September 28, 1905] 



NA TURE 



54; 



THE FORM ATI OX OF ICE AND THE 

 GRAINED STRUCTURE OF GLACIERS^ 



T N the following pages I have the honour to lay before 

 the Royal Society the results of a lengthy research on 

 the formation of ice and the grained structure of glaciers, 

 which may serve as a complement to the previous investi- 

 gations on the same subject published in the Philosophical 

 Transactions and Proceedings of the Royal Society by 

 Forbes, Tvndall and Huxley, Tvndall, Faradav, T. Graham, 

 J. F. xMain, J. C. McConnel, 'and D. A. K'idd, and else- 

 where by Guyot, Agassiz, James Thomson, and Sir William 

 Thomson (now Lord Kelvin), Hermann and Adolf 

 Schlagintweit, Person, Lcvdolt, RCidorff, Bertin, Grad, and 

 A. Dupr^, Moseley, A. Heim, J. T. Bottomley, K. R. 

 Koch and Klocke, Forel, Ed. Hagenbach-Bischoff, E. von 

 Drygalski, Miigge, H. Hess, and others. 



(I) It will be convenient at ;he outset to define the 

 precise meaning with which it is proposed to employ 

 certain words, some of which are in vague popular use, 

 while others are less familiar, or new. 



By an oily liquid will be meant one which has surface 

 tension in the common surface with other liquids with 

 which it may be in contact. According to this definition 

 a solution of any salt will, in comparison with pure water 

 or a weaker salt solution, be called, in certain circum- 

 stances, an oily liquid. 



.\n emulsion is a watery liquid containing suspended 

 drops of oily liquid, or drops of any sort enclosed in an 

 oily skin. These drops can coalesce into larger drops, or 

 the oily skins can join on to one another, and form a 

 continuous mass of bubbles, or foam. Thus foam consists 

 of portions of watery liquid enclosed in, and separated 

 from one another by adjacent partitions of oily liquid. 

 Each space thus enclosed will be called a foam-cell, and 

 the enclosing partition the foam-wall. If the foam-cells 

 are very small, and the fluid foam-walls very thin (or 

 invisible), the whole is then a liqitid jelly. The jelly is 

 stiff, the foam stiff or solid, when the walls or the contents 

 of the foam-cells, or both, have become solid. 



" Nearly pure " applied to water or ice will be used in 

 the special sense of " containing only very small amounts 

 of any salt." Salt itself is used throughout in the general 

 chemical sense, that is, not restricted to sodium chloride. 



(2) I have allowed pure water, and water containing 

 dissolved salt, to freeze in the dark at various rates, and 

 to melt away slowly in the dark, in open air, and in sun- 

 light. The ice prisms employed were from i mm. to 

 :ooo mm. thick, and as the thawing proceeded their various 

 layers were systematically examined — sometimes for days 

 together — with the naked eye, with the microscope, and 

 with polarised light. The same appearances presented 

 themselves in the same order as those which for thirty- 

 seven years past I have investigated and described in 

 solutions of silicic acid, glue, or other colloids, when these 

 are evaporated to form gelatinous masses or thin films, and 

 develop fissures. I have shown that thin viscous oily films 

 of more concentrated solution exist in a less concentrated 

 solution of the same substance, and form folds, straight 

 and twisted tubes, cylinders or cones, spheres and bubbles, 

 open and closed foam-cells with visible and invisible foam- 

 walls. Thin solid films behave like films of very viscous 

 liquid. Whether the oily films form tubes or bubbles and 

 foam-cells joining on to one another depends on the 

 viscosity of the oily liquid. The mutual inclination of the 

 foam-walls, and their surface tensions, continually change 

 as the concentration of the oily liquid changes, and in the 

 case of invisible foam-walls may depend also on the thick- 

 ness of the oily film. When the oily film is verv thin, its 

 surface tension diminishes with diminishing thickness of 

 the film. Oily foam-walls that are formed against solid 

 surfaces are normal to these surfaces. If three oily foam- 

 walls meet in a common edge at equal angles of 120°, they 

 have equal surface tensions. 



The foam-cells of a liquid jelly immersed in water can 

 increase or diminish in volume by the diffusion of water 

 through the foam-wall inwards or outwards, i.e. the liquid 

 jelly can siucll or shrink. Two clots of liquid jellv can 



NO. 1874, VOL. 72] 



coalesce into one, which does not occur with clots of solid 

 jelly, nor can these latter swell or shrink. 



A liquid jelly becomes for the time being positively or 

 negatively doubly refracting when the viscous walls, or 

 the viscous contents of the foam-cells, are expanded or 

 compressed. .'V jelly remains permanently doubly refract- 

 ing when the walls or the contents of the foam-chambers 

 solidify while in an expanded condition. 



(3) Now, ice is a liquid jelly, with foam-walls of con- 

 centrated " oily " salt solution, which enclose foam-cells 

 containing viscous, doubly refracting, pure or nearly pure 

 water. 



(4) The further the temperature falls below 0°, the 

 greater is the viscosity of both liquids — in the walls and 

 in the interior of the foam-cells — and the less the plasticity 

 of the ice. 



(5) .^.t very low temperatures, the ice breaks with con- 

 choidal fracture at the surface of the invisible spherical 

 foam-walls, which as the whole cools have contracted 

 differently from their contents. 



(6) The " glacier grains " are foam-cells filled with pure 

 or nearly pure ice, and separated from one another by 

 visible or invisible walls of oily salt solution. 



(7) The union of two pieces of ice under water (" rege- 

 lation "), and the increase in size of the glacier grains 

 as they approach the lower end of the glacier, correspond 

 to the running together of two gelatinous clots (of silicic 

 acid, or glue) containing liquid foam-cells and liquid cell- 

 contents. .At the same time the oily foam-walls between 

 the glacier grains become thicker, and then get thinner 

 again through the draining away of the liquid salt solution 

 at the foot of the glacier. 



(8) All water, even the purest, contains traces of salt. 

 As the water cools, ice crystals and oily mother liquor 

 separate at short intervals, or periodically. Under the in- 

 fluence of the surface tension, the oily salt solution forms 

 invisible foam-walls, the surface-tension of which decreases 

 as the thickness of the walls and the concentration of the 

 salt solution diminish. Otherwise, as the cooling proceeds, 

 the salt solution becomes continually more concentrated, 

 and the wall thinner. Finally, the concentrated salt 

 solution also freezes to ice and solid salt. The value of 

 the surface tension determines the angles at which three 

 walls meet in a common edge. If three foam-walls meet 

 at equal angles of 120°, the three walls have equal surface 

 tensions, whereas an inclination of 90° means that fluid 

 foam-walls have been formed in contact with old and 

 already solidified ones. 



(9) When water containing air freezes, the air, like the 

 salts dissolved in the water, separates out at short intervals, 

 or periodically. The white places in ice, which are those 

 containing these air bubbles, are also the richest in salt. 



(10) As water containing salt, but free from air, cools, 

 the periodical separation of ice and salt gives rise, alike 

 in sea ice, in artificial ice, and in glacier ice, to layers 

 of ice containing varying amounts of salt. By pressure 

 or by absorption of radiation (sunlight, electric light, or 

 daylight), the parts of the ice which are rich in salt melt 

 sooner than pure ice. 



(11) In sunlight or electric light furrows are formed at 

 the places rich in salt on the surface of sea ice, artificial ice, 

 and glacier ice. (Forel's stripes; Forbes's "dirt bands"; 

 foam-walls of the great foam-cells' of the Kjendal Glacier.) 



(12) The salt solution formed in sea..ice, artificial ice, or 

 glacier ice, through pressure or sunshine, shows, by the 

 hollows which it fills, the forms assumed under the in- 

 fluence of the surface tension by the boundary between 

 the oily salt solution and the water, just before the freezing 

 of the water. .As the ice melts, it contracts. Thus in 

 sea ice pressure or absorption of heat radiation causes the 

 formation, in horizontal layers parallel to the frozen 

 surface, of Tyndall's liquefaction figures, vacuous bubbles, 

 ice flowers, and " fir trees " with branches meeting at 

 120° and go", just like those obtained when colloid solutions 

 are evaporated to dryness, or when salt solutions are 

 allowed to crystallise. 



In the case of artificial ice which has been frozen in deep 

 prismatic troughs, these liquefaction figures are formed 

 in the diagonal and median planes of the ice block, which 

 were the last parts to freeze, and where the mother liquu. 

 had accumulated. 



