The Theory of Glacier motion. 131 



Ouand on agit sur un morceau de glace, qu'on le frappe, on 

 lui trouve une regidite qui est en opposition directe avec 

 les apparences dout nous venons de parler. Peut-etre que 

 les experiences faites sur de plus grandes masses donneraietit 

 d'autres residtats " (Phil Trans.j 1 846). 



In 1855, when Forbes wrote the article on glaciers in 

 the Enc. Britt., he spoke in very emphatic terms about his 

 theory, which he said was then very generally accepted. In 

 answer to the obvious fact that ice is superficially a brittle 

 solid, and does not seem readily plastic, he urged that sealing 

 wax, pitch, and other similar bodies adapt themselves with 

 time to the surfaces on which they lie even at atmospheric 

 temperatures, while they maintain at the same time the 

 quality of excessive brittleness under a blow or a rapid 

 •change of form. He went on to press that ice does not 

 pass at once and per saltum from the solid to the liquid 

 state, but absorbs its latent heat throughout a small range 

 of temperature (between 28°*4 and 32° of Fahrenheit) which 

 is precisely that to which the ice of glaciers is actually 

 •exposed ; that a glacier is not a crystalline solid like ice 

 tranquilly frozen in a mould, but possesses a peculiarly formed 

 and laminated structure, through which water enters (at 

 least for a great part of the year) into its intrinsic composition. 

 Putting together these facts, and admitting the differential 

 motion of the parts, which no one now contests, the quasi 

 fluid or viscous motion of the ice of glaciers is not a theory 

 but 2, fact ; a substance which is seen to pour itself out of 

 a large basin through a narrow outlet, without losing its 

 continuity, the different parts of which, from top to bottom, 

 and from side to centre, possess distinct though related 

 velocities, which moves over slopes inconsistent with the 

 friction between its surface and the ground on which it 

 rests — which surmounts obstacles, and even if cleft into two 

 streams by a projecting rock, instead of being thereby 

 anchored as a solid would necessarily be, re-unites its streams 



