We can now judge of the enormous amount of moisture carried up by the sun and dispersed over the earth in rain, which swells our brooks and rivers, cleanses the air of its impurities, supplies our springs, carries with it into the sea lime from the rocks for the shells of marine animals, and then leaving its salts, is again evaporated to form clouds, which discharge the fresh water continually upon the earth in a never-ceasing rotation.
Snow.
“We all know what Snow is,” you will say, perhaps. Well, then, will any ordinary young reader tell me what he knows about snow? “It falls from the sky in white flakes,” says one. “It’s frozen rain,” remarks another. “Why, snow is snow,” says a third. “There’s nothing like it; it’s white rain-water frozen.”
Fig. 721.—Crystals of snow.
The last answer we received is the nearest of all. Snow is not snow, paradoxical as that sounds. Snow is Ice! Flakes of snow are ice-crystals—white, because reflecting light. In the section of Mineralogy we mentioned crystals, which are certain definite shapes assumed by all substances, and we gave many examples of them. Just as alum crystallizes and rock crystal assumes varied and beautiful forms, so ice crystallizes into six-rayed stars.
It is to Professor Tyndall that the world is chiefly indebted for the descriptions of snow crystals and ice flowers. In his work upon “Heat as a Mode of Motion,” this charming writer shows us the structure of ice flowers. He describes a snow shower as a “shower of frozen flowers.” “When snow is produced in calm air,” he says, “the icy particles build themselves into stellar shapes, each star possessing six rays.” We annex some drawings of snow crystals, which are, indeed, wonderfully made. Hear Professor Tyndall once again:—
“Let us imagine the eye gifted with a microscopic power sufficient to enable us to see the molecules which compose those starry crystals: to observe the solid nucleus formed and floating in the air; to see it drawing towards it its allied atoms, and these arranging themselves as if they moved to music, and ended by rendering that music concrete.” This “six-rayed star” is typical of lake ice also.
Fig. 722.—Ice crystal.