Mr. Dalton on the Constitution of the Atmosphere. 334 
of the Newtonian hypothesis, Mr. D. puts a case which he 
thinks has not before been considered, and which may assist 
us materially in forming a correct notion of such mixed at- 
mospheres. 
Two equal cylindrical pipes are conceived to be placed per- 
pendicular to the horizon, in contact, and of indefinite length, 
close at the bottom, and open at the top. These are supposed 
to be filled with two gases of different kinds, the one with car- 
bonic acid, and the other with hydrogen, in order to show the 
contrast more strikingly. The columns of gases are assumed 
each to be of the weight of 30 inches of mercury, and conse- 
quently will represent vertical columns of atmospheres of the 
respective gases equal in weight to like columns of the earth’s 
atmosphere. Mr. D. calculates from known principles that 
the column of carbonic acid gas will terminate at 30 or 40 
miles of elevation, or at least will become of such tenuity as 
that it may be disregarded. In like manner that of hydrogen 
will be found to become insignificant above 1200 miles of al- 
titude. The author then supposes that horizontal air-tight 
partitions are made across both tubes at any given intervals of 
distance, and that openings are made, so that the gases in the 
corresponding horizontal cells may communicate with each 
other; in which case each gas, as is well known, would divide 
itself equally between the two cells. For 30 or 40 miles both 
gases would be found in each cell; but for the rest of the co- 
lumn, namely, for 1000 miles or upwards, there would be no- 
thing but hydrogen in both cells. 
In the next place, Mr. D. conceives the horizontal partitions 
to be withdrawn, and considers what change would ensue, 
There would have been many cells about the summit of the 
carbonic acid atmosphere which, when opened for the purpose 
of communication, would part with half their contents to the 
collateral cells, but half the contents would not be able to fill 
the whole space of the cell, by reason that the gas was at its 
minimum density before. Hence the gas would be confined 
to the lower half of the cells, and there would be no carbonic 
acid in the upper parts. Of course when the partitions were 
removed, the carbonic acid in each cell would descend till it 
came in contact with the like gas of the inferior cell. Thus 
there would be a slight descent of the upper regions of car- 
bonic acid gas. ‘The same also would happen to the hydro- 
gen gas about the summit of its atmosphere, and a still more 
considerable descent would take place. Mr. D. seems to think 
there would be no material change in the mixed atmospheres 
afterwards. ‘Thus the two ioe atmospheres would exhibit 
equal volumes of each gas in the lowest cells, or at the surface 
of 
