Prof. J. Thomson on Crystallization and Liquefaction, 395 



each chemical substance, but they are variable properties, depending 

 on the physical conditions in which the particles are placed, and the 

 chemical substances with which they are associated. 



" On the Aquiferous and Oviducal System in the Lamellibranchiate 

 Mollusks." By George Rolleston, M.D., F.L.S. ; and C. Robert- 

 son, Esq. 



"Notes of Researches on the Poly- Ammonias. — No. XVI. Tri- 

 atomic Ammonias. — No. XVII. Mixed Triammonias containing Mon- 

 atomic and Diatomic Radicals. — No. XVIII. Tetrammonium-Com- 

 pounds." By A. W. Hofmann, LL.D., F.R.S. 



" On the Contact of Curves ; and on the Calculus of Functions." 

 By William Spottiswoode, Esq., M.A., F.R.S. 



*' On the Action of Hydriodic Acid upon Mannite." By J. A. 

 Wanklyn, Esq., and Dr. Erlenmeyer. 



"The Lignites and Clavs of Bovey Tracey, Devonshire." By 

 William Pengelly, Esq., F.G.S. 



"The Fossil Flora of Bovey Tracey." By Dr. Oswald Heer. 



December 5, 1861. — Major-General Sabine, R.A., President, in the 



Chair. 



The following communications were read : — 



u On Crystallization and Liquefaction, as influenced by Stresses 

 tending to change of form in Crystals." By Professor James Thom- 

 son, Queen's College, Belfast. 



In a paper submitted to the Royal Society, and printed in the 

 Phil. Mag. for May 1862, I directed attention in a note (page 409), 

 to the question of how the surface of a bar of ice in ice-cold water, 

 as distinguished from the interior of the bar, may, by the appli- 

 cation of tension to the bar, be influenced in respect to tendency 

 either to melt away, or to solidify to itself additional ice from the 

 water ; but did not then venture to offer a positive answer. I pointed 

 out as a matter deserving of special attention, and as affording scope 

 for much additional theoretical and experimental investigation, the 

 distinction between the application to ice in ice-cold water, of stresses 

 tending to change its form, the stresses not being participated in by 

 the water ; and the application directly to the water, and through 

 that to the ice, of cubical or hydrostatic pressures or tensions, these 

 being participated in by the water and the ice alike ; and I pointed 

 out that the theory and quantitative calculation which I had origi- 

 nally given* of the effect of pressure in lowering the freezing-point 

 of water, or of diminution of pressure in raising it, applied solely to 

 effects of pressure communicated to the ice through the water, and 

 therefore equal in all directions, and equally occurring in the ice and 

 the water ; but that when changes of pressure in one or more direc- 

 tions are applied to the ice as distinguished from the water, the theory 

 does not apply in any precise way to determine the conditions of the 



* Transactions Roy. Soc. Edin. vol. xvi. part 5, 1849 ; and Cambridge and 

 Dublin Math. Journ. Nov. 1850. 



2D2 



