90 



NATURE FOR ITS OWN SAKE 



and it would inevitably fall to earth as a 

 shower. 



It is now generally held, I believe, that the 

 cause of clouds and rain is largely, if not en- 

 tirely, the cooling of air by expansion as it as- 

 cends ; and that intermingled cold and warm 

 air, and the chilling of air by cold bodies such 

 as mountain-tops, have little or no effect. Cer- 

 tainly the expansion of air is the final but not 

 always the most immediate cause. The chill- 

 ing produced by warm air driven against cold 

 air and its result may be frequently witnessed 

 in the winter season along the Atlantic coast of 

 North America. When the wind shifts to the 

 east we are all quite sure that thirty-six hours 

 at least will bring rain, and usually it is not so 

 long before the clouds begin to drift inland 

 from the sea. It is sometimes thought that 

 there is a storm on the ocean, and that it has 

 been travelling landward for hundreds of miles. 

 Occasionally that is the case, but more often 

 the clouds and rain are formed along our own 

 coast, and in this way : The sea is much warmer 

 than the land, especially in the Gulf Stream 

 region. Vast bodies of moist air overhanging 

 it are driven in upon the land by the eastern 

 winds. This land is ice-locked and very cold. 



