Mr. Dalton on the constitution of the atmosphere. 1 77 
an atmosphere of hydrogen gas in it, so as that it would 
support the mercury in the barometer at 30 inches. Let the 
tube B have an atmosphere of carbonic acid gas also capable 
of supporting 30 inches of mercury. Now supposing it pos- 
sible for the atmosphere to be for a few moments of uniform 
density throughout the column, and that density the same as 
at the surface of the earth, the height of the hydrogen 
atmosphere would be about 66 miles, and that of the carbonic 
acid about 3.3 miles ; or the heights would be in the ratio of 
20 to 1 nearly. Afterwards, when the atmospheres were 
expanded to their natural extent, equal elasticities of the two 
gases would also be at altitudes as 20 to 1 ; that is, if at two 
miles of elevation the carbonic acid atmosphere supported 
15 inches of mercury, that of hydrogen would support the 
same at 40 miles elevation. These are positions too obvious 
to be insisted upon. Conceiving now the atmospheres to 
have acquired their perfect equilibrium, or to be at rest in 
the respective columns, let numerous air-tight horizontal 
partitions be imagined across both tubes at equal intervals 
from the ground upwards. These intervals may be either 
small, as a foot, or larger, as a mile, as may suit our 
purpose. 
Let now a communication be opened between each two 
horizontal portions of the tubes, either by a perforation or a 
small tube, as represented in the annexed figure, ati, 2, 3,4, 
&c. Then it is well known that the two gases would inter- 
mix, and finally obtain such equilibrium, that one half of the 
gas at first in each division would pass into the opposite 
division, and the other half remain where it was. Hence, the 
whole weight of gases in each whole tube would be still the 
2 A 
MDCCCXXVI. 
