TRANSACTIONS OF THE SECTIONS. 25 



that viscid water could be produced in any large quantities desired, like as it is sup- 

 posed to be produced in small quantities in the hypothetical thin film at the surface 

 of hard ice — an inference which is plainly contrary to all experience, as no person 

 has ever, by any peculiar application of heat to, or withdrawal of heat from, a quan- 

 tity of water, rendered it visibly and tangibly viscid, so that it could be poured in a 

 thick state like honey. We even know that water may be cooled much below the 

 ordinary freezing-point, and yet remain fluid. 



Professor Forbes, however, although, in his recent writings, maintaining the views 

 just alluded to, had not rejected the author's theory as altogether unfounded. He 

 had rather admitted that it points out some of the causes which may impart to a 

 glacier a portion of its plasticity ; and also that it meets with verification to some 

 extent in the moulding of ice subject to rapid alternations of pressure under the 

 Bramah's press. 



Mr. Faraday, in his recently published ' Researches in Chemistry and Physics,' had 

 adhered to his original mode of accounting for the phenomenon he had observed, 

 and had developed farther the explanation of his ideas on the subject, and adduced 

 examples of the action of numerous other substances in passing from the liquid to 

 the solid, or from the solid to the liquid state, and also in passing from the liquid 

 to the gaseous state. Professor J. Thomson, however, considered that the general 

 bearing of all the phenomena adduced, is not to sustain the view of Mr. Faraday, 

 but to show that the particles of a substance, when existing all in one state only, 

 and in continuous contact with one another, or in contact only under special cir- 

 cumstances with other substances, experience a difficulty of making a beginning of 

 their change of state, whether from liquid to solid, or from liquid to gaseous, or pro- 

 bably also from solid to liquid. He did not admit that anything had been adduced 

 showing a like difficulty as to their undergoing a change of state when the substance 

 is present in the two states already, or when a beginning of the change has already 

 been made. He believed that when water and ice are present together, their free- 

 dom to change their state on the slightest addition or abstraction of heat is perfect. 

 He therefore could not admit the validity of Mr. Faraday's mode of accounting for 

 the phenomena of so called " regelation." 



Thus the fact of " regelation," which Professor Tyndall had taken as the basis of 

 his theory for explaining the plasticity of ice, did, in the author's opinion, as much 

 require explanation as the plasticity of ice which it was applied to explain. The 

 two observed phenomena, namely, the tendency of two separate pieces of ice to 

 unite when placed in contact, and the plasticity of ice, are, he believed, cognate re- 

 sults of a common cause, and are explained by the theory he had himself offered. 



The experiment by Professor Forbes adduced in opposition to the author's theory 

 was to the following effect : — 



Two slabs of ice, having their corresponding surfaces ground tolerably flat, on 

 being suspended in an atmosphere a little above the freezing-point, upon a horizontal 

 glass rod passing through two holes in the plates of ice, so that the plates may hang 

 vertically, and in contact with one another, were found in a few hours to be united 

 so as to adhere strongly together. This Professor Forbes had supposed would prove 

 that mere contact without pressure is sufficient to produce the union of two pieces 

 of moist ice. The author, on the contrary, explained the fact by the capillary forces 

 of the film of interposed water as follows : — First, the film of water between the 

 two slabs — being held up against gravity by the capillary tension, or contractile force 

 of its free upper surface, and being distended besides, against the atmospheric press- 

 ure, by the contractile force of its free surface round its whole perimeter — except for 

 a very small space at bottom, from which water trickles away, or is on the point of 

 trickling away — exists under a pressure which, though increasing from above down- 

 wards, is everywhere, except at that little space at the bottom, less than atmospheric 

 pressure. Hence the two slabs are urged towards one another by the excess of the 

 external atmospheric pressure above the internal water pressure, and are thus pressed 

 against one another at their places of contact by a force quite notable in amount. 



Secondly, the film of water existing, as it does, under less than atmospheric press- 

 ure, has its freezing-point raised in virtue of the reduced pressure; and it would 

 therefore freeze even at the temperature of the*surrounding ice, namely, the freezing- 

 point for atmospheric pressure. Much more will it freeze in virtue of the cold 



