CHAPTER XX 



WINDS AND STORMS 



Winds. We are all familiar with the sometimes 

 regular, but more often fitful and irregular movements 

 of the air, which we call winds. 



Winds are important in many ways. They transfer 

 great masses of air from one part of the earth to an- 

 other ; they carry away the impurities of city air ; they 

 furnish power for windmills and sailing vessels ; they 

 cool hot regions and warm cold ones. Most changes 

 of weather are due to changes in the direction of the 

 wind. Some winds are agree- 

 able and favorable to life. 

 Some bring suffering, de- 

 struction, and death. Even 

 light breezes effect a con- 

 tinual change of air which is 

 beneficial for both plants and 

 animals. To man, winds are 

 as a rule stimulating and 

 invigorating, while calm air 

 is often enervating. 



Cause of winds. A piece 

 of wire gauze is placed over 

 the flame of a Bunsen burner. 

 If very small pieces of cotton are dropped upon the 



137 



P 



_<fr. 



FIG. 51. When air is 

 heated it expands, becomes 

 lighter, and is pushed up by 

 the colder air which is 

 drawn down beneath it. 



