SNOW, in meteorology, water solidified in stellate crystals, variously modified, and floating in the atmosphere. These crystals arise from the congelation of the minute vesicles which constitute the clouds, when the temperature of the latter is below zero. They are more reg ular when formed in a calm atmosphere. Their form may be investigated by col lecting them on a black surface, and view ing them through a strong lens. The reg ularity, and at the same time variety, of their forms are truly beautiful. These crystals are united together in such a manner as to reflect light to the eye in great abundance from all, thus producing a sensation of whiteness. The presence of air in snow renders it opaque, other wise it would be transparent, like ice and other crystallized bodies. Regular crys tals of snow are only found where the air is still and the temperature very cold; they do not, therefore, often occur in tem perate regions. In the polar regions snow has been seen of red, orange, and salmon color. This phenomenon occurs both in the fixed and floating ice, and seems to result in some cases from vegetable, and in others from animal matter suspended in the water and deposited on the sur rounding ice. In general, the electricity of snow is positive, and by chemical analysis it has been found that snow water contains a greater proportion of oxygen than rain or river water—a fact which accounts for its superior activity in causing iron to rust, etc.
In the economy of nature snow answers many valuable purposes. By its gradual melting in high regions it serves to supply streams of running water, which a sudden increase in the form of rain would convert into destructive torrents or standing pools. In many countries snow tempers the burn ing heat of summer by cooling the winds which pass over it. On the other hand, in colder climates snow serves as a de fense against the severity of winter, where it protects plants against the frost and serves as a shelter to animals, which bury themselves in it. The elevation at which mountains are covered with perpetual snow is called the "snow line," or plane of perpetual snow. The snow line on the N. side of the Himalayan Mountains is 18,600 feet; on Chimborazo, 15,802 feet.
The altitude of perpetual snow under the equator was fixed by Humboldt at 15,748 feet; toward the poles it is considerably lower. The snow line of the Alps, N. lat itude 46°, is only 8,860 feet; and that of the Pyrenees about 8,850 feet. At the North Cape, in latitude 71°, it is only 2,300 feet. The position of the snow line in all mountains, however, depends so much on variable causes that no general rule can be laid down for determining the altitude of perpetual snow.