604 



paratively superficial, and do not disturb the general continuity of 

 the mass in which they occur. The water contained in these cre- 

 vices is only the principal vehicle of the force which acts upon it : 

 and the irresistible energy with which the whole icy mass descends 

 from hour to hour with a slow but continuous motion bespeaks of 

 itself the operation of a fluid pressure acting on a ductile or plastic 

 material. 



March 5, 1846. 



The MARQUIS OF NORTHAMPTON, President, in the Chair. 



" On the Physics of Media that are composed of free and perfectly 

 elastic Molecules in a state of Motion." By J. J. Waterson, Esq, 

 Communicated by Captain Beaufort, R.N., F.R.S. 



This memoir contains the enunciation of a new theory of heat, 

 capable of explaining the phenomena of its radiation and polariza- 

 tion, and the elasticity of various bodies, founded on the hypothesis 

 of a medium consisting of a vast multitude of minute particles of 

 matter endowed with perfect elasticity, and enclosed in elastic walls, 

 but moving in all directions within that space, with perfect freedom, 

 and in every possible direction. In the course of these motions, the 

 particles must be supposed to encounter one another in every pos- 

 sible manner, during an interval of time so small as to allow of their 

 being considered infinitesimal in respect to any sensible period ; 

 still, however, preserving the molecular vis viva constant and un- 

 diminished. 



The author then enters into extensive analytical investigations ; 

 first, of the conditions that determine the equilibrium of such a 

 homogeneous medium, as is implied by the hypothesis, and of the 

 laws of its elasticity ; secondly, of the physical relations of media 

 that differ from each other in the specific weight of their molecules ; 

 thirdly, of the phenomena that attend the condensing and dilating 

 of media, and of the mechanical value of their molecular vis viva ; 

 fourthly, of the resistance of media to a moving surface ; fifthly, of 

 the vertical equilibrium of a medium surrounding a planet and con- 

 stituting its atmosphere ; and lastly, of the velocity with which im- 

 pulses are transmitted through a medium so constituted. 



In an Appendix, the author enters into a full explanation of a 

 table of gases and vapours, drawn up with reference to the subjects 

 discussed in his paper. 



March 12, 1846. 



The MARQUIS OF NORTHAMPTON, President, in the Chair. 



" On the Blow-hole of the Porpoise." By Francis Sibson, Esq. 

 Communicated by Thomas Bell, Esq., F.R.S. 



The external opening of the air-passage of the porpoise is so 



