SNOW (AS. snuw, Goth. snolies, 011G. soCo, Ger. Schnee, snow; connected with Lat. nix, Gk. (ace.) 140a, nipha, 01r. sneehia, ()Church Slay.
sne'gri, snegas, Lett. snegs, Av. snow, Skt. snip, to be sticky or oily). Alinute crys tals of ice formed in the atmosphere when the aqueous vapor is condensed at temperatures below freezing. These crystals usually com bine into groups that are sometimes large and flocculent, but more frequently are small and ar ranged with great regularity. The elementary ice crystals or spiculfe are prisms of six sides whose ends are perpendicular to their lengths. When the length of the crystal is very small as compared with its diameter these needles become thin flat plates. The early meteorological ob servers have recorded the figures of snow crystals, as observed under a magnifying glass, but later observers have secured photographs of the crys tals as seen through the compound microscope. The longer rays that constitute the arms of the six-rayed stars arc generally hollow tubes; they are evidently built up by additions to the edge of an original crystal.
\\lien a mass of snow is melted to water the latter occupies much less volume than the origi nal snow. It is customary to say that in a gen eral way a depth of ten inches of snow is equiva lent to a rainfall of one inch of water, but it is never safe to use any specific ratio for the con version of snowfall into rainfall, but in all eases the snow should be freshly caught and melted and the exact amount of equivalent water prop erly measured. The white color of snow results from the fact that the Snow crystals are so mi nute that each cell of the retina receives a gen eral impression produced by the combination of different wave lengths reflected from innumerable minute facets. An analogous case is the white light produced by reflection from pounded glass or any foaming liquid or from a surface covered with hoar frost. Red snow, and more rarely oth er colors, such as green, blue, or black snow, are produced by the action of innumerable fungi, known as the Microcoecus niraiis. Snow rarely falls at sea level south of the parallel of 30 de grees north latitude, and on the Pacific coast of North America it occurs at sea level only north of 47 degrees north latitude. The melting of snow on the mountains adds a great deal to the drainage from the watershed into the river and the flooding of the river: carries fertility into all regions.
The great accumulations of snow by sliding downward in ravines until they join together in the river valleys and form glaciers (q.v.), con stitute an important factor in the study of phys ical geography. A heavy snowfall is not mere ly a question of low temperature, but of inflowing and uprising cool moist air. In this respect the physical processes that determine the formation of snow arc entirely similar to those that deter mine the formation of rain. The ordinary limits of snowfall and glaciation at sea level are north of the parallel of 30° north and south of the parallel of 30° south. Snow is an exceedingly poor conductor of heat, owing to the non-homo geneous texture of the mass, which may be con sidered as composed of alternate thin layers of ice and air. A covering of snow on the ground, or a hut hastily built of blocks of snow, is a perfect protection against the cold storms from the north. The roots of the most tender vegetation prosper under a covering of snow, which, ordinarily. maintains them at a uniform temperature of about F.
During the winter season snow falls at irregu lar intervals; sometimes in connection with rain, and a few days of dry air, clear sunshine, and strong wind cause the snow to evaporate and disappear. From an agricultural and a geologi cal point of view the amount of snow on the ground at any time is highly important. The United States Weather Bureau publishes monthly maps showing this feature of climatology; a gen eral map has also been compiled showing the normal amount ofsnowfall for the whole year as a help to the of the conditions that favor the accumulation of snow and the pos sible occurrence of a glacial period in North America.
BIBLIOGRAPHY. The principal collection of Bibliography. The principal collection of snow photographs are those that we owe to Dr. Neuhanss, of Berlin, 1892-93; G. Norden skiold, of Stoekholm; A. A. Sigson, of Rybinsk, Russia ; and, most important of all, those of W. A. Bentley, of Jericho, Vermont. See articles in Appleton's Popular Science Monthly, Slay, 1898, and in the Monthly Weather Review for May, 1901.