V] OF SNOW-CRYSTALS 411 



recognised when met with again, has been recorded as a species — 

 for we need not concern ourselves with the occasional discussions, 

 or individual opinions, as to whether such and such a form deserves 

 "specific rank," or be "only a variety." And this secular labour 

 is pursued in direct obedience to the precept of the Systema Naturae 

 — ''ut sic in summa confusione rerum apparenti, summus conspiciatur 

 Naturae ordo.'' In like manner the physicist records, and is entitled 

 to record, his many hundred "species" of snow-crystals*, or of 

 crystals of calcium carbonate. Indeed the snow-crystal illustrates to 

 perfection how Nature rings the changes on every possible variation 

 and permutation and combination of form: subject only to the 

 condition (in this instance) that a snow-crystal shall be a plane, 

 symmetrical, rectilinear figure, with all its external angles those of 

 a regular hexagon. We may draw what we please on a sheet of 

 "hexagonal paper," keeping to its lines; and when we repeat our 

 drawing, kaleidoscope-fashion, about a centre, the stellate figure so 

 obtained is sure to resemble one or another of the many recorded 

 species of snow-crystals. And this endless beauty of crystalline 

 form is further enhanced when the flakes begin to thaw, and all 

 their feathery outlines soften. But regarding these "species" of his, 

 the physicist makes no assumptions: he records them simpliciter; 

 he notes, as best he can, the circumstances (such as temperature or 

 humidity) under which each occurs, in the hope of elucidating the. 

 conditions which determine their formation f; but above all, he 



* The case of the snow-crystals is a particularly interesting one; for their 

 "distribution" is analogous to what we find, for instance, among our microscopic 

 skeletons of Radiolarians. That is to say, we may one day meet with myriads 

 of some one particular form or species, and another day with myriads of another 

 while at another time and place we may find species intermingled in all but 

 inexhaustible variety. Cf. e.g. J. Glaisher, Illustrated London News, Feb. 17, 1855 

 Q.J. M.S. m, pp. 179-185, 1855; Sir Edward Belcher, Last of the Arctic Voyages, 

 II, pp. 288-306 (4 plates), 1855; William Scoresby, An Account of the Arctic Regions, 

 Edinburgh, 1820; G. Hellmann, Schneekrystalle, Berlin, 1893; Bentley and Hum 

 phreys. Snow Crystals, New York, 1931; and the especially beautiful figures of 

 Nakaya and Hasikura in Journ. Fac. Sci. Hokkaido, Dec. 1934. 



t Every snow-crystal tells, more or less plainly, the story of its own development. 

 The cold upper air is saturated with water- vapour, but this is scanty and rarefied 

 compared with the space in which snow- crystallisation is going on. Hence 

 crystallisation tends to proceed only along the main axes, or cardinal framework, 

 of the crystalline structure of ice ; in so doing it gives a visible picture or actual 

 embodiment of the trigonal-hexagonal space-lattice, in the endless permutations 

 and combinations of its constituent elements. 



