308 PRESSURE IN THE AIR, 



of air, is the cause of its elastic force being 

 greater at the surface, than at the top." It 

 appears to me, as far as I am able to com- 

 prehend Mr. DALTON'S opinion upon this 

 subject, that we think very much alike. It is 

 His opinion, that the different gases, which con- 

 stitute the mass of our atmosphere, are mecha- 

 nically combined together; arid this, he conceives 

 accounts for the uniformity with which they are 

 mixed together in it, first, because the parti- 

 cles of any individual gas, repel each other; 

 and secondly, because the particles of mixed 

 gases, neither attract nor repel each other ; they 

 are perfectly indifferent to each other, and are 

 not affected by their mutual proximity. When 

 they are mixed, they are diffused and joined 

 together, without separating, or uniting. Every 

 gas, by its elasticity,* or the repulsion of its 

 particles diffuses itself over the space in which 

 it is confined, neither attracting or repelling 

 each other, and therefore mixes without uniting 

 together. If, for example, there subsists on 

 the surfac^ of the earth, a column of oxygen 

 gas, it will rise to an indefinite height by its 

 elasticity ; if on the same surface, it be sup- 



* It is really vexatious to see the best informed of our 

 philosophers, ignorant of the distinction which exists between 

 things, and, consequently, using false terms to express the 

 phenomena which they want to describe ! 



