[Illustration: FIG. 26.--Tracks of West Indian hurricanes. The circles on the tracks indicate the position of the storm centres at Greenwich mean noon on successive days. The date of the several storms is as follows: 1. Aug. 27-Sept. 1, 1890. 2. Aug. 19-Aug. 25, 1890. 3. Aug. 19-Aug. 31, 1891. 4. Sept. 4-Sept. 9, 1891. 5. Sept. 16-Sept. 25, 1891. 6. Sept. 28-Oct. 7, 1891. 7. Aug. 17-Aug. 22, 1892. 8. Aug. 15-Aug. 22, 1893. 9. Aug. 23-Aug. 28, 1893. 10. Sept. 6-Sept. 9, 1894. 11. Sept. 20-Oct. 4, 1894. 12. Oct. 5-Oct. 10, 1894. 13. Oct. 12-Oct. 18, 1894. 14. Oct. 24-Oct. 27, 1894. 15. Oct. 18-Oct. 25, 1895. 16. Sept. 5-Sept. 10, 1896. 17. Sept. 9-Sept. 25, 1896. 18. Sept. 26-Sept. 29, 1896. 19. Oct. 9-Oct. 14, 1896. 20. Oct. 23-Oct. 26, 1897. 21. Oct. 20-Oct. 23, 1897. 22. Sept. 11-Sept. 20, 1898. 23. Aug. 3-Aug. 25, 1899. 24. Aug. 30-Sept. 7, 1899. 25. Sept. 8-Sept. 14, 1899. 26. Sept. 1-Sept. 11, 1900.] The analogy of a tropical hurricane to a tornado has already been referred to, but while a tornado may lay waste a tract of country perhaps half a mile wide, and in exceptional cases 20 to 30 miles in length, a hurricane is from 200 to 300 miles in diameter, and may continue to be destructive, on account of the rapid inflow of air from the periphery towards the centre, for 2,000 or 3,000 miles. The velocity of the spirally blowing winds which are the characteristic feature of these great storms is frequently 100 miles or more per hour. In spite of their magnitude, however, the conditions leading to their origin and growth are essentially the same as in the case of tornadoes, and even of the much smaller whirlwinds. They have their birth where the moist, still air above the ocean in the region of the doldrums at the season when the equatorial belt of calms is farthest north, becomes highly heated and rises on account of the pressing in of cooler and heavier air from adjacent regions. The ascending column is at first carried slowly westward, in obedience to the general flow of the atmosphere in the intertropical belt, and at the same time the currents coming in from opposite directions give the ascending air a rotary motion. As the currents from the northeast are stronger than those from other directions, this whirling motion is from right to left, or opposite to the movement of the hands of a watch. The whirling air column extends into the upper atmosphere, and as it moves along past the West Indies becomes influenced by the prevalent flow of the upper air-currents, and is carried northwestward, and later eastward in a path which approximates to a parabolic curve. The inward-rushing spiral winds leave a calm centre, the "eye of the storm," which corresponds to the hollow core of a whirlwind and the calm centre sometimes noted in tornadoes. The upward ascent of warm, humid air is accompanied by a