492 



MAGNETISM AND ELECTRICITY 



attracted toward the 

 magnet, and as it 

 moves toward it the 

 circuit is broken at 

 ((7). Because of this 

 break the current no 

 longer flows through 

 (M) and the soft iron 

 cores instantly lose 

 their magnetic power. 

 Since the hammer is 

 no longer attracted 



FIGURE 161. -ELECTRIC BELL to y^ ^ . g thrown 



back by the spring (S) to its original position, thus closing 

 the circuit again and reestablishing magnetic attraction 

 at (M). This alternate 

 closing and breaking of 

 the circuit at (C) goes 

 on so rapidly that the 

 successive taps of the 

 clapper on the bell blur 

 into an almost continu- 

 ous sound. As soon as 

 the button (P) is re- 

 leased, the circuit is broken at that point and the bell 

 ceases ringing. 



The Electric Telegraph. In 

 1832 an American, Samuel F. B. 

 Morse, invented the commercial 

 telegraph. This was the first step 

 in the wonderful progress that has 

 FIGURE 163 been made during the last century 



FIGURE 162 



