PROCEEDINGS 



OF 



THE ROYAL SOCIETY. 



1846. No. 63. 



February 26, 1846. 



The MARQUIS OF NORTHAMPTON, President, in tiie Chair. 



Lieut. Kay, R.N,, and Major Moore were elected Fellows of the 

 Society. 



" Illustrations of the Viscous Theory of Glaciers." By James 

 David Forbes, Esq., F.R.S. &c. Part HI. 



The author inquires, in this part of his paper, into the motion of 

 those comparatively small isolated glacial masses, reposing in the 

 cavities of high mountains or on cols, and called by De Saussure 

 glaciers of the second order. A glacier of this description in the 

 neighbourhood of the Hospice du Simplon, lodged in a niche on the 

 northern face of the Schcenhorn, immediately behind the Hospice, 

 and at an elevation of about 8000 feet above the sea, was selected 

 for observation. The average velocity of its descent was found to 

 be about one inch and a half in twenty-four hours : those parts in 

 which the slope was 20° moving with a velocity about one-third 

 greater than those in which the slope was 10°. The author next 

 enters into general views on the annual motion of glaciers, and on 

 the influence of seasons ; and gives tabular details of the observa- 

 tions made with reference to these questions at two stations ; the 

 one on the Glacier des Bossons, and the other at the Glacier des 

 Bois, which is the outlet of the Mer de Glace towards the valley of 

 Chamouni. In both these glaciers, the motion in summer exceeds 

 that in winter in a greater proportion as the station is lower, and 

 consequently exposed to more violent alternations of heat and cold. 

 He also found that the variations of velocity due to season are 

 greatest where the variations in the temperature of the air are 

 greatest, as in the lower valleys ; excepting that variations of tem- 

 perature below the freezing-point produce scarcely any appreciable 

 change in the rate of motion of the ice. He concludes with some 

 general illustrations of the plastic or viscous theory of glacier mo- 

 tion. A glacier, he contends, is not a mass of fragments or parallel- 

 opipedons ; neither is it a rigidly solid body ; and although it may 

 be extensively intersected by crevices, these " crevasses" are com- 



