184 Mr. Dalton on the constitution of the atmosphere. 
physical principle, that whenever two or more such gases or 
vapours as we have been describing are put together, either 
into a limited or unlimited space, they will finally be 
arranged each as if it occupied the whole space, and the 
others were not present ; the nature of the fluids and gravi- 
tation being the only efficacious agents. 
We may now apply this doctrine in considering the earth's 
atmosphere, on the supposition of its being in a quiescent ' 
state. The gases constituting it are azotic and oxygenous 
chiefly, a very small proportion of carbonic acid, and a small 
proportion of aqueous vapour. If we assume the weight of 
the atmosphere = so inches of mercury, and neglect the 
carbonic acid and aqueous vapour as inconsiderable in weight, 
we shall have of 30 = 6.3 inches for the weight of the 
oxygenous atmosphere, and of 30 = 23.7 inches for the 
weight, of the azotic atmosphere. For the weights of the 
whole atmospheres c, this view are proportional to the vo- 
lumes found at the surface of the earth, and totally inde- 
pendent of their specific gravities. The weight of the aqueous 
vapour atmosphere is variable, and may be on an average 
= .4 of an inch of mercury, and that of carbonic acid = .03 
of an inch of mercury. 
The limit of altitude in a full atmosphere (of 30 inches 
mercury ) of oxygen gas being assumed at 45 miles, that of 
an atmosphere of the same gas of 6.3 inches of mercury will 
be found by calculation on the above principles to be about 
38 miles, the atom of oxygen being 7 ; and that of azotic 
gas of 23.7 inches weight will be found 54 miles, if the atom 
of azote be taken as 5 ; but if the atom of azote be double 
this weight, as is supposed by many, but I think without 
