41 G PHYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOROLOGY. 



has its hurricane season in the opposite season of the year, and 

 when the north-west monsoon prevails in the East Indian 

 Archipelago." 



785. Tlie cyclone theory. — Under the head of hurricanes, tj'phoons 

 and tornadoes, I. include all those gales of wind which are 

 known as cyclones. These .have been treated of by Eedfield 

 in America, Eeid in England, Thorn of Mauritius, and Pidding- 

 ton 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 j)arallel 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 b}^ 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 



