Electricity 257 



people back and forth 

 to work in city street 

 cars, for lifting great 

 pieces of iron and steel 

 in the yards where huge 

 electromagnets are used, 

 for countless pieces of 

 work in all parts of the 

 globe. Yet the use of 

 electricity is still only in 



its beginning. Tremen- FIG. 145. An electric motor of commercial 



dous amounts of water 



power are still running to waste ; there is almost no limit 

 to the amount of electricity we shall be able to generate 

 as we use the world's water power to turn our dynamos. 



Application 62. Explain how pressing a telegraph key 

 can make another instrument click hundreds of miles away, 

 and how you can hear over the telephone. Is it vibrations 

 of sound or of electricity that go through the telephone wire, 

 or does your voice travel over it, or does the wire itself 

 vibrate? Explain how electricity can make a car go. 



Inference Exercise 

 Explain the following : 



371. When a fuse blows out, you can get no light. 



372. If you lay your ear on a desk, you hear the sounds in the room 



clearly. 



373. If you touch a live wire with wet hands, you get a much worse 



shock than if you touch it with dry hands. 



374. A park music stand is backed by a sounding board. 



375. The clapper of an electric bell is pulled against the bell when 



you push the button. 



376. A hot iron tire put on a wagon wheel fits very tightly when it 



cools. 



