3 22 



SCIENCE OF HOME AND COMMUNITY 



ADJUSTING SCREWS 

 CONTACT- 



BUTION 



130. Telegraph key. 



How the telegraph works. Some improvements have 

 been made in the telegraph since Morse's day, but in prin- 

 ciple the telegraph in use to-day is the same as that invented 

 by Morse. The telegraph consists of four parts, the sender, 

 or key, the sounder, the relay, and the batteries. Figure 132 



shows how these various 

 parts are arranged. 



The key. The structure 

 of the sender, or key, is 

 shown in figure 130. This 

 consists of a lever with a 

 button at one end. On the 

 under side is a point which 

 makes contact with another 

 point directly beneath it. These two points are ordinarily 

 separated by a spring. When the key is not being used, the 

 switch is shut so that the circuit is closed. When the key 

 is to be used, the switch is opened. When the button is 

 pushed down, the two points come in contact and the current 

 passes through, thus affecting 

 the relay and the sounder at 

 the other end. 



Sounder. The sounder is 

 shown in figure 131. This 

 consists of two electromag- 

 nets, and over these a bar, 

 pivoted at one end. Just 

 over the electromagnets is 

 the armature. Ordinarily the bar is kept back by a spring so 

 that the armature does not touch the electromagnet. The 

 distance that the bar can be pulled down is controlled by a 

 screw. When the key of the sender is closed, the current 

 passes through the coils of wire and the electromagnet be- 

 comes magnetized, thus pulling down the armature. When 

 the key is open the current ceases to flow through the coils so 



FIG. 131. Telegraph sounder. 



