16 THE ATMOSPHERE. 



51. With the addition of more oxygen, just enough to 

 form water, humin and then humic acid are formed. By 

 the addition of still more oxygen, the humus is turned, 

 successively, into geic acid, crenic acid, (krene, a foun 

 tain,) and apocrenic acid. Several of these are often 

 found, at once, in a mass of humus. 



52. If nitrogen be present in a moist, decaying mass 

 of substance, it unites with hydrogen, and forms ammo 

 nia ; and a part of the ammonia, acted upon by oxygen, 

 is gradually turned into nitric acid. 



CHAPTER III. 



THE ATMOSPHERE AND THE FORCES ACTING IN IT. 



53. The air forms about the earth a coat which we call 

 the Atmosphere, (vapor-ball,) and which extends upwards 

 forty or fifty, perhaps two or three hundred, miles from 

 the surface of the earth. 



54. The atmosphere is the great ocean in which all 

 animal and vegetable lives exist, and all the influences 

 and agencies which act upon them are at play. Among 

 those are light, by which all visible things are made 

 known to us ; heat, which pervades, and expands, and 

 moves all things, and is essential to the life both of animals 

 and of plants ; moisture, alike essential, and by which 

 nearly nil things are softened or mollified; sound, with 

 out whiv-li the earth would be a silent desert, and voice 

 and music, and the pleasure of social life could not 

 exist; and the wonderful cause of thunder and lightning, 

 which we call electricity. 



