1863.] 681 



ment enabled the author to examine the influence of the sifting 

 which occurred in the first chamber on the absorption effected by 

 the second one. The thermal coloration of the various gases was 

 rendered very manifest by these experiments the heterogeneity of 

 the obscure calorific flux being demonstrated, and the selective action 

 of the gases on particular constituents of the flux exhibited. A 

 stratum of carbonic oxide 8 inches thick being placed in front of a 

 tube containing 41*4 inches of the same gas, those 8 inches inter- 

 cept 6*02 per cent, of the whole radiation ; the same 8 inches being 

 placed behind the column 41*4 inches in length, the absorption 

 effected is almost nil. So with carbonic acid : 8 inches in front 

 absorb 6 '25 per cent., while behind they absorb a scarcely mea- 

 surable quantity. Similar remarks apply to the other gases, the 

 reason manifestly being, that when the 8-inch stratum is in front, it 

 intercepts the main portion of the rays which give it its thermal 

 colour, while when it is behind, these rays have been in great part 

 withdrawn, and to the remainder the gas is transparent. 



From analogous reasoning we conclude that the sum of the ab- 

 sorptions of the two chambers, taken separately, must always be 

 greater than the absorption effected by a single column of gas of a 

 length equal to the sum of the two chambers. This conclusion is 

 illustrated in a striking manner by the results ; and it is further 

 found that if the mean of the sums of the absorptions of the two 

 chambers, taken separately, be divided by the absorption of the sum, 

 the quotient is the same for all gases. It is also to be inferred from 

 the foregoing considerations, that the sum of the absorptions must 

 diminish as the two chambers become more unequal in length, and 

 must be a maximum when they are equal. 



In these days a special interest attaches to the radiation from any 

 gas through itself, or through any other having the same period of 

 radiation. The author records the results of an elaborate series of 

 experiments on this point. The experimental tube, 4 9 '4 inches long, 

 was divided into two compartments by a partition of rock-salt. The 

 compartment nearest to the pile was filled with the gas which was 

 to act as absorber, while the chamber most distant from the pile 

 contained the gas which was to act as radiator. This latter gas was 

 warmed by the destruction of its own vis viva within the chamber.. 

 The radiation was what the author has called dynamic radiation. 



