Electricity 247 



pointed carpet tack that would go across the wires, but not 

 through them, and if driven tightly into the wall would hold 

 the wire more firmly than would the loop. 

 Which way was best? 



Inference Exercise 

 Explain the following : 



361. If the insulation wears off both wires of a lamp cord, the fuse 



will blow out. 



362. Street cars are heated by electricity. 



363. The handles of pancake turners are often made of wood. 



364. Glue soaks into the pores of pieces of wood and gradually 



hardens. 



365. The glue then holds the pieces tightly together. 



366. You need a fuse of higher amperage, as a lo-ampere fuse, 



instead of a 6-ampere one, where you use electricity for an 

 iron, and one of still higher amperage for an electric stove. 



367. You should be careful about turning on electric lights or 



doing anything with electric wires when you are on a ce- 

 ment, iron, or earthen floor, or if you are standing in water. 



368. The keys and buttons with which you turn on electric lights 



are usually made of a rubber composition. 



369. Defective wiring, because of which bare wires may touch, 



has caused many fires. 



370. A person wearing glasses can sometimes see in them the 



image of a person behind him. 



SECTION 40. Electromagnets. 



How is a telegram sent ? 



What carries your voice when you telephone ? 



So far we have talked about electricity only making 

 heat and light by being forced through something that 

 resists it. But everybody knows that electricity can 

 be made to do another kind of work. It can be made to 

 move things, to run street cars, to click telegraph 

 instruments, to vibrate the thin metal disk in a tele- 



