i8o Mr, D ALTON 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. vii^i^Him 



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 gass 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 



