THE ELECTRIC TROLLEY 



263 



are brought together, if the north end of one is brought near 

 the south end of the other, they will be drawn towards each 

 other. (See figure 97.) If the two north ends or the two 

 south ends are brought together, they will be pushed apart. 

 This can be well illustrated by means of a bar magnet 

 and a compass, which is a magnet mounted so that it can 

 rotate. If the south end of the magnet is brought near 

 the north end of the needle, the needle will turn around 

 till its north end points towards the south end of the 

 magnet. If the magnet be constantly moved, 

 the needle may be kept in constant motion. 

 When an electric current is passed through 

 a motor, the field magnets and armature 

 both become magnets and on account of the 

 attraction of unlike poles and the repulsion 

 of like poles, the armature is caused to re- 

 volve. This is so constructed as to make 

 the motion continuous as long as the current 

 passes through the motor. The motor is 

 connected with the axles of the car by means of gears, and 

 thus the wheels are made to rotate and the car to move. 



Thus the long story that began with the burning of coal 

 in the fire box of an engine at the power house, is now com- 

 pleted when the energy thus generated is made to move 

 wheels of a trolley miles away. 



FIG. 97. Illustrat- 

 ing principle of 

 electric motor. 



LABORATORY EXERCISE 27 



Purpose. To see how the motor works. 



Apparatus. Two bar magnets, wire, two long nails, small 

 motor, two cells. 



Directions. I. In order to understand the principles in- 

 volved in the motor, we will first study the action of two bar 

 magnets towards each other. Make a stirrup of a piece of wire 

 and suspend a bar magnet in this by means of a string. Bring 

 the north pole of the other magnet near the north pole of the 



