817 



ICE. 



ICE. 



818 



an insignificant thaw at the surface, which, therefore, wastes eren thour/h 

 the water be what is called ice-cold.' Now, the conclusion arrived at, 

 namely, that a quantity of viscid water could be produced in the 

 manner described, is, I am satisfied, quite contrary to all experience. 

 No person has ever, by any peculiar application of heat to, or with- 

 drawal of heat from, a quantity of water, rendered it visibly and 

 tangibly viscid. We even know that water may be cooled much below 

 the ordinary freezing point and yet remain fluid." 



Professor Forbes regards Mr. Faraday's fact of regelation as being 

 one which receives its proper explanation through his theory described 

 above ; and, in confirmation of the supposition that ice has a tendency 

 to solidify a film of water in contact with it, and in opposition to the 

 theory given by Professor J. Thomson, that the regelation is a conse- 

 quence of the lowering of the melting-point in parts pressed together, 

 he adduces an experiment made by himself. He states that mere 

 contact without pressure is sufficient to produce the union of two 

 pieces of moist ice, and then describes as follows his experiment by 

 which he supposes that this is proved : " Two slabs of ice, having 

 their corresponding surfaces ground tolerably flat, were suspended in 

 an inhabited room upon a horizontal glass rod passing through two 

 holes in the plates of ice, so that the plane of the plates was vertical. 

 Contact of the even surfaces was obtained by means of two very weak 

 pieces of watch-spring. In an hour and a half the cohesion was so 

 complete that, when violently broken in pieces, many portions of the 

 plates (which had each a surface of twenty or more square inches) 

 continued united ; in fact, it appeared as complete as in another expe- 

 riment, where similar surfaces were pressed together by weights." He 

 concludes that the effect of pressure in assisting " regelation " is 

 principally or solely due to the larger surfaces of contact obtained by 

 the moulding of the surfaces to one another. 



Professor J. Thomson has himself repeated this experiment, and has 

 found the results described by Professor Forbes to be fully verified. 

 It was not even necessary to apply the weak pieces of watch-spring, as 

 he found that the pieces of ice, on being merely suspended on the glass 

 rod in contact, would unite themselves strongly in a few hours. This 

 fact Professor Thomson explains by the capillary forces of the film of 

 interposed water, as follows : Firstly, 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 pressure, by the same 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 downwards, is everywhere, except at that little space at bottom, 

 leu than the 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 its amount. 

 If, for instance, between the two slabs there be a film of water of such 

 size and form as might be represented by a film one inch square, with 

 its upper and lower edges horizontal, and with water trickling from its 

 lower edge, it is easy to show that the slabs will be pressed together by 

 a force equal to the weight of half a cubic inch of water. But so small 

 a film as this would form itself, even if the two surfaces of the ice 

 were only very imperfectly fitted to one other. If, again, by better 

 fitting, a film be produced of such size and form as may be represented 

 by a square film with its sides 4 inches each, the slabs will be urged 

 together by a force equal to the weight of half a cube of water, of 

 which the side is 4 inches ; that is, the weight of 32 cubic inches of 

 water, or 1'15 pound, which is a very considerable force. Secondly, 

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

 pressure, has ita freezing-point raised in virtue of the reduced pressure. 

 Much more, he adds, will it freeze in virtue of cold given out in the 

 melting by pressure of the ice at the points of contact, where, from the 

 first two causes stated above, the two slabs are urged against one 

 another. 



The different explanations and interpretations which have been enun- 

 ciated of the facts of regelation have been stated in this article partly 

 in the words of their authors, and partly in those of Professor James 

 Thomson, by whom the subject has been most recently treated. 

 References to some .of the original memoirs will be found in his 

 paper in the ' Proceedings of the Royal Society ' (vol. x.), for Nov. 24, 

 1859, pp. 162-160; and others will be indicated in the sequel of this 

 article. 



\t is manifest that the subject of regelatiou is one of great import- 

 ance in physics and in the history of nature, being connected with that 

 of the mutual relations of the different states of aggregation in which 

 the same species of ponderable matter the same substance, chemically 

 speaking can exist, and also with those " hidden and unseen motions," 

 to use the language of Boyle, by which the molecular condition of 

 such matter is perpetually changing. Some bodies, the equilibrium 

 of the proximate elements of which is veiy unstable, present, in the 

 solid state, phenomena, seemingly at least, analogous to those presented 

 by water, and others in their alternation between the liquid and the 

 solid states. Of these, glass is an example, and the now well-known 

 fact of the incorporation into one mass of two or more plates of (plate-) 

 glass, the polished surfaces of which have been placed in close contact 

 with each other, presents a curious parallel to the incorporation into 



ARTS AND SCI. IlIV. VOL. IV. 



one of several slabs or other separate portions of ice by regelation, as 

 taking place in the experiments described in this article, and to deter- 

 mine in what manner these two subjects are related to each other 

 would appear to deserve careful investigation. The principal facts, so 

 far as glass is concerned, with the bearings on molecular philosophy 

 they appeared to possess before the phenomena of regelation had been 

 scientifically considered, will be found in the abstracts of two lectures 

 on that substance delivered by Mr. Brayley before the Pharmaceutical 

 Society of London in 1845, published in the ' Pharmaceutical Journal ' 

 (vol. v.) for August and October of that year. 



In a paper on the Physical Properties of Ice, Professor Tyndall has 

 shown that when a sunbeam traverses a mass of ice, the latter melts 

 at innumerable points in the track of the beam, and that each portion 

 melted assumes the form, not of a globule, but of a flower of six 

 petals. The planes in which these flowers are formed are independent 

 of the shape of the mass, and of the direction of the beam through it ; 

 they are always formed paraUtl to the surface of freezing. This, he 

 observes is a natural consequence of the manner in which the particles 

 of ice are set together by the crystallizing force. By the slow abstrac- 

 tion of heat from water in the process of freezing, its particles build 

 themselves into these little stars, and by the introduction of heat 

 into a mass so built, the architecture is taken down in a reverse order. 

 In watching the formation of artificial ice, by the machine of Mr. 

 Harrison (noticed under FREEZING-APPARATUS), Professor Tyndall 

 has seen little solid stars formed, which were the exact counterparts of 

 the little liquid stars formed by melting. 'Phil. Trans.' 1858, pp. 

 211-227 ; Ib. 1859, pp. 298, 299. Appended to the former paper is a 

 letter from Professor Faraday on the irregular fusibility of ice. 



Another important part of the history of ice is its production on the 

 bed of rivers, when it receives the name of Crround-ice, Bottom-ice, 

 and Ground-grtt ; the Glace-du-fond of the French, and the (jrund-eis 

 of the Germans. It is generally imagined that rivers freeze only at 

 the surface ; this however is not the fact, ice being frequently formed 

 at the bottom of running water. Thus, according to the late Rev. 

 Dr. Farquharson, F.R S., the phenomenon is so common, and so well 

 known in certain parts of Aberdeenshire, that the inhabitants have 

 given it the name of Ground-gru, a name which that gentleman has 

 adopted in his paper on the subject in the 'Philosophical Transactions' 

 for 1835, p. 329. Gru is the name by which the people of Aberdeenshire 

 designate snow saturated with or swimming in water ; and as the ice 

 formed at the bottom of rivers very nearly resembles that in appearance, 

 a better name than Ground-gru could hardly be given, though it would 

 be more precise to call it subaqueous ice, in contradistinction to that 

 found at the surface, and because the term ground-ice, which this 

 formation has also received, has been sometimes given to the ice 

 occasionally met with at certain depths in the ground in northern 

 countries. 



Common, however, as may be the phenomenon of subaqueous 

 ice, .and although it has been noticed at various times, it has but 

 lately attracted the serious attention of observers. Ireland, in his 

 'Picturesque Views of the River Thames,' published in 1792, 2 vols. 

 8vo., mentions the ground-ice of that river, and on the subject quotes 

 Dr. Plott, who says, " The watermen frequently meet the ice-meers, or 

 cakes of ice, in their rise, and sometimes in the underside enclosing 

 stones and gravel brought up by them ab into." 



M. Arago published an interesting paper on the subject in the 

 ' Annuaire du Bureau des Longitudes' for 1833, in which he mentions 

 the following observations made on ground-ice : In the Thames, by 

 Hales, in 1730; in the river De'ome, department of Ardeche, France, 

 by Desmarets, in 1780 ; in the Elbe, by M. Braun, in 1788 ; in the 

 Teine, Herefordshire, by Mr. T. A. Knight, in 1816 ; in the Canal de la 

 Birze, near Bale, by M. Me>ian, in 1823; in the Aar, at Soleure, by 

 M. Hugi, in 1827 and 1829; in the Rhine, at Strasburg, by Professor 

 Fargeau, in 1829 ; and in the Seine, by M. Duhamel, in 1830. More 

 lately still, Colonel Jackson, in a paper on the congelation of the 

 Neva, published in the 6th volume of the ' Journal of the Royal Geo- 

 graphical Society,' mentions the formation of ground-gru at the bottom 

 of that river ; and in the 6th volume of the same journal there is a paper 

 expressly on the ice formed at the bottom of the Siberian rivers. The 

 Rev. Mr. Eisdale has, in the ' Edinburgh New Philosophical Journal,' 

 vol. xvii., p. 167, a paper on ground-ice ; and, finally, Ur. Farquharson, 

 as already mentioned, published his observations on the ground-gru of 

 the rivers Don and Leochal, in Aberdeenshire. 



Almost all who have written on ground-gru have endeavoured to 

 account for its formation, though no explanation yet given is perfectly 

 satisfactory. Dr. Farquharson, whose paper contains an original 

 investigation of the subject, says it is the result of radiation, and 

 endeavours to substantiate his reasoning upon the principles of the 

 formation of dew. It was remarked in this article, as originally pub- 

 lished, that he seems to forget that Dr. Wells maintains expressly that 

 wind and shade are alike obstacles to radiation ; and that consequently 

 a body of moving water o deep as to be impervious to light, and par- 

 ticularly when covered, as in the case of the Neva, with a sheet of ice 

 three feet thick, and as much more of snow, must present an insur- 

 mountable obstacle to the radiation of heat from the bottom of the 

 river. This objection, however, is unsound, and is removed, as in 

 many other instances of the supposed insufficiency of the principle of 



3 u 



