Page:Physical Geography of the Sea and its Meteorology.djvu/152

 126 are felt by the air which the south-cast trade-winds bring to the equatorial Doldrums of the Indian Ocean: it rushes over into the northern hemisphere to supply the upward draught from the heated plains as the south-west monsoons. The forces of diurnal rotation assist (§113) to give these winds their westing. Thus the south-east trades, in certain parts of the Indian Ocean, are converted, during the summer and early autumn, into south-west monsoons. These, then, come from the Indian Ocean and Sea of Arabia loaded with moisture, and, striking with it perpendicularly upon the Ghauts, precipitate upon that narrow strip of land between this range and the Arabian Sea an amount of water that is truly astonishing. Here, then, are not only the conditions for causing more rain, now on the west, now on the east side of this mountain range, but the conditions also for the most copious precipitation. Accordingly, when we come to consult rain gauges, and to ask meteorological observers in India about the fall of rain, they tell us that on the western slopes of the Ghauts it sometimes reaches the enormous depth of twelve or fifteen inches in one day. Were the Andes stretched along the eastern instead of the western coast of America, we should have an amount of precipitation on their eastern slopes that would be truly astonishing; for the water which the Amazon and the other majestic streams of South America return to the ocean would still be precipitated between the sea-shore and the crest of these mountains. These winds of India then continue their course to the Himalaya range as high winds. In crossing this range, they are subjected to a lower temperature than that to which they were exposed in crossing the Ghauts. Here they drop more of their moisture in the shape of snow and rain, and then pass over into the thirsty lands beyond with scarcely enough vapour in them to make even a cloud. Thence they ascend into the upper air, there to become counter-currents in the general system of atmospherical circulation. By studying Plate XIII., where the rainless regions and inland basins, as well as the course of the prevailing winds, are shown, these facts will become obvious.

299. The regions of greatest precipitation—Cherraponjie and Patagonia.—We shall now be enabled to determine, if the views which I have been endeavouring to present be correct, what parts of the earth are subject to the greatest fall