SNOW. 



tSXl\V. 



Hi 



uniUtl together in iu-h a manner u to reflect light to the eye in great 

 abun.Unoo fn-m all, tliu* producing a sensation of whiteness, the 

 Mawnblngn ' crystals constitute mow. In all probability it in formed 

 by the immediate (reccing of aqueoui vapour, without the sensible 

 intarreotioo of the liquid state. Proximity to the earth'* surface U 

 not required for its production ; Mr. Green, the Bronaut, met with a 

 severe anow-storm at the height of a mile and a quarter. The forma- 

 tion of mow through a considerable tract of the atmosphere appears 

 u a Uuiah, 



at a distance u a 



eti 



indigo-blue, has*. 



M. Honge ohiervea ('Annales de Chimie,' vol. v., p. 1), that the 

 crystallisation of sal-ammoniac preaenta phenomena similar to those 

 which are observed in the formation of Know. If a saturated solution 

 of sal ammoniac in a warm state be allowed to cool in a tranquil air, 

 the surface of the liquid is that which first arrives at a state of super- 

 Kituratimi, and there the first crystals are formed ; these sink imme- 

 diately, and in descending they unite with similar crystals formed in 

 the liquid itself, so that they arrive at the bottom of the vessel in 

 white Hakes. 



The flakes of snow usually consist of brilliant spicular icicles, which 

 diverge from a centre in six directions, and resemble stars having BO 

 many rays, upon each of which small crystals are sometimes formed ; 

 but if the atmosphere w agitated, the original flakes strike against each 

 other, and uniting in groups by regelation [ICE], in consequence of 

 small quantities of moisture adhering to them, they descend in 

 irregular forms. In regions of the earth far to the north or south, 

 the ah-, when allowed to enter through a small aperture into a heated 

 apartment, has frequently caused the worm vapour to be converted 

 into snow. (' BiMiothcque Univereclle,' 1830.) 



Beccaria observed that his apparatus for ascertaining the electrical 

 state of the atmosphere indicated the presence of electricity in snow 

 as well as in rain ; and, according to the observations of Schiibler, it is 

 more commonly positive than negative. The lightness of the Bakes, 

 by which they float about in the air when agitated, is the result of 

 their surface being great when compared with their volume. The sp. gr. 

 of snow has been stated to be very variable ; and according to Muss- 

 chenbroek, that of some, of the stelliform kind, was only of the 

 pacific gravity of water, but this must have been the specific gravity 

 of the mass, a mixture in fact of air and ice ; and M. Quetclet has since 



found that the greatest density is nearly ^g of that of water, the tem- 



perature being 34'5 (Fahr.). He ascertained also that the density of 

 fine snow having no determinate form was about !, the temperature 

 being 32, and that the least density varied from ,'->*" i'u of '-hat of 

 water, at which time the snow had the form of small stars, and the 

 temperature varied from 29*7 to 18'5. It is, however, difficult to 

 understand these results ; it would appear that they also must relate 

 to an aggregate of snow and air, as there is no reason why the specific 

 gravity of crystals of snow should differ greatly from that of ice, which 

 is always crystalline, and has the sp. gr. 0-918. 



Snow has been observed to fall in a fine powder, not having any 

 appearance of regular crystaht, and sometimes in grains, as fine oa those 

 of what is called basket salt 



The flakes have, even in temperate regions, many varieties of form, 

 and are often very elegant ; but the polar regions of the earth are those 

 in which it has been supposed that nature has displayed her power in 

 creating this species of beauty in the highest degree and to the greatest 

 extent. In the ' Phil. Trans ,'1775, maybe seen numerous delineations 

 of the figures assumed by flakes of snow as they were observed by Dr. 

 Nettis, of Middelburg in 1740 ; but the late Rev. Dr. Scoresby, in his 

 ' Account of the Arctic Regions,' has given still greater varieties ; the 

 latter gentleman, besides dividing them into classes, has also expressed 

 their magnitudes, and the state of the barometer and thermometer 

 when the snow fell. 



( ii these classes the first is called " lamellar," and is divided into 

 many different species : one of the latter is a thin transparent hexagonal 

 plate, or a hexagonal plate with white lines parallel to the sides of 

 the polygon, and sometimes there is a starlike figure in the centre ; 

 the magnitudes vary, and the greatest is about -f a inch diameter. 

 Another species, and this is the most ordinary appearance of snow, is the 

 etelliform ; the figures 1, 2, and 3 represent some of the moat remark- 

 able varieties of this kind ; its magnitude varies, but the diameter of the 



greatest is about ( inch, and it occurs most abundantly when the tem- 

 perature of the air is near the freezing point of water. Sometimes 

 the stars appear to have twelve points, but Dr. Scoresby thinks that 

 thaw are formed merely of two stellar plates applied one on the other 

 The six following figures represent assemblages of hexagonal crystals 

 the diameters of the first two kinds are respectively fa and -,' inch 



and those of the rest are { inch diameter ; they are usually formed at 

 temperatures between 82 and 20* (Kahr.). 



c 



The second class is also lamellar, but it differs from the form, r in 

 having a spherical nucleus, either transparent or white, about J inrh 

 diameter ; and sometimes spicular radii proceed from thence in ditl'.-i . nt 

 directions at angles of 60 with each other. The temperature at which 

 this class is formed varies also from the freezing-point to 20 (Fahr.). 



The third class consists of spicula* or six-sided prisms ; of the 

 finer sort, which ore formed at the temperature of 28, resemble white 

 hairs very delicate and clear, and about J inch long ; the coarser kinds 

 are formed in the lower region of the atmosphere, at about the freezing 

 temperature. 



The fourth class is of a pyramidal form and about jg inch high, but 

 Dr. Scoresby could not determine whether the base was triangular or 

 hexagonal. The fifth class consists of hexagonal crystals united together 

 by a slender spicular crystal, so as to resemble two wheels with an axle. 

 Both of these kinds are very rare. Dr. Scoresby saw the latter only 

 twice and the former only once. 



M. Huber Burnand, speaking of the character of the snow which fell 

 at Yverdun in 1829 and 1830, states that it was crystallised in stellar 

 plates with six rays, along each of which were disposed filaments 

 arranged like feathers, and these again supported finer filaments 

 similarly arranged ; the plates, which were extremely thin, were per- 

 fectly plane and regular. (' Bibl. Univ.,' 1830.) It is also related 

 in the same work, that in 1829 the frost at Yverdun assumed every 

 day a different form, being sometimes disposed in parallel groups or 

 fillets ; sometimes it resembled leaves, and occasionally spines about 

 an inch long, which were terminated by a flat rosette with six 

 divisions. 



The severe weather experienced in the vicinity of London, and over 

 the south-west and eastern parts of England at the beginning of the 

 year 1855, of which no parallel had taken place since that of 1814, 

 which it greatly resembled, as well for depression of temperature as for 

 the duration of the frost, was remarkable also for the peculiar character 

 and continuous fall of snow, which first made its appearance on 

 January 16th, and lay on the ground till after the end of February. 

 We are indebted to Mr. Glaisher, the Secretary of the British Meteoro- 

 logical Society, for a particular account of this snow and its crystals, 

 which is annexed to the Report of the Society read at the fifth annual 

 meeting, May 2'2. 1855. Much of this snow, Mr. Glaisher observes, 

 was " of that iwculiar character which former writers designated Polar 

 Snow, it having been chiefly composed of crystalline particles, \vhirh 

 they supposed to be confined, with rare exceptions, to the Arctic 

 regions. This supposition, however, is not supported by the recent 

 prevalence of innumerable crystals, that have exhibited a degree of 

 crystalline formation equal to any that has been recorded in colder 

 latitudes The primary figure or liase of each crystal I deter- 

 mined to be a star of six radii, or a hexagon of lamimc, and tin 

 pound varieties to include combinations of spicuhc, prisms, cubes, and 

 rhomboids, aggregated upon and around the central figure, ace" 

 to the degree of its complexity." The paper is illustrated by 88 HnaQ 

 and 63 greatly enlarged figures of the snow crystals, the joint pro- 

 ductions of the pencils of Mr. and Mrs. Glaisher, and probably the most 

 valuable series of such representations extant. The figures nliov-, 

 miiieil from Dr. Scoresby, 6, 7, and 8, it will be observed, have an 

 inner tracing of the hexagon. Similar crystals to these were ol > 

 by Mr. Glaisher, who had not seen them previously, nor any figures of 

 them, except those of Dr. Scoresby of those seen by him in the Arctic 

 Seas. But the forms of snow-crystals are doubtless dependent on the 

 temperature of the air and the amount and distribution of the aqueous 

 vapour it contains, the differences in those respects of tin' diilm-nt 

 strata of air, the interchange of currents, and other phyie:il cir- 

 cumstances, and not otherwise upon difference of locality than as that 

 may involve a difference in those circumstances. The forms ordimrlly 

 characteristic of the snow of one latitude or region may be produced 

 in any other, wherever snow can occur. It does appear, however, 

 that the moat regular and complex stellate aggregations accompany 1 1 ID 



