290 Macquorn Eankine on Molecular Vortices. 



The Hypothesis of Molecular Vortices. 



TO THE EDITOR OF THE EDINBURGH PHILOSOPHICAL JOURNAL. 



Sir, — As the article on Thermodynamics in the North British 

 Review" is perhaps the most complete history of that science 

 which has yet appeared, and is written with a scientific precision 

 which is unusual in journals not specially devoted to science, I wish 

 to correct an oversight that the Reviewer has committed in describ- 

 ing the " Hypothesis of Molecular Vortices," or " Centrifugal 

 Theory of Elasticity," as proposed by me in 1849.* He speaks 

 of atmospheres of ether surrounding nuclei of ordinary matter ; 

 whereas in the hypothesis, as I put it forward, the nuclei perform 

 the functions of ether, and the atmospheres those of ordinary 

 matter. Radiance is supposed to consist in oscillations of the 

 nuclei, transmitted in waves by means of the forces which they 

 exert on each other at a distance ; and thermometric heat is sup- 

 posed to consist in an agitation of the atmospheres, producing 

 outward pressure according to the known laws of centrifugal force. 

 Emission of radiance takes place when the atmospheres whirl 

 faster than the nuclei oscillate, so that the nuclei are undergoing 

 acceleration, and the atmospheres retardation ; absorption of radi- 

 ance takes place when the nuclei oscillate faster than the atmo- 

 spheres whirl, so that the nuclei are undergoing retardation and 

 the atmospheres acceleration. In perfect gases, the nuclei oscil- 

 late with little impediment from the atmospheres, and the trans- 

 mission of radiance is rapid ; in substances in a m.ore dense condi- 

 tion, each nucleus is, as it were, loaded with a part of its atmosphere 

 (like a pendulum in a resisting medium), and the transmission of 

 radiance is slower. It is this peculiar view of the respective 

 functions of the nuclei and the atmospheres, that constitutes the 

 main distinction between the hypothesis put forth by me and 

 other hypotheses involving atomic nuclei and atmospheres (as 

 that of Mossotti), or accounting for the phenomena of heat by 

 molecular motions (as that of Mr Herapath). 



Of course a mechanical hypothesis does not form an indispensable 

 part of Thermodynamics, more than of any other physical science ; 

 but if a hypothetical theory of Thermodynamics is to be used, it 

 appears to me that its fundamental principles must be such as I 

 have described. — I am, Sir, your most obedient servant, 



W. J. Macquorn Rankine. 



Glasgow, \st March 1864. 



* Transactions of the Royal Society of Edinburgh, 1850-51. 



