Interesting observations have been made on the relations between ice and snow. The difference seems to lie only in the more or less compacted arrangement of the frozen particles. Water and air, each being transparent when separate, become opaque when intimately mingled; the reason being that the inequalities of refraction break up and scatter every ray of light. Thus, clouds cast a shadow; so does steam; so does foam: and the same elements take a still denser texture when combined as snow. Every snow-flake is permeated with minute airy chambers, among which the light is bewildered and lost; while from perfectly hard and transparent ice every trace of air disappears, and the transmission of light is unbroken. Yet that same ice becomes white and opaque when pulverized, its fragments being then intermingled with air again,--just as colorless glass may be crushed into white powder. On the other hand, Professor Tyndall has converted slabs of snow to ice by regular pressure, and has shown that every Alpine glacier begins as a snow-drift at its summit, and ends in a transparent ice-cavern below. "The blue blocks which span the sources of the Arveiron were once powdery snow upon the slopes of the Col du Géant." The varied and wonderful shapes assumed by snow and ice have been best portrayed, perhaps, by Dr. Kane in his two works; but their resources of color have been so explored by no one as by this same favored Professor Tyndall, among his Alps. It appears that the tints which in temperate regions are seen feebly and occasionally, in hollows or angles of fresh drifts, become brilliant and constant above the line of perpetual snow, and the higher the altitude the more lustrous the display. When a staff was struck into the new-fallen drift, the hollow seemed instantly to fill with a soft blue liquid, while the snow adhering to the staff took a complementary color of pinkish yellow, and on moving it up and down it was hard to resist the impression that a pink flame was rising and sinking in the hole. The little natural furrows in the drifts appeared faintly blue, the ridges were gray, while the parts most exposed to view seemed least illuminated, and as if a light brown dust had been sprinkled over them. The fresher the snow, the more marked the colors, and it made no difference whether the sky were cloudless or foggy. Thus was every white peak decked upon its brow with this tiara of ineffable beauty.