RELATIONS BETWEEN WATER AND LIFE 15 



fields and woods. Yesterday, when I looked from my win- 

 dow, the whole surface of the earth was green as far as I 

 could see. But to-day it is beginning to turn brown, be- 

 cause the blue grass is ripening. 



You saw that it is heat that causes the changes and 

 movements of water. And it is changes in the amount of 

 heat that cause the seasons of the year. You can see that 

 this would be a very still and dead world indeed if it were 

 not for heat. 



QUESTIONS 



1. How much of the earth is covered by water? 



2. What is the purpose of digestion ? 



3. What determines the three states of water? 



4. What is the force that drives the steam-engine? 



5. Why does it cool your face to fan it? 



6. How does the size of a substance change when it is heated? 



7. Why do water-pipes burst in winter? 



8. What are clouds? 



