264 SCIENCE OF HOME AND COMMUNITY 



suspended magnet. Bring it near the south end. What dif- 

 ference in action do you note? Bring the south end of the 

 magnet near the south end and then near the north end of the 

 suspended magnet. What is the law governing the action of 

 magnets towards each other ? 



2. Make two electromagnets by winding six or seven feet 

 of insulated wire around a long nail. Connect each electro- 

 magnet with a cell. Suspend one the same as was done with 

 the magnet in the previous experiment. Bring the ends of the 

 other electromagnet in turn near the ends of the suspended 

 magnet. What happens? 



3. Connect a small motor with a cell and notice how the 

 parts work. How does the previous experiment help you to 

 understand what takes place ? 



Brakes. Some of the smaller cars are stopped by means 

 of hand brakes, but most of the larger cars are fitted with 

 brakes operated by compressed air and similar to those 

 used on railway trains. The air is compressed by means of 

 a motor which works automatically, always keeping the 

 pressure up to a certain point. We often hear this machine 

 whirring while we are riding on the trolley; it suddenly 

 stops when a certain air pressure has been reached, and then 

 starts again when the motorman has used the brakes and 

 the pressure has been lessened. 



Lighting and heating. The cars are lighted and usually 

 heated by current taken from the trolley wire. The electric 

 heaters are usually placed at intervals on both sides of the 

 car. 



In many cars there is a system of electric buttons, con- 

 nected with a bell near the motorman for signaling. When 

 a person wishes the car to stop, he pushes a button and this 

 causes the bell to ring as a signal to the motorman. 



Electric locomotive. There are conditions in which the 

 smoke of the ordinary locomotive is very offensive and in 

 fact unsafe. To insure safety in tunnels and to avoid the 



