Page:Physical Geography of the Sea and its Meteorology.djvu/320

294 vapour-springs for that valley to be situated in the direction supposed, the rising up of a continent from the bottom of the sea, or the upheaval of a range of mountains in certain parts of America, Africa, or Spain, across the route of the winds which brought the rain for the Caspian water-shed, might have been sufficient to rob them of the moisture which they were wont to carry away and precipitate upon this great inland basin. See how the Andes have made Atacama a desert, and of Western Peru a rainless country: these regions have been made rainless simply by the rising up of a mountain range between them and the vapour-springs in the ocean which feed with moisture the winds that blow over those now rainless regions.

544. Countries in the temperate zone of this hemisphere that are under the lee of land in the trade-wind regions of the other are dry countries.—That part of Asia, then, which is under the lee of southern trade-wind Africa, lies to the north of the tropic of Cancer, and between two lines, the one passing through Cape Palmas and Medina, the other through Aden and Delhi. Being extended to the equator, they will include that part of it which is crossed by the continental south-east trade-winds of Africa after they have traversed the greatest extent of land surface (Plate VII.). The range which lies between the two lines which represent the course of the American winds with their vapours, and the two lines which represent the course of the African winds with their vapours, is the range which is under the lee of winds that have, for the most part, traversed water surface or the ocean in their circuit as south-east trade-winds. But a bare inspection of Plate VII. will show that the south-east trade-winds which cross the equator between longitude 15° and 50° west, and which are supposed to blow over into this hemisphere between these two ranges, have traversed land as well as water; and the Trade-wind Chart shows that it is precisely those winds which, in the summer and fall, are converted into south-west monsoons for supplying the whole extent of Guinea with rains to make rivers of. Those winds, therefore, it would seem, leave much of their moisture behind them, and pass along to their channels in the grand system of circulation, for the most part, as dry winds. Moreover, it is not to be supposed that the channels through which the winds blow that cross the equator at the several places named are