510 Mr. Rankine on ike Centrifugal Theory of Elasticity, 



The second contains the algebraical investigation of the statical 

 relations between the heat and the elasticity of a gas. 



The third relates to temperature and real specific heat. 



The fourth treats of the coefficients of elasticity and dilatation 

 of gases, and compares the results of the theory with those of 

 M. Regnault's experiments. 



The fifth treats of the laws of the pressure of vapours at satu- 

 ration. 



The sixth relates to the properties of mixtures of gases of dif- 

 ferent kinds. 



I have endeavoured throughout this paper to proceed as directly 

 as possible to results capable of being compared with experiment, 

 and to carry theoretical researches no further than is necessary 

 in order to obtain such results with a degree of approximation 

 sufficient for the purpose of that comparison. 



Section I. On the Hypothesis of Molecular Vortices. 



(2.) Tlie hypothesis of molecular vortices may be defined to 

 be that which assumes — that 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 those atmospheres, 

 revolving or oscillating about their nuclei or central points. 



According to this hypothesis, quantity of heat is the vis viva 

 of the molecular revolutions or oscillations. 



Ideas resembling this have been entertained by many natural 

 philosophers from a very remote period ; but so far as I know. 

 Sir Humphry Davy was the first to state the hypothesis I have 

 described in an intelligible form. It appears since then to have 

 attracted little attention, until Mr. Joule, in one of his valuable 

 papers on the production of heat by friction, published in the 

 London and Edinburgh Philosophical Magazine for May 1845, 

 stated it in more distinct terms than Sir Humphry Davy had 

 done. I am not aware, however, that any one has hitherto ap- 

 pHed mathematical analysis to its development. 



(3.) In the present stage of my researches, there are certain 

 questions connected with the hypothesis as to which I have not 

 found it necessary to make any definite supposition, and which 

 I have therefore left indeterminate. Those questions are the 

 following. 



First. Whether the elastic molecular atmospheres are conti- 

 nuous, or consist of discrete particles. This may be considered 

 as including the question, whether elasticity is to a certain ex- 

 tent a primary quality of matter, or is wholly the result of the 

 repulsions of discrete particles. 



Secondly. Whether at the centre of each molecule there is 



