418 Mr. Raukine on the Hypothesis of Molecular Vortices, 

 and, consequently, 



(31) 



dV 



This agrees with equation (16) of Professor Thomson's paper^ 

 if - in his notation =t—k. 



If the body be a perfect gas, then , 



The fact that the specific heats of all nearly perfect gases for 



unity of weight are inversely proportional to their specific gra- 



AM 

 vities, shows that -; — is the same for each of them*. 



(13.) Velocity of Sound in Fluids. — Let a denote the velocity 

 of sound in a fluid, and d . P the total differential of the pressure. 

 Then 



«=^(-^f)=^M-^-"-il)}- • (-) 



If it were possible to maintain the temperature of each particle 

 of the fluid invariable during the passage of sound, this velocity 

 would be simply ,/ dV \ 



V 



* The fact, recently ascertained by M. Regnault, that the specific heat 

 of atmospheric air a* constant pressure is sensibly constant throughout a 



great range of temperature, proves that at ordinary temperatuies — is an 



T 



inappreciably small fraction. (December 1853.) The specific heat of atmo- 

 spheric air was accurately predicted by means of these equations, three 

 years before M. Regnault ascertained it experimentally. 



>.(33) 



