199 



be impelled to freeze by the joint action of this condition with the 

 cold given out in the melting by pressure of the ice at the points of 

 contact where the two slabs are urged against one another. 



To this explanation of Principal Forbes' s experiment I still adhere 

 as mainly correct, though admitting of some further development 

 and slight modification in reference to a point to which I shall have 

 to make further allusion in what follows, and which seems to me to 

 be as yet rather obscure : the influence, namely, of the tension in 

 the ice due to its own weight, which makes it not be subject in- 

 ternally to simply atmospheric pressure : and though I shall also, in 

 what follows, point out some additional conditions, almost necessarily 

 present in the experiment, which, under my general view of the 

 plasticity of ice, would act in conjunction with those already adduced, 

 and would increase the rapidity of the union. 



Professor Faraday, holding it in view to remove the ground on 

 which my explanation of Principal Forbes' s experiment was founded, 

 has contrived and carried out a set of new and very beautiful experi- 

 ments from which the capillary action referred to Jias been com- 

 pletely eliminated, and he has still found the union of the ice to 

 occur, and to increase with time, and has met with a curious addi- 

 tional phenomenon of "flexible adhesion"*. In these experiments, 

 when two pieces of ice, rounded so as to be convex at their points 

 where mutual contact is to be allowed, are placed in water, and are 

 either anchored so as to be wholly under water, or are placed floating 

 when so formed that they can touch one another only under water, 

 and that, at the water surface, there shall be a wide space between 

 them so that there shall be no capillary action drawing them to- 

 gether, he showed that the pieces of ice, in either of these cases, if 

 brought gently into contact, will adhere together ; unless indeed the 

 movement bringing them into contact be so directed as to introduce 

 forces capable of tearing them apart again by obliquity of action, by 

 agitation of the water, or by other disturbances. He showed also 

 that, if when the two pieces of ice have become attached at their 

 point of contact, a slight force, such as may be given by one or two 

 feathers, be applied, tending to separate them, at one side of their 

 point of contact, they will roll round one another with a seemingly 

 flexible adhesion ; or that, if the point of a floating wedge-shaped 

 * Proceedings of Royal Society, April 26, 1860, vol. x. p. 440. 



