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Page:Popular Science Monthly Volume 38.djvu/535

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much importance. Were it not for the snow-fall the problem of climate would be materially modified, and the temperature of the earth's surface much ameliorated. The seasons would gain a regularity which they do not now possess, the agricultural period of the colder zones be much extended, and the domain of agriculture be considerably widened, by the recovery of broad regions which are now covered during much or all of the agricultural season by snow.

In the winter the frost-laden strata of the atmosphere descend to the surface over much of the globe, and produce a direct refrigerating influence upon the surface soil and waters. This winter freezing, however, is of minor importance, as it, except in the polar regions, quickly yields to the spring suns, while its influence upon the summer temperature of lower latitudes is but slight. Only for the snow-fall this would be our sole source of cold. But the vast blanket of snow which descends annually upon the colder zones conveys downward the severe chill of higher layers of the air, borrowing from a mighty storehouse of cold which broadly impends above the earth. This snow blanket must be removed, and its stored cold overcome by solar heat, before agriculture can begin, and in this process weeks or months pass away, the effect being greatly to reduce the area of the earth's surface which is suitable for human habitation.

The snow of the frigid zones does not wait for the sun to reach it. It travels toward the tropics to meet the sun. This creep of the snow, as we may call it, takes the forms of the glacier and the iceberg. It also acts in another curious method, not generally known, but which is described by Nordenskiöld, in his Voyage of the Vega. Speaking of the natural conditions at a winter station near Bering Strait, he says: "The fall of snow was not great, but, as there was in the course of the winter no thaw of such continuance that the snow was at any time covered with a coherent melted crust, a considerable portion of the snow that fell remained so loose that with the least puff of wind it was whirled backward and forward. . . . Even when the wind was slight and the sky clear, there ran a stream of snow some centimetres in height along the ground in the direction of the wind, and thus principally from northwest to southeast. . . . The quantity of water which in a frozen form is thus removed in this certainly not deep but uninterrupted and rapid current, over the north coast of Siberia to more southerly regions, must be equal to the mass of water in the giant rivers of our globe, and plays a sufficiently great rôle among others as a carrier of cold to the most northerly forest regions to receive the attention of meteorologists." It may be that a similar condition prevails over northern America, though concerning this we have no evidence