3i6 POPULAR SCIENCE MONTHLY. 



WPIAT MAKES THE TROLLEY CAR GO. 



By WILLIAM BAXTER, Jr., C. E. 

 I. 



OE all the wonderful operations accomplished by the aid of 

 electricity at the present time, none so completely mystifies 

 the beholder as the action of the trolley car. The electric light, 

 although incomprehensible to the average layman, does not excite 

 his curiosity to the same extent. The glowing filament of an in- 

 candescent lamp or the dazzling carbon points of an arc light stimu- 

 late the inquisitive proclivities to some extent, but as the popular 

 notion with respect to the nature of electricity is that it is some 

 kind of fluid that can flow through wires and other things like water 

 through a pipe, the conclusion arrived at is that the current, in its 

 passage through the filament or the carbon points, generates a suffi- 

 cient amount of heat to raise the temperature of the material to 

 the luminous point. The fact that energy is required to raise the 

 temperature of the mass to the incandescent point is not taken into 

 consideration by those not versed in technical matters, owing to 

 the fact that, as nothing moves, it is not supposed that power can 

 be expended. When a trolley car is seen coming down the street 

 at a high rate of speed the effect upon the mind is very different. 

 Here we see a vast amount of weight propelled at a high velocity, 

 and yet the only source through which the power to accomplish 

 this result is supplied is a small wire. The mystifying cause does 

 not stop here, for if we look further into the matter we see that 

 the energy has to pass from the trolley wire to the car through 

 the very small contact between it and the trolley wheel. After 

 contemplating these facts, it appears remarkable that the energy 

 that can creep through this diminutive passage can by any means 

 be made to develop the force necessary to propel a car with a 

 heavy load up a steep grade. An electrical engineer, if asked to 

 explain the action, would say that the force of magnetic attraction 

 was made use of to accomplish the result, but this explanation 

 would fail to throw any light upon the subject. In what follows, 

 it is proposed to explain the matter in a simple manner, and then 

 it will be seen that what appears to be an incomprehensible mys- 

 tery, when not understood, is, in fact, no mystery at all. 



Electricity and magnetism are two forces that are intimately 

 associated with each other, and, although radically different, it is 



NoTK. — The illus^trations of railway motor, penerator, and switchboard (Fifjs. 15, 16, l*/) 

 were made from photographs kindly furnished by the manufacturers, the Westinghouse 

 Electric and Manufacturing Company. 



