USES OF ELECTRICAL ENERGY 



163 



that a is below and b above the horizontal position, a 

 commutator c changes the direction of the current in the 

 coil, so that b becomes the negative and a the positive 

 pole of the armature. Thus the motion goes on always 

 in the same direction. 



Such a motor would use a direct current. Motors 

 are now commonly made without commutators, to use 

 an alternating current. These are often built upon the 

 same frame as the dynamo which furnishes the current. 



187. Electric Cars. An electric car is driven by 

 means of a motor. This is on the under side rf the car 



FIG. 119 



m (Fig. 119) ; as its armature turns, the motion is trans- 

 mitted to the wheels by a set of gear wheels ( 72). 

 The current is supplied from a wire w, or from a " third 

 rail" beneath the car. After passing through the con- 

 troller s to the motor, the current leaves through the 

 wheels, traveling through the rails back to the dynamo. 



