Snow, in the form of cylinders and spheres or spheroids, has been occasionally observed in North America. The former were produced by the snow deposited in a second shower upon some which had pre viously fallen, and the surface of which had been covered by a thin coating of ice. A violent wind then caused the particles of snow to roll on the ice, and the masses thus produced assumed perfectly cylindrical forms of various sizes, the greatest being 24 or 3 feet diameter ; they were hollow at each end. The spherical balls were from 1 inch to 15 inches in diameter, and were also formed chiefly by rolling, though some were found in enclosures where they could not have rolled, and, therefore, they are supposed to have been formed in the atmosphere itself; they were very light, and were composed of crystals irregularly united. (Silliman's Journal,' vols. ii. and vi.) Similar balls were observed in East Lothian, in 1830, by Mr. Sheriff; and this gentleman relates that they were composed only of snow,.for one of them being cut through was found to have no hard body for its nucleus. (' Edin. Phil. Journal.,' ii. 58.) Mr. Luke Howard records an instance, in which, with the surface at 33° or 34°, and during a strong wind, the snow, instead of driving loose before the wind, was collected occasionally into a ball, which rolled on, increasing till its weight stopped it : thousands of such balls were seen lying in the fields, some of them several inches in diameter. The balls of snow, torrents of which constitute what are called rolling avalanches [AvataNcees], appear to be formed in a similar manner, though by means chiefly mechanical, in addition to regelation, which must have place in all these accretions.
When an extensive tract of country is covered with newly-fallen snow, its glare has a painful and injurious effect on the eyes, from which the traveller has to guard them by a crape veil, the natives using various similar means of protection. It is, however, from such
snow 'done that much inconvenience is felt, indicating, probably, that it is owing to the light reflected from the myriads of facets which the crystals of snow present. Dr. Joseph D. Hooker remarks, that he has never suffered inconvenienco from this cause in crossing beds of old snow, or glaciers with weathered surfaces, which absorb a great deal of light, and reflect comparatively little, and that little coloured green or blue. The changes to which snow is subject after descending to the ground, according to tho circumstances of temperature, weather, ex posure, and the nature of the surface upon which it has fallen, are evaporation, liquefaction, and conversion into a compact ice. It evapo rates at all temperatures. Mr. Howard found a circular area, of five inches diameter, to lose 150 grains troy from sunset to sunrise, and about 50 grains more by the following sunset, the temperature varying from 18' to 30'. This evaporation probably supplies the vapour which appears in the form of mist after a snow-fall, and also that which Ls condensed again in the form of a secondary fall of snow.
The process of conversion of snow into glacier ice has been noticed in the article Grtetens, in NAT. HIST. Drv. A similar conversion, in localities of a different character, has been observed by Dr. Hooker, who describes the beds of perennial snow in the Sikkim Himalaya, which extend below the true inferior limit of perpetual snow (see the following article), as having great resemblance to glaciers, from which, indeed, he considers them undistinguishable. Though broad and con vex, and occupying mountain slopes,—not filling hollows like glaciers commonly so called,—they display the ribboned structure of glacier ice, and descend at a rate and to a distance depending on the slope and on the amount of annual accumulation behind. [amen ; Ham.]