1858.] On Regelation. 377 



or T^oflth of a degree would be far less : and if we suppose that 

 only g^th of a piece of ice is brought into the condition of melt- 

 ing before the rest of the mass, and that the salts in that pro- 

 portion were originally in the whole of the water, then its quan- 

 tity there may be so small as to escape detection except by very 

 careful analysis. However, it would be desirable to examine 

 the water chemically which is produced by ice distinguished 

 by having in its interior much, that liquefies before the rest. 



It is easy to make ice perfectly free from air, and, as I believe, 

 from salts, by a process I formerly described*. It would be 

 interesting to see if such ice had within it portions melting at a 

 lower temperature than the general mass. I think it ought not. 



Ever truly yours, 



Royal Institution, Dec. 9, 1857. M. FARADAY. 



On Regelation. 



THE subject of regelation has of late years acquired very great 

 interest through the experimental investigations of Tyndall, 

 J. Thomson, Forbes and others, and in its present state will 

 perhaps justify a few additional remarks on my part as to the 

 cause. On the first observation of the effect eight years ago, 

 I attributed it 10 the greater tendency which a particle of fluid 

 water had to assume the solid state, when in contact with ice 

 on two or more sides, above that it had when in contact on one 

 side only f. Since then Mr. Thomson has shown that pressure 

 lowers the freezing-point of water J, and has pointed out how 

 such an effect occurring at the places where two masses of ice 

 press against each other, may lead first to fusion and then 

 union of the ice at those places ; and so he explains the fact of 

 regelation. Prof. J. D. Forbes does not think that pressure 

 causes regelation in this manner, though it favours it by moulding 

 the touching surfaces to each other. He admits Person's view 

 of the gradual liquefaction of ice||, and assumes that ice must 

 be essentially colder than ice-cold water, i. e. the water in con- 

 tact with it. 



* P. 373. t Pp. 373, 374. 



Belfast Society Proceedings, December 2, 1857. 



Royal Society Edinburgh Proceedings, April 19, 1858. 



|| Comptes Renclus, 1850, xxx. 526. 



