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II. " Observations on Glaciers." By JOHN TYNDALL, Esq., 

 F.R.S., and THOMAS H. HUXLEY, Esq., F.R.S. Received 

 January 15, 1857. 



(Abstract.) 



On the 6th of June, 1856, certain views were advanced by one of us 

 on the origin of slaty cleavage, and soon afterwards his attention was 

 drawn by the other to the observations of Prof. J. D. Forbes on the 

 structure of glacier ice, as suggesting the idea that the ice structure 

 might be due to the same cause as the slate cleavage. On consulting 

 the observations referred to, the lecturer at once perceived the proba- 

 bility of the surmise, and the consequence was a joint visit for a few 

 days to the glaciers of Grindelwald, the Rhone, and the Aar. The 

 subject being a physical one, it was followed up by the physicist on 

 his return from the Continent. Reading, reflection, and experiment 

 extended the inquiry until it embraced the main divisions of the 

 problem of glacial structure and motion ; and the paper now sub- 

 mitted to the Society contains an account of the investigation. 



The first division is devoted to the consideration of certain phe- 

 nomena connected with the motion of glaciers. The power of gla- 

 ciers to accommodate themselves to the sinuosities of the valleys which 

 they occupy, and the resemblance of their motion through such 

 valleys to the motion of a river, suggest ideas which find their 

 clearest expression in the viscous theory of glacier motion, pro- 

 pounded by Prof. J. D. Forbes. Numerous appearances indeed 

 seem to favour this notion. The aspect of many glaciers as a whole, 

 their power of closing up crevasses, and of reconstructing themselves 

 after having been precipitated down glacial gorges ; the beridings and 

 contortions of the ice, the quicker movement of the central portion 

 of the glacier where it is uninfluenced by the retardation of the 

 banks, are all circumstances which have been urged with such 

 ability as to leave the viscous theory without any formidable com- 

 petitor at present. To these may be added, the support which the 

 theory derived from its apparent competency to explain the laminar 

 structure of the ice, a structure which it is affirmed is impossible 

 of explanation upon any other hypothesis. 



