354 Mr. Rankiue on the Hypothesis of Molecular Vortices, 



half an incli or more iu diameter, may be examined, and it will 

 be found that the liquid is at no point in contact with the metal. 

 While, therefore, I agree with M. Buff in rejecting the explana- 

 tion which attributes the pheenomenon to a propping-up of the 

 drop by the caloritic rays, I think the facts justify the opinion 

 that an interval exists between the liquid and the metal. This 

 interval, as proved by Poggendorff, is sufficient to interrupt 

 an ordinary voltaic current ; but being filled with vapour at a 

 high temperature, it is quite conceivable, as surmised by M. 

 Buff, that a small portion of a strong current may pass through 

 it. M. Buffos observation, that the phrenomenon is not exhibited 

 except by those liquids which are capable of furnishing the ne- 

 cessary vapour, is also confirmatory of the above view : and the 

 fact that good conductors, which quickly supply the heat neces- 

 sary for evaporation, show the ph?enomenon better than good 

 radiators which do not furnish this supply, appears to be equally 

 corroborative of the opinion which I have ventured to espouse. 



XLVIII. On the Hypothesis of Molecular Vortices, or Centri- 

 fugal Theory of Elasticity, and its Connexion with the Theory 

 of Heat. By William John Macquorn Rankine, C.E., 

 F.R.SS.L. 4- E., F.R.S.S.A. ^-c* 



Section First. — Relations betiveen Heat and Expansive 

 Pressure. 



(1.) TN February 1850, I laid before the Royal Society of 

 J- Edinburgh a paper, in which the laws of the pressure 

 and expansion of gases and vapours were deduced from the sup- 

 position, that that part of the elasticity of bodies which depends 

 upon heat, arises from the centrifugal force of the revolutions of 

 the particles of elastic atmospheres surrounding nuclei or atomic 

 centres. A summary of the results of this supposition, which I 

 called the Hypothesis of Molecular Vortices, was printed in the 

 Transactions of this Society, vol. xx., as an introduction to a 

 series of papers on the Mechanical Action of Heat; and the 

 original paper has since appeared in detail iu the Philosophical 

 Magazine for December 1851. 



In that paper, the bounding surfaces of <itoms were defined to 



* Communicated by the Author, having been read to the Royal Society 

 of Edinburgh, December 15, 1851. 



[The following pa])er is republished by permission of the Coimcil of 

 the Royal Society of Edinburgh. It has received no alterations except 

 some verbal corrections, some additions to the forms of notation, and the 

 omission of some unnecessary repetitions. A few notes have been added, 

 which are distinguished by dates.] 



