536 BESSEL ON BAROMETRICAL 



the latter, — the communications with the external air, — and the 

 temperature at different heights. Nor is the case examined 

 sufRciently simple to be a fit subject for strict calculation. But 

 to obtain an approximate view, I have proceeded from the rule 

 adopted in Prussian towns, which prescribes that in buildings, 

 which are to contain assemblages of people, not less than 100 

 cubic feet shall be allowed for each person. I have further di- 

 minished this space by one-third, and have taken Davy's expe- 

 riments*, which show that each person diminishes in one mi- 

 nute the nitrogen by 4*9 cubic inches, and the oxygen by 19*5 

 cubic inches, and increases the carbonic acid gas by 15 '4 cubic 

 inches. If we assume that the diminution of 9 cubic inches is 

 compensated by the necessary inpressing of the external air, 

 on account of the continual augmentation of temperature which 

 takes place, we find from these numbers that the proportion of 

 the three gases of the atmosphere given in the first article, viz. 



V = 0-78605 

 V, = 0-21325 

 Vi, = 0-00070 



will be altered in the course of an hour to 



V = 0-78719 

 V, = 0-20405 

 v,, = 0-00875. 



If we deduct from the mixed air the carbonic acid gas, the 

 proportion of the two other gases is at first as 0-7866 : 0-2134, 

 and at the end of an hour as 0*7941 : 0-2059. The calculated 

 result is not so dissimilar from the experiment as to afford! 

 a conclusion that the supposition on which the calculation isf 

 founded is incorrect. It would, indeed, seem as if the com-i 

 parison might rather be alleged against Dalton's view than] 

 in favour of it. I believe that if we desire decisive experiments 

 on this point, they would most easily be obtained by observing 

 the ingress, from pi'essure, of atmospheric air into a closed' 

 space not air-tight, and filled either with one of the constituents 

 of the air, or with both mixed in a different proportion from 

 that in which they exist in the atmosphere. In order to sim- 

 plify the experiments, and to obtain most conveniently the bases 

 of their calculation, the space ought not to be the interior of a 

 building, but that of a bell glass. | 



* According to Gilbert's calculation, Ann. dcr Physik, vol. xix. p. 312. ! 



