ICE AND GLACIERS. 149 



therefore be formed more rapidly in the surrounding water than 

 it was in the flask, where the side of the glass was interposed 

 between the ice. and the water. Even with a much smaller 

 weight the same result will follow in the course of an hour. 

 The broader the bridges become, owing to the freshly formed 

 ice, the greater will be the surfaces over which the pressure 

 exerted by the upper piece of ice is distributed, and the feebler 

 it will become ; so that with such feeble pressure the bridges 

 can only slowly increase, and therefore they will be readily 

 broken when we try to separate the pieces. 



It cannot, moreover, be doubted, that in Faraday's experi- 

 ments, in which two perforated discs of ice were placed in con- 

 tact on a horizontal glass rod, so that gravity exerted no pressure, 

 capillary attraction is sufficient to produce a pressure of some 

 grammes between the plates, and the preceding discussions show 

 that such a pressure, if adequate time be given, can form bridges 

 between the plates. 



If, on the other hand, two of the above-described cylinders of 

 ice are powerfully pressed together by the hands, they adhere in 

 a few minutes so firmly, that they can only be detached by the 

 exertion of a considerable force, for which indeed that of the 

 hands is sometimes inadequate. 



In my experiments I found that the force and rapidity with 

 which the pieces of ice united were so entirely proportional to 

 the pressure, that I cannot but assign this as the actual and 

 sufficient cause of their union. 



In Faraday's explanation, according to which regelation is due 

 to a contact action of ice and water, I find a theoretical difficulty. 

 By the water freezing, a considerable quantity of latent heat 

 must be set free, and it is not clear what becomes of this. 



Finally, if ice in its change into water passes through an inter- 

 mediate viscous condition, a mixture of ice and water which was 

 kept for days at a temperature of must ultimately assume 

 this condition in its entire mass, provided its temperature was 

 uniform throughout ; this however is never the case. 



As regards what is called the plasticity of ice, James Thomson 

 has given an explanation of it in which the formation of cracks 

 in the interior is not presupposed. No doubt when a mass of ice 

 in different parts of the interior is exposed to different pressures, 



