Pxof. Faraday on Regelation. 147 
touch ; but rot with ice below the freezing-point, 7. e. with dry ice, 
or ice so cold as to be everywhere in the solid state. 
Three different views are taken of the nature of this phenomenon. 
When first observed in 1850, I explained it by supposing that a 
particle of water, which could retain the liquid state whilst touching 
ice only on one side, could not retain the liquid state if it were 
touched by ice on both sides; but became solid, the general tem- 
perature remaining the same*. Professor J. Thomson, who dis- 
covered that pressure lowered the freezing-point of water‘, attributed 
the regelation to the fact that two pieces of ice could not be made 
to bear on each other without pressure ; and that the pressure, how- 
ever slight, would cause fusion at the place where the particles 
touched, accompanied by relief of the pressure and resolidification of 
the water at the place of contact, in the manner that he has fully 
explained in a recent communication to the Royal Society{. Profes- 
sor Forbes assents to neither of these views ; but admitting Person’s 
idea of the gradual liquefaction of ice, and assuming that ice is 
essentially colder than ice-cold water, 7. e. the water in contact with 
it, he concludes that two wet pieces of ice will have the water be- 
tween them frozen at the place where they come into contact$. 
Though some might think that Professor Thomson, in his last 
communication, was trusting to changes of pressure and tempera- 
ture so inappreciably small as to be not merely imperceptible, but 
also ineffectual, still he carried his conditions with him into all the 
eases he referred to, even though some of his assumed pressures 
were due to capillary attraction, or to the consequent pressure of the 
atmosphere, only. It seemed to me that experiment might be so 
applied as to advance the investigation of this beautiful pomt in 
molecular philosophy to a further degree than has yet been done; 
even to the extent of exhausting the power of some of the principles 
assumed in one or more of the three views adopted, and so render 
our knowledge a little more defined and exact than it is at present. 
In order to exclude all pressure of the particles of ice on each 
other due to capillary attraction or the atmosphere, I prepared to 
experiment altogether under water ; and for this purpose arranged a 
bath of that fluid at 32°F. A pail, surrounded by dry flannel, 
was placed in a box; a glass jar, 10 inches deep and 7 inches wide, 
was placed on a low ‘tripod in the pail; broken ice was packed be- 
tween the jar and the pail; the jar was filled with ice-cold water to 
within an inch of the top ; a glass dish filled with ice was employed 
as a cover to it, and the whole enveloped with dry flannel. In this 
way the central jar, with its contents, could be retained at the un- 
changing temperature of 32° F. for a week or more; for a small piece 
of ice floating in it for that time was not entirely melted away. All 
that was required to keep the arrangement at the fixed temperature, 
was to renew the packing ice in the pail from time to time, and also 
* Researches in Chemistry and Physics, 8vo. pp. 373, 378. 
+ Mousson says that a pressure of 13,000 atmospheres lowers the temperature 
of freezing from 0° to —18° Cent. 
~ Phil. Mag. vol. xix. p. 391. 
-§ -Proceedings of the Royal Society of Edinburgh, April 19, 1858. — 
L 2 
