482 Mr. J. J. Waterston on the Theory of Sound. 



take for this measure only the density of caloric produced in a 

 space by the radiation of neighbouring bodies." 



P. Ill, line 19. "A supposition that it appears very natural 

 to admit is, that the action of the caloric of a molecule of gas on 

 the caloric of another piolecule, &c." 



P. 113, line 6. "We have supposed, in that which precedes, 

 that the caloric of a molecule was i-etained on it by the attraction 

 of the molecule, which experienced no sensible action except by 

 the repulsive force exerted on this caloric by the caloric of the 

 surrounding molecules." 



P. 117, hne 16. "It is then extremely probable that the at- 

 tractive force of the caloric of one molecule by another molecule 

 is insensible in the state-:of gas." 



Professor Thomson, who has written largely on the dynamical 

 theory of heat (Philosophical Magazine; Edinb. Phil. Trans.; 

 London Phil. Trans.), has the following in a memoir " On the 

 ThermalEflPectsofFluidsinMotion" (Phil. Trans. 1854,p. 361) :— 



"In the notes (Prof. Thomson's notes) to Mr. Joule's paper 

 on the Air-engine (Phil. Trans. 1852, p. 82), it was shown that 

 if Mayer's hypothesis be true, we must have approximately — 



Specific heat of air with constant pressure "2374 

 Specific heat of air with constant volume '1684 



because observations on the velocity of sound, with Laplace's 

 theory, demonstrate that A:= 1"410 within ^^^th of its own value. 

 Now the experiments at present communicated to the Royal 

 Society prove a very remarkable approximation to the truth in 

 that hypothesis* ; and we may therefore use these values as very 

 close approximations to the specific heats of air." 



The ratio k was found by Mi\I. Gay-Lussac and Welter to be 

 1'37, and by MM. Clement and Desormes 1"35. The same 

 experiments repeated by the author of the article ' Ilygrometry ' 

 in the Encyc. Brit., impressed him with the conviction that the 

 initial ratio was exactly |. 



Here, therefore, we have an instance of a zealous adherent and 

 expounder of the dynamical theory of heat showing such confi- 



* At p. 341, under the heading "Theoretical deductions from these Ex- 

 periments," Prof. Thomson arrives at the conclusion that air and carbonic 

 acid " evolve more heat than the amount mechanically equivalent to the 

 «ork of compression," thus representing the experiments as proving an 

 exception to Mayer's hypothesis. That such cooHng effects must take 

 place in consequence of the deviation from Mariotte's law discovered by 

 Regnault, if Mayer's hypothesis and the dynamic theory of heat hold 

 good, seems obvious enough (see Phil. Mag. vol. xiv. p. 279). So that 

 they are actually a dehcate test of the accuracy of that hypothesis ; and 

 taken as supplementary to Mr. Joule's previous experimental inquiries, 

 seem completely to establish it as a tlieory proved by induction. 



