conductors would act as a telephonic trans- mitter owing to the variations of resistance caused between them by the impact of the sound waves. The simple means he employed caused much astonishment. Three nails arranged as in Fig. 21, and joined up v.'ith a battery and a Bell receiver, were found to be HISTORY. 49 sufficient to convey speech, and were even so sensitive as to render audible the most minute sounds, such as the wallcing of a fly, etc. The best effect was obtained with carbon in one shape or another, that given in Fig. 22 being one of the best forms. Two carbon blocks, c C', have a cup-shaped hollow made in each, in which the carbon pencil A is loosely held; Fig. 22. C C are attached to a sounding-board of thin deal, wires being connected to c c' for joining up the battery and receiver. The complete instrument is shown in Fig. 23, and forms the parent of a very numerous class of telephone transmitters ; indeed, nearly all transmitters in use are but modifications or amplifications of some form or other of Hughes's microphone, E so PRACTICAL TELEPHONE HANDBOOK. Edison's Loud-Speaking Receiver.— This was a very interesting instrument, and was much used at one time. It was based on the fact discovered by Edison and utilized by him for the construction of a telegraphic instrument, that the friction between a metal and a substance capable of electrolytic action varies in pro- portion to the strength of a current passing through ^^ Fig. 23. the points of contact. The telephone-receiver con- structed on this principle is shown in Fig. 24. A diaphragm of mica is mounted over an opening in a box, as shown, and a strip of platinum, C (only the end of which' is shown), is attached to its centre and projects at right angles from it. The end of c lies flat on the surface of a chalk cylinder, A, which is moistened with a solution of some easily decomposed electrolyte, such HISTORY. 51 as potassic iodide. The platinum strip c and the metal supports of A are connected in circuit with a battery and a carbon transmitter. On turning the cylinder by the handle w so that the top moves away from the mica disc, the friction (which can be regulated by the Fig. 24. screw E) will cause the centre of the disc to be pulled inwards. On a current passing the friction at the con- tact will be reduced in proportion to the strength of the current, and the disc will partly recover its position. On passing the undulatory currents from a transmitter through the contact and continuously rotating the 52 PRACTICAL TELEPHONE HANDBOOK. cylinder the disc will be caused to vibrate, and will give out a sound similar to that sounded in the transmitter. It was a very powerful instrument when properly adjusted, giving sounds capable of being heard by a large audience. The tone of the instrument left much to be desired, however. This, and the necessity of keeping the cylinder moist and turning the handle, led to its discontinuance. The rod G being raised brought a small roller saturated with the solution from the reservoir T into contact with A in order to renew its moisture. Many other interesting telephonic instruments have since been invented, such as Bell & Tainter's photo- phone, in which the fact that some substances, such as selenium, have their electrical resistance affected by light is utilised to construct an instrument worked by light falling on an arrangement of selenium included in a circuit with a Bell receiver. In Tainter's radiophone the same effect is produced by heat rays, and in the thermo-telephone of W. H. Preece the expansions and contractions caused in a wire by the undulatory currents from a transmitter are utilised to produce a receiving instrument. For further particulars of the instruments mentioned, the reader is referred to Preece & Maier's book, " The Telephone." Dolbear has produced a receiver which works on the principle of the condenser. The charged coatings, one of which forms the diaphragm of the instrument, exert more or less attraction on each other, according to the difference of potential to which they are charged. The HISTORY. 53 potential is varied by connection to a telephone trans- mitter and battery. Telephonic Exchanges. — The telephone at first was used almost exclusively for private purposes, but very early it was recognised by Mr. Hubbard, the father-in- law of Prof. Bell, that its usefulness would be greatly enhanced by the establishment of telephonic exchanges. Each member who joined one of these had to pay a certain subscription, for which he was supplied with a set of telephonic instruments and a line wire which joined him up to a central office, where switch-boards were fixed and operators in attendance to connect the line of any one subscriber to that of any other one, so that they might converse together. The first telephonic exchange was established in Boston, U.S.A., in May, 1877. In this country they were not established until the latter part of 1879, when the invention of the microphone had greatly extended the practical usefulness of the telephone. Very few towns in civilized countries are now without their telephonic exchange, and in most large towns business would be completely disorganised by the cessation of its advantages for a few days. CHAPTER IV. RFXEIVERS IN GENERAL USE. The Bell Receiver. — The form of receiver universally used by the telephone companies in this country until a few years ago is shown in section in Fig. 25, about two-thirds full size. The dimensions of the different parts are given in millimetres. The permanent magnet is a compound one, made up of four thin bars, provided with pole-pieces of soft iron, as shown in the side view, Fig. 26. On one of the pole-pieces is a small boxwood bobbin, wound with silk-covered copper wire of S mils diameter to a resistance of about 75 ohms. The case is of polished ebonite, provided with a screw cap, and the ends of the coil are connected to thick covered wires attached to the terminals at the end of the handles. This instrument held its own for a number of years, and proved its superiority for simplicity and efficiency against many competing instrumeiits. It is now, however, giving way to smaller and lighter ones, more convenient to handle, and of the double-pole form. RECEIVERS IN GENERAL USE. 55 ^0 ■ 1 1, i li Fig. 26. Scale |. 56 PRACTICAL TELEPHONE HANDBOOK. The Gower Receiver. — This has been extensively used by the British Post Office authorities and by many of our railway companies. It is more powerful than the Bell, but is more cumbrous. Its points of Fig. 28. difference are that it has a larger and thicker diaphragm (about 4i inches as compared with 2\ inches diameter), a powerful horse-shoe magnet of the shape shown m Fig. 28, the two poles of which are brought close together, and. each furnished with a flat, soft iron RECEIVERS IN GENERAL USE, 57 pole-piece, on which is fixed a flat coil of wire. The magne^ is placed inside a shallow brass box, furnished with two binding screws, to which the cojls, which are joined up in series, are connected. The diaphragm of tinned iron is clamped in the lid of the box by a brass ring and screws, as shown at M. On the other side of the diaphragm a brass tube is fixed, into which a flexible tube with mouth or ear-piece is inserted (Fig. 27), or, in place of this, a Y tube is often connected with two flexible tubes. The coils are wound to a resistance of 100 ohms each. An attachment used in the early days, when the instrument served both as transmitter and receiver, is shown at A, and on a larger scale at L T, Fig. 28, It was for the purpose of signalling from one station to another, and consisted of a flat tube bent at right angles, furnished with a vibrating reed. On blowing into the flexible tube this reed was set in vibration, and caused corresponding vibrations in the diaphragm, producing powerful pulsatory* currents, which, passing through the instrument at the other end, set its diaphragm in powerful vibration, making sufficient noise to call attention. From the dimensions given it will be evident that the instrument is too heavy and bulky to put to the ear. and the consequent necessity of using flexible tubes detracts considerably from its effectiveness, as they enclose a large body of air, all of which has to be set in vibration, the amplitude of the vibrations which reach the ear being thereby lessened. 58 PRACTICAL TELEPHONE HANDBOOK. Ader Receiver. — This was invented by M. Ader of Paris, and has been very extensively used in France and Belgium, and has everywhere given great satisfaction. In the Ader a new feature is introduced to enhance the effect of the magnet. To illustrate the speciality, a model was shown at the Paris Electrical Exhibition in 1 88 1. It consisted of a permanent magnet, with a sheet-iron armature arranged in front of its poles, but kept a short distance apart by a spring. On sliding a block of soft iron up behind the armature, the latter was at- tracted to the poles, showing that the mass of iron behind had strengthened the action of the magnet on the arma- ture by apparently concen- trating the lines of force upon it. This principle was introduced in the Ader receiver by using a soft iron ring, or washer, let into the cap of the instrument, as shown at X X in Fig. 29. A circular magnet, A, is used, both poles, B B, being provided with two flat coils, like the Govver, and wound to about the same resistance. A metal box, M M, is screwed to the magnet, as shown, and is provided with an ebonite cap and ear-piece. A modified form of Ader has recently come into use Fig;. 29. RECEIVERS IN GENERAL USE. 59 in this country, and has proved to be superior to most Bell receivers, being also smaller and handier. The only important difference is in the shape and size of the magnet, which is altogether en- closed in the metal box, as shown in Fig. 30, to a scale of one-half. Fig. 32.— Scale J. The novel form of magnet adopted is shown separately in Fig. 31. It is of a circular form, made up of two thin rings of steel, fastened together and magnetised across one of their diameters N S, two soft iron pole pieces, B B, being screwed to these Scale \. ^o PRACTICAL TELEPHONE HANDBOOK, points and brought to the centre, where they are furnished with flat coils. These are joined in series, and the two free ends brought out through ivory bushes in the case and attached to the binding posts D D. A wooden handle, with loop, F, is attached. D'Arsonval Receiver. — In the Gower and Ader both poles of the magnet are used, each fitted with a coil ; in the D'Arsonval both poles are utilized, but only one coil. As shown in Fig. 32, one pole is furnished with a round coil, B, and the other is attached to a soft-iron cylinder, T, which fits over it, thus forming a box electro-magnet, which concentrates the lines of force due to the operat- ing currents and the magnet in the centre of the diaphragm. The core N, shown separately, screws into the pole of the magnet, and also serves as clamping screw to secure the box D. » Siemens' Receiver. — This instrument is chiefly used in Germany, and a remarkable testimony to its excel- lence is the fact that, to the year 1888, it served both as transmitter and receiver to the exclusion of carbon transmitters. Fig. 34 shows the internal parts, and Fig. 33 the iron outer case in which they are fixed : N S is a powerful horse-shoe magnet, with pole pieces n s and coils e e ; d dare connecting wires to terminals on wooden block/", through which passes a fixing and adjusting screw into the magnet ; g" is the suspending loop, and a the base of the instrument, which fits against the lower part of the outer case k. RECEIVERS IN GENERAL USE. 61 The instrument is shown to a scale of one-half full size, from which it will be seen to be rather large. Many of the double or bi-polar receivers which have Fig. 33. Scale J. Fig. 34. Scale J. come into such extensive use of late years follow the general plan of the Siemens instrument, but are smaller and fitted in ebonite cases, or a combi- nation of iron tube covered with ebonite, similar to that of 62 PRACTICAL TELEPHONE HANDBOOK. Fig. 35- Fig. 25, which form they are rapidly dis- placing, owing to their superior power. The bobbins of such receivers are generally wound with wire of 35 mils diameter to a resistance of between 100 and 120 ohms the pair. Another form of Siemens' receiver, Fig- 35. is now much used, in which the pole-pieces and coils are fixed on the sides of the magnet, instead of at the ends. The magnet is wrapped with leather, and is grasped by the hand in using. The Watch Receiver. — Tiiis is a double pole receiver of a neat and compact form, being only about the size of an ordinary watch. It is the type of a numerous class of small instruments. Fig. 36 gives a view of its inside construction : A is a block of vulcanite on which the terminals are fixed, the con- ducting wires are taken out through holes in the metal case, being protected from con- tact or fraying by being enclosed in india-rubber tubes. Fig. 36.— Scale §. Relation between strength of magnet and size of Dia- RECEIVERS IN GENERAL USE. 63 phragm. — Mercadier has conducted a series of experi- ments having for their object the determination of the above problem. From these experiments he has arrived at the following conclusions : — 1. For every telephone of a given magnetic field there is a thickness of diaphragm which gives a maximum effect. The stronger the magnet the thicker should be the diaphragm. 2. The thickness of diaphragm being known for a certain magnetic field, there is one diameter for the diaphragm which gives the best result. This diameter will be greater the stronger the magnetic field. 3. That arrangement of magnet and coils will give the best result in which the greatest number of lines of force run through the coil in a direction at right angles to the plane of the coil, and in which these vary inost with any movement of the diaphragm. From the above researches M. Mercadier was led to devise a very small and light receiver, which he called the bitelefhone, and which he claims is as effective as the ordinary form. See Appendix for further details. CHAPTER V. TRANSMITTERS IN PRACTICAL USE. As before stated, the transmitters now used are all based upon some form of Prof. Hughes's microphone. They may be roughly divided into three classes : — I, the Metal and Carbon ; 2, the Pencil Carbon ; and 3, the Granulated Carbon. The prototype of the first class is the Blake, of the second the Crossley, and of the third the Hunnings. Blake's Transmitter. — This is probably the most important of all, judging at any rate by the number in use. It was invented soon after the microphone, and was at once adopted by all the Bell Telephone companies, and is still almost exclusively used for all exchange work in America and this country. When properly made and adjusted, it probably gives a purer and more perfect reproduction of the voice than any other. It has the demerit of requiring adjustment at times, and, as a rule, is not sufficiently powerful for long-distance talking. Fig. 37 shows the inside of the instrument when open, and Fig. 38 a section through the centre of 7RANSMITTERS IN PRACTICAL USE. 66 PRACTICAL TELEPHONE HANDBOOK. the transmitter proper, which is fixed on the door of a small box. The framework is a brass or iron casting, forming a ring, r r, with projections, b b, at top and bottom. Into a recess in this ring the sheet-iron dia- phragm e is inserted, its edge being clipped by an indiarubber ring, ti u. The diaphragm is kept in position by a clip, v, bearing »i^ on the india-rubber ring, and by a spring, ^ V, which presses nearer its centre, being " insulated from it by a pad of felt or india-rubber. To the top projection, f>, an arm, c, is attached by means of the spring 711 and screws. To a pro- jection of this arm a small steel spring, g, and a very slender german-silver spring, f, are clamped by two screws at i. The spring / is carefully insulated by being clamped between two pieces of vulcanite. It has at its extremity a small pellet of platinum, which presses against the centre of the dia- phragm on one side, and against a round button of hard carbon let into a Scale J. brass socket, /, on the other. This brass piece is attached by a screw to the end of the spring g. The spring m tends to throw the arm c from the diaphragm. Its distance therefrom, and the consequent pressure of the carbon button on the platinum pellet is regulated by the screw n pressing against the lower part of the arm c. TRANSMITTERS IN PRACTICAL USE. 67 The circuit through the instrument is made by connecting /■ to one of the hinges, and r r to the other. The flat springs on the hinges ensure a good contact, the hinges themselves being apt to fail in this respect. One of the hinges is connected to the left-hand one of the four terminals provided, and the other to one end of the primary wire of an induction coil, R, the other end of the coil being connected to the second terminal. Between these terminals a Leclanch^ cell is connected when the instrument is to be used, the other two terminals on the right being connected through a switch to the line and instruments at the other end. Use of Induction Coil. — The working of a microphone depends upon the variation of the resistance of the circuit in which it is included when the sound waves impinge upon it. The greater this variation, the more intense will be the reproduced sound. The variation will be relatively greater the lower the total resistance of the circuit. Therefore, to attain the greatest efficiency the total resistance of the circuit must be kept as low as possible. It follows that the efficiency will decrease as the distance transmitted increases if it is done directly. For example, the resistance of a Blake carbon after adjustment is about 5 ohms, and the variation caused by a certain sound may be i ohm ; assume the rest of the circuit to be 15 ohms, and the variation would then be is of the whole, but if the total resistance had been 1,000 ohms, a variation of only irnnr would have been obtained, and the relative effect on the same receiver would not have been more than is of that in the first case. An increase of battery 68 PRACTICAL TELEPHONE HANDBOOK. would, to a certain extent, restore the power, but would be costly and troublesome. By using an induction coil, and including the micro- phone and battery in the primary circuit of thick wire, its circuit resistance may be kept very low, and the relative variation will then be great. By making the secondary coil of a great number of turns of wire, the currents induced in it by the variations in the primary will have a high E.M.F., and will be able to overcome much resistance in the line and instruments at the other end with comparatively little loss of strength. Figs. 37 and 38 are drawn to a scale of one-half. The diaphragm is 2f in.dia.,and 19 mils thick. Resistance of induction coil: — primary,"5 ohms; secondary, 175 ohms. It should be understood that the inertia of the brass piece p is the secret of the Blake's action, it being too heavy to follow the very rapid movements of the diaphragm, and the carbon is subjected to great variations of pressure in con- sequence. Metal-cased Blake. — Figs. 39 and 40 represent a form of Blake fitted in a round nickel-plated metal case, designed for use with switch-boards. Being much smaller than the ordinary form, it does not hide so large a part of the board from the operators. The general arrangement is the same, only the adjustment is managed rather Fig- 39.— Seale i- differently. The instrument is sus- TRANSMITTERS IN PRACTICAL USE. 69 pended by two flexible conductors, which pass through insulating bushea in the case, and are attached to terminals inside, one of which is insulated. The induction coil is not contained in the case, but is fixed in any con- venient position near. Transmitter of the S octet e des Telephones. — This is a kind of double Blake, in which the effects produced by the movement of the diaphragm are doubled. Fig. 41 is a diagram of its connections: — a a 'is, the diaphragm, ^ is a block of carbon fixed in the centre, c is another carbon block rigidly attached to b by the non-conducting half ring d. a pivot carries on one end a counterweight, and on the other a cone-shaped piece of platinised metal, e, which fits between the carbon blocks b and c. The induction coil J is made three wires, primary and secondary. Fig. 40. — Scale \. An arm balanced on up of two one One end of one of the primary coils is connected to b, and the opposite end of the second primary to c, the two 70 PRACTICAL TELEPHONE HANDBOOK. free ends being connected together and to a battery, the other pole of which is connected to e. Any movement of the diaphragm will cause an increase of pressure of the piece e (which is practically a fixture) on one carbon and a diminution of pressure on the other, so that a current flowing through the former will be increased, and through the latter diminished. The currents passing in opposite directions through the two primary coils will both have the same effect on the secondary coil, producing an induced current of double strength. Every variation caused by the movement of the diaphragm will have a similar effect, so that the transmitting power of the instrument should be double that of the Blake. It is certainly more powerful, but the tone of the instrument is not so good as the Blake. Pencil Microphones. — These are simply a number of Hughes's carbon pencils arranged and joined up in various ways. The tendency has been to gradually increase the number of pencils used, these being joined up in multiple circuit, so as to reduce the resistance and give a more equable result. This form of trans- mitter has the advantage of not requiring adjustment. The Crossley was the first of the class brought into practical use, and it is still used to a considerable extent by the railway companies. As shown in Figs. 42 and 43, it consists of a deal board, DD, about ^th of an inch in thickness, on which are cemented four carbon blocks, B b' b" b'". Between these are four carbon pencils, C C C" C'", whose ends have been turned down so as to fit loosely into holes in the blocks. The TRANSMITTERS IN PRACTICAL USE. 71 board D D is glued by its four corners to four cork pads, which are also attached to F H, forming the sloping lid of a box containing the induction coil, Fig. 43. switches, etc ; E is a funnel-shaped opening, into which the voice is directed. The connections to the induction coil and battery (which generally consists of three or four Leclanche cells) are shown in the figure. It will Fig. 'M- be seen that the current divides into two branches having two pencils in each. The instrument is not so powerful as others of the class, owing probably to the high resistance of the primary circuit. Ade/s Transmitter. — This, as shown in Figs. 44 and 45, is somewhat similar to the Crossley, but has twelve pencils in place of four, giving a resistance of only about one-third. 72 PRACTICAL ■JELEPBONE HANDBOOK. The pine board on to which the blocks B B' b" are cemented is varnished on the opposite side, and has strips of india-rubber, C C', cemented round its edges, by which it is fastened so as to form a cover to an opening Fig. 44- formed in the slanting lid of the instrument case. The person using the instrument simply directs his voice on to the varnished board. Fig. 45- The Ader is used extensively in France, and gives very good results. TheGower. — The pencils of this transmitter are eight in number, radiating from a central block to other carbon blocks arranged in the form of an octagon, as shown in Fig. 46. The outside blocks are divided into two sets of four, each set being joined by copper pieces, s and s', to which the connections are made. One of the pencils is shown full size. The whole is fixed on a pine board 9 in. by 5 in. by Jin. thick, fixed in a box similar to that of the Crossley, except that a porcelain mouthpiece is TRANSMITTERS IN PRACTICAL USE. 73 in ;. 46. an ingenious now used. The pine board, was formerly open like tlie Ader.the voice being directed on to it. Many thousands of these instruments are in use in this country. It was adopted from the first by the British Post Office, and is looked upon as a powerful instru- ment. D'Arsonval's. — The pecu- liarity of this pencil instru- ment is that it is capable of adjustment. This is managed manner. Fig.^ 47 gives a back view, and Fig. 48 a section of the instrument : — D is the pine board in this case fixed upright. Each of the four carbon pencils C C' c" c"' is. encased in a tnin sheet-iron jacket, F f' f" f'". a horse-shoe magnet,A,is arranged behind the pencils as shown by the dotted outline, and can be brought near or withdrawn from them by a screw not shown. The nearer the magnet is to the pencils Fig. 47. 74 PRACTICAL TELEPHONE HANDBOOK. the less sensitive will be the instrument, owing to the increased pressure at the carbon contacts. De JongKs. — This is a novel form of instru- ment which has come extensively into use. Fig. 49 gives a section about half-full size : — D is the diaphragm clamped in position by the front of the case. On D are fixed, some distance apart, two sets of four carbon blocks, one set being shown at B B' B" B'". The blocks of each set are connected together by wire wound round them, and connected to a terminal as shown. Two rows of brass pins are driven into the back of the instrument in a slanting position, as at Fig. 48. p p, p„ p,„^ ^jj.^jj gj^^^g jj^jj the number. On each pair of these pins is placed a long carbon pencil, shown in section at C c c" c'", one being also shown separately at c. These would roll off the pins only that they are stopped by the carbon blocks. In this way the microphonic contact is made, the two sets of blocks being joined to a battery and a primary wire of an induction coil. Mix & Genest's Transmitter. — This instrument is the one adopted by the German TRANSMITTERS IN PRACTICAL USE. Post Office, and a great deal has been heard of it in this country recently. The novelty is in the means taken to prevent the rasp- ing sound often heard in pencil microphones, due to the pencils rolling in their loose bearing Fig. 50.— Scale , holes. The pencils are held up to their work and pre- vented from rolling by being pressed up from behind by means of a soft pad. In Figs. 50 and S\,b b are two carbon blocks fixed to the pine wood diaphragm M, and k k k three carbon pencils of the ordinary kind, having behind them a soft pad of felt, d, mounted on a brass plate, which is itself mounted on a spring, f, capa- ble of adjustment. The frame and mouthpiece T is of cast- iron. Fig. 51.— Scale \. Granulated Carbon Trans- mitters, — These are undoubtedly the most powerful for 76 PRACTICAL TELEPHONE HANDnOOK. long-distance work. They possess a very piercing quality of sound, which seems to carry better than the tones from other forms of transmitters. Many different forms are constructed, but all contain crushed retort carbon or oven-coke sifted through wire gauze, so as to obtain even grains of about the size of those of fine gunpowder. A quantity of this is enclosed in a cell with a flexible diaphragm. Some forms have the drawback that the carbon tends to settle down and, to a certain degree, consolidate, and require to be shaken up now and then. On account of the number of loose contacts the variation of resistance is very great, which explains their power. Sometimes the granules are impregnated with mercury to lessen their resistance. The Hunnings Transmitter. — This was the first of the type. It is made up of a round wooden case, about 3 in, in diameter, shown in section in Fig. 52, to about half natural size. In the bottom of a recess, G, turned in it, a thin plate of carbon, B, is cemented, a wire connecting it to terminal c'. At the front of the recess a platinum foil dia- phragm, D, is clamped by the brass ring A A and screws ; A A Fig. 52.— Scale J. is connected to terminal c. The recess formed is filled about three-fourths full of the carbon granules. A cap with a funnel mouthpiece is then screwed on, as shown. The bottom of the funnel TRANSMITTERS IN PRACTICAL USE. 77 has generally a piece of wire gauze or crossed wires fixed over it, to prevent the foil being damaged by- thoughtless persons poking it with pencils, etc. The instrument is generally held in the hand in using, and can therefore be easily shaken to prevent con- solidation. It was at first used without an induction coil, but works much better with one. The Moseley. — Instead of a platinum diaphragm, the Moseley has one of thin pine wood, in the centre of which is cemented a thin, block of carbon, connected by fine wire to one of the terminals. The front of the diaphragm must be varnished to prevent the absorption of moisture, the amount of which, in consequence of having to put the instrument close to the mouth in using, is rather large, and is a decided drawback to this class of transmitter. Instead of holding it in the hand when using, the instrument is often mounted on a block by means of a dovetail wedge arrangement, which makes the connections, and enables the instrument to be re- moved for shaking when necessary. Marr's Inertia Transmitter. — This wonderful little instrument was introduced by the late Mr, Charles Moseley for the purpose of transmitting operatic per- formances from the Manchester theatres, and proved a remarkable success not only for that purpose, but as a long-distance transmitter ; its performances in the latter respect being superior to the best known forms of transmitters experimented with by the writer. Fig. 53 gives a section of the instrument. The dia- phragm and brass frame are similar to that of a Blake, 78 PRACTICAL TELEPHONE HANDBOOK-. \ J ^-:i! ][ 'fV IlJ but they are mounted in a round wooden case : — c is a small brass frame, on one face of which is cemented a piece of sheet india-rubber, B. On the centre of this is cemented a piece of carbon, E, of such a size as just to fit easily inside c, but prevented from touching by the latter being lined with thin paper. On the opposite side of B, a small piece of card- board, F, same size as the carbon E, is glued, by means of which the whole is glued to the diaphragm. The brass cell is closed in on the other side by a block of carbon, D, fixed to it by small screws. The space left between the carbons being filled three-fourths full with carbon granules. The cell is fixed to the dia- phragm, about \ in. above its centre. The instrument works on the inertia principle, the heavy brass piece, a full-sized view of which is given in Fig. 54, remaining prac- tically stationary, whilst the flexible india-rubber B allows the carbon block E to vibrate with the dia- phragm. The Berthon is another modifica- tion of the Runnings, the foil diaphragm being replaced by a thin carbon disc. Between two carbon discs, P p (Fig. SS), is formed a sort of truncated conical cell, c, three-fourths full of granules. The plates are Fig. 53— Scale \. ] Fig. 54- TRANSMITTERS m PRACTICAL USE. 79 separated from each other and from the ebonite case a by india-rubber rings, B B' e, the vvhole being kept together by a brass ring, D. The round holes in the case are to allow the air to escape, so as not to Fig- 55-— Scale J. impede the vibrations. The Berthon is used in France, especially for switch-room service. The Roulez appears to have been very suc- cessful on the London-Paris line. The vibra- ting diaphragm is a carbon plate 4 inches in diameter, to which is attached a light block of wood carbon 2\ inches long. A piece of Bristol board is cemented between them, as shown in Fig. 56. Three holes are made "into the block through the card- board, and these are filled up with frag- Fig, much ■.56. So PRACTICAL TELEPHONE HANDBOOK. ^^;\\ ments of broken incandescent electric lamp filaments, through which the circuit is carried between the carbon block and the diaphragm. The Berliner Universal. — The diaphragm of this is a carbon disc, d, Fig. 57, which is arranged in a horizontal position with the granules above it. This arrangement is adopted in order to get over the diffi- culty of the granules settling down, as they are shaken up each time the in- strurhent is used. The carbon disc is clamped down by the cover B, and a brass ring M, by which connection is Fig. S7.-Scale \. ^^^^ ^ cylindrical space is formed by a wide felt ring, F, at the bottom of which the carbon granules are placed. Above, and just fitting the felt ring, is a cylindrical block of carbon, c, in the lower face of which a series of concentric conical grooves are turned. C is held in position and adjusted by the screwed pin L and terminal nut E. The head of L fits tightly into a hole bored in the carbon, and part of it is turned down, on to which part a short: piece of india-rubber tubing, G (shown in section), fits and TRANSMITTERS IN PRACTICAL USE. 8i extends to the carbon disc, on which it lightly presses, serving to damp its vibrations. Into a hole in the lower face of the wooden case B a brass tube, H, is screwed, on which fits the rubber funnel of the peculiar shape shown. The instrument is fitted to any case by two projecting bolts and nuts, only one of which is shown. This is one of the best long-distance transmitters made, having a very piercing tone. Two No. i agglo- merate cells are generally used to it. Thornberrys Long-Distance.— This is the one used most extensively for long-distance work in America. It is somewhat the same shape as the Berliner. Fig. 58 is a section to a scale of one-half. A is a platinum foil diaphragm, clamped at its edges in the shallow brass cylinder B B. Inside this, but insulated from it by the vulcanite rings C and D, is a brass cylindrical ring E, on the top of which rests a brass piece of the shape shown at F F, which reaches nearly to the diaphragm. The space around this is nearly filled with granules of coke, and the cell thus formed is placed in the recess made G 82 PRACTICAL TELEPHONE HANDBOOK. in an iron casting, G. The bottom of G is fitted with an ebonite disc, in which two holes are made, one opening into the funnel J K, and the other for the passage outside of a terminal which is screwed into the brass box B. The casting is bushed with ebonite, to prevent contact with this terminal. The brass cap L, placed over the cell and screwed down on to it, makes contact with the brass piece F. The casting has a boss, which fits on to an iron rod, M, so that it may be adjusted in height and then clamped in position by the screw N. M is attached to an iron box which contains the induc- tion coil. The brass tray-like piece F maintains contact with the granules, relieves the foil of their weight, and reduces the resistance. Comparison of Transmitters. — By using a very delicate dynamometer, Prof. Cross, of Boston, has made direct measurements of the strengths of the currents generated in the secondary wire of a transmitter induction coil by the variations in the primary coils, and has been thereby able to compare the power of different transmitters, a matter difficult to do when judging by the ear alone. Three instruments^ — Edison's, Blake's, and Runnings' — were thus tested, an organ-pipe sounding under an equal pressure of wind acting on the transmitters at equal distances. The strengths of the currents registered were as follows : — Edison, '072 milliampere ; Blake "132 m.a. ; and Runnings, '556 m.a. This shows a marked superiority in the case of the Runnings which bears out practical experience. TRANSMITTERS Itr PRACTICAL USE. «3 Experiments were also made by sounding the different vowel sounds, the results coming out in about the same proportion as above. It would be interesting to have other transmitters tested in this manner. Transmitter Induction Cbz/j.— Experiments made by M. Abrezol, of Geneva, on lines of varying length, to determine the best dimensions to be given to induction coils in order to obtain the best effects, resulted in the recommendation of a coil of the following dimensions: — Primary wire, i8o turns of wire 24 mils dia. (23 gauge), giving a resistance = '5 ohms. Secondary wire 4,200 turns of wire 6 mils dia., giving a resistance = 250 ohms. Experiments made by Mr. Preece resulted in corroborating the above figures. For full particulars of these experiments and of others with different transmitters, and also for particulars of many other receivers and transmitters, see Messrs. Preece & Stubbs' " Manual of Telephony." Note. — Mix attd Genest Transmitter, — In a later form of this instrument the carbon pencils are pressed from the front backwards by springs formed of hog's bristles,, which retain their elasticity better than the felt, pads. CHAPTER VI. SIGNALLING APPARATUS. Although signalling between telephone stations has been accomplished by means of the telephone itself, as mentioned on page 57, the universal practice at present is to use some form of electric bell, operated either by a battery or by electricity generated mechanically by magneto machines. The signalling and switching apparatus thus required led to the adoption of what are called switch-bells, in which the above apparatus is compactly arranged, and the necessary switching is managed by the aid of an automatic switch, which consists of a pivoted lever so arranged that the mere hanging of the receiver on one end of it, when a conversation is finished, changes the connection from the telephone apparatus on to the signalling device and disconnects the transmitter battery circuit, so as to prevent the battery working to waste. The automatic switch was patented in America, but not in this country, so that its use here is free. LLING APPARATUS. 8S f ^^0 ©e 1 • - < - .^ i . . . . -— ^ o- - - - 1- - - 1 , 7^ v' '.''■,'•,•': ' ' ! 1 Electric Bells. — As these are much used in telephony, a short description is desirable. The term electric bells is generally applied to those bells which are actuated by batteries, those operated by magneto induction currents being called magneto bells. The latter will be described further on in this chapter. Electric bells are of two kinds, single stroke and trem- ble/-. The former are the simpler, and consist of an electro-magnet, the armature of which has a hammer attached, which strikes on a gong each time, a battery is connected to its terminals. The trembler bell has, in addition, an arrangement which automatically breaks the circuit when the armature is attracted. Fig. 59 shows a common and reliable form : — A and B are two terminals ; A is connected to one end of the magnet coils a a, the other end being soldered to the iron frame ; B is connected to pillar b, which is insulated from the frame by an ebonite bush. Attached to the armature is a spring, c, which in its normal position presses against a contact screw in the top of b, which contact forms part of the circuit. On sending a current through the coils the armature is attracted, and the spring c leaves © S9.— Scale J. 86 PRACTICAL TELEPHONE HANDBOOK. the contact screw and breaks the circuit. The armature then falls back and again makes contact, and is again attracted, thus giving rise to repeated strokes of the hammer don the gong e, as long as the outside circuit is complete to a battery. The contact should be platinised, or bad connection will ensue, owing to the sparking. Other practical points are the same as those given for electro-magnets in Chapter I. The Silvertown Switch-Bell. — Fig. 60 is probably the most common form of switch-bell employed in this country. The connections to the different parts, as shown by the dotted lines, are made by covered wires run in grooves cut in the wooden base of the instru- ment, which are afterwards filled up with paraffin wax to protect from damp. Tracing the connection from terminal L, to which the line wire is attached, it passes to a, the pivot of the automatic switch lever b, one end of which is formtd into a hook, on which the receiver is hung when not in use, and by its weight brings the lever into contact with stud c. From c connection is made to spring of ringing- key L® '-®E LINE ^ ea. ^ -E ® BELL w Fig. 65. switch lever and its pivot should be bridged over with a fine spiral of copper wire, to ensure good contact. Relays. — When a telephone line worked by battery is above a certain length, say above three or four miles, it becomes desirable to use what is called a relay in con- nection with the instrument. The object of the relay is to save battery power, by enabling a battery to ring Signalling apparatus. 93 the instrument bell at its own station, the relay itself being operated by a comparatively weak current. The simplest form is an electro-magnet wound with rather fine wire, with an armature delicately balanced, so that a comparatively weak current will cause it to be attracted. When this happens the armature, or a spring attached to it, makes contact with an insulated pin which closes a circuit, including a battery and instru- ment bell. When a relay is used, the instru- ment bell is usually cut out of the line circuit, and the coils of the relay are joined up in its place. The instrument bell, or, better, a low resistance bell, is then included in the relay contact circuit with a battery of two or three cells, as is shown in Fig. 65. Fig. 66 shows a delicate form of relay, called the Post Office pattern. The coils of battery switch-bells are usually wound with wire of 13 mils dia. to a resistance of about 30 ohms. Relay coils to 100 or 200 ohms. Magneto Switch-Bells.— \n the early days of the telephone batteries were almost exclusively used for signalling purposes, but they have now generally given way to mechanical generators of electricity, based on Faraday's discovery that currents can .be generated Fig. 66.— Scale J. 94 PRACTICAL TELEPHONE HANDBOOK. by the movements of coils of wire in the vicinity of magnets. The magneto switch-bells have the advantage that they are more self-contained than the battery arrangements, and that they will operate through lines of very high resistance, which would require very strong batteries and relays to work by battery. Magneto switch-bells consist of four principal parts : — 1. The magneto-generator, with its driving gear, by means of which the signalling currents are produced, 2. The automatic cut-out, an arrangement for short- circuiting the generator coils when the generator is not being used. 3. The polarised bell, which is operated by the currents produced by a magneto generator. 4. The automatic switch, which serves the same purpose as those already described in connection with battery switch-bells. The magneto-generator, or simply the generator, usually follows the form of a machine first constructed in 1858 by Dr. Werner Siemens, in which a cylindrical armature which he had just previously invented was employed, being caused to revolve between the poles of a powerful horse-shoe magnet. Figs. 6^ and 68 show the magnets of a common form of generator fitted on to cast-iron pole- pieces. The pole -pieces are braced together by four brass rods, only two of which, c and D, are shown. The whole is next bored out so as just to allow the Siemens' armature (which is generally about i^ inches diameter) to revolve freely within. Three horse-shoe SIGNALLING APPARATUS. 9S magnets are clamped by iron plates and screws to the pole-pieces A and B, so that all their marked ends are on one side. The screws shown at the bottom are for clamping the generator to the bottom of the containing case. Fig. 67.— Scale J. Fig. 68.— Scale J. The armature for the machine is made by winding silk;covered copper wire of about 5 mils diameter on a soft iron core of the shape shown in plan in Fig. 69 and in end view in Fig. 70, being a cylinder of iron, out of which has been cut two deep and wide slots, one on each side, leaving only a comparatively thin web and a pivot in the centre, on which it may be made to revolve. As shown in Fig. 6g, the web is cut away at each end to allow for the wire, which is wound on longitudinally in the recesses thus formed, the surface of the recesses having been first covered with varnished paper to prevent 96 PRACTICAL TELEPHONE HANDBOOK. accidental contacts. The wire being wound on until the armature is nearly filled to the circular form, one end is connected to a small pin, A, Fig. 6g, screwed or driven into the metal, and the other end to a pin, B, which is insulated by being im- bedded in a small ebonite tube, but makes connection with another brass pin, c, also insulated by a vulcanite tube let into the centre of the pivot. Brass end pieces ate attached by screws to the ends of the magnet pole- pieces, having bushes in their centre, in which the pivots of the armature fit. On the pro- jecting end D of the armature a small-toothed wheel is fitted, which gears into another toothed wheel about four times its diameter, carried on a shaft which works in bearings connected to the brass end pieces of the armature box. This shaft is driven by a crank handle, brought outside the instrument case, the armature making four revolutions for each one of the crank. Mode of Action. — The space between the pole-pieces of the magnets is a powerful magnetic field, in which the lines of force go across almost in straight lines from one pole to the other. The coil of wire, in revolv- ing in this field, is continually varying the number of lines of force which pass through it, the number passing through being greatest when the web of the iron core is D Fig. 69.— Scale J. SIGNALLING APPARATUS. 97 in a position straight across from pole to pole, and least when it is in a position at right angles to this. The direction in which the lines of force pass through the coil alternates with each half revolution, and therefore a complete revolution gives rise to two currents, alter- nating in direction, if the circuit through the coils is completed. Another, and perhaps simpler, explanation of the action will be understood by noting the fact that the core of the armature is induced into a magnet by the lines of force passing through it, and that its polarity is reversed twice in every revolution, each of the reversals inducing a current in the surrounding coil, which is opposite in direction to that produced by the previous reversal. The faster the armature is revolved, the greater the speed of the changes which take place, and the greater is the E.M.F. induced, which is also increased in pro- portion to the number of turns of wire on the armature, the strength of the magnets, and the softness or permeability of the iron of which the core is made. Driving ^ Gear. — Toothed - wheel gearing is now usually employed for revolving the generator armature. The teeth of the wheels must be fine and accurately cut by machinery, otherwise they make a disagreeable noise when worked. It was this noise which prevented toothed gearing coming into general use sooner, many people preferring the usually quiet methods of driving by friction gear or india-rubber bands and grooved pulleys. Automatic Cut-out. — Wh^n the generator is not H 98 PRACTICAL TELEPHONE HANDBOOK. actually in use for ringing, it is important that its resistance, which is considerable, should be cut out of the circuit, since it is useless, and would weaken the received signals on the bells. In order to effect this purpose many ingenious devices have been invented which are called automatic cut-outs. In most cases the force required to turn the armature is utilized to cause the removal of a short circuit of the armature coil, and thus throw its wire into the circuit. Perhaps the most novel and interesting plan is that adopted in the Post pattern magneto-bell, in which centrifugal force is made to effect the object. Fig. 71 is a section through the pivot of the armature core of this bell. At the Fig. 71.— Scale \. point a, where one end of its coil is connected, a spring, b, is clamped, having attached at its opposite end a small brass block, e, which presses against the insulated pin c, to which the other end of the coil is attached, as in Fig. 6g. Directly the armature is revolved, block e flies out, and the short- circqit of the coil, which previously existed, is broken, and remains so as long as the revolution continues ; e and b are prevented from flying out too far by a loop attached to e, which passes round the axle. The cut-out adopted in the Western Electric Com- pany's magneto-bells is shown in Fig. 72. The driving shaft A runs in bearings, c and D^ attached to the end pieces of the armature box. E is a toothed-wheel SIGNALLING APPARATUS. 99 gearing into a smaller one attached to the armature. E is driven by a steel pin driven through the shaft bearing against the inclined face of a V-shaped recess cut in its boss, F. On attempting to turn the crank B, some force is necessary before the armature can be moved, and the result of applying this force is that the pin G moves up the inclined face of the recess, withdrawing the end of the shaft from the spring j, against which it is usually pressed by the spiral spring H. The spring j also presses against the insulated Fig. 72.— Scale J. pin at the end of the armature pivot, to which one end of the coil is attached, and as the other end of the coil is attached to the framework, through the pivots, it is plain that when the shaft A touches j the coils will be short-circuited, and, when drawn away by the act of driving, this short circuit will be broken. The Polarised Bell. — As the currents which work this, produced by a generator, follow each other with great rapidity (each turn of the handle generating eight separate currents, and being turned on an average about four times each second, thus producing thirty-two 100 PRACTICAL TELEPHONE HANDBOOK. separate currents per second), it follows that the bell must be very sensitive to respond to each of these pulsations. The speed of turning the handle of the generator also varies greatly with different persons, so that the bell must be able to respond equally well to varying speeds. An ordinary battery bell will only respond satisfactorily to currents following each other at a certain rate, and will therefore not be suitable for magneto-generated currents. It has been known for a long period in telegraphy that the instruments which respond best to rapid pulsations of currents are those which are polarized, that is to say, in which the moving parts are magnetic in themselves, or are maintained in a magnetic state by the induction of magnets. The well-known Siemens' relay is constructed on this prin- ciple, and a modification of it was adopted to form the polarized bell. Figs. 73 and 74 represent a common form of the bell. An electro-magnet is formed of bobbins, A and B (wound to about a resistance of 100 ohms each), screwed to a soft-iron base, C, serving as its yoke. In the centre of C is screwed one pole, N, of a permanent magnet. At the ends of the base C two brass rods, E and F, are screwed, the prolongation of the screws serving to clamp the bell to the instrument case G. E and F are also furnished with screws and nuts at their opposite ends, with which the brass bar H is secured in position, and can be adjusted. In the centre of H a pivot is formed, in which a soft-iron armature, J, can vibrate about its centre, just in front of the ends of the SIGNALLING APPARATUS. lot magnet cores, in which brass pins are fitted to prevent magnetic contact. The hammer and rod, K, is attached to one side of the armature, and moves with it, striking alternately on the gongs L and M fixed outside on the front of the case G. The s pole of the magnet comes over the centre of the armature J, and polarises it by induction, the middle being made of north polarity, and the ends of south polarity, whilst the ends of the cores are made of north polarity by the N pole of the magnet. Fig- 73. Scale J. rr ^ Fig. 74. Action. — The effect of passing a current through the coils is to strengthen the north polarity of one core, and to weaken or altogether neutralise the north polarity of the other core, the effect being that the armature is strongly attracted to one core and not at all by the other. The next reversal of current causes the core which was strengthened before to be weakened, and vice versd, so that the armature vibrates over to the opposite 102 PRAC7ICAL TELEPHONE HANDBOOK. core, and in doing so causes the hammer to strike on the gongs, and so on repeatedly. Sometimes two polarising magnets are used, one to each core, but the action and effect are similar. Automatic Switch. — This differs but little from that used on battery switch-bells in regard to principle, but each maker adopts a different pattern. There is, how- ever, one point in which it differs from those described, which is that the local battery contact is made on the metal of the lever itself, there being no necessity to insulate it from the lever as with battery switch-bells, where the transmitter cell forms part of the ringing battery, which has its zinc pole permanently connected to earth, so that if the local contact were made on the lever a current would pass to line whenever the instru- ment was used for speaking. This will not occur with a magneto bell, with which the transmitter battery is the only one used, and is not connected to earth. A very common and satisfactory form of switch is shown in Figs. 75 and ^6 : — A A is a piece of ebonite on which the pivot brass piece D is mounted, the pronged lever B being pivoted at C. Attached at right angles to B is a wedge-shaped brass piece, e e, which, when the receiver is off the lever, makes contact with the three springs, a b c, being drawn up against them by the tension of the spiral spring f. Line being connected to the lever, and spring c to the telephone instruments, the circuit will be complete for speaking, the local battery circuit being completed through the springs a and b, and the portion of the lever against which they press. SIGNALLING APPARATUS. loj On hanging the receiver on the prong the lever is depressed and brought into contact with spring d, which is connected to the generator and polarised bell, the other end of these being to earth, as shown in Fig. 83. The spring g (Fig. "]€), to which a*connection is made from the line terminal, presses continually on the top of Fig. 75. Scale \. Fig. 76. e, and ensures a good contact. The spring E presses on the insulated pin at the end of the generator-armatures and the automatic shunt of its coils is made and broken at the point F. A switch which has been recently introduced by the Western Electric Company is shown in Figs. TJ and 78, and has some rather novel features. Corresponding lo4 PRACllCAL TELEPHONM HANDBOOK. parts are lettered similarly to Fig. 75. The strong spring (3? serves both as the bell contact spring and in place of the spiral spring for throwing up the lever when the receiver is removed, its end bearing on a button of ebonite, w, on the lever when the latter is up, and on a metal piece, x, when the lever is down. Similarly the ends of the three springs ab c, shown separately in Fig. 78, press on the ebonite piece y when the lever is down, and on the contact plate z when the lever is up, all the springs changing contact by a kind of S| 2 ,r^ 1 1 rA^; Ub Fig. 78. < V '^ rolling motion from metal to in- ^ fMj sulator and vice versd,. As the . ^~^ lever is long, and the contacts Fig- 77-— Scale \. close to the pivot, the leverage is great, and the springs can be made strong and the contacts firm. It would seem to be desirable that hooks should take the place of prongs, as the original form of Bell receiver for which they were designed is rapidly giving way to other forms, for which the prongs are not suitable. Lightning Arresters. — As the bell and armature coils SIGNALLING APPARA TUS. 105 of a magneto bell are of fine wire and high resistance (the former being about 200 ohms and the latter 400 or 500 ohms) they are especially liable to damage by lightning, and should therefore be provided with some form of lightning discharger or protector. By far the most common form is one in which a plate with saw teeth is clamped close to, but not touching, one or two other plates, the terminal screws of the instrument being usually attached to these plates, as shown in Figs, "jg and 80, which show two of the most common forms. The third intermediate terminal is furnished in case the instrument is used as an inter- mediate one on a line of three or more stations, or on a Fig. 79. B "A Fig. 80 metallic circuit line, the earth being then only con- nected to c. If it is used for a terminal station, B and c are both connected to earth, and A to the line wire. .Fig. 80 protector is adjusted by screwing down the pins shown. To give the best protection the saw teeth should be milled sharp, and adjusted very close, when ■io6 PRACTICAL TELEPHONE HANDBOOK. Fig. 81. a charge of high potential electricity will spark across the space, instead of going through the coils of the instrument, and perhaps fusing them. It is not advis- able to adjust too closely, as they are apt to short- circuit the instrument, by getting together, through the warping of the timber, etc. Fig. 8 1 shows a form of protector used by the British Post Office, which consists of two metal discs kept apart by a thin disc of mica, having three perforations. The ter- minal passes through both brass discs,but is insulated from the upper one by the ebonite collar e. The earth connection is made to terminal E, and Hne to disc A. Fig. 8 1 is two- thirds full size. Connections. — Fig. 82 shows how the various parts of a magneto switch- bell are connected to- gether. Terminals are Fig. 82. SIGNALLING APPARATUS. 107 shown on the right for an extra receiver. If one is not used, these terminals must be joined together by a piece of thick wire. Four terminals are shown at the top; three, L, E, and Y, are the ordinary ones just de- scribed, and X B is provided so that an extension bell (which is merely a polarised bell in a case by itself, so that it may be fixed away from the telephone instrument) may be connected in the manner shown, so that it may not be included in the speaking cir- cuit. If an extra bell is not required, X B and E must be looped together by a short piece of wire. The rest of the sketch will, it is hoped, ex- plain itself. Fig. 83 shows a Western Electric Company's magneto switch-bell, complete, with Blake transmitter and box for transmitter cell fitted on a backboard. The top of the ""^s- ^3- cell box forms a small writing-desk. Fig. 84 gives a general view of the internal arrangement of a similar switch-bell, on the door of which is fitted a Blake transmitter. io8 Practical telephone handbook. Fjg. 85 shows a useful form of movable desk magneto set, made by the Consolidated Telephone Company! Cartfs Magneto-Bell. — Fig. 86 gives the con- nections of this instru- ment, which has been lately introduced in America, and appears likely to replace the ordinary arrangement. The novelty consists> not in the construction, but in the connections of Fig. 85. SIGNALLING APPARA TUS. 109 the different parts. The generator and bell, instead of being joined in series in the same circuit, are con- nected in multiple circuit, the bell being also joined permanently to line between the L and E terminals of the instrument. Instead of an automatic cut-out, an automatic cut-in is used to join the generator coil to line when in action, Fig. 86. No this coil being disconnected when not in use lower contact to the automatic lever is necessary. The bell coils are wound to a resistance of 1,000 ohms, so that as many as 20 or 30 stations may be joined up on one line, and will ring and speak well, whilst not more than five or six can be satisfactorily worked with the ordinary magneto joined up in series. no PRACTICAL TELEPHONE HANDBOOIC. Comparison of Battery and MagJieto Systems. — Experience with both systems of working has shown that for short lines of one or two miles in length the battery system is most economical ; but the reverse is the case for long lines, because larger batteries and relays have to be used for battery signalling, which add to the cost and complication. For simplicity the magneto has a great advantage, as it requires no addition, whatever length of line it has to work through (a good magneto being able to ring through 12,000 ohms' resistance), and only two wires have usually to be run in connecting it up, as compared with the four or five required for battery systems. The magneto does not lend itself readily, however, to special arrangements for ringing off and signalling, and the noise and trouble of working is sometimes complained of by subscribers. The chief item of maintenance in both systems is in connection with the transmitter cells, which require to be inspected at least every four months. Ringing batteries have comparatively little work to do, and their cost of maintenance is but small. Large-sized cells should be used for the transmitters, as, containing more working material, they are not so soon exhausted. Instrument Fixing. — Many practical points need to be attended to in fixing or fitting up the instruments, a few of which will be briefly mentioned. Position of Instruments. — A position should be chosen which will be as quiet as possible, on a solid wall, not SIGNALLING APPARATUS. iii subject to vibration, and on which a good light falls. Care should also be taken that room is left for the user to hold up the receiver to his ear without his arm coming into contact with a side wall or other object. The height should be regulated so that the transmitter funnel will be on a level with the mouth of the shortest person who has to use it, as it is easy for a tall person to stoop, but very inconvenient for a short person to stretch up. In speaking, the face is naturally directed downwards. If the above conditions cannot be obtained, and a noisy position has to be chosen, a second receiver should be used to exclude the noise, or a silent cabinet con- structed, in which to place the instrument. If the wall vibrates it will give rise to noise in the transmitter unless the latter is isolated by being suspended on flexible springs, preferably of india-rubber. Having marked the position of the fixing screws (inquiry having previously been made as to the position of buried gas-pipes), round plug-holes are made in the wall, and round or octagonal-sectioned wooden plugs, of about 3 inches in length, tightly driven in. To these the backboard of the instrument is firmly screwed. The instrument should have been previously set up and thoroughly tested before leaving the workshop or test- room. The wires are next connected up to the proper terminals, copper wire, braided with cotton and paraffined, and of about No. i8 gauge, or 48 mils diameter, being used, if the room in which they are fixed is thoroughly 112 PRACTICAL TELEPHONE HANDBOOK. dry. If this is at all doubtful, gutta-percha (or G.P., as it is commonly termed) covered wire, with an outer covering of cotton, should be used, the cotton covering preventing the G.P. from crumbling and falling away from the wire, which it is apt to do after a time. In stapling the wires care must be taken that the covering is not damaged. Tinned steel staples of a U shape and about | inch in length are used. If more than one wire is secured under the same staple, which is seldom advisable, special precautions, such as putting a slip of leather under the staples, should be taken to prevent damage. Care should be taken that staples used for adjacent wires should not come into contact. If a battery is used, a cool place somewhere out of sight should be chosen for it, a cellar being often selected. All joints in the wires must be soldered. This is best done by using resin as a flux ; but a very good soldering solution, suitable for all soldering purposes, may be made up of the following ingredients : — i pint of methylated spirits, 2 ozs. of glycerine, and 3 ozs. of chloride of zinc. The earth connection for the instrument should be made with a thick copper wire, well soldered on to a main water-pipe. If such cannot be obtained, an earth plate of galvanised iron, about two feet square, should be buried in damp ground, and the earth wire connected. Tools Required. — The tools necessary for fixing are: Cutting pliers, large and small screw-drivers, gimlets, SIGNALLING APPARATUS. 113 bradawls, plugging chisel, large and small hammer, 2-foot rule, bell-hanger's augur, tenon saw, and soldering iron. In addition to above, a joiner's chisel, detector galvanometer, and a pair of tweezers will often prove useful. The plugging chisel should be 9 or 10 inches Fig. 87. long, and be provided with a cutting edge, somewhat of the shape of a metal drill (Fig. 87). It is advisable that the small tools should be mounted on a slip of leather, such as used by joiners. This can be rolled up, and will protect the tools, and a glance will show whether all the tools are collected. Note. — See Appendix for other forms of desk- sets, etc. CHAPTER VII. INTERMEDIATE SWITCHES AND SWITCH-BOARDS. The simplest form of a telephone installation is a single-line wire connected to a telephone set at each end. Next to this in simplicity is the arrangement in which one instrument serves two lines, each having a telephone set at the other end, or, in other words, v.'hen fm n n Fig. there are three instruments connected to one line, one being intermediate to the other two. Such an arrange- ment may be Avorked without the addition of special apparatus, either by connecting the intermediate station apparatus directly in the line circuit, without an earth connection, as shown in Fig. 88, or, which is the more satisfactory plan, by connecting the intermediate INTERMEDIATE SWITCHES AND SWITCH-BOARDS, iij instrument as a shunt to the line running direct between the end stations, as shown in Fig. 89. The objections to both these plans are that no privacy can be observed, as ringing and speaking are common to all the stations, and a code of signals is necessary for ringing, to inti- mate which station is required. The first plan has the further disadvantage that the bell coils will have to be spoken through, which is very injurious to the speaking. More than three instruments may be joined up to a line on either of these plans, and such arrangements are n LINE N? 2 Fig. 89. preferred by many firms, and have given satisfaction, especially the shunt plan, by which a large number of instruments may be worked on one line. Intermediate switches are, however, much oftener used for the working of three stations on one line. What is required with these is that the intermediate station, where the switch is fixed, shall be enabled to get into connection with either of the end stations, and while so switched on to one, the other station shall be able to signal. The two end stations must be able to --speak together, without their conversation being in 116 PRACTICAL TELEPHONE HANDBOOK. danger of being overheard at the intermediate station, but so that they can signal the latter when required. Fig. 90 shows a form of switch, many of which are now in use, devised by the writer in 1880 to satisfy these requirements. Five terminals, marked IN, Lj^, B2, Lj, and E, are arranged in a row at the upper part of the instrument. Clamped under the three centre m o Fig. 90. terminals, and held by lock nuts, are three springs, b c and d, c being longer and furnished with a handle knob. The springs are joined together with an ebonite bar, e, so that they all move together. The ends of b and d can make contact on to the brass studs f g hj and k, and the handle bar on to the earth plates E E, except when in its middle position, when it is insulated on the piece of ebonite /. The two lines are connected to the terminals L, and Lj. Tracing the connection (which is ^iven in dotted lines) from Lj when the handle is on the left-hand side, fts shown, it goes by spring b and stud / to terminal INTERMEDIA TE S WITCHES AND S. WITCH-BOARDS, j 1 7 IN, to which is connected the line terminal of the telephone set. Speaking and ringing can therefore go on with the station connected to No. i line. From L2 the connection is by spring d to stud h, thence to stud j and terminal B, through an extension bell, as Fig. 91.— Scale J. shown, to terminal B2, handle bar c, to earth - plate E so that signals can therefore be sent from the end station on line No. 2. On moving the handle over from left to right the line connections will be reversed, No. 2 line being then connected to the telephone set, and No. i line to the extension bell. On putting the handle ia the central position the telephone set will be altogether cut out, and the end stations will be connected directly to each other, with the extension bell attached to the switch rncJuded in Ii8 PRACTICAL TELEPHONE HANDBOOK. the circuit, in order to signal the intermediate station when finished. By arranging that the extension bell shall be con- nected as a shunt to earth when the end stations are through to each other, the connections of the switch may be much simplified, as shown in Fig. 91. This is also a more satisfactory plan of working, as the coils of the bell have not to be spoken through. Of course, more than three stations on a line may be worked by provid- ing each of the intermediate ones with a similar switch. The second plan of working is then much the more satisfactory. Miller's Intermediate Switch. — This /--— ^L is a very neat and reliable instrument, ^''"''■'^k designed for the same purpose as -^ above by Mr. Miller, of Dundee. Figs. Fig. 92.— Scaie \. ^2 and 93 are views of the instrument, to a scale of one-third, and Fig. 94a diagrammatic repre- sentation of its connections. Six terminals, Lj, Bj, Bj, Lj, IN, and E are provided, and six german silver springs con- nected to the terminals are arranged to bear on brass segments fastened to the outside surface of an ebonite cyhnder, a, provided with a handle, b. The figures show the divisions between the segments, and how some of them are connected together. It will be seen that the top segment is sub-divided in its width. Four of the springs are clamped to the ebonite block f. tNTERMEDIATE SWITCHES AND SWITCH-BOARDS. 119 In the position shown the end stations are through to each with the extra or extension bell intermediate. On turning the handle to the right No. i line will be connected to the telephone set, and No. 2 line to the extra bell, and vice versd when the handle is turned to the left. Cxfihanae line i f^ Ljitra 8eO^ i^ijenitanlfne licVl Fig- 93-— Scale J. Fig. 94. Different toned bells and gongs should be provided in connection with these intermediate switches, so that there may be no difficulty in deciding which of the two bells, the instrument or the extension, has rung at any time, otherwise much trouble may be occasioned. When through connection between the end stations is not required or desirable, the connections of the switches above described are so altered that there is no circuit J2a PRACTICAL TELEPHONE HANDBOOK. i.\HEWX , through when the handle is in the centre, or a simpler form of switch may be used, such as shown in Fig. 95. This is called a doithle-bar switch. The connections will be understood from the sketch. It frequently happens that subscribers leave the office in which their telephone is fixed, and when they return wish to know if the bell or bells have been rung in their absence. In such cases an indicating disc may be attached to the bell, in such a manner that the bell hammer in moving shall release a catch, and allow the Fig- 95- disc to fall into view. Such arrangements are, however, liable to produce faults, and it is a better plan to have recourse to drop indicators connected up in place of the bell coils. A bell and battery may be connected up with these so that as long as the shutter of the indicator is down the bell will continue to ring, but a two-way switch should be pro- vided in the circuit of the bell in order to prevent it ringing at night or when not desirable. Two-ivay switches are often required for the purpose of breaking a circuit or to change on to different apparatus. Figs. 96, 97 and 98 show a good form. The handle is attached to the centre of a brass spring A A, one end of which bears on piece B, and the other end on one of the brass pieces c or D, according to the direction in which the handle is turned. INTERMEDIATE SWITCHES AND SWITCH-BOARDS. 121 Fig- 99 is a back view of what may be called a perfect two-way switch designed by Mr. A. R. Bennett. The front is similiar to Fig. 96. The comb springs c and d. c M Fig. 96, Fig. 97. Fig. 98,— Scale Fig. 99, are attached to the terminals c and D. Under- neath, but not touching c and d, is a double comb spring, b b b, connected to the handle terminal B ; and attached to the handle is a double wedge- shaped brass arm, a a, which presses between the springs b and c, or ^and dwhtn thehandle is put to one side or the other, thus ensuring a double means of con- tact, one from the handle direct by arm a, and another from comb b through arm a. Sivitch-boards. — When more than two lines have to be Fig- 99.— Scale ; 122 PRACTICAL TELEPHONE HANDBOOh. served by one telephone instrument, it is usual to employ what is called a switch-board in place of a handle-switch and bells, each line being connected to a drop indicator provided on the board, and special arrangements made for connecting any pair of lines together. The construc- tion of a handle-switch for, say, four lines, although possible, would be difficult, owing to the large number of connec- tions required to provide for the different combinations. Before describing the boards themselves it will be advisable to explain the Drop Indicators or Annunciators which are used in connection with them. These usually consist of an electro-magnet, with an armature so arranged that when it is attracted, a shutter, which was held in position by it, is allowed to fall and expose a num- ber or surface, which will attract attention. Fig. 100 shows an old form. The electro-magnet, a b, attracting the soft iron armature c, allows the lever/; pro- vided with red disc h, to fall, the end of/ being previously hooked in a hole in the end of c. c is pivoted at e, and is provided with a counter weight, ^,and an adjusting screw,>^. The faults of this drop are that too much friction is put on the armature by the weight of the overhanging disc and lever _/, and that the space between the armature and the core of a must be rather large to allow of sufficient catch on the drop, and since the magnetic Fig. 100. INTERMEDIATE SWITCHES AND SWITCH-BOARDS. 123 attraction diminishes very rapidly, as the distance of the armature increases, there will be a loss of power. The best effect will be produced when the attraction is exerted near the pivot of the armature, and the necessary movement of the releasing catch obtained by using a long light lever attached to it. The armature can then be adjusted, comparatively close to the cores, but must be prevented by brass core pins from actually touching when attracted. The Western Electric Company's drop is constructed on this plan, and has almost superseded all other forms. Fig. 10 1 is a sectional side view, showing only one coil Fig. loi. Full size. of the horse-shoe electro-magnet. P is the drop shutter pivotted at the bottom ; D a lever attached at right angles to the armature, very near to the cores of the magnet M. These cores at the other end are attached by iron screws to the strip of iron B (shown in section) which forms the yoke and support for some five or ten drops. Along the back of B a strip of ebonite is attached through which, below the centre of each drop, a screw c projects to the front through a hole drilled in B. 124 PRACTICAL TELEPHONE HANDBOOK. On the drop P being released, it falls and presses the end of a light spring s against the end of c. One end of a circuit, including a battery, is connected to the strip B and the other end to each of the screws c on the board. On s (which is clamped to the framev/ork) and c coming into contact, the bell is caused to ring by the completion of what is called ^Qlocalox night-bell dixoAt, and continues to ring until the drop is raised. During the day the local circuit is usually disconnected by a two-way switch, as Full size. operators are then in attendance at each table, and a falling drop secures instant attention. The resistance of such drops is usually lOO ohms. They are made in several sizes which differ only in detail. Ironclad Ring-off Drop. — Fig. io2 represents the ring- o^drop used on the Western Electric Company's switch- boards. It differs from the ordinary ones in being longer, in only having one coil in place of two, and having that coil enclosed in a soft-iron casing F, which is in magnetic connection with the core. The armature INTERMEDIATE SWITCHES AND SWITCH-BOARDS. 125 A forms the lid of the iron box. Corresponding letters are used to those of Fig. i o i . It is wound to a resistance of 1,000 ohms, and offers great impedance to the rapidly varying telephone currents. The drops being always connected as shunts to the main line thus effectually prevent leakage of the speaking currents whilst offering no special resistance to the ringing currents. Other forms of drops will be described when dealing with switch- room systems. Small Switchboards. — Fig. 103 shows a type of switchboard, design- ed by the writer in 1 88 1 for private telephone exchanges and small public ones. The one shown is intended for five lines or six stations (including the switch- board station itself). The line wires are attached to the terminals i, 2, 3, 4, 5, each of these being connected to a W. E. drop and a switch-handle numbered corre- spondingly. As shown, these handles are all making con- tact on earth-studs beneath. The corresponding pairs of the two sets of brass bars A, B, C, D, are connected together behind the board, and any two stations can be Fig. 103. 12$ PRACTICAL TELEPffONM HANDBOOK. connected by turning the ends of the spring handles on to the same or corresponding bars. Ring-off drops may be connected in shunt to each of the bars, or the ordinary ones used in direct circuit. Fig. 104. A pattern of small switchboard very much used is shown in Fig. 104, VV. E. drops are employed, besides INTERMEDIATE SWITCHES AND SWITCH-BOARDS. 127 which each line is furnished with what is called a Spring' jack or Switch-jack. Connections are "^yT^"''^''''"^''^' made between the lines by means of round I>■*~!nr^-^, J brass plugs carried at the ends of flexible conducting cords. Spring-jacks have now become very important adjuncts to the telephone, and a very large number are in use. Fig. 105 is a side view of a form much used : — M K is a brass or bronze casting which is turned at the K end, and bored for the insertion of the brass plug shown in Fig. 106. At Y a hole is drilled and bushed with vulcanite through which a pin is inserted and secured by a nut, which r\ also secures a spring connection^ r. At the end of M is a screw pin Fig- 105.— Scale §. furnished with nuts and washers, which clamp the phosphor bronze spring R in position ; R is insulated from the casting by pieces of vul- canite, and presses strongly on the head of the pin Y. (For use on any switch-boards but the multiple, which will be described in the next chapter, it is not necessary to insulate the spring R.) The spring-jacks are fixed in position by inserting the part K in holes bored in the woodwork of the switch-boards, and securing Fig. 106. by a screw passing through the projecting flange ^"'^ *• shown. Referrin about 50 of which are provided on each table. The operator's set Fig. 109. — Scale J. Fig. no. — Scale |. is connected to one of the rods, and also to one of the vertical bars o P. Some of the rods are kept for local connections on the one table, and the rest are joined to the other boards in the room for connecting a subscriber on one board to one on another. Ring-off drops are attached to the connecting rods, and form a shunt to earth. The Gilliland Board is a form which has done good 132 PRACTICAL TELEPHONE HANDBOOK. service. The line and connecting bars are in this board formed of strips of brass bent into peculiar shapes, so as to bring them both to the same surface level. The line strips i, 2, 3, 4, 5 (Fig. 1 1 1) extend from front to back of the table, and are of a crimped form. The connecting strips pass under these at right angles, but Fig. III. are bent so as to project up between each pair of line strips, and connection is made by inserting double connecting springs at these points, as shown at H and i, Nos. 4 and 7 lines being there shown connected. Line strip L is connected to the operator's telephone, and M is connected to generator or battery. Connecting strip B is to earth, and each line is normally plugged on to this. The lines go first through the drop, and then on INTERMEDIATE SWITCHES AND SWlTCS-BOAkDS. 133 to the line strip, so that the drops are always in circuit, ^^■l\i') — ¥^-=i / ■hi • !■- -iV|Bal-in I-. I ^r r _„ !L, iiiiilt ntnnmiTnnTT ...^^. j"ll,L-._-- Fig. 112. and have to be spoken through. Strips c and D are 134 PRACTICAL t£LEPHONE HANDBOOlt connected to operator's telephone and ringing generator respectively. The line strips are divided into groups of ten, and the connecting strips into groups of five, some of the latter groups being for connection to other tables, and some for local connec- tions. Fig. 112 gives a general view of a Gilliland So-line board, fitted with operator's transmitter and receiver fitted on brackets, the receiver being adjustable. Standard Switch-board. — This is a form of plug-and- cord board which is now very much used for .small ex- ' changes of up to 400 or 500 lines. It is made by the Western Electric Company. The board shown in Fig. 113 is for 100 lines, and is in- tended to be worked by one operator. In a busy centre this would entail very heavy work. In such cases it is more usual to employ 50-line boards. Subscribers' drops of small slae are arranged at the top in rows of ten. Below these, in five rows of 20 each, are the spring-jacks INTERMEDIATE SWITCHES AND SWITCH-BOARDS. 135 Spring-Jack, connected to the drops ; below these is another row of 20 jacks, which are used for the purpose of transferring connections to other tables when the jack of the subscriber wanted is out of the direct reach of the plugs and cords used. The latter, 20 in num- ber, are arranged in pairs on a hori- zontal table, the cords passing through holes bored in the table, and kept straight and tidy by weights and pulleys. The plugs rest in an upright position on the table, on which are arranged ten cam switches, for connecting the operator's telephoneto any pair of cords, and ringing keys Drofi t Fig. 114. Bn''''"/'n'' JQl Rm^SiOrop Cam hvey Fig. ITS. for calling the subscribers. Just above the table is fixed a row of ten ring-off drops, one to each pair of cords. Fig. 1 14 shows the connections of one of the lines, and 136 PRACTICAL TELEPHONE HANDBOOIC. Fig. IIS of a pair of cords to the ring-off drops and the operator's instruments. Suppose plug A is inserted in the spring-jack, the line connection will be diverted from its drop through the cord and ringing key to the operator's set, if the cam lever is in the position shown. To connect a second line, plug B is inserted in its jack. the ringing key b is pressed for a few seconds, bringing the cord and line connected to it into connection with the magneto generator (which is usually driven by power) or a ringing battery. The two lines will then be complete through the ring-off drop, and the operator, after noting that conversation has commenced, cuts out her instrument from the circuit by raising the cam-lever INTERMEDIATE SWITCHES AND SWITCH-BOARDS. 137 to the upright position. When finished speaking, the subscribers give a turn or two on their magneto, which operates the ring-off drop, and the plugs are withdrawn from the jacks by the operator. Many improvements have been made in the operator's apparatus used on these tables. Instead of the cam- lever a form of double switch, called the Dewar Table- key (Figs, n6 and 117), is now used. It is a kind of plug: Fig. 117. double press-button, mounted on a block of ebonite, and operated by pressing the handle-bar A pivoted at B between the two ebonite buttons c C. The effect of this is to press out the two springs D D from contact plates F F to the outer contact plates G G. As shown, D D are connected to the cords and plugs, F F are connected together and to one end of the ring-off drop coils, the other end of the latter being earthed. G G are connected to ringing keys H H, and from thence to operator's set, which is included directly in the circuit. •38 PRACTICAL TELEPHONE HANDBOOK. To allow the operator to speak when answering a call with a single cord, it is arranged that the plugs when resting on the table shall make an earth connection. This is attained by the metal of the plugs, which is prolonged past the vulcanite sleeve (as shown in Fig. io6), resting on metal plates or sockets screwed under Fig. li8.— Scale §. t the table, and connected to earth. This earth connection is severed directly the cord is raised. The ring-off drops are connected in shunt in order to get rid of the harmful effects of their electro-magnetic inertia, or self-induction, on the speaking. The self- induction even plays a useful part when the apparatus is connected as a shunt, as it offers a great resistance to the passage of rapid alternations of the speaking currents, whilst to the comparatively slow alternations of the ringing currents it offers little or no extra resist- Fig. 119.— Scale f. ance. For this reason the self-induction of the ring-off drops is increased as much as possible, by using large and long cores for a single coil, and enclosing the latter mTERMEbiAtE SmTCHS.S AND SWITCH-BOARDS, ij^ in a soft-iron tube, to form a box or armoured electro- magnet, as described on page 124. Anew pattern of spring-jack (Figs. 118 and 119) is used on the later boards of the Western Electric Company. The contacts are all doubled, two-line springs being used, between which a connecting plug is forced in making a connection, lifting the springs from the central contact plate. Single Cord Switch-boards, — These are made similar in form to the " Standard," but each line is connected iLine. Line. Fig. 120. to a cord and plug, so that a 100-line board would be provided with 100 cords and plugs. The connection of two subscribers is accomplished by using the plug of either of the subscribers to be connected, leaving in circuit for ring-off purposes the drop belonging to the line whose plug is thus used. This, of course, reduces the time taken in making connections, and would appear to be a great advantage, but this merit is neutralised in some forms of the board by the number of operations necessary in answering and ringing by the operator. 140 PRACTICAL TELEPHONE HANDBOOK. Q Fig 1 20, represents the connections of two lines on a very good form of board made by the Western Electric Company. The shanks of all the subscribers' plugs are insulated by a sleeve of ebonite, as shown in Fig. 121, so that when inserted in a spring-jack they only make contact with the line spring. The operator uses for answering the calls a double plug and cord, Fig. 122, to which her instru- ment and ringing generator are connected by means of a Dewar key, as shown in Fig. 123. On a drop falling, the operator inserts her plug in the subscriber's jack, and her instru- Fig. 121. Scale g. Fig. 122. — Scale §. ment is then connected directly in the circuit. The calling subscriber's plug is next inserted in the jack Fig. 123. of the number required ; the operator turns over the INTERMEDIATE SWITCHES AND SWITCH-BOARDS. 14! Dewar key and rings through both lines, and when she hears them commence conversation, she disconnects herself by taking out her plug. Operators' Transmitters. — These should be small, as large ones, such as the ordinary Blake, hide a large part of the switch-board from the operator. Metal-cased Blakes, Figs. 39 and 40, are often used. A good form of suspension is shown in Fig. 113, the connections to it being made by the flexible suspending copper ropes, which pass over ebonite pulleys carried on a horizontal arm capable of adjustment. The weight of the trans- mitter is balanced by one or two lead weights, so that the transmitter may be adjusted in a moment to what- ever height may be desirable. The ebonite pulleys should not be too small, as the continual bending to which the suspending wires are subjected in passing over them is very severe, and rapidly wears them through, unless pulleys of not less than I inch dia. are used. The flexible wire is made up of a large number of copper wires, .about 6 or 7 mils dia., stranded together. It should offer little resistance, for being in the primary circuit it would otherwise affect the efficiency of the transmitter. The best plan, however, is that shown in Fig. 124^ which has been adopted in the New Telephone Company's switch-room at Manchester. The trans- mitter is of the vertical granular type, pivotted on its axis so that the distance of the indiarubber funnel from the mouth may be easily adjusted. The whole is mounted on an aluminium breast-plate suspended by an 142 PRACTICAL TELEPHONE HANDBOOK. adjustable band round the neck, A key-switch fixed at the bottom of the plate when turned to one side puts on the transmitter cell permanently, and when on the other side requires to be pressed down to make the necessary connection, so that the battery may be saved. The Fig. 124. operator also wears a small and light head-receiver, held to the ear by a padded flexible steel spring. Most of the fittings of these instruments being of aluminium, they form a very light and handy arrange- ment, leaving the operators perfectly free for making connections. INTERMEDIATE SWITCHES AND SWITCH-BOARDS. 143 Fig. 125 shows a device introduced by the writer for the above purpose. When the receiver is not in use it is laid on prong B, carried in an ebonite bush, A, let into Fig, 125. — Scale \. the switch-table. Its weight presses down the spring c from a platinum contact on the brass plate D ; c and D form part of the primary circuit of the transmitter. An ingenious plan for the same purpose, called Gray's Contact Breaker, is shown in Fig. 1 26. The receiver is --'yv^- rtT'^^ Ia«ySi«it| v. A/" Fig. 126. — Scale J. furnished with three terminals, ABC. Under A is fastened the flat spring D. From B a wire extends to a contact plate, F. The connections to the transmitter are shown 144 PRACTICAL TELEPHONE HANDBOOK. in the figures, and it will be seen that the connection to B is common to both the secondary and primary circuits. The operator, in taking up the instrument, closes the primary circuit by pressing D against F. An objection to this form is that the flexible tinsel telephone cord is introduced into the primary circuit, the resistance of which is rather high, and gets higher with use. The operator has always to grasp the instrument in the same manner, and she is always in circuit with the secondary circuit, which is objection- able during lightning storms. In addition to the above arrangements, it is desirable to provide a two-way switch in the primary circuit, joined up to two cells, so that the operator may, by movingover the switch now and then during the day, change the working cell. The connec- tions for this are shown in Fig. 126. Domestic Switch-boards. — Fig. 127 shows an instru- ment made by the Western Electric Company, designed for the joining up by telephones of a number of rooms in the same or adjoining buildings, so that a person at any mTERMMDIATM SWITCHES AND SWItCH-BOARbS. 14S one station may ring and speak to any other one with- out the aid of an ordinary switch-board and operator. To accomplish this an instrument like Fig. 127, which comprises switch-bell, microphone, and switch -board, is fixed in each office, each instrument being numbered. A wire from every one station to every other one is run through and attached to the terminal at the top of the instrument corresponding to its number. If ten offices «f m , Rttitrp. Wirt Fig. 128. are to be connected, ten wires will be run, making the circuit of the whole, and an eleventh wire will be needed for the return circuit if earth is not used. The ter- minals are connected to sockets let into the bottom of the instrument, into which the plug A, connected to the telephone set, fits without touching the springs I, 2, 3, etc., screwed on a bar, B, which is connected to one end of a battery. L 146 PRACTICAL TELEPHONE HANDBOOK. The figure represents the No. S instrument, and it will be observed that the No. S socket and spring are absent, No, 5 line being connected direct to the instru- J t ■■"■. z3*iiz: Fig. 129. ment terminal. When No. 6 requires No. 4, the No, 4 spring on No. 6 instrument is pressed against the socket, causing No. 4 bell to ring. No. 6 then puts his instru- ment plug into No. 4 socket, and will be in communi- INTERMEDIATE SWITCHES AND SWITCH-BOARDS. 147 cation with the person at No. 4, when the latter takes up his receiver. Fig. 128 gives the connections for three stations. Wires with coverings of diiiferent colours should be used in running the lines so as to render the tracing of them easy. Many other similar arrangements have been brought out by different firms since the above, the most notable being that of the Gent & Company, called Slopet's Secret System, in which, by the use of a special switch, the ordinary return wire can be cut off, and by arrangement between any two stations the two ordinary line wires of those stations used to form a metallic circuit, when it is required that the conversation shall not be overheard. For full description of this and other systems see the " Manual of Telephony." CHAPTER VIII. MULTIPLE SWITCH-]}OARDS, In a large telephonic exchange, where more than three or four switch-boards similar to those described in the last chapter are employed, the connection of any two subscribers out of the reach of the operator who answers the call gives rise to much trouble and delay. Some means of communicating between the operators on different tables has to be adopted, and whichever way this communication is accomplished time and trouble are expended, and the connection is delayed. To overcome this difficulty the multiple board was invented, the principle of which is that, instead of having to connect any one subscriber at some one invariable position in the exchange, as in the old form of board, by the multiple any subscriber can be joined to any other at every table in the central office. The connecting places of subscribers are therefore multiplied, hence the name multiple. Any operator can connect any two subscribers together without moving more than a step) thus getting rid of the complicated methods of MULTIPLE SWITCH-BOARDS. 149 connecting and at least one-half the number of operations necessary on the other switch-boards, when the lines to be joined were not on the same table. Many multiple systems have been invented, but the only one which has been extensively employed so far is that of the Western Electric Company, in the perfecting of which a large amount of ingenuity and inventiveness has been exhibited. Since its first introduction the board has undergone many modifications, which are still in progress, important improvements having been madeduring the lastfewyears. Fig. 130 represents a table, or section, of the Manchester board installed in the year 1888. The upper portion of the table is divided into six panels. In these six panels is fitted a spring-jack for each subscriber whose wire is centred in the switch-room. The spring-jacks are arranged in groups of 100, made up of five horizontal rows of 20. Each group is numbered from i to 100, a number painted on the framework of the panels denoting the particular hundred. The first group (the bottom left-hand one) is numbered o, the next to the right i, the next 2, and so on to the sixth panel ; then another row above from left to right, thus building upwards. These groups are called the ordinary jacks, to distinguish from the 200 local jacks arranged along the length of the table just below. The local spring-jacks are those into which the operators plug in answering the calls of the subscribers whose wires terminate on the table. They correspond to the jacks in the " Standard " switch- board described in last chapter. ISO PRACTICAL TELEPHONE HANDBOOK. The indicator drops in connection with the local jacks are arranged at a lower level, in four groups of 50, making 200 in all, which is the number of subscribers whose lines are terminated on each table, and whose calls are answered by the three operators attending to it. Between the local jacks and the drops a ledge or Fig. 131. — Scale J. shelf is formed, through holes in which the connecting cords pass, the plugs attached to them resting when not in use on brass earth-plates screwed underneath the shelf. The brass prolongation of the plug thus makes earth, as in the " Standard." The cords are arranged in pairs, one in front of the other. Connected to, and in a vertical line beneath each pair, is a ring-off drop, fixed below the calling drops. On another shelf, just below, a Werner table-switch and two ringing keys are provided MULTIPLE SWITCH-BOARDS. 151 for each of the 45 pairs of cords. The cords and accessories are arranged in three groups of 15 for the operators who attend to each table. The Werner table- switch, Figs. 131 and 132, answers the same purpose as the Dewar switch already described. As many sections or tables as there are multiples of Fig. 132.— Scale 4 200 subscribers connected in the switch-room are fixed end to end to form a complete multiple board. Engaged Test, — As in a multiple board there may be many sections, on each of which any subscriber in the room may be connected, it is evident that some means is required, before connecting a subscriber's line on any one table, of ascertaining if the wire is already connected on another section, or one wire may get connected to several others at the same time, and lead to trouble and confusion. A test for this is a necessity in any multiple system. The means by which the test is made in the Western Electric Company's board can be explained by reference to Fig. 133, which gives a sketch of the connections of a subscriber's line, and Fig. 1 34, which gives the connec- tions of the operator's instruments. It will be seen from the latter that, in addition to the operator's ordinary »S2 PRACTICAL TELEPHONE HANDBOOK. instruments, a test cell is included in the line or secondary circuit of the telephone. The subscriber's line is connected to the spring of his jack on the first section of the board. From the back contact of this the line goes to the spring of the corre- sponding jack on the next section, and so on until the whole of the jacks belonging to the same number, in- cluding the local jack, have been so connected. The tm - loaa mbu iOOl ~ lyLOO G Tdbtc liat-lboo iboi-tnoa 1 Local ut 1=» Fig- 133. back contact of the last spring-jack is connected to the earthed indicator on the same table as the lecal jack. Fig. i33^shov/s the connections of No. 1,120 line at the last five tables. Besides the line connections, it will be seen that the sockets of the spring-jacks are insulated, and are all connected to a separate wire, which is called the test or click wire, which is carefully insulated. On the insertion of a plug at any one of the jacks the socket is thereby connected to the line, and gets earth through the subscriber's instrument. The effect of the insertion of a plug is shown at the H table, where MULTIPLE SWITCH-BOARDS. IS3 we suppose the line is connected to some other number. All the jacks behind the H table and the drop are cut out from the line connection, which is diverted to the plug and cord. If 1,120 is now asked for on another table, the operator having turned over the table switch, so as to put her telephone set in connection with the pair of cords she is using, and having her receiver to her ear, takes up the second plug of the pair (the first being Fig. 134. already connected to the calling subscriber's line), and before pressing it into No. 1,120's jack, taps the end of the plug on the socket of the jack. If she then hears a click in her receiver, she knows that the number is engaged on another section, as would be the case in this instance. The click is caused by the test cell getting a com- plete circuit through No. 1,120's test wire and the lines of the two subscribers. If the number had been disen- gaged, the test wire and sockets would remain insulated, no click would have been heard, and the operator would 1 54 PRACTICAL TELEPHONE HANDBOOIC. have completed the connection by pressing in the plug. Thus a fraction of a second suffices to find out if a subscriber's line is engaged at any part of the room. Spring- Jacks. — Two classes of these are used in multiple boards, the larger shown in Figs. 105, ii8, and 1 1 9, being so made that each is complete in itself. The smaller which is used on most of the later multiple boards, is made up in sets of twenty, the springs, sockets, and contact screws of the set being fitted on strips of ebonite, and form a very neat and compact arrangement, as shown in Figs. 135 and 136, the latter being a section. The strips are secured to the framework of the tables by a screw at each end of the strip, so that their Fig. 135. fixture or removal is a much simpler matter than that of the separate jacks. The MULTIPLE SWITCH-BOARDS. 155 insulation of the jacks on the strips is very good, which is important in a large exchange where each line is connected to a number of jacks, each forming a point for leakage. Being more enclosed, the contacts are much better protected from dust, which is a great advantage, as most of the trouble met with in switch- boards arises from dust settling on the contacts. Another good point is that the space occupied on the tables is only about one-half that of the larger-sized jacks, 100 small jacks taking up 40 square inches, and 100 of the larger ones 80 square inches. The latter point governs the number of jacks which can be fitted into any one section, so that the operators and the connect- ing cordc can reach to connect, and thus settles the number of ^'^- ^^e-Scaie }. subscribers which can be provided for in one centre, or what is called the ultimate capacity of the board. The ultimate capacity of the Manchester board. Fig. 130, is 4,200, but it is shown fitted for only 1,800 lines. Cabling or Wiring. — The great number of connections that have to be made to the jacks necessitates the adoption of some definite plan of dealing with the mass of wires in order to avoid confusion. The number of connections increases as the square of the number of lines in the centre, so that a compact method of wiring is especially necessary in a large exchange. The method of wiring adopted should allow of the jacks being readily accessible in case of faults. The shorter the length of wire used the better, as IS6 PRACTICAL TELEPHONE HANDBOOK. both dynamic and static induction increase with the length. The wires used should not impede access to other parts of the tables, and they should occupy as little space as possible. The cables used are oval in section, \ in. x f in., each containing 21 pairs of wires, which provide for both the line and test wires of a row of 20 jacks. Each pair of wires is twisted together, one beifig for the line wire and the other for the test, being dis- tinguished by different coloured coverings. The lengths of cable for each 20 lines are so con- nected to the jacks, and bound up together, from one end of the board to the other, that they look like a single straight cable with strips of jacks fastened at regular intervals (equal to the width of a section = about 6\ feet). The fitting to the jacks is done apart from the switch-board on a long bench fitted with forming blocks, one of which is shown in Fig. 137 (which also shows the underside of a strip of jacks), fixed at distances apart equal to the width of the sections of the board. In this manner the joints can be more carefully soldered and inspected than if they had to be done in position behind the tables, as was the case with the former system of cabling. The forming block. Fig. 137, is made up of a block of wood D (fixed to the bench), to which the strip of jacks is temporarily screwed. F F is a smaller wooden block, from the top of which 20 small iron pins project, round which the wires are bent in connecting 1S8 PRACTICAL TELEPHONE HANDBOOK. to the jacks. The lengths of cables (which are rather longer than the width of the switch-board sections), whilst being connected to the jacks, are fixed in the clamps shown, a length of cable coming from each side. Testing for the proper wires is done by means of plugs and cords connected to a battery and bell, so that the bell sounds when the same wire is touched by a plug at each end. When a whole length has thus been connected. ,^ y$-^cy^ Fig. 138.— Scale \. soldered and tested, and the wires bound up as shown, it is released from the forming blocks, lifted off the pegs in F F, carried to its position behind the tables, and the jacks screwed in their proper places. Fig. 138 gives a section of the cables required to fit up 600 lines, being 30 cables for 30 rows of jacks, and shows how they are supported by steel rods c C, screwed into steel strips, B. A A is an end view of five rows of jacks in one panel. Fig- 139 shows how the cables are arranged one behind the other by making the connecting wires from the MULTIPLE SWITCH-BOARDS. IS9 cables to the rows of jacks in six lengths, differing from each other by f in., the width of the cable. By this method the cables are very compactly arranged, the shortest possible length of cable is needed, access to the other parts of the tables is not impeded in the least, and the strips of jacks can be brought out behind for inspection and the remedying of faults. Scribner's Single-Cord Multiple Board, — This is a board also made by the W. E, Co., in which a plug and cord is^rovided for each subscriber's line, as before described. As shown by Fig. 140, which gives the con- nections of two lines and the opera- tor's set, it is rather complicated. It is no doubt this fact which has prevented its coming into more general use. The plugs in their normal position are held fast within the so-called earth-switch c, by a weight and pulley. The lever switcJies a serve for connect- ing and disconnecting the operator's aet, and also for ringing up the called- for subscriber. A special call-key, b^, and b^, with plug and cord : < ■ .^a ^; 1 IT I i 1 < t5 QilL^s 1 ( 'B' 1 1 ; i i I i6o PRACTICAL TELEPHONE HANDBOOK. connections, b, enables an operator to assist an over- burdened colleague. The working is as follows : — As soon as the operator sees, say, drop Ji, fall, she lifts up plug i, thereby con- necting her telephone to the line. After receiving instructions, she taps i on the socket of the subscriber wanted, and, if engaged, gets the ordinary test click. If jlpiVOXcYS S(t Fig. 140. free, she inserts the plug, and to ring him up depresses the button a, so as to bring the spring d^ on to battery or generator contact tP. After thus connecting, the operator cuts out her own instrument by pressing the ebonite block d under spring d^ by means of the button a. The ordinary indicator drop of the calling subscriber serves as the ring-off drop. As it is spoken through, its coils should be Joined up in multiple to lessen the self-induction. MULTIPLE SWITCH-BOARDS, i6i It IS advisable to provide double cords and switches in conjunction with the operator's set in case of accident, and to better assist neighbouring operators. One hundred subscribers are allotted to each operator Although the above board has a great advantage in the fewness of the motions necessary to make a connec- tion, and the consequent rapidity, there are many draw- backs in connection with it, which have prevented its being used to any great extent. A strong objection to single-cord boards is that they cannot be converted into metallic circuit boards, which will be important in the future. The central office at Hamburg, which is one of the largest in the world, fitted for over 6,000 lines, is worked on the single-cord multiple system and appears to have given much satisfaction. For Metallic-Circuit and Branch Multiple Switch- Boards, see Chapter XV. M CHAPTER IX. SPECIAL EXCHANGE SYSTEMS. In this chapter a few telephonic systems which have special features differing from the ordinary run of telephonic exchanges will be briefly described. British Post Office System. — The system adopted at New- castle, and other places where the Post Office authorities have established telephonic exchanges, is of a novel and interesting character. The instruments used by the subscribers are the Gower transmitter with, until re- cently, the Gower receiver ; but they are now more ^ig- '4i- generally furnished with two double-pole receivers, these being found more efficient. The former arrangement of instrument is shown com- plete in Fig. 141, and Fig. 142 shows the internal arrangements, the cover and transmitter being re- moved. Batteries are used for signalling. SPECIAL EXCHANGE SYSTEMS, 163 R is the magnet of the receiver, i the transmitter induction coil of resistances : — primary • 5, and secondary 250 ohms. SS' are two automatic prong switches, in which the ear-pieces of the flexible tubes are placed when not in use. The right-hand one serves to break the local microphone circuit, the left-hand lever is the usual bell and telephone automatic. K is the ringing button, B a Post Office relay for operating the local f^'^.~^'Mt\ Fig. 142. bell. Six terminals are fixed at the bottom of the case. Between ZE and c are connected the two Leclanche cells required for the microphone. Between BC and ZE five Daniell cells. When the left-hand lever is down this battery is permanently connected to line. This constitutes the peculiarity of the system as it is worked on the closed circuit system, a battery current always passing through the line when the instrument is not in use. No earth is used- to the 164 PRACTICAL TELEPHONE HANDBOOK. instrument, double or metallic circuits being almost exclusively employed, and are absolutely necessary, owing to the fact that the lines are run in close prox- imity to single-wire telegraph circuits, the . iriduction from which on single-wire telephone lines would render seen OANiEii BATTERV fig. 143- the voice nearly or quite inaudible. The use of metallic circuits for the purpose of suppressing induction will be referred to in Chapter XII. Central Office Apparatus. — The subscriber's lines on entering the switch-room are connected to a special form of indicator, shown in Figs. 144 and 145. The electro-magnet M M is screwed to a, ring of brass, which forms the framework of the droo. In a boss at the SPECIAL EXCHANGE SYS7EMS. i65 Fig. 144.— Scale \. bottom of this a pillar is fitted, to which is pivoted at a the thin iron washer A A, which forms the drop shutter- Whilst a current passes through the coilsj A A is held in the position shown by the attraction, but on the current ceasing A A drops until its lower edge rests against the insulated pin S S, to which a local night- bell circuit is attached. Between the poles of the magnet a small magnetic needle, i, is suspended, which is attracted to one pole or other of M M, according to their polarity. A card of the shape shown is fixed behind a, on which the number, etc., is written. Under normal conditions, when the line is not in use, the needle points to the left, as shown. If the line current ceases by the subscriber taking up the tubes, A A falls, and the needle points to the centre of the card, which indicates to the operator that the subscriber desires attention. The operator answers by in- serting a flat double plug attached to her instru- ment into a kind of flat spring-jack, both being shown in Fi^. 146. c c' are two strips of brass fastened on Fig. 145.— Scale J. i66 FIUCTICAL TELEPHONE HANDBOOK. the two sides of a piece of ebonite, the double connecting cord G is attached to c c', and to the two terminals of the operator's instrument, s and S' are brass springs with thickened ends which form the jack, being kept from contact by pieces of ebonite B, b'. A double cord with a plug at each end is used to connect two subscribers together, the indicators of both subscribers being left connected on the shunt or Indge system. These drops are of high resistance (i,ooo ohms) and offer considerable impedance to the speaking currents. ( A) Line TELEPHONE Fig. 147. Fig. 147 shows the connection for four lines, the indicators at the right and the connecting jacks at the left. Lines 3 and 4 are shown connected together with both indicators left in circuit. Line i is shown connected to the operator's set, and line 2 normal. To call up the subscribers a strong battery is used at the central office, which, together with the subscriber's battery, is sufficiently powerful to actuate the relay in SPECIAL EXCHANGE SYSTEMS. 167 the subscriber's instrument, which has been so biased by means of a spring that the subscriber's battery is not in itself strong enough to actuate it. The ring-off signal is automatically given by the subscribers hanging up the tubes and thus reconnecting the permanent current to line, which deflects the needle magnet at the central office. ' Subscribers may be furnished with a commutator with which to reverse the permanent current going to line, and cause the indicator needle to point to the right, which indicates to the operator that the subscriber is leaving his office. The permanent current is also a permanent test as to the state of the line or instrument, a fault happening to them deranging the current. Although a very perfect system for a small exchange, its advantages are dearly bought, as the frequent attention necessary to the Daniell batteries and the constant waste of material constitute very serious draw- backs. Manchester National Telephone Company's System. — The exchange in connection with the National Tele- phone Company at Manchester is worked by batteries combined with apparatus by means of which a special ring-off system is arranged, enabling each subscriber to call up any other when connected without the interven- tion; of the operators, and without actuating the ring-off signal. This arrangement overcomes the difficulty which is met with in exchanges having no special ring- off system (which is the case with most exchanges), that I5S PRACTICAL TELEPHONE HANDBOOK. the subscribers, if they do not at once get through to the subscribers they ask for, will persist in ringing them- selves, notwithstanding that the effect of this is to cause the ring-off drop to fall at the exchange, much annoyance ensuing to both subscribers and operators. The Manchester system was invented and brought into use in 1880 by the writer. The subscribers are each furnished with a set of instruments, comprising Blake transmitter. Bell re- ceiver, switch-bell (Silver- town or Liverpool pattern), and a special commutator press-button, by means of which the current sent from the battery is reversed in direction to that sent by the ordinary signalling button. The commutator button is shown in Figs. 148 and 149, the former being a Fig. 149— Scale J. pj^n with the cover and button removed, and showing the connections to the switch-bell and battery. L and E are two doubled back brass springs connected respectively to line and earth, with their ends normally making contact on the brass plates i N and Z. Plate Z also passes under the end of L spring, and under the end of E is the plate C. On pressing the ordinary ringing button the carbon end of the battery is connected to line, and the zinc end to earth through the spring^ E. On pressing the commu- Fig. 148.— Scale J. Special exchange systems. 169 tator button the L spring is brought into contact with Z and the zinc end of the battery, and the E spring with C and the carbon end, thus sending a reversed current to line. The commutator button is black and the ordinary one white, to distinguish them. Polarized Ring-off Drop. — The ring-ofif drop at the central office is polarized by a permanent magnet (some- what similarly to the magneto polarized bell), and is so arranged that it only responds to a current from the zinc end of the battery, and is neutral to a copper current. The ring-off drops are connected each .to a pair of cords and table switch in such a manner that they form a shunt to earth, as shown in Fig. 132. They have much iron about them and are wound to a resistance of 100 ohms, so that they offer considerable impedance to the speaking currents. This system, which was the first in which ring-off drops were connected in derived circuits, has given great satisfaction to the subscribers, especially since it was allied with the W. E. Co.'s multiple switch-board, which was fitted up at the Royal Exchange in 1888, under the superintendence of the writer, forming a switch- room so complete that it is still looked upon as one of the model centres of the United Kingdom. A general view of the room is given in Fig. 150, the boards on the right being the ordinary multiple tables, and those at right angles in the back-ground the trunk- line switch-boards. Further details of the arrangement are given in Chapters VIII. and X. 170 PRACTICAL TELEPHONE HANDBOOK. The Call- Wire System. — This system, introduced into New York in the early days of telephony, differs materi- ally from the ordinary systems of exchange working, inasmuch as no mdicator - drops are necessary at the Central offices, the instructions to the operators being given by means of special " Call-wires," altogether dis- tinct from and in addition to the subscribers' ordinary lines, which are run as usual. A Call-wire is not confined to one subscriber, but is connected to the instruments of a group of perhaps forty or fifty. At the exchange end of any one of these Call-wires, an operator is continually listening during business hours, and a subscriber of the group has merely to press a special key or lever on his instrument (which changes the connection of his instrument from his ordinary line to the Call-wire), to place himself in instant communication with the operator, whom he then tells his own number and that of the subscriber he wishes to speak with. The operator then joins the ordinary lines of these two numbers by cords, plugs, and switch-jacks as on an ordinary board, enabling the subscribers concerned to ring or speak as they wish, pressing the Call-wire key and telling the operator to disconnect when they have finished their conversation. So long as the state of the wires is kept good, this system is very simple, rapid, and efficient, the subscribers being always in touch with the operators, and as no drops are in connection the speaking on the lines is very good. There are two methods of joining up the Call-wire to &PECIAL EXCHANGE SYSTEMS. 171 the subscribers: — («) The original so-called Law system as carried out by the Law Telegraph Company in New York, in which the Call-wire was so run as to join up suc- cessively every subscriber's instrument in a group so that the subscribers are connected in series, as shown in Fig. 151, and {b) the system in- troduced into Dundee in 1882, called the Mann sys- tem, in which the subscriber's instruments are joined on branches to the main Call- wires, as shown in Fig. 152 (the numbers in the circles representing subscribers), the earth being used as return. The figures do not show the subscribers' ordinary lines. The former («) method of joining was peculiarly liable to faults, a simple break on any part of the Call- wire or in any of the switches employed disconnecting a whole group of subscribers, whilst in the Mann system a similar break might only disconnect one or a few. On any system, however, these Call-wires require particular care and attention, the Mann system being most affected by earth faults. By returning the main branch of the Call-wire to the 172 PRACTICAL TELEPHONE HANDBOOK. Central office and combining the outgoing and incoming parts, as shown by the dotted lines in Fig. 152, the immunity from faults is increased, as a second path is provided in case the main wire should be broken at any point. This plan was adopted by Mr. Miller of Dundee. The New Telephone Com- (l3) @ ' 6hf^ party's Manchester System. — ^^^ '<«» ^^ This was installed in 1891, and has given great satis- faction and aroused much interest in telephone circles. It combines the Mann Call- wire system with metallic circuits and the multiple principle, and seems as near a perfect exchange system as one can conceive. The special arrangements are due to Mr. A. R. Bennett, the General Manager of the New Telephone Company. The lines are run in overhead cables, which have lately been of the dry-core type (see Chap. XIV.) of various sizes, but mostly containing 52 twisted pairs of wires, these being enclosed in a lead tube protected on the outside by wrappings of tape well painted. The cables are manufactured by the Fowler Waring Company. Three wires are carried into each subscriber's office, MANN Jig 152. SPECIAL EXCHANGE SYSTEMS. 173 where they are terminated on a special lightning- arrester, shown in Fig. 153. Two of th£ wires, L^ and Lg, form the subscriber's main metallic circuit, and the third wire, c w, is a branch from the nearest Call-wire. Each of these is connected to a carbon block C, | in. square in section, supported on ebonite strips. It will be seen that earthed blocks come between each pair of the wires. These carbon arresters have proved more effective than the ordinary metal form. From the arresters, leads are run to the instruments, which comprise a combination switch containing an automatic switch lever, a call-wire key, in- duction coils, magneto genera- tor and call-bell, with a double- pole receiver and carbon trans- mitter, the latter being generally of the granular type, as made by the General Electric Com- pany. A large number of the Johnson pencil form are also in ig- IS3- ca e i. ^gg ^^j. descriptions of these see Appendix.) A sketch of the connections of these instruments is shown in Fig. 154. It will be seen that the receiver-lever is connected directly to the call-wire lever, and. that an insulated metal piece on the latter lever puts earth on the speaking or signaling instru- ments when the key is depressed, at the same time, dis- connecting the loop-lines and connecting the call-wire. The secondary wire of the induction coil is divided into 174 PRACTICAL TELEPHONE BANDS 00 iC. two equal coils s and Sj^, between which the receiver is connected. This plan has been adopted by Mr. A. R. Bennett, in order that the loop circuit of the main line shall be perfectly balanced, which is not the case with .the ordinary mode of connection. I LOOP a CjW LARTH © ^ 0— 1 Fig. 154. Central Office Arrangements. — The cables and wires from the outside are terminated on the standard shown in the frontispiece, and from there are carried to iron terminal boxes, from which wires lead to a test-board, which also is provided with very efficient carbon light- ning arresters. The test-board and cross-connecting SPECIAL EXCHANGE SYSTEMS. 175 board are made up of square panels, each providing for 200 wires or 100 loops. The Switch-board is of a simple and novel form. No drops being necessary, the subscribers' main lines are simply connected to a series of double sockets. The latter are made in squares of 100, of which Fig. 155 shows a section of three. They are constructed as follows : A slab of ebonite 5 inches square and J inch thick is studded with 100 round brass or bronze sockets arranged in ten rows of 10 in each. A quarter of an Fig- '^SS- Full Size, inch below this is clamped a similar slab with 100 smaller sockets with smaller holes. These 100 line squares are fixed horizontally in long recesses made in a table about 35 feet in length, of which a section is shown in the lower part of Fig. 156, which shows four of these recesses T T. In the full length of each are fixed 100 of the 100 line squares. Any one pair of wires of a subscriber's main line is connected to the pair of sockets on one of the first ten squares, and to the same numbered socket on every tenth one from this along the table, thus being multi- plied ten times in the whole length. All these con- nections are made by flexible wires soldered to the sockets and to the main lines of the subscribers, which run from end to end of the table in the recesses, thus con- necting by the branch system. This system is free from many of the troubles incidental to the ordi- PRACTICAL TELEPHONE HANDBOOK, nary series arrangement.' In the latter, a large number of contacts have to be rung and spoken through, all these con*- tacts being liable to get faulty by access of dust, etc., and the larger the exchange the more liable it becomes to these defects. The 200 wires required for 100 subscribers are made into a cable which is run from the cross - connecting board and along the whole length of. the switch-board, each wire having 10 soldered connections. Ten of these cables are put in each recess, the whole being given a complete twist in every 52|- ins. this bringing each connected 100 line square into its proper posi- tion at the top, thus forming one large cable containing 2,000 wires, with 20,000 connections to the sockets. Each of the 100 line squares is numbered along its outer edge to distinguish the sockets^ and has a large number painted on it distinguish the particular hundred. The table is 23 inches wide, Fig. I5t. ticale T^\ii. SPECIAL EXCHANGE SYSTEMS. 177 and, having four recesses, will provide for 4,000 sub- scribers when fully occupied. As shown in Fig, 156, two recesses are filled, thus providing for 2,000 lines. The advantage of this flat form of board is that the operators are enabled to get at the sockets from both sides of the table, so that when the board is fully utilized the multipling will be only one-half that necessary with the ordinary upright board ; this constituting a very great saving in cost, as only half the sections, sockets, etc., are required. Connection between subscribers is made by meacs of double cords and plugs suspended from above, as shown in Fig. 156. The form of plug used is shown full size in Fig. 157, L^ and L^ being the connecting parts slightly tapered. The spring and collar r help to ensure good contact with the upper sockets. The cords are arranged in pairs, different colours being used to Fig. 157. distinguish the different pairs. En Fig. 168. Fig. 169. panel for 600 lines. The numbering is from top to bottom of the panel. The projecting pins at the back, covered with vulcanite sleeves, are used simply to form troughs to guide the wires and keep them tidy. The wires from the switch-boards are brought in cables to the bottom of the board and up through the troughs, and are then connected to the terminal-plates in regular arithmetical order, so that any subscriber's number is the same as the number of the terininal to i88 PRACTICAL TELEPHONE HANDBOOK. which it is attached. On the test-board this is not the case, the line wires being attached to that board in the order in which they are brought in, disregarding \yhat subscriber they belong to. The cross-connecting board is arranged in a line with the switch-board, and the test-board is placed at ^-_ -^^'~^/ — v—^ right angles. Connections ( L,nt L,„d,' T between the two are made ki \[ : ,\'~ , :, ,;'":. ,; . ^ in a special manner, de- signed to keep the wires used for the purpose in an orderly condition/ and so that they can readily be taken out and others run between different points of the boards. This is managed in the following manner : — In a vertical line over each of the troughs TT, Fig. 163, a series of fourteen |-inch holes are bored in the frame- work, as shown in Fig. 170. The connecting wires are e : : Fig. 170.— Scale ^. passed from the test-board through these holes, are then led horizontally along and round the corner, until they arrive over the part of the cross-connecting board on which their numbers are situated, when they are threaded through other holes and down to the terminal pla.tes. All connecting wires for subscribers whose numbers are between I and 300 pass through the TEST-ROOM APPLIANCES. 189 lowest of the 14 holes in any trough. All between 300 and 600 pass through the second hole from the bottom, and so on, rising a hole higher for every 300 subscribers, so that the top or fourteenth row of holes will only be used when the full capacity of the switch- board (4,2CX3 lines) is nearly attained. In 1891 the number of subscribers connected was 1,600, and the sixth set of holes from the bottom was in use. As the numbers on the test-board are no guide to the subscribers connected, it is necessary to provide a book in which two lists are given : (i) A list of subscribers in numerical order, showing the numbers on the test-board to which each one is connected ; and (2) the test-board number iti numerical order, showing what subscribers are connected to each. A column is left in each list for recording alterations. The Manchester installation, as given above, was the first occasion on which the distributing board was used in connection with the telephonic exchanges in this country, although it had for some years been considered indispensable to a complete system in the United States. Any one who has seen the awful tangle and confusion in which the leads are involved in any of the large exchanges not employing one would recognise its utility. The tangle was due to the fact that on the frequent occasions on which leads had to be changed, they would have to be dragged out and put in other places. When using a distributing-lDoard the leads when once connected need never be disturbed, only the connecting wires between the two boards being altered. 1 90 PRACTICAL TELEPHONE HANDBOOK, the special arrangement above described allowing this to be done with the greatest ease and regularity. Since its installation in 1888, the Manchester system has worked very successfully. The whole of the con- necting blocks, etc., were made by the Western Electric Company. Fig 171 gives a general view of the test- board and back of cross-connecting board, and also shows the testing instruments. Subsidiary Distributing Board. — Many of the ex- changes in America are provided with two distributing boards, one in the position described above, and a second at the opposite end of the switch-board. To this additional one the cables, after connecting up all the ordinary spring-jacks, are brought before connecting up the local spring-jacks. For the ordinary purpose of getting connection between subscribers by the multiple board, it does not matter how the 200 subscribers which the operators on any one table attend to are com- posed. They need not be in numerical order, as, when a call is made, the operator simply inserts a plug in the corresponding local jack to answer the call and con- nects the number asked for by plugging into one of the ordinary jacks, to which the subscribers must be con- nected in proper numerical order. The object of the second distributing board is to divide the specially busy numbers among the operators, so as to equalise their work. Some English exchanges are now fitted as above. Coleman & Jackson's Test-Board. — Figs. 172 and 173 show the arrangement of springs and lightning arresters used on this test-board, which is somewhat similar to TEST-ROOM APPLIANCES. 191 the Manchester form, except that the hne springs C C are arranged on horizontal shelves, and the contact blocks D D are provided with other springs, F F, which press against the main springs and ensure a good con- -Scale J. tact. When the test-shoe is inserted the two springs are separated. The line wires are connected to terminals G G, and the switch-board wires are soldered to wires H H, connected to the contact blocks. This board is in use in many exchanges, including Birmingham and Bradford, and serves its purpose well. A neat form of test-board is shown in Figs. 174 and 175. For each line two brass pieces, A and B, are clamped to a base board, one of which overlaps the '^' '^5-— caej. other but does not touch it. Connection is made between the two by a sliding piece of brass, C, dove- tailed on to B, and furnished with a knob ; A, B, c form part of the circuit of the lines. On wishing to test the piece, c is drawn from under A, and a brass plugr Fig. 174. 192 PRACTICAL TELEPHONE HANDBOOK. attached to the test set is inserted into holes D or F, according to which part of the line is to be tested. The Power Generator. — This is simply a magneto generator mounted on a stand or base, and arranged to be driven by a machine of some kind, generally a water- motor. Bailey & Co.'s "Thirlmere" water-motors are Fig. 176.— Scale \'. very convenient for the purpose, the smallest, or No. size, generally sufficing. When the exchange is not large the ordinary size of generator will be sufficient to supply the current required, but special large-sized ones are made for centres where the demand upon them is considerable, In such cases it will often happen that ringing will be TEST-ROOM APPLIANCES. t9?. taking place over several lines at the same time, and as the lines vary very much in resistance, some, such as the trunk lines of high resistance, may get little current. To remedy this, it is necessary to keep the generator of a low resistance, but at the same time the E.M.F. must be kept up. To fulfil these requirements it is necessary to employ generators of larger size, so that a large number of turns of thick wire may be put on the armature. Fig. 176 shows a form of generator much used, having a resistance of about 65 ohms. The current is collected by means of copper brushes, as in a dynamo machine. The generators are generally fixed in a closed case provided with a glass front, so as to keep out the dust and yet allow them to be visible to the attendant. A Pole-changer is a very useful instru- ment for use in exchanges where power is not always available. By means of it the connections of a battery of about 10 cells are automatically changed by ^'S- i77- the swinging of a pendulum, so that rapidly alternating currents can be sent to work magneto bells. It is made up of a polarised electro-magnet and armature, as shown in Fig. 177. The armature forms part of the pendulum the bobbin on which may be adjusted for different rates of vibration. The upper part of Fig. 178 shows the con- nections of the driving mechanism, which consists of O '9+ PRACTICAL TELEPHONE HANDBOOK. coils S and s' with polarised armature vibrating between. This is worked by battery B, of one or two Daniell cells. The lower part shows the means of tontinually reversing the ringing battery B'. A simpler form of pole-changer is shown in Fig. 179 Llr.t EARTH hltHH|.|«|ihH Fig. 179. which also shows the connections. A double battery is required for this, as shown. Much trouble is experienced in exchanges using generators and pole-changers, but especially the latter, owing to the inductive effects upon other wires when ringing. It is not so pronounced in the c:,se of the TEST-ROOM APrUANCES. '95 generators, because the currents from these are more in the form of a regular wave, whilst with the latter they are sudden makes and breaks. Mr. Miller, of Dundee, ha(S found that the connection of a condenser of one or two microfarads between the terminals of a pole-changer diminished the trouble very much, and in some cases suppressed it entirely. Rough Testing Set. — The great majority of lines in a telephonic exchange are not more than half a mile in length, so that elaborate tests to determine the locality of faults are seldom necessary, and would usually result in waste of time, as the linesmen would generally have cleared the trouble in the time taken to locate by test. Many of the faults, such as contacts, do not require any test, and the telephone itself is such a delicate instrument that very frequently by its aid alone faults can be roughly located by an experienced test- clerk who has got used to the characteristic sounds given by the line under certain conditions. For faults which require rough tests the instruments required are : i, a galvanometer; 2, a battery of, say, 30 cells, so connected to a switch that a current from i, 2, 4, 10, 20, and 30 cells may be obtained at will ; 3, a telephone set with magneto bell ; 4, switches and testing shoes. Fig. 180, 196 PRACTICAL TELEPHONE HANDBOOK. The galvanometer should be one having a soft iron needle polarised by permanent magnets, as shown in Fig. 1 80, as small magnetic needles are not reliable, the readings with the same current strength varying very much from time to time. The soft iron needle is of a tuning-fork shape, pivoted at the top, the same pivot carrying a pointer at the front, as shown in dotted lines. Fig. 181. The instrument should be wound with two coils of wire, one of about 200 ohms resistance, provided with a x^jfth shunt, and the other of about •$ resistance. Fig. 181 shows the connections of a convenient arrangement of the testing instruments : — A is the testing shoe for single lines ; B for metallic circuit lines, C the telephone set and magneto ; D galvanometer ; F G TEST-ROOM APPLIANCES. 197 H, J, K, two-way switches for altering the connections ; L a rotary switch for altering the battery power ; M a battery key, By F connection can be made to one side or the other of the double test shoe ; by G the galvo. can be put in or out of circuit; by H the shoe can be put directly to earth ; by J a permanent current can be put to line; and by K the earth connection can be taken off the telephone set, and the latter included directly in the loop circuit. Instruments for Electrical Measurements, — For such measurements as the conductivity, insulation resistance, or the static capacity of lines, more sensitive and accurate instruments are required, for descriptions of which, and their use, see Chapter XVII. CHAPTER XI. OUTDOOR CONSTRUCTION. Selection of Route. — In selecting a route along which to run a telephone line, care should be taken to avoid; as far as possible, longer spans than about 80 yards. Where only one or two wires are concerned in towns it is better not to erect poles, as they are expensive, and are in most cases objectionable to the neighbourhood. It is better to select strong chimneys, on the highest buildings, for the attachment of the insulator supports. The route chosen should be as straight as possible, in order to lessen the materials required, and to prevent excessive strain on the supports. In crossing over thoroughfares the wires must be at least 30 feet from the ground, in order to prevent accidents from fire- escapes. The wires should also cross the streets as near as possible at right angles, in order that they shall be seen as little as possible, and that if any should break there would be less danger of their falling into the street, to the danger of passers-by. The wires should not pass closely over chimneys, as the heated air very OUTDOOR CONSTRUCTION. 199 materially weakens the wire, especially during showery weather, when it is subjected to frequent alternations of heat and cold. In the country, efforts should be made to keep clear of trees,, the branches of which, if touching the wires, give rise to excessive leakage to earth. As permission to run wires along the public roads is somewhat difficult to obtain, recourse must generally be made to private property, and care must be taken that no damage is done to trees, fences, etc. Poles should be kept near the hedges, and should not be fixed in the middle of fields, or, at any rate, stays should never be used where cattle would be liable to be injured by them. Railways should be crossed as little as possible,' as the railway companies are very exacting in their con- ditions. In exposed situations advantage should be taken of any shelter from the prevailing winds. Way-leaves or Easements.-— Before the wire can be erected, it is necessary to obtain what are called way- leaves or easements, which are forma) permissions from the owners of the property for the erection of poles or the attachment of wires to any building. To obtain these is frequently a very difficult matter, and one which requires much tact, judgment and perseverance. A nominal payment of is. per annum is usually made for the way-leave, but often a heavy payment is demanded and frequently has to be paid. Wire. — Previously to about 1884 the wire used for running telephone lines was mostly of iron galvanised to 200 PRACTICAL TELEPHONE HANDBOOIC. protect it from rusting, which, however, it failed to do for long, especially in manufacturing districts, where its life was only about four or five years, and in many places much less. The size of wire used was generally No. II, or 121 mils diameter, having a resistance of about 24 ohms to the mile. Copper or bronze wire is now almost exclusively used, and for many reasons is much superior to iron. Copper is used for all trunk lines. As pointed out in Chapter I., it is one of the two best conductors, its resistance being only ^th that of iron. This in itself would have ensured its adoption long ago, but that until a few years ago its mechanical properties were unequal to the requirements. By a process of what is called hard-drawing its mechanical strength has been raised from about 6'S tons per square inch to about 29 tons, and it is now in every way suitable, being stronger than iron and equal in strength to mild steel. Copper corrodes but very slowly, in pure atmospheres hardly at all, so that the expense of renewal and maintenance is much reduced, especially in manufacturing districts. In order to obtain an equal resistance, a wire of copper much thinner than of iron can be used. On this rxcount copper wire does not attract so much attention on the part of the public, and, therefore, does not raise so much objection as iron wire. The electrostatic capacity, being proportional to surface, is small in this thin copper wire. This is a very important matter in long-distance working. The magneto-induction, or self-indiiciion, for the same forni OUTDOOR CONSTRUCTION. 201 of wire is much less for copper than for iron, as shown by the experiments of Professor Hughes. This also is a very strong point in favour of copper wire for long- distance working. The supports for the lighter wire need not be as large or costly. The old wire will command a good price as old copper. Silicium-Bronze Wire. — All the advantages given above apply also to silicium-bronze wire, so called not because silicium enters into the composition of the wire, but because its compounds are used as a flux in the manufacture of the alloy, which is composed of copper about gy and tin about 3 parts in 100. The properties of iron, steel, silicium-bronze, and hard- drawn copper wircjs of common sizes are given in the table below : — Gauge Dia. in Weight Res. Ohm- Tensile S. W. G. Mils. in lbs. per mile. per mile. Mile Constant Strength in lbs. Iron Wire ..• •.. 1\ 170 400 12 4800 1069 II 120 ZOO 24 fl 535 16 66 60 80 }} 160 Steel ... 7.. 16 66 60 103 ^200 36a Silicium Bronze •■■ 16 66 64 30-5 1950 331 18 48 38-5 50-1 )i 187 Hard- drawn Copper "J 110 zoo 4-46 892 750 14 79 100 8-92 1} 375 16 66 70 12-74 260 It will be seen that the great strength of the bronze wire is obtained at the expense of a high resistance, for which reason it is only used for short local wires. Bronze wire loses its strength if soldered in the ordinary 202 PRACTICAL TELEPHONE HANDBOOK. manner, as the heat necessary weakens the wire very materially. A mechanical joint or solder melting at a very low temperature should be used. No i6 hard-drawn copper wire is used for local lines, No. 14 for trunk lines up to 50 miles, and the ii| for long trunk-lines. No. 18 silicium-bronze wire is that generally used for local exchange lines. Insulators. — As the wire used for telephone lines is mostly bare and must be supported at frequent intervals, it is necessary to provide special insulators to whichthe wire may be attached, and so prevent excessive leakage through the poles, which are not sufficiently good insulators in themselves. In addition to having high insulating qualities, the insulators must have sufficient strength to resist the strains to which they are sub- jected. Material. — This has varied from the original goose- quill to earthenware, glass, ebonite and porcelain. White porcelain has given the best results, but well-glazed earthenware comes closely behind it, and has the merit of being cheaper. The principal requirement is that the material must not be porous, and must have a fine glazed surface which will not attract moisture. Experience has shown that the leakage does not pass through the body of the insulator, but is altogether a matter of surface conduction by means of the films of dirt or moisture deposited on them. Form. — In designing the form the object has been to make the surface over which the leakage must pass as OUTDOOR CONSTRUCTION. 203 long and narrow as possible consistent with strength, as the law of resistance is the same for films of moisture as for other substances. A dry portion of such surface must also be preserved in the wettest weather, which object is attained by making the insulator in the form of an inverted cup or cups. Cordeaux's Screw Insulator. — This is probably the one which answers the above and certain other require- ments to the fullest extent, for which reason it is mostly used for important telephone lines. Fig. 182 shows it partly in section and the galvanised iron bolt used in con- junction with it.. It is a double-skcd form of insulator, which means thit it it. in the form of an inverted double cup. Single- shed insulators have only one inverted cup. It will be seen that a great length of surface is opposed to the leakage between the wire (which is fastened in the groove) and the bolt. The screw arrangement shown allows of the insulator being taken apart from the bolt, when in position, for the purpose of cleaning out the inside or to change the position of the wires on the Scale J. poles. An ihdia-rubber ring, put- over the screw, is used to, allow for the difference in expansion by heat between the iron and the porcelain. The wire is placed against one side of the groove and is then bound to the insulator by two lengths of i8's soft copper-wire, in the manner shown in Fig. 183, the 204 PRACTICAL TELEPHONE HANDBOOK. binding wire being first wrapped round the line wire in order to prevent injury from the continual friction against the insulator. The wires are then whipped round the line from B to E, thence back to D ; then from the upper side of the line wire round the neck of the'insulator to the under side of the line at C» back over the first layer to B, and then finished off as a single layer to A. For the very heavy trunk lines recently run by the British Post Office (of wire 800 lbs. per mile) copper tape Fig. 183. has been adopted for binding purposes, being applied in a somewhat similar manner to that shown in Fig. 183. In many circumstances the Cordeaux insulator is not suitable, such as when excessive strain is put on the supports by the wires going off at an angle. Also when the wires have to be terminated or shackled off, which means that the wires coming to and going from are fastened to the insulator independently of each other. OUTDOOR CONSTRUCTION. 205 The Laiigdon Insulator, Fig. 184, is much used for such cases. It has three grooves, in each of which a wire may be terminated. The bolt cemented inside goes far above the grooves, so that if ths insulator should break the wire cannot fall. When circumstances require that additional security should be given, as when wires cross over important thoroughfares, they should always be terminated on each side. In many places all over-house wires are terminated. Fig. 184.— Scale J. Fig. 185.— Scale \. Bennett's Insulator, Fig. 185. — This serves for termi- nating equally as well as the Langdon, and is superior to it in insulating powers and in other respects. It 2C6 PRACTICAL TELEPHONE HANDBOOK. was specially designed to meet the various demands of telephone work by Mr. A. R. Bennett, and has been very extensively used and found to answer all require- ments. It has four grooves in which wires may be terminated. If the wire is a light one, both terminations may be made in the top groove. The Bennett insulator is especially strong in resisting damage by stone throwing, usually a costly item in maintenance. Double Shackle Insulator, Fig. i86. — This was almost universally used in England for over-house work until a r^ m ^ r-\ Fig. i86. — Scale J. few years ago, when attention was drawn to its very poor insulating power. For short lines this did not so much matter, but when long-distance telephoning became more extensive the electrical condition of the lines was required to be as perfect as possible, and the double shackles were discarded for the other forms of terminating insulators described, which give at least eight times better insulation. They are still used now and then, where great strength is absolutely necessary. Fig. 1 86 shows the method of terminating by their means. Wooden Poles are used for nearly all but over-house OUTDOOR CONSTRUCTION. so? work for the support of the wires and insulators. They are generally round in section, but square ones are sometimes used to suit the taste of the proprietors of tlie land on which they are erected. Creosoting. — Before use the poles should be subjected to some preservative process, many of which have been suggested and tried, but the only one which has given satisfaction is creosoting. This consists in forcing into the pores of the timber, when thoroughly seasoned, a quantity of creosote, an oily and antiseptic product of coal-tar. About lo lbs. of creosote should be absorbed per cubic foot of timber. This process, if properly carried out, effectually protects the pole, from wet-rot, which attacks unprotected poles at the ground line, where there are great alternations of temperature and -moisture. The poles used are mostly Norwegian or Swedish firs, felled in winter, when the sap is least plentiful. It is important that the natural butt of the tree should be attached. An objection to creosoted poles is that they cannot be properly painted, as the oil oozes through. Their appearance is not therefore prepossessing. Poles up to 65 or jo feet, in length can now be creosoted. When longer -ones are required two poles should be spliced together, the top of one and the bottom of a smaller one being fitted together for some eight or ten feet, and then firmly clamped with iron bands, or wrappings of stay wire and bolts. Poles are supplied in two sets, liglit and stout. The =o8 PRACTICAL TELEPHONE HANDBOOK. first are for use on lines of not more than ten or twelve wires, and the latter for heavy lines above that number. Erection of Poles. — The poles are planted in the ground about one-fifth of their length, except the longer ones, which need not be planted more than seven or eight feet in good solid ground. In digging the hole an oblong space is first cut I'lg. 187. out about eighteen inches wide and four or five feet long, the longest side, if possible, being parallel with the line of the wires to be erected. This space is then dug out in steps until the end where the pole is to rest has reached the proper depth. The pole, with the arms attached, is then brought to the hole so that the butt lies over the deepest part. It is next tilted up, and three or four strong ladders of different lengths are put under the top end. By a couple of men or so at each ladder the pole is gradually OUTDOOR construction: 205 raised a few inches each lift, the ladder^ being shifted in position pne at a time, so as to keep them as near right angles to the pole as possible, to get the best effect and prevent slipping. This is further prevented by passing light ropes over the tops of the ladders after being fastened at the butt end of the pole. Fig. 187 will give an idea of the method, A showing the form of the hole, B the pole, c, D, E the ladders, longer ones being used as the pole gets more upright, when it is also steadied by ropes. At F a board is shown at the end of the hole, which is to prevent the end of the pole digging into the soil and so impeding its erection. The sides of the hole prevent the pole falling over sideways, When the pole is upright the earth is filled in and well rammed or punned down with punning tools. This punning is very important, and should on no account be scamped, as the firmness of the pole depends altogether upon it. When exceptionally large poles have to be raised, or poles have to be put in positions where ladders cannot be employed, a smaller pole is erected in some con- venient position to be used as a derrick. Pulley blocks are attached to an arm at the top and to about the centre of the pole to be raised. By this means the latter pole can be swung round and its ends got in posi- tion, and then, by ladders and ropes c^&di sash-lines, brought to the upright. Walls haive often to be taken down before the work can be completed, and- the skill of the men is often taxed in effecting the purpose. Arming the Poles.— The arms used vary in length, 810 PRACTICAL TELEPHONE HANDBOOK. according to the n amber of wires they "are to carry, whether two, four, ur six wires on each, the most common lengths being 24, 42, and 54 inches respectively. The centre wires should not be less, than 14 or 15 inches apart, in order to allow the men to get up between. Fig. 188. Scale ^. Fig 189. The arms, which are usually of good sound oak, about 2\ in. square in section, are fitted into grooves, sawn qii one side of the poles at about 12 inches apart, and are secured by a bolt which passes through pole and arm, as shown in Figs. 188 and 1 89, which also shbVv the pole roof of galvanised iron fitted on the top of a pole and surmounted by a saddle bracket, into which the bolt OUTDOOR CONSTRUCTION. 211 of an insulator is fitted for carrying what is called the cap wire. Earth Wiring. — Figs. i88 and 189 also show a wire which is run up from the bottom of the pole (where a coil of it is buried), and is stapled round the arms between each pair of insulators. This is intended to intercept any leakage which may occur over the insu- lators, and prevent its leaking into the adjoining wires carrying it off to earth instead. The earth wire is sometimes con- nected to the bolts of the insulators but this is a mistake, as unless the wire makes good earth (which is very seldom the case) it helps the leakage from one wire to another, and causes excessive leakage to earth in wet weather. Stays. — When the poles are exposed to heavy strains by the wires going off at an angle, stays or guys are used to prevent thej pole going over in the direction of =2 the strain. They are usually made up of seven No. 8 "^^ ^'^- '9°- galvanised iron wires twisted together. One end of this is taken twice round the top part of the pole, the best position being midway between the top and bottom arms, so that it may act at the resultant point of the total pull of the wires on the pole. Vi!rV=t'Hj PRACTICAL TELEPHONE HANDBOOK. A hole is dug as far from the foot of the pole as is convenient, and in this hole a block of creosoted timber is placed, through which a long bolt, called a stay-rod, provided with a large washer-plate, is passed. The whole should be undercut, as shown in Fig. 190, so that the puU may be against solid earth. The top of the stay-rod is provided with a swivel, to which one end of the stay is attached. The swivel is so arranged that by turning a nut the stay can be tightened up. Sometimes two or three stays are re- quired where the strain is excessive. Where the wires go off at nearly a right angle, it is better to fix two stays or two double stays, one being fixed in a. line with one direction of the wires, and the second in a line with the other direction. Struts. — In cases where stays cannot conveniently be fixed, struts are used, which consist of a rather shorter pole fixed at an angle to the main one and on the same side as the pull of the wires, A block of creosoted timber is attached to the foot of the strut by means of an four feet in the ground. Struts should be avoided, if possible, as they are not nearly so satisfactory as stays. In many cases it is better to truss the pole, as shown in Fig. 191, where an outrigger, A, is screwed to the pole ^'ii^'. Fig. 191. iron strap, and this is buried about OUTDOOR CONSTRUCTION. Z13 on the opposite side to the pull, and a strong stay is passed through an eye in the end of the outrigger, and attached to a stay-rod and block buried near the foot of the pole, or the stay-wire may be secured to the bottom of the pole itself, being provided with a stay- tightener to strain the stay, as shown at B. Over-house Work. — Chimney brackets, firmly nailed to the chimney, as shown in Fig. 192, are used to support the insulator of wires attached to chimneys or the corner of buildings. The bolt of the insulator is fixed in the socket at A. Care should be taken that the angle chosen is such that the pull of the wire is towards the chimney. If this cannot be managed, and the chimney shows any sign of weakness, an iron band should be fitted round it, or several loops of -^'S- i92- stay run round, so as to rest on the bracket and one or two courses of brickwork. Complaint is often made of the noise caused by the vibration or humming of the wires attached to a build- ing. A very simple method of preventing this is to wrap a long strip of lead, about \ inch thick and \ inch wide, tightly round the wires, for about 8 inches on each side of the insulator. Another method is to terminate the wires on double shackles, the iron straps and bolts of which are replaced by tarred rope passed through the shackle 214 PEACnCAL TELErriONE HANDBOOI'. cups. This forms what is called a Sourdine. Light and stranded wires do not give so much trouble in this respect. Standards. — For carrying the wires of a telephonic Fig- 193- - Scale ^. exchange, where the buildings are high, standards are used which are fixed on the roofs. Some managers prefer wood for these standards, and others iron. The OUTDOOR CONSTRVCflOM. 11% latter have a neater appearance arid are fast supplanting the wooden ones. The style which is now generally used in this country was designed some years ago by Mr. A. R.' Bennett. Fig- 193 shows one of these iron standards, and the method of fixing on the ridge of a building. The upright part is a wrought-iron tube of from 3I to 4J inches diameter, the bottom of which is tightly wedged in a socket formed in a cast-iron chair, made so as to fit over the ridge of the roof. Before being put in position, sheet lead and two or three thicknesses of roofing felt are fitted on the ridge. Tubes for these standards are made 3, 3J, 4, and 4^ inches diameter, the metal being \ inch thick, so that the smaller sized ones fit into the next size above. The usual lengths are 15, 18, and 24 feet. Many standards are formed by two tubes, one fitted inside the other for a length of about 2 feet, and secured by two boltsj passing through the tubes. Standards of 40 feet or more in length may thus be obtained. Iron Arms. — Fig. 194 gives a view of one of the arms on a larger scale. They are formed of two lengths of channel iron, so shaped that when screwed together by the bolts shown they grip the tubes, and leave spaces for the bolts of six insulators. The arms thus formed are 5 feet long, i J inch wide, and i^^ inch deep. ■ Fig. 195 gives a section to a scale of one-third. Four wire arms are also made for use where" heavy wires are used, or the number of wires is small. Iron standards must be well stayed, in order to resist 2i6 PRACTICAL TELEPHONE HANDBOOK. the strains upon them. For short ones it is usual to attach four stays, as shown in Fig. 193, each provided with stay-tighteners, and attached to wrought-iron j/^jj'-^^ clips, which are iron bands passed r.Ound arid clamped on to the strongest beams of the roofs, leaving an iron ring projecting through the roof, to which' the stays are ' I'o & . f ,10 Qt fCt ■ al "Ifa "nnn "■ fl^Vo : n r t ] Fig. 194.— Scale ^. attached. The foof at thiese points must be ^iij,^/^/ with sheet lead to prevent leakage of wafer'. < ' If the standard is a long one, or is' subjected to specially severe strains, taore stays arS^ attached. Some beirig fixed at a lower point' of the standard. Two or more stays may be fixed to the same eye-clip. The staying of iron standards is very important, and great care should be tafeeft that • '^' '^5- ji jg. thoroughly well done. Trussed Standard, — Where difficulty is experienced in arranging sufficient stays,' an arrangement like Fig. 196, also due to Mr. Bennett, may be adopted. The trussing is effected by four steel or iron rods, fastened at their upper and lowef ends by screws arid nuts, by means of which they can be strained over a cast-iron disc fastened to the tube midway between the foot and the lowest arm. Fig. 197 gives details of A on a largei" scale, and Fig. 198 details of B and c. OUTDOOR CONSTRUCTION. 217 g=S=£ iiJ I. ^ q a Another method of fixing iron standards is to fit a block of timber about 6 feet long, and 8 or 9 inches square in section to the ridge of the roof. The tube is fitted into a hole bored in the block, fi which takes the place of the iron chair, and strengthens the roof by spreading the pressure over several principals. Double, triple, and multiple standards are made up of two, three, or more upright tubes or combinations of tubes, connected together by specially long arms. On the principal routes in Glasgow five double tubes eire thus connected by long arms, 32 wires being carried on each of the latter, 30 of these arms being fixed from top to bottom tliiis giving a carrying capacity of 960 wires. The frontispiece to this book shows the square standard on the roof of the New Telephone Com- r pany's Exchange in Manchester, formed of combinations of the, tubes and arms braced together F g. 196.— Scale ^. by iron rods and rings, making a very neat and strong structure. When wooden standards are used for over-house work they are generally square in section, and are taken through 2l8 PRACTICAL TELEPHONE HANDBOOK. the roof and firmly bolted and braced to the timber work cr to one of the walls of the building, through which an fttL in m Fig. 197.— Scale ,;^j. Fig- 198.— Scale ^. clips are passed and large wall-plates fixed so as to brace the standard firmly to the wall. Sometimes the standard is fixed outside against a wall with clips and wall-plates inside. Stays may often be dis- pensed with for wooden standards. Clayton Standards. — Objection is often raised to the standard passing through the roof, in which case a Clayton standard may be used which is a wooden frame- Fig. 199- work so constructed that it strides over the ridge as shown in Figs. 199 and 200, OUTDOOR CONSTRUCTION. 219 It is braced by an iron rod as shown. These standards have the advantage that they can be made so that the arms cross the ridge of the roof at any angle. They should be well stayed to give stability. Fig. 201 shows an arrangement of Mr. Bennett's by means of which two wire arms may be converted into &. =^ M, -s©- ■"^gr Fig. 200. Fig. 201. into six, the Scale j\y. four wire arms, and four wire arms extending piece being of wrought-iron formed into a boss at one end. Running the Wires. — The wire is supplied from the makers in coils of about 70 pounds in weight and 18 inches diameter. It should not be directly unwound from the coils, or it would be apt to get into kinks and twists. A kind of wheelbarrow, provided with a drum, on which the coil fits, is used, from which the wire may be unwound under tension. On straight runs in the country the wires are ter- minated at about every sixth pole, being simply bound to the insulators of the intermediate poles. The 220 PRACTICAL TELEPHONE HANDBOOK. terminating is done to prevent the running back if a span should break. Dip or Sag. — The amount which a wire falls at the centre of the span when its points of suspension are at equal heights .is called its sag. There will always be some sag, no matter how tightly the wire is stretched. In order not to strain the wire more than one-fourth of Fig. 202. its breaking stress, the sag should be as given in the table below, (taken from Preece and Maier's book), for hard-drawn copper wire of lOO pounds to the mile. 100 LBS. HARD-DRAWN COPPER WIRE. Span. Low 'Winter Ordinary Winter Average Summer High Summer Temp. Temp. Temp. Temp. Yards. Sag. Stress. Sag. Stress. Sag. Stress. Sag. Stress. ft. in. lbs. ft. in. lbs. ft. in. lbs. ft. in. lbs. 100 2 8 8o 3 7 59 4 3? 49 4 "i 43 go 2 2 8o 3 I Sb 3 94 46 4 44- 40 8o I 8f 8o 2 6J 53 3 2i 424 3 8J 3b 70 I 3§ 8o 2 If 49 2 8f 38 3 2i 33 60 "§ 8o I 9 44 2 34 34 2 8J 29 5° 8 8o I4§ 39 I 10 29 2 2| 24 For other wire the sag should be the same, but the stress will be in proportion to the weight per mile, 200-pound wire producing double the stress given in OUTDOOR CONSTRUCTION. 221 the table. For different spans the sag should vary as the square of the length. The wire is drawn up by being gripped by a draiu- vice. Fig. 202, to the drum of which the wire, after being taken round the insulator, is attached. By using the key shown to turn the drum, the wire may be drawn to any degree of tightness, being held from running back by the ratchet and pawl until the wire is jointed. Regulating. — One of the wires is then regulated for sag by the wire men, who use their judgment in regard to it. (They cannot be got to use the special dyna- mometers, provided with a Salter's spring and scale. Fig. 203. to show the tension, which are made for the purpose (the use of which should be much more satisfactory). After one wire is regulated the others are drawn up until they are paralkl with it. The wire, after bending round the insulator, is bound with a piece of No. 18 soft copper wire. The soldering of this and other joints must be done with a hot soldering bolt, and as quickly as possible, to prevent the heating and weakening of the wire. In joining two lengths of wire together, the Britannia joint, Fig. 203, should be used, the ends being finished off as shown, and the whole quickly soldered. 222 PRACTICAL TELEPHONE HANDBOOK. Length of Spans. — The greater the number of wires carried by a line of poles, the shorter should be the distance between the poles, to give greater strength. Snow often plays havoc with the wires under certain ' conditions by adhering to them until they become perhaps one or two inches thick, putting a great strain on the wires and the poles, especially if the wind is strong at the time. For heavy lines of, say, 30 wires, the spans should be little over 50 yards, but may reach 80 yards for light lines. The height of poles should be arranged so that the lowest wires will not be less than 20 feet from the ground, and over public roads not less than 25 or 30 feet. When taller poles have to be used at special points of a route, the poles on each side should be also higher, so as to gradually raise the height of the line, for the sake of appearance and to save stress on the poles. Heavy lines, even on straight routes should be stayed at every few poles, to give lateral strength to resist wind pressure. Cables. — At a large telephonic exchange where the outside wires become crowded, and in many other cases, it is advisable to make use of cables consisting of a number of insulated wires twisted together and finally firmly bound and protected by an outside covering impervious to weather influences. The insulated wires of which a cable is composed are sometimes each encased in a covering of lead-foil, which is also OUTDOOR CONSTRUCTION. 223 connected to ian outer covering of lead joined to earth. This effectually prevents cross-talk, but gives a large static capacity. Some cables, such as those of Glover & Co., are made up of No. 20 gauge wires, insu- lated with gutta-percha or indiarubber, covered with tape soaked in ozokerit, and then enclosed in an outer covering of lead, prepared tape, and a firm braided covering soaked in a bituminous compound. By using white coverings to some wires and black to others, and arranging them in a peculiar manner, it is possible to pick out any special wire without testing. An 84 wire cable of this class gives a static capacity of "4 micro- farads per mile. These cables appear the best adapted for overhead purposes, as their flexibility enables them to withstand the stresses to which they are exposed, and even if the outer covering is penetrated by weather influences the coverings of the wires offer much re- sistance to the damp. Some cables are intended specially for use with single wire systems and others for metallic circuit systertis, the wires for the latter being twisted in pairs or fours, or sometimes eights, so as to get rid of speaking induction. Other cables, such as those described in Chapter XIV., in which the protected wires are enclosed in a lead tube, are sometimes used for overhead work, but their great weight is much against their use for such purpose. Cable Suspension. — Very few cables are strong enough in themselves to support their own weight, so that they are generally carried on strong suspending wires which 224 PRACTICAL TELEPHONE HANDBOOK. are often made of a stranded steel wire composed of seven No. i6 galvanised steel wires twisted togetner. Double shackles of extra strength are used to support the suspending wires, and the cable is supported at dis- Fig. 204. tances of every 3 or 4 feet by suspenders, which are either made up of short lengths of stiff wire, or, what is better, and has come much into use lately, by short pieces of raw hide attached to a hook or ring, which is threaded on the suspending wire, as shown in Fig. 204, which also shows the cowhide, etc., on a larger scale at A. CHAPTER XII. LONG-DISTANCE WORKING. Where long trunk lines are concerned the conditions of working must be the best possible, in order that good articulation may result. All points that affect the good electrical condition of the circuit must be looked to. The points for consideration come under two divi- sions : — I, Those in connection with the lines; and 2, those in connection with the instruments. In regard to the latter, care must be taken that only good and firm contacts are made in switching from one line to another; that all joints included in the circuit shall be perfect; that there shall be no unnecessary shunts to earth; and, even more important than the above, that the apparatus included directly in the circuit shall oppose as little electro-magnetic inertia — also called inductance — as possiole to the rapidly-alternating speaking currents. The relative value of the inductance of different forms of apparatus used in telephony, as determined by Q 226 PRACTICAL TELEPHONE HANDBOOK. Messrs. Ayrton & Perry's secohmmeter, is given in the following list : — I mile of round copper wire = I I do. do. soft iron wire = 6 Ordinary telephone receiver = 7 to 9 Siemen's receiver = 14 Secondary wire of transmitter induc- tion coil of res = 150 ohms, = 26 Drop indicator, res = 9 ohms. = 7 Do. do. without armature, res = 142 ohms. = ^J Do. do. with armature = 155 Electric bell (bobbins in series) = 86 The same with bobbins joined in parallel = 21 . Electro-magnet, res = 260 ohms. = 240 The list shows that the inductance of the electric bell coils joined up in series is four times that of the same coils joined mparallel or multiple. Electro-magnet coils that must be included directly in a speaking circuit should therefore be joined up in the latter manner. For the same winding of the coils this would result in weakening the magnetic power by one-half; but the latter may be restored by winding each coil to double its former resist- ance, and the inductance will still be reduced by one-half. A copper wire equal to 6 or 8 times the resistance of the coils, joined up to the latter as a shunt, will con- siderably reduce the retarding effect, with but little weakening o*" the magnetic power. LONG-DISTANCE WORKING. 227 A condenser joined to the two ends of the magnet coils has also a similar effect. The Line. — The principal trouble in regard to long trunk lines is due to the inductive action of one line upon others running side by side with it. After running thus for two or three miles, the induction enables nearly- all that is said on one line to be heard on the others, and the overhearing gets more pronounced the longer the lines run together. The overhearing may be also due to the leakage of the electric currents from one line to the others, and this is often the main cause of the trouble. Shackle cup insulators, defective pole earth-wiring, and bad earths for the pole earth wires, are the main causes of this leakage. The trouble is a serious one, as the overhearing of a firm's messages by another firm in the same line of business is very objectionable. Besides inductive voices, other noises are heard on single-wire lines which interfere with speaking and are irritable to those who use the lines. The noises are of several kinds, such as bubbling, crackling, hissing, whistling, and rasping sounds. They appear to be mostly caused by the swaying of the wires generating induced currents by cutting through the lines of force due to the earth's magnetic action ; by the conditions of temperature at different points along the lines ; by earth currents, and by induction from telegraphic and sometimes electric light circuits. The only method of getting rid of these noises and 228 PRACTICAL TELEPHONE HANDBOOIC the speaking induction is by dispensing with the earth as the return part of the circuit, and using metallic or loop circuits. It is necessary that the two wires of a metallic circuit, be so arranged that they are equally exposed to any outside inductive influence, such as from telegraphic or other telephonic wires. Two methods are adopted in practice to attain this object of equidistance. One called the twist system, by which the two wires of the line are continually twisted round each other and round a common axis, and the cross system, in which the wires are run straight and parallel to the outside wires, but their positions are reversed at certain points, so that the left-hand wire goes to the right, and vice versA. The number of crossings having to be such as to make both wires (taking their whole length) the same average distance from other lines running near. The twist system was suggested by Professor Hughes, and was first arranged in practice between Manchester and Oldham by Mr. J. E. Heys, for the late Mr. Charles Moseley. Figs. 205 and 206 show the plans adopted. In Fig. 205 a telegraph wire is shown on one end of the arms, and a twist telephone loop circuit on the other end. The wires of the latter make a complete revolution round each other in every four spans of the route, the position at every fourth pole being the same. The induced currents in both the loop-line wires, caused by the starting of a current in the telegraph line being in the same direction and of equal strength, will meet and neutralise each other at the ends of the loop. In order LONG-DISTANCE WORKING. 229 that the neutralisation may take place in the telephones at each end, it is necessary that the resistance of each branch of the loop shall be equal or baiaticed. If the balance is disturbed, overhearing and noises will ensue. Fig. 206 shows two loop circuits run on the same poles, two arms of each being utilised. Four circuits may be run on two longer arms, as shown diagrammatically in Figs. 205 Fig. 207, two circuits on each side of the poles being twisted together. The loop wires are i and 3, 2 and 4, 5 and 7, and 6 and 8, and the diagram shows the position on five successive poles. Although the twist system answers its purpose per- fectly, there are certain drawbacks in connection with it Wires run on the twist are more liable to faults, especially PRACTICAL TELEPHONE HANPJBOOIi. contacts, and much more difficulty is experienced in tracing the faults, as it is not easy for the linemen when walking along the route to see when lines are in contact, as even when the wires are in good order they appear to cross each other. The wires are more difficult to regulate, and from a distance always look as though they were out of regulation. Experience has shown that on most telephone routes very few turns or crossings of the loop wires are necessary to produce silence. Three or four, or even less turns made evenly along the route are in most cases 1 s S H f 3 8 7 ± !__£_£ S f 7 S X 1 i J }. .? i > / # s a 1 2 S i # 3 8 .)• Fig. 207, sufficient to ensure silence in a 20-mile line. In many cases one half turn is sufficient. On the twist system, as described above, seven or eight turns are made per mile, or about 140 turns in a 20-mile line. This seems far more than is necessary to procure a silent line. The Cross System. — This method has been used since 1884 on the trunk lines, which were under the control of Mr. A. R. Bennett, in Scotland, and the plan is generally followed on the Continent and in America. The wires run straight on the poles, just as ordinary single lines, but at certain points the wires are terminated on double arms and insulators, or on double brackets LONG-DISTANCE WORKING. 231 and insulators, as shown in Fig. 208, which also shows the method of crossing adopted by Mr. Bennett, stranded wires, consisting of three or four pieces of the copper line wire, being twisted together, one of the two crossing pieces being straight, and the other arched under or over the straight one. These stiff connections cannot easily be brought into contact by birds, etc. Two or three loop lines may be run on the same arm. Fig. 208. all such loops having their crossings made at the same poles. The same number of loops may be run on the next arm, but, in order to neutralise all induction, it is necessary that the crossings shall be made midway between the crossings on the upper arm, and a similar relation must exist between the crossings on the second and third arms. Fig. 209 will explain this : — A repre; senting one pair of loop wires on the top arm, with one crossing ; B, a loop line on the second arm 233 PRACTICAL TELEPHONE HANDBOOK. with two crossings midway between that of A ; and C, a loop on the third arm with four crossings. Loops on a fourth arm would require eight crossings, on a fifth arm i6 crossings, and so on. The number of crossings on a route may be twice or four times as many as those given above. The plan of crossings given is not the only one which may be adopted, but appears to be the one which requires the least number of crossings. The system appears to answer its purpose perfectly well, and has none of the drawbacks mentioned in regard ^} ^ A X '^V ^ CI^ ^tB ~ X~ " X~ B# ^ iD«Tc~ X X X X ~^>=^ Fig. 209. to the twist system. A careful consideration of the points of crossing is necessary, the men being instructed on what numbered poles the wires are to be crossed. Translators. — The fact that most telephonic exchanges were worked by single lines and earth circuits when metallic circuit trunk lines were first adopted gave rise to a difficulty in connecting the two kinds of circuits together without interfering with the efficacy of the loop lines. An earth connection made to the latter at any point at once destroys its quietude, so that it was not possible to connect the single lines direct to the double lines. A way out of this difficulty was found by Mr. A. R LONG-DISTANCE WORKING. 233 Bennett, by his invention of the translator or repeater, which is an induction coil, the primary and secondary wires of which are equal, or nearly equal, in resistance, and are wound on the bobbin together. A translator is used at each end of the loop line, one of its coils being joined direct to the loop lines, the other coil being joined one end to earth, and the other to the switch-board, for connection with the sub- scriber's lines. Fig. 210 shows the connection adopted by Mr. Bennett :— T and T/ are the two translators ; S METAULie CIRCUIT. nc and s' two spring-jacks inserted in the loops, so that two such loop lines may be connected together, directly, by means of double cords and double plugs or shoes, one part of the plug connecting to the spring, and another part to the back contact shown. By the use of s and s/ the repeaters are cut out when two loops are joined together. I and I ' are two drops included in the loop circuit for calling purposes ; K and k/ two double table switches, like the Dewar, for ringing pur- poses. When the lever is pulled down the two loop 234 PRACTICAL TELEPHONE HANDBOOK. wires are connected directly to the batteries or gene- rator. SS and ss/ are two spring-jacks by which the subscribers' lines are connected. It has been found that each repeater reduced the intensity of the sound by 30 or 40 per cent., and as the sound passes through two repeaters, evidently the received sound is much reduced in intensity. When iron wire was used for the line wires this reduction was felt very seriously, but now that copper line wires are used the loss can in most cases be spared, a good margin of strength being left, so that the loss is not so much noticed. Complete metallic circuits, used for both subscribers' and trunk lines, enabling the translators to be discarded, will give a much more satisfactory service, and will no doubt be universally adopted before long. Translators have been recently introduced, the soft iron cores of which are constructed of thin wires, about 2\ times the length of the bobbin, round which they are bent (after the coils are wound on) until they overlap on the outside, so that they form a complete magnetic circuit, and completely envelope the coils. This form, called the Liverpool repeater, gives improved results in speaking, and has the further advantage that ringing can be repeated, so that subscribers are able to ring through to each other. This, however, is seldom advisable, as the ring-off signal is given by so doing; An indicator drop for signalling is necessary with this translator, as with the older form, but is generally in- cluded in the home circuit instead of the loop. It is advisable to get rid of this drop and its injurious LONG-DISTANCE WORKING. 235 effect on the speaking. With this object in view, a translator was invented by Messrs. Coleman and Jack- son, in which the drop forms part of the repeater itself. Fig. 211 gives a view of the instrument. The repeater coils, with core, are enclosed in a soft iron cylinder, Fig. 211. to the open end of which one end of the armature is pivoted, the latter having a lever attached, a hook on the end of which supports the drop fixed in front. The instrument serves its purpose very well both for ringing and speaking. Switch-Room Arrangements. — Trunk lines, as a rule, require more attention on the part of operators than the ordinary local subscribers' lines, by reason of the greater difficulty of speaking and being so constantly engaged, and also because the connections have to pass through at least two switch-rooms, and two operators at least are concerned in making the connections. Single-wire trunk lines are being fast superseded by metallic circuits, for the working of which special apparatus is employed. Where only a few trunk lines are concerned — say up 236 PRACTICAL TELEPHONE HANDBOOK. to 8 or lO — they may be worked with the ordinary subscribers' lines and by the same operators, If they are single lines this can be done without alteration of the general arrangement, the trunk lines simply taking the place of an ordinary line. Where the number of trunk lines is more than lo, it is generally better to work them on separate tables, by special operators who can devote all their attention to them. A good and quick method of working single-line trunks is by means of the single-cord system, each trunk line ending in a cord and plug, in circuit with which is provided a Dewar or other table-switch and ringing keys, as shown in Fig. 212. The drop should be of high resistance if the line is a long one, say, from 200 to 400 ohms, and should preferably be a box or ironclad LONG-DISTANCE WORKING. 237 drop, so as to have a good amount of inductance, as it is joined in shunt when the line is connected to another one. The operator's set is provided with a test cell for multiple testing. Fig. 2 1 3 is a sketch of the connections for working a Net. Fig. 213. Coleman-Jackson translator. It will be seen that the local circuit of the translator is not complete when the line is not in use. This arrangement is adopted because the drop is much more sensitive under such circum- .stances. A test cell for multiple testing is shown also in Fig. 213. 238 PRACTICAL TELEPHONE HANDBOOK. The connections to the Liverpool pattern repeater are similar to Fig. 2io, but the signal drop is included in the local circuit instead of in the loop circuit. Limiting Distance of Speech. — Mr. Preece has shown that the length of line through which it is possible to speak is dependent upon (i) The total resistance of the circuit ; (2) the total electro-static capacity ; (3) the electro-magnetic inertia of the circuit. As copper is now universally employed for long-distance lines, the latter may be neglected, except in regard to the instruments. When the product of the total resistance and the total capacity of the circuit (or what is called the K. R.) is not greater than 15,000 on overhead lines and 12,000 for underground or submarine circuits, Mr. Preece states that it is just possible to speak, but the product should only amount to two-thirds of the above figures to ensure good results. Single-line earth circuits and metallic circuits have the same limiting length, as although the resistance of the latter is double that of the former, the total capacity is only one-half that of the single line or only one-quarter per mile of wire. The difference in regard to overhead and cable lines is owing to the fact that the leakage on the former enables the static charges to escape easier to earth. The capacity of cables is much greater than of over- head lines (over 20 times greater), and therefore the limiting distance is soon reached, for which reason open wires should be used for trunk lines where possible. The table below gives the limiting distance of speech LONG-DISTANCE WORKING, 239 through afew sizes of overhead copper wire and two sizes of cables. For the latter the top numbers represent the gauge of wire, and the lower numbers the gauge of its covering of gutta-percha. Gauge. Diameter in mils. Res. in ohms, per mile. Capacity 1 er mile in microfarads. Limiting dis- tance of speech. Distance at which speech is easv. 16 % 65 83 100 65 83 13 8-4 57 13 8-4 •008 ■0103 ■0124 ■240 •290 380 427 461 62 70 3J6 miles 350 „ 376 „ 50 „ 56 „ The London and Paris Telephone Line is the most striking instance of long-distance telephony in connec- tion with this country. A few details will therefore be of interest. The submarine cable is laid between St. Margaret's Bay, near Dover, and Sangatte, in France, and is about 21 knots, or 2\\ miles, long. The conductors in the cable are four in number, each composed of seven copper wires, and weighing i6o lbs. per knot, with a resistance of 7J ohms. Each conductor is insulated with three alternate layers of Chatterton's compound and gutta-percha, the total weight of each core being 460 lbs. The capacity per knot is about "3 microfarad. Fig. 214 gives a full-sized section of the cable, showing how the four conductors are arranged. The latter form part of two looped circuits, opposite or diagonal wires forming a pair. They twist round each other so as to guard against outside inductive influences. Over the four conductors tanned hemp is wrapped. Outside this 240 PRACTICAL TELEPHONE HANDBOOK. js a spiral protective sheathing of l6 galvanised iron wires, the whole being coated with mineral pitch and sand. The land lines in England are about 84-5 miles long, and consist of four wires, each weighing 400 lbs. per mile, and giving a resistance of 2'2 ohms per mile. The lines are run on the twist system, to prevent induction, on poles 70 yards apart. On the French side only two wires for one circuit are Fig. 214. run, each weighing 600 lbs. to the mile, and of a length of 204 miles. The K.R., or product of the total resistance into the total capacity of the one complete double circuit, is given as 7,359, with which speech should be good. The instrument used at the London end is the Gower Bell, and at the Paris end the D'Arsonval receiver with the Roulez transmitter. Speaking is said to be excellent, although the total length of line is 311 miles. CHAPTER XIII. FAULTS AND THEIR LOCALISATION. With the best class of instruments faults occur at times which interfere with, or altogether upset, the working of a station or stations. It pays to get instruments of the best class made by firms of high reputation, as the maintenance of such instruments is much less costly than that of cheaper ones. In telephonic exchanges tests are made by the opera- tors to each subscriber every morning of both ringing and speaking, and a list of those numbers found defective in any way is mac'e out for further tests and rectification by the fault inspectors. Complaints of other defects are received during the day from the subscribers themselves, or from the renters of private instruments. The most common descriptions of faults are such as: — wires in contact, can ring but cannot speak, cannot ring, cutting off whilst speaking, cannot get attention. Such faults, with the exception of those in connection with private lines, are first reported to the test-clerk in R 242 FRACflCAL TELEPHONE HANDBOOIt the test-room, who, with his instruments, endeavours to find out something more definite in regard to them, so as to guide the fault inspectors in tracing the cause, and to determine whether any faults exist at the switch- room end of the line. The faults, which are not in the switch-room, are reported to the instrument fault inspec- tors, with the exception of those which are obviously line faults, such as contacts between wires, when ringing or speaking on-one of the wires is received on the others. The cause of the latter fault can only be in the switch- room or on the lines, except in very rare cases where the earth connections of two or more subscribers are obtained from the same water pipe, which has become defective from some cause or other. When the fault inspector arrives at the subscriber's office, unless he is quite sure of the nature of the fault, he should make a few inquiries from the person who uses the instrument before he touches it. A few judicious questions will often throw much light on the nature of the fault, and as to in what part of the instru- ment the defect will most likely be found, whether in the bell part of the circuit, the speaking part, or in the local microphone circuit. For example, if the subscriber says he can hear from the other end perfectly, but they cannot hear him at all, it will be evident that the local microphone circuit must be faulty, or the secondary wire of the induction coil is short circuited. If he says his bell rings, but he can neither hear nor he heard, the speaking circuit must be looked to. If the instrument is a magneto, and his own bell does not ring when he FAULTS ANt) THEIR LOCAUSATIO^. i4i turns the handle, the fault may be a disconnection in the bell part of the circuit, or somewhere outside, or the generator or bell is short circuited. Before touching anything the inspector should make a careful examination of the parts affected, This will often disclose the cause of the trouble in a broken wire, a wire out of a terminal, or, perhaps, some bare part of wire touching another wire or terminal, or the earth connection may be severed or loose. If nothing is disclosed by this survey, and the last description of fault is indicated, the first thing to do is to connect the line and earth terminals of the switch-bell by means of a wire or other conductor, and try if the bell rings on turning the generator. If it does, the bell and generator will be all right, and the fault must be a disconnection in the earth or line circuit. If the bell does not ring, the fault must reside somewhere in it, and if it is further ascertained that the bell rings from the other end, the generator must be faulty, being either short circuited or disconnected between the automatic shunt points, and should be taken out and tested with a galvanometer and cell as to whether it shows a break or a very low resistance. The subscriber may not know whether his bell rings or not. In which case it will be advisable to test the generator by connecting the galvanometer to the pole- piece, and to the spring which bears on the insulated pin at the end of the armature pivot, at the same time making a break in the bell circuit. By now turning the handle slowly, it will be evident if the generator is 244 PRACTICAL TELEPHONE HANDBOOK. perfect by the deflections obtained. If the deflections are satisfactory, the bell must be looked to and tested for break or short circuit by the galvo and a cell. If ringing is all right between the stations, but speaking is not heard eitJter way, it will be evident that the secondary speaking circuit is defective. The receiver may be short-circuited or disconnected. A frequent cause of these faults is found in the connection of the flexible cord. Too much conductor is bared, and these bared parts get together, or the terminals work loose, and one of the conductors is pulled out. If this is not the faulty part, the switch hook contact should be cleaned, and if this does not remedy the trouble, the different parts of the circuit should be short-circuited one after the other, until the working of the instrument is restored. If the subscriber can hear bat cannot be heard, the local microphone circuit is affected. The defect may be caused by a bad cell, a dirty local spring contact, the latter being bent and failing to make a contact, a break or short circuit in some other part of the primary circuit or in the secondary wire of the induction coil. If a close inspection does not disclose the cause, and the battery cell is proved to be in good order by testing with a galvo, the different parts of the circuit should be tested by means of a length of wire, gradually by its means bridging over successive parts of the circuit until a sound is heard in the receiver, when the transmitter is blown upon. The break will then, as before, reside in the part last bridged over. FAULTS AND THEIR LOCALISATION. 245 A good method of proceeding, if nothing definite can be learnt in regard to the fault, is, after looking over all the outside connections, to quietly take the receiver from the hook and put it to the ear. If the ordinary induc- tive noises are heard, it may usually be concluded that the secondary speaking circuit and the line wire at that end are all right, except that the secondary coil may be short-circuited, which, however, seldom happens. If now, on blowing into the transmitter a characteristic noise is heard in the receiver, it will be known that the speaking parts of the instrument are right. If the noise is heard on blowing, but the inductive noises are absent, the secondary circuit may be short-circuited or getting earth. If the disconnecting of the line wire from the line terminal of the instrument prevents the noise being heard, it will show that the instrument part of the speaking circuit is not at fault ; but to make sure that it is not in the leading wires, the line should be cut where it goes through the window, if there is the least suspicion that the trouble may be caused by staples, etc. If the noise, on blowing, does not disappear on disconnecting the line, the fault must reside in the instrument, and breaks must be made in the circuit and a battery cell and galvo used to find out which parts that ought to be separate are connected together, looking especially after points where wires cross each other. Screws or tacks used to fasten portions of the instrument often cause trouble by coming into contact with the connecting wires behind. If the noise, on blowing, is faint, a fault may reside in 246 PRACTICAL TELEPHONE HANDBOOK. the transmitter or cell, or in the receiver, which should be examined by taking off the cap to see if there is any loose dirt in the bobbin recess, which might get between the pole-pieces of the magnet and the diaphragm, and weaken its vibration. This dirt is a very frequent source of trouble, and is one of the first things to look for in inspecting an instrument. By the method of bridging over the connections when a break occurs, and of disconnecting and testing with a cell and galvo for a short circuit or earth, faults can, as a rule, be very soon located, and the necessary repairs are then a comparatively easy task, which, however, sometimes requires the changing of part of the instru- ment. Receivers, diaphragms, cords, zincs, and battery salts should be carried by the inspectors. The principal tools required by the latter are a small pair of cutting pliers, tweezers, a medium-sized and a small screw- driver, a pad handle with loose bradawls, gimlets, etc. Intermittent Faults. — The faults spoken of above may be called lasting or complete faults, which exist continuously until rectified. The faults which often give far more trouble to locate are those which come on now and then and last but a short period, the instru- ment working in the intervals perfectly well. Such faults are often very difficult to discover, as there is nothing definite to work upon. The chief thing is to make inquiries under what circumstances the fault is observed, and how it affects the working, and from the answers obtained form some conclusion as to what part of the instrument or line is affected. After which a FAULTS AND THEIR LOCALISATION. 247 close search for loose contacts, bad joints, broken wires, etc., must be made. The telephone -cord frequently causes intermittent faults by the tinsel conductors be- coming broken, or by part of the tinsel of one conductor piercing through the worsted covering and coming into contact with the other conductor causing a short circuit. This fault may usually be detected by putting the receiver to the ear and then continuously blowing on the transmitter, whilst with the other hand the cord is pulled, twisted and moved in different ways.. If the fault is in the cord, this movement will cause the noise of blowing to chop off every now and then. Those intermittent faults which occur on windy days may be put down to the line, as they are most likely due to a loose joint in the wire, a broken conductor in the leading wires, or caused by the wire itself swinging against some earth connection. Two inspectors are often required to locate a fault of this kind, one at each end of the line. Most Common Faults. — Many of the defects which crop up in connection with instruments have already been mentioned. Below will be found the most common faults which occur. Receivers. — Cores too near diaphragm, not allowing sufficient space for vibration. This is often caused by the receiver being dropped. It can be remedied in the Bell receiver by carefully knocking back with - a hammer. Diaphragm buckled, often caused by users poking pencils at it. A new one is often required. 848 PRACTICAL TELEPHONE HANDBOOK. Dirt between Cores and Diaphragm. — Already re- ferred to. Bad soldered connection between the terminals and the wires leading to the coils, causing an intermittent fault. This may be detected by pressing in a certain direction on the terminals whilst listening and blowing on the transmitter or connecting to a battery. Loose Bobbins. — Weak Magnet. — Tran smitters. — The Blake. — Bad connections across hinges owing to rust and dirt. The safety springs should be bent well out, and the surface against which they press well cleaned. Bad Soldered Connections. — Cai'bon button pitted, by the users knocking against the front of the case or the diaphragm. A new button is often required, but sometimes the consequent faintness may be remedied. by turning the button so that the platinum pellet bears on a fresh surface. Diaphragm rusted, preventing its free vibration. Rubbing a soft black-lead pencil over the surface of a carbon-button will often improve its working, as does also the drawing of a piece of notepaper between the contacts, which clears out dust and dirt. Pencil Microphones. Dirt in contact holes of carbon blocks, causing bad contacts and faintneSs. Pencils should be taken out and the holes cleared. Bad wire connections, through faulty soldering of loose terminals. fa ul ts and their l causa tion. 249 Granulated Carbon Transmitters. Damaged Diaphragms. — Being very thin, these are very liable to get punctured or cracked, thus allowing the granules to escape. Faulty connections to carbon or platinum often occur. Magneto Bells. Driving Gear Slipping. — This does not often occur with toothed gearing, but was a frequent source of trouble with frifction driving gear. Short circuits are sometimes caused by particles of brass ground off defective driving gear. Telephone lever sticking and not making proper contact for speaking when receiver is removed. Spring should be strengthened and the lever taken off and pivot cleaned and rubbed with black-lead, as also any springs which bear upon it. No oil should be used on lever, as it will attract dust, thicken, and spoil the connection. Black-lead is much more satisfactory to use as a lubricator than oil in these cases. Bad contacts on lever can be cured by scraping and rubbing with black-lead, as above. Weak-polarising magnet should be replaced. Gongs out of adjustment. Lightning arrester plates short circuited, caused, perhaps, by loose nails, pins, etc., lying across. Battery Switch-Bells. Bad Contact on Telephone Lever.— ^Sce above. Faulty contacts on local contact springs caused by dust. Trembler hell contact faulty through dust, causing a break in ringing circuit. 250 PRACTICAL TELEPHONE HANDBOOK. Residual magnetism, causing a break by attracting the armature and keeping the spring from the contact pin. Faulty contact against back stop of ringing key. Batteries. Cracked cell, allowing the solution to run away. Corroded, loose or dirty terminals or wires. Faulty connection of wire to zinc rod. Faulty connection between lead cap and carbon. Exhausted solution, shown by crystals forming on zinc and porous pot. Zinc rod consumed. Switch-Room Faults. Indicators sticking, owing to rusted pivots preventing armature moving, or to the shutters being too upright, so that they do not fall over when released. A little bending over will generally remedy the latter fault. Bad contacts in spring-jacks, caused by dust. By means of a thin steel spring, provided with a handle and roughened by being cross-filed with a coarse file, the contacts in the jacks may be cleaned from the front of the table. Bad joints, due to defective soldering. Dust on the back contacts of ringing keys. For locating faults on the W. E. Co.'s multiple board, an ebonite spring-jack plug is used to lift up the springs from their contacts without connecting them to the test- wire. By doing this on successive tables, and testing from the test-room, an earth or contact can be traced to a certain part of the board. Line Faults.— When faults are traced to the line FAULTS AND THEIR -LOCALISATION. 251 they are handed over to the Linesmen, whose duty it is to find the cause and remedy it, and who should be perfectly familiar with the various routes and the wires upon them Line faults come under three principal headings : I. Contacts between different lines; 2, Earth Faults, caused by wires coming into contact with some con- ductor connected to earth through more or less resist- ance ; 3, Breaks, either total or partial, caused by bad joints or a fracture in the line or leaders at some point. I. In tracing contacts it is generally possible to find out what wires are in contact, and, knowing this, the linesmen can often walk at once to the point, as they may know that the lines can only come together at one point where their routes meet. When the position cannot be so ascertained, a lines- man will walk over the route of one of the lines, or both, if they run together, and carefully scrutinize the wires as he goes along. By so doing he will probably come to the seat of the trouble. If the contact cannot be found in this way, it becomes necessary to disconnect one of the wires at some point, and then make a test from the other end to discover if the contact has dis- appeared. If it has, the contact must be further away from the testing station, and, the wire being again joined up, other breaks are made further along, until the- lineman arrives at a point where the contact does not disappear. The fault will then lie between the two last disconnections. On long trunk lines test-boxes 252 PRACTICAL TELEPHONE HANDBOOK. are fixed along the route, into which the lines are led by G.P. covered wires, and attached to double terminals so that tests may be easily made. 2. Earth Faults. — The procedure followed in tracing an earth fault is much the same as for a contact. 3. Breaks. — If a line is broken down, the linesman walks over the route until he comes to the broken span. On long lines, and when the fault is a difficult one to find, an earthed battery is connected to one end of the broken line, and the linesman every now and then connects the faulty line to earth through his galvo, and notes if he gets an indication of the current on the line. When he has passed the break the deflection will not be obtained. If an earth connection is not available, another wire may be used in place. For partial breaks when the wire shows a very high resistance, the same procedure may be followed. A much weakened deflection will then be obtained when the fault is passed. Inteiinittent line faults are a source of great trouble in locating, as in the case of similar instrument faults. The linesmen should be provided with a portable telephone set, with either a battery of small dry cells or a small magneto bell for calling up the switch-room or test-room, but as these instruments cannot be made very light, and the men have often to walk long dis- tances, the signalling is sometimes dispensed with, only light receivers being carried, appointments being made with the test-clerk to speak on the wire at certain times. Morning Tests of Trunk Lines. — Special tests are FAULTS AND THEIR LOCALISATION. 253' made every working morning of all the important trunk lines of a telephonic exchange. They are begun at 6 a.m., in order that the faulty lines may be rectified as far as possible before the general business hours commence. The tests made are rough insulation tests, in which the wires are disconnected at one end one at a time and a battery and galvanometer connected to each line in succession at the other end, the test man at the latter end noting any advance upon the ordinary deflections, which will indicate excessive leakage. Contacts will also be indicated by this test, and by the dropping of the indicators if in contact with exchange wires. Breaks are indicated when the test men at the two ends are unable to speak to each other on the lines, and also by putting a current to line through a galvanometer, the other ends ^ being all joined to earth. Partial breaks are shown by less deflections than usual being obtained. The faults on the lines are located as far as possible by testing to intermediate stations, if there are such, and then handed to the linesmen concerned. The lines should be periodically tested with more sensitive instruments for insulation, resistance, con- ductivity, and capacity, records being made of the results for future comparison. For the methods of making such tests and measurements see Chapter XVII. CHAPTER XIV. UNDERGROUND WORK. Only a very small proportion of the telephone lines of this country are at present run underground, but it appears likely that there will be a great extension of their use in the near future, and that we shall have to follow the lead of the United States, where underground lines are becoming very general. A short description of the methods followed in America should therefore be useful. The principal objection made to underground lines is the increased cost of installation, but it appears certain that the diminished cost of maintenence of a good system would soon counterbalance this. A more serious objection is in regard to the increased statical capacity, which seriously affects long-distance working. The main point, therefore, in regard to the design of cables for the work is to ensure that the capacity of the wires is kept as low as possible. On account of the great number of different forms of cable used in America, a conference of leading experts has met yearly since 1889 to confer on the best type tJNDMEGROUND WORK. 455 of cable foi* underground work. The following are some of their latest suggestions, and constitute what are called dry-core cables : — The cables should be made up of copper wires of not less than 98 per cent, con- ductivity, '035 in. diameter, twisted in pairs, each twist to be complete in about 3 ins. Each wire to be covered with some dry material, as cotton or special paper, to a diameter of •125 in. These pairs of wires to be put up in layers laid in opposite directions. The cable thus formed to be enclosed in a pipe made of 97 per cent, lead and 3 per cent, tin, this alloy being used to resist the injurious action of creosote. The tube to be '125 in. in thickness and of a maximum outside diameter of 2*25 ins. The pipe to be covered with asphaltic paint, two coverings of braid or tape saturated with asphaltic paint, and a final coating of powdered soapstone to facilitate its drawing through the ducts. The inductive capacity of each wire after laying not to exceed "oSj mf. per mile, and the insulation not less than 100 megohms. Several cables have been made by different firms conforming to these requirements but differing in details, the chief endeavour being to get as much air space as possible between the wires, as air gives the least capacity. To maintain their efficiency it is necessary to keep the insides of these cables very dry, so that the joint- ing, etc., must be very carefully and quickly done, or the damp of the atmosphere will be drawn in at the ends. To prevent this as much as possible, the Western is6 Practical telephone handbook. Electric Company plug-up the ends of their cables for a few feet with a mixture of paraffin and air or carbonic oxide gas (as they formerly impregnated the whole length of their Patterson cable), thus securing very good insulation with the lowest capacity, which, in a so-pair cable, only amounts to 'oj mf. per mile. The wires in this cable are covered with prepared paper, which has been crumpled (by passing between rollers), thus pro- viding a good air space round the wires. In the " Norwich " Conference Cable the insulation consists of several layers of a special paper, which gives very high insulation, but not quite so low capacity as the Patterson. This cable is also made in this country by the British Insulated Wire Company, and a similar one to the following by the Fowler Waring Company. The " Brooks " Conference Cable. — In this the wires are covered with layers of prepared paper, laid on and crumpled longitudinally. This is kept in place by winding over it a few threads of cotton. The capacity of this cable is also about '07 mf. The above cables have now replaced others in which cotton-fibre wound on the wires was impregnated with various oils, such as pyroligneous, as formerly used by the Faraday Electric Company ; and resin oil, as used by the Brooks Company, which, although very effective in keeping out moisture, gave a higher capacity. Conduits. — Receptacles for the cables, called conduits, are constructed under the roadways, generally close to the curbstones, and are of several types; Three types appear to have turned out most successful in America. UNDERGROUND WORIC 257 1. Creosoted Wooden Blocks are laid in cement, some 3 or 4 ft. under the roadway, having holes about 3 or 4 in. dia. for the reception of the cables. Such conduits appear to have stood the test of experience very well, the only trouble with them having been an injurious action of the creosote on the lead tubes. The alloy of lead and tin recommended by the Conference completely with- stands the action. 2. Cement-lined Pipes. — These are constructed as follows : — A sheet-iron tube, 8Tt. long, is held vertically. Inside this is placed a smaller brass tube, and semi- liquid cement is then poured into the space between the tubes. When the cement has solidified the brass tube is withdrawn, and the tube, with others, is then fixed underground in a bed of cement, the tubes being con- nected in lengths by means of a kind of ball and socket joint. Ducts, as they are called, formed of these tubes appear to be rapidly increasing, 3. Wrought-iron Pipes. — This appears to be the most successful form of duct. The pipes are 20 ft. long and •217 in. thick. In laying them, a trench is dug about 4 ft. deep along the side of the street. A layer of hydraulic cement concrete is then laid and rammed on the bottom. On this is laid a row of iron pipes, side by side. On top of these another layer of concrete, then another set of pipes, and so on until there are sufficient ducts, a thick cover of concrete being laid over all. The pipes are joined end to end by a coupling screw- joint, so that they can be quickly put together. ThQ inside of the tubes is often asphalted to prevent rust s 258 PRACTICAL TELEPHONE HANDBOOK. Manholes. — In order to place the cables in the ducts and to make the necessary connections to them, man- holes are provided along the route. Along the principal conduits these are generally constructed of brickwork, well cemented to render them water-tight. They are made about 6 ft. square and from S to lo ft. in depth, at distances of about 70 yards apart. Fig. 215 is a section of a manhole, showing the iron casting which is placed over the brickwork, reaching to the level of the UNDERGROUND WORK. 959 roadway. To this are fitted two round or oval covers, one large and heavy at the street level, and the other, a smaller one, below, the latter being made to fit closely by india-rubber on to the ledge of the casting, so as to render the manhole perfectly water-tight. Ventilation. — The great trouble with the underground system is not with water, but coal-gas, which leaks from the mains and finds its way into the conduits and manholes, forming, with the air, a dangerous explosive mixture. Many serious explosions have occurred by the gas becoming ignited in some manner. To prevent the accumulation it has been found necessary to venti- late the subways by means of fans placed at convenient points and communicating by special pipes with several manholes, A hand-fan for temporary ventilation is shown in Fig. 215, which also shows the iron cage used over the openings to prevent accidents. Drawing in the Cables. — To enable the cables to be drawn into the ducts what is called r adding is resorted to, and consists in passing a flexible steel rod of about i in. dia, thtX)Ugh from one manhole to the next, or, which is considered a better plan, a set of wooden rods provided with joints so that they may be put together to form one long rod is threaded through, When the next manhole is reached a rope is attached and drawn back by the aid of the rods, unjointing the latter as they come out. The cable or cables, sometimes to the number of six, are then firmly and carefully attached to the rope and are drawn into the pipes by the men alone, or more 25o PRACTICAL TELEPHONE HANDBOOK. often by the aid of a winch or windlass. All rough or sharp edges about the pipes must be carefully avoided to prevent damage. Jointing of the wires and cables requires great care and considerable skill. Unless carefully done it will give rise to much trouble. To cover the joints made in con- necting lead-covered cables, a lead tube is used about 18 in. long, and large enough to slip on the cable-tube. This is slipped on one cable before the jointing is done. When the latter is completed the wires are tied together, the lead sleeve is drawn over them and soldered on to the pipes by a plumber's wiped joints the sleeve having been previously filled with paraffin wax. Distribution of the Wires. — From a manhole near the premises to which the wires are to be joined, small subsidiary ducts are laid to the wall of the nearest building. Cables are threaded through these and other pipes to the roof of the building, where a pole is erected, from which open wires are radiated to the subscribers' premises. The distribution constitutes the most difficult pa'-t of the arrangement. Many thousand miles of such ducts are now laid in America, New York city alone having considerably over a thousand miles. English Practice. — The general practice for under-- ground telephone work in this country has been to construct ducts of cast-iron pipes, usually 3 in. internal, 4 in. external diameter, and 9 ft. in length. The interior surface of these must be smooth, and must be so regular as to allow a steel rimer 2| ins. in diameter to pass VNt)ERGRdUND WOktC. 261 through them. They are cast with socket joints, which, after fitting together, are packed with hemp, and sealed and secured with melted lead so as to be perfectly waterproof. By means of a strong iron or steel wire threaded wMm&MSS^^^ I Fig. 216. Scale 3^. through each length of pipe as it is laid, or a hauling rope drawn through by this wire, the cables, usually of 100 pairs of wires, are drawn through the ducts, by the help of a windlass, into the manholes constructed at distances of from 50 to 150 yards apart, according to the nature of the route. 2^2 PRACflCAL TELEPHONE HA^jbEOOlt. Fig. 2i6 is a section of one of these manholes, which vary in size from a maximum of 6 ft. square and about 7 ft deep. They are built of blue waterproof bricks, well cemented, laid on a concrete foundation forming the floor C C. The square cast-iron flush box cover F B, and waterproof tray T, with indiarubber packings, are supported on two iron girders G G, 5 ins. deep by 4^ ins. wide, laid on the brickw^orkj wrought-iron plates on the girders supporting the rest of the roadway over the hole, the brickwork being arched over on the other sides, as shown in the figure, which also shows the ducts D D, terminated by bell-mouthed ends. The cast-iron ducts are rather liable to fracture by subsidence of the ground or heavy weights passing over them. Where the traffic is especially heavy, therefore, special precautions should be taken by laying them deeper or protecting them by wrought-iron plates, or arches. CHAPTER XV, METALLIC-CIRCUIT WORKING. The advantages of the metallic-circuit system for both trunk and ordinary exchange lines are now very generally acknowledged, and as electric lighting and electric traction are getting so general, it is becoming absolutely necessary to discard the earth return, as the leakage from the motive power mains especially, renders single-wire working in their vicinity almost impossible. A general movement is therefore in progress for con- verting all single-wire exchange lines into metallic- circuit ones. As these also dispense with repeaters for trunk line working, much greater efficiency is obtained in long-distance telephoning. Subscribers' Apparatus. — The alterations needed in the apparatus used by the subscribers is very small, it being only necessary to replace the earth connection by a return wire in each case. An efficient lightning arrester is, however, of nmch importance, as loop-lines are much more liable to damage by lightning discharges than single-wire circuits. The changes necessary in the Central office apparatus are more extensive, and as the conversion to metallic 264 PRACTICAL TEIEFHO-VE HANDBOOK. circuits cannot be completed at once, rather more com- plexity is introduced by ' having to provide for the OPERATOR'S Fig. 217. working of both single and loop lines on the same board. This is called the mixed system. METALLIC-CIRCUIT WORKING. 265 Small Exchanges. — The connections for a Western Electric Company's mixed system non-multiple switch- board are shown in Fig. 217, a loop-line and a single- wire circuit being shown connected together by a pair of cords with an ironclad ring-off drop shunted between the conductors of the double-connection cord. The spring-jacks used are of a similar type to those shown in Figs. 118 and 119, but have four springs insulated from each other and from the plug-socket, as shown in Fig. 218, Double contact plugs, as shown in Fig. 122, are used. Fig. 218. When a plug is ipserted in a jack, the two outer springs are forced open from contact with the two inner ones and the double coi-d is brought into the line circuit. The table-key of the operator's set is a Dewar (Figs. 116 and 117), with an additional insulated spring, moved against a contact by one of the other springs, an ebonite stud kfeeping the springs apart. Multiple Switch - boards. — In order to provide an engaged test for a mixed syatem multiple-board some further complication bscame necessary, the nature of 266 PRACTICAL TELEPHONE HANDBOOK. which will be seen from Fig. 219, which shows the operator's table connections. In addition to two double - spring ringing keys, a Fig. 2ig. special high-resistance ironclad coil is connected to each pair of double cords. All such coils are connected to a common earthed battery, which by the insertion of an METALLIC-CIRCUIT WORKING 267 answering plug into a caller's socket is connected to line, making the latter, as it were, the battery terminal. Any earthed receiver touching the line in any part will give' a click and thus indicate that the line is engaged. The high impedance resistance coil is used to prevent the telephone currents going to earth, or disturbing currents going to line. To receive the click the opei'ator's receiver is earthed, but in order that it shall not interfere with the balance of a line when connected, the receiver and secondary In C XT AT Section C Fig. 220. wire .of the induction coil are each wound with two equal coils, the receiver coils being between the secondary ones and the. earth connected to the junction of the receiver coils. This is called differential winding. Only one-half the coils are used in testing, and the speaking in answering a call is done through a con- denser of about one microfarad capacity, joined up as 2^8 Practical telephone HANbBOdk. shown, the left-hand plug being used. This is used in order to prevent the possibility of a false test, which under certain circumstances might occur. The ring-off drop is joined as a shunt across the loop, as is also the operator's set when the table-key is pressed. Fig. 220 shows the connections of a loop-wire to three jacks and an indicator, with the method of testing simplified; In the case of single-wire lines connected to -the same board, the wiring is done in the same manner, but that wire which is connected to the sockets of the jacks is earthed at the cross-connecting or test- board through a resistance, interposed to prevent the test-battery getting direct earth when connected. The above sj/stem of testing is not, however, altogether satisfactory, as any leakage on the lines gives rise to overhearing and noise, this being in proportion to the leakage. The only satisfactory way of getting over this difficulty is to provide a separate test circuit, altogether distinct from the line wire or wires. This has been done by the National Telephone Company's engi- neers, and applied to several of their London and provincial switch-boards, and also by the Western Electric Company in their " Branching " system, which has been introduced into the National Company's Lime Street centre. The National Company's System. — In this (the appara- tus for which has been made by the Western Electric Company), the spring-jacks are each provided with an extra spring, which normally presses against a projection on the socket. All these special springs of any one h"ne METALLIC-CIRCUIT WORKING. 269 are connected together by a special test-wire, the whole being insulated until a connecting plug is inserted. This, in lifting one of the line springs, also, by means of an insulated stud, presses outward the test-line spring from its contact with the socket and brings it into contact with an earthed pin, thereby earthing the test-wire and all the remaining sockets of that line, as shown in Fig. 221 LINES TEST WIRE EARTH EARTH Fig. 22 1. The operator's sets are wound differentially, the centre of the receiver coils being to earth through a test- battery or cell. The other arrangements are shown in Fig. 222, and it will be noticed that the connections are very symmetrical. The Western Electric Companfs "Branching"'' System.— This is the latest development in connection with multiple boards, and as it combines several novel features of importance, it has already been extensively adopted. • 270 PRACTICAL TELEPHONE HANDBOOK. The name comes from the fact that the spring-jacks, instead of being joined up to the loop wires one after the other in series, are connected by permanently soldered branches from the loop wires. Figf. 22?. The advantage of this system in getting rid of the defects due to dirty and imperfect contacts incidental to the series system has alrea,dy been mentioned, on METALLIC-CIRCUIT WORKING. 271 page 176. A further advantage of the branch system is that the balance of the lines when connected together is left perfect, whilst, in the case of the ordinary series system at least one of two lines connected together has one of its legs prolonged beyond the actual connecting jack. This may be seen in Fig. 220, which shows the top leg prolonged through the indicator, such being the shortest possible prolongation, as the connection is made on the last jack. The capacity and leakage of these prolongations may, especially in a large exchange, inter- fere with the balance of the loop lines and give rise to noise and overhearing. A more interesting part of this board is, however, the self-restoring drop device. This drop indicates to the e ^ Fig. 223. operator when a call is made, and the act of plugging in the answering jack serves by the aid of a battery to restore the drop to its original state, and keep it so until the line is disengaged and the plug taken out. The indicator is a kind of double-drop, as seen in Fig. 223, being similar to an ironclad ring-off drop o, with another coil R attached to one end of it, the latter 27J FRACTICAL TELEPHONE HANDBOOK. being fitted with a heavy armature a' pjvotted at the bottom, and a very light aluminium shutter Ppivofted at the top. The core of R is prolonged, and its end pro- jects into a recess in A'. The coil O of this combination occupies the place of the drop in an ordinary system. Its armature A is furnished with a long lever D, ori the Fig. 224. ■ end of which is a detent which retains A' in its place On A being attracted, D is raised, and A' is rekased,and falling forward against P has sufficient weight to lift up the latter and so disclose the number painted on A'. Fig. 224 shows the drop in this position. Fig. 225. The shutter is restored by the passage of a current of sufficient strength through the coil R. This causes' the attraction of A', allowing P to fall into the vertical position, a' cannot again fall forward as long as the current is kept on, even if D is raised. The spring-jacks are made up in twenties, mounted on METALLIC-CIRCUIT WOR ICING. 273 ebonite strips, Fig. 225, showing a section through a jack ; Lj_ is a brass socket, and L^ a spring, to both of which a branch from the loop-wires is soldered ; T and t are two other springs, the former being connected to the test-wire and the latter to earth. Let into the front face of the jack is a narrow brass socket T^, L" L' Fig. 226 insulated from L^, but connected to the test-wire and spring T. The internal diameter of this socket is large enough to be quite clear of a plug when such is inserted in the jack. The plug used is shown in Fig. 226, and differs from the ordinary double-plug in being fitted with a small J., TEST V -£ Fig. 227. brass collar T, insulated from and altogether indepen- dent of the other parts. On the insertion of a plug into a spring ■ jack, the T 274- PRACTICAL TELEPHONE HANDBOOK. springs T and t are connected together by the collar T, of the plug, and the test-wire and sockets Ti of that . number are thereby connected to earth, and will give RINC-OFF INDIC? EARTH TABIE KEY L \ BA/tTH COILS Fig. 228. the test -click from an earthed battery through the operator's set, as in the National Company's system. From Fig. 227, which shows the line connections, it METALLIC-CIRCUIT VPORKING. ili will be seen that the cpil o of the self-restoring indicator is joined as a permanent connection to the loop wires L^ and L^, and that one end of the coil R is joined to the test-wire, and the other end to an earthed battery B. (This is also joined to the operator's set to serve as the click battery.) When, therefore, a plug is inserted, as is shown in Fig. 229, this battery finds a complete circuit through the earthed test-wire, restores the drop, and retains it until the line is disengaged. Special ring-off drops are provided as usual, and these are also of the self-restoring type, as shown in Fig. 228 which gives the operator's table connections. There will thus be three drop coils connected as shunts when a line is engaged, but as these are high impedance ones they do not affect the speaking to any extent. •LINE 972 Fig. 229. Fig. 229 also shows, in a simplified manner, the con- nections in testing for an engaged line. It will be evident that much of the operator's time 276 PRACTICAL TELEPHONE HANDBOOK. will be saved by the use of this arrangement, and, as it allows of the indicators being fixed high above the operators, more space is left within their reach for spring-jacks. The ultimate capacity of the boards may therefore be made larger. The Post Office Multiple System.— T\^t British Post Office have adopted the multiple principle in connection with their permanent current system at Newcastle. When a subscriber's instrument is in use the line current, which in the ordinary case is cut-off (see page 163), is still left on the line, but is reversed in direction. The operators at the exchange have the means of test- ing the direction of the current on the lines at the different sections of the board, and can thus at once determine if a line is engaged, the connecting sockets being joined up on the branch system. For full particulars of this interesting system and of other multiple systems used on the Continent, see the " Manual of Telephony," Trunk-line Working. — It is desirable here to mention the methods of- working trunk lines on the mixed system, every large centre having such lines of both loop and single circuits, as is also now the case in regard to subscribers' lines. The trunk lines are usually divided into incoming-call lines and outgoing-call lines, the former being all termi- nated at, confined to, and attended to on one board, not being multipled, and the latter are multipled, at some centres on the trunk-line boards only, and at other centres on both the trunk and subscribers' sections. M&TAt.UC-CtRCUIT WORKING, ill 478 PRACTICAL TELEPHONE HANDBOOK. For the outgoing lines, it is usual to provide two spring-jacks for each line at each section, one to connect metallic circuits together direct, or a metallic circuit to a single line through a repeater, and the other to con- nect single trunk lines together direct, or a single trunk line to a loop circuit through a repeater, the latter being usually of the Liverpool pattern. The trunk lines usually terminate on cords, and are worked on the single-cord system (see page 236), and to distinguish the single from loop circuits, the National Company in London have red cords for the former and white cords for the latter. Fig. 230 shows the connec- tions of a loop trunk line (Liverpool No. i), and Fig. 231, of a single junction line (Woolwich No. i), on the London system. For the junction lines between the different centres instructions are given between the operators on the call-wire system, special operators being continually listening, and the other centre opera- tors communicating with them by pressing call-wire keys with which they are furnished, ^[^^^ T^IM.> i B e Fig. 232. Multiplex Telpehony. — By arranging resistances in connection with a loop line in the manner shown in Fig, 232, two circuits may be worked independently. No. i (Ti and Ti'), as single line and earth circuit, and the METALLIC-CIRCVIT WORKING. ■ -279 other, No. 2 (T^ and T^'), as a loop, circuit. In the former case, the two wires are used as one of double size. The resistances R and R must be equal, as must also be R' and r', and it is necessary that the wires composing the loop be properly balanced in regard to conductivity, leakage, and capacity, or overhearing will ensue. Fig. 233 shows how four circuits, three loops and one single, may be obtained from two metallic circuits, or four wires and resistances. This, however, is too com- plicated to work well in practice, although three loop Fig- 233- circuits are often obtained and used by omitting the four outer resistances. But for the difficulty experienced in keeping the balance such arrangements would be more frequently used. The plans shown were patented by Mr. Jacobs in 1882. Based on the same principle of obtaining two circuits with a single loop, Messrs. G. J. Somerville and R. McLean have invented a call - wire arrangement, shown in Fig. 234, by which the advantages of a metallic circuit call-wire may be obtained without an extra line to the ordinary loop. 28o PRACTICAL TELEPHONE HANDBOOK. At the Central Office an electromagnet M M is con- nected as a permanent shunt to the loop, an earthed battery being connected to its centre as shown. The depression of the subscriber's call-lever gives a path to earth for the battery through his speaking instruments wound differentially, and the armature of the electro- magnet is attracted (if properly wound). This causes the connection of the operator's set to the loop wire, and the subscriber can thus give instructions for con- nection or disconnection as long as his call-lever is depressed. Fig. 234. This plan has the advantage that the lines connected to the operator are only those actually calling at any time, so that the leakage and capacity are reduced to a minimum, and as the instructions are given on the loop line, the speaking is very loud and clear. Bennett's Ring-off System. — Somewhat on the lines of the multiplex system, Mr. A. R. Bennett has devised a ring-off system for ordinary exchanges, using loop circuits and drops. This, like the writer's system (see page 167), enables subscribers connected together to MnTALT.IC-CIRCViT WOkRiNC. 281 ring each other without actuating the ring-off drop, but has the advantage that the ordinary magneto signalling apparatus may be used. Each subscriber is furnished with a special button or lever, as R.O.L. in Fig. 235, by means of which he can connect both his loop wires to earth, this completing the circuit of a common battery at the Central Office through the ring-off drop and the twin resistance coils, as Fig. 235. shown, when the subscriber is joined through to another one by a pair of cords. More simply, the resistance coils may be dispensed with by winding the ring-off drop differentially and connecting it across the cord con- ductors with an earthed battery joined to the centre of its coils. CHAPTER XVI. MISCELLANEOUS TELEPHONE APPARATUS AND APPLICATIONS. Automatic Call-Office Arrangements. — In most towns having a telephonic exchange public call-offices are provided, into which any person may enter, and, by paying certain charges, be put into communication with a person at some other office connected to the system. In many of these offices a special apparatus is pro- vided which serves to collect the money and at the same time automatically call up the central office. Many different forms have been invented, but pro- t/dbly the first one operated by coins was that of Messrs. Crossley, Harrison and Emmott, which was originally constructed with the view of being used in connection with an ordinary subscriber's instrument, to enable him to pay a certain amount each time he used his instru- ment, thus paying on the toll system, instead of, or in addition to, a yearly subscription. A box was provided with a slot large enough to admit Practical telephone handbook. 283 a penny. When the latter coin was put through the slot, it rolled down an inclined tube and fell on to a balanced scale pan, which overbalanced and allowed the coins to fall into a cash drawer underneath. At the same time a contact was closed in a local circuit which included an electro-magnet. The armature of the latter being attracted pressed against a contact, com- pleting the line circuit to the telephone set. Being polarised, the armature remained in that position until, at the end of the conversation, the operator at the central office sent a current through the line and the electro- magnet, by means of which the armature was attracted to the other side and the telephone set again discon- nected from the line circuit. Mamis Automatic. — The next apparatus of the kind was invented by Mr. J. J. Mann, and was designed to automatically cut off the user after the lapse of a certain period allowed for conversation, in addition to signalling the office and checking the money paid. It was arranged somewhat the same as the automatic sweet-boxes, with the addition of a clock, which caused a disc to revolve once during the time allowed for conversation. The writer is not aware of its having been brought into practical use. Poole and Mclver's Automatic. — Figs. 236 and 237 represent an instrument designed by the writer, who believes it was the first put into practical use. It was arranged to serve the same purposes as the "Mann" (and was invented about the same time), with the addition of showing which of two charges (a trunk line 284 TMLEPHOM ApPAkAfUS AMD APPLICATIONS. charge of 6d., or a local charge of 3d.) had been paid. It was also arranged that the time allowed for a conver- sation should commence from the time the subscriber asked for was in comnmnication with the caller. Fig- 237 shows the inside mechanism, A, A' are the shoots into which the coins are dropped and which guide them on to the scale pans C, C Threepence in copper on c overcomes the counterweight D and is tilted into the cash drawer below. The spring F being re- leased by the tilting comes into contact with G, to which an earthed battery is connected, and a cur- rent passes through the line wire to the central office. The right-hand scale is operated in a simi- lar manner by sixpence in silver, but a current F^&- 236. of opposite polarity is sent to the central office. The apparatus required at the central office to dis- tinguish the calls is a polarised double-contact relay, in the two local circuits of which are two drops, one actuated by a threepenny call and the other by a sixpenny call. The clockwork shown in Fig. 237 is working continuously and drives a wheel with roughened edge J, on which, at the will of the operator at the central office, an arm may be caused to ride for three minutes, at the end of which time it falls against a spring L and TELEPHONE APPARATUS AND APPLICATIONS. 3S5 causes a break in the telephone circuit. The three minutes may be renewed at any time at the will of the central office operator. An index-finger attached to the riding-arm indicates to the user how his time is progressing. Instead of putting in the coins in the first instance, Fig. 237. the call may be originated by press-button or magneto, and the instrument used to check the coins put in the box and limit the time. This remedies the difficulty experienced of returning the money when the sub- scribers asked for were engaged. 286 PRACTICAL TELEPHONE HANDBOOK: To accomplish this, and still keep a perfect check, a special button was used which on being pressed sent a positive and a negative current to line, one after the other, causing both the 3d. and the 6d. drops to fall. When the subscriber asked for was obtained the operator instructed the caller to put in his money, and checked the receipt of it by listening to the ro!a .actual fall of the coins and ob- serving which of the two drops fell, so that she had both an au- dible and a visual check upon the amount deposited. Smith and Sinclair s Apparatus. — This is simply a checking, apparatus, signalling being done in the ordinary manner. When pennies are put in the slot provided, they fall down a shoot and press aside two small springs, as seen in Fig. 238, which interrupt a permanent current put on the line by the operator. The latter receives a signal on a bell or gal- vanometer for each coin put in. When a sixpence is put in another slot, two other springs are pressed aside for a moment and break the primary circuit of the induction coil. This break causes a sharp click in the listening operator's receiver. The boxes are also provided with slots, into which special keys, supplied to ordinary subscribers, can be inserted, and, W -0 F'g. 238. ■ TELEPHONE APPARATUS AND APPLICATIONS. 287 on turning, give the necessary signals to the operator. In this way the subscribers may make free use of the call-offices. The above apparatus is extensively used in the Glasgow district. CotterelVs Apparatus. — This is the simplest checking arrangement of all. The coins, after running through the shoots, strike against bell-gongs. The gong for the pence has a different tone to that for the sixpence, so that the operator, listening whilst the coins are put in, can readily distinguish which gong has been struck. The instrument is much used in the Birmingham district. Mix and Genes fs Automatic Cail-Box. — This is a checking apparatus which is substantially made, and would appear to answer its purpose very well. Fig. 239 shows the instrument open and with a telephone set attached. When a coin of a certain value and size is inserted into the slot, it first passes through an arrangement which tests its diameter and thickness and rejects it if not satisfactory in those respects (directing it at once into a refunding box at the bottom). If satisfactory, it is guided into a grooved channel, where, after depressing a lever, which closes the line circuit, if its weight is satisfactory, it rests on the upper of three wheel seg- ments, the rims of which protrude into the grooves. These segments are geared together, and are irevolved by a lever connected to the armature of an electro- magnet. When the armature is attracted, the coin is Fig. 239— Scale J. TELEPHONE APPARATUS AND APPLICATIONS. 289 released by the turning of the segment and falls until arrested by the second segment, and on the release of the armature it falls to the third segment, where it rests until the ring-off signal is given, which operates the electro-magnet, turns the segments, and allows the coin to fall into the cash-box, pushing aside, on its way thither, a leyer which breaks the line circuit" to the telephone set. If the line required is engaged, the electro-magnet is not operated, and the caller presses a white button, which turns the upper part of the grooved channel about an axis and releases the coin, which falls into the refunding box at the bottom of the instrument. If the caller should neglect to ring off and the coin be left resting on the third segment in the groove, the coin inserted in the slot by the next caller presses aside a small roller attached to a lever, which operates the segments and releases the coin left in. This and the other call-office instruments could be used in conjunction with a subscriber's instrument to enable him to pay each time he uses his instrument, on what is called the toll system. This system would appear to be the most natural way of paying for the use of a telephonic exchange instrument, only that it ordinarily entails so much extra clerical labour, which an automatic apparatus, such as above described, would dispense with. Theatre Arrangements. — Much interest was evinced at the Paris Electrical Exhibition of 1881 in the arrangements by which the operas performed in the U ago PRACTICAL TELEPHONE HaNDBOOM. Theatre Franpais were transmitted to a room in the ex- hibition, and there listened to with dehght by thousands of visitors. Fig. 240 shows the manner in which the apparatus was arranged. Ten Ader transmitters, T, t, t, i, t, and T', t, f, f, f, werefixed five on each side of the prompter's box. Each transmitter was connected by a double line to eight Ader receivers fixed in the room at the exhibition. Ill STAGS OF THE OPER\ t TELKPHONE-BOOM Fig. 240. These, with eight other receivers connected to a trans- mitter fixed on the opposite side of the prompter's box, formed eight pairs for eight listeners. Fig. 240 shows the connection of two such transmitters, T and T', to TELEPHONE APPARATUS AND APPLICATIONS. 291 sixteen receivers arranged in pairs, a b, ab. A listener using a pair of receivers would thus be connected by the left-hand one a to the left-hand transmitter T, and by the b receiver to the right-hand transmitter, T '. With such an arrangement the transmitted sounds will be most intense from that one of the two transmitters which is nearest the singer on the stage, so that a distinctly different effect is obtained from the two receivers of each pair. The effect of a singer crossing the stage is very curious and realistic, being somewhat analogous to the action of a stereoscope in giving solidity to a double photographic picture. In the case of the telephone it is difficult to imagine that the singer is not close in front of the listener. The arrangements adopted in Manchester for trans- mitting operatic music from the theatres has for many years given great pleasure to those who have been privileged to listen. Two Marr transmitters are used at each theatre, suspended by india-rubber bands to the sides of the proscenium, at about six feet above the stage-floor, and arranged to point towards the centre of the stage. The battery of four gravity cells for working each of the transmitters, instead of being provided at the theatre itself, as at Paris, is placed at the central office, the induction coils for working being also fixed there. By such an arrangement the current can be switched on and off at any time without going near the theatres. Fig. 241 shows the manner of connecting up so as to be able to connect the secondary wire of the induction 292 PRACTICAL TELEPHONE HANDBOOK. ■ '* coil to any subscriber's line wire : — A represents one of the theatre transmitters, one terminal of which is earthed and the other connected to the line to central office, where it is joined to the primary wire of the induction coil B (res. about i ohm). The other end of the primary wire is connected to spring-jack C, to which a battery may be connected by the plug and cord D. The ends of the secondary coil of B (res. about 50 ohms) are connected to jacks G and H. Through G one end gets earth, and by H a single wire line may be UNg TO THEATRE \fX Tsmwn^A (7 ^ Fig. 241. i the latter is high, however, it becomes necessary to use a strong battery in order to obtain reliable results. Fig. 249 shows another plan of loop test which is some- times preferred, or may be used to check the figures arrived at by the other plan. In this the connections of the galvanometer and battery are exchanged, so that the current splits from the terminal G, instead of C, and the right-hand set of resistances in the top arm are kept plugged up. When a balance is obtained the unplugged resistances on each side of G are to each other as the two portions of the loop divided by the fault, or « : R = j' ; ;?. From this and I -= x ■\- y . /R we get .r = - a+R and r = a+R Actual examples are shown in Figs. 248 and 249, which may be used as exercises. The unplugged resistances are figured. Loop Test for Contact. — Either of the loop tests given Fig. 2y. above may be used to localise the point of contact between two lines, if a loop can be formed with a faulty wire and a good one, and if the other line in contact can be put to earth. If such a loop cannot be formed, 304 PRACTICAL TELEPHONE SANbPOOk. the lines may be joined up as shown in Fig. 250, one of the wires in contact being joined to the battery, as shown, the other end being disconnected, and the far end of the other wire earthed as shown. The other connections and calculations are the same as in the last loop test, but X and y must now be considered as the near and distant portions of the same wire. If the contact offers no appreciable resistance, half the resistance of the loop formed by the near portions of the two wires in contact will give the resistance to the fault if the wires are of similar size and material, but it is seldom advisable to rely on such a test. Insulation Resistance. — This is the measure of the resistance of the insulating materials used to confine Fig. 251. the current to the required path through the line, and may be obtained by means of the Wheatstone bridge when the total resistance does not exceed 1,111,000 ohms (= I'll I megohms), (as in the case of long open lines), by connecting one end of the line as shown in Fig. 25 1, keeping the other end insulated, the terminal E and battery being earthed. It will need the 1,000 MLkCTRlCAL MEASUREMENtS. ioS ohms resistance in b and the loohms in a, the balancing resistance in R being then multiplied by lOO to get the absolute resistance. The number thus obtained, mul- tiplied by the length of the line in miles, will give the resistance per mile of the wire. It will be neces- sary to U£e a strong battery for this test, and the galvanometer used should be a sensitive one. For measure- ments of high in- sulation and very accurate tests it is necessary to employ a Kelvin Astatic Reflecting Gal- vanometer. — A very good form of this, made by the Silvertown Telegraph Com- pany, is shown in Fig. 252. It consists of four fine wire coils fixed to an upright brass plate, two at the top. and 3o6 PRACTICAL TELEPHONE HANDBOOK. two below, so as to form, as it were, two larger coils. Within cylindrical openings through these coils are suspended, by means of a fibre of raw silk, two sets of very small magnets, the top set being cemented on the back of a circular glass mirror f inch in diameter, and the lower set connected at right angles to an aluminium vane intended to steady the movements of the combina- tion. The two sets of magnets afe rigidly joined together in the same plane, but so that the north poles of the top set arf; over the south poles of the lower set, forming an astatic combination, by means of which the earth's action is neutralfsed. The coils are so joined up that a current passing through all tends to turn the combination in the same direction. The terminals of the instrument are fixed on an ebonite base, fitted with levelling screws, and the coils, etc., are covered with a case having glass sides. Over the instru- ment is a curved magnet, which can be raised or lowered to alter the sensi- tiveness of the instrument, or swung round a brass pillar to set the needles at -r any desired zero point. About 3 feet away from the front of the instrument is set a lamp supported on a stand furnished with a graduated screen, shown without the scale in Fig. 253, -53- ELECTRICAL MEASUREMENTS. 307 A hole in the centre of the stand is furnished with a brass tube in which a lens is fitted, through which a beam of light is made to fall on the mirror in the galvanometer, from which it is reflected on to the graduated screen. An image of a fine vertical wire fixed close to the lamp is focussed on the screen, and enables the readings to be taken very accurately. Shunts. — As the instrument would be much too sensitive for many purposes, a set of shunts is used Fig- 254' with it. By means of these its sensitiveness may be reduced to Jj,, -^^ or ^J^^, by diverting ^, -S^^, oi 3^V(j of the current from tlie galvanometer. Such a Shunt-box is shown in Fig. 254, and a plan of it in ^ig- 25 S— the shunts being marked §, ^V. and g|^, these being the fractions of the resistance of the galvano- meter required for the -f^, ^^, and -^^^t^ shunts respec- tively. The shunts are inserted by plugging in between the 3o8 PRACTICAL TELEPHONE HANDBOOK. blocks, and the instrument itself and galvanometer can be short-circuited by a plug inserled at s C, so as to prevent damage by accidental currents. A much more convenient method of doing this, however, is by means of a separate short-circuiting key, such as that shown Fig. 255. at S C K in Fig. 256, which is simply a well-insulated spring key with a top contact, and an ebonite catch to fasten down the spring when not required. By proper manipulation of this key the readings of the deflections ^=^=4^^ Fig. 256. can be very quickly taken, and much time saved, one reason of this being the elimination of the throw of the needle caused by the capacity of the wire being tested, when the battery connection is first made. The galvanometer must be kept very steady, as the ELECTRICAL MEASUREMENTS. 309 slightest jar will set the mirror quivering, so that the readings cannot be taken. For this reason the instru- ment is usually set on a heavy stone, which rests on indiarubber blocks set on a structure built into a solid wall. The advantages of such an instrument over the ordinary form of galvanometer are that the turns of wire can be brought very near to the needles, and so act powerfully on the astatic system, and a less length of wire is required. The beam of light also forms a very long and weightless index, which moves twice as far as an actual fixed index of the same length by reason of the law of reflection. The reflecting galvanometer is used to measure all very high resistances and very feeble currents. In order to make these measurements it is necessary to obtain the constant of the instrument. This, which ex- presses^the value of the deflections, is obtained by joining up the instruments as in Fig. 256, the current being sent through a known high resistance, usually 100,000 ohms, the galvanometer being shunted so' as to get a convenient deflection on the scale. If this. cannot be done with the xffW shunt (which is usually the case), a part only of the battery (such as one-tenth of the whole) should be used. The deflection being noted, it is multiplied by the shunt number (10, 100, or 1,000), This will give the deflection which we may imagine would be obtained if it were possible to do without the shunts. This number is now multiplied by the resistance (as 100,000) 310 PRACTICAL TELEPHONE HANDBOOIC and again by lo if ^ of the testing battery has been used. The constant so^obtainei (say, 50,000,000,000, ohms, or 50,000 megohms) will represent the resistance through which the testing battery will give a deflection of 1°, Dividing the number by any deflection obtained (allowing for the shunt), the resistance in the path of the battery is obtained. Unless very accurate results are required the resistance of the galvanometer may be neglected, especially when the shunts are used. Fig 257. Fig. 257 shows the connections for making an insula- tion test of a cable wire. The resistance box is short- circuited by a brass bar, and the wire to be tested put on at L in place of earth, the full battery being of course used. The opposite end of the wire must be carefully insulated. If the wire is in a cable the outer covering of the latter at the far end should be stripped off, and the wires opened out from each other for about four inches. After the battery is connected to the wire, a minute ELECTRICAL RIEASUREMENTS. 311 is allowed to elapse before the reading is taken. This is for what is called the electrification of the cable wires, which is an effect due to a polarization of the molecules of the insulating material, causing it to offer a greater and greater resistance to leakage, shown by a steady fall in the deflection. This is an evidence of good insulation, and is one of the principal points to be observed. After the one minute's electrification the deflection is observed, and multiplied by 10, 100, 1,000, according to the shunt used. The constant is then divided by this number, and the quotient is the insulation resistance of the wire. Suppose the constant is 50,000,000,000 ohms, or 50,000 megohms, and the deflection 560° (allowing for , . , 50)0<^o „ , , . , . , shunt), then — r? — = 89'3 megohms, which is the absolute insulation resistance. The insulation resistance per mile, which is of even more importance, will be obtained by multiplying the absolute insulation resistance by the actual length in miles, or, if in yards, by multi- plying by the number of yards and dividing the product by 1,760. For example, suppose th^ length of cable to be 1^320 yards, or 075 mile, then 89-3 X 1320 „ ^ , ., , r-So " "^ ^'^ ^ °'^^ ~ "^ megohms per mile of wire. In testing cable wires it is usual to connect all the wires except that under actual test to earth. Where the wires are used to form metallic circuit lines it is ' usual to test them in pairs, the two ends being connected 312 PRACTICAL TELEPHONE HANDBOOK. together on the one terminal ; in this case the total length of wire tested must be used in obtaining the mileage insulation. Capacity Tests. — The evil effects of the- storage capacity of wires, more especially of cable wires, upon telephonic currents, has already been mentioned, and it is of much importance to ascertain the capacit}- of the wires in use. To effect this, in addition to a reflecting Fig;. 258. galvanometer, a standard condenser and a discharge key are required. Fig. 258 shows the former, which is a round brass box containing a large number of discs of tinfoil, each one laid between somewhat larger discs of thin mica. Every alternate disc of tinfoil is connected to one of the two terminals on the ebonite cover, and the remaining tinfoil discs to the second terminal, the two sets of tinfoil discs forming, as it were, the inner and ELECTRICAL MEASUREMENTS. 313 outer coatings of a Leyden jar. The plug~shown in the figure is used to thoroughly discharge the instrument before use. An instrument of a capacity = 0-5 micro- farad is a very convenient size. Fig. 259.— Scale J. A very good form of discharge key is shown in Figs, 259and 260, and is known as the " Kempe." It consists of a spring lever with top and bottom contacts fixed on Fig, 260. — Scale J, ebonite pillars in order to get very good insulation, and is provided with two trigger keys marked "Insulate" and "Discharge" which keep down the lever on the lower 314 PRACTICAL TELEPHONE HANDBOOK. contact. On depressing the "insulate" key the lever leaves the lower contact and is kept insulated until the " discharge " key is depressed, when it springs to the top contact. Depressing the " discharge " key at first allows the lever to spring from the bottom to the top contact at once, as it carries the "insulate " key with it. The " constant " for capacity tests is obtained as shown in Fig. 261. The battery is connected to the bottom con- tact of the discharge key through the battery reverser. The lever of the discharge key connected to one ter- .^^ Fij. 261. minal of the condenser is pressed down, and the condenser thereby charged. After about 15 seconds the "^discharge " trigger is depressed, the lever springs up against the top contact, and the condenser discharges itself through the galvanometer, shunted, if necessary, to give a convenient deflection, which latter is only a momentary one. The short-circuit key (if used) must be kept open. Suppose the illuminated spot is thrown 720^^ by the discharge, this, divided by the capacity of the condenser, say O'S, gives -7^ = 1440", which would be the deflec- tion given by i m.f capacity. The deflections produced ELECTRICAL MEASUREMENTS. 315 by other capacities, divided by this number, will give the measure of those capacities. Thus, suppose a cable wire (with further end insulated) joined up as shown in Fig. 262, gives a throw of 480° (allowing for shunt). This would show that the capacity of the wire was 480 . c 1440 The capacity per mile will be fhe actual capacity of the wire divided by the length in miles, or, if in yards, by the actual capacity multiplied by 1,760 dp. Fig. 262. and divided by the length in yards. Suppose, as before, the length of cable is 1,320 yards, or 75 mile, then the capacity per mile shown by the above tests will be 3 X 1760 1320 = '4 m.f per mile of wire. For important tests it is necessary to make measure- ments, for both insulation and capacity, with reversed battery connections, taking the mean of results obtained in each case. Special Loop Line Tests. — It is often desirable in the case of loop lines to be able to find the actual insulation 3i6 PRACTICAL TELEPHONE HANDBOOK. and capacity between the two wires forming the loop, as this may be of more importance to the worle Force. — The measurement of this is com- paratively simple. The cell or battery is joined up in the place of the battery shown in Fig. 256 (the arrange- ment for taking the constant in insulation testing). The deflection through some known high resistancfe, say, 100,000 ohms, is noted, and then the cell or battery is replaced by a Latimer- Clarke's standard cell (of mercury and silver) and the deflection again noted. The E.M.F.'s of the two cells will be in direct proportion to the deflec- tions produced in the two cases (of course allowing for shunt), and, knowing the E.M.F. of the standard cell, it is easy to calculate the unknown one. Thus, suppose the first deflection was 11,000° (allowing for shunt) and the standard cell gave 10,300°. At the temperature of the test, 19° C, the E.M.F. of the Clarke cell is 1-45 volt; ELECTRJCAL MEASURI^MENTS. %\1 from these the E.M.F. of the cell to be tested jr=i'45 x 11,000 ,.^^ 1, — ■ = I 55 volt. 10,300 An even better method is to charge a condenser with the battery to be tested and the standard cell respectively, noting the discharge deflections in the two cases, as in the capacity constant tests. The E.M.F.'s are again directly proportional to the discharge deflections. Internal Resistance of Cells or Batteries. — This is a more difficult matter to determine correctly, as the polarisation of the cells varies as the amount of resistance ■1 ig. 263. in the circuit when the cell is working, and thus gives rise to variation in the electromotive forces of the cells. The most common method is to connect up the cell by short and thick wires to a reflecting galvanometer, shunted with a piece of wire whose resistance may be neglected. A convenient deflection being obtained by varying the length of wire forming the shunt, a resistance of, say, I ohm is unplugged in a resistance box included in the circuit, and the reduced deflection observed. Fig. 263 shows the connections using a Post-Office bridge. The deflections in the two cases will be proportional to 3iS rkACf/CAL TkLEPtiOMS. HANDBOOK. the strength of the currents producing them, and there- fore inversely proportional to the resistances in circuit in the two cases, which will be r and r-\- i respectively, if r = the internal resistance of the cell. Suppose the ■deflections arel6o°and 50°, then r ^- I : r = 160 : 50, or 50 ^^ + 50 = i6or, from which r =-^ = -455 ohm. no ^•'^ Fig. 264. mi CELL- CONDENStI T G' 9r f Sli.BOX. ~o- Fig. 265. —0-1 B ' The defect of this method is that the E.M.F. may vary during the two tests, the current being st-ronger in the first case, and the polarisation consequently greater. The most perfect method is that known as Munroe's, shown in skeleton diagram in Fig. 264, and Fig. 265 .-shows the connections required using the P.O.Wheatstone ELECTRICAL MEASUREMENTS. %\ff bridge. The disconnecting plug is taken out bctwecni the terminals G^ and M to which the cell to be tested is. connected by short thick wires. All the resistances are plugged up with the exception of, say, i ohm, in the zigzag R. The left-hand key G being now depressed a. deflection is obtained from the galvanometer by the current from the cell going to charge the condenser (which must be short-circuited by the plug for a moment just before). This deflection is noted, and when the needle has come to rest (still keeping the key depressed) the right-hand key is depressed, which closes a shunt to the cell. This will cause a deflection in the opposite direction, due to a partial discharge of the condenser. The cell resistance r is tlien given by the formula r =; S X — - > C being the charging deflection, d the partial discharge deflection, and S the shunt resistance. Thus, suppose c = 290°, d = 60^ and S = i ohm, then r = — , = -261 ohm. 290-60 The advantages of this method are that the cell has no' time to polarize, as its circuit is only closed long enough to read the deflection when the right-hand key is depressed ; it is also independent of any resistance except the shunt. This plan may also be used to measure the E.M.F. by making a second test with a standard Clarke cell, as the throw of the needle on depressing the left-hand key is in direct proportion to the electromotive forces in each case. 320 PRACTICAL TELEPHONE HANDBOOk. Current Strength. — The strength of the current passing through a conductor is determined by finding the total resistance in ohms in its path (including battery resistance) and the electromotive force in volts of the battery. Dividing the latter by the former by Ohm's law f c = ~- ) the strength of the current is given in amperes. As currents of as much as i ampere in strength are little used in telephony, it is more usual to measure in milliainperes , which is a unit = of an ampere. lOOO The formula then becomes C = . It is important to remember that the combined resistance must be taken when shunts are used, or the current splits into two or more paths. Rules for finding combined resistances are given on page 14. Resistance of Earth Connection. — This should be measured and tabulated whenever possible, as the efficiency of working depends much on a proper earth connection. It should not offer more than 10 ohms resistance. When two wires can be obtained between the points where the earth connections are made, it is easy by means of the Wheatstone bridge to measure the earth resistance. The two wires are short-circuited at the far end, and the resistance of the loop L obtained. The wires are next earthed at the far end and their resistances with earth return measured separately; two tests being made of each, with reversed test battery and the mean taken, so as to eliminate the effects ELECTRICAL MEASUREMENTS. . 321 of earth currents. Let r and r^ be these resistances. The earth resistance E will then be given by the formula E = ( ^1 + ^2) ^ Theresultwill, of course, 2 include the resistance of the earth wire leads at both ends. SHde-Bule. — For the calculations necessary in elec- trical testing, the slide-rule will be found of the greatest service, as the trouble is reduced to a minimum, and by the use of a good make, such as the " Gravet," the accuracy can be ensured to within o'5 per cent., which is usually near enough for practical purposes. APPENDIX. The following are a few of the different forms of transmitters and receivers which have lately come into prominence : — The Hunnings " Cone " Transmitter. — This is made Dy the General Electric Company, and is more exten- sively used in this country than any other Running form, which is good evidence of its efficiency. Fig. 266 is a front view, with one-half of the mouth- 266. ' Fig. 267. piece and thin carbon diaphragm removed, so as to show the back carbon block, with its face formed into a number of square cones, between which the granulated carbon rests. The points of the cones in the centre are APPENDIX. 323 removed, and small silk tufts are cemented in their place. These serve to prevent the solidification of the granules. A ring pad of cotton, vi^ool also keeps the granules in the centre. Fig. 267 is a section. The instrument is made in several forms, Fig. 268 representing a skeleton form made to fit inside a Blake transmitter case, Fig. 269 showing it in position. Wire gauze is fitted in the mouth-piece to prevent the diaphragm being tampered with. Tlie Solid-Back Transmitter is shown in section in Fig. 270. It is made by the Western Elec- tric Company, and is much used for long -. distance work in America. The small brass cell c is pro- vided with a screwed cover, which serves to clamp a small mica diaphragm, to the centre of which is clamped a thin carbon electrode rather smaller than the inside of the brass cell. This electrode is faced by another carbon one, fixed to the back of The latter is rigidly fixed to the arm s, which extends across the instrument. The mica disc is clamped by the screw shown to a comparatively large ordinary iron diaphragm, with indiarubber round its edge, held in position and damped similarly to a Blake diaphragm. Fig. 269. 324 PRACTICAL TELEPHONE HANDBOOH. The inside of the cell C is lined with paper, and nearly filled with carbon granules. The induction coil used is a large one, wound with comparatively thick wires, to a resistance of -3 ohm for primary and 14 ohms for secondary coil, which latter resistance is rather startling. Mary's Tranvii'ter. — This is a new form of Hun- Fig. 270. ning's, the peculiarity of which consists in arranging the granule cell opposite the upper portion of the thin carbon diaphragm, instead of opposite its centre, as in others. Fig. 271 is a section of the instrument, G being the granule cell (shown without the granules), reaching to just below the centre of the carbon diaphragm D. The latter is protected by wire gauze z in the mouth- piece. This gauze also serves to get rid of the moisture. Appendix. iii The instrument is fixed at an angle by two brackets of the shape shown ,whJrh also serve for connections. The Fig. 271. instrument is a very effective one, especially for long distances. The loi Transmitter.— K neat little transmitter, made by the Consolidated Telephone Com- pany, is shown in Fig. 272. It is constructed somewhat on the lines of the " Berthon," shown in Fig. 55, but, instead of using carbon granules, small carbon pellets about the size of small shot are used between the carbon electrodes. A ferrotype diaphragm is used in front of the thin carbon one to protect it Fig; 272. 32d Practical telephone ranDboojc. The instrument has a remarkably clear and natural J ^ ^ ^$ — 1 p rj tone, and the pellets have no tendenry to solidify. It APPENDIk. 327 is provided with long terminal screws, by means of which it can be fixed in place of other transntiitters. The " Johnson " transmitter is used rather exten- sively, especially for private installations, and gives very good results. It is a simple pencil microphone, made up of two carbon pencils and three carbon blocks mounted on the slant on a thin pine board, as shown in Fig. 273, which also shows the connections to the battery switch-bell used in connection with it. The front of the wooden diaphragm is protected from moisture by a thin sheet of mica. Whistling Effect. — A very curious effect may be pro- duced with a good form of granulated carbon transmitter worked by a battery of three or more cells. If a receiver in circuit with such a transmitter have its ear-piece brought close to the transmitter and then slightly jarred, a musical note will be given out, caused by the action and reaction of the two instruments on each other. The sound will also be set up in other receivers in the same circuit and may be loud enough to be heard all over a room, so that it can be used to call a subscribej's attention when his receiver is left accidentally in circuit with the line. The Collier Receiver. — This instrument differs con- siderably from the ordinary class of receivers, as will be seen from Figs. 274 and 275, giving side views, and Fig. 276, an end view of one form of the instrument. A bobbin of wire, c, c, with a soft iron wire core, is fitted into a round of ebonite block. On each side of the bobbin soft iron diaphragms, d and d\ are clasped round their edges by 328 PRACTICAL TELEPHONE HANDBOOK. outside covers of ebonite. A magnet, N S, has its poles let into the covers, and through both magnet and covers . are screwed the soft iron pieces n and s, until they nearly touch the diaphragms. The top of the instrument is shaped for fitting to the ear, and is put into communica- tion with the internal spaces between the diaphragms and the sides of the bobbin by small holes, as shown. The ends of the coils are connected to terminals A and B. The diaphragm and coil being in a strong magnetic Fig. 274.— Scale \. Fig. 275.— Scale \, Fig. 276.— Scale J. field, the core of the coil is strongly magnetised by induction. The instrument has proved a very efficient one, especially for long distances. Mercadie/s Bitelephone, — As mentioned on page 63, M. Mercadier was led from his researches to the con- struction of very light receivers. Fig. 277 represents a full-size section of one of these. In an ebonite case of APPENDIX. 329 three parts, B, E, and C are two bobbins fixed on the ends of a curved laminated magnet M, the whole being mounted on an iron disc A, so that by means of the screw a the ends of the magnet cores can be adjusted very near to the iron diaphragm D. The cap c has a projection (with a removable cover of indiarubber) for fitting in the ear. Fig. 277.— Full Size. Two such instruments as above are fitted on the two ends of a piece of steel wire, by means of which the pressure on the ears can be adjusted. The pair thus connected are used in the manner shown in Fig. 278, from which it will be seen that the bitelephone is very convenient, as it leaves both hands at liberty fqr writing, etc. The single instrument only weighs i| oz., and the pair with steel wire spring only 4^ oz., so that it is 33d Practical telephonM handbook. much lighter than ordinary receivers, which weigh about lO oz. each. Fig. 279 shows an instrument called a microlelephone^ Fig. 27S. made by the General Electric Company, which com- bines a transmitter and a receiver, and leaves the user more free in his movements than when he has to direct Appendix. 331 his voice towards a fixed transmitter. Most firms make similar instruments, some of which, suCh as that shown in Fig. 281, have a button or lever spring, the pressure Fig. 279. Fig. 280. of which by the fingers in the act of holding closes the microphone battery circuit. Table Sets. — Fig. 280 represents a neat form of magneto set intended for desk or table use, made by the Consoli- dated Telephone Company. The transmitter is of the Running's form. 332 rkACTtCAt fELEPHONE HANDS 60 J^. A more elaborate magneto desk set of very artistic design and good finish, made by Ericsson, of Stockholm^ isshowninFig, 281. A light aluminium-mounted micro- telephone is used, the weight of which, when laid in the double-fork holder, operates the automatic switch of plunger pattern, under which is the induction coil. The Fig. 281. bell domes are fixed to the bottom of the generator casing. The transmitter is a very good one of Running's form, with an iron diaphragm gilded on the inner surface, on which also are punched a number of small projec- tions. These enter into the granulated carbon, and prevent its consolidating. Post Office "Universal" Set. — Fig. 282 shows an instru- APPENDIX. li% ment set made to Post-Office specification. It has a Gower transmitter and two double-pole receivers, and is furnished with eight terminals; The internal connections are so made that it can without alteration be adapted to all the different modes of working. Fig. 282. Fig. 283 shows the internal connections when a relay is not used. The external connections are, counting from the left : — Bell between terminals i and 3 ; line on 4; earth or return on 5 ; first cell of battery between 6 and 7 ; whole battery (z) on 5 and (c) 7, 334 PRACTICAL TELEPHONE HANDBOOK. When the instrument is furnished with relay, the bell is connected between Nos. 6 and 8 terminals, Nos. I and 3 being short circuited. Fig. 283. Railway Set. — Fig. 284 shows a set very much used by the various railway companies for communication between signal boxes. The " Running's Cone " trans- mitter, and two double-pole receivers are used, the bell being actuated by a relay. The top part is furnished with a cover. Private Installations. — For the convenience of private firms or individuals a few sheets of connections of different instruments used in private installations are given (in fuller detail than in Chapters VI. and VII.) at the end of the book, APPENDIX. 335 Fig. 2S4. Diagram i gives the connections of tliree sets of instru- ments with Johnson transmitters, Station A being interme- diate and furnished with a switch similar to that described on page 116, a short arm taking the place of the long one. Diagram 2 gives connections for a central station to communicate with five other stations. The central or local station is provided with five electric bell indicators for calls from the other stations and an in- dicator switch to switch himself on to any of the other stations. Diagram 3. — If inter - communica- tion between all 336 PRACTICAL TELEPHONE HANDBOOK. stations is required, the arrangement of domestic switch (see page 144) may be used. Four stations are here shown, connected by four line wires and a common return wire, or earth connections. This plan requires the instrument plug to be replaced in its proper jack after use. Diagram 4. — The " General" System. With this apparatus there is no necessity to replace the handle switch after use, as a station can be called whatever position its connecting handle may happen to be left. This diagram shows ten stations, joined by ten line- wires and two battery-wires. Only one ringing battery is required. One of the battery wires also serves as the common return wire for the stations. \_These Diagrams are placed at the end of the hook in consecutive order — Trotter's Wire Gauge. — A form of wire gauge very SSSSSCcMu- w.r&LOVERSiCS ' 'ji'j,J,Ji'' I I'l' '^5 >" SALFORD Js 3 MANCHESTER^ TROTTEfe PATENT Fig. 285.— Full Size. useful to telephone engineers is shown in Figs. 285 and I000i«"2o 15 10 5 i. A * 4 8 12 16 20 24 28 K 36 <0 I'ij-. 2S6.— Full She. 286. It is worked on the vernier principle and will show APPENDIX. 337 the gauge number, diameter in mils and in millimeters, and the sectional area of wires of all sizes. Poolers "Electrician's" Wire Gauge. — The two sides of this gauge, invented by the writer, are shown in Figs. 287 and 288. By the simple process of moving the wires in the slots shown, until they are stopped, the instrument shows eight different particulars in regard to any wire between No. 10 S.W.G. and the smallest size, thus including the sizes almost exclusively used Fig. 287.— Scale §. Fig. 288.— Scale |. in telephony. The particulars given will be seen on the figures. Both the gauges are sold by W. T. Glover & Co., of Salford, "Blackley" Ta^e.— This is a tape made by Connolly Bros., of Blackley, which will be found very useful for the covering of joints in covered wires. It is so made as to be self-adhesive, and therefore needs no heat, solvent or such like, having also very good insulating properties. ABSTRACT OP PAPER On Notes of a Trip to the United States AND TO Chicago, 1893. Read before the Institution of Electrical Engineers in yanuary, 1894, by W. H. Preece, C.B., F.R.S., etc. The following table shows the progress in the use of the telephone in the United States between the years 1884 and 1893 : — Miles of Wires Miles of Underground Wire Sets of Instruments in Use Exchange Subscribers ... Number of Exchanges . . . Staif Employed Underground work is now compulsory in many cities. Several cities have more than half their circuits metallic- circuit ones, the total number of the latter being 23,053. Exchanges. — The Western Electric Co.'s multiple board is mostly used, the largest (and the largest in the world) being at Cortlandt Street, in New York. It is 263 ft. long, has 40 sections, and a capacity for 6,000 subscribers. Each operator attends to 60 sub- scribers. It is found that the multiple boards can become too large and unwieldy, giving rise to troubles, especially when there are several large centres in one city. An 1884 189.^ 115,255 440,793 nil 91,463 162,787 276,360 123,625 232,140 1,325 1,351 4,762 9,970 APPENDIX. 339 arrangement called the " divided board " is being tried in some of the largest cities as a remedy. In this board the operations of answering and connecting are allotted to different operators. By this means the trunk (junction) connections are expedited, but the local connections are slightly retarded. The Trunk Working (between centres in the same city) is wonderfully well done, a large number of junction lines being used. In Chicago there are 954 junction lines for the eleven central offices, the principal one having 344 outgoing and 325 incoming. Instructions are given between operators by call wire. Long-distance Working. — Only metallic circuits are switched on to long-distance lines. The incoming lines end in plugs, and the outgoing in "jacks." Subscribers' circuits are cut off from the local switchboards when con- nected on a long-distance trunk-board. New York has 535 call offices for the use of the public; There are three loop circuits between New York and Chicago (nearly 1,000 miles apart) which work remarkably well and are kept busy. The charge for long distances is on the basis of I cent per mile for five minutes' conversation. Rate of Working. — Each operator attends to from 50 to 100 subscribers, or from 3 to 10 long-distance trunk lines. The average number of calls is 8*03 per day per subscriber, but in Chicago it averages 13 '6, and in one of its central offices as many as 24-3 per day. Underground Work. — The cables (dry-core or paper insulated) are mostly of 100 pairs of wires. They are 340 PRACTICAL TELEPHONE HANDBOOK. all carefully tested for" " cross talk " by means of buzzers, in addition to the ordinary tests. There are 14,034 miles of underground wire in New York, 160 cables entering the Cortlandt Street centre. The cables are led to test and distributing boards, by means of which the busy lines' are divided among the operators so as to equalise the work. For the 11 exchanges in Chicago there are 48 miles of conduit ; 433 miles of duct ; 107 miles of underground cable, containing 17,995 miles of wire ; 888 man-holes ; 66 miles of aerial cable, containing 5,185 miles of wire; giving a total of 23,180 miles of wire in cables. Miles of wire on poles is 7,958. Disturbances To prevent as much as possible the disturbing effects of electric railways, very thick (No. o gauge) return conductors are used for the latter, to which the rails (themselves bonded together) are soldered. Lightning Protection. — Protection from lightning, and from danger of fire caused by contact with electric light and traction mains, is obtained by providing all circuits with (i) a fine wire fuse or cut-out; (2) an air-space carbon protector, and (3) an ingenious heat coil which earths the line when the " stray currents " exceed a certain strength. Rates. — These vary. considerably, but are usually very high, owing to the excessive rentals of buildings arid Cost of way-leaves, and to the fact that the companies are heavily taxed by both the State and the munici- APPENDIX 341 palities. In a few cases a toll rate is charged instead of a yearly subscription, or in addition to a small yearly subscription. In Buffalo the toll is 10 cents for each five minutes' conversation. The following table gives various particulars of some of the principal cities of the United States and of this country : — NO. OF SUBSCRIBERS, RATES, ETC., OF PRINCIPAL CITIES. Population. Exchange Substribers Average No. of Inhabitants per Business Kates. Metallic ■ Single Subscriber. Circuit. Wne. New York 1,515.301 9,066 i67 $i8b $100 . Chicago 1,099,850 9,684 114 125 100 Philadelphia .. 1,046,964 3,620 289 130 100 Brooklyn 806,343 4,439 182 100 — Boston 448,477 5,668 79 no 96 Cincinnati 334,279 4,015 83 100 72 San Fran .isto 298,997 4,528 66 •72 *6o Detroit 205,876 4,287 48 50 British— London 4,363,294 6,7op 636-3 Liverpool 513,790 4,500 114-1 Manchester 510,998 -2,300 222-1 Glasgow 669,059 3,200 209 Edinburgh 264,787 900 294-2 Birmingham 483,526 1,200 402-9 Leeds 375,540 1,300 2888 *Also " toll " of 5 cents per conversation. ABSTRACT OF PAPER ON THE TELEPHONING OF GREAT CITIES. By a. R. Bennett, M.I.E.E. Read at the British Association Meetings 1891. The paper discusses how the extensive demand for telephonic exchange communication, which, in the course of a few more years, is certain to arise in all large cities — a demand of which no conception can be formed from the present condition of telephone exchanges in this country — can be met and satisfied. Given low rates and a fairly-efficient service, the time will come, and that' at no distant day, when every shopkeeper, and almost every householder, will look upon a telephone exchange connection as as much of a necessity as gas or water. Indications are not wanting, even now, of what may be expected when the inhabitants of large towns come to realise what an important business and social auxiliary a properly conducted telephone exchange is ; for in Galashiels, and some other towns, there is already a telephone for every 200 inhabitants, the principal supporters, alter the manufacturers and merchants, being professional men, shopkeepers, and householders. If telephoned to the same extent as the towns named, AFFENDIX. 343 London, with its 5,600,000 inhabitants, would possess 28,000 subscribers ; but owing to its greater wealth and extent, it is not only possible, but almost certain, that eventually London will require a telephone for every 50 inhabitants, which, with its present populationi would mean 1 1 2,000 subscribers. That number would only represent four times the proportion already existing in the small towns referred to. A successful telephonic scheme for London, or any large town, would require to comprise several essential conditions. Firstly, privacy and efficient speaking must be secured ; secondly, the connecting together of subscribers and their subsequent disconnection and, if required, reconnection with others, must be rendered rapid and certain ; thirdly, the rates must be within the reach of small shopkeepers and householders, and should not exceed ;^8 per annum ; fourthly, the system must be laid out so as to be capable of indefinite expan- sion, without the necessity of periodical reconstruction ; and lastly, the undertakers of the system must have equal rights with gas and water companies in laying their conductors underground. All these requirements, excepting the fourth, have from time to time severally been met and conquered, but no existing exchange system, so far, comprises them all, although, technically and commercially, it is perfectly practicable to com- bine them so as to attain as nearly to perfection as possible. The sanction of the' Legislature to the laying of underground conductors constitutes the only doubtful quantity. 3^4 PRACTICAL TELEPHONE HANDBOOK. The Post Office has demonstrated the feasibility of perfect privacy and effective speech in conjunction with a system of underground wires ; and the Mutual Tele- phone Company, in their recently-constructed Exchange at Manchester, has shown that privacy, distinct speech, and rapid and certain switching are quite compatible with as low a rate of subscription as ^S per annum. The only essential requirement that has not yet been demonstrated, is the laying out of a system so as to permit of vast and easy expansion in every direction ; and this, the paper shows, is a problem admitting of easy solution, provided that the laying of wires i,s made inde- pendent of private caprice. The leading feature of a cheap, efficient, and easily- extensible exchange in a large town is a division, as far as feasible, of the area to be telephoned into sections not exceeding a square mile in extent, with some, smaller ones in situations where, as in the City of London, very great commercial activity prevails. In the centre of each section will be situated a switch- room, to which the wires of the subscribers resident within that square mile will be led. As some subscribers will be resident quite near the switch-room, and others at maximum distance from it, it is assumed that, with the mile squares, the average length of a subscriber's line will be about a quarter of a mile, and, therefore, cheap to construct. Each of these secondary switch- rooms will be connected, according to the geographical configuration of the town, to either one or two central switch-rooms by a sufficient number of junction wires. APPENDIX. 345 Such a multiplication of switch-rooms would be im- practicable with the ordinary methods of switching, but a system exists which has been thoroughly proved in practice during the last nine years, and which is specially applicable where a very large number of subscribers has to be dealt with. By the aid of this system, which is known as the " Mann," or a modification of it devised by the author, with the switch-rooms distributed as described, the maximum time for establishing a con- nection between two subscribers situated at the extreme opposite limits of a telephone area as large as London would not exceed ten seconds. The "Mann " switching system only requires apparatus at the switch-rooms of extreme simplicity and com- pactness, and calls for only a minimum expenditure of labour on the operators, while it interposes no obstacle in the shape of signalling electro-magnets at the inter- mediate switch-rooms to the freest possible passage of telephonic speech. The system is, consequently, better adapted than any other for communicating over long distances. Privacy and long-distance speaking would be secured by the universal adoption of metallic circuits. Such a system would afford the maximum possible telephonic efficiency, and would enable (supposing it were like- wise fitted in other towns) London subscribers to talk from their own offices direct to the offices of subscribers, not only in the most distant cities of Great Britain and Ireland, but in Paris and other continental cities. It is asserted that such a system would lead to such a rapid 346 PRACTICAL TELEPHONE HANDBOOK. and phenomenal increase in the number of subscribers, that an annual subscription of ;^8 would, even in the largest towns, be sufficient to yield a large profit on its cost; even if all the wires were placed underground. BRITISH STANDARD WIRE GAUGE. 347 BRITISH STANDARD WIRE GAUGE. S.W.G Nearest B.W.G. Dia. in Mils. iMil= Pure Copper Wire at 59° r- Weight in lbs. per mile. sp. gr. 89 Resistance. •001 in. Ohms per Ohms per Yards per yard. Mile. Ohm. 4 4 232 •000S7S I -01 1740 862 s 212 •000687 I-2I 1458 ''i? 6 192 ■000838 I -48 II94 588 7 7 176 ■000997 1-75 1004 497 8 8 160 ■00120'' 213 8«S 408 9 9 144 ■OOI94I 263 671 331 10 10 128 •001885 3-32 53' 262 II II 116 •002290 4-04 436 215 12 12 104 •00286 5-03 350 176 13 »3 92 •00364 6-41 275 135-8 J4 14 80 •0048 -« 8-50 207 102-4 15 15 72 •00595 10 -47 168 83-0 16 16 64 ■007S4 13-26 133 6S-7 17 17 56 •00988 17-39 lOI So-i 18 18 48 •01 345 2368 74-S 36-7 19 19 40 •0193 35-2 51-8 24-7 20 20 36 •0238 418 421 20-4 21 21 32 •0302 53-2 33-2 '6-35 22 22 28 •0394 694 25-4 12-54 23 23, 24 •OS37 945 18-6S 9-20 24 24' 22 •0638 II 2-4 15-67 7-75 2S 2S 20 •0773 136-0 12-95 6-40 26 26 18 •0952 167-S 10-51 5-21 27 27 164 •1144 201-2 8-75 4-33 28 28 14-8 •1409 248-0 7-10 3-51 29 29 13-6 •1675 294-5 5-975 2-95 30 30 I2'4 •201 354-4 4-98 2-45 31 II-6 •229 404-5 4-37 ^'W 32 10-8 •26S 467-0 3-78 1-86 33 31 10 •309 544-8 3-24 i-6o 34 32 9*2 •364 642-0 2-75 1-355 35 3J 8-4 •438 770-S 2-28 1-129 36 34 7-6 ■535 942 1-87 ■92* 37 6-8 •668 "75 1-49 •740 38 6 •863 i5«9 1-16 •573 39 S'2 1141 2010 •878 •433 40 35 4'8 1-340 2360 'l''l •369 1 41 4-4 IS9S 280s •628 •3" 42 36 4 1929 3412 -519 •255 INDEX. Ader Receiver, 58, 59 Transmitter, 71 Ampere, 12 Applications, Military, 293 Armature, Siemens, 94 — • — Generator, 95 Astatic Galvanometer, 305 Automatic Call - Office Apparatus, 282 Cut-out, 94, 97 Post Pattern, 98 W. E. Co.'s, 98 Switch, 84, 94, 102 B Batteries, 28 Secondary, 38 Battery Boxes, 37 Reverser, 300 Measurements, 316 Bell, Electric, 85 Local or Night, 124, 181 Polarised, 94, 99 Single Stroke, 85 Trembler, 85 Bell's Telephone, 42, 44, 54 Bennett & McLean's Exchange Sys- tem, 181 Bennett's Arm Extender, 218 Exchange System, 173 Iron Standards, 215 Paper on the Telephoning of Great Cities, 342 Translator or Repeater, 232 Trussed Iron Standard, 216 Two-way Switch, 121 Binding. .Wire to Insulator, 204 Bitelephone, Mercadier's; 328 " Blackley " Jointing Tape, 337 Bolton Exchange Systein, 181 Breast Transmitter, Ericsson's, 141 Bridge,Wheatstone, 295 ■ — ^ — Post Office Pattern, 298 British Standard Wire Gauge,25,,347 Cable, " Brooks,'' 256 "Conference," 255 ■ " Faraday," 256 ■ " Fowler Waring," 172, 256 GJover & Co.'s, 223 "Paterson," 256 '■ "Norwich," 256 Suspension, 223 Cables,; 172, 222, 255, 339 - — Dry Core, 171, 255 Overhead, 171, 222 Paper Insulated, 256 Underground, 255, 339 Cabling Switchboard, IS5 Call-Office Apparatus, 282 ^ Cotterill's, 287 — — Crossley's, 282 Mann's, 283 Mix&Genest's,287 Pooled Mac Iver's, 283 '— Smith & Sinclair's, 286 INDEX. Call-Wire System, 170, 280 ' — Arrangements, 181 Capacity Inductive^ 24 Measurement of, 312 Carbon Lightning Arrester, 173 Carty's Magneto-Bell, 108 Cells, Battery, Qualities desirable in, 28 Dry, 36 Storage, 38 Cell, Daniell, 34 Gravity, 35 Leclanchfe, 29 Agglomerate, 32 Chimney Brackets, 213 Circuit, 13 Short, 14 Circuits, Divided, 14 Res. of, 14 Metallic,, 13 Clayton Standard, 218 Coercive Force, 17 . Coleman & Jackson's Test-Board, 190 Collier's Receiver, 327 Communication with Divers, 293 Commutator Press-button, 168 Comparison of Battery and Mag- neto Working, no Compound Magnet, 17 Conductivity, 10 Percentage, 27 Conductivities, Table of, 10, 201 Condenser, Standard, 312 " Conference " Cable, 255 Conduits, 256 Constant, Galvanometer, 309 Contact Breaker, Gray's, 143 -. Poole's, 143 Contact, Loop Test for, 303 Copper Wire, 26, 200 Formulae for, 26 : — Table of, 347 Cordeaux's Insulator^ 203 Cotterill's Call-Office Apparatus, 287 Creosoting of Poles, 207 Cross-Connecting Board, 186 Cross System for Metallic Circuits, 230 - . Crowfoot Gravity Cell, 35 Current Electric, 9 Induced by Magnets, 17 Induction, 18 Strength, Measurement, of, 319 Daniell Cell, 34 Derived Circuit, 14 Detector Galvanometer, 21 Dewar Table Switch, 137 Difference of Potential, 1 1 Dip or Sag of Wires, 220 Discharge Key, 312 Distributing Board, 182 Poole's, 186 Subsidiary, 190 Disturbances, Line, 227, 340 Divided Circuits, 14 Resistance of, 14 Switchboard, 339 Divers, Communication with, 293 Domestic Switchboards, 144, 336 Double-Pole Receivers, 61 Driving Gear of Magnetos, 97 Drop Indicator, 122 ■ Ring-off, 124, 169 Self-Restoring, 271 Dry Cells, 36 Ducts for Underground Lines, 257, 261 Earth Connection, 13, 112 Wiring of Poles, 2H Easements tor Wires, 199 Edison's Carbon Transmitter, 46 Loud-speaking Receiver, 50 Electrical Measurements, 295 Electrification of Cables, 311 Electric Bells, 8s — — . Current, 9 Electro-Magnet, 19 INDEX. Electrio-magnetic Inertia, 23 Electro Motive Force, 11 — Measurement of, 316 Engaged Test, 151, I77. 267, 274 Erection of Poles, 208 Exchange Switchboards, 129 Systems, 162 System, Bennett's, 173, 280 — Bennett and McLean's, 181 Post Office, 162, 276 Law, 171 Manchester, 167, 172 Mann's, 171 Poole's, 167 Exchanges in United S.ates, 338 " Faraday " Cable, 256 Faults, Instrument, 241 Intermittent, 246, 252 Line, 250 Most Common, 247 Fire Alarm Arrangements, 293 Fixing, Instrui»ent, no Galvanometer, 20, 196 Detector, 2 1 Kelvin Reflecting, 305 Gauges, Wire, 25, 27, 3.36. Generater, Magneto, 94 Power, 192 Gilliland Switchboard, 131 Glover's Wire Tables, 27 Cables, 223 Gower Receiver, 56 Transmitter, 72 Gravity Cells, 35 Gray's Contact-Breaker, 143 H Head-Receiver, 142 Heys, W. E., and the Twist System; 228 Hughes's Microphone, 48 Suggestion of Twist, 228 Hughes and the Self-induction of Wires, 200 Humming Wires, 213 Impedance, 23 Indicators, Drop, 122 Induced Currents, 17, 22 Inductance, 225 of Apparatus, 226 Inductive Capacity, 22 Induction Coil, 21 Use of, with Transmitter, 48,67 Best Size for, 83 Inductive Disturbances, 227 Instrument -Fixing, no Insulation Resistance, 304, 310 Insulators, II Form of, 203 Material of, 202 Insulator, Bennett, 205 Cordeaux, 203 Double Shed, 203 Langdon, 204 Shackle, 206 Single Shed, 203 Intermediate-Switch, iij Double Bar, 120 Miller's, 118 Poole's, 116 Iron Arms, 215 Ironclad Ring-Off Drop, 124 Iron Standards, 214 "Johnson" Transmitter, 174, 327 Jointing Tape, " Blackley," 337 K " Kelvin " Reflecting Galvano- meter, 305 Key, Discharge, 312 — — Kempe's, 313 Shorteircuiting, 308 INDEX. Langdon Insulator, 204 "Law" Exchange System, 171 Law, Lenz's, 18 Ohm's, 15 Leclanche Cell, 29 Agglomerate, 32 Lenz's Law, 18 Lightning Arrester, 104 Board, 185 Carbon, 173 Protection in U.S.A., 340 Limiting Distance of Speech, 238 Local Action, i&, 30 Localising Faults, 242, 301 London and Paris Line, 239 Long Distance Working, 225 in U.S.A., 339 Loop Test, 301 Loud-Speaking Receiver, 50 M Magnetic Field, 15 Lines of Force, 15 Magnets, 16 Magnetising, 17 Magneto Generator, 94 Magneto Switch Bell, 93 Carty's, 108 Connections of, 106 Manchester System, NatiorialCo.'s, 167 New Tel. Co.'s, 172 Manholes, 258, 262 Mann's Call-Office Apparatus, 283 Exchange System, 171 McLean & Bennett's Exchange System, 181 McLean & Somerville's Exchange System, 280 Measurements, Electrical, 295 , Battery, 316 Mceohm, 12 Megadier's Bitelephone, 328 Law for ReceiTers, 63 Metal-Cased Blake, 68 Metallic Circuits, 13, 227 Cross System for, 230 Switchboards for, 265 Twist System for, 228 Working of, 263 Microfarad, 24 Micrometer Wire Gauge, 25 Microphone, Hughes's, 48 Microtelephone,^ 330 Military Applications, 293 Miller's Cure for Induction, 195 Intermediate Switch, 118 Return Call Wire, 1 72 Milliamp&re, 12 Mix and Genest's Call-Office Ap- paratus, 287 Mixed System, Switchboard for, 264 Morning Tests, 241, 252 Multiple Switchboard, 148 Bennett's 175 for Metallic Circuits, 265 Multiplex Telephony, 278 N New Telephone Co.'s Standard, 217 System, 172, 344 Night Bell, 124 Notes of a Trip to the U.S.A. 338 Ohm, The, 12 Ohm-Mile, 25 Ohm's Law, 15 Operators' "Transmitters, 141 Outrigger, 212 Overhouse Work, 213 "Paterson" Cable, 256 Permeability, 19, 97 Photophone, 52 Polarisation, 29 IhDEX. Polarised Bell, 94, 99 Ring-Off Orop, 169 Pole-changer, 193 Pole Roofs, 210 Pole Stays, 2 1 1 Poles, Creosoting', 207 Earth Wiring, 211 Erection of, 208 — — Spliced, 207 Wooden, 206 Police and Fire-Alarm Arrange- ments, 293 Poole and Maclver's Call-Office Apparatus, 283 Poole's Commutator Push Button, 168 Contact Breaker, 143 Exchange System, 167 Intermediate Switch, 116 Ring-Off Drop, 169 Test Board, 183 Wire Gauge, 337 Post Office Multiple System, 276 Relay, 93 System, 162 Trunk Lines, 204 Universal Set, 322 Wheatstone Bridge, 298 Potential, 11 Power Generator, 192 Preece's Limiting Distance of Speech, 238 Thermo-Telephone, 52 Notes of a Trip to the U.S.A., 338 Private Installations, 334 Radiophone, 52 Railway Set, 334 Rate of Working in U.S.A., 339 Rates in U.S.A., 340 Receiver, Ader's, 58 Bell's, 44, 54 Collier's, 327 D'Arsonval's, 60 • Receiver, Dolbear's, 52 Edison's, 50 Ericsson's, 142 — — Gower's, 55 Mercadier's, 328 Siemens', 60 Watch, 62 Reflecting Galvanometer, 305 Regulating Wires, 221 Reis's Telephone, 39 Relay, 92 Post Oifice, 93 Repeater, Bennett's, 232 Coleman & Jackson's, 235 Liverpool, 234 Resistance, 10 . of Batteries, 217 Divided Circuits, lo Earth, 320 Insulation, 304 Reverser, Battery, 300 Ring-Off Drop, 124, 169 Roulez's Transmitter, 79 Rule, Slide, 321 Running Wires, 219 Saddle Bracket, 210 Sag of Wire, 220 Selection of Route, 198 Self-Iuduction, 23, 200 Self-Restoring Drop, 271 Scribner's Single Cord Switchboard, Shackle Insulator, 206 Short-Circuiting Key, 308 Shunt-Box, 307 Shunts, 307 Siemens' Receiver, 60 Single-Cord Switchboards, 139, IS9 Smith & Sinclair's Call-Office Appa- ratus, 2 86 Slide-Rule, 321 Sloper's Secret System, 14? Somerville & McLean's Exchange System, 280 mr>Bx. Sruodines, 214 Spring-Jacks, 127, 139, 154, 265, 268, 272 Spliced Poles, 207 Standard, 214 Clayton, 218 Condenser, 312 — — New Telephone Co.'s, 217 — — Trussed, 216 " Standard " Switchboard, 1 34 Static Induction, 24 Stay-Eye Clip, 216 Stays, Pole, 211 Stay Tighteners, 213 Struts, Pole, 212 Spans, Length of, 222 Switch-Bell, 84 Liverpool, 89 Magneto, 93 Silvertown, 86 Switchboard, Bennett's, 175 Gilliland's, 13: Mixed System, 264 Poole's, 124 Single-Cord, 139, 159 Standard, 1 34 Williams', 130 Switch-Boards, 121 Branch Multiple, 176,269 ' Divided, 339 Domestic, 144, 336 Metallic Circuit, 265 Multiple, 149 Switches, Intermediate, 115 Two- Way, 120 Table-Switch, Dewar's, 137 Werner's, 150 Table Sets, 331 Tape, Jointing, 337 Telephone, Bell's 42, 44, S4 Reis's, 39 Telephonic Exchanges, 5 3 Test-Board, 182 Coleman & Jackson's, 190 Test-board, Poole's, 183 Test-Clerk's Equipment, 183 Test, Engaged, 151 Loop, 301 Testing Set, 195, 197 Test-Room Appliances, 182 Tests, Morning, 241,252 Capacity, 312 Theatre Arrangements, Manches ter, 291 Paris, 289 Tools for Fixing, 112 Translator, Bennet's, 232 Coleman & Jackson's, 23; Liverpool, 234 Transmitter, Ader's, 71 Berliner's, 80 Berthon's, 78 Blake's, 64 Crossley's, 70 D'Arsonval's, 73 De Jong's, 74 Edison's, 46 Hunning's, 76 "Cone," 322 "Marr,"77 " Marr's," 324 Mix & Genest's, 74 Moseley's, 77 Roulez's, 79 Society des T^lephones's, 69 " Solid-Back," 323 Thornberry's, 81 The " loi," 325 Trunk-Lines, Post Office, 204 Trunk-Line Working, 276 in U.S.A., 339 Trussed Pole, 212 Standard, 216 Twist System of Running Wires, 228 U Underground Work, 254, 261,-339 Universal Set, P.O., 322 Transmitter, Berliner's, 80 A I INDEX United States, Notes of a- Trip to, 338 Volt, The, 12 W Watch Receiver, 62 Way-Leaves, 199 Werner's Table-Switch, 150 Wheatstone Bridge, 295- P.O. Patterns, 298 Whistling Effect with Transmitters, 327 Wire, 199 Copper, 26, 2C0 Gauge, Standard, 347 Poole's, 337 Trotter's, 336 Gauges, 25 Silicium-BronM, 201 Wires, Humming of, 213 Regulating, 221 Sag of, 220 Wiring Tables, Glover's, 27 WILLIAM RIDER AND SON, LTD., PRINTERS, LONDON. EARTH OR RETURN EARTH EVERYTHING ':^JS!p^°"? '°' — — — == EVERY position. The " Hunnings cone " (skeleton form). ZE c nc L D. P. Bell Receiver, in Ebonite case. No. 40B. Complete Station for short distances. No. 65 B. Complete Station for long distances. For Particulars apply to — THE GENERAL ELECTRIC COMPANY L™- (G. BINSWANGER, Managing Director). 69 and 71, QUEEN VICTORIA. STREET, LOWDOlf, B.C. Works— 45, Chapel Street, SALFORD. Branch Offices— 196, St Vincent St. GLASGOW, and :,g Corporation St., BIRMINGHAM W. T. GLOVER & Co. (Henry Edmonds and Godfrey B. Samuelson), " SALFORD, MANCHESTER. London— 39, VICTORIA STREET, S.W. Telegrams— " Glovers," Salford, "Phonoscope," London. Telephone Nos.— 1187, Manchester; 3191, London. Contractors to the British, and Colonial, and Foreign Govern- ments, the National Telephone Co., and the principal Railway and Electric Light Companies in the United Kingdom. GLOVER'S PATENT IMPROVED ANTI INDUCTION TELEPHONE GABLE For Single or Metallic Circuits. MAKERS OF GLOVER'S PATENT TWIN "MAGPIE" TELEPHONE GABLE For Metallic Circuits only. Patentees and Sole Manufacturers of COMPRESSED SOUP-ENDED AR MATURE BARS. Makers of every description of VULCANIZED ELECTRIC LIGHT WIRE & CABLE FOR GENERAL AND SPECIAL PURPOSES. THE COMBINATION SOLE AGENTS FOR POOLE'S PATENT WIRE GAUGE SOLE AGENTS FOR TROTTER'S PATENT WIRE GAUGE. Micrometer and other Gauges supplied. Established 17^3. October, 1895. FOR CIVIL, ELECTRICAL, & MECHANICAL Engineers, AND FOR STUDENTS IN SCIENCE AND TECHNOLOGY. PUBLISHED BY WHITTAKER <5r= CO., Paternoster Square, London, E.G. {^For Index of A uikors and Subjects see end,) THE SPECIALISTS' SERIES. ' Whittaker's excellent Specialists' Series for Engineering Students.* — Saturday Review. ' Whittaker's well-known and valuable Specialists' Series.' — Electrician. ' The Specialists' Series of technical books is well known and appreciated.* — Nature. ' Messrs. Whittaker's excellent Specialists' Series.' — Daily Chronicle. By GiSBERT Kapp. TRANSFORMERS for Single and Polyphase Alter- nating Currents. [Shortly. By G. R. BODMER, A.M.Inst.C.E., Author of ' Hydraulic Motors.' RAILWAY MATERIAL. The Inspection of. Contents : — Introduction — Rails, Ordinary and Tramway — Sleepers for Rail and Tramway — Fastenings — Tyres and Axles — Plates, &c. — Rolling Stock — Billets and Blooms — Wire Rods and Wire. \Shortly. By W. H. Preece, C.B., F.R.S., President of the Institution of Electrical Engineers, Engineer in Chief and Electrician at the General Post Office ; and A. J. Stubbs, A.I.E.E., Technical Officer, General Post Office. A MANUAL OF TELEPHONY. With Illustrations, Appendix, Tables, and full Index. Second Edition. 15.?. Contents : — I. Transmitters and Receivers — II. Apparatus and Circuits — III. Simple Telephone Exchange Systems — IV. Multiple Switches — ^V. Mis- cellaneous Switching and other Systems — ^VI. Construction, Wires and Cables. ' The most complete epitome of present-day telephonic practice.' — Electrical Engineer. ' The work is exhaustive of its subject, without being overburdened with minute technical details.' — Times, 2 Wkittaker's Technological and Scientific List. THE SPECIALISTS' SERIES (Continued). By G. A. T. MiDDLETON, A.R.I.B.A., M.S. A., Author of 'Strains in Structures,' &c., &c. SURVEYING AND SURVEYING INSTRU- MENTS. With 41 Illustrations. 4J. 6d. Contents : — Surveys with Chain only — Obstructions in Chain-Line and Right-Angle Instruments — The Uses of the Level — Various Forms of Level and their Adjustments — The Uses of Angle-measuring Instruments — The Theodolite and other Angle-measuring Instruments — Instruments for Ascer- taining Distances. ' This is a very neat little text-book, and very suitable for students preparing to pass the Institute examinations.*^/o«r«. of Royal Inst, of British Architects, By J. O. Arnold, Professor of Metallurgy, Sheffield Technical School. STEEL WORKS ANALYSIS. With 22 Illustrations and Diagrams. Crown 8vo. loj. dd. Contents : — The Steel Works — Laboratory and Appliances — Section I. Analysis of Steel and Wrought Iron ; II. Analysis of Iron Ore ; III. Refrac- tory Materials ; IV. Fuel ; V. Sundries. ' This book is of an essentially practical character.' — Engineer. ' Everything that a steel-works' analyst may fairly be called upon to examine finds a place in this volume Frof. Arnold lUas rendered steel-works' analysis a decided service by the publication of his work.' Prof. John Parry in Nature. ' We can heartily recommend this book,' — Electrician. By C.C. Hawkins, M.A., A.I.E.E., and F. Wallis, A.I.E.E. THE DYNAMO, ITS THEORY, DESIGN AND MANUFACTURE. With 190 Illustrations, mostly from original Drawings. 530 Pages. loj. 6d. Contents :— The Magnetic Field— The Magnetic Circuit— The Production of an E. M. F.— The Magnetic Pull— Self Induction— Classification of Dynamos — Bi- and- Multi-polar Alternators — Unipolar Alternators — Open- Coil Armatures, — Closed-Coil Armatures— The Magnetisation of Iron — Armatures — Field Magnets — The Ampere — Turns of the Field — Series, Shunt, and Compound Winding — Sparking and Angle of Lead — Heating of Dynamos'-:— Typical Dynamos — Dynamo Designing — The Working, and Management of Dynamos. ""A work of no mean ability. One valuable feature throughout the bock is'the excellence and number cf the illustrations.' — Electrical Engineer. 'The work is well-arranged . . . the explanations are clear and the formulse .simple. . . . The classification of dynamos is very good and rational.' — Electrical Review. ' - 'We welcome this book as a ttoroughly trustworthy anduaefal work.' Ekctrician. Whittaker's Technological and Scientific List. THE SPECIALISTS' SERIES {Continued). By GiSBERT ICapp, C.E., Member of the Institution of Civil Engineers, Member of the Institution of Electrical Engineers. ELECTRIC TRANSMISSION OF ENERGY, and its Transformation, Sub-division, and Distribution. A Practical Hand- book. Fourth Edition, mostly re-written. 455 pp. xii. pp. With 166 Illustrations. Crown 8vo. 10s. 6d. *»* The work has been brought up to date, both as regards theory and practice. Specimen of Illustrations from Kapp's ' Electric Transmission of Energy.' ' This book is one which must of necessity be found in the hands of every one who desires to become acquainted with the best, and latest information on the finbject.' — Electrical Engineer. ■The book la an excellent one In every way, and will, we imagine, long be regarded as the standard treatise on the electrical transmission of enbrgy.' Mechanical World. * Although, ^therefore, the-bopk will be of greater interest to the trained specialist, it has an Intrinsic value tat the average mannfactnrer who is willing to give a little' study to the subject.' — Textile Recorder. 'Is one of the inost generally useful books to the electrical engineer which has -been p\:h\is]itit'-:— Industries and Iron. Whittaker's Technological and Scientific List. TME SPECIALISTS' SERIES (Continued). By Sir D. Salomons, Vice-President of the institution of Electrical Engineers, A.I.C.E., M.Amer.I.E.E., M.P.S., F.R.A.S., F.C.S., &c., &c. ELECTRIC LIGHT INSTALLATIONS. Vol. I.— ACCUMULATORS. With 33 Illustrations. 5J. ' A capital practical handbook.' Mechanical World, ' The best work on the subject.' English Mechanic. Vol. II.— APPARATUS.— I. Engines — 2. Dynamos and Motors — 3. Instru- ments — 4. Governors — 5. Switches and Switch Boards— 6. Fuses, Cut-outs, Con- nectors, and Minor Apparatus — 7, Arc Lamps — 8. Practical Applications. With 305 Illustrations, "js. 6d. Vol. III. — APPLICATION. With 32 Illustrations, 340 pp. y. Contents : — Precautions — Con- ductors — Testing — Methods of Working^ — Alternate Currents — Estimates, Index, &c. 'The book in its present form is more useful than any of the earlier editions, and contains much more information.' Engijieer. ' A seventh edition reviews itself. It says, ' ' I am wanted, and therefore I am here." ' Electrical Engineer. *The great characteristic of Sir David Salomons' writings is their exceedingly practical common sense.' - Indian Engineer, Di igram of Photometer, from Salomons' ' Electric Light Installations." 3 vols. By Oscar Guttmann, Assoc. M.Inst.C.E., F.I.C., Member of the Societies of Civil Engineers and Architects of Vienna and Budapest, Corresponding Member of the Im. Roy. Geological Inst, of Austria, &c. EXPLOSIVES: The Manufacture of. A Theoretical and Practical Treatise on the History, the Physical and Chemical Pro- perties, and the Manufacture of Explosives. With 328 Illustrations. In two Vols. Medium 8vo. 2,1. 2s, *»* The work contains the most recent information on Gunpowder, Gun- cotton, Dynamite, Smokeless Powders, Fulminates, &c. ' The author has been fortunate in finding a clear field for a fall and compre- hensive wori giving the details of the most modern systems of manufacture. This has been so well done In the volumes before us, that we regret that the space at command prevents us from giving more than a brief indication of their contents,' — Engineer. ' A work of such magnitude and Importance, that it will undoubtedly lake a leading place in the literature on the subject." — Arms and Explosives, wmttaker's Technological and Scientific List, TME SPECIALISTS^ SERIES {Continued),. 'This work commends itself most strongly to all manufacturers and users of explosives, and not less to experts.' — Chemical News. ' He who wants to know all about everything in the way of cordite and its rival " ites," will find whatever he can possibly desire to know in Mr, Guttmann's volumes.' — Daily Chronicle. ' Well conceived, well arranged, well executed.* — Scotsman. • The work is full of valuable information.' — Manchester Guardian. Specimen of Illustrations from Guttmann's ' Explosives.' Whitiaker's Technological and Scientific List. THE SPECIALISTS' SERIES (Continued). By G. R. BODMER, A.M.Inst. C.E. HYDRAULIC MOTORS : Turbines and Pressure Engines. With 204 Illustrations. Tables arid Index. Secoiid Edition, thoroughly Revised and Enlarged. 141. ' A distinct acquisition to our technical literature.' — Engineering. ' The best text-boolc we have seen on a little-known subject.' — Marine Engineer. 'A well-known and deservedly successful work.' — Electrician. ' An excellent treatise.' — Nature. * This standard work has been now considerably enlarged The best book that exists on the subject.' — Electrical Revieiit. Specimen of Illustr^tiSkl.ffom'&airaet's 'Hydraulics, By W. Fletcher, Mechanical Engineer, Author of ' Steam Locomotion on Common Roads.' THE STEAM JACKET: Practically Considered. Second Edition,- Revised and Enlarged. With 63 Illustrations. Crown 8vo. Ts. 6d. ' Contents : — History of the, Steam Jacket— Cylinder Condensation- Means proposed for PreveiitiiJl;;' Cylinder Condensation— The Abuse of the Steam Jacket— PracticalTroofs of the Efficacy of the Steam Jacket, .&c., &o. ' It ongbt to be read not only by engineers, but by Jiteam usors.' • 'An excellent little \>ooTs..'— Electrical Review. ' A most .excellent work on th§ subject.'-T-^,fea»wA^.\ - Textile Recorder. Whitfaker's Technological and Scientific List, THE SPECIALISTS' SERIES (Continued). By Oliver J. Lodge, LL.D., D.Sc, F.R.S., M.I.E.E. i-rofessor of Experimental Physics in the University College, Liverpool. LIGHTNING CONDUCTORS AND LIGHTNING GUARDS. A Treatise on the Protection of Buildings, of Telegraph Instruments and Submarine Cables, and of Electric Installations generally, from Damage by Atmospheric Discharges. In one volume, with numer- ous Illustrations. CrownSvo. 15^. ' How they are essential, and in what manner they may be made most effective, is elaborately shown in the Professor's compreliensire and most instruc- tive treatise, which is the work of one of our best authorities on modern theories of electricity and their practical appU cation. — Times^ • There is probably no one who knows more about lightning conductors than Dr. Lodged — IndnstrieSn Single Pattern Form of Guard for Cables, {Specimen of llhistrccttons.) By Thomas H. Blakesley, M.A., M.Inst.C.E., Hon. Sec. of the Physical Society. ALTERNATING CURRENTS OF ELECTRICITY. Third Edition, enlarged, s^- Contents :— Self Induction — Mutual Induction — Condensers-— Contjenser in Circuit — Several Condensers — Combination of Condensers with Self induc- tion—Condenser Transformer — Distributed Condenser — Telephony-^The Transmission of Power — Upon the Use of the Two-coil Dynamometer with alteniating Currents — Silence in a Telephone — On Magnetic Lag^Further [Contributions to Dynamometry. , . 'It is written with great clearness and compactness of statement) and well maintains the character of the series of books with which it is now associated.'— ^/i?c^(Vz««. By Stuart A. Russell, Assoc.M-Inst.C.E., M.IiE.E. ELECTRIC -LIGHT CABLES, AND THE DIS- TRIBUTION OF ELECTRICITY. With 107 Illustrations. 7^. 6d. ' The various systems of main distribution, heating losses, jointing; cost of distribu- tion, testing, safety devices, &c., are dealt with. . .' * . A boob Of very great V9\\l&,^-^— Electrical Review. ' ' A more thorough book conld not have been Vfritten.'r— Electrician. . ' We expected a really valuable book from Mr. Russell, and his work has mora than come up to our expectations.' — Itidtatries. Whittaker's Technological and Scientific List. TME SPECIALISTS' SERIES {Coniinued). By William Anderson, F.R.S., D.C.L., Member of the Council of the Institution of Civil Engineers, M.I.M.E., and Director-General of Ordnance Factories, Royal Arsenal, Woolwich. ON THE CONVERSION OF HEAT INTO WORK, A Practical Handbook on Heat-Engines. With 62 Illustrations. Third Edition. 6s. Contents :— Chap. I. Nature of Heat — Composition of Motions — Rota- tory Motion — Reciprocating Motion — Impact, &c. Chap. II. Oscillatory Motion — Conduction of Heat — Latent Heat, &c. Chap. III. Properties of Gases — Laws of Boyle, Mariotte, Charles, and Gay-Lussac — Work of Ex- panding Gases — Metallic Heat-engine, &c. Chap. IV. Laws of Carnot— Forms of Energy — ^Table of Properties of Fuels — Siemens' Radiating Furnace —Possible duty of Furnaces, &c. Chap. V. The Blast Furnace— The Discharge of Cannon — Internal Stress on Guns— Pressure of Gases in Bore of Guns, &c. Chap. VI. Heat Engines Proper— The Gas Engine— The Hot Air Engine — The Rider Engine — The Steam Boiler — Properties of Steam — Varieties of Boilers — The Injector, &c. Chap. VII. Classification of Steam Engines — ^The Compound Engine — The Functions of Steam in an Engine — Petroleum Engines, &c. '^We have no hesitation in saying there are young engineers — and a good many old engineers, too — ^who^can read this "book, not only with.'profit, but pleasure, and this is more than can be said of most works on heat.' — The Engineer. 'The volume bristles from be^nning to end with practical ex- amples cnlled from every department of technology. In these days of rapid book-making it is quite refreshing to read through a work like this, having originality of treatment stamped on every page.' — Electrical Review. By G. W. SUTCLIFFE, M.Inst.CE. (Whitworth Scholar). STEAM POVt'^ER AND MILL WORK: Modern Practice in. With numerous Tables, Illustrations, &c. Crown 8vo. zis. Contents : — Heat and Work — Fuel and Combustion — Calorimeters — Storage and Manipulation of Coal — Coal Washing for the Removal of Solid Waste — Connexion, Circulation, Evaporation, and Priming in Boilers —Forced Draft — Gas Firing — Use of Liquid Fuel — Analysis of Gasses produced in Combustion — ^Water for Use in Boilers — Boilers — Boiler Houses and Boiler Setting — Chimneys — Economisers — Crossheads and Connecting Rods — Crank Shafts, Gearing, &c., &c. ' A peculiarly nsefal and well-written ToooTl.'— Daily Chronicle. ' Students of engineering will find the book invaluable.'— .Strfftonan. ' Strikes us as being particularly deserving of a wide circulation. The author has excellent qualifications for writing such a work.' — Leeds Mercury. ' The author has arranged his matter in a sensible manner, and explains himself in a practical way.' — Nature. ' One of the most useful treatises of the kind. To students It will be found a most excellent text-book,' — English Mechanic. 'The book will well repay careful etaAy.'— Engineer. ' We feel sure that this will be a valuable and useful contribution to the literature of the subject.' — Marine Engineer. ' The work is one which is to be commended to the notice of naval architects and marine engineers.* — Steamship. Whittaker's Technological and Scientific List. THE SPECIALISIS' SERIES (Contimied). By 'A Foreman Pattern Maker.' HELICAL GEARS ; A Practical Treatise. By the Author of 'Practical Ironfounding.,' 'Metal Turning,' 'The Principles of Pattern Making,' ' The Principles of Fitting.' With IC30 Illustrations and Frontispiece. 7j. M. ' To pattern-makers, iron founders, and engineers generally, we can recommend the perusal of the book.' — Marine Engineer^ 'The author has contributed a useful book to machinists.' — Builder. By D. W. Taylor, Naval Constructor, United States Navy. RESISTANCE OF SHIPS AND SCREW PRO- PULSION. With Seventy-three Figures and numerous Diagrams. Medium 8vo. cloth, 15^. ' The book will well repay carefml study.' — Engineer. ' A valuable and nsefnl comtrlbntion to the literature of the subject.' Marine Engineer* By GusTAv May. BALLOONING: A Concise Sketch of its History and Principles. From the best sources, Continental and English. With Illustrations. 2,s. 6d. ■ Mr. May gives a clear idea of all the experiments and improvements in aero- navigation from its beginning, and the various useful purposes to which it has been applied.' — Contemporary Review. By Geor<3E Lunge, Ph.D., Professor of Technical Chemistry, Zurich, and Ferdinand Hurter, Ph.D., Consulting Chemist to the United Alkali Co., Limited. THE ALKALI MAKERS' HANDBOOK. Tables and Analytical Methods for Manufacturers of Sulphuric Acid, Nitric Acid, Soda, Potash, and Ammonia. Second Edition, Enlarged and thoroughly Revised . Revised. In crown 8vo., with Illustrations, lOJ. 6d.; strongly bound in half leather, 12s. ' The present edition gives abundant evidence that care is being taken to make the book a faithful record of the condition of contemporary quantitative analysis.' Professor T. E. Thorpe in Nature, ' That excellent book.' — The Jate Pkofessor W. Dittmar. < It Is an excellent book, and ought to be ia. the hasids of every chemist.' — Professor J. J. Hummel. lo Whittaker's Technological and Scientific List. THE SPECIALIST'S SERIES (Continued). By Professor Roberts Beaumont, Director of the Textile Industries Department, The Yorkshire College. COLOUR IN WOVEN DESIGN, Coloured Plates and 203 Illustrations. 21s. With thirty-two Contents :— Theories of Colouring— Attributes of Colours— Contrast and Harmony— Mixtures — Elements of Textile Colouring — Stripes — Check Patterns— Simple Colourings— Compound Colourings— Fancy Shades applied to Special Designs— Colouring of Combination Designs— Spotted Effects- Colouring of Double Weaves and Reversibles — Figured Textiles Coloured in the Warp— Weft-coloured Figured Fabrics— Curl Textures. (Specimen of Illustrations.) ' An excellent work on the application of colour to woven design.' Textile Manufacturer, ' The illustrations are the finest of the kind we have yet come across, and the pnbllshers are to be congratulated on the general excellence of the •moxk.,'— Textile Mercury. Wkittaker's Technological and Scientific List. 1 1 THE SPECIALISTS' SERIES (Continued). By A. B. Griffiths, Ph.D., F.R.S. (Edin.), F.C.S. A TREATISE ON MANURES; or, the Philosophy of Manuring. With Illustrations and Index. A Practical Handbook for the Agriculturist, Manufacturer, and Student. Second Edition, revised and enlarged. Crown 8vo. is. 6d. ' The book Is very fall of matter, and may be recommended.' — Engineer, ' The hook is brimful of highly useful information,' — Live Stock foimial. ' We gladly welcome its appearance as supplying: a want long felt in agricultural literature, and recommend every farmer and agricultural student to possess himself of a copy without delay.* — Farm and Home. ' We consider this work a very valuable addition to the farm library. ' Saturday Review. By J. W. Slater, F.E.S., Editor oi Journal of Science. SEWAGE TREATMENT, PURIFICATION, AND UTILISATION. A Practical Manual for the Use of Corporations, Local Boards, Medical Officers of Health, Inspectors of Nuisances, Chemists .Manufacturers, Riparian Owners, Engineers, and Ratepayers. With Illustrations. f>s. ' The writer, in addition to a calm and dispassionate view of the situation, gives two chapters on " Legislation " and " Sewage Patents."' — Spectator. By W. Lee Beardmore, Assoc. M. Inst. C.E., Member of Council and Hon. Sec. of the Civil and Mechanical Engineers' Society, Author of ' House Drainage Scientifically and Practically Considered}' and 'Com- pulsory Registration of Certain Buildings as to their Sanitary Efficiency. ' THE DRAINAGE of HABITABLE BUILDINGS. Illustrated. 5^.'. ' A useful little volume.'— &o/i»/a». ' "Automatic Flushing'' and the notes on the hath are particularly well done.' National Observer. * Gives in a small compass a large amount of useful information. — Industries. ' A thoroughly practical work.'— Nt?rt& British Economist. By Captain M. P. Nadi^ine. A new treatise on SANITARY DRAINAGE and the Treatment of 12 Whittaker's Technological and Scientific List. %Mvcc^ of #reat J^rtttus^trtes* By C. J. BowEN Cooke, Assistant, London and North-Western Locomotive Department. BRITISH LOCOMOTIVES. Their History, Con- struction, and Modern. Development. With. I so Illustrations. Second Edition, Bevised. Crown 8vo. ^s. dd. •^ 6 ft. 6 in. Coupled Engine, L. & N. W. Ry. ' Charles Dickens.' {^Specimen of Illustrations^ Contents r— I. Early History— II. The Rainhill Contest, and subsequent Development — III, Action of Steam in the Cylinder — IV. Valve Motion — ^V. The Boiler — ^VI. Boiler Fittings— VII. Cylinders, Pistons, and Connecting- rods — ^VIII. General Details— IX. How an Engine is put together in the Erecting Shop — X. How the Slide Valves are set — XI. Classifieation of Engines — XII. Tenders — XIII. Brakes — XIV. Modern Locomotives — XV. Modem Locomotives (contin-ued) — XVI. Compound Locomotives — XVII. Lubrication and Packing' — XVIII. Combustion and Consumption of Fuel — XIX. Engine-Drivers and their Duties — XX. Duties of Drivers and Firemen vifhen Working a Train — Concluding Remarks — Index. *We congratulate the author on producing a book which will be deservedly successful.' — Railway Ensi-neer^ ' This new wort constitutes undoubtedly a luost vaTuaWe addition to railway literature.' — Railway Herald. ' A very attractive and instructive little ymTs..'— Times, Oct. sth, 1893. ' A mostlnt^esting book..'— Nature. ' Interesting and valuable.' — Sun. W/iittaker's Technological and Scientific List. 1 3 ZIBBABY OF GREAT INDUSTRIES (,Continued). By the late Sir George Findlay, Assoc. Inst. C.E., Vice-Chairman of the London and North-Western Railway. AN ENGLISH RAILWAY, THE WORKING AND MANAGEMENT OF. Fifth Edition, thoroughly Revised, and Enlarged, with a short Biography, of Sir G-eorge rindlay, and Portrait, Appendix, and numerous Illus- trations. Crown Svo. cloth, Ts. dd. Contents : — Management — ^The Staff— The Permanent Way — Signals and Interlocking — Telegraphs —Rolling Stock — Working of Trains — Shunting and Marshalling ot Goods Trains — Working of Goods Station — Rates and Fares — Division of Traffic — The Railway Clearing House — The State and Railways — On the State Purchase of Railways — Passenger Traffic — On the Law as between EngUsh Railway Companies and the Pubhc — On the Railway as a means of Defence — Index. ' This is a dellghtftil book.' — Engineer. ' Sir George Findlay's book displays so much knowledge and ability that it well deserves to rank as a standard work on the subject.' — Nature. ' A very interesting v\rork throughout.' — Railway Engineer. ' Sir George Findlay's book will take a high position in the library of practical science.' — Athenaum. By J. Alexanper. MODEL ENGINE CONSTRUCTION. With Practical Instructions to Artificers and Amateurs. With S9 Illustrations and 21 Sheetsof Working Drawings by C. E.Jones. 324 pp. Crown Svo. ios.6d. Contents :— Part L Boiler and Engine Details -*. Jl -_^ , with Tools.— Part II. Different Types of Engines : {M III C M^ Stationary, Locomotive, Marine, •vX^a^iSlcrJDaiiih xWW'sVsV Sfecimen of Illustrations from 'Model Engine Construction.' ' Excellent drawings and ample instrnctive raaX\,«t;—PailyChrmide. ' An instructive book, which we do not hesitate in recommending to oiir apprentices and amateurs.* — Railway Herald, ' In this book Mr. Alexander, aided by the drawing of Mr. C. E. Jones, has made things considerablj easier for the model miiker.'— Engineer. ' This book, besides affording an efficient and comprehensive guide to the construction of model engines of several kinds, is of considerable educational value.' ,.-—.,, ._ . „ Morning Past. Will be cordially welcomed by all who revel in the fascinating pursuit of model engine-making.' '''■■"f '^ J. LiNEHAM, in the Technical World. 14 Whittaker's Technological and Scientific List. LIBRAItr OF GBEAT IJH^DUSTMIJES (Continued). By R. Nelson Boyd, M.Inst.CE. COAL PITS AND PITMEN. A Short History of the Development of the Coal Trade, and the legislation affecting it. Second Edition, Revised and Enlarged, with Illustrations. Crown 8vo. Js. 6ii. * The story of the development of the great coal industry of the United Kingdom is told in these pages in an interesting mzxin^r J -r- Engineering. ' Mr. Boyd's well-written and eminently practical book.' * It cannot fail to prove interesting.* — Speaker. Daily CkroHtcie. \ Not only a well-written and fascinating work, but also a valuable history of the I^islatioa and changes which have taken place in the coal industry.' — Industries. Specimen of lllustratio ns from Boyd's ' Coal Pits.' By A. J. Maginnis, M.Inst.N.A., recently Assistant Superintendent ofthe White Star Line. THE ATLANTIC FERRY. With Eighty Illustrations, many of them from scarce prints in the Author's possession. Complete lEiditioil. Crown 8vo. cloth, "js. 6d. A Popular Edition, with about 50 Illustrations, 2s. ed. * Will furnish passengers with a compendious and authentic history of the develop- ment, construction, and organization of the great floating palaces which now conduct the service of the ferry across the Atlantic' — Times. ' Mr. Maginnis' handsome volume has had a well-deserved success,' _ * Tlie work is one of great merit.' — Engineering. Engineer ' No one who is interested in steam navigation should be without a copy,'- -Marine Engineer. Wkittaker's Technological and Scientific List. 1 5 By A. A. Blair, Chief Chemist U.S. Board appointed to Test Iron, Steel, and other Metals, &c. THE CHEMICAL ANALYSIS OF IRON. A com- plete account of all the best-known methods for the Analysis of Iron, Steel, Pig Iron, Iron Ore, Limestone, Slag, Clay, Sand, Coal, Coke, and Furnace and Producer Gases. Second Edition, revised. Half- leaiher, cloth sides, 16s, By James Dredge. A RECORD OF THE TRANSPORTATION EX- HIBITS AT THE WORLD'S COLUMBIAN EXPOSITION OF 1893. Imperial 4to. handsomely bound in Half Morocco. Weight, 18 lb. Price 3/. 3J. [Partly Reprinted from ''Engyae^snng. This Volume contains about 190 plates, and 800 pages of text and illustra- tions, forming, it is believed, a very complete record of the most important objects collected in the Transportation Exhibits Building at the World's Columbian Exposition of 1893. THE NEW CUNARDERS, 'CAMPANIA' AND ' LUCANIA,' and the WORLD'S COLUMBIAN EXPOSITION of 1893. Royal 4to. 134 Pages, gilt lettered. Price 6s. Weight 3 lb. 6 oz. Illustrated by Nine two-paged and Four single-page Plates, and nearly 300 Figures in the Text. Printed throughout on special- plate paper. [Reprinted from ' Engineering.' By James Dredge, Dr. M. F. O'Reilly, and H. Vivarez. ELECTRIC ILLUMINATION. Vol. II. Edited by James Dredge. Demy 4to. cloth. Price 30^-. With 900 Pages and about 1500 Figures. Weight 74 lb. 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A popular guide by a well-known writer, giving in clear and easily under- stood language the information necessary to those about to introduce the electric light into their dwellings. ' Accurate, Incld, ana suitable for the vvLrvoBe.'—Blecirtciatt, ' The chapter on accumulators is perhaps one of the best in the book.' Electrical Review. * A shilling spent on this book will be well repaid.* — Engineer's Gazette. ' Will be found very useful to those desiring elementary knowledge on the subject.* Iron. By A. D. SOUTHAM. ELECTRICAL ENGINEERING AS A PROFES- SION, AND HOW TO ENTER IT. Second Edition. Illustrated. Crown 8vo. /^. dd. ' It gives much valuable information.' — Engineering. ' Mr. Southam, in this excellent little work, gives, many valuable hints.' — Iron. * The author of this book has done a useful service to parents and guardians by supplying them with a guide to the various means of entering the profession of engineering.' — English Mechanic. ' This is really the only book we have seen that attempts to deal with the question in a practical manner.' — Lightning. By A. R. Bennett, M.I.E.E. THE TELEPHONING OF GREAT CITIES AND THE ELECTRICAL PARCEL EXCHANGE SYSTEM. Two Papers read before the British Association. Demy 8vo. Sewed, u. By Dr. Frederick Bedell and Dr. Albert C. Crehore, of Cornell University. ALTERNATING CURRENTS. An Analytical and Graphical Treatment for Students and Engineers. 325 pages. With 112 Illustrations. Second Edition. Medium 8 vo. cloth, loj. BaT. By Frank B. Cox, B.S. CONTINUOUS-CURRENT DYNAMOS and MO- "TORS : Their Theory, Design and Testing. With Sections on Indicator Diagrams, Properties of Saturated Steam, Belting Calculations, &c. An ^. ..-._-.^---^---_r__o...j._ .„ /^i„.i,. -^ipp. 83 Illustrations. Ts.dd. 1 8 Whittake/s Technological and Scientific List. By O. T. Crosby and Dr. Louis Bell. THE ELECTRIC RAILWAY IN THEORY AND PRACTICE. 400 Octavo Pages, 179 Illustrations. Second Edition, Revised, los. 6d. This is the first Systematic Treatise that has been published on the Electric Railway, and it is intended to cover the General Principles OF Design, Construction and Operation. Contents : — General Electrical Theory — Prime Movers — Motors and Car Equipment — The Line — Track, Car Houses, Snow Machines — The Station — The Efficiency of Electric Traction — Storage Battery Traction— Miscellaneous Methods of Electric Traction — High Speed Service — Com- mercial Considerations — Historical Notes. Appendices : — Electric Railway vs. Telephone Decisions — Instructions to Linemen — ^Engineer's Log Book — Classification of Expenditures of Electric Street Railways — Concerning Lightning Protection, by Prof. Elihu Thomson. By O. Gregory, late Professor of Mathematics in the R.M.A., &c. HUTTON'S MATHEMATICAL TABLES, con- taining the Common, Hyperbolic, and Logistic LOGARITHMS ; also Sines, Tangents, Secants, and Versed Sines, both Natural and Logarithmic. Together with several other Tables useful in Mathematical Calcula- tions ; also the Complete Design and Use of the Tables. With Seven additional Tables of Trigonometrical Formula. Nevir Edition, Med. 8vo. cloth, 12s. By Lieut. C. D. Parkhurst, Assoc. Mem. Am. Inst. E.E. DYNAMO AND MOTOR BUILDING FOR AMA- TEURS. With Working Dravfings. With 22 Illustrations, ^r. 6d. By Wm. Maver, Jun., and Minor M. Davis. THE QUADRUPLEX. With Chapters on the Dynamo- Electric Machine in Relation to the Quadruplex, the Practical Working of the Quadruplex, Telegraph Repeaters and the Wheatstone Automatic Telegraph by W. Maver, jun. Large 8vo. cloth. With 63 Illustrations. 6s. 6d. By H. A. Foster, Mem. Am. Inst. E.E. CENTRAL STATION BOOK - KEEPING AND SUGGESTED FORMS. With an Appendix for Street Railways and numerous Diagrams. los. 6d. By Gisbert Kapp. ALTERNATING CURRENTS of ELECTRICITY, their Generation, Measurement, Distribution, and Application. With 37 Illustrations and 2 Plates. +5. 6d. By Philip Atkinson, A.M., Ph.D. ELEMENTS OF STATIC ELECTRICITY. With full description of the Holtz and Topler Machines, and their Mode of Operating. Second Edition, Rev},sed. With 64 Illustrations, bs. bd. Wkittaker's Technological and Scientific List. 19 By Carl Hering. ELECTRIC RAILWAYS, RECENT PROGRESS IN. About 400 pages, and I20 Illustrations. Price 5^. Thomson- Houston, W. P. Railway Motor. [Specimen of f Llustrations. ) By Nikola Tesla. EXPERIMENTS WITH ALTERNATE CUR- RENTS OF HIGH POTENTIAL AND HIGH FREQUENCY. With a Portrait and 35 Illustrations, and Biographical Sketch of theAuthor. ^Ad. By E. J. Houston, Ph.D. ELECTRICITY ONE HUNDRED YEARS AGO AND TO-UAY. With Notes, &c. v- ("i- By E. J. Houston, A.M., Professor of Natural Philosophy in the Central High School, Philadelphia ; Professor of Physics in the Franklin Institute of Philadelphia ; Electrician of the International Electrical Exhibition. DICTIONARY OF ELECTRICAL WORDS, TERMS, AND PHRASES. Third Edition. With an Appendix. 667 Pages, 582 Illustrations. Price 2\s. * Fills a very large gap that previously existed in electrical literature.' A. E. Kennellv (Edison Laboratory). ' The name of the author is a sufficient guarantee of the excellence of the work.' Electrical Review, ' A book of this kind is absolutely necessary to the general reader who wishes to understand any modern article on applied electricity.'— JV«a/ Vi/ri Herald. By T. D. Lockwood, Electrician, American Bell Telephone Company. PRACTICAL INFORMATION FOR TELE- 20 Whittaker's Technological and Sc entific List. By E. A. Merrill. Complete Rules for the Safe Installation of Electrical Plant. ELECTRIC LIGHTING SPECIFICATIONS. For the use of Engineers and Architects. With the Phoenix Fire Rules. Price ds. The author has drawn up a set of specifications covering the various classes of lighting installations, which may serve as forms for any special type or character of plant, and which are at the same time full enough to cover the ordinary installation of electrical apparatus and electric light wiring. The book will prove especially useful to architects and engineers. By R. W. Webkes, Whit.Sch., A.M.I.C.E. ALTERNATE CURRENT TRANSFORMER DESIGN. 2j. By N. Scott Russell, M.Inst.C.E. TOWN COUNCILLORS' HANDBOOK TO ELEC- TRIC LIGHTING. Illustrated: Price \s. ' Seems to have accomplished the object in view.' — Nature. * Has done yeoman service in preparing this little book.' — Electrical Engineer. ' A useful shilling handbook that every town councillor should read.' Buildins News. Part I. — By Martin Hamilton Kilgour. Part II. — By H. Swan and C. H. W. Biggs. ELECTRICAL DISTRIBUTION : ITS THEORY AND PRACTICE. Illustrated, los.td. * Mr. Kilgour's treatment of his subjects will commend iiself to all who are interested in them.' — Engineer. * An excellent compendium on the subject.* — Electrical Engineer. ' Of high interest and usefulness.' — Nature. By Dr. G. Gore, F.R.S. THEORY AND PRACTICE OF ELECTRO-DEPO- SITION, including every known mode of depositing metals, preparing metals for immersion, taking moulds and rendering them conducting. Illustrated. Crown 8vo. I.r. 6d. By J. T. Niblett. PORTATIVE ELECTRICITY. Illustrated. 2s. 6d. By various Authors, including Gisbbrt Kapp, M.Inst.C.E., A. Reckenzaun, M.I.E.E., C. Capito, M.I.E.E., and Hamilton Kilgour. PRACTICAL ELECTRICAL ENGINEERING. Being a complete treatise on the Construction and Management of Electrical Apparatus as used in Electric Lighting and the Electric Trans- mission of Power. With many Hundreds of Illustrations. 2 Vols. Imperial 4to. 2/. 2s. net. By H. J. Skelton. ECONOMICS OF IRON AND STEEL. Illustrated. Crown 8vo. Price 5s, Whittaker's Technological and Scientific List. 21 By Arthur F. Guy, A.M.Inst.C.E. ELECTRIC LIGHT AND POWER. Giving the Re- suits of Practical Experience in Central Station Work. Illus. Cr. 8vo. 5 j, ' There are many similar works in the market, but we do not know of one better suited to give the manipulator of electric dynamos an intelligent knowledge of the forces with which he has to deal.' — Nature. By Alex. Black, C.E. FIRST PRINCIPLES OF BUILDING. Illustrated. Crown 8vo. 3^. (>d. By John Imray and C. H. W. Biggs. FIRST PRINCIPLES OF MECHANICAL EN- GINEERING. Illustrated. Crown 8vo. 3^-. dd. * The book will be found useful to learners.' — Engineer. By C. H. W. Biggs. FIRST PRINCIPLES OF ELECTRICAL EN- GINEERING. Illustrated. Second Edition. Crown 8vo. 2J. 6rf. * The first principles of the dynamo are clearly and accurately given.' — Nature. ' We commend the book to the perusal of students.' — Electricity. By Capt. Ironside Bax, General Manager of the Westminster Electric Supply Co. POPULAR ELECTRIC LIGHTING. Illustrated. Crown 8vo. 2j. By A. Reckenzaun. ELECTRIC TRACTION, MORE ESPECIALLY AS APPLIED TO TRAMWAYS. Illustrated. \os. (,d. *His book is certainly interesting and 'ras.x.tviz'a.w^* —Electrical Remew. ' The most useful to English readers." — Engineer. ' Invaluable to electrical engineers commencing traction work.' Electrical Engineer. By M. Reynolds. FIRST PRINCIPLES OF THE LOCOMOTIVE. 45 Illustrations. Crown 8vo. 2.s. 6d. ' Those who would like to know all about the locomotive will find it in this Utile book.' — Essex Herald. By GiSBERT Kapp, M.Inst.C.E., M.I.E.E. DYNAMOS, ALTERNATORS, AND TRANS- FORMERS. Crown 8vo. loj-. (>d. ' Invaluable to the advanced student and dynamo designer.' — Electrician. ' We can heartily recommend it.' — Electrical Engineer. ' A valuable contribution to electrical VAexa.ta.re.' —Electrical World. _ ' The reader will find valuable information concerning dynamo design. —Nature. By J. A. EwiNG, M.A., B.Sc, Professor of Mechanism and Applied Mechanics in the University of Cambridge. MAGNETIC INDUCTION in IRON and OTHER MTCTAT-S. •!'7n natres. T CO Illustrations. Second issue. \QS. dd. 22 Whittaker's Technological and Scientific List. By Dr. Gboegk Gore, LL.D., F.R.S. THE ART OF ELECTROLYTIC SEPARATION OF METALS (Theoretical and Practical). Fully Illustrated. \os. 6d. No other book entirely devoted to the Electrolytic Separation and Refining of Metals exists in any language ; those on Electro-Metallurgy hitherto pub- lished being more or less solely devoted to electro-plating. The present book contains both the science and the art of the subject, i.e., both the theoretical principles upon which the art is based, and the practical rules and details of technical application on a commercial scale, being thus suitable for both student and manufacturer. By Charles Jones, M.Inst.C.E. REFUSE DESTRUCTORS : WITH RESULTS UP TO THE PRESENT TIME. A Handbook for Municipal Officers, Town Councillors, and others. With numerous Diagrams. Cr 8vo. 5'- By H. P. BouLNOls, M.Inst.C.E., Past-President of Municipal and County Engineers ; City Engineer, Liverpool. CONSTRUCTION OF CARRIAGEWAYS AND FOOTWAYS. S^- By E. B. Savage, A. M.Inst.C.E. SEWERAGE AND SEWAGE: Disposal of a Small Town. Illustrated. 5^. By E. Parnell Hooley, A.M.Inst.C.E., County Surveyor of Nottingham. MANAGEMENT OF HIGHWAYS, i^. By R. Godfrey, A.M.Inst.C.E., Surveyor to the Rural Sanitary Authority, King's Norton. "WATER SUPPLY IN RURAL DISTRICTS. \Nearly Ready. By E. P. SiLCOCK, A.M.Inst.C.E., Borough Surveyor, King's Lynn. HIGHWAY BRIDGES. \Nearly Ready. By C. Mason, M.Inst.C.E., Surveyor, St. Martin's-in-the-Fields, London, W.C. STREET and TOWN SANITATION. {Nearly Ready. By Professor J. A. Fleming, M.A., D.Sc, F.R.S., M.R.L, Professor of Electrical Engineering in University College, London. ELECTRIC LAMPS and ELECTRIC LIGHTING. Being a Course of Four Lectures delivered at the Royal Institution, April — May, 1894. Fully Illustrated. 8vo. cloth, 7^. dd. By A. E. Kennelly and H. D. Wilkinson, M.I.E.E. PRACTICAL NOTES FOR ELECTRICAL STUDENTS. LAWS, UNITS, AND SIMPLE MEASURING INSTRUMENTS. 320 pages, 155 Illustrations, ds. 6d. Wktttaker's Technological and Scientific List. 23 By Magnus Maclean. ELECTRICAL UNITS. 2s. dd. By J. A. Fleming, M.A., D.Sc, F.R.S., M.R.I., &c., Professor of Electrical Engineering in University College, London. THE ALTERNATE CURRENT TRANSFORMER IN THEORY AND PRACTICE. In two vols, demy 8vo. Vol. I.— THE INDUCTION OF ELECTRIC CURRENTS. Seepages, 157 Illustrations, third issue. 7j. td. COMTENTS : — Introductory — Electro-Magnetic Induction — The Theory of Simple Periodic Currents — Mutual and Self Induction — Dynamical Theory of Current Induction. Vol. II.— THE APPLICATIONS OF INDUCED CURRENTS. 600 pages, 300 Illustrations. \2s. 6d. Contents : — Chapter I. The Historical Development of the Induction Coil and Transformer — Chapter II. Distribution of Electrical Energy by Transformers — Chapter III. Alternate-Current Electric Stations — Chapter IV. The Construction and Action of Transformers — Chapter V. Further Practical Applications of Transformers. By F. Martin Weymohth. DRUM ARMATURES AND COMMUTATORS (Theory and Practice). A complete treatise on the the theory and con- struction of Drum Winding, and of Commutators for Closed Coil Arma- tures, together with a fiiU resumi of some of the principal points in their design ; and an exposition of Armature Re-actions and Sparking. With 162 Illustrations. Demy 8vo. 7^. 6d. Edited by W. W. Beaumont, M.I.C.E., M.I.M.E., &c. THE STEAM-ENGINE INDICATOR AND INDI- CATOR DIAGRAMS. 3^. 6d. A Practical Treatise on the Steam Engine Indicator and Indicator Dia- grams, with Notes on Steam Engine Performances, Expansion of Steam, Behaviour of Steam in Steam Engine Cylinders, and on Gas Engine Diagrams. By Dr. George Gorb, LL.D., F.R.S. ELECTRO-CHEMISTRY. Second Edition. 2S. By Oliver Heavyside. ELECTRO-MAGNETIC THEORY. Containing Intro- duction — Outline of the Electro-magnetic Connexions — The Elements of Vectorial Algebra and Analysis — Theory of Plane Electro-magnetic Waves, &c. Vol. I. izs. 6d. Arranged by J. A. Fleming, M.A., D.Sc, F.R.S. ELECTRICAL LABORATORY NOTES AND FORMS : Elementary and Advanced. Fcap. folio, cloth, 12s. 6d. net. By Professor Oliver Lodge, F.R.S. THE WORK OF HERTZ AND SOME OF HIS SUCCESSORS. With Appendices, 31 Illustrations, and Portrait, Crown 8vo, zs. 6d. 24 Wkittaker's Technological and Scientific List. By W. Geipel and H. Kilgour. ELECTRICAL ENGINEERING FORMULiE, &c. This Pocket-Book is a departure from previous attempts to provide for Electrical Engineers and Electricians varied information for every-day use. The book will be invaluable to Electrical Engineers, a very large space being devoted to heavy engineering details, formulse, &c. 7j. 65. By H. D. Wilkinson, M.I.E.E., &c., &c. SUBMARINE CABLE-LAYING and REPAIRING. An Original Work on this important subject, which has not previously been treated in a thoroughly practical manner. Fully Illustrated. [Shortly. By W. S. BOULT. THE INTERNATIONAL COMPREHENSIVE WIRE TABLE. Cloth, t,s. In Two Vols, stout paper covers, 2s. ; strong cloth, 2s. 6d. each volume ; Single Primers, 3d. PRIMERS OF ELECTRICITY. Fully Illustrated. A Series of Helpful Primers on Electrical Subjects for the use of Colleges, Schools, and other Educational and Training Institutions, and for young men desirous of entering the Electrical professions. Table of Contents: — Volume I. — Theory. — Primer No.: i. The Effects of an Electric Current — 2. Conductors and Insulators — 3. Ohm's Law — 4. Primary Batteries — 5. Arrangements of Batteries — 6. Electrolysis — 7. Secondary Batteries — 8. Lines of Force — 9. Magnets — to. Electrical Units — II. The Galvanometer — 12. Electrical Measuring Instrurnents — 13. The Wheatstone Bridge — 14. The Electrometer — 15. The Induction Coil — 16. Alternating Currents — 17. The Leyden Jar — 18. Influence Machines — 19. Lightning Protectors — 20. Thermopiles. Volume II. — Practice. — Primer No. : 21. The Electric Telegraph — 22. Automatic and Duplex Telegraphy — 23. The Laying and Repair of Submarine Cables — 24. Testing Submarine Cables — 25. The Telephone — 26. Dynamos — 27. Motors — 28. Transformers — 29. The Arc Lamp — 30. The Incandescent Lamp — 31. Underground Mains — 32. Electric Meters — 33. Electric Light Safety Devices — 34. Systems of Electric Distribution — 35, Electric Transmission of Energy— 36. Electric Traction — 37. Eleclpo Depo- sition — 38. Electric Welding. By Albion T. Snell, A.M.Inst.C.E., M.Inst.E.E. ELECTRIC MOTIVE POWER. The Transmission and Distribution of Electric Power by Continuous and Alternate Currents, with a Section on the Application of Electricity to Mining Work. 8vo. cloth, 10s. 6d. Edited by W. H. Fowler, Wh.Sc, M.Inst.M.E., Assoc. M.Inst. C.E. THE 'PRACTICAL ENGINEER' POCKET BOOK AND DIARY FOR 1896. Price, bound in leather, is. ; roan, gilt edges, with pocket and elastic band, is. 6d. The above work is subject each year to a THOROUGH REVISION, and the information brought down to the latest date. ' The rules and data are judiciously selected with a view to practical requirements.* Engineer. Whittaker's Technological and Scientific List. 25 By Gilbert S. Ram. THE INCANDESCENT LAMP AND ITS MANU- FACTURE. is. 6d. By Chas. H. Innes, M.A., Lecturer on Engineering at the Rutherford College, Newcastle-on-Tyne. PROBLEMS IN MACHINE DESIGN. For the Use of Students, Draughtsmen, and others. Crown 8vo. cloth, 3^. 6d. ' There are many to whom this hook will be of service, and it should well fulfil the object the author had in view in writing it.' — Engineer and Iron Trades Review, By Charles Day, Wh.Sc. THE INDICATOR AND ITS DIAGRAMS; with Chapters on Engine and Boiler Testing. Including a new Table of Piston Constants, compiled by W. H. Fowler, Wh.Sc, M.InstM.E., Assoc.M.Inst.C.E. Crown 8vo. cloth, y.dd. This book is of a thoroughly practical character, and will be found of special value to enginemen and inspectors. It contains numerous diagrams from actual practice. By W. W. F. 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'The book will be found of special value to the engineering students preparing for the honours stages of the Science andArt and Technological Examinations in machine construction and mechanical engineering.' — Steamship. By Alfred H. Gibbings, A.I.E.E., Electrical Engineer to the Corporation of Bradford. DYNAMO ATTENDANTS and their DYNAMOS. A Practical Book for Practical Men. Second Edition, Revised. Crown 8vo. cloth. Illustrated. \s. ' Should be useful to those attending to dynamos, both m private installations and 'mcea:aa!i!.\3.iwas,:— Electrical Engineer. ' A handy little book, containing many useful hints and suggestions. _ jir-y/^ 26 Whittaker's Technological and Scientific List. By Edward C. R. Marks, Assoc.M.Inst.C.E., M.I.M.E. MECHANICAL ENGINEERING MATERIALS. Crown 8vo. \s. 6d. By G. Croydon Marks, A.M.I.C.E., M.I.M.E., Lecturer on Engineering at the Midland Institute, Birmingham. HYDRAULIC MACHINERY EMPLOYED IN THE CONCENTRATION AND TRANSMISSION OF POWER. Crown 8vo. cloth, lettered, y. 'The subject is treated in an eminently practical manner, and tlie various forms of hydraulic appliances are illustrated and explained. — The Steamship. By Jas. Bell, A.I.E.E., Certificated Teacher City and Guilds of London Institute. TELEGRAPHIST'S GUIDE TO THE NEW EX- AMINATIONS IN TECHNICAL TELEGRAPHY. With between seventy and eighty Diagrams, including a full-page Plan of the Test Box (with twenty practical examples), Duplex (Differential and Bridge Methods), Quadruplex, Multiplex, Connections of Single-needle, Single- current (with and without Relay), Double-current Morse (Simplex and Duplex), Wheatstone Automatic, Repeaters, Tangent Galvanometer (both forms). Battery Testing Instruments, Universal Battery System, Wheat- stone Bridge, New System of Morning Testing (six Diagrams), and other Diagrams. Second Edition, Revised. Crown 8vo. cloth. Illustrated. Price I J. dd. 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By M Powis bale, A.M.I.C.E., Author of 'A Handbook for Steam Users.' MODERN SHAFTING AND GEARING AND THE ECONOMICAL TRANSMISSION OF POWER. 112 pp. Illustrated. Price 2s. 6d. ' A useful little work, inasmuch as it touches on data regarding things which are too new lu be found in the standard works on engineering. It contains only about 100 pages — and as far as it goes is excellent.' — Electrical Review. 'A very useful guide to users of shafting, gearing, pulleys, belts, and other annlianr.es for transmittinff newer.' — /ran and Steel Trades /ournal. 28 Whittaker's Technological and Scientific List. Edited by J. LUKIN, B.A. SCREWS and SCREW-MAKING. With a Chapter on Milling. Crown 8vo. y. By J. LuKiN, B.A. TURNING LATHES. A Guide to Turning, Screw Cutting, Metal Spinning, &c. Third Edition, 3^. ' This is by far the best treatise ever published.'— £»jfi«e«»-. Translated from the French of the Count des Cars by C. S. Sargent, Professor of Arboriculture in Harvard College, U.S.A. TREE PRUNING: a Treatise on Pruning Forest and Ornamental Trees. 64 pp. 54 Illustrations. Price 2s. 6d. * " Tree Pruning" is translated from a French treatise which is generally accepted as a standard work on the Continent. It has the further recommendation of being translated by an arborist who is himself a recognised authority ; and under these circumstances it cannot fail to be useful to all who are interested in the care and growth of woods and plantations.'— Glasgow Herald. ' A very useful handbook, freely illustrated, translated from the work of one of the highest French authorities.' — A^ricuitural Gazette. By A. D. Webster, Wood Manager to the Duke of Bedford on the Woburn and other Estates. PRACTICAL FORESTRY. 120 pp. Price 3.y. 6d. * Mr. Webster has done a good service by the publication of his excellent manual, "Practical Forestry." Such manuals as these tend more to disseminate correct information on the subjects of which they treat than the more bulky and elaborate volumes to which we have of late been accustomed. The author has condensed into a compact form the essence of all that need be said on the subject of which he treats.' Journal of Hortculture, *This, one of those little handbooks now so popular among the different trades and crafis, is, I believe, the first of its kind on forestry, and will be welcomed by many foresters and woodmen who object to pay a stiff price for, or to be encumbered with a huge "tome," blown out to Family Bible dimensions for reasons known only to authors. "Practical Forestry" is condensed and practical, is written by a forester who knows what he is talking about, and who is fairly abreast of the times on his subject.' The Garden. By W. Stevenson. TREES OF COMMERCE. A Practical Manual, giving within reasonable limits, and in a popular form, an account of the trees that yield the staple of the British timber trade. 226 pp. Price * Gives within reasonable limits and in a popular style an account of the trees that yield the staple of that important branch of British commerce, the trade in home-grown and imported timber.' — Contract Journal. ' Gives a simply written, comprehensive, and instructive account of its subject, and will prove useful to young foresters and to men preparing themselves for the timber trade.' — Scotsman. Wkittaker's Technological and Scientific List. 29 HOLTZAPFFEL'S TURNING and MECHANICAL MANIPULATION. Volume I. — Materials, their Differences, Choice, and Prepar- ation ; Various Modes of Working them, Generally Without Cutting Tools. Introduction. Materials from the Vegetable, the Animal, and the Mineral Kingdoms — Their uses in the Mechanical Arts depend on their structural differences, and physical characters. The modes of severally preparing, working, and joining the materials, with the practical description of a variety of Processes, which do not, generally, require the use of Tools with cutting edges. 300 Woodcuts, price 15^. net. Volume II. — The Principles of Construction, Action, and Appli- cation, of Cutting Tools used by Hand ; and also op Machines Derived from the Hand Tools. The principles and descriptions of Cutting Tools generally— namely. Chisels and Planes, Turning Tools, Boring Tools, Screw-cutting Toojs, Saws, Files, Shears, and Punches. The hand tools and their modes of use are first descrihed ; and subsequently various machines in which the hand processes are more or less closely followed. 700 Woodcuts, j)rice 20s. net. Volume III. — ^Abrasive and Miscellaneous Processes, which can- not BE Accomplished with Cutting Tools. Grinding and polishing, viewed as extremes of the same process, and as applied both to the produc- tion of form, and the embellishment of surface, in numerous cases to which, from the nature of the miterials operated upon, and other causes. Cutting Tools are altogether inapplicable. Varnishing, lackering wood, and metal, bronzing and miscellanasa. 430 Woodcuts, price zar. net Volume IV. — The Principles and Practice of Hand or Simple Turning. Description of various Lathes ; — applications of numerous Chucks, or apparatus for fixing work in the Lathe. Elementary instructir >ns in turning the soft and hard woods, ivory and metal*, and also in Screw-cutting. With numerous Practical Examples, some plain and simple, o'hers difficult and complex, to show how much may be done with hand tools alone. With numerous Practical Examples. 750 Woodcuts, price 22J. net. Volume V. —The Principles and Practice of Ornamental or Complex Turning. Sliding Rest with Fixed Tools— Revolving Cutters, used in the Shding Rest with the Division Plate and Overhead Motion. Various kinds of Eccentric, Oval, Spherical, Right-line, and other Chucks. Spiral and Reciprocated turning. The Spherical Rest, &c. With numerous Practical Examples. 590 Woodcuts, Autotype and other Plates, price 30J. net. The above work is recommended to Students preparing for Examination in Mechanical subjects. Every volume is a complete treatise, and may be had separately. By T. Eustace Smith, Barrister-at-law. HO^V TO PATENT AN INVENTION AVithout the Intervention of an Agent. Third Edition, revised and enlarged. 2j. 6d. net. ' This is an excellent little 'book..'— Builder, FODEN'S MECHANICAL TABLES. 5th Edition. 3© Whittaker's Techwlogical and Scientific List. By Philip Crellin, Chartered Accountant. BOOKKEEPING. For Commercial, Civil Service, and Evening Classes. With numerous Examples and Questions, and a Glossary of Terms appended. Crown 8vo. cloth, \s. 6d. A Key, zs. net. 'An excellent little work.' — Morning Post. ' This is undoubtedly a good book. A valuable feature is the glossary of com- mercial terms.' — Schoolmaster. PONCE DE LEON. SPANISH TECHNOLOGI- CAL DICTIONARY. Containing Terms employed in the Applied Sciences, Industrial Arts, Mechanics, Fine Arts, Metallurgy, Machinery, Commerce, Shipbuilding and Navigation, Civil and Military Engineer- ing, Agriculture, Railvifay Construction, Electro-technics, &c. Svo. Vol. I. — English-Spanish, i/. i6j. Vol. II. — Spanish-English. \l. \2s. WERSHOVEN (F. J,), TECHNOLOGICAL DIC- TIONARY OF THE PHYSICAL, MECHANICAL, and CHEMICAL SCIENCES. English, German, and Ger.-Eng. 2 vols, cloth, is. (sd. each. By R. Nelson Boyd, M.Inst. C.E., &c. PETROLEUM : Its Development and Uses. Crown 8vo. cloth, 2s. ' A most interesting little book.' — Globe. ' Should be of much interest to all engaged in the petroleum and lamp trade.' British Trade Journac. 'A readable and intelligible account of valuable natural product.' — Scotsman. * This useful little book.' — Industries. ' A valuable little book.' — Reynolds. * If this little volume had a wide circulation, petroleum accidents would be few and far between.' — Daily Chronicle. * A very interesting little handbook.'— £/tfc/?-zVa/ Review. 'We have here a_ most useful manual of the origin, composition, properties, and and uses of mineral oils.' — Ch^tnical News. * We can recommend this little book.' — Electrician. By Charles Scholl. PHRASEOLOGICAL DICTIONARY OF COM- MERCIAL CORRESPONDENCE IN THE ENGLISH, GERMAN, FRENCH, AND SPANISH LANGUAGES. With an Appendix, containing Lists of Commercial Abbreviations, Geographical Names, the Principal Articles of Commerce, &c. Second Sdition. In One Volume, Bound in Half Morocco, l/. is. English-French, English-German, English-Spanish, Bound separately in cloth. Price, 8^. each. * The book is likely to prove of service to others than business men, ths phraseology is so variedand full.' — The Times. ' There is a true business ring in the idiomatic phrases, whicli constitute so important a feature of the work. It will be a boon to correspondence clerks of all nationalities and in all parts of the world.' — The Daily Chronicle. ' The Dictionary promises to be of much practical utility to those who are engaged n mercantile affairs. — Daily Neivs. Whittaker's Technological and Scientific List. 31 A Work for Artificers in Gold, Silver, and other Metals, Leather, Wood, &c. An entkely New Edition. FAIRBAIRN'S BOOK OF CRESTS OF THE FAMILIES OF GREAT BRITAIN AND IRELAND. Edited by Arthur Charles Fox-Davies. 2 vols, large 4to. Half morocco, 4/. 4J. Artificers' Edition, specially bound in pigskin, 3/. 13^. (>d. net. Buckram Edition, 3/. is. net. Full prospectus post free on application. ' As heraldry is really a most interesting and valuable handmaid to history and to a variety of archasological pursuits, we welcome this book in its revised form.' Athenaum Library Edition, 5/. 5^-. net. ARMORIAL FAMILIES. Compiled and Edited by Arthur Charles Fox-Davies. With Engraved Plates of Armorial Bearings amounting to 600. Full prospectus and subscription forms on application. 3/. 3J. net. Strongly Half-bound, 3/. los. THE BOOK OF PUBLIC ARMS ; A Cyclopsedia of the Armorial Bearings, Heraldic Devices, and Seals, as Authorised and as Used, of the Counties, Cities, Towns, and Universities of the United Kingdom. Derived from the Official Records. Edited by A. C. Fox- Davies, Editor of ' Fairbairn's Book of Crests,' &c., and M. E. B. Crookes. Edited, with Notes and Historical Introduction, by S. Baring Gould, M.A. ENGLISH MINSTRELSIE : a National Monument of English Song. With Airs in both Notations. Eight volumes, loj. each. Sold in Sets only (Vols. I. and II. now ready). Edited and Arranged by John Greig, Mus.Doc. SCOTS MINSTRELSIE : a National Monument of Scottish Song. With Airs in both Notations. Six Volumes. Cloth gilt, red edges, 5IJ. Edited by Joseph Parry, Mus.Doc. CAMBRIAN MINSTRELSIE : a National Monu- ment of Welsh Songs. With Airs in both Notations. Cloth gilt, red edges, 5 1 J. Edited by John Greig, Mus.Doc. THE MUSICAL EDUCATOR: A Library of Musical Instruction by Eminent Specialists. In Five Volumes. Cloth, yjs. dd. (Vols. I. and II. are now ready.) 32 Whittaker's Technological and Scientific List. Stubents* tTeyt ^oo\^^. By J. T. Hewitt, M.A , D.Sc, Ph.D., F.C.S , Profesor of Chemistry, and F. G. Pope, Assistant Lecturer and Demonstrator in the People's Palace Technical Schools. ELEMENTARY PRACTICAL CHEMISTRY, In organic and Organic. Limp cloth, <)d. net. * This little book will certainly rank amonsst the best in the market.' — Teacher^ Aids ' Excellently arranged.' — Board Teacher. ' The arrangement is clear, and the typical analyses are an excellent feature of the work.' — Educational Times. ' Will certainly become popular in practical chemistry circles. — Practical Teacher. By Matthew Wyatt, F.R G.S., F.I.L, Author of ' A Treatise on Linear Perspective,' &c. DIFFERENTIAL and INTEGRAL CALCULUS: An Introduction to the. For the use of Students reading without the aid of a Tutor. Crown 8vo. %s. 6d. El^t' Mr. Wyatt explains the fundamental principles in such a simple manner, any one with a little trouble could, in a short time, learn sufficient from his'book for most practical purposes.' — Bttilder. * That at first the Calculus does present to the mind of the ordinary student great difficulties will, we think, be generally admitted, and the way in which Mr. Wyatt smoothes these over is indeed a work of art.' — Railway Engineer. By Sidney H. Wells, Wh.Sc, Assoc. M.Inst.C.E., Assoc.M.Inst.M.E., Principal of the Battersea Polytechnic Institute. MECHANICAL LABORATORY WORK, Notes and Experiments in. 8vo. lo^. net. By Henry Adams, M.Inst.C.E., M.Tnst.M E., F.S.E., Professor of Engineering at the City of London College. PRACTICAL TRIGONOMETRY. For the Use of En- gineers, Architects, and Surveyors. 2s. dd. net. Contents : — Angular Measurements — Principles of Trigonometry — Construction and Use of Logarithms— Trigonometrical Formulae — Practical Examples. By Henry Adams, M.Inst.C.E., M.Inst.M.E., Professor of Engineering at the City of London College. JOINTS IN WOODWORK A Paper read before the >^i^ Civil and Mechanical Engineers' Society, containing information upon the Varieties, Properties, Market Sizes, &c., of Timber, the Principles of Designing Joints, the Form and Arrangement of Joints and Fastenings, Proportions of Bolts, Strength of Fastenings, &c Third Edition. Sixth Thousand. Demy 8vo. 44 pp. with Large Plate of 80 Joints, \s. ' This unpretentious little pamphlet is an excellent treatise on a subject rarely dealt with in so small a compass.' — Technical World. ' Replete with solid information in a compart form.'— Caiinet Maker's Guide. ' The ^ paper may be ri^ad with advantage by all students of wood or timber construction.' — Building News. Whittaker's Technological and Scientific List. 33 OF art0, Sciences, Q^anufactutes, anli 31nliustrie0. Illustrated. In Square Crown 8vo. Cloth. ' Messrs. Whittaker's valnable series of practical mannals.' Electrical Review, By W, Perren Maycock, M.I.E.E. FIRST BOOK OF ELECTRICITY AND MAG- NETISM. Second Edition, Revised and Enlarged, with 107 Illustra- tions. 2J-. 6d. 'Students who purchase a copy, and carefully study it, will obtain an excellent groundwork of the science.' — Electrical Review. ' As a first book for such students as have to pass examinations, it is admirable.' Electrical En^neer, * It is pre-eminently a practical book by a practical teacher.' — Educational News. ' This is a capital book to place in the hands of beginners in the study of electricity and magnetism. — Electricity. ' An admirable work.' — Board Teacher, Speeimen of Illustrations from Maycock's 'Electricity and Magnetism.' By J. HOPKINSON, D.Sc, F.R.S. DYNAMO MACHINERY, ORIGINAL PAPERS ON. With 98 Illustrations, S-f. 'Must prove of great value to the student and young ensaxa.'— Electrical Review. 'A most valuable work.' — English Mechanic, 34 Whittaker's Technological and Scientific List. Whittaleer's lAhrary of Arts, Sciences, &c. (Contimed). FITTING, THE PRINCIPLES OF. For Engineer Students. By the Author of ' The Principles of Pattern Making, ' Prac- tical Ironfounding,' and ' Metal Turning.' Illustrated with about 250 Engravings, and containing an Appendix of Useful Shop Notes and Memoranda. 5J. * A practical manual for practical people.' — English MecJianic. ' Calculated to aid and encourage the most useful set of liandicraflsmea we have amongst MS.'—Daily Chronicle, Sfecimen of Illustrations in ' Principles of Fitting. ' By G. E. BoNNEY. ELECTRICAL EXPERIMENTS. With 144 Illustra- tions. 2s. 6d. ' This Is an excellent book for boya.'— Electrical Review. Electrical Chimes. . Electric Mortar. Sfecimen of Illustrations in ' Electrical Experiments.' i Whittakef' s Technological and Scientific List. 35 Whittaker's Library of Arts, Sciences, Sc. (.Continued). With numerous By H. Orford. LENS WORK FOR AMATEURS. Illustrations. Small crown 8vo. 3^. * The book is a trustworthy guide to the manufacturer of lenses, suitable alike for the amateur and the young workman.' — Nature. * The author is both a sound practical optician and is able to convey his knowledge to others in a clear manner.* — British Journal of Photography By J. Traill Taylor, Editor of ' The British Journal of Photography.' THE OPTICS OF PHOTOGRAPHY AND PHO- TOGRAPHIC LENSES. With 68 Illustrations. 3^. ^d. ' An excellent guide, of great practical use.* — Nature. * Personally we look upon this book as a most valuable labour-saving invention, for no questions are so frequent, or take so long to answer, as those about lenses.' Practical Photographer. ' Written so plainly and clearly that we do not think the merest tyro will have any difGculty in mastering its contents.' — Amateur Photographer. By Joseph Poole, A.I.E.E. (Wh. Sc. 1875), Chief Electrician to the New Telephone Company, Manchester. THE PRACTICAL TELEPHONE HAND-BOOK. With 228 Illustrations. Second Edition. Revised and considerably Enlarged. 55. The gratifying reception .accorded ihis book _now eijaHes,th.e, author Jo - tissue a new edition in a considerably enlarged form. New chapters on Metallic - Circuit Working and on Electrical Measurements have been added, the former in order to keep pace with the rapid advance which has been made in that direction during late years, and the latter in order to make the book more complete. From the Preface. ' This essentially practical book is published at an opportune moment.' — Electrician. * It contains readable accounts of all the best- known and mostf widely used instruments, together with a considerable amount of information not hitherto published in book form.' — Electrician. ' Will be found both useful and interesting to persons who use the. telephone, as Mr. Poole's ex- position of telephonic apparatus is both clear and comprehensive.' — Saturday Review. The Runnings Transmitter. (Specimen of Illustrations). PRACTICAL IRONFOUNDING. By a Foreman Pattern Maker. Illustrated with over 100 Engravings. Second Edition^ ^-r. ' Every pupil and apprentice would find it, we think, an assistance to obtaining a thorough knowledge of his work. The book, however, is riot intended merely ior the student, but contains much usefal information for practical meDj' ; Industries. 36 Whittaker's Technological and Scientific List. Whittaker's Library of Arts, Sciences, tSc. (.Continued), By W. Perren Maycock, M.I.E.E. ELECTRIC LIGHTING AND POWER BUTION. An Elementary Manual for Students preparing for the Preliminary and Ordinary Grade Examination of the City and Guilds of London Institute. Written in accordance with the new '■ Syllabus. With 280 Illustrations, I Vol. 6s. DISTRI- Induction of Currents [Specimen of Illustrations). _ * We can congratulate Mr. Maycock upon having produced a took which cannot fail to be useful to all who are genuine students of electricity and its methods.' Electrical Review t By D. Denning. THE ART AND CRAFT OF CABINET MAKING. A Practical Handbook to the Construction of Cabinet Furniture, the Use of Tools, Forma- tion of Joints, Hints on Designing and Setting Out Work, Veneering, &c. With 219 Illustra- tions. 5j. ' We heartily commend it.' — Cabinet Maker. ' Well planned, and writ- ten in a pleasing and simple style . ' — Nature. ' A carefully-considered and well-written book.' IVeri. By Edwin J. Houston, A.M., Professor of Natural Philosophy and Physical Geography in the Central High School of Philadelphia, Professor of Physics in the Franklin Institute of Pennsylvania, &c. ADVANCED PRIMERS OF ELECTRICITY. Vol I. -ELECTRICITY AND MAGNETISM. 3^. 6d. Vol II.— ELECTRICAL TRANSMISSION OF INTELLIGENCE. 5^. Voll III.— ELECTRICAL MEASUREMENTS. S^- Plain Dovetail. Ditto with badly-formed pins. [Specimens of Illustrations.) Whittaker' s Technological and Scientific List, 3 7 Whittaker'8 Library of Arts, Sciences, &c. (.Continued)^ THE PRINCIPLES OF PATTERN MAKING. Written specially for Apprentices, and for Students in Technical Schcxjls. By the Author of ' Principles of Fitting,' ' Practical Ironfounding,' ' Metal Turning,' &c. Illustrated with loi Engravings, and containing a Glossary of the Common Terms employed in Pattern Making and Moulding. 3^. 6d. ' The book is well illustrated and for its size will be found one of the best of its kind,' — Industries. * This is one of those works which have a more than ordinary value,' — Steamship, \-^^—\ Striking up a Loam Pattern. V^^ Specimen of Illustrations to ' Pattern Making.' By G. E, INDUCTION COILS. Amateur Coil - makers. With loi Illustrations. ' In Mr, Bonney's nsefal book every part of the coil is described minutely in detail, and the methods and materials re- quired in insulating and winding the wire are fully considered.' — Electrical Review. BONNEY. A Practical Manual ' for nder (Specimen of Illustrations). 38 Whittaker's Technological and Scientific List ^ WMttaker's lAbrary of Arts, Sciences, <&c, (Contimied). By F. C. Allsop, Author of ' The Telephones and their Construction.' PRACTICAL ELECTRIC-LIGHT FITTING. A Treatise on the Wiring and Fitting up of Buildings deriving current from Central Station Mains, and the Laying down of Private Installations, ^msss. including the latest edition of the Phoenix Fire Office ■,^^mk\ Rules. With 224 Illustrations. Second Edition, IvMMM Revised. 5^. i/>. :' ■' •' '' '•'- - Whittaker's Technological and Scientific List. 43 riDebical Mocks. By C. J. S. Thompson. THE CHEMIST'S COMPENDIUM AND DIARY. A Pocket-book of Reference for Pharmacists, Assistants, and Students. Roan limp, rounded corners. 228 pp. 2s. dd, net. Contents : — i. Synopsis of the British Pharmacopoeia, with Additions of 1890—2. Posological Table and Doses of B.P. — 3. Formulary of British Pharma- ceutical Conference — 4. , Spray Solutions of Throat Hospital Pharmacopoeia — 5. Lozenges of Throat Hospital Pharmacopoeia — 6. Hypodermic Injections — ■ ■ 7. Organic Materia Medica, Natural Orders, Habitats, and Active Principles —8. Modern Remedies, Characteristics, and Doses — 9. Table of Proportion of Active Ingredients in P. B. Preparations — 10. Formulae for Unofficial Tinctures — rr. Apothecaries' Weights and Measures — 12. Table of Comparison . between English and Metric Weights and Measures^is- Metric System— 14. Stains for Microscopic Objects — 15. Media for Mounting Sections — 16. Hints to Dispensing French and German Prescriptions — 17. Hints to Dispensing Homoeopathic Prescriptions — 18. Terms used in Oculists' Prescriptions— 19. Special Excipients for Pills — 20. Analytical Charts — 21. Colour Reactions of Alkaloids— 22.. Special Tests for Drugs and Chemicals— 23. Milk Analysis • - — 24-. Urinalysis — 25. Photographic Chimicals and Formulae for Solutions — 26. Poison Schedule — 27. Poisons and their Antidotes — 28. Weight of Twenty •,-^Drops. otVariouiS Fluids — 29. Table of Equivalents, Liquids and Solids — 30. Freezing JMixtures — 3r. Table of Grains Converted into Grammes — • 132. Dosage Table for Cattle, Horses, and Dogs — 33. Formulae for Artificial TTOit-Essences^.34.- Thermometers— 35. Table Showihg Centigrade Degrees and their Equivalents in Fahrenheit — 36. Saturation Table— 37. Gaubius' Table— 38. Specific Gravity— 39..- Table of Solubilities in Water and Alcohol ^o. Medicine Chests for Ships — Etc'. Etc. A New and Revised {Twelfth) Edition. Fast Sva. los.-6d. HOBLYN'S DICTIONARY OF TERMS USED IN MEDICINE AND THE COLLATERAL SCIENCES. Re- vised and Enlarged by J. A. P, Price, B.A., M.D. Dxon., Assistant- Surgeon to the Royal Berkshire Hospital ; late Physician to the Royal Hospital for Children and Women, 'This'well-tncwn work.'— Xa«M/. • . : ., 'As a handy reference volume for the physician, surgeon, and pharmacist, it will 'prove invaluable.'-^P^arntaceitizcat /oternal. ■ ^ .'-' _, 'From considerable experience df'Hoblyn's Dictionary, we are able to say that it .'.teis.ihe,rare merit «f:sapplying in almost every case what you have a nght to expect in consulting it,'— Gtasgmv Medical /otc^nal: 44 Whittaker's Technological and Scientific List. Whittalter's Medical Works (Contimud). A NEW WORK FOR MEDICAL STUDENTS AND PRACTITIONERS. By C. Gordon Brodie, F.R.C.S., late Senior Demonstrator of Anatomy, Middlesex Hospital Medical School ; Assistant Surgeon, North -West London Hospital. DISSECTIONS ILLUSTRATED: A Graphic Hand- book for Students of Human Anatomy. With 73 Coloured Plates Drawn and Lithographed by Percy Highley. In i Vol. imperial 8vo. strongly bound in half buckram, flexible back, plates mounted on tape, 2/. 2s. In Four Parts : — Part I THE UPPER LIMB. Ss. 6d. „ II.— THE LOWER LIMB. los. „ III.— HEAD, NECK, AND THORAX. los. „ IV.— ABDOMEN. With 16 Coloured Plates and 13 Diagrams. lOJ. ' A book which will certainly make its influence felt in the teaching of anatomy in this country.' — British Medical Journal. ' The plates are exceedingly well drawn and placed on the stone. . . . The explanatory letterpress is clear and concise.' — The Lancet. • This work meets a distinct -naal.'— Edinburgh Medical Journal. ' We have to call attention to the excellence of the work.' Glasgow Medical Journal 'The scheme is admirably carried out and the plates most reliable.' Guys Hos^tal Gatetie. ' The work is excellent.'— ^c&a/ Reporter. ' This very useful anatomical mlas.'— Hospital. ' The student will be in possession of an excellent atlas of anatomy.' t Medical Press. J ■ Students will find this an invaluable hand-book. The plates are drawn sol clearly, and they are so large that the muscles, vessels, and nerves of each dissection I can be found without any difficulty.' — Nature. \ * They will furnish to many professional men a very valuable work Of reference.' — Glasgaw Medical Journal. ' No hospital library should be considered complete unless it contains at least one i copy of this vnluftble •moilL:— Nursing Record. Whittaker's Technological and Scientific List. 45 Boof^s for ^ecbnological anb fiDanual draining Classes. 'THE ENGLISH SLOYD.' MANUAL INSTRUCTION — WOODWORK. By S. BARTER, Organizer and Instructor of Manual Training in Woodwork to the London School Board and Orgamizing Instructor to the Joint Committee on Manual Training in Woodwork of the School Board for London, the City and Guilds of London Technical Institute, and the Worshipful Company of Drapers. With a, Preface by George Ricks, B.Sc. Lond. Illustrated by 303 Drawings and Photo-Engravings. Fcap. 4to. cloth, 7^. (sd. Contents : — Introduction — Drawing — Timber — Tools ^ Bench- work — Work-room and its Fittings — List of Tools Required, &c. The above Work covers the Requirements of the Examinations of the City and Guilds of London Institute and the Science and Art Department in the subject. Sir Philip Magnus says: — 'Mr. Barter, in his book on "Woodwork," has succeeded in showing, what is most^ important, the educational value of manual training in school instruction, and has thus rendered a great service to those seeking a trustworthy guide in the practical study of the subject.' J. H. Reykolds, Esq., Director and Secretary Municipal Technical Schools, Manchester, says : — ' One of the best, if not the best book, that has hitherto been published on this subject, whether EJnglish or American.' Professor W. Ripper, of Sheffield Technical .School, sa3;s_:— ' Mr. Barter, by his ability, experience, and success as an instructor of manual training classes, is the right man to write a book on woodwork, and the book he has produced is a most valuable adttit-ion to our literature on manual training — in fact, so far as I am aware, it is the most complete and satisfactory work, as a course of instruction for schools, yet pub- lished in this country.' 4-6 Whittaker's Technological and Scientific List. llliittalter's Hooks for Manual Training {Continued). By S. Barter, Author of ' Manual Instruction — ^Woodwork.' DRAWING FOR MANUAL INSTRUCTION CLASSES. Showing the application of Geometrical Drawing to Manual Instruction in Wood and Metal. To cover the requirements of the City and Guilds of London Examination. [/» the Press. By CHARLES G. LELAND, M.A. DRAWING AND DESIGNING. In a Series of 29 Lessons. With 42 Illustrations. Second Edition. Fcap. 4to. sewed, is. ; cloth, is. 6d. ' It has a good equipment of plates, and the text is fall of valuable practical directions for hegianeTB.'—Scotsman. 'Mr. Leland npholds the principle that drawing and designing should go together! and maintains that inventive powers are cramped by the system of teaching which requires a high standard of manipulative skill before the student is instructed in design. In this we entirely agree with him.* — Literary World. ' The book deserves the widestisuccess.' — Scottish Leader. ' The system >is simplicity itaelV— Liverpool Daily Post. By THE Same Author. WOOD-CARVING. With numerous Illustrations. Fourth Edition. Fcap. 4to. Sj. 'An excellent manual.' MomiTi^ Fast. ' An admirable little book.' ^wilder. ' Such patient, explicit, step-by-step teaching as Mr. Leland's is indeed the only road to excellence.' Saturday Review. ' A very useftal book.' —Mr. W. H. Howard, Sec- retary to the Institute of British Wood Carvers, and Instructor at King's College, London. 'A splendid help for Amateurs and those beginning the trade. Without exception it is the best book I have read at present.'— Mr. T. J. Peerin, Society of Arts Medallist,ln5tructor in Wood- carving at the People's Palace. ' I c onslder it the best manual I have seen.' — Miss Hodgson, Instructor in Wood-carving at Manchester Technical School. A Companion Volume to 'Wood-Carving,' by the Same Author. LEATHER -WORK. Stamped, Moulded, and Cut. Cuir-Bouilli, Sewn, &c. A Practical Manual for Learners. With numerous Illustrations. 5.;. ' A delightftil addition to the series of practical manuals.' — Times. Initial Letter (Specimen of Illustrations). Whittaker's Techiiohgical and Scientific List. 4f- Whittaker's Books for Manual Training (Continued). By THE Same Author. METAL WORK. Including Repouss^, Bent or Strip Work' Cut Sheet Metal Work, Nail or Knob,. Wire, Easy Silver Ornament and Chasing Work. An Elementary Manual for Learners. With numerous Illustrations. S'''- By THE Same Adthor. PRACTICAL EDUCATION. A Work on Preparing the Memory, Developing Quickness of Perception, and Training the Constructive Faculties. Fourth Edition. Crown 8vo. cloth, 6j. By John Southward, Author of ' Practical Printing,' ' The Principle and Progress of Printing Machinery,' ' A Treatise on Modern Typography' in En^clopadia Britannica, &c. MODERN PRINTING. A Treatise on the Science and Practice, of Typography. Ninth Edition, l .vol. 8vo. cloth, \d. By Florence B. Jack, Head Teacher of Laundry Work, Edinburgh School of Domestic Economy. ' LAUNDRY ^VORK, The Art of; Practically De- monstrated for use in Homes and Schools. With many IllusTirations." Post 8vo. IS. By Mrs. Charles Marshall, Author of ' Gas Cookery.' GRANDMAMA'S CAKES: A Book of Recipes. Fc.ap. 8vo. paper cover, \s. ■ ■ All the recipes in ' Grandma's Calces ' are genuine old-fashioned oftes; and were originally.collected in manuscript form by my 'grandmother, who was ' famous for the good things at her table.' — FroTK Preface. THE MANUAL TRAINING SCHOOL:. ITS AIMS, METHODS, AND RESULTS, with Figured Drawings of , Shop Exercises in Wood and Metals. By C. M. Woodward, Director of the Manual 'Training SchoolLWashington University. SvoL cl.Qth,4J:. Jie.L_ IND^USTRIAL INSTRUCTION. A Eedagogic^nd Social Necessity. By R'.'SeideL", Mollis, ■Switzerla:hd. Crown 8v'o. cloth, 2s.(id. 48 Whittaker's Technological and Scientific List. THE DURHAM UNIVERSITY CALENDAR and ALMANAC. Published annually in January. Crown 8vo. cloth, ij'. 6d, net. PROGRAMME OF TECHNOLOGICAL EXAMI- NATIONS OF THE CITY AND GUILDS OF LONDON INSTI- TUTE. Including Regulations for the Registration and Inspection of Classes in Technology and Manual Training, Syllabus of Instruction and Lists of Works of Reference in each Subject, this year's Examination Questions, Names of Teachers of Registered Classes, &c. Published annually in August, lod. net.; post free, is. id. THE TECHNICAL WORLD, AND SCIENCE AND ART. 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