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<h2>CHAPTER XXI.</h2> 440. What is snow? Snow is congealed vapour, which would have formed rain; but, through the coldness of the air, has been frozen in its descent into crystalline forms. (Fig. 1.) 441. Why is snow white? Because it reflects all the component rays of light. 442. Why is snow said to be warm, while white garments are worn for coolness? Snow is warm by virtue of its light and woolly texture. But it is also warm on account of its whiteness; for, had it been black, it would have absorbed the heat of the sun, which would have thawed the snow. Instead of which, it reflects heat; and the reflected heat falls upon bodies above the snow, while the warmth of the earth is preserved beneath it. White clothing is cool, because it reflects from the body of the wearer the heat of the sun. White snow is warm, because it reflects the sun's heat upon bodies. There are few persons but have felt the effect of the sun's rays reflected by the white snow on a clear wintry day. And, as regards the warmth of snow towards the earth, by preventing the radiation of heat, it has been found that a thermometer buried four inches deep in snow has shown a temperature of nine degrees higher than at the surface. 443. Why are lofty mountains always covered with snow? Because the upper regions of the atmosphere are intensely cold. 444. Why are the upper regions of the atmosphere intensely cold? Because the atmosphere retains but little of the heat of the sun's [Pg 106] rays as they pass to the earth. Because at high altitudes the air is greatly rarefied. And because the radiation of heat from the earth does not materially affect such high regions. <hr class="bible-verse" /> "He causeth the vapours to ascend from the ends of the earth: he maketh lightnings for the rain: he bringeth the wind out of his treasuries."—Ps. xxxv. <hr class="bible-verse" /> 445. What is meant by the snow line? The snow line is the estimated altitude in all countries where snow would be formed. Even at the equator, at an altitude of 15,000 to 16,000 feet from the level of the sea, snow is found upon the mountain summits, where it perpetually lies. As we proceed north or south from the equator the snow line lessens in altitude. Had we in England a mountain 6,000 feet high, it would be perpetually crowned with snow. 446. Why do we hear of red snow? Red snow is the name given to the snow in the arctic regions upon which a minute vegetable (probably the Protoccus nivalis) grows, imparting to the snow a red colour. Recent microscopic investigations have shown it to consist of a minute vegetable cell, which secretes a red colouring matter. Snow is found to be of greater importance to man than is generally supposed. But, although in this country we are enabled to recognise the hand of Providence in the gift, there are latitudes wherein the blessing thus conferred is more deeply felt. In such countries as Canada, Sweden, and Russia, the falling of snow is looked for with glad anticipations, quite equalling those which herald the "harvest-home" of England, or the "vintage" of France. No sooner is the ground covered with snow, than cranky old vehicles that had been jolting over rough roads, and sticking fast in deep ruts of mud, are wheeled aside, and swift sledges take their place. Towns distant from each other find an easy mode of communication; the markets are enlivened, and trade thrives. Snow supplies a kind of railroad, covering the entire face of the country, and sledges glide over it, almost with the speed of the locomotive. 447. What is sleet? Sleet is snow which, in falling, has met with a warmer current of air than that in which it congealed. It therefore partially melts and forms a kind of wet snow. 448. What is hail? Hail is also the frozen moisture of the clouds. It is probably formed by rain drops in their descent to the earth, meeting with an exceedingly cold current of air by which they become suddenly frozen into hard masses. [Pg 107] It is also supposed that the electrical state of the air and of the clouds influences the formation of hail. <hr class="bible-verse" /> "If the clouds be full of rain, they shall empty themselves upon the earth."—Eccles. xi. <hr class="bible-verse" /> 449. Why is it supposed that the electrical state of the air and the clouds affects the formation of hail? Because hail is more common in the summer than at other seasons, and is frequently attended by storms of thunder and lightning. 450. Why do hail-storms most frequently occur by day? Because the clouds, being charged with vapour to saturation, favour the formation of hail by sudden electrical or atmospheric changes. In the gradual cooling of night, the clouds would expend themselves in rain. Astonishing facts respecting hail-storms are upon record. In 1719 there fell at Kremo, hailstones weighing six pounds. In 1828 there was a fall of ice at Horsley, in Staffordshire, some of the pieces of which were three inches long, by one inch broad; and other solid pieces were about three inches in circumference. Hail storms are most frequent in June and July, and least frequent in April and October. Hail clouds float much lower in the sky than other clouds; their edges are marked by frequent heavy folds; and their lower edges are streaked with white, the other portions being massive and black. (Fig. 10.) <hr class="chap" /> <div style="break-after:column;"></div>

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