THE PUSH BUTTON 



219 



tr 



000 



soft iron strip or armature S ; and from S the current flows back 

 to the battery. As soon as the current flows, the coils become 

 magnetic and attract the soft iron armature, drawing it forward 

 and causing the clapper to strike the bell. In this position, S no 

 longer touches the screw P, and hence there is no complete path 

 for the electricity, and the current ceases. But the attractive, 



magnetic power of the coils 

 stops as soon as the current 

 ceases ; hence there is nothing 

 to hold the armature down, 

 and it flies back to its former 

 position. In doing this, how- 

 ever, the armature makes con- 

 tact at P through the spring, and the current 

 flows once more. As a result the coils again 

 become magnets, the armature is again 

 drawn forward, and the clapper again strikes 

 the bell. But immediately afterwards the 

 armature springs backward and makes con- 

 tact at P and the entire operation is repeated. 

 As long as we press the button, this process 

 continues, producing what sounds like a con- 

 tinuous jingle ; in reality the clapper strikes 

 the bell every time a current passes through 

 the electromagnet. 



The push button. The push button is an 

 essential to the operation of every electric 

 bell, because without it the bell either would not ring at all, or 

 would ring incessantly until the cell was exhausted. When the 

 push button is free, as in Figure 90, the cell terminals are 

 not connected in an unbroken path, and hence the current does 

 net flow. When, however, the button is pressed, the current 

 has a complete path, provided there is the proper connection at 



FIG. 89. The electric 

 bell. 



