of Heat by Gaseous and Liquid Matter. 87 



Olefiant gas. Sulphuric ether. 



Thickness of 0'05 . . 5-37 Thickness of O05 . . 2*07 

 Thickness of 2 inches . 32*80 Thickness of 2 inches. 35*1 

 Sulphuric ether vapour, therefore, commences with an absorp- 

 tion much lower than that of olefiant gas, and ends with a higher 

 absorption. This is quite in accordance with the result esta- 

 blished in my second memoir*, that in a short tube the absorp- 

 tion effected by the sparsely scattered molecules of a vapour may 

 be less than that of a gas at a tension of an atmosphere, while in 

 a long tube the gas may be exceeded by the vapour. The deport- 

 ment of sulphuric ether indicates what mighty changes of climate 

 might be brought about by the introduction into the earth's at- 

 mosphere of an almost infinitesimal amount of a powerful vapour. 

 And if aqueous vapour can be shown to be thus powerful, the effect 

 of its withdrawal from our atmosphere may be inferred. 



§ 2. The experiments with the piston apparatus being com- 

 pleted, greater thicknesses of gas were obtained by means of the 

 composite brass experimental tube already referred to. The 

 arrangement adopted, however, was peculiar, being expressly 

 intended to check the experiments, which were for the most part 

 made by my assistants. The source of heat and the front cham- 

 ber remained as usual, a plate of rock-salt dividing, as in my 

 previous investigations, the front chamber from the experimental 

 tube. The distant end of the tube was also stopped by a plate 

 of salt ; but instead of permitting the tube to remain continuous 

 from beginning to end, it was divided, by a third plate of rock- 

 salt, into two air-tight compartments. Thus the rays of heat 

 from the source had to pass through three distinct chambers, 

 and through three plates of salt. The first chamber was always 

 kept filled with perfectly dry air, while either or both of the 

 other chambers could be filled at pleasure with the gas or vapour 

 to be examined. For the sake of convenience I will call the 

 compartment of the tube nearest to the front chamber the first 

 chamber, the compartment nearest to the pile the second chamber, 

 the term ' front chamber ' being, as before, restricted to that near- 

 est to the source. The arrangement is sketched in outline in fig. 2. 

 The entire length of the tube was 49'4 inches, and this was 

 maintained throughout the whole of the experiments. The only 

 change consisted in the shifting of the plate of salt S' which 

 formed the partition between the first and second chambers. 

 Commencing with a first chamber of 2*8 inches long, and a 

 second chamber 46*4 inches long, the former was gradually aug- 

 mented, and the latter equally diminished. The experiments 

 were executed in the following manner : — The first and second 

 chambers were thoroughly cleansed and exhausted, and the needle 

 * Phil. Trans, part 1, 1862 ; and Phil. Mag. vol. xxiv. p. 343. 



