The subsequent development of the subject by the moulding of ice into various forms by pressure is too well known to need dwelling upon here. In applying these results to glaciers, I dwelt with especial emphasis upon the fact that while the power of being moulded by pressure belonged in an eminent degree to glacier ice, the power of yielding, by stretching, to a force of tension, was sensibly wanting. On this point Prof. Helmholtz speaks as follows: ‘Tyndall in particular maintained, and proved by calculation and measurement, that the ice of a glacier does not stretch in the smallest degree when subjected to tension—that when sufficiently strained it always breaks;’ and he adds, in another place, that the property thus revealed establishes ‘an essential difference between a stream of ice, and one of lava, tar, honey, or mud.’
Fig. 7
Fig. 8.
In the beautiful experiments of M. Tresca recently executed, the power of ice to mould itself under pressure has been very strikingly illustrated. Professor Helmholtz also, in the presence of his audiences at Heidelberg and Frankfort, illustrated this property in various ways. From snow and broken fragments of ice he formed cakes and cylinders; and uniting the latter, end to end, he permitted them to freeze together to long sticks of ice. Placing, moreover, in a suitable mould a cylinder of ice of the shape represented in fig. 7, he squeezed it into the cake represented in fig. 8. In fact he corroborated, by a series of striking experimental devices of his own the results previously obtained by myself.
With regard to the application of these results to the phenomena of glaciers, Professor Helmholtz, after satisfying himself of the insufficiency of other hypotheses, thus finally expresses his conviction: ‘I do not doubt that Tyndall has assigned the essential and principal cause of glacier-motion, in referring it to fracture and regelation.’
It is perhaps worth stating that the term ‘regelation’ was first introduced in a paper published by Mr. Huxley and myself more than seven years after the discovery of the fact by Faraday, and that it was suggested to us by our friend Dr. Hooker, Director of the Royal Gardens at Kew. As already remarked, the formation and motion of glaciers, and other points of a kindred nature, had been referred to regelation long before I occupied myself with the cause of regelation itself. This latter question is not once referred to in the memoir in which the regelation theory was first developed.[33] The enquiries, though related, were different. In referring the motion of glaciers to a fact experimentally demonstrated, I referred it to its proximate cause. To refer that cause to its physical antecedents formed the subject of a distinct enquiry, in which, because of my belief in the substantial correctness of Faraday’s explanation, I took comparatively little part.