546 On the Constitution of mixed Gases, Bc. 
Voisier taught us there were two essentially 
distinguishable fluids to be found in it, and 
certain other substances accidentally or chemi- 
cally combined with them; it now appears there 
are at least four distinct elastic fluids found in 
every portion of atmospheric air subject to exa- 
mination. And these, for aught that appears, 
are totally independent one of another; so 
much that if anyone of them was wholly with. 
drawn from the surface of the earth, the rest 
would not at all be affected by the circumstance, 
either in their density or situation; or if an 
atmosphere of another kind were added to them, 
they would still retain their respectiye stations 
and densities, provided that added had no che- 
mical affinity for any one of them in the com. 
mon temperature. 
The azotic atmosphere is by far the largest 
and densest of them all: it supports the mercury 
in the barometer at a medium nearly 21. 2 
inches: it is the same in quantity all over the 
surface of the earth; because not condensible 
into a liquid form at any temperature found 
there. 
The oxygenous atmosphere is the next in quan- : 
tity; its pressure on the surface of the earth 
amounts to about 7, 8 inches at a medium; it 
is the same nearly in quantity every where, be- 
