WHAT MAKES THE TROLLEY CAR GO. 



413 



as belonging to the series parallel type, the name being given from 

 the fact that when the car is running slow, the current passes 

 through the two motors in series — that is, through one after the 

 other; but when the motors are running fast, a separate current 

 passes through each machine. 



If, when a car is running, the controlling switch is turned to 

 cut the current off, the eifect will be that the speed will gradually 



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Fig. 20. 



-View uf Elkijtkk' Kailway Truck with (J.nm: ihaui; 

 VIDEO WITH Magnetic Brakes. 



J^ LAtU Ai. 



reduce ; but if it is desired to effect a sudden stop, it becomes neces- 

 sary to cheek the headway by means of a brake. For this purpose 

 the hand brake ordinarily used on all types of cars is employed, 

 but magnetic brakes are also used in some cases. Fig. 20 shows 

 a car truck equipped with two motors and magnetic brakes, one 

 on each axle. Looking at the front end of the truck, the brake 

 is seen on the left side of the axle, between the motor bearing and 

 the car wheel. The larger drum, on the right side, is the casing 

 within which the g€ar wheel and pinion are inclosed. These mag- 

 netic brfikes are operated by a current generated by the motors, and 

 not by that of the main line. As was explained in the first article, 

 an electric motor can be made to act as a generator of electric cur- 

 rent by simply reversing the direction in which the armature re- 

 volves. If we do not desire to reverse the direction of rotation, 

 the result can still be attained by reversing the direction in which 



