180 Mr. Dalton on the constitution of the atmosphere 
taken into consideration the variable force of gravity. At the 
height of 1400 miles the force of gravity is reduced one half, 
nearly ; on this account the elevation of the hydrogen atmo- 
sphere will be increased between 1 and 2 hundred miles 
more, so as to make it amount to twelve or thirteen hundred 
miles. The variation of temperature in ascending does not 
materially affect our views. 
Thus it appears that upon the assumption we have made, 
the hydrogen atmosphere must be 40 times the altitude of 
the carbonic acid atmosphere. If we had assumed the utmost 
height of the carbonic acid atmosphere less than 30 miles, 
the disproportion of the two heights would have been still 
greater ; and if more than 30 miles, it would have been less ; 
but in this case the absolute difference would be greater. 
If it be true that atmospheres have limits, or certain degrees 
of rarefaction beyond which they cannot be extended, it will 
produce certain modifications in the mixtures of the two 
gases in our tubes A and B, which will now require con- 
sideration. 
Suppose the cell 1000 to be that at the summit of the 
hydrogen column A, or where the hydrogen atmosphere 
terminated before any communication was made with the 
column B. Then, on opening the communication of that cell 
with the corresponding one of B, one half of the g ass would 
flow out as usual ; but the two cells, instead of being filled 
with the dilated gas, would only be half filled with it. The 
gas would fill the lower half of each cell, pressing upon the 
lower partition, and the upper half would exist as a void. 
The same remark would apply, but in a less degree, to the 
inferior cells 999 , 998 , &c. and it would not be till a descent 
