TELEPHONE 



5739 



TELEPHONE 



electrical connection between the instruments 

 of persons desiring to talk with each other. 

 The one who makes the call removes his re- 

 ceiver from the hook and a "drop" at the 

 switchboard is released, showing the telephone 

 number of the person making the call. At the 

 same instant the lighting of a small electric 

 bulb calls the attention of the operator to the 

 call. The operator then inserts an "answering 

 plug" corresponding to the number calling. 

 After ascertaining the number wanted the 

 operator inserts the "calling plug" in that num- 

 ber and presses a key which closes the ringing 

 circuit of the party who is being called; then 

 she throws the key into position for talking. 

 A plug consists of the ring-shaped terminals of 

 the wires in the connecting cord. 



The multiple switchboard used' in large ex- 

 changes is so arranged that each operator can 

 call from her own section of the switchboard 

 any subscriber whose line is connected with 

 that exchange, but she can be called by only a 

 limited number. The advantages are that the 

 calls are divided among a number of operators, 

 and each operator can complete any call from 

 her own section of the switchboard. 



How to Make a Simple Telephone. Two boys 

 can easily make and set up between their 

 homes a good, 

 working tele- 

 phone line. It 

 will be necessary 

 to have two tele- 

 phone receivers, 

 which will serve 

 also as transmit- 

 ters. The re- 

 ceivers may be 

 purchased in an 

 electrical shop, or 

 they may be 

 made as follows: 

 Cut off a piece 

 of curtain pole 

 about one inch 

 and one-eighth in 

 diameter and 

 three and one- 

 half inches long; 

 or, if a wood- 

 turning lathe is 

 at hand, turn out 

 such a piece. 



TRANSMITTER 

 Simple sketch of the mech- 

 anism which receives and 

 transmits the words spoken 

 in telephone conversation. 

 The parts are (a) cover; (b) 

 round or square block; (c) 

 mouthpiece; (d) diaphragm; 

 (e) bolt; (/) granules of 

 carbon. 



Bore a hole three-eighths of an inch in diameter 

 lengthwise through the center. .Bore two holes 

 one-sixteenth inch in diameter lengthwise 



through the rod by the side of the first hole. 

 The last two holes are for the wires to pass 

 through. 



A round, wooden box about two and one-half 

 inches in diameter is needed; a wooden pill 

 box can be used, or one can be turned on the 

 lathe. If a pill box is used two wooden lugs 

 must be glued to the bottom of the box to 

 hold the screws by which the cap is fastened. 

 If the box is lathe-turned the sides can be 

 made thick enough for the screws. The cap is 

 made of thin wood, hard rubber, or hard fiber, 

 cut to fit the box and having a hole about half 

 an inch in diameter in the center. It must 

 have a thin rim or collar to separate it from 

 the disk. The disk is made of thin, soft iron, 

 such as photographers use for tintypes, and this 

 must be of the thinnest variety. The magnet 

 is made of a piece of steel rod three-eighths of 

 an inch in diameter and four and one-quarter 

 inches long. If soft steel is used, it can be 

 hardened by heating it red hot and then plung- 

 ing it into cold water. The steel rod can be 

 magnetized at the nearest electric light plant, 

 where the dynamo tender will no doubt be will- 

 ing to hold it for a few minutes against the 

 field magnet of one of the large dynamos. The 

 parts described, when put together, appear as 

 in the illustration on page 5738, which represents 

 the receiver as if it were sawed through length- 

 wise from end to end. In addition to the two 

 receivers, two electric bells, two switches, two 

 push buttons, and four dry cells are needed. 

 These are connected as in the illustration on 

 next page. Care must be taken to connect the 

 dry cells in series, otherwise one battery will 

 neutralize the effect of the other. The push 

 buttons are for the purpose of ringing the bells, 

 the switches for making the proper connections 

 for ringing and talking. It will be well to set 

 up both sets in one room and experiment with 

 the switches and push buttons to learn how to 

 make the proper connections before setting up 

 the line between two houses, as corrections are 

 then more easily made. 



Power Required for a Telephone. The power 

 required to operate a telephone is very small. 

 The telephone receiver is more sensitive to an 

 electric current, that is, it responds to a weaker 

 current, than any other instrument in common 

 use. The power required to ring an electric 

 doorbell would keep millions of telephone 

 receivers buzzing for an equal length of time. 

 Many times as much power is required for 

 the ringing of the telephone bell as for operat- 

 ing the talking circuit. 



