THE AIR, 



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FIG. 2. STORM, WITH HEAVY RAIN. 



THE earth is surrounded in all directions by a covering of 

 air about forty miles in thickness, which bears about the 

 proportion to the earth itself that a coating one inch thick 

 would to a ball seventeen feet through, being about airoth of 

 its diameter. This air, though invisible, may at all times be 

 felt while in motion (such is the wind), and by rapidly passing 

 the hand backwards and forwards it may be perceived to 

 press against and slightly obstruct it ; this air is composed 

 of about twenty parts oxygen and eighty parts nitrogen. 



