NOTE ON THE PRINCIPLE OF REGELATION, ETC. 67 
the fact cited by Faraday and Tyndall, that dry, hard-frozen snow 
has not the property of becoming compacted into a snow-ball. The 
cases seem not to be comparable, because the brittleness of the con- 
stituent crystals of snow when in this state, its porous nature as a 
whole, and its being consequently pervaded by air, will prevent the 
required apposition of surfaces. Nor, as I conceive, is it proved by 
Prof. Tyndall’s most instructive experiment of crushing a ball of ice, 
cooled by carbonic acid and ether, into white and opaque hard frag- 
ments ; for in this also the required apposition of surfaces would 
be wanting. Further, it may be asked, whether this very experi- 
ment does not demonstrate the limitation of the lowering of the 
melting or freezing-point by pressure? and if so, there can be no 
tendency to union at 100° below freezing. 
In discussing the philosophy of the union of two surfaces of glass, 
I have alluded to the theory of regelation enunciated by Prof. J. 
Thomson ; but I wish to be understood as not adopting, exclusively, 
in these notes, any existing theory on the subject. Admitting the 
operation of cohesive attraction and consequent pressure in the first 
instance, the phenomenon, with respect to glass, readily admits of 
explanation by the original view of Mr. Faraday, which is, ‘that 
a film of water must possess the property of freezing when placed 
between two sets of icy particles, though it will not be affected by a 
single set of particles.” If we regard the two apposed surfaces of 
glass, each consisting of a thin stratum of particles, taken together, 
as representing the film of water, then the other strata of particles 
in contact with them respectively, and making up the entire thick- 
ness of the plate on each side, will correspond to the two sets of 
icy particles, the action of which by freezing the film of water effects 
‘ the union of the two portions of ice, and the phenomenon may be 
consistently explained in the terms of Mr. Faraday’s theory. And 
here we seem to find points of coincidence between cohesive force, 
as ordinarily considered, the principle of regelation, and that partic- 
ular view of the former which has been announced by Mr. Faraday 
in accounting for the phenomena presented by and connected with 
the latter. 
2. But we are led by the preceding facts and considerations to 
some further inferences, if not indeed to a definite hypothesis, upon 
the subject of the molecular constitution or physical nature of glass. 
Mr. Faraday’s view of it has been cited already; he regards glass, 
