508 THE LIFE OF JAMES D. FORBES. [CHAP. 



Perhaps by long observations and well-made experiments 

 on ice and snow, we may be able to apprehend it, but 

 these first elements are still wanting." 1 



' I feel bound also to quote the significant expressions 

 of Captain Hall, pointing to the conception of a semi-fluid 

 glacier. " When successive layers of snow," he says 

 speaking of the Glacier de Miage, " often several hundreds 

 of feet in thickness, come to be melted by the sun and 

 by the innumerable torrents which are poured upon them 

 from every side, to say nothing of the heavy rains of 

 summer, they form a mass, not liquid indeed, but such as 

 has a tendency to move down the highly inclined faces 

 on which they lie, every part of which is not only well 

 lubricated by running streams resulting from the melting 

 snows on every side, but has been well polished by the 

 friction of ages of antecedent glaciers. Every summer a 

 certain but very slow advance is made by these huge, 

 sluggish, slushy, half-snowy, half-icy accumulations/' : It 

 is plain, I think, that the author had an idea that liquid 

 pressure might drag a mass over its rocky bed, which 

 would not move upon it as a solid/ 



* But such speculations could not pass into a theory until 

 supported by the definite facts of which M. Rendu deplores 

 the want. I too, like my predecessors, though indepen- 

 dently of them, had compared the movement of glaciers 

 to that of a ductile plastic mass, in 1841, when I spoke 

 of the Glacier of the Rhone as " spreading itself out much 

 as a pailful of thickish mortar would do in like circum- 

 stances/' 3 and again, when I likened the motion of glaciers 

 to that of a great river, or of a lava stream. 4 But I 



1 '"Le fait du mouvement existe, la progression des glaciers est 

 de"montree ; mais le mode est entierement inconnu. Peut-etre avec de 

 longues observations, des experiences bien iaites sur la glace et la neige 

 viendra-t-on a bout de la saisir ; mais ces premiers elements nous 

 manquent encore." ' Theorie des Glaciers, p. 90. 



2 'Patchwork, vol. i. p. 104, et seq. The whole passage, which is too 

 long to quote, gives an admirable picture of the glacier world/ 



8 ' Ed. Phil. Journal, January 1842.' 



* 'Edinburgh Review, April 1842, p. 54. Both these articles were 

 written in 1841.' 



