ELECTRICAL COMMUNICATION 



493 



SOUNDER 



UNE BATTERY 



FIGURE 164 



in communicating rapidly between distant points. The 

 necessary instruments used in this form of communication 

 are a sounder (Figure 162) and a key (Figure 163). The 

 following experiment illustrates the ar- 

 rangement and operation of a simple 

 telegraph. 



Electrical Communication. Experiment 

 160. Attach one end of a wire to a pole of a 

 dry cell and the other end to one of the bind- 

 ing posts of a telegraphic sounder. From the 

 other binding post of the sounder lead a wire 

 to a binding post of a telegraphic key. Con- 

 nect the free binding post of the key with the 

 free pole of the battery (Figure 164). When 

 the key is pushed down, the circuit is closed 

 and the sounder clicks. If a relay can be procured, remove the 

 sounder and connect two of the binding posts of the relay in the 

 same way that the sounder was connected. 



Connect one of the free binding posts of the relay with a binding 

 post of the sounder and the other binding post with the pole of a 

 dry cell. Connect the other pole of the dry cell with the free 

 binding post of the sounder. When the key closes the circuit 



through the relay, 

 the circuit through 

 the sounder and its 

 dry cell is closed 

 by the relay (Fig- 

 ure 165), and the 

 sounder clicks. This 

 is the usual arrange- 

 ment in a simple 

 telegraph office. The sounder in the first part of the above experi- 

 ment can be replaced by an electric bell (Figure 166) and the 

 key by a push button, thus showing the arrangement of the 

 ordinary doorbell. 



FIGURE 165 



