THE BALANCE OF NATURE. 171 



intensely heated. This may give rise to an im- 

 pression that the sun's heating power has in- 

 creased. 



Certain causes may tend to temporarily prevent 

 the free interchange of heat energy that usually 

 exists between hot and cold parts of the earth. 

 There will thus result an increase of temperature 

 in one locality and a marked deficit in another, 

 which would thus give rise to the impression that 

 variations in the solar radiation existed, when, in 

 reality, such variations existed. 



In the case of the evaporation of water effected 

 by the sun, if the total value of the sun's heat be 

 constant it might at first sight be supposed that 

 the total quantity of evaporation must remain con- 

 stant, and that, therefore, the total quantity of 

 heat remaining the same, no change in its distri- 

 bution could effect a change in the amount of the 

 evaporation, and, consequently, in the value of the 

 rainfall. It must be remembered, however, in this 

 connection, that if circumstances existed in the 

 air of any locality by which during the time of 

 greatest heat the moisture was retained in the air 

 of such locality, and not be removed therefrom, 

 evaporation would necessarily be much smaller 

 than if such moisture were removed by any cause. 



