CHAPTER LIII 



THE ATMOSPHERE 



'TP you pass your hand quickly before your face, 

 A you feel a breath blow on your cheeks. This 

 breath is air. In repose it makes no impression on 

 us ; put in motion by the hand, it reveals its presence 

 by a light shock that produces an impression of 

 freshness. But the shock from the air is not al- 

 ways, like this, a simple caress. It can become very 

 brutal. A violent wind, which sometimes uproots 

 trees and overthrows buildings, is still air in mo- 

 tion, air that flows from one country to another like 

 a stream of water. Air is invisible, because it is 

 transparent and almost colorless. But if it forms a 

 very thick layer through which one can look, its 

 feeble coloring becomes perceptible. Seen in small 

 quantities, water appears equally colorless; seen in 

 a deep layer, as in the sea, in a lake, or in a river, 

 it is blue or green. It is the same with air : in thin 

 strata it seems deprived of color ; in a layer several 

 leagues in thickness, it is blue. A distant land- 

 scape appears to us bluish, because the thick bed of 

 intervening air imparts to it its own color. 



"Now air forms all around the earth an envelope 

 fifteen leagues thick. It is the aerial sea or atmos- 

 phere, in which the clouds swim. Its soft blue tint 

 causes the sky's color. It is in fact the atmosphere 



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