94 Prof. Tyndall on Ice and Glaciers. 



ice, in contact with an internal cavity, may be liquefied by the 

 heat which has been conducted through the substance. The 

 water thus produced must have a temperatm-e of at least 32°; 

 but the ice has been the conductor of this temperature, and there- 

 fore cannot possibly be \inder 32°. Such ice, however, exhibits 

 all the phsenonieua of regelation. Slabs of it freeze together; 

 and if crushed and pressed, it can be welded and moulded in the 

 manner which I have more than once had occasion to describe. 

 These facts, I think, prove that the explanation of Prof. Porbes 

 does not apply to the phsenomena. I agree with him that " con- 

 tact without pressure" produces regelation, and, I think, for 

 reasons which have been already assigned. * 



There is one more point on which, in justice to myself and to 

 others, I feel called upon to say a few words. 



Since the publication of the paper by Mr. Huxley and myself*, 

 I have been reminded by more than one writer, that Prof. Forbes 

 had himself abandoned the theory of the veined structure which 

 was examined, and, I think, proved to be untenable, in the paper 

 referred to. Pi'of. Thomson, for example, states that, in his 

 thirteenth letter upon glaciers. Prof. Forbes " formally abandons 

 the notion that the blue veins are due to the freezing of infil- 

 trated waterf." 



The second section only — a very short one — of the thirteenth 

 letter refers to this subject. The title of that section is simply 

 " On the Conversion of Neve into Ice ;" and there is not a word 

 referring to a new theory of the veined structure. In the first 

 paragraph Prof. Forbes form ally mentions the subjects of which he 

 is going to treat : he says, " I shall now add a few observations 

 tending to throw light on two of the most obscure glacial phse- 

 nomena : first, the conversion of the snow of the neve into pure 

 ice; and secondly, on the apparent ejection of stones from the 

 surface of the glacier :" there is not a syllable about abiindoning 

 a theory which formed the most important part of his glacier 

 investigations. 



Before the publication of the paper by Mr. Huxley and myself, 

 every fact or speculation of any importance, in the work of Prof. 

 Forbes, was vividly present to my mind. With regard to the 

 conversion of neve into ice, I knew that he had expressed himself 

 thus : — " No doubt the transition is efi"ected in this way : — the 

 summer's thaw percolates the snow to a great depth with water; 

 the fi'ost of the succeeding year penetrates far enough to freeze 



* Phil. Trans, part 2, 1857. Phil. Mag. 1858, vol xv. p. 365. 

 t Phil. Mag. S. 4. vol. xvi. p. 465. 



