Page:Physical Geography of the Sea and its Meteorology.djvu/442

416 has its hurricane season in the opposite season of the year, and when the north-west monsoon prevails in the East Indian Archipelago."

785. The cyclone theory.—Under the head of hurricanes, typhoons and tornadoes, I include all those gales of wind which are known as cyclones. These have been treated of by Redfield in America, Reid in England, Thom of Mauritius, and Piddington of Calcutta, with marked ability, and in special works. I refer the reader to them. The theory of this school is, that these are rotary storms; that they revolve against the hands of a watch in the northern, and with the hands of a watch in the southern hemisphere; that nearer the centre or vortex the more violent the storm, while the centre itself is a calm, which travels sometimes a mile or two an hour, and sometimes forty or fifty; that in the centre the barometer is low, rising as you approach the periphery of the whirl; that the diameter of these storms-is sometimes a thousand miles, and sometimes not more than a few leagues; that they have their origin somewhere between the parallels of 10° and 20° north and south, travelling to the westward in either hemisphere, but increasing their distance from the equator, until they reach the parallel of 25° or 30°, when they turn towards the east, or "recurvate," but continue to increase their distance from the equator—i. e., they first travel westwardly, inclining towards the nearest pole; they then recurve and travel eastwardly, still inclining towards the pole; and that such is their path in both hemispheres, etc.

786. Puzzling questions.—The questions why these storms should recurve, and why they should travel as they do, and why they should turn with the hands of a watch in the southern, and against them in the northern hemisphere, are still considered by many as puzzles, though it is thought that their course to the westward in the trade-wind region, and to the eastward in the counter-trades, is caused by the general movement of the atmosphere, like the whirls in an angry flood, which, though they revolve, yet they are borne down stream with the currents as they do revolve. The motion polarward is caused, the conjecture is, by the fact that the equatorial edge of the storm has, in consequence of diurnal rotation, a greater velocity than its polar edge. There seems, however, to be less difficulty with regard to their turning than with regard to their course; the former is now regarded as the resultant of diurnal rotation and of those forces of translation