318 PRESSURE IN THE AIR, 



to five miles only, are far too limited ; and 01* 

 the contrary, that it has the power of expand- 

 ing to an indefinite extent. 



Instead of the different gases of which the 

 atmosphere is composed, obeying the lav of 

 relative weight,* they act in direct opposition 

 to it. If gases acted by virtue of their weight, 

 instead of the atmosphere being one united 

 whole, composed of parts, whose essential pro- 

 perties are alike, but whose secondary, or che- 

 mical qualities, are different ; it would consist 

 of separated parts, out of which one disjointed 

 and tesselated whole was formed. Instead of 

 being, as it is found to be, of one uniform 

 homogeneous nature, combined together in a 

 manner the most intimate and imperceptible 

 the parts would separate into different layers, 

 or strata the lightest would form the summit, 

 the heaviest gas the base of the whole : we 

 would have hydrogen at the top oxygen and 

 nitrogen in the middle, and carbonic acid at the 

 bottom. If we were to have what we ac- 

 tually have not, the human race, in general, 



* I beg to observe, that as there is no such thing as abso- 

 lute weight; and as weight is ever to be considered the measure 

 of the density of one body, with relation to the rarity of ano- 

 ther, the terms relative and absolute, ought to be entirely aban- 

 doned ; and that when we speak of a body being heavy, or 

 Jight, it is either dense, or rarer, than another one. 



