548 On the Constitution of mixed Gases, Fe. 
The hydrogenovs atmosphere is so small in 
quantity as scarcely to be at all appreciable ; yet, 
as various processes on the surface of the earth 
disengage this gas, and as it ‘mixes with all ‘the 
other gases constituting the atmosphere without 
combining with any, or rising above them, we 
ought to find a proper hydrogenous atmosphere. 
Perhaps we have got no tests for ascertaining 
very small quantities of it.. 
Lavoisier: describes the’ atmosphere to be 
* a compound of all the fluids which.are sus- 
** ceptible of the vaporous or permanently elas- 
tic state in the usual temperature, and wnder 
** the common pressure.” This last limitation 
should be omitted; he seems moreover to con- 
ceive that atmospheric pressure is the cause why 
water retains its liquid form at the common tem- 
perature: this notion is certainly wrong; were 
every atmosphere, except that of aqueous vapour, 
instantly annihilated, little addition would ‘be 
made to the aqueous atmosphere, because it al- 
ready exists in every place, almost entirely up 
to what the temperature will admit; the eva- 
poration of water would be essentially'the same 
in that case!as it is at present; only the full 
effect would take place in less time. In short 
this notion of pressure preventing the evapora- 
tion of liquids, which seems to have been taken 
$e 
