50 Royal Society. 



tion. A glacier, he contends, is not a mass of fragments or parallel- 

 opipedons ; neither is it a rigidly solid body ; and although it may 

 be extensively intersected by crevices, these " crevasses" are com- 

 paratively superficial, and do not disturb the general continuity of 

 the mass in which they occur. The water contained in these crevices 

 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 ope- 

 ration of a fluid pressure acting on a ductile or plastic material. 



March 5. — " 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 phasnomena 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. — " 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 

 situated at the upper part of the head as to admit of the animal's 

 breathing while only a small portion of its head is above the water. 

 In its descent through the skull, between the cranial and facial bones, 

 the tube is divided by a thin plate of bone into two nasal canals, 

 which form, below this partition, a single muscular tube opening at 

 its lower part into the pharynx by a constricted aperture, through 

 which the larynx projects upwards quite through the pharynx, di- 

 viding it into two channels. A series of pouches, five in number, 

 capable of great dilatation, and provided with a muscular apparatus 



