TELEGRAPH 



5733 



TELEGRAPH 



United States possesses about 1,500,000 miles of 

 wire, or twenty-five per cent of the lines of the 

 world ; Canada has 135,000 miles. The total land 

 telegraph investment of the world, including 

 wires, offices and all equipment, is $700,000,000 ; 



the cable systems cost $350,000,000. There is, 

 therefore, over a billion dollars applied to an 

 invention which was unknown within the mem- 

 ory of men yet living and which is yet a nov- 

 elty in many thickly-settled countries. E.D.F. 



The Making of the Telegraph 



Telegraph and Doorbell Compared. An elec- 

 tric doorbell circuit is similar to a telegraph 

 circuit. When a caller arrives at the door he 

 telegraphs the fact of his arrival by means of 

 the electric bell. The bell corresponds to the 

 telegraph sounder. The push button at the 

 door corresponds to the telegraph key. If two 

 wires are connected to an electric battery and 

 to an electric bell, the bell rings because the 

 current from the battery flows through the coils 

 of the electromagnet which is part of the bell. 

 If one of the wires is cut and the ends are 

 separated, the bell ceases to ring because the 

 circuit is open and the current cannot flow. 



it makes an electrical contact which closes the 

 circuit and permits a current to flow through 

 the electromagnet coils of the receiving instru- 

 ment. The electromagnet then attracts the iron 

 armature, pulling it down, and with it the brass 

 arm of the sounder. This causes a click. When 

 the key is released the circuit is broken, the cur- 

 rent ceases in the electromagnet, the sounder 

 arm is released, and the spring pulls it .up, 

 causing a second click. 



A Simple Telegraph. Two boys can easily 

 set up a telegraph line between their homes. 

 Two sounders, two keys, and one electric bat- 

 tery, which may consist of two or three dry 



A BOY CAN MAKE A SIMPLE SOUNDER AND KEY 



If the ends of the cut wire are pressed together 

 the bell again rings. 



It would be inconvenient to press the ends 

 of two wires together every time one wished 

 to ring the bell, so a push button is used, the 

 end of one wire being connected to a spring 

 and the end of the other to a second spring 

 under the first. When the button is pressed the 

 two springs are pressed together and this is 

 the same as pressing the ends of the wires to- 

 gether. Pressing the button causes the bell to 

 ring, because this closes the circuit and permits 

 the current from the battery to flow through 

 the bell. See ELECTRIC BELL, page 1983. 



In the telegraph, pressing the key closes the 

 circuit and permits a current to flow through 

 the electromagnet coils of the sounder. The 

 electromagnet then pulls a piece of iron called 

 an armature; it pulls only when a current is 

 flowing through the coils of the magnet. When 

 the key at the sending station is pressed down, 



cells, which may be purchased for a slight sum, 

 are needed. The magnet of an old electric bell 

 can be used in making the sounder, or an elec- 

 tromagnet can be made, as follows: 



With a hack saw or a file cut off two pieces 

 of soft iron rod, each about an inch and a half 

 long, and file the ends smooth. Cut out two 

 round disks of hard fiber or stiff cardboard and 

 fit them to the ends of the iron rods so as to 

 form spools. Wind about fifty turns of magnet 

 wire on each rod, winding the two coils in the 

 same direction. The two coils are to stand up- 

 right on the base of the instrument and to rest 

 on a strip of iron. It is better if the strip of 

 iron can be fastened to the rods with machine 

 screws, but this is not necessary. Connect the 

 coils so that when connected to a battery the 

 upper end of one rod is a north pole and the 

 upper end of the other is a south pole. The 

 polarity can be tested by means of a pocket 

 compass. Another strip of iron is used for the 



