over 3,000,000 miles nearer the earth, are said to be even some degrees cooler than the same seasons in corresponding localities of the northern hemisphere. And to take an extreme example, Mars, which is 50,000,000 miles farther from the sun than the earth is, has snow-lines about its poles which reach no nearer the equator than on our planet in corresponding seasons. But the excess or diminution of eight days, in the winters of climates which even in their warmest seasons barely balance on the thawing point of ice, is a true cause in polar conditions and differences. Considering that these days affect chiefly the period of briefest sunshine, it amounts to quite one-twentieth of the whole power of the sun on a hemisphere. This difference would not be apparent in the warm regions of the globe, where there is always an excess of heat which is carried off by evaporation and ocean-currents; but it would exert nearly its full force in polar regions which are unaffected by those influences.
It cannot be denied that it is the sun's heat which prevents the temperature of the earth from sinking to, or very near to, the absolute zero of cold, wherever in the thermometrical scale that may be. Chemists have produced a cold estimated at 257° below zero, of Fahr.[1] It is not by any means probable that this reaches the entire absence of heat. But, on the supposition that it is so, and that polar regions are unaffected by the air or water currents of the tropics, then an excess of eight winter days would lessen a polar temperature 15°, and unquestionably amount to the difference of an accumulation of ice and snow year after year, instead of the annual thawing during each summer, of the winter's increase.
This is precisely what is, or has been, taking place at the respective poles of the earth. Year after year, probably for a long period, there has been a steady accumulation of ice-material about the south pole, adding weight to that hemisphere. Then, in proportion to this increase, the centre of gravity of the earth has moved a little toward the south; and the waters, always obedient to this controlling point, have gradually gathered into the southern seas, covering the lowlands and plains of islands and continents. At the same time the waters were drawn away from the north-polar regions, uncovering lands, and leaving bays and sounds and inlets innumerable. The geography of the countries fully corresponds to these inferences. The seas of the arctics are comparatively shallow and deeply cut up, and the lands are low-lying. In the antarctics the oceans are deep and bayless, and all the mainlands and islands are precipitous and craggy, as if they were the peaks and table-lands of mountain-ranges.
It is now the question whether this state of things is a permanent arrangement—whether we of the north side are always to have the advantage of extent of territory, of fertile lands and healthful homes
- ↑ The temperature of stellar space is estimated by Sir John Herschel and others at -239° Fahr.
