400 



NATURE 



[August 22, 1901 



weights are given in grammes. They were determined on a 

 Salter's spring balance which carried 500 grammes, and its 

 scale was divided into intervals of 10 grammes each. Ice- 

 grains which weighed more than 500 grammes were divided in 

 two. 



As has been already pointed out, the figures in the tables do 

 not give an exact statistical account of the blocks of ice. The 

 smallest grains have most frequently escaped being weighed, 

 therefore the average sire of the grain comes out higher than 

 the truth. The figures in the tables give a general idea of the 

 constitution or anatomy of a block of ice taken from the lower 

 part of a large glacier. They are particularly interesting when 

 we reflect that every grain, even the largest, has grown, accord- 

 ing to the rigid laws of crystallomorphic development, from a 

 single snow crystal which probably weighed no more than one 

 or two centigrammes. 



In the Mergelin See, glacier ice can be studied in a way that 

 is possible in no other place. The fragments of the Aletsch 

 Gl-icier which float in it are veritable icebergs, and behave in 

 the same way as their relatives in the Arctic or Antarctic Ocean. 

 In the middle of summer, however, they are exposed to a much 

 more powerful sun than either the northern or the southern 

 bergs. Consequently, the weathering and disintegration, as well 

 as ihe melting, proceed at a much more rapid rate. 



The action of the sun's rays on glacier ice is twofold ; it dis- 

 articulates the ice into its constituent grains, and it splits the 

 individual grain up into lamina perpendicular to the principal 

 axis of the crystal and bounded by the planes of fusion dis- 

 covered and described by Tyndall. These planes are the 

 distinguishing characteristic of the individual ice-grain. 



Under the influence of radiant heat an ice-crystal begins to 

 melt at the surfaces which separate these laminx, and the 

 process of disintegration and decay is directed by their plane. 

 On the other hand, an ice-crystal, floating in water and losing 

 heat, generates ice lamina; which are directed by the same 

 planes, which form the continuati.jn of the corresponding 

 lamina; of the parent crystal. This was well ob erved at the 

 end of August, 1S95. Every night a thin skin of ice was 

 formed at the shallow end of the lake, where the ice blocks are 

 collected. As the grains in a block of glacier ice are dis- 

 tributed quite irregularly, the water line of a floating block 

 necessarily cuts a great number of grains, all of which are 

 oriented differently. The ice which was formed during the 

 night along this line was oriented crystallographically by the 

 grain with which it was in contact and from which it appeared 

 to spring in continuation of its crystalline lamin;^. This produces 

 a remarkable pattern of lines on the surface of the lake ice 

 contiguous to a block of glacier ice. 



I'yndall has described and figured the minute features of the 

 disintegration of the crystal under the absorption of radiant heat. 

 Similar and complementary features are observed when ice is 

 generated from an existing crystal under the dissipation of heat. 

 To do justice to them, however, would require the services of a 

 skilful, patient and resourceful artist. 



The disarticulating and analysing action of the sun's rays is 

 no: accomplished without the selection and expenditure of 

 en;rgy. Accordingly we observe that one grain protects another. 

 The disarticulation into sep-irate grains, although very thorough 

 n;ar the surface of a glacier, does not penetrate far. A stroke 

 or two with an ice axe reveals the fresh blue ice. The analysis 

 of the individual grain into crystallographically oriented lamina; 

 can be particularly well studied in the Mergelin See. It is only 

 the grains that are exposed to the sky, and above water, that are 

 s > analysed ; and prolonged exposure of this kind reduces a 

 grain to the last stage of dilapidation. The grains beneath 

 the surface, whether of ice or -Mater, are almost completely 

 unattacked. 



The importance, or rather the necessity, of direct sky-light for 

 the disarticulation of glacier ice into its constituent grains is 

 very well seen in the artificial grottoes which are maintained at 

 easily accessible parts of most popular glaciers. The thickness 

 of the layer of completely disarticulated ice is so small that it is 

 hardly noticed, and the whole grotto appears to be cut out of 

 pure blue ice. If the observer, on penetrating for a few 

 paces, turns round and looks outwards, he sees the surface of 

 the ice-walls of the grotto etched with strange line-figures. 

 These are most strongly marked near the opening, and they 

 cease exactly at the spot where the last ray of direct sky-light 

 strikes the ice. The lines .so developed are formed by the inter, 

 section of the surface of the ice-wall of the cave with the 



NO. 1660, VOL. 64] 



separating surfaces of contiguous ice-grains. The photographic 

 picture thus presented is one of very great interest. 



It is only perfectly pure water, received directly as it flows 

 from the still, that can be frozen into homogeneous glass-like ice. 

 All natural ice proceeds from impure water. 



In lake ice of moderate thickness the crystalline axis is per- 

 pendicular to the surface of the lake. Consequently, Tyndall's 

 planes of fusion are parallel to this surface. When exposed to 

 a powerful sun, and with an air temperature even much below 

 0° C. , the ice weathers into horizontal lamin^v separated by 

 Tyndall's planes of fusion, and into vertical columns. The 

 column in lake ice and the grain in glacier ice are homologous 

 features. They express the form which the individual crystal 

 takes in these different varieties of natural ice. 



Were it not for the fact that a glacier is made up of distinct 

 grains of ice, and that this substance has the property of melting 

 and freezing at different temperatures, according to the composi- 

 tion of the water with which it comes in contact and to the 

 pressure to which it is subjected, there is little doubt that a 

 glacier would be as motionless as any other mass of crystalline 

 rock. J. Y. Buchanan. 



.■\ugust 6. 



Problems of Geometry. 



In Klein's "Famous Problems of Elementary Geometry," 

 geometrical proofs are given for solving the problems ot " the 

 duplication of the cube" and " the trisection of an angle " by 

 means of the cissoiJ and the conchoid respectively. I find, 

 however, that in " Chambers' Encyclopa;dia" it is stated, with- 

 out proof, that the cissoid and the conchoid are capable of 

 furnishing geometrical constructions for the solution of both 

 problems. Can any of your readers furnish me with the 

 necessary references, or supply a proof of the " trisection of an 

 angle " by means of the cissoid, and of the " duplication of the 

 cube " by means of the conchoid ? A. B. Basset. 



Fledborough Hall, Holyport, Berks, August 9. 



Forecast and Fact. 



In Nature of January 12, 1S93 (P- 246), I represented as 

 probable an early descent of the smoothed curve of rain days at 

 Greenwich, there given, " and a commencing series of (on the 

 average) drier summers than we have had lately." 



The following table may now be compared with this : — 



Relation to av. (6-80 

 -1-41 

 4-1-52 

 -I -07 

 -174 

 -I '29 



-2-86 

 -3'96 



-0-55 



Per contra, there is the chastening reflection that a rule which 

 held good (with one exception) since 1S15 (see Symons' Met. 

 l\fag., June 1898, p. 70), and which was quoted in your 

 columns, has broken down on this occasion, viz. that in the 

 group of five summers ending with a sunspot minimum, there 

 are more wet summers than dry ! A. B. M. 



Boomerangs. 



In relation to the interesting article on boomerangs in your 

 issue of August i, it may perhaps be of interest to some of 

 your readers to know that Schiaparelli, in his famous book, 

 " Entwurf einer astronomischen Theorie der Sternschnuppen," 

 p. 13, speaks of " bumerangs." He says :—" Very likely the 

 catcja described by Isidor of Seviglia was nothing but a sort 

 of bumerang." "Est genus Gallici teli, ex materia quam 

 maxime lenta, qu:T; jacta quidem non longe propter gravitatem 

 evolat, sed quo pervenit, vi nimia perfringit : quod si ab artifice 

 mittatur, rursus redit ad eum qui misit." Isidori Hispalensis, 

 Origg, xviii. Ottavio Zanotti Bianco. 



"Torino (Italy) Via della Rocca 2S. 



