1862.] on the Motion of Glaciers. 417 



therefore subject to internal pressures and tensions. These internal 

 strains might become, from the sliding of the glacier, of enormous 

 intensity. When they became large enough to overcome the cohesion 

 of the particles to ea6h other, the mass, supposed always to be solid in 

 the sense which had been defined, would be broken into open fissures, 

 or crushed into numerous solid fragments. Its state of internal con- 

 straint would be thus relieved, its onward motion would be continued, 

 and the continuity of its mass and of its crystalline structure imme- 

 diately restored by regelation. The continuous motion of the glacier 

 would result from the repetition of this process, and the approximate 

 uniformity of the motion of the whole mass, notwithstanding the oppo- 

 sition of local obstacles, would result from the fact that those obstacles, 

 considered with reference to the whole glacier, would at all different 

 times be acting in the same manner. 



The two important points in this theory were the sliding of the 

 glacier, and its dislocation and regelation. The fact of the sliding 

 had been established by observation, and the nature of the motion 

 resulting from it had been explained by means of a simple and accu- 

 rate experiment. The property of regelation in ice, regarded as a 

 brittle crystalline substance, also rested on the clearest experimental evi- 

 dence. What more could be required to complete our theory of the 

 general and ordinary phenomena of the motion of glaciers? The 

 experimental results on which this view of the subject was founded 

 were clear and certain ; while the Viscous Theory was founded on an 

 assumed property of ice, which, so far from being proved, was never 

 even clearly defined. That theory the speaker doubted not had 

 effectively passed away, however some of its advocates might still be 

 disposed to cling to it. At the same time he should be sorry not to 

 do justice to the claims which its author had established to the best 

 thanks of all those who interest themselves in glacial phenomena. By 

 the number of Alpine objects and phenomena which he had observed, 

 and the force and vigour with which he had delineated them, he had 

 been the first to excite in this country an interest in the subject of 

 glaciers, which was still maintained both in a popular and scientific point 

 of view. Mr. Hopkins had always been a declared opponent, and he 

 hoped a candid one, of the Viscous Theory. He had never been satis- 

 fied with the principle on which it rested, and had always contended 

 that much of its mechanical reasoning, and the conclusions drawn 

 therefrom, were essentially erroneous. At the same time he considered 

 Principal Forbes, though not absolutely the first to observe certain 

 fundamental characters in the motion of glaciers, was undoubtedly the 

 first glacialist whose mind was fully imbued with a sense of the im- 

 portance of taking account of the molecular mobility within the mass 

 of a glacier in any theory of its motion ; and though the theory which 

 he was thus led to put forth was, in Mr. Hopkins's opinion, erroneous, it 

 had had the effect of leading the thoughts of other glacialists in the 

 same direction, and in this manner could hardly have failed to have 

 its influence in advancing the science, and in conducting to the dis- 



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