Clout>*3formaticm jSvaporation. 61 



is transparent, as well as much lighter than 

 the air at the surface of the earth. Being 

 lighter than the air, it rises when disengaged 

 and floats to the upper regions of the atmos- 

 phere. The atmosphere will contain a certain 

 amount of these transparent globules of mois- 

 ture in the spaces between its own molecules. 

 If the air is warm the molecules will be 

 farther apart and it will contain more moist- 

 ure than when it is cold. 



The process of evaporation is one of the 

 most important in the catalogue of nature's 

 dynamics. Without it there would be no 

 verdure on the hills, no trees on the plains, no 

 fields of waving grain, and no animal life upon 

 the land surface of the globe. Evaporation is 

 nature's method of irrigation, and the system 

 is inaugurated on a grand scale, so that there 

 are but few neglected spots upon the face of 

 the earth which moisture, carried up from the 

 great reservoirs of water, does not reach. The 

 rate of evaporation, other things being equal, 

 depends upon the extent of surface; therefore 

 a smooth surface like that of the lake or ocean 

 will not send up as much vapor from a given 

 area in square miles as an equal area of land 

 will do, when it is saturated with moisture, for 

 the reason that there is a much larger evapor- 

 ating surface on a square mile of land, owing 

 to its inequalities, than upon an equal area of 

 smooth water. Of course, if the earth is dry 



