?82 



NA TURE 



[August 20, 1908 



by Prof. Forel in the remarkable natural grotto of the 

 Arolla glacier, of which he has given so fascinating a 

 description in the Archives des Sciences physiques ct 

 natiireUes, Geneve, 1887, xvii., p. 49S. The delineation 

 of the etched figures by rime was observed by him in the 

 month of July in a remote and secluded chamber nearly 

 250 metres from the entrance of the grotto. In artificial 

 grottos like that of the Morteratsch glacier, in which the 

 air circulates freely, the hoar-frost disappears very quickly 

 with the end of winter. 



The Grain of Lake Ice. 



It is not glacier ice alone which suffers disintegration 

 when exposed to a powerful sun. Lake ice beliaves in a 

 similar way. Beautiful examples of this can be seen 

 in Alpine seas every winter. During the harvesting of 

 the ice from tjie lake, the blocks often lie for a day or 

 more before they are carted away to the ice-houses. 

 Occasionally some of them get overlooked and remain 

 for many days exposed to the powerful sun of February, 

 while maintaining the low temperature of the air usual 

 in that month. No melting takes place, but after even a 

 few hours' exposure to the sun the block shows the figure 

 of its grain in development. It is being etched by the 

 sun's radiation. 



The grain of lake ice has a very different appearance 

 from that of glacier ice, but both are individual crystals. 

 The difference in their appearance is to be traced to the 

 difference of treatment which they have received during 

 their existence. The glacier grains have been practically 

 rolling over each other during their descent, while those 

 of the lake have established themselves at right angles to 

 the surface of the water, and have remained there. So 

 long as the ice is increasing in thickness, the temperature 

 of its upper surface is very low. It is perfectly trans- 

 parent, and its surface is smooth, dry, and polished like 

 glass, and it shows no trace of crystalline figure. When 

 the ice is undisturbed this develops itself onlv at the end 

 of the season when the thaw sets in. Then the whole 

 ice-sheet rises to its melting temperature, and is at the 

 same time exposed to the direct radiation of the sun. 

 This produces disarticulation of the ice into groups of 

 vertical prisms which are then floating independently ; they 

 are kept together only by crowding. Ice in this state 

 is said to be rotten ; and it will be recognised that, how- 

 ever thick the ice-sheet may be, when it gets into this 

 condition it is dangerous. In the neighbourhood of the 

 outflow the crowding is relieved, the disarticulated groups 

 become disengaged, the smaller groups and individual 

 prisms are able to assume their attitude of stability and 

 to float on their sides. .'\II then drift towards the outlet. 

 The ice " breaks up," and the lake is cleared in an 

 astonishingly short time. 



If it were not for the law that even impure water in 

 freezing always forms pure ice, the impurity remaining in 

 the liquid and generally entangled in the interstices of 

 the grains, and that the pure ice which is in contact with 

 this impure liquid melts at a lower temperature than that 

 which is in contact with nothing but the water formed by 

 its own melting, the ice-covering of a lake would be a 

 continuous sheet offering no points of weakness, and it 

 would have to melt as a whole. It is doubtful if lakes 

 such as those, met with in the Upper Engadine, would 

 get rid of their ice-covering at all. On the Silser See 

 the ice is usually more than 60 centimetres thick when 

 the thaw sets in, but when once the ice begins to break 

 up the lake is cleared in a day. Sixty centimetres of ice 

 would take a long time to disappear on the basis of surface 

 melting alone. 



While the winter lasts, the ice on the lake shows no 

 crystalline structure. This develops only after removal 

 from the water and exposure to the sun. The ice then 

 splits up into prisms in a vertical plane. These are at 

 first of irregular section, and as sun-weathering proceeds 

 the thicker prisms split up into thinner. When a block 

 has Jain exposed to the February sun and cold it mav fall 

 to pieces, each piece being a long, thin, triangular prism, 

 with some resemblance to a razor-blade. When the ice is 

 cold and dry the outlines of the grains are lines ; when the 

 ice has a temperature of 0° C. it melts preferably round 

 the grain, forming troughs in which the water collects, 



NO. 2025, VOL. 78] 



and the aspect is that of a dark polygon surrounded by 

 light-coloured canals. The columnar grains have their 

 striation like those of the glacier. In one piece, which 

 was much weathered, I counted twenty-four such grains 

 in an area of g square centimetres. In a slab which had 

 not been lying long I counted twenty-three grains in an 

 area of 150 square centimetres, giving an average area of 

 6-5 square centimetres per grain ; the largest had an area of 

 12 square centimetres. In another slab there was a very 

 large grain which measured 7 centimetres in one direction 

 and 4 centimetres at right angles to it. In a slab in which 

 the sun-weathering had proceeded very far I counted 113 

 grains in a disc of 5 centimetres radius, which gives 0.69 

 centimetre as the average area per grain. 



In the absence of actual experience, one is apt to expect 

 a slab of lake ice, when subjected to sun-weathering, to 

 be disarticulated into hexagonal columns ; but this expecta- 

 tion is quite gratuitous. Ice may crystallise in a form 

 bounded by plane faces, according to the laws of its 

 crystallographic system, if it has the freedom which it 

 possesses when crystallising out of an independent medium 

 such as a saline solution or air. But the foreign matter 

 dissolved in fresh water is present in so small quantity 

 that what we have before us is the solidification rather 

 than the crystallisation of ice, and each column as it tries 

 to develop itself is interfered with by its neighbour, and 

 the resulting slab of ice is made up of elementary prisms 

 crowded together, but preserving parallelism of crystallo- 

 graphic axis. 



The second part of the discourse dealt with the part 

 played by glaciers and rivers in modifying the features of 

 the surface of the earth, but it cannot be usefully con- 

 densed so as to be included in this communication. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



The University of Jena, at its recent jubilee, conferred 

 the degree of M.D., honoris causa, on Sir William Ramsav, 

 K.C.B., F.R.S. 



Mr. W. J. HoRN'E. lecturer in physics at the South 

 .African College, Cape Town, has been appointed to the 

 inspectorate of the Transvaal Department of Public Educa- 

 tion as organiser for technical education. 



Upon the authority of the Cologne Gazelle, a Reuter 

 correspondent states that the question of the admission of 

 women to university study in Germany has been settled. 

 Women who are subjects of the German Empire w'ill be 

 admitted on the same footing as men, but women of other 

 countries will require the permission of the Minister of 

 Public Instruction for matriculation. 



A PAPER on the educational aspect of domestic subjects 

 was read recently by Prof. A. Smithells at Bradford, the 

 occasion being the fourth annual meeting of the Northern 

 LInion of Domestic Economy Associations. A verbatim 

 report appears in the first .August number of Education, 

 and we learn therefrom that Prof. Smithells considers that 

 the increased attention being paid to the teaching of 

 domestic subjects is very gratifying. He wishes to bring 

 such subjects within the purview of universities, as it is 

 desirable to connect every branch of education with what 

 should be the most abundant and vivifying springs of 

 knowledge. The introduction of domestic subjects into the 

 normal educational curriculum for girls would add a much 

 wanted ingredient, as in the household arts we have a 

 direct educational instrument for conferring upon girls the 

 very great gift of manipulative skill, and of doing it by 

 teaching the very work that will He nearest to them in 

 their normal dailv life when they have left school. 

 Domestic subjects include much that affects the cultivation 

 of the moral and resthetic side of human nature, and a good 

 teacher will make them mentally stimulating. 



The Revue scicntifique for August 8 reproduces the 

 address given by Prof. Paul Appell, the president of the 

 French .Association for the Advancement of Science, at the 

 meeting at Clermont-Ferrand on August 3. As we men- 

 tioned in our issue of August 13, the address deals with 

 the teaching of science and the formation of the scientific 



