Of 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 incandescent lamp or the dazzling carbon points of an arc light stimulate 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 sufficient 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 mystery, when not understood, is, in fact, no mystery at all. NOTE.--The illustrations of railway motor, generator, and switchboard (Figs. 15, 16, 17) were made from photographs kindly furnished by the manufacturers, the Westinghouse Electric and Manufacturing Company.