178 Mr. Dalton on the constitution of the atmosphere. 
same as before, namely, 30 inches of mercury ; half of which 
in each tube • would be carbonic acid, and the other half 
hydrogen. 
Very great differences would be found in the proportions 
of the two gases in ascending, viewing them either in regard 
to volume or to weight. In the lowest division, or No. 1, we 
should find equal volumes of carbonic acid and hydrogen. 
At the height of two miles, we should find about one volume 
of carbonic acid mixed with two of hydrogen ; at the height 
of four miles, the carbonic acid would be to the hydrogen as 
one to four, nearly ; and at the height of 40 miles, there would 
probably be no carbonic acid at all in either tube, but the 
hydrogen would there be of one half the density it was in 
No. 1. Above this, or above the limits of the carbonic acid 
atmosphere, wherever it might be, there would be nothing 
but hydrogen gas in each tube up to the limits of the hydro- 
gen atmosphere. 
The limits of the atmosphere having been mentioned, it 
may be proper to observe, that on the hypothesis of the 
density of any atmosphere diminishing in geometrical pro- 
gression to intervals of ascent in arithmetical progression, 
every atmosphere must be unlimited, or of infinite extent. 
But if any atmosphere is constituted of particles on the New- 
tonian hypothesis, it is obvious that such atmosphere must 
have a limit ; this limit will exist where the repulsion of two 
particles becomes equal to the weight of one of them. 
We have no data from which to determine the absolute 
height above the surface of the earth to which any one 
atmosphere can ascend ; but we can form a pretty accurate 
comparison of the relative heights to which two atmospheres 
