Page:Physical Geography of the Sea and its Meteorology.djvu/391

Rh or of any other great river, to his senses. 



681. The cause of.—Monsoons are, for the most part, trade-winds deflected. When, at stated seasons of the 3^ear, a trade-wind is turned out of its regular course, as from one quadrant to another, it is regarded as a monsoon. The African monsoons of the Atlantic (Plate VIII.), the monsoons of the gulf of Mexico, and the Central American monsoons of the Pacific are, for the most part, formed of the trade-winds which are turned back or deflected to restore the equilibrium which the overheated plains of Africa, Utah, Texas, and New Mexico have disturbed; these winds, carrying their fuel (§ 254) with them in vapour, have their equilibrium still further disturbed by the heat which is liberated when that vapour is condensed. Thus, with regard to the N.W. and the S.W. monsoons of the Indian Ocean, for example: a force is exerted upon the N.E. trade-winds of that sea by the disturbance which the heat of summer creates in the atmosphere over the interior plains of Asia, which is more than sufficient to neutralize the forces which cause those winds to blow as trade-winds; it arrests them and turns them back; but, were it not for the peculiar conditions of the land about that ocean, what are now called the N.E. monsoons would blow the year round; there would be no S.W. monsoons there ; and the N.E. winds, being perpetual, would become all the year what in reality for several months they are, viz., N.E. trade-winds.

682. The region of.—Upon India and its seas the monsoon phenomena are developed on the grandest scale. These remarkable winds blow over all that expanse of northern water that lies between Africa and the Philippine Islands. Throughout this vast expanse, the winds that are known in other parts of the world as the N.E. trades, are here called N.E. monsoons, because,