SNOW

(Ger. schnee.) Congealed water, which falls from the bosom of the atmosphere. Very little is yet known respecting the formation of this meteor. It has not been ascertained, for instance, whether the clouds which produce it are composed of vesicular vapours, or of frozen particles; nor whether the flakes are completely formed before they begin to descend, or receive an increase in pa ing through the lower strata of the atmosphere. The temperature of the flakes, and the circumstances which determine their form and volume, are likewise unknown. The only observations which may be considered as in any degree complete are with reference to the different forms which the flakes a ume. This subject was considered by Kepler, Hooke, Ca ini, Muschenbroek, and many others; but the most interesting series of observations we po e are those of Scores by {Account of the Arctic Regions, 1820), who has reduced the different forms into cla es, and given a number of excellent representations of tlie flakes in different states. Generally speaking, when examined with the microscope they present modifications of stelliform and hexagonal crystals; and frequently they consist of a star of six rays formed of prisms united at angles of 60*^, from which other prisms shoot at similar angles, giving the whole an appearance of exquisite beauty and great regularity. The variety of modifications is probably owing to the state of the atmosphere when the snow is formed. If the crystallization takes place when the air is calm, the crystals will be regularly formed; on the contrary, they will be irregular and imperfect when the air is much agitated. Sometimes the flakes present no traces of crystallization. Snow is much le dense than ordinary ice. The hulk of a given weight of ice is only about a ninth part greater than that of the water from which it is formed, while the bulk of new-fallen snow is ten or twelve times greater than that of the water obtained by melt'ng it. At moderate elevations above the sea, and in the mean latitudes, snow most frequently falls after some days of pretty hard frost, and when the temperature of the air, though still a few degrees above the freezing point, is sensibly mitigated. On this circumstance is founded the remark that it cannot snow in very severe cold; and though the remark does not always hold good, it will do so generally, for two reasons: — in the first place, the air which comes from very cold regions contains a small portion of watery vapour; and secondly, because the formation of clouds, by diminishing the radiation, nece arily mitigates the severity of the cold. As snow can only be formed when the temperature of the atmospheric strata containing the aqueous vapour is below the ireezing point, it is obvious that if the snow in falling pa es into strata of a higher temperature, it will be melted before arriving at the surface of the earth. Hence it follows that it never snows in the torrid zone, nor in the heats of summer, excepting on the tops of very elevated mountains. Red Snow — It had been remarked by the ancients that snow sometimes a umes a red tint, and Pliny ascribes the cause to age: — Ipsa nix vetustate rnbescit. Many modern observers have described and examined this curious phenomena, which appears to be met with in all parts of the world.. Sau ure observed red snow on the Bevern in 1760, and on St. Bernard in 1778; and he supposed the colouring matter to consist of a vegetable dust. Ramond met with it in the Pyrenees, Captain Ro in Baffin's Bay; Parry, Franklin, and Scores by collected it in still higher northern latitudes; and it has been found abundantly in New Shetland in latitude 70° south. Among the Alps it is generally found in low sheltered spots, and penetrating to the depth of two or three inches; or rather the strata in which it is found (for it occurs overlaid at considerable depths) seldom exceed two or three inches in thickne . The colouring matter of this singular substance has been examined by WoUaston, R. Brown, De Candolle, The nard, Bauer, . Dr. Wollaston first remarked that it is composed of minute spherical globules, which have a transparent envelop, and are divided into seven or eight small cells filled with a species of red oil insoluble in water. Mr. R. Brown and De Candolle supposed the globules to be a kind of algae. Mr. Bauer {Fhil. Trans. 1820) found the globules to be exactly identical in snow collected in Baffin's Bay and New Shetland; and he supposed them to be small mushrooms of the genus Uredu, forming a peculiar species, to which ho gave the name of Uredo nival is. 4 C 3 [s. 1138]