Btmospbere, 43 



arrangement of the atoms, new molecules are 

 formed, and a new substance is the result. 



About 99 1-2 per cent, of air is oxygen and 

 nitrogen and one-half per cent, is chiefly car- 

 bon dioxide. Carbon dioxide is a product of 

 combustion, decay, and animal exhalation. It 

 is poison to the animal, but food for the vege- 

 table. However, the proportion in the air is 

 so small that its baneful influence upon ani- 

 mal life is reduced to a minimum. The nitro- 

 gen is an inert, odorless gas, and its use in the 

 air seems to be to dilute it, so that man and 

 animals can breathe it. If all the nitrogen 

 were extracted from the air and only the oxy- 

 gen left to breathe, all animal life would be 

 stimulated to death in a short time. The 

 presence of the nitrogen prevents too much 

 oxygen from being taken into the system at 

 once. I suppose men and animals might have 

 been so organized that they could breathe pure 

 oxygen without being hurt, but they were not, 

 for some reason, made that way. 



Air contains more or less moisture in the 

 form of vapor; this subject, however, will be 

 discussed more fully under the head of evapo- 

 ration. The air at sea-level weighs fifteen 

 pounds to the square inch, and if the whole 

 envelope of air were homogeneous the same 

 in character it would reach only about five 

 miles high. But as it becomes gradually rare- 

 fied as we ascend, it probably extends in a 



