THE ELECTRIC TROLLEY 261 



ing the dynamo is the steam engine. In some places the gas 

 engine is used." 



How the current is conducted to the car. From the power 

 house the electricity is conducted by means of wires to the 

 trolley cars. In the system most commonly used, the 

 electricity is conveyed by a wire suspended over the tracks. 

 The electricity passes from this to the car through the trolley 

 pole. Powerful springs at the base of the pole push the pole 

 and the little wheel at its end upward and in constant con- 

 tact with the wire. From the trolley base the current is 

 conducted to the various parts of the car, and returns by 

 means of the rails on which the car runs. In order to com- 

 plete the circuit, the ends of the rails are either connected 

 by wires or else welded. In order to supply enough elec- 

 tricity to all parts of the system, different wires, known as 

 feeders, are run from the main supply of the current, and 

 connect with various parts of the system. 



Controller. As we watch the motorman running the car, 

 we notice that he controls the car by means of three handles, 

 one for the brakes, and two on a boxlike structure called 

 the controller. When he wishes to start the car, one of the 

 handles is turned a notch at a tune till a place is reached 

 where it is allowed to remain stationary. When he wishes to 

 stop, the handle is turned back again and the brakes applied. 

 If he wishes to make the car go backwards, he moves another 

 handle and then turns the first handle as before. 



This controller serves three purposes: first, it connects 

 the motor with the circuit, so that the car can be started or 

 stopped; second, it regulates the amount of electricity 

 which passes to the motor, so that the speed of the car can 

 be controlled ; and third, it governs the direction in which 

 the car goes, so that it can be made to go either forward or 

 backward. 



If the full current were turned into the motor suddenly, 

 it would cause the car to start with an unpleasant jerk and 



