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XLVII. On the Structure and Motion of Glaciers. By John Tyn- 

 DALL, F.R.S., Professor of Natural Philosophy, Royal Institu- 

 tion; and Thomas H. Hfxley, F.R.S., Fullerian Professor 

 of Physiology, Royal Institution*. 



§1. 



IN a lecture given at the Royal Institution on the 6th of June, 

 1856, by Mr. Tyndall, certain views regarding the origin of 

 slaty cleavage were brought forward, and afterwards reported in 

 the ' Philosophical Magazine ' for July. A short time subse- 

 quently the attention of the lecturer was drawn by Mr. HuxlejT 

 to the observations of Professor J. D. Forbes on the veined or la- 

 minar structure of glacier ice, and the surmise was expressed, that 

 the same explanation might apply to it as to slaty cleavage. On 

 consulting the observations referred to, the probability of the 

 surmise seemed apparent, and the result was a mutual aiTange- 

 ment to visit some of the Swiss glaciers, for the purpose of observ- 

 ing the structure of the ice. This arrangement was carried out, 

 the field of observation comprising the glaciers of Grindelwald, 

 the Aar, and the Rhone. After returning to England, the one 

 in whose department it more immediately lay, followed up the 

 inquiry, which gradually expanded, until at length it touched 

 the main divisions of the problem of glacier structure and motion. 

 An account of the experiments and observations, and our joint 

 reflections on them, are embodied in the memoir now submitted 

 to the Royal Society. 



§ 2. On the Viscous Theory of Glaciers. 

 A glacier is a mass of ice which, connected at its upper extre- 

 mity with the snow which fills vast mountain-basins, thrusts its 

 lower extremity into the warm air which lies below the snow-line. 

 The glacier moves. It yields in conformity with the sinuosities 

 of its walls, and otherwise accommodates itself to the inequalities 

 of the valley which it fills. It is not therefore surprising that 

 the glacier should have been regarded as an ice-river by those 

 who dwelt in its vicinity, or that tliis notion should have found 

 a place in the s])eculations of writers U])on the subject. The 

 statements of M. Rendu in connexion with this point are parti- 

 cularly distinct :—" There are," he writes, "a multitude of facts 

 which seem to necessitate the belief that the substance of gla- 

 ciers enjoys a kind of ductility which permits it to remodel itself 

 ou the locality which it occupies, to become thin and narrow, 

 and to elongate itself like a soft pastef," But this observer put 

 forward his speculations with great caution, and often in the 



♦ From the Pliilosophiral Transactions, Part II. for 18,57; having been 

 received and read ])y the Royal Society January 1.'), IHFiJ. 

 t 'I'h^oTie <hf (llnnorn (h In Hiivoii\ p. HI. 



