The Phenomena of the Atmosphere. 79 



the proportion the heights of these bear to each 

 other in the small, the same proportion will be 

 certain to hold in the great, between a pillar of 

 water thirty-two feet high, and a pillar of air 

 that reaches to the top of the atmosphere, the 

 height of which we wish to know. Thus, for 

 instance, we find a certain weight of water 

 reaches one inch high, and a similar weight of 

 air reaches seventy-two feet high : this then is 

 the proportion two such pillars bear to each 

 other in the small. Now, if one inch of water is 

 equal to seventy-two feet of air, to how much air 

 will thirty-two feet of water be equal ? By the 

 common rule of proportion we readily find, that 

 thirty-two feet, or three hundred and eighty-four 

 inches of water, will be equal to three hundred 

 and thirty-one thousand seven hundred and 

 seventy-six inches, which makes something more 

 than five miles, which would be the height of the 

 atmosphere, were it homogeneous, or its density 

 every where the same as at the earth's surface, 

 where seventy-two feet of air were equal to one 

 inch of water. 



But this is not really the case ; for the air's 

 density is not every where the same, but de- 

 creases as the pressure upon it decreases; so 

 that the air becomes lighter and lighter the 

 higher we ascend ; and in the upper regions of 

 the atmosphere, where the pressure is scarcely 

 any thing at all, the air, dilating in proportion, 

 must be expanded to a surprising degree; and 



