EFFECTS OF EVAPORATION ON CLIMATE. 5O 



lar. For the same reason the coolness of the early winter 

 is subdued and greatly modified by the heat given out by 

 large bodies of water in the act of freezing; and in this way 

 lakes and rivers, as well as the ocean, have a very import- 

 ant influence upon the climate of adjacent localities. Late 

 frosts are avoided and the intense cold is delayed until later 

 in the winter. This fact has given rise to the common 

 adage, "As the days begin to lengthen, the cold begins to- 

 strengthen," by which is meant that the cold does not be- 

 come severe until the beginning of the new year, when the 

 waters and the ground have become frozen and all their 

 latent heat has been given out. 



The heats of the summer are also much reduced in in- 

 tensity by the excessive evaporation from bodies of water and 

 from cultivated soil. It has been found that the climate of the 

 great western plains has been favorably modified by the in- 

 troduction of irrigation and the breaking up of the vast 

 areas of dry prairie which have been brought under tillage. 

 Evaporation of the water thus used, or gathered in the por- 

 ous soil by the rains, which are absorbed instead of flowing 

 as heretofore, from the dry hard surface in vast sheets and 

 floods to the nearest stream, both cools and moistens the 

 air; supplies the vapor for clouds which shade the soil and 

 temper the sun's rays, and which in turn descend again to 

 the soil whence they came in genial cooling showers. This 

 is a remarkable instance of how man's industry modifies, 

 climate by changing the natural conditions prevailing and 

 so fits the earth for his occupation and use. 



