THE ELECTRIC BELL 



491 



of this kind are called electromagnets. If the nail had been 

 hard steel and the battery exceedingly strong, the steel would 

 have remained a magnet after being taken out of the coil. 

 Electromagnets have come to be of almost inestimable 

 use in modern life. The telegraph, the telephone, the mag- 

 netic crane, the electric motor, and almost innumerable 



Courtesy of Illinois Central Railroad 

 ELECTROMAGNETIC CRANE 



Loading steel rails on a freight car. The magnet is lifting seven rails, a 

 burden of about three and one half tons of steel. 



other mechanical devices are dependent largely upon the 

 principle of electromagnetism for their usefulness. 



The Electric Bell. One of the simplest applications of 

 the electromagnet is the electric bell (Figure 161). When 

 the punch-button (P) is pushed down it closes the circuit 

 through the electromagnet (M). The hammer (H) is then 



