WHAT MAKES THE TROLLEY CAR GO. 409 



results are accomplished in an electrically operated car can ba 

 understood from Figs. 18 and 19, which are line drawings, in a 

 simplified form, of an ordinary trolley car. Fig. 18 is an eleva- 

 tion showing the outline of the car body and the wheels in broken 

 lines, while the motors and the wires through which the current is 

 conveyed thereto are drawn in solid lines. Fig. 19 is a plan in 

 which the outline of the car floor and the platforms is represented 

 in broken lines, the solid lines being the motors and connecting 

 wires. 



In almost every instance railway cars are provided with two 

 motors, as shown at M M in these two figures. This arrangement 

 is adopted not because one motor can not furnish all the power 

 required, but simply for the purpose of making the equipment more 

 reliable. Everything of human make is liable to fail; hence if 

 only one motor were used there would be more or less liability of 

 its giving out at a critical moment, and then the car would be help- 

 less. If two motors are provided, should one give out the car 

 would not be disabled, for the remaining machine would be able 

 to run it to its destination. In order that this result may be suc- 

 cessfully accomplished, each motor is made of sufficient capacity 

 to run the car without being overtaxed, unless the load is abnor- 

 mally large; but even under the latter conditions the machine will 

 in ninety-nine cases out of a hundred withstand the strain. Some 

 roads, in small towns, where the traffic is light and the expense 

 must be kept down to the lowest point, use single-motor cars, so 

 as to effect a saving in first cost. This course, however, is verv 

 seldom followed, except in places where there are no heavy grades 

 or where there is very little probability of the loads becoming ex- 

 cessive, except at rare intervals. If the cars are provided with a 

 single motor, when one becomes disabled from any cause it has to 

 wait until overtaken by the car behind it, so that it may be pushed 

 by the latter to the end of the road. 



The electric current for operating the motors is generated in 

 a power house that is located at some convenient point along the 

 route. The current is conveyed to the moving cars by means of 

 a trolley wire, which is marked T in the drawings. Unless the 

 road is very small and operates but a few ears, this wire will not 

 be sufficient to carry all the current, hence in most cases there are 

 a number of supplementary wires, which are called feeders. These 

 wires are carried along on poles, and at proper intervals are con- 

 nected with the trolley wire T. The electric current passes from 

 the trolley wire through the motors on the car, and thence to the 

 rails R, and through these, and also through the ground, back to 

 the power house. The exact path of the current is as follows: 



TOL. LTI. 82 



