Page:Physical Geography of the Sea and its Meteorology.djvu/109

 Rh show that, if ever it be answered by man, he must consult the science of astronomy. It has been recently all but proved, that the earth and sun, with their splendid retinue of comets, satellites, and planets, are all in motion around some point or centre of attraction inconceivably remote, and that that point is in the direction of the star Alcyon, one of the Pleiades! Who but the astronomer, then, could tell their "sweet influences?" And as for the general system of atmospherical circulation which I have been so long endeavouring to describe, the Bible tells it all in a single sentence: "The wind goeth towards the south, and turneth about unto the north; it whirleth about continually, and the wind returneth again according to his circuits."—Eccl. i. 6.

217. Sloughing off from the counter trades.—Of course, as the surface winds, H J K, and T U V, approach the poles, there must be a sloughing off,—if I may be allowed the expression,—of air from them, in consequence of their approaching the poles. For as they near the poles, the parallels become smaller and smaller, and the surface current must either extend much higher up, and blow with greater rapidity, or else a part of it must be sloughed off above, and so turn back before reaching the calms about the poles. The latter is probably the case. Such was the conjecture. Subsequent investigations have established its correctness, and in this way: they show that the south-east trade-winds, as in the Atlantic, blow, on the average, during the year, 124 days between the parallels of 25° and 30° S., and that as you approach the equator their average annual duration increases until you reach 6° S. Here between 5° and 10° S. they blow on the average for 329 out of the 365 days.

218. The air which supplies the south-east trade-wind in the band 5° does not cross the band 25°.—Now the question may be asked, Where do the supplies which furnish air for these winds for 329 days come from? The "trades" could not convey this fresh supply of air across the parallel of 25° S. during the time annually allotted for them to blow in that latitude. They cannot for these reasons: (1.) Because the trade-winds in lat. 5° are stronger than they are in lat. 25°, and therefore, in equal times, they waft larger volumes of air across 5° than they do across 25°. (2.) Because the girdle of the earth near the equator is