Page:Physical Geography of the Sea and its Meteorology.djvu/441

Rh part of this sea. In the square between 15° and 20° north, 110° and 115° east, there appears to be a system of three monsoons; that is, one from the north-east in October, November, December, and January; one from east in March and April, changing in May; and another from the southward in June, July, and August, changing in September. The great disturber of the atmospheric equilibrium appears to be situated among the plains and steppes of Asia ; their influence reaches up to the clouds, and extends to the China Seas; it is about the changing of the monsoons that these awful gales, called typhoons and white squalls, are most dreaded.

783. The Mauritius hurricanes.—In like manner, the Mauritius hurricanes, or the cyclones of the Indian Ocean, occur during the unsettled state of the atmospheric equilibrium which takes place at that debatable period during the contest between the trade-wind force and the monsoon force (§ 699), and which debatable period occurs at the changing of the monsoon, and before either force has completely gained or lost the ascendency. At this period of the year, the winds, breaking loose from their controlling forces, seem to rage with a fury that would break up the very fountains of the deep.

784. The West India hurricanes.—So, too, with the West India hurricanes of the Atlantic ; these winds are most apt to occur during the months of August and September. There is, therefore, this remarkable difference between these gales and those of the East Indies: the latter occur about the changing of the monsoons, the former during their height. In August and September, the south-west monsoons of Africa and the south-east monsoons of the West Indies are at their height; the agents of one drawing the north-east trade-winds from the Atlantic into the interior of New Mexico and Texas, the agents of the other drawing them into the interior of Africa. These two forces, pulling in opposite directions, assist now and then to disturb the atmospheric equilibrium to such an extent that the most powerful revulsions in the air are required to restore it. "The hurricane season in the North Atlantic Ocean," says Jansen, "occurs simultaneously with the African monsoons; and in the same season of the year in which the monsoons prevail in the North Indian Ocean and the China Sea, and upon the Western coast of Central America, all the seas of the northern hemisphere have the hurricane season. On the contrary, the South Indian Ocean