THE PRACTICAL MOTOR 



337 



two ; the armature likewise consists of several portions, and 

 even the commutator may be very complex. But no matter 



FIG. 231. A modern power plant. 



how compl'ex these various parts may seem to be, the prin- 

 ciple is always that stated in Section 309, and the parts are 

 limited to field magnet, commutator, and armature. 



The motor is of value because by means of it motion, or 

 mechanical energy, is obtained from an electric current. 

 Nearly all electric street cars (Fig. 232), are set in motion by 



Trolley wire or Third rail 



J- 



Track 



\ Motor 

 FIG. 232. The electric street car. 



powerful motors placed under the cars. As the armature 

 rotates, its motion is communicated by gears to the wheels, 



CL. GEN. SCI. 22 



