SECT, xv.] HDEEICANES. J 39 



to E., S., W., and N. again. At the Royal Observatory at 

 Greenwich, the wind accomplishes five circuits in that direc- 

 tion in the course of a year. When circumstances combine 

 to produce alternate north and south winds in the southern 

 hemisphere, the gyration is in the contrary direction. Al- 

 though the general tendency of the wind may be rotatory, 

 and is so in many instances, at least for part of the year, yet 

 it is so often counteracted by local circumstances, that the 

 winds are in general very irregular, every disturbance in at- 

 mospheric equilibrium from heat or any other cause producing 

 a corresponding wind. The most prevalent winds in Europe 

 are the N.E. and S.W. ; the former arises from the north 

 polar current, and the latter from causes already mentioned. 

 The law of the wind's rotation was noticed by Dr. Dalton, 

 but has been developed by Professor Dove, of Berlin. 



Hurricanes are those storms of wind in which the portion of 

 the atmosphere that forms them revolves in a horizontal circuit 

 round a vertical or somewhat inclined axis of rotation, while 

 the axis itself, and consequently the whole storm, is carried 

 forward along the surface of the globe, so that the direction 

 in which the storm is advancing is quite different from the 

 direction in which the rotatory current may be blowing at 

 any point. In the West Indies, where hurricanes are fre- 

 quent and destructive, they generally originate in the tropical 

 regions near the inner boundary of the trade-winds, and are 

 probably owing to a portion of the superior current of wind 

 penetrating through the lower. By far the greater number 

 of Atlantic hurricanes have begun eastward of the lesser 

 Antilles or Caribbean Islands. 



In every case the axis of the storm moves in an elliptical or 

 parabolic curve, having its vertex in or near the tropic of 

 Cancer, which marks the external limit of the trade-winds 

 north of the equator. As the motion before it reaches the 

 tropic is in a straight line from S.E. to N.W., and after it 

 has passed it from S.W. to N.E., the bend of the curve is 

 turned towards Florida and the Carolirias. In the southern 



