Page:Physical Geography of the Sea and its Meteorology.djvu/484

458 the curve itself so regular, that we feel no hesitation about projecting this curve into the unexplored spaces of the south, and asserting, with all the boldness consistent with the true spirit of philosophical deduction, that, whether the actual barometric pressure at the south pole be as low as 28.14 or not, it is nevertheless very much lower in the antarctic than in the arctic regions.

861. The question why the barometer should stand lower about the south than the north pole considered.—The question now arises, Whence this unequal distribution of atmosphere between the two hemispheres, and why should the mean height of the barometer in circumpolar regions be so much less for the austral than for the boreal? No one, it is submitted, will attempt to account for this difference by reason of any displacement of the geometrical centre of the earth with regard to its centre of attraction, in consequence of the great continental masses of the northern hemisphere; neither can it be ascribed to any difference in the forces of gravitation arising from the oblateness of our globe; neither can it be accounted for by the effects of diurnal rotation after the Halleyan theory: that would create as low a barometer at one pole as the other. The air, in its motions to the east and in its motions to the west, is in equipoise between the parallels of 35° and 40° N., 25° and 30° S. There is near each pole and about the equator a place of permanently low barometer. The air from all sides is continually seeking to restore the equilibrium by rushing into those places of rarefaction and reduced pressure; consequently there ought to be between each pole and the equator a place of high barometer from which the air on one side flows towards the equator, on the other towards the pole. Observation (p. 455) shows this high place to be between the parallels of 25° and 40° in the north, and of 20° and 30° in the southern hemisphere: thus the barometer as well as the winds, Plate XV., are both indicative of a greater degree of rarefaction about the south than about the north pole. Were there no friction, and were the atmosphere ordained to move without resistance, the air from these null belts would carry with it to the polar calms the easterly motion which it had acquired from the earth in its motion around its axis at these null belts. Were this motion so impressed, the wind would arrive, rushing with an hourly velocity about the polar calm places of 700 miles in the arctic, and 800 in the antarctic. Such a velocity would impart a centrifugal force