76 Review of the Controversy Regarding the Motion of the Glacier. 



pieces of ice in a melting state, if brought together, unite and become 

 one. It was therefore suggested by Tyndall, that this newly discovered 

 property of ice might be made to supersede the necessity of assuming, 

 with Forbes, a plasticity, of which there was no proof, in order to 

 account for the changes of form exhibited by the glacier in the course 

 of its progress. Tyndall argued, that the ice might be broken into 

 thousands of fragments, and that these would, under the pressure, 

 again unite and form a single mass, adapting itself in this way to any 

 new shape that might be requisite. By this means he endeavored to 

 explain the passage of the Mer de Glace, which at the junction of its 

 tributary stream is 2,597 yards wide, through the narrow gorge of 

 Trilaporte, the width of which is only 893 yards. 



But this glacial theory, if such it can be called, leaves the subject 

 in even a worse position than did the viscous theory of Forbes, 

 inasmuch as it supplies no moving force to account for the motion of 

 the ice. Granted, that the ice moves and breaks, regelation may 

 then account for cementation of the fragments into one mass. But by 

 denying the plasticity of ice, the very posssibility of its motion is 

 destroyed. Canon Moseley has shown* that a solid body, such as 

 glacier ice, would show no tendency to flow down the slope of the 

 Mer de Glace, but would stand as firmly on its base, unless urged by 

 a pressure from behind, as Avould a column of ice of one square foot in 

 area, and of the same height as the glacier. If then the ice breaks, 

 it is not plastic enough to flow, and if it is not plastic enough to flow 

 under the influence of gravitation, it must be urged on by some other 

 force, sufficient to overcome its high unit of shear. What that force 

 is, the theory in question does not suggest. If put forward as a help 

 to the viscous theory, it proves a dangerous ally. Regelation can not 

 occur without antecedent fracture, and fracture excludes the funda- 

 mental assumption of the viscous theory. 



Moreover, regelation does not occur unless the ice is in a melting state, 

 or at 32° (F.) of temperature, whereas a glacier is more solid during 

 the winter, when the thermometer ranges below the freezi-ng point, 

 than in the summer, when the ice is comparatively soft and thawing 

 over its whole surface. The fractures therefore produced by the 

 movement of the ice in winter should not close until the warmth of 

 spring has again raised the temperature of the ice to regelation point, 

 or 32° (F.) 



The experiments by which Prof. Tyndall has endeavored to prove 

 that ice can change its form by means of its property of regelation — 

 beautiful as they no doubt are— lie open to an objection which renders 

 thetu irrelevant. He has compressed snow under hydraulic power, 



* Proceedings of the British Naturalists'' Society, for 1869. 



