[ 391 ] 
LII. Proceedings of Learned Societies. 
ROYAL SOCIETY. 
[Continued from p. 317.] 
November 24, 1859.—Major-General Sabine, R.A., Treasurer and 
V.P., in the Chair. 
4 pee following communication was read :— 
«On Recent Theories and Experiments regarding Ice at or 
near its Melting-point.”” By Professor James Thomson, Queen’s 
College, Belfast. 
My object in the following paper is to discuss briefly the bearings 
of some of the leading theories of the plasticity and other properties 
of ice at or near its melting-point, on speculations on the same sub- 
ject advanced by myself*, and, especially, to offer an explanation of an 
experiment made by Professor James D. Forbes, which to him and 
others has seemed to militate against the theory proposed by me, but 
which, in reality, I believe to be in perfect accordance with that theory. 
In the year 1850, Mr. Faraday+ invited attention, in a scientific 
point of view, to the fact that two pieces of moist ice, when placed in 
contact, will unite together, even when the surrounding temperature 
is such as to keep them in a thawing state. He attributed this pheno- 
menon to a property which he supposed ice to possess, of tending to 
solidify water in contact with it, and of tending more strongly to so- 
lidify film or a particle of water when the water has ice in contact 
with it on both sides than when it has ice on only one side. 
In January 1857, Dr. Tyndall, in a paper (by himself and Mr. 
Huxley) read before the Royal Society and in a lecture delivered 
at the Royal Institution, adopted this fact as the basis of a theory 
by which he proposed to explain the viscosity or plasticity of ice, 
or its capability of undergoing change of form, which was pre- 
viously known to be the quality in glaciers in virtue of which their 
motion down their yalleys is produced by gravitation. Designating 
Mr. Faraday’s fact under the term “ regelation,” Dr. Tyndall de- 
scribed the capability of glacier ice to undergo changes of form, as 
being not true viscosity, but as being the result of vast numbers of 
successively occurring minute fractures, changes of position of the 
fractured parts, and regelations of those parts in their new positions. 
The terms fracture and regelation then came to be the brief expres- 
sion of his idea of the plasticity of ice. He appears to have been led 
to deny the applicability of the term viscosity through the idea that 
the motion occurs by starts due to the sudden fractures of parts i 
themselves not viscous or plastic. ‘The crackling, he pointed out 
might, according to circumstances, be made up of separate starts 
distinctly sensible to the ear and to the touch, or might be so slight 
* Proceedings of Royal Society, May 1857. Also British Association Proceed- 
ings, Dublin Meeting, 1857, Also Philosophical Magazine, S. 4. vol. xiv. p. 548. 
+ Lecture by Mr. Faraday at the Royal Institution, June 7, 1850 ; and Report 
of that Lecture, Athenzum, 1850, p. 640. 
2D2 
