TIIEOEY OF CYCLONES. * 289 



above the sea of the Bermudas, and about the 50th degree of north 

 latitude, it did not occupy a space less than 1750 miles ; but at the 

 same time its destructive effects diminished in proportion to its 

 expansion. 



The same wind, vy^hich has just razed a town in the Antilles, and 

 broken ships like playthings, sometimes contents itself, when it 

 arrives at the Irish coasts, with uprooting a few trees and overturn- 

 ing some already trembling rocks. 



Such is the theory proposed by Dove, and which seems the most 

 probable, at least, for the hurricanes of the Atlantic. As to the 

 cyclones of the Indian Ocean, they are, perhaps, produced by the con- 

 flict of the south-easterly trade- winds, and the monsoon, which tends 

 towards the continent of Africa. M. Bridet sees in them only the 

 result of the meeting of two winds, one from the equator, the other 

 from the southern hemisphere. That from the equator, participat- 

 ing in the great angular speed of this part of the globe, deviates 

 towards the east, in proportion as it advances towards the tropic of 

 Capricorn ; the south wind, carried less rapidly around the earth, de- 

 viates, on the contrary, towards the west, and from these two 

 deviations in opposite directions there results, at the meeting of 

 the winds, a revolving movement in the direction from east to west 

 by the south. On an average, the cyclones of the Indian Ocean have 

 a diameter of from 250 to 300 miles in the commencement of their 

 course, from 430 to 560 miles towards the middle, and from 560 to 

 700 towards the end ; their influence is sometimes felt as far as 1200 

 miles from the axis of the storm. It is true that two or more cyclones 

 often follow one another at a little distance ; lateral eddies accompany 

 the principal whirlwind in the same way as occurs on the surface of 

 the sea, beside the great revolving funnel, formed by the meeting of 

 contrary waters, many circles of the second order are hollowed out. 

 Bridet has collected numerous examples of these simultaneous 

 C3''clones.* 



Local obstacles, such as plateaux and mountain- chains, may like- 

 wise cause hurricanes, when the aerial masses dash directly against 

 them. Thus, in the Bay of Bengal, at the time of the change from 

 the north-east to the south-west monsoon, the latter strikes against 

 the mountains of Arracan, and in consequence of this shock a sudden 

 cyclone occurs, which turns back towards the north-west, and 

 traverses the whole of Bengal and the northern provinces of Hindos- 

 tan as far as the Hindoo-Koosh. It is possible that the typhoons of the 

 * Etude sur les Oiiragans de V hemisphere Austral. 

 u 



