of Heat by Gaseous and Liquid Mattel'. 97 



Table XXXII. —Formic Ether, 05 inch. 





Sum of 



Absorption 



ength of chambers. 



absorptions. 



of sum. 



2-8 46-6 



80-4 



64-4 



8-0 41-4 



82-4 



63-4 



17-8 31-6 



88-4 



60-3 



23-8 25-6 



92-8 



60-2 





Means 86'0 



62-07 



Table XXXIII. 



— Acetic Ether, 0*5 



inch. 



2-8 46-6 



77-2 



62-9 



80 41-4 



88-8 



64-6 



122 372 



96-7 



64-2 



15-4 34-0 



99-9 



62-4 



23-8 25-6 



103-6 



64-7 



36-3 13-1 



100-7 



64-8 



Means 94-5 63*9 



An inspection of the foregoing Tables discloses the fact that, 

 in the case of vapours, the difference between the sum of the 

 absorptions and the absorption of the sum is, in general, less 

 than in the case of gases. This resolves itself into the proposi- 

 tion that for equal lengths, within the limits of these experi- 

 ments, the sifting power of the gas is greater than that of the 

 vapour. The reason of this is that the vapours are examined in 

 a state of tenuity which is only g-\jth of that possessed by the 

 gases. Thus, no matter how powerful the individual molecules 

 may be, their distance asunder renders a thin layer of them a 

 comparatively open screen. 



§ 3. The entrance of a gas into an exhausted vessel is accompanied 

 by the generation of heat ; and the gas thus warmed, if a radia- 

 tor, will emit the heat generated. Conversely, on exhausting a 

 vessel containing any gas, the gas is chilled, and thus an exter- 

 nal body, which prior to the act of exhaustion possessed the same 

 temperature as the gas within the vessel, becomes, on the first 

 stroke of the pump, a warm body with reference to the gas 

 remaining in the vessel ; and if the external body be separated 

 from the cooled gas by a diathermic partition, it will radiate into 

 the gas and become chilled by this radiation. It was shown in 

 my second memoir* that this mode of warming and of chilling 

 a gas or vapour furnished a practical means of determining, 

 without any source of heat external to the gaseous body itself, 

 both its radiative and absorptive energy. For the sake of con- 



* Phil. Trans, part 1, 1862 ; and Phil. Mag. vol. xxiv. p. 337. 

 Phil. Mag. S. 4. Vol. 28. No. 187. Aug. 1864. H 



