382 Professors Tyndall and Huxley on the Structure 



the following passage : — " It will be understood that I do not now 

 suppose that there is any parallelism between the phfenomenon 

 of rocky cleavage and the ribboned structure of the ice." This 

 reads like the giving up of a previously held opinion ; the term 

 now being printed in italics by Professor Forbes himself. The 

 adoption of the viscous theory appears to have carried the renun- 

 ciation of this idea in its train. 



Later still, and from a source wholly independent of the former, 

 we have received additional testimony on the point in question. 

 The following quotation is from a letter, dated 16th November, . 

 1856, received by one of us from Professor Clausius of Zurich, 

 so well known in this country through his important memoirs 

 on the Mechanical Theory of Heat : — " I must now," writes M. 

 Clausius, " describe to you another singular coincidence. I had 

 read your paper upon the cleavage of rocks .... and it occurred 

 to me at the time that the blue veins of glaciers, which indeed I 

 had not seen, but which had been the subject of repeated con- 

 versations between Professor Studer of Berne, Professor Escher 

 von der Linth, and myself, might be explained in the same man- 

 ner. When, therefore, I reached the Rhone glacier for the first 

 time, I walked along it for a considerable extent, and directed 

 my attention particularly to the structure. I repeated this on 

 the other glaciers which I visited during my excursion. I did 

 not indeed pursue the subject so far into detail as to be able in 

 all cases to deduce the blue veins from the existing conditions 

 of pressure, but the correctness of the general explanation im- 

 pressed itself upon me more and more. This was particularly 

 the case in the glacier of the Khone, where I saw the blue bands 

 most distinctly, and where also their position harmonized with 

 the pressure endured by the glacier when it was forced to change 

 the direction of its motion. \ou can therefore imagine how 

 astonished I was to learn that at the same time, and on this very 

 •glacier among others, you had been making the same investiga- 

 tions." It ought also to be remarked, that a similar thought 

 occurred to Mr. Sorby, from whom after his return from Switzei'- 

 land one of us received a note, in which pressure was referred to 

 as the possible cause of the veined structure of glacier ice. 



A fine example of ice lamination is that produced by the 

 mutual thrust of two confluent glaciers. The junction of the 

 Lauter Aar and Finster Aar glaciers to form the glaciers of the 

 Unter Aar is a case in point, and the results obtained with a 

 model of this glacier were highly interesting. Fig. 9 is a sketch 

 of the trough in which the experiments were made. The branch 

 terminating at UL is meant to represent the Lauter Aar glacier ; 

 that ending at FN the Finster Aar branch. The point at A 

 represents the " Abschwiing," so often referi-cd to in the works 



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