WHAT MAKES TBI: TROLLEY CAR GO. 



415 



of the car. The reversing shaft is also provided with a number 

 of segments, but these are not so easily seen, although they can be 

 discerned on close examination. The wires from the cable e e e 

 and also wire d d are attached to the stationary pieces with which 

 the segments carried by the two shafts make contact when the 

 latter are moved around by the motorman. These Avires can be 

 seen back of the main switch shaft, and also above the board located 



Fig. 21. — View of Interior of Car Controller. 



at the lower left-hand corner. All these wires enter the controller 

 through an opening in the bottom. 



In addition to the apparatus shown in Figs. 18 to 21, electric 

 cars are provided with a safety fuse and a lightning arrester, the 

 object of the latter being to protect the motors from the destruc- 

 tive effects of lightning strokes. The object of the safety fuse is 

 to protect the motor from injury when the current becomes too 

 strong. An electric current in passing through a wire generates 

 heat, and the stronger the current the greater the heat. If the wire 

 is large and the current weak, the heat developed may be insufficient 

 to raise the temperature to a noticeable degree; but, on the other 

 hand, if the wire is small or the current very strong, the heat gen- 

 erated may be capable of raising the temperature of the metal to 

 the fusing point. In fact, the incandescent lamp operates upon this 

 principle; the carbon filament is traversed by a current of a 

 strength sufficient to heat it to a point where it becomes intensely 



