in determining Gaseous Combination. S^5 



upon which it rests, constitutes the most satisfactory explana- 

 tion hitherto proposed of this class of actions. As regards 

 the statical relations subsisting between gases and their bound- 

 ing solids, it is perfectly accordant with the analytical deduc- 

 tions of Laplace ^ ; and as respects an attractive force in so- 

 lids, inducing gaseous condensation on their surface, many 

 analogous facts assembled by Mitscherlichf may be added to 

 the numerous illustrations supplied by Dr. Faraday himself. 

 There is, however, one element of Dr. Faraday's reasoning, the 

 validity of which appears to me questionable. In considering 

 the mutual relations of mixed gases, he has assented to the 

 doctrine of Dr. Dalton in the form in which it was first pro- 

 posed, viz. " that gaseous molecules are only self-repulsive, or 

 that the particles of one gas are indifferent to those of another 

 gas." But this doctrine, soon after its announcement in the 

 " Manchester Memoirs," was strongly controverted ; and 

 among the objections raised against it, some were regarded 

 by Dr. Dalton himself as sufficiently cogent to induce him, 

 when treating the same topic in his " New System," to admit 

 " that the phgenomena of mixed gases may be accounted for 

 without the postulatum that their particles are mutually in- 

 elasticX" 



Without reiterating arguments long ago ably urged §, it 

 may be contended, that if heat be the sole cause of repul- 

 sion, as is implied in Laplace's theory of elastic fluidity, it is 

 impossible to admit that the atmosphere of heat surrounding 

 the atoms of any gas A, and constituting those atoms mu- 

 tually repulsive, can be indifferent to portions of the same 

 heat associated with the atoms of another gas B. Laplace, 

 therefore, in applying the analytical calculus to the condi-! 

 tion of mixed gases, and of gases mixed with vapours, re- 

 jects the supposed absence of repulsion between the mole- 

 cules of different gases as theoretically improbable, and as in- 

 consistent with known phaenomena ||. Finally, the admission 

 of repulsive forces between unlike, as well as like, gaseous 

 atoms, seems essential to the consistency of Dr. Faraday's 

 reasoning (in section 630). For " the deficiency of elastic 

 power" is there stated to influence union partly " by abstract- 

 ing a part of that power (upon which depends their elasti- 

 city) which elsewhere in the mass of gases is opposing their 



* La densite du gaz contenu dans iin vase est partout la meme, excepte 

 dans les points tres voisins des parois a una distance egale on plus petite 

 que le rayon de la sphere d'activite sensible des forces attractives et re- 

 \mh\\' ea.— Mec. CeL, liv. xii, § 1. torn. v. p. 93. See also p. 105. 



t Lchrbuch der C/ieniie, b. i. p. 397- 



% « New System," pp. 189 and 162. § Ibid. p. 150-193. 



II " Cette hypothese est bien pen naturelle, elle est d'ailleurs contraire 

 a plusieurs pheiiom^nes." — Mec. CeL, torn. v. p. 109 and 110. liv. xii. § 5. 



