SBCT. XV. HURRICANES. 119 



cause it to veer to the N. W. and N. Thus two alter- 

 nations of north and south wind will cause the vane at 

 any place to go completely round the compass, from N. 

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

 at Greenwich, the wind accomplishes five circuits in that 

 direction 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. Although the general tendency of the wind 

 may be rotatoiy, 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 atmospheric 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 men- 

 tioned. 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 frequent 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 hi 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 toward Florida 



