WATER. 



CHAPTEK XIX. 



RIVEKS AND FLOODS. 



Water covers such a large proportion of the 

 earth's surface and is such an important fac- 

 tor in the economy of nature that it becomes a 

 matter of interest to study the process of its 

 distribution. Water is to our globe what 

 blood is to our bodies. A constant circulation 

 must be kept up or all animal and vegetable 

 life would suffer. Here, as in every other 

 operation of nature, the sun is the great heart 

 and motive power that is active in the distri- 

 bution of moisture over the face of the globe. 



The total annual rainfall on the whole sur- 

 face of the earth amounts to about 28,000 

 cubic miles of water. Only about ene-fourth 

 of this amount ever reaches the ocean, but it 

 is either absorbed for a time by animal and 

 vegetable life or lifted through the process of 

 evaporation into the air as invisible moisture, 

 when it is carried over the region of rainfall 

 and there condensed into water and falls back 



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