196 Common Science 



287. The water will be no higher on the inside of a leaky boat 



than it is on the outside. 



288. A bass viol is considerably larger than a violin. 



289. Ships that are used by men testing the earth's magnetism 



carry very sensitive compasses. Explain why such ships 

 are made entirely of wood and brass. 



290. Thunder rolls ; that is, after the first peal there is a rever- 



berating sound that becomes less and less distinct. 



SECTION 32. Static electricity. 



What is electricity? 



What makes thunder and lightning? 



Why does the barrel or cap of a fountain pen pick up small 

 bits of paper after it has been rubbed on your coat sleeve ? 



Why do sparks fly from the fur of a cat when you stroke 

 it in the dark? 



The Greeks, 2000 years ago, knew that there was 

 such a thing as electricity, and they used to get it by 

 rubbing amber with silk. In the past century men 

 have learned how to make electricity do all sorts of useful 

 work : making boats and cars and automobiles go, 

 ringing bells, furnishing light, and, in the telephone and 

 telegraph, carrying messages. But no one knew what 

 electricity really was until, within the last 25 years, 

 scientists found out. 



Atoms and electrons. When we talked about mole- 

 cules, we said that they were as much smaller than a 

 germ as a germ is smaller than a mountain. . Well, a 

 molecule is made up, probably, of some things that are 

 much smaller still, so small that people thought that 

 nothing could be smaller. Those unthinkably tiny things 

 are called atoms; you will hear more about them when 

 you come to the parts of this book that tell about 

 chemistry. 



