Mr. J. Gill on Regelation. 121 



again and throws out the heat of liquidity of the frozen particles 

 into the surrounding ice. 



But in the case of instantaneous regelation in fragments of ice 

 merely touching each other, and even when floating in warm 

 water, there does not seem to be sufficient cause of the pressure 

 required by J. Thomson's explanation, even keeping in mind the 

 fact pointed out by Helmholtz, that the pressure is not equally 

 distributed over the whole of the two appressed surfaces, but 

 is concentrated on a few points of contact. Moreover, in the 

 case of wet surfaces, or when the fragments of ice are floating in 

 warm water, it is not easy to imagine how any pressure acting 

 on the pieces of ice should not at the same time act on the films 

 of water interposed between the surfaces of contact. 



It must therefore be allowed that, in such cases of regelation, 

 a sufficient cause of pressure is not apparent; yet Helmholtz 

 insists on the probability of pressure being the proximate cause 

 of regelation. He says, " I find the strength and rapidity of 

 the union of the pieces of ice in such complete correspondence 

 with the amount of pressure employed, that I cannot doubt that 

 the pressure is actually the sufficient cause of the union." On 

 this, Tyndall remarks that Faraday's contact-action would also 

 increase underpressure, from the greater extent of surface which 

 would be brought into play ; and he insists on the difficulty of 

 imagining any sufficient cause of pressure in the regelation of 

 fragments of ice floating in warm water which freeze together at 

 their points of contact " in a moment >J — convex surfaces freeze 

 together — "virtual points that touch each other, clasped all 

 round by the warm liquid which is rapidly dissolving them as 

 they approach each other." (Phil. Mag., December 1865.) 



Evidently the chief difficulty in the inquiry is to explain the 

 existence of a sufficient cause of pressure on the surfaces of solid 

 contact, while at the same time the liquid films enclosed between 

 these surfaces should be free from pressure; and as none of the 

 explanations hitherto given seem to satisfy these conditions, the 

 following hypothesis is offered as apparently meeting the phy- 

 sical requirements of the case. 



It seems probable that all bodies are continually sending off 

 particles of their substance into the surrounding atmosphere. 

 Ice certainly is known to evaporate at all temperatures, from the 

 freezing-point to the lowest temperature which has been ob- 

 served ; and the " disgregation " or " metamorphic " action con- 

 stituting the phenomenon may be supposed to involve an expen- 

 diture of heat (or other energy) equal to convert the particles of 

 solid ice into particles of gaseous steam, though we should ima- 

 gine the motion of the disgregated particles to be straight-line 

 motion, or the true motion of free gaseous particles in space, the 



