Mr. Dalton on the constitution of the atmosphere. 181 
of 40 miles that the gas of one cell would be adequate to fill 
two cells, making the density in each the same as that in 
No. 1000 before the communication. In all that interval of 
40 miles the continuity of the atmosphere would be inter- 
rupted, each cell having a partial void, and the partition 
having a pressure on it from above, and none beneath. In 
like manner it might be shown that the carbonic acid atmo- 
sphere, were it alone, and subsequently made to communicate 
with empty cells, would be two miles below the summit of 
the atmosphere before one cell of gas could fill two cells.* 
After a complete equilibrium of intercourse had taken 
place between every two adjacent cells, let us next conceive 
all the horizontal partitions to be withdrawn from the two 
tubes, and consider what results will ensue. 
It is evident the descent of the upper part of the hydrogen 
column in each tube would be immediate, as there would be 
vacuous places to fill up in it. The same would take place 
with the carbonic acid column ; but the great body or weight 
of the mixed atmospheres would remain unchanged, except 
a slight condensation. The column of hydrogen in each tube 
would support 15 inches of mercury, and would in all respects 
resemble the upper half of the first column, A, of hydrogen 
gas, that supported 30 inches, excepting a slight difference 
occasioned by distance from the earth and temperature ; and 
the same may be observed of the carbonic acid column in 
each tube. But would this constitution of the mixture be 
* Query, might not the absolute height of an atmosphere of carbonic acid gas 
(or any other) be found, by perfectly exhausting a tall receiver, then letting in a 
small given portion of the gas, and finding by some chemical test that the gas 
existed in the lower but not in the upper portion of the receiver ? 
