42 THE WORLD'S LUMBER ROOM. 



contains perhaps not more than a fifteenth of the saturating 

 quantity. If it were quite dry, no animal or vegetable could 

 exist in it. 



But besides preserving all living things from being dried 

 to chips, the moisture of the air also benefits us in another 

 way, by keeping the earth both cool and warm. By day it 

 acts as a screen to moderate the fierce heat of the sun, and 

 by night it serves as a blanket to keep in some of the heat 

 received during the day; and accordingly, where the air 

 is comparatively dry, as in the desert, the nights are in- 

 tensely cold while the days are scorching hot. 



When warm air laden with moisture rises into higher and 

 colder regions, or meets a current of colder air, some of the 

 moisture becomes liquid and condenses into a cloud of very 

 minute globules. This is what happens in the case of our 

 breath on a cold day; and though whales have been 

 popularly believed to suck in the jets of water which they 

 throw up, they, too, really discharge only breath, the moisture 

 of which condenses and falls down like a fountain from a 

 very fine rose, or a shower of rain from a cloud. 



And this brings us back to the shower, whose history we 

 are going to investigate. Part of it, 'then, has returned to the 

 air, part has been sucked up by the roots of trees, &c., and 

 the remainder sinks farther into the ground and goes on sink- 

 ing until it meets with something to stop it. In a very light, 

 porous soil, the water drains through so rapidly that none 

 but the least thirsty plants get enough to satisfy them, and 

 the ground is consequently barren. 



If, on the other hand, the soil be close and impervious, 

 like clay, very little water will sink in, and the greater part 



