Cambridge Philosophical Society. 607 



thus shown to be utterly incompetent to explain the insepara< 

 ble association of cohesion, chemical affinity and inertia with 

 gravitation ; while the existence of a vacuity between New- 

 tonian atoms, mainly relied upon as the basis of an argument 

 against their existence, is shown to be inconsistent both with 

 the ingenious speculation, which has called forth these re- 

 marks, and those Herculean "researches" which must per- 

 petuate his fame? 



LXXXVIII. Proceedi?igs of Learned Societies. 



CAMBRIDGE PHILOSOPHICAL SOCIETY. 

 [Continued from p. 79.] 

 Dec. 11, i^N the Motion of Glaciers. Bv William Hopkins, M.A., 

 1843. ^<-^ F.R.S., Fellow of the Society (Second Memoir). 

 In a previous memoir Mr. Hopkins had given the details of cer- 

 tain experiments, by which it was proved that ice will descend with 

 a very slow unaccelerated motion down an inclined plane, presenting 

 a surface like that of a common slab of paving-stone, at an angle 

 scarcely exceeding half a degree (and probably also at still smaller 

 angles), provided the lower surface of the ice in immediate contact 

 with the inclined plane be in a state of constant but slow disintegra- 

 tion. This experimental conclusion was brought forward in support 

 of tlie sliding theory of De Saussure, and the author endeavoured to 

 explain, according to that theory, different phsenomena connected 

 with the motion of glaciers. He there considered glacial ice as a 

 solid substance, having a certain degree of plasticiii/ and flexibility, 

 and the general mass of the glacier as a dislocated mass, the greater 

 motion of the central portion of the glacier being much facilitated by 

 these dislocations, though due partly, but in a comparatively small 

 degree, to the plasticity of the general mass. In the present memoir 

 Mr. Hopkins considers what would be the nature of the motion under 

 other hypotheses respecting the constitution of glaciers. (1.) The 

 lower part of a glacier may be conceived to be crushed, and conse- 

 quently disintegrated, by the superincumbent weight, each compo- 

 nent particle still retaining its soUdity ; or (2.) the whole mass may 

 be conceived to be plastic, and to move by a change of form, pro- 

 duced by gravity, in each component element. The author contends, 

 if either of these hypotheses were true, that, cceteris paribus, the more 

 superficial portion of the mass must tend to move the faster as the 

 depth of the glacier should be greater ; and that, consequently, the 

 part of the glacier near the upper extremity must generally tend to 

 move much faster than that near the lower extremity, assuming 

 always the whole, or much the greater part of glacial motion, to be 

 due to the plasticity of the mass, and to be independent of sliding 

 over its bed. But in such case it is manifest that the general state 

 of a glacier must be one of longitudinal compression, more particu- 

 larly during the summer months, when the motion is greatest. Now 

 the author contends that the general existence of transverse fissures 

 (at least during summer) is a conclusive proof against the existence 



