But the further experimental inquiry to which he has now sub jected the phenomena of regelation, appears to have conducted him to a view of them which is not altogether reconeileable with his previous inferences respecting the extension of the principle. He now asks, " Is this remarkable property peculiar to water, or is it general to all bodies! In respect of water, it certainly seems to offer us a glimpse into the joint physical action of many particles, and into the nature of cohesion in that body when it is changing between the solid and liquid state. I made some experiments on this point ;" which he proceeds to relate.
The metals bismuth, tin, and lead did not present the slightest trace of an action corresponding to regelation. Melted nitre appeared st times to Mow traces of the power ; but, on the whole, Dr. Faraday is inclined to think that the effects observed resulted from the circum stance that the solid rods experimented with had not acquired through out the freezing temperature. Nitre, however, he remarks, "is a body which, like water, expands in solidifying; and it may possess a certain degree of this peculiar power." Glacial acetic acid, he finds, is not merely without regelating force, but actually presents a contrast to it.
" Many results were tried (without much or any expectation), crys tals of them being brought to bear against each other by torsion force, in their saturated solutions at common temperatures. In this way the following bodies were experimented with :—Nitrates of lead, potassa, soda ; sulphates of soda, magnesia, copper, zinc ; alum ; borax ; chlo ride of ammonium ; ferro-prussiate of potassa ; carbonate of soda ; acetate of lead ; and tartrate of potassa and soda; but the results were all negative." Dr. Faraday's "present conclusion, therefore, is that the property' of regelation is special for water, and that the view " he has " taken of its physical cause "—" that a particle of water, which could retain the liquid state whilst touching ice only on one side, could not retain the liquid state if it were touched by ice on both sides, but became solid, the general temperature remaining the same"—" does not appear to be less likely now than at the beginning of this short investigation, and therefore has not sunk in value among the three explanations given," namely, his own and those of Professor James Thomson and Principal Forbes, respectively, which have been stated in our former account of this subject.
In the ' Proceedings of the Royal Society' for May 2, 1861 (vol. xi., pp. 198-204), appears a note by Professor James Thomson, in which he states that ho still adheres to the explanation of Principal Forbes's experiment, cited from a former paper by him in our article Ice, as mainly correct, though admitting of modification in reference to a point which seems to him to be as yet rather obscure :—" the influence, namely of the tension in the ice duo to its own weight, which makes it not be subject internally to simply atmospheric pressure." Professor Thomson also points out some additional conditions, almost necessarily present in the experiment, which, under his view of the plasticity of ice, would act in conjunction with those originally adduced, and would increase the rapidity of the union. But his principal object in this communication is to dissent from the interpretation given by Pro fessor Faraday of his recent experiments, as above, and to express the opinion that they are in perfect accordance with, and t.; r.l to con.
firm, his own theory, and its application to the various observed cases of the union of two pieces of moist ice when placed in contact. This he does, after describing Faraday's results, in these terms :—" 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 con sequent 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 previous 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 be readily supposed, tends to preserve the isthmus, inter nally at least, in the state of ice, whatever may be its influence on the external molecules of the isthmus, and to solidify such water as, having occupied pores in the interior during previous compression, may now, by the linear tension or pull, be reduced in cubical pressure or hydro. static pressure, because the melting-point of wet ice is raised by dimi nution of pressure of the water in contact with it. The pull applied to the isthmus thus appears to put it out of the condition in which my theory has clearly indicated a cause of plasticity, and, I presume, makes it cease, or almost entirely cease, to be plastic. I believe no plastic yielding of ice to tension has been discovered by observation in any case, and I think there are theoretical reasons why ice should be expected to be very brittle in respect to tensile forces. The isthmus then being supposed devoid of plasticity at its extended side, ultimately breaks at that side when the opening motion caused by the feathers has arrived at a sufficient amount to cause fracture ; and the ice newly formed on the compressed side comes now to act as a tie, instead of the part which has undergone disruptiou, and holds together the two pieces of ice, or serves as a fulcrum under tension to communicate a compressive force to the points of the two pieces of ice immediately beyond it; and so the rolling action with a constant union at the point of contact goes forward. It is to be observed, that the leverage of the
forces applied by the feathers is so great, compared with the distance from the fulcrum or tensile part of the isthmus, to the compressed part in process of formation at the other side as that the compression may usually be considered almost equal to the tension ; and the tension in the extended part cannot be of small intensity, being sufficient to break that side of the isthmus. In the experiments which gave flexible adhesion seemingly under tension, it is not to be admitted that tension was really the condition under which the ice existed at the places where the union was occurring. To apply a simple disruptive force to the whole isthmus of ice, it would be necbsaary to take very special precautions in order to arrange that the line of application of the dis ruptive forces should pass through the point of contact of the two pieces. If that were done, and the forces were gradually increased till the cohesive strength of the isthmus were overcome, it is clear that the two pieces of ice would separate altogether, and there would be no flexible adhesion ; but the flexible adhesion, when it occurs, is essen tially dependent on the existence of an intense pressure at the side of the isthmus remote from the line of the externally applied disruptive forces, or of the single force applied in sonic of the experiments to one only of the pieces, and resisted by the inertia of the other." While Dr. Faraday was engaged in the experimental corroboration of the cause to which he had originally assigned regelatioo, and in the limitation of the inferential views of its extension which he had first taken, a less conspicuous inquirer had been led to found upon those views and upon a known fact in the physical history of glass, a theory of the universality of regelation. This had been indicated, and the fact in question stated, at the end of our former account of the subject in the article Ice. In the Proceedings of the Royal Society' (vol. x., pp. 450-460), Dr. Faraday's Note on Regelation ' is followed by Mr. Brayley'e ' Notes on the Apparent Universality of a Principle analogous to Regelation ; on the Physical Nature of Glass ; and on the Proba bility of the Existence of Water in a state analogous to that of Glass.'* In the first of the three Notes' of which Mr. Brayley's paper consists, the view of the subject taken in Ice (col. 817) is resumed in greater detail, the facts there mentioned being regarded as " indicating the existence of a condition of matter which may be termed arrested liquidity, but yet is not, in the most perfect sense, solidity." It is assumed also to bo highly probable that the process by which two plates of polished plate-glass become ono is, in reality, analogous to that of regelation in ice, and finally dependent on the same principles, whatever their true character may be conceived or shall ultimately be determined to be. Facts are stated, from which it is inferred that the state of the interior portions of a plate of plate-glass is similar to that of glass in general at certain temperatures much below its fusing point, when it presents such remarkable characters of plasticity, tenacity, and ductility. These facts are stated to recall the view taken by Person, and adopted by Principal Forbes [Ice, col. 816 ; THAW], of the siud laritv of the liquefaction of ice to that of fatty bodies or of the metals, "which in melting pans through intermediate stages of softness or lloosity ;" and it is remarked, also, that Sir J. F. W. llerschel, when he terms regelation " a sort of welding" [I lam, col. 6031, appears to concur in this view. Mr. Brayley asks, to conclusion of this part of the sub ject, "Are all cases of the union of two apparently solid surfaces of the same substance by cohesive attraction cases of melting and rege Lstion, an infinitesimally thin film of liquid being womeutarily pro duced and as instantly solidified !" ; and having in discussing the philosophy of the union of two surfaces of glass followed the reasoning of Professor J. Thomson, on the cause of repletion, he stetter, nets withatanding, that he wishes to be understood as not adopting, exclusively, any existing theory on the subject. Admitting the operation of cohesivo attraction and consequent pressure in the first instance, the phenomenon, with respect to glass, it is shown, readily admits of explanation by the original view of 31r. Faraday with respect to ice. [ICE, col. 814.] Tho object of Mr. Dmyley's second 'Note' does not, strictly belong to the subject at present before ua, but to preserve the sequence of the whole inquiry in its bearing on the physics of water, we may mention that he finds reason to regard the molecular constitution of glass as being analogous to that of "water cooled below the freezing point, but still remaining liquid, until by a tremor, or the percussive contact of a solid body, or the mere contact of a crystal of ice, its temperature rises to 32°, and it becomes ice," or to that of a saturated solution of salt in hot water. " H so," he remarks, "glass will be a substance in which this state of arrested liquidity, or potential solidity, is perma. tient" Instructive parallels are also noticed between the crystallisation of water and that of glass and some other bodies, which are presented by the experiments of Gregory Watt, and Faraday.