xv.] FORBES' GLACIER DISCOFERIES. o!3 



* 1. The "pure and simple" phenomenon of regela- 

 tion discovered by Faraday, and as I hold adequately 

 explained by me [Occcis. Papers, p. 228], has never been 

 proved to be an efficient agent in the functions of glaciers. 

 During summer, when they move fastest, it may be 

 doubted whether it comes into play at all, in consequence 

 of the gorged state of the capillary fissures of the glacier 

 and the constant trickling and drainage of water through 

 them. At the same time it is not part of my case to 

 deny that true regelation is a constant operation in a 

 glacier. If so, it helps to form the blue bands. 



' -2. Dr. TyndaD's so-called proofs that it is through 

 " fracture and regelation" that a glacier moulds itself to 

 its bed, are to my mind no proofs at all. They will be 

 found, I believe, to rest exclusively on experiments with 

 ice under Bramah's press. Now (a) these experiments so 

 much vaunted are in the first place not new. I find 

 them recorded in my Journal of 1846 as having been 

 successfully made by Dollfuss-Ausset. They were made 

 later by Schlagintweit : but (6) in the second place, I 

 attribute the plasticity of ice in this case to a cause 

 perfectly distinct from true regelation. It is beyond all 

 doubt due to the internal liquefaction and general soften- 

 ing of the bruised ice under intense pressure, on the prin- 

 ciples discovered and enforced by the Messrs. Thomson. 

 . I am not as yet inclined to allow that there is any 

 true analogy between this last case (6) and the mould- 

 ing properties of a glacier ; though here I fear that I 

 difier (as he knows) from Prof. Thomson. In order to 

 convert bruised ice into a homogeneous solid under 

 Bramah's press, the pressure must be applied and 

 relaxed with a certain suddenness. 1 I cannot admit that 

 this takes place in a glacier. The changes of pressure 

 within a glacier, in consequence of the slowness of its 

 motion, must be almost infinitely gradual, and therefore 

 plenty of time must elapse for the perfect restoration of 



1 Principal Forbes forgets here that the 'sudden 1 relaxation, 

 whether required or not, is always necessarily present in consequence 

 of the diminution of volume whenever the ice melts. F. G. T. 



I. I. 



