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306 parently left behind by the more rapidly moving earth as it turns from west to east and the wind draws accordingly more and more from the east to the west, forming the northeast trades in north latitudes andthe southeast trades in the south latitude. Similarly, the air which starts from the region of high pressure in middle latitudes and moves toward the poles, is starting with the linear velocity of the earth from west to east in those latitudes and moving toward a region where the velocity of the earth's surface is continually grow- ing less, thus making the wind blow more and more from the westward in each hemisphere. This is the general circulation of the winds on the surface of the earth, from east to west in the tropics, both north and south of the equator, and from west to east in high latitudes. This general circulation may be and frequently is in- MARINE REVIEW In the North Pacific, the Philippine islands are located directly in the path of the cyclonic storms which occur there. They appear to originate at sea some- where in the neighborhood of Guam and usually cross the Philippines north of latitude 10 degrees N. before re- curving to the northward. In the South Pacific, the details of cyclonic storms are not so well known, due to the scarcity of observing sta-. tions in these waters. Samoa, Fiji, and the Tonga islands are, however, directly in the path of the majority of these storms. The storms of the Indian ocean have several peculiarities which distinguish them from other cyclonic storms and ap- pear to occur with the greatest frc- quency in the neighborhood of Mauri- tits. In the earlier stage of its existence, the moticn of the storm center has in ine oe ae 0 0 1 0 0 GUNG eee oss 0 Z 0 0 0 Augusti. 405 1 1 1 4 0 September..... 2 2 1 0 2 October).....7.. 1 3 4 2 3 November..... 2 0 1 1 0 ) OCCURRENCES OF WEST INDIA HURRICANES 1890. 1891. 1892. 1893. 1894. 1895. 1896. 1897. 1898. 1899. 1900. Total FREQUENCY OF TYPHOONS 1 Z 8 19 22 4 ore OOO SKHnoooe One OOO COncocoO OFNE OO Sances IN NORTH PACIFIC Fre- Period. Class. quency. Per cent. eee Ida ol Middle of June to end of September. IAb 2 Middle of July to middle of October. Ib 0 Late in the year. Ic 4 fans to the end of September. Id 2 ay to September, inclusive. Il4 2 July, August, and September. . IIb i August and September. é IIc a June to September. Maximum in July. IId 4 July and August. IIIa 14. October and November. IIIb 1 October. ate i July, gual one une to October. ost frequent in August and Sept ; . IIIe 12% ie to December. : . ' prcmres IVA 84% May to December. Rare in 'August. 1Vab 3 Beginning and end of typhoon season. ee v2 pembe 1 9 Decomecr | Most common in November. ¢ eginning and end oft oon season. Most i IVd 1 April and December. if Pe reavent iapilayn terfered with by local conditions, par- ticularly in the northern hemisphere.: Ii at any point in the above-des- cribed system of air circulation there occurs a local area of low pressure the air from the surrounding region of high pressure is forced inward toward the center with a velocity depending upon the rapidity of the change from hich to low pressure. This inward flow is converted by the rotation of the earth in the manner ex- plained above into an atmospheric whirl around which the winds circulate, turning to the left or against the sun "1 the northern hemisphere and in the opposite direction in the southern hem- isphere. : The tropical cyclone storm of the North Atlantic is known under the name "West India hurricane," from the fact that its effects most frequently are experienced in that particular re- general a certain amount of westing, due to the general westward drift of the atmosphere throughout the low latitudes in which the storm originates. The area throughout which this occurs in the Atlantic covers the Caribbean sea and the region to the eastward of the Windward islands. Here, owing to the high temperature and the excessive hu- midity of the air, combined with the frequency of calms, the atmospheric equilibrium is unstable, and uprising columns of warm air 'are apt tobe frequent, the place of ascending heated and more humid air being taken by the cooler and drier surrounding air, which flows inward from all sides to re- store the disturbed equilibrium. A system of air currents is thus established, all directed radially inward. When not closer than 5 or 8 degrees to the equator such a system of currents is converted into. an atmospheric whirl. The -ma- July, 1921 jority of these whirls are in all likelj- hocd promptly dissipated. Under faver- able conditicns, however, one may sur- "vive, and in such event is borne alony to the westward by the general move- ment of the atmosphere in the tropics very much as an eddy is borne along by the current of a river. : Fully developed, the storm consists of a well defined areaymore or less cir- cular in shape, threughout which the atmospheric pressure diminishes rapidly on all sides toward the center or point of lowest barometer, the rate of this diminution amounting in the case of severe storms to 0.01 or even 0.02 of an inch for each mile of approach. Within this area, on the sides, as it were, of the barometric depression, the winds blow with full hurricane force, the velocity of the moving air increasing with the steepness of the barometric slope, the direction, however, being not toward but around the center, the motion of the air suggesting very forcibly, on a gigantic scale, the familiar path fol- lowed by water in escaping from a cir- cular basin by a central opening in the bottom. At the center itself--the point of lowest pressure--is a region not more than 10 or 15 miles in diameter | throughout which comparative calm pre- vails. Here, too, the dense canopy of cloud which overhangs the storm area is at times pierced, forming the so- called. "eye of the storm." | The. seas within this area are, however, violent and confused, sweepirig in from. ail sides with overwhelming violence. In the tropics the motion of the storm center as well as being tv the westward is away from _ the equator. In order to fix in one's mind the di- rection of rotation of the winds in both hemispheres, a storm may be considered as a large wheel lying flat on the earth and rolling along the equator to the westward. As the center draws away from the equator until the limit of the trades is reached the path of the storm ordinarily, but not always, recurves and turns east: ward and toward the pole. When this occurs the storm loses the characteris- tics peculiar to tropical cyclonic storms. The occurrence of tropical cyclonic storms is confined to the summer and autumn months of the respective hemis- pheres and to the western parts of the several oceans--the North Atlantic, North? Pacific,: South 'Pacific, and: In- dian oceans. They are unknown in 'the South Atlantic. The Arabian sea and Bay of Bengal are also visited by cyclonic storms, which occur most frequently in Miay and October. 'In the Atlantic, the occurrence of these storins is confined almost exclusively to the period June--November, attain- ing a maximum frequency in Septem- ber and October. The number actually