132 ICE AND GLACIEES. 



From the facts which I have brought before you it 

 results that the ice of a glacier flows slowly like the 

 current of a very viscous substance, such for instance 

 as honey, tar, or thick magma of clay. The mass of 

 ice does not merely flow along the ground like a solid 

 which glides over a precipice, but it bends and twists in 

 itself ; and although even while doing this it moves along 

 the base of the valley, yet the parts which are in contact 

 with the bottom and the sides of the valley are per- 

 ceptibly retarded by the powerful friction ; the middle 

 of the surface of the glacier, which is most distant both 

 from the bottom and the sides, moving most rapidly. 

 Rendu, a Savoyard priest, and the celebrated natural 

 philosopher Forbes, were the first to suggest the similarity 

 of a glacier with a current of a viscous substance. 



Now you will perhaps enquire with astonishment how 

 it is possible that ice, which is the most brittle and 

 fragile of substances, can flow in the glacier like a 

 viscous mass ; and you may perhaps be disposed to 

 regard this as one of the wildest and most improbable 

 statements that have ever been made by philosophers. 

 I will at once admit that philosophers themselves were 

 not a little perplexed by these results of their investiga- 

 tions. But the facts were there, and could not be got 

 rid of. How this mode of motion originated was for a 

 long time quite enigmatical, the more so since the 

 numerous crevasses in glaciers were a sufficient indication 

 of the well-known brittleness of ice; and as Tyndall 

 correctly remarked, this constituted an essential difference 

 between a stream of ice and the flow of lava, of tar, of 

 honey, or of a current of mud. 



The solution of this strange problem was found, as is 

 so often the case in the natural sciences, in apparently 

 recondite investigations into the nature of heat, which 

 form one of the most important conquests of modern 



