Prof. Tyndall on Ice and Glaciers. 



395 



as follows: — "Tyndall in particular maintained, and proved 

 by calculation and measurement, that the ice of a glacier does 

 not stretch in the smallest degree when subjected to tension — 

 that when sufficiently strained it always breaks ;" and he adds 

 in another place, that the property thus revealed establishes 

 " an essential difference between a stream of ice, and one of lava, 

 tar, honey, or mud." 



In the beautiful experiments of M. Tresca recently executed, 

 the power of ice to mould itself under pressure has been very 

 strikingly illustrated. Professor Helmholtz also, in the presence 

 of his audiences at Heidelberg and Frankfort, illustrated this 

 property in various ways. From snow and broken fragments 

 of ice he formed cakes and cylinders ; and uniting the latter, end 

 to end, he permitted them to freeze together to long sticks of 

 ice. Placing, moreover, in a suitable mould a cylinder of ice 



Fig. 2. 



Fig. 3. 



of the shape represented in fig. 2, he squeezed it into the cake 

 represented in fig. 3. In fact he corroborated, by a series of 

 striking experimental devices of his own, the results previously 

 obtained by myself. 



With regard to the application of these results to the pheno- 

 mena of glaciers, Professor Helmholtz, after satisfying himself of 

 the insufficiency of other hypotheses, thus finally expresses his 

 conviction : — " I do not doubt that Tyndall has assigned the 

 essential and principal cause of glacier-motion, in referring it to 

 fracture and regelation." 



It is perhaps worth stating that the term " regelation " was 

 first introduced in a paper published by Mr. Huxley and myself 

 more than seven years after the discovery of the fact by Faraday, 

 and that it was suggested to us by Dr. Hooker, now Director 

 of the Royal Gardens at Kew. As already remarked, the 

 formation and motion of glaciers, and other points of a kindred 



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