404 Prof. Tyndall on Ice and Glaciers. 



less to say that the fact is general — that a crystal of any salt 

 placed in a saturated solution of the salt always provokes crys- 

 tallization. Applying this fact to the minute film of water en- 

 closed between two appressed surfaces of ice, it seems to me in 

 the highest degree probable that the contact action of Faraday 

 will set in, that the film will freeze and cement the pieces of ice 

 together. 



Apart from the present discussion, the following observation 

 is perhaps worth recording. It is well known that ice during 

 a thaw disintegrates so as to form rude prisms whose axes are at 

 right angles to the planes of freezing. I have often observed 

 this action on a large scale, during the winters that I spent as a 

 student on the banks of the Lahn. The manner in which these 

 prisms are in some cases formed is extremely interesting. On 

 close inspection, a kind of cloudiness is observed in the interior 

 of a mass of apparently perfect ice. On closer inspection, this 

 cloudiness appears arranged in strise at right angles to the planes 

 of freezing, and when the direction of vision is across these planes 

 the ends of the strise are apparent. The spaces between the 

 strise are composed of clear unclouded ice. The objects which 

 produce this cloudiness are exceedingly small, but when duly 

 examined they turn out to be piles of minute liquid flowers, 

 whose planes are at right angles to the direction of the strise. 



John Tyndall. 



Royal Institution, 

 November 1865. 



Since writing the above, I have been favoured with a copy of a 

 Discourse delivered by Professor De la Rive, at the opening of 

 the forty-ninth meeting of the Societe Helvetique, which assem- 

 bled this year at Geneva. From this admirable resume of our 

 present knowledge regarding glaciers I make the following extract, 

 which, together with those from the lecture of Helmholtz, will 

 show sufficiently how the subject is now regarded by competent 

 men : — " Such, gentlemen," says M. De la Rive, "is a descrip- 

 tion of the phenomena of glaciers, and it now remains to explain 

 them, to consult observation, and deduce from it the fundamental 

 character of the phenomena. Observation teaches us that gra- 

 vity is the motive force, and that this force acts upon a solid body 

 — ice — imparting to it a slow and continuous motion. What 

 are we to conclude from this ? That ice is a solid which pos- 

 sesses the property of flowing like a viscous body — a conclusion 

 which appears very simple, but which was nevertheless announced 

 for the first time hardly five and twenty years ago by one of the 

 most distinguished philosophers of Scotland, Professor James D. 



