733 



WATER. 



WATER. 



734 



' The theories of glacier motion of Forbes, Thomson, and Tyndall (in- 

 chiding the explanation of the plasticity of ice by the latter), and the 

 views respecting it of Hopkins and Whewell, may prove to be equally 

 true, or some of them unnecessary. Under the reciprocal changes of 

 pressure and temperature going on in a glacier, it will follow that every 

 part of it must be perpetually changing from a truly viscous or plastic, 

 colloidal, dynamic state, maintained only for a short time, to the rigid, 

 crystalloidal, statical condition of ordinary ice ; which, under the same 

 changes will again transiently assume the colloidal form, only to 

 undergo the corresponding change, and so on in a succession which can 

 terminate only with the final liquefaction of the ice, and its separation 

 from the glacier by flowing away in the form of water. All the conditions 

 of viscosity or plasticity, and rigidity, which the phenomena of glaciers 

 and the known properties of ice require to be fulfilled, may thus be 

 capable of explanation agreeably to the laws .of nature. But many of 

 Mr. Graham's results are independent of his assumption respecting ice. 

 It is stated by him, as above, that colloidal bodies affect the vitreous 

 structure ; and he recognises the vitreous form of silica as the colloidal 

 one. It is now evident, indeed, that what, looking primarily from 

 organic substances, he has termed the colloidal state, is identical, 

 allowing for inherent difference of properties, with that, which, looking 

 primarily frui.i inorganic bodies, has been termed the vitreous or 

 glassy state. Every description of glass must, agreeably to Mr. 

 Graham's inductions, be a colloidal body, and the union of two surfaces 

 of it at all temperatures, while the solid condition is maintained, 

 must be that cementation and redintegration which is physically 

 identical with regelation itself; and thus Mr. Brayley's arguments 

 for the virtual identity with regelation of the process by which two 

 plates of plate-glass become one, which Dr. Faraday's new results 

 appeared to invalidate, will be confirmed; while regelation, as also 

 suggested by him, may be found to be universal, as respects all bodies 

 which can assume the colloid form, Dr. Faraday's experiments indi- 

 cating its non-extension having been confined to crystalloids. The 

 mutability and continued metastasis of colloids are manifested in the 

 unstable condition of arrested liquidity or potential solidity recognised 

 by Mr. Brayley ; and Mr. Graham's comparison of a colloid in that 

 respect "to water while existing liquid at a temperature below its 

 usual freezing point, or to a supersaturated saline solution," is a 

 repetition of Mr. Brayley's view of the molecular constitution of glass 

 already cited. Colloidal ice (if it shall be proved to exist), and unfrozen 

 water below 32, are evidently degrees of the same condition, and thus 

 Mr. Urayley's suggested homologue of the glassy condition of water is 

 almost equivalent to the former, and if, as seems conformable with 

 known facts, we assume that the colloid state of water cannot begin 

 until it is reduced to the temperature of its greatest density, that 

 homologue will include, almost explicitly, Mr. Graham's colloidal con- 

 dition of ice. Some nice questions of temperature will, however, have 

 to be settled by experiment ; and indeed the subject is now ripe for 

 those quantitative determinations in which the existing discussions of 

 t ion are remarkably deficient, and which must necessarily be of a 

 minute and delicate description. 



But here we must conclude on this subject ; having merely indicated 

 how wide a field for experimental research, observation in nature, the 

 verification of hypotheses, and mathematical investigation, all relating 

 to ice and water, has probably been opened to science by Mr. Graham's 

 researches on liquid diffusion. 



From the preceding view of the obvious characters and actual nature 

 of ice, we proceed to describe some of its properties in relation to heat, 

 and some also of water in its two fluid states. The dilatation of ice by 

 heat was measured in the years 1845 and 1846, at the Imperial Obser- 

 vatory of Pulkowa, by Schumacher and his associates, and the par- 

 ticulars of their experiments were communicated by M. Struve to the 

 Academy of St. Petersburg, in 1848, and were afterwards published in 

 its ' Memoirs.' The measurements had reference to observed tempera- 

 tures of the block of ice employed, varying from 2-3 R. to 22 R. 

 ( + 5-175 to + 17'5 Fahr.) 



After applying the requisite corrections, it resulted from them that 

 the coefficient of expansion of ice is for 1 R. (2 '25 Fahr.) '00006468 ; 

 which, according to the Rev. Canon Moseley, F.R.S., " is nearly twice 

 as great as the coefficient of dilatation of load, and mure than twice 

 as great as that of any other solid." [HEAT, col. 637.] 



\V<: do not know the modulus of elasticity of ice,* or the pressure 

 under which it disintegrates; but Mr. Moseley has observed that " If 

 it were as elastic as slate and did not resist crushing more than hard 

 brick, a block of it placed with its ends between two immoveable 



* The expression "modulus of elasticity," we believe, ha not been explained 

 in any preceding article. It is thus defined by Dr. Thomas Young, Sec. B. L., 

 by whom it was Introduced. " The modulus of the elasticity of any substance 

 is a column of the same substance, capable of producing a pressure on its base 

 which is to the weight, causing a certain degree of compression, as the length 

 of the substance is to the diminution of its length." This definition is given in 

 Dr. Young's * Mathematical Elements of Natural Philosophy,' appended to his 

 celebrated 'Lectures,' Lond., 1807, vol. ii. f p. 46. It occurs in Section ix, 

 treating ' Of the equilibrium and strength of elastic substances.' These ele- 

 ments are not inserted in Professor Kelland's edition of that work ; but the 

 section is reprinted in the late Dr. Peacock's collection of the ' Miscellaneous 

 Works' of Dr. Young, vol. il., p. 129. The application of the expression is 

 explained and illustrated in Lectures xiii. and xxxl. 



obstacles, would crumble when its temperature was raised one degree 

 of Fahrenheit. It is its great dilatability which gives to ice this ten- 

 dency to disintegrate, when, not being free to dilate, its temperature is 

 raised, even so slightly as this. Agassiz describes a disintegration of 

 the transparent ice of the blue bands of glaciers when laid bare, which 

 appears to be due to its expansion." 'Bulletin [Bibliothtfque] de 

 Geneve,' vol. xliv.,p. 142 ; (' Proc. of Roy. Soc.' vol. xi., pp. 171, 172.) 



According to the experiments of Melloni on the transmission of 

 radiant heat, ice transmits none (absorbs all) of the calorific rays issuing 

 from copper at 212", or at 752 Fahr., nearly approaching a red heat; 

 and transmits only 0'5 of those from incandescent platinum, and only 

 6 per cent, of such rays from the Locatelli lamp. In these cases the 

 heat is absorbed in the internal liquefaction of the ice. 



The colour of liquid water varies, according to the thickness of the 

 quantity examined, from a yellowish green of all degrees of intensity 

 through green and blue-green to intense blue, such as that observed in 

 great depths of the sea. Professor Tyndall has introduced into British 

 demonstrative science, if indeed he has not devised, an experiment in 

 which the colour of water is exhibited by passing the light from the 

 voltaic lamp through a long tube of water closed by glass at both ends, 

 and receiving the image on a screen. In this experiment, with no 

 greater thickness than twenty feet, the colour of water is seen to be 

 yellowish green. Ice, probably, h;.!3 the same range of colour ; being, 

 like water, colourless in small masses ; it is greenish or bluish in large 

 masses. Pure aqueous vapour is colourless in the greatest thicknesses 

 in which it has been examined. 



Many important facts, and inductions from them, relating to the 

 electrical properties of water in all its three states of aggregation, will 

 be found referred to under their respective appellations in the Indexes 

 to Faraday's ' Experimental Researches in Electricity,' and in ' Che- 

 mistry and Physics,' indexes which are enhanced in value by having 

 been constructed by the author of those researches himself. 



The process of the solidification of water by depression of tempera- 

 ture is noticed under FREEZING, and FREEZING AND MELTING. POINTS. 

 The lowering of its freezing-point by pressure, as discovered by Pro- 

 fessor J. Thomson, is stated in the article hist cited, and has been 

 referred to in the present article, and also under ICE. The theory and 

 quantitative calculation he originally gave respecting it will be found 

 in the ' Transactions of the Royal Society of Edinburgh," vol. xv., and 

 the ' Cambridge and Dublin Mathematical Journal ' for November 

 1850. Ice, as a crystalline substance has been described under HAIL, 

 HOAR-FBOST, and SNOW. Its specific gravity is stated in the last. Mr. 

 J. Chapman, Professor of Mineralogy in the University of Toronto, in 

 the ' Canadian Journal of Science ' tor 1861, has questioned the truth 

 of referring the crystallisations of ice to the rhombohedral system. A 

 mode of investigating the process of formation of the stellar and other 

 aggregations of crystals so characteristic of snow, under circumstances 

 more convenient than those of observations which must be made at a 

 temperature below 32 Fahr., has been pointed out by Mr. Joseph 

 Spencer, and adopted by Mr. Glashier. It consists in observing the 

 crystallisation of camphor, in which similar aggregates are produced ; 

 and has been described in papers read before the Greenwich Natural 

 History Club, in the year 1856, and issued by the British Meteorological 

 Society. The compressibility and ELASTICITY of water have both been 

 treated of under the latter head. 



The phenomena of the conversion of liquid into gaseous water or 

 aqueous vapour, and its properties in that condition, have been stated 

 in the articles BOILING oc LIQUIDS; EBULLITION; EVAPORATION; 

 STEAM; VAPOUB ; and VAPOUR OPALESCENT; those of its reconversion, 

 or condensation, into liquid water and ice, under several heads above 

 referred to, and also in the articles DEW and RAIN. The evaporation 

 of ice has been noticed under SNOW. 



The absorptive power for heat of aqueous vapour has recently been 

 examined by Professor Tyndall, in his researches on the absorption and 

 radiation of heat by gases and vapours, (' Phil. Trans.' 1861) ; in which 

 he found that hydrogen, the two gases which are the essential con- 

 stituents of the atmosphere, and atmospheric air itself, absorb respec- 

 tively about 0'3 per cent, of the calorific rays emanating from a copper 

 surface coated with lamp-black, heated by boiling water. " On a fail- 

 November day," he adds, " the aqueous vapour in the atmosphere 

 produced fifteen times the absorption of the true air of the atmosphere. 

 It is on rays emanating from a source of comparatively low temperature 

 that this great absorptive energy is exerted ; hence the aqueous vapour 

 of the atmosphere must act powerfully in intercepting terrestrial 

 radiation ; its changes in quantity would produce corresponding 

 change of climate. Subsequent researches must decide whether this 

 vera causa, is competent to account for the climatal changes which 

 geologic researches reveal" ' Proc. of Royal Soc.' vol. xi., pp. 101, 102. 

 Under EVAPORATION, HYGROHETRY, and VAPOUR, an account has 

 been given of Dr. Dalton's researches and views respecting the produc- 

 tion and tension of aqueous vapour and its relations to the atmosphere, 

 which for many years have been almost universally accepted and relied 

 upon. Meteorologists, accordingly, have been accustomed to separate 

 the pressure of the aqueous vapour from the whole barometric 

 pressure of the atmosphere, and thence to infer the pressure of the 

 permanently elastic portion, or as it has been called, the ffaseom 

 oressurc, or the jtrettitre of the dry air. Colonel Sykes, in a paper read 

 Before the Royal Society some years since, and Lieut.-Col, Strachey 



