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centre, winds, system, anti-cyclone and pressure

CYCLONE (Gr. uwhirling,p a term originally applied to the violent rotatory tempests of the tropical and sub-tropical regions, called in the West Indies hurricanes; in Senegal, tornadoes; at the Cape of Good Hope, trovados; in the Chinese Sea, typhoons; and on the west coast of Central America, papagallos. The diameter of rotation of such storms is from 200 to 300 miles and sometimes exceeds 500, and the velocity of the wind, according to Humboldt, is sometimes as much as from 200 to 300 miles an hour. The centre of the storm often advances 30 miles an hour. Since the discovery of the rotatory course of winds even at a distance from the tropics the term cyclone has, however, been applied to any system of winds blowing round a centre of low pressure, and a cyclone is distinguished from an anti cyclone, which is a system of winds with a centre of high pressure. These two systems are always in proximity to each other, though their centres may be, and usually are, very wide apart. In the cyclone there is a gradual rise of barometric pressure from the centre to the circumference, in the anti-cyclone a gradual fall; in consequence of this the tendency of the winds in a cyclone is toward the centre, in an anti-cyclone it is from the centre; a cyclonic system travels in a certain direction from the region where it originates till it is dissipated or destroyed; an system generally remains in the region where it is formed, its centre only shift ing about within comparatively narrow limits; the isobaric lines of a cyclone, especially near the centre, are almost circular, those of the anti-cyclone extremely irregular, and the at mospheric gradient (that is, the rate of increase or decrease of pressure) is usually greater in the former than in the latter. While the general

tendency of cyclonic winds is toward the centre of the cyclone, their actual course is not directly toward that space, but spirally round it, the lines of rotation being nearly the same as those of the isobaric curves. The direction of rota tion is stated in