320 Professor J. Tyndall, [Jan. 23, 



1857. 



WEEKLY EVENING MEETING, 



Friday, January 23. 



Sir Charles Fellows, Vice-President, in the Chair. 



Professor John Tyndall, F.R.S. 

 Observations on Glaciers. 



The speaker commenced, by stating the circumstances in which 

 the discourse of the evening originated. On the 6th of June, 1856, 

 he had given a lecture upon slaty cleavage, at which Mr. Huxley 

 was present. A short time afterwards his attention was drawn 

 to the observations of Professor J. D. Forbes on the veined 

 structure of glacial ice, by Mr. Huxley, who surmised that the 

 theory of slate cleavage might also apply to the ice structure. 

 On consulting the observations referred to, the probability of the 

 surmise was immediately perceived, and an arrangement was 

 made for a joint visit to the glaciers of Grindelwald, the Aar, and 

 the Rhone. This arrangement was carried out, and the subject 

 being a physical one, it fell to the lot of the speaker to follow it 

 up after his return to England. By reading, reflection, and 

 experiment, the boundaries of the investigation were extended, 

 until finally it embraced the main divisions of the problem of 

 glacier structure and motion. The results of the enquiry con- 

 stituted the subject of the evening's discourse. 



Certain phenomena connected with the motion of glaciers were 

 first passed under review. The power of a glacier to accommodate 

 itself to the sinuosities of its bed, the motion of the mass through a 

 valley of variable width, and a number of similar facts had been 

 adduced as evidence of the ductility of glaciers by M. Rendu 

 and others. To these evidences Professor J. D. Forbes added, in 

 1842, the important observation that the centre of a glacier moved 

 more quickly than its sides ; and he was led finally to a definite 

 expression of his views in the well-known Viscous Theory of glacial 

 motion. Numerous appearances, indeed, seem to favour this idea 

 of viscosity. 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 bending and 



