Prof. J. Thomson on Regelation. 409 



remain until a force sufficiently great to break through it is applied. 

 But if the direction of the force resorted to can be relieved by any 

 hinge-like motion at the point of contact, then I think that the union 

 is broken up amongst the particles on the opening side of the angle, 

 whilst the particles on the closing side come within the effectual 

 regelation distance ; regelation ensues there and the adhesion is 

 maintained, though in an apparently flexible state. The flexibility 

 appears to me to be due to a series of ruptures on one side of the 

 centre of contact, and of adhesion on the other, — the regelation, 

 which is dependent on the vicinity of the ice surfaces, being trans- 

 ferred as the place of efficient vicinity is changed. That the sub- 

 stance we are considering is as brittle as ice, does not make any dif- 

 ficulty to me in respect of the flexible adhesion ; for if we suppose 

 that the point of contact exists only at one particle, still the angular 

 motion at that point must bring a second particle into contact (to 

 suffer regelation) before separation could occur at the first ; or if, as 

 seems proved by the supervention of the rigid adhesion upon the 

 flexible state, many particles are concerned at once, it is not possible 

 that all these should be broken through by a force applied on one 

 side of the place of adhesion, before particles on the opposite side 

 should have the opportunity of regelation, and so of continuing the 

 adhesion." 



The interpretation thus put by Prof. Faraday on his experiments 

 is not convincing to me ; but, on the contrary, I think the experi- 

 ments are in perfect accordance with my own theory, and tend to its 

 confirmation. My view of the phenomena of these experiments is as 

 follows : — The first contact of the two pieces of ice cannot occur 

 without impact and consequent pressure ; and, small as the total 

 force may be, its intensity must be great, as the surface of contact 

 must be little more than a geometrical point. This pressure produces 

 union by the process of melting and regelation described by me in pre- 

 vious papers. On the application of the forces from the two feathers, 

 at one side of the point of contact, tending to cause separation, 

 the isthmus of ice formed by the union of the two pieces comes to 

 act as a tie or fulcrum subject to tensile force ; and consequently a 

 corresponding pressure will occur at the side of the isthmus, far from 

 the feathers ; and that pressure will effect the union of the ice at the 

 side where it occurs. The tensile force, it may readity be supposed, 

 tends to preserve the isthmus, internally at least, in the state of ice, 

 whatever may be its influence on the external molecules of the isth- 

 mus, and to solidify such water as, having occupied pores in the in- 

 terior during previous compression, may now, by the linear tension 

 or pull, be reduced in cubical pressure or hydrostatic pressure, be- 

 cause the melting-point of wet ice is raised by diminution of pressure 

 of the water in contact with it*. The pull applied to the isthmus 



* How the surface of a bar of ice immersed in cold water, as distinguished 

 from the interior of the bar, may in respect to tendency cither to melt away, or 

 to solidify to itself additional ice from the water, be influenced by the applica- 

 tion of linear tension to the bar, I am not quite prepared to say positively. 

 The application of tension, whether linear, superficial, or cubical (that is, 



