186 HISTOEY OF THEEMOTICS. 



the caloric. But the doctrine of latent heat again modifies 1 the 

 hypothesis, and makes it necessary to include latent heat in the 

 calculation ; yet there is not, as Ave might suppose there would be if the 

 theory were the true one, any confirmation of the hypothesis resulting 

 from the new class of laws thus referred to. Nor does it appear that 

 the hypothesis accounts for the relation between the elasticity and the 

 temperature of steam. 



It will be observed that Laplace's hypothesis goes entirely upon the 

 materiality of heat, and is inconsistent with any vibratory theory ; for, 

 as Ampere remarks, " It is clear that if we admit heat to consist in 

 vibrations, it is a contradiction to attribute to heat (or caloric) a 

 repulsive force of the particles which would be a cause of vibration." 



An unfavorable judgment of Laplace's Theory of Gases is sug- 

 gested by looking for that which, in speaking of Optics, was men- 

 tioned as the great characteristic of a true theory ; namely, that the 

 hypotheses, which were assumed in order to account for one class of 

 facts, are found to explain another class of a different nature : the 

 consilience of inductions. Thus, in thermotics, the law of an intensity 

 of radiation proportional to the sine of the angle of the ray with the 

 surface, which is founded on direct experiments of radiation, is found 

 to be necessary in order to explain the tendency of neighboring bodies 

 to equality of temperature ; and this leads to the higher generaliza- 

 tion, that heat is radiant from points below the surface. But in the 

 doctrine of the relation of heat to gases, as delivered by Laplace, 

 there is none of this unexpected confirmation ; and though he explains 

 some of the leading laws, his assumptions bear a large proportion to 

 the laws explained. Thus, from the assumption that the repulsion of 

 gases arises from the mutual repulsion of the particles of caloric, he 

 finds that the pressure in any gas is as the square of the density and 

 of the quantity of caloric ; 8 and from the assumption that the tem- 

 perature is the internal radiation, he finds that this temperature is as 

 the density and the square of the caloric. 9 Hence he obtains the law of 

 Boyle and Mariotte, and that of Dalton and Gay-Lussac. But this view 

 of the subject requires other assumptions when we come to latent heat ; 

 and accordingly, he introduces, to express the latent heat, a new qu autity .' 

 Yet this quantity produces no effect on his calculations, nor does he apply 

 his reasoning to any problem in which latent heat is concerned. 



7 



Mic. Cel. t. v. p. 93. e P = 2 IT II K P V (1) p. 107. 



q' n (a)- (J c" (2) p. 108. l The quantity i, p. 113. 



