These facts have been applied by Professor Tyndall to explain the phenomena of the motion of glaciers. [Gsaciens, in NAT. HIST. Div.] This is a most important subject : the very introduction into the philosophy of glaciers of the principle of regclation, "without which," Professors Tyndall and Huxley remark, "it may be doubted whether the existence of a glacier would be at all possible," and the relation of which to glacier action the former was the first to discover, opens in itself a new field of investigation. For the details of this application we must refer to the original paper ; but the following is a summary view of the subject, derived partly from that and partly from a more brief account given in the ' Proceedings' of the Royal Institution, vol. ii. p. 322.
All the phenomena of motion in glaciers, on which the idea of the viscosity of ice has been based, are brought by such experiments as those recited above into harmony with the demonstrable properties of ice. The glacier valley is a mould through which the ice is pressed by its own gravity, and to which it will accommodate itself, while pre serving its general continuity, as the " band-specimens " (to use a term familiarly applied to rocks) do to the moulds made use of in the experiments. Two confluent glaciers unite to form a single trunk, by the regelation of their pressed surfaces of junction. Crevasses are closed up, and the broken ice of a cascade, such as that of the Tallfre or the Rhone, is recompacted to a solid continuous mass. "But if the glacier accomplish its movement in virtue of the incessant fracture and regelation of its parts, such a process will be accompanied by a crack ling noise, corresponding in intensity to the nature of the motion, and which would be absent if the motion were that of a viscous body. It is a well-known fact that such noises are heard, from the rudest crashing and quaking up to the lowest decrepitation, and they thus receive a satisfactory explanation.* It is manifest" also "that the continuity of the fractured ice cannot be completely and immediately restored after fracture. It is not the same surfaces that are regelated, and hence the coincidence of the surfaces cannot be perfect. They will Inclose for a Ciao copillary fissures, and thus the above theory accounts satisfactorily for the known structure of glacier-ice. Pr etoe'er Tyndall made an experiment on this point in which, by a gradually Increasing pressure. he produced in ice fissures of this description accurately resembling those made evident by the infiltration experi ments of M. Agaseix ui the glacier of the Aar.
Since the publication of Dr. Tyudall's researches, and that of the papers by Principal (late Professor) James D. Forbes and Professor James Thomson, the contents of which were stated in the former article, Dr. Faraday has entered into a new experimental investigation of it, which has appeared in the ' Proceedings' of the Royal Society, vol. x. p. 440-450, under the title of ' Note on llegelation,' in which he has also more fully described that property than in his previous papers. Of the now facts he has observed, and of the conclusions he has founded upon them, the following are the most important.
" Two p.ecca of thawing ice if put together adhere and become one; at a place where liquefaction was proceeding congelation suddenly occurs. The effect will take place in air, in water, or in vacuo. It will eccur at every point where the two pieces of ice touch, but not with ice below the freezing point, that is, with dry ice, or ice so cold as to be everywhere in the solid state." "Though some might think," Dr. Faraday resumes. "that Professor Thomson, in his last communication [IcE, cob S16], was trusting to changes of pressure and temperature so inappreciably small as to be not merely imperceptible, but also ineffectual, still he carried his con ditions with him into all the cases he referred to, even though some of his assumed pressures were due to capillary attraction, or to the con sequent pressure of the atmosphere only." In order to exclude all pressure of the particles of ice on each other due to capillary attraction or the atmosphere, Dr. Faraday prepared to experiment altogether under water, arranging a bath of that fluid, maintained at 32' Fehr., which by the method he employed it could be for a week or more. [THAW.] Two similar blocks of good Wenham-lake ice were placed in the water with their opposed faces about two inches apart, each being moored to a particular place, by woollen thread attached to pieces of lead, so that they were sunk entirely under the surface of the ice-cold water. If brought near to each other and then left unrestrained, they separated, returning to their first position with considerable force. If brought into the slightest contact, regelation ensued, the blocks ad hered, and remained adherent, notwithstanding the force tending to pull them apart. They would continue thus, even for twenty-four hours or more, until they were purposely separated, and would appear (by many trials) to have the adhesion increased at the points where they first touched, though at other points of the contiguous surfaces a feeble thawing action went on, causing a dissection of the ice, develop ing its mechanical composition, and showing it to consist of layers of greater and less fusibility, horizontally disposed in the ice whilst in the act of formation. " In this case, except for the first moment, and in a very minute degree, there was no pressure, either from capillary action or any other cause. On the contrary, a tensile force of considerable amount was tending all the time to separate the pieces of ice at their points of adhesion ;" where still the adhesion went on increasing. Arrangements were next made to ascertain whether anything like soft adhesion occurred, such as would allow slow change of position without separation during the action of the tensile force.- It was found that not the slightest motion of the blocks in relation to each other took place in the thirty-six hours during which the experiment was continued. " This result, as far as it goes, is against the necessity of pressure to regelation, or the existence of any condition like that of softness or a shifting contact." Torsion force was then employed as an antagonist to regelation. The ice-blocks being separate, were adjusted in the water so as to be parallel to each other, and about 16 inch apart. If made to approach each other on one side, by revolution in opposite directions on vertical axes, a piece of parer being between to prevent ice-contact, the torsion force set up caused them to separate when left to themselves ; but if the paper were away, and the ice pieces were brought into contact, by however slight a force, they became ono, forming a rigid piece of ice, though the strength seas, of course, very small, the point of adhesion and solidification being simply the contact of two convex surfaces of small radius. it was found, also, that there was no more tendency to a changing shape than in the case before examined. If the aeparating force were increased, but unequally, as respects the two pieces, then the congelation at the point of contact would give way, and the pieces of ice would move in relation to each other. Yet they would not separate. though the torsion force employed was constantly tending to separate them. If a clip of wood, applied to change the mutual position of the two pieces of ice without separating them, were re tained for a second undisturbed, then the two pieces of ice became fixed rigidly to each other in their new position, and maintained it when the wood was removed, but under a state of restraint ; and when sufficient force was applied, by a alight tap of the wood on the ice to break up the rigidity, the two pieces of ice would re-arrange themselves under the torsion force of their respective thread'', yet remain united; and, assuming a new position, would in a second or lees again become rigid, and remain inflexibly conjoined as before. By managing the continuous metier' of one piece of ice, it could be kept associated with the other by a flexible point of attachment for any length of time, could be placed in various angular positions to it, could be made (by retaining it quiescent for a moment) to assume and hold permanently any of these positions when the external force was removed, could be changed from that position into a new one, and, within certain limits, could be made to possess at pleasure and for any length of time either a flexible or a rigid attachment to its associated block of ice. In
observing these states, convex surfaces of contact are necessary, so that the contact may be only at one point. If there be several places of contact, apparent rigidity is given to the united mass, though each of the place.* of contact might be in a flexible, and, so to say, adhesive condition. " It is not at all difficult to arrange a convex surface, so that, bearing at two places only on the sides of a depression, it should form a flexible joint in one direction, and a rigid attachment in a direction transverse to the former." The following are Dr. Faraday's inductions from these results, which cannot be abridged :—" So regulation includes a flexible adhesion of the particles of ice, and also a rigid adhesion. The transition between these two states takes place when there is no external force like pressure tending to bring the particles of ice together, but, on the contrary, a force of torsion is tending to separate them ; encl, if respect be had to the mere point of contact on the two rounded surfaces where the flexible adhesion is exercised, the force which tends to separate them may be esteemed very great. The act of regelation cannot be considered as complete until the junction has become rigid, and there fore I think that the necessity of pressure for it is altogether excluded. No external pressure can remain (under the circumstances) after the first rigid contact is broken. All the forces which remain tend to separate the pieces of ice ; yet the first flexible adhesions and all the successive rigid adhesions which are made to occur are as much the effects of regelation as those which occur under the greatest pressure." " The phenomenon of flexible adhesion under tension looks very much like sticking and tenacity; and I think it probable that Professor Forbes will see in it evidence of the truth of his view. I cannot, however, consider the facts as bearing such an interpretation; because I think it impossible to keep a mixture of snow and water for hours and days together without the temperature of the mixed mass becoming uniform ; which uniformity would be fatal to the explanation. My idea of the flexible and rigid adhesion is this :—Two convex surfaces of ice come together; the particles of water nearest to the place of contact, and therefore within the efficient sphere of action of those particles of ice which are on both aides of them, solidify ; if the con dition of things be left for a moment, that the heat evolved by the solidification may be conducted away and dispersed, more particles will solidify, and ultimately enough to form a fixed and rigid junction, which will 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 among the particles on the opening aide of the angle, whilst the particles on the closing side come within the effectual regelation distance ; regulation 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 transferred as the place of efficient vicinity is changed. That the substance we are con sidering is as brittle as ice, does not make any difficulty 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 aide should have an oppor tunity of regelation, and so of continuing the adhesion." The changes of temperature and pressure in the process of regela tion, as here investigated, Dr. Faraday thinks, are too infinitesimal to go for anything; and in Illustration of this opinion, he describes an experiment. For this, however, as well as for the manipulation of the experiments in general, we must refer to his paper ; but an addendum to it we now cite, as it details an easy method of examining the various phenomena of regelation which have been ascertained. " Take a rather large dish of water at common temperatures. Prepare some flat cakes or bars of ice, from half an inch to an inch thick, render the edges round, and the upper surface of each piece convex, by holding it against the inside of a warm saucepan cover, or in any other way. When two of these pieces are put into the water they will float, having perfect freedom of motion, and yet only the central part of the upper surface will be above the fluid ; when, therefore, the pieces touch at their edges, the width of the water-surface above the place of contact may be two, three, or four inches, and thus the effect of capillary aetiou be entirely removed. By placing a plate of clean dry wax or spermaceti upon the top of a plate of see, the latter may be entirely submerged, and the tendency to approximation from capillary action converted into a force of separation., When two or more of such floating pieces of ice are brougl.1 together by contact at some point under the water, they adhere; first with an apparently flexible, and then with a rigid adhesion. When five or six pieces are grouped in a contorted shape, as an S, and one end piece be moved carefully, all will move with it rigidly ; or, if the force be enough to break through the joint, the rupture will be with a crackling noise, but the pieces will still adhere, and in an instant become rigid again. As the adhesion is only by points, the force applied should not be either too powerful or in the manner of a blow. I find a piece of paper, a small feather, or a camel-hair brush applied under the water very convenient for the purpose. When the point of a floating wedged shaped piece of ice is brought under water against the corner or side of another floating piece, it sticks to it like a leech ; if, after a moment, a paper edge be brought down upon the place, a very sensible resistance to the rupture at that place is felt. If the ice be replaced by like rounded pieces of wood or glass, touching under water, nothing of this kind occurs, nor any signs of an effect that could by possibility be referred to capillary action ; and finally, if two floating pieces of ice have separating forces attached to them, as by threads connecting them and two light pendulums, pulled more or less in opposite directions, then it will be seen with what power the ice is held together at the place of regelation when the contact there is either in the flexible or rigid condition, by the velocity and force with which the two pieces will separate when the adhesion is properly and entirely overcome." In Dr. Faraday's second published notice of regelation (` Exp. Res. in Chem. and Phys.; pp. 380, 381), ho had adduced the growth of crystals of camphor and of iodide of cyanogen, by the deposition of solid matter upon them from an atmosphere unable to deposit like solid matter upon the surrounding glass, except at a lower tempera ture ; and that of crystals in a solution, by the deposition of solid matter upon them which is not deposited elsewhere in the solution, to illustrate the extension of the principle of action which is manifested in regelation. In his reasoning on the nature of that principle, he also rested on the fact, that ice has the same property as camphor, sulphur, phosphorus, metals, &c., which cause the deposition of solid particles upon them from the surrounding fluid, that would not have been so deposited without the presence of the previous solid portions.