THE EARTHS OCEAN OF VAPOR. 93 



When clouds reach the higher regions of the 

 atmosphere they disappear, because the particles 

 of water of which they are composed pass rapidly 

 into an invisible vapor, on account of the great 

 relief of pressure in the higher regions. 



The earth's ocean of vapor is of the greatest 

 importance to its present race of animals and 

 plants. If any considerable change in either the 

 quantity or distribution of vapor should be main- 

 tained for any considerable time, the present race 

 of animals and plants would disappear. 



Some of the more important ways in which the 

 ocean of vapor affects the economy of the earth 

 are as follows : 



1. By the action of the winds, the water vapor 

 is carried from the warm regions of the earth to 

 the colder regions, where, falling as rain or snow, 

 it gives out its heat and raises the temperature of 

 the air over such regions. 



An interchange is thus effected between the too 

 great heat of the equatorial regions and the too 

 feeble heat of the poles, and a more equable, uni- 

 form temperature is insured than would otherwise 

 exist. 



The earth's ocean of vapor therefore acts to 

 moderate the excessive temperatures that would 



