WORK AND MACHINES 

 SUMMARY 



171 



The close connection between magnetism and electricity is manifest 

 in the fact that pieces of iron and steel are best magnetized by passing 

 a current of electricity through a wire wound many times around the 

 body to be magnetized. When the steel is removed from the coil of 

 wire it is found permanently magnetized. No manifestation of the 

 occurrence of any change has been apparent in the process. A piece 



FIG. 58. Wireless telegraphy. 



of soft iron loses its magnetism when the current ceases, however 

 powerful as a magnet it may have been while the current was passing 

 around it. 



The employment of electromagnets in door bells and in telegraph 

 instruments illustrates their usefulness in causing motion back and 

 forth through short spaces. The electrical impulses causing this 

 motion may originate at far distant places. As the soft iron bar 

 (armature) is alternately drawn to the magnet and then released, its 



