the car, and also for the purpose of graduating the strength of the current that passes through the motors in the act of starting. These rheostats are very seldom in use when the car is in motion, because it is a waste of power to pass the current through them. After the current has passed through the motors it enters the ironwork, and thus gets into the car wheels and finally to the track.

The lines drawn in Fig. 18 to indicate the position of the wires in the car do not show their actual position, but only the general direction they follow. From the trolley base to the first hood switch the wire, as a rule, is run along the car roof on one side of the ventilator, and the wire leading from the first to the second hood switch occupies a corresponding position on the opposite side of the roof. From the last hood switch, b, the wire is run down one corner of the car body, being either within the car body, or, if not, so covered by moldings as to not be reached by the hands of passengers. The wires d and e are generally run under the car, and are firmly secured to it by means of suitable fastenings.

The controlling switches C C are provided with one and sometimes two handles, one of which is used to regulate the speed of the car and stop and start it, while the other is for the purpose of reversing the direction in which it runs. The handle h is for the purpose of regulating the speed, and by means of k the direction of motion is changed. Before h is moved from the inactive position k is turned so that the car may run either forward or backward, as may be desired; then, when h is moved, the car will start, and by varying the position of h the speed can be changed. If it is desired to reverse the car, h is brought back to the stop position, k is shifted to the reverse motion, and then h is again turned to the running position. When the controlling switch is provided with only one handle this is turned in one direction to run the car ahead, and in the opposite direction to run it backward, the graduations in velocity being obtained by placing the handle in positions intermediate between the stop position and the highest speed position.

As will be noticed, the wire d d branches at c and runs in both directions. Now, when the controller handles are both turned to the stop position the current from the trolley can get no farther than the ends of d in either switch, but if one of them is turned to the running position, the current at once passes to the wires in the cable e e e, and thus to the two motors. If the switches C C are in proper working order and there is no disarrangement of the wires leading to the motors or those within the latter, the current will obey the movements of the handle h, but under other conditions it may not. If such an emergency arises, the motorman reaches up to the hood and turns the safety switch a or b, and thus cuts the current off.

The force with which the motors turn the car wheels around depends upon the strength of the current; this is owing to the fact that the magnetic force is increased or decreased by variations in the current strength. If the current is doubled the magnetic force of the armature is nearly doubled, and so is that of the field magnet, therefore the pull between the poles is nearly four times as great. From this it will be seen that the force with which the car is pushed ahead can be increased enormously by a comparatively small increase in the strength of the current. If the current strength is doubled, the propelling force is practically quadrupled; and if the current is increased four times, the propelling force is made nearly sixteen times as great.

The speed at which the car runs depends upon the force that impels the current through the wire, and which is called electro-motive force. The greater the electro-motive force, the higher the velocity. If the current passes from the wires in the cable e e e through each motor separately, and thence to the rails R, each machine will receive the effect of the whole electro-motive force of the current; but if after the current has passed through one motor it is directed through the other, then each machine will be acted upon by only one half the electro-motive force, and, as can be seen at once, the velocity in the first instance will be twice as great as in the last. This fact is taken advantage of in regulating the speed of the car, and controlling switches arranged so as to direct the current through the motors in this way are designated 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.

Fig. 20.—View of Electric Railway Truck with One Motor on each Axle and provided with Magnetic Brakes.

If, when a car is running, the controlling switch is turned to cut the current off, the effect will be that the speed will gradually reduce; but if it is desired to effect a sudden stop, it becomes necessary to check 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 gear wheel and pinion are inclosed. These magnetic brakes 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 current by simply reversing the direction in which the armature revolves. If we do not desire to reverse the direction of rotation, the result can still be attained by reversing the direction in which the current passes through the armature coils. It is evident that the direction of a car motor can not be reversed at the instant that it is desired to have it act as a generator—that is, when it is desired to put the brakes on; hence the direction of the current through the armature is reversed.

When a car is provided with magnetic brakes, the controlling switches are so made that when the handle h is moved back to the stop position it disconnects the motors from the trolley wire and at the same time connects them with the magnetic brakes in such a manner that they will act as generators and thus send current through the coils of the latter. In order that the force with which the brakes are applied may be graduated, the controlling switches are arranged so as to be moved several steps back of the point which in the ordinary type of switch would be the final stop position. When the handle h is placed on the first brake position the current generated by the motors is not very strong, and as a consequence the force of the brake is light, but sufficient to bring the car to a stop in a reasonable distance. If a quicker stop is desired the handle is moved to the second, third, or fourth brake position, thus increasing the