102 matured /^trades* 



there is no expansion, because there is no 

 depth of air; and the effect will be that the 

 expanded air will overflow toward the 

 mountain, and be deflected up its sloping side. 

 If we apply this same principle to the whole 

 mountain side we can see that there will be, 

 during the day, a constant current of air flow- 

 ing up the mountain. As night comes on this 

 upward movement will cease and there will be 

 a season of quiet until the earth has become 

 colder than the air, and we have a phenomenon 

 of exactly the opposite kind, when the air con- 

 tracts instead of expands, which produces a 

 downward current from the mountain top. 



These currents are as regular at certain sea- 

 sons of the year as the land and sea breeze. 

 Of course, they may be obliterated for the 

 time being, by the presence of a stronger wind 

 due to some other cause, such as during the 

 prevalence of a storm. In some of the regions 

 of California hottest during the day time, the 

 nights are made endurable, and even delight- 

 ful, by the cool breezes that sweep down from 

 the tops of the mountains. It often happens 

 that on the shady side of a high and steep 

 mountain where the sun's rays strike it so 

 obliquely, if at all, that the earth will be but 

 little heated, there will be a vast mass of cold 

 air stored up. After the valley has become in- 

 tensely heated by the sun there is an ascend- 

 ing current of air which in turn causes a down 



