GENERATING ELECTRICITY COMMERCIALLY 197 



240. Electric Motor. An electric motor (Figs. 88, 89, 90, 

 91) is a machine for transforming electrical into mechanical 

 energy. An electric current causes the armature to rotate, 

 and the mechanical energy due to the rotation may be uti- 

 lized to drive machinery. The motor is quite similar to a 



FIG. 88. An Electric Motor. 



dynamo; in fact, the direct current motor is almost identical 

 with the dynamo in structure and circuit, although in detail 

 of design its external appearance is sometimes quite different. 

 The principle of magnetism on which the direct current motor 

 works is as follows: 



When a current of electricity is passed through a coil of 

 wire on the armature, the coil will always revolve so as to 

 include as many lines of force as possible. When it reaches 

 this position, the commutator changes the current in the 



