124 RANKINE'S DYNAMICAL THEORY OF HEAT. 



development of the modern dynamical theory of heat in 

 almost all of its important applications, came as a surprise. 



Rankine founded his theory on the " Hypothesis of 

 Molecular Vortices " — " tJiat each atom of matter consists of 

 ■a nucleus or central point enveloped by an elastic atmosphere 

 which is retained in its position by attractive forces \ and that 

 ■the elasticity due to heat arises from the centrifugal force of 

 iJwse atmospheres revolving or oscillating about tJieir nuclei 

 or central points? 



"According to this hypothesis," Rankine proceeds, 

 *' quantity of heat is the vis viva of the molecular revolu- 

 tions or oscillations." 



" Ideas resembling this have been entertained by many 

 natural philosophers from a very remote period ; but, so far 

 as I know, Sir Humphrey Davy was the first to state the 

 hypothesis I have described in an intelligible form. It 

 appears since then to have attracted little attention till Mr. 

 Joule, in one of his papers on the production of heat by 

 friction, published in the London and Edinburgh Philoso- 

 phical Magazine for May, 1845, stated ft in more distinct 

 terms than Sir Humphrey Davy had done. I am not aware, 

 however, that anyone has hitherto applied mathematical 

 analysis to its development." 



It thus appears that Rankine acknowledges Joule's 

 priority in adding the definition of this hypothesis. That 

 he does not give Joule credit for the important de- 

 velopments he had made in determining the absolute 

 zero of temperature and the law of specific heats, must be 

 attributed to the fact that they were not included in the 

 paper to which Rankine refers, namely, that on " The 

 Changes of Temperature produced by the Rarefaction and 

 Condensation of Air," but were published previously, 

 and had not been seen by Rankine. 



