HUEEICANES. 221 



air afc the same altitude. This relative warmth of the cloudy storm area 

 maintains the outflow of the upper currents in the same way as the Equa- 

 torial warmth causes the Poleward flow of the lofty Anti-Trades. 



(158.) Direction of Rotation, &c.— In the Northern Hemisphere, as 

 already explained on page 183, the winds in Cyclonic Storms invariably 

 revolve from right to left, past the North, or against the sun, i.e. in the 

 opposite direction to the hands of a watch lying face upwards. Originating 

 within the Tropics, the Storm progresses bodily to the W.N.W., then 

 N.W., and North, forming a cycloidal curve in about lat. 30°, and runs off 

 to the N.E. 



South of the Equator, or in the Southern Hemisphere, this rule is reversed, 

 the Storm revolving from left to right, or with watch-hands, passing onwards 

 in a S.W., and finally in a S.E. course. These Storms, however, do not 

 seem to be encountered in the South Atlantic Ocean, within the S.E. 

 Trade Wind area. 



The illustrative diagrams will give the reader a better idea of the 

 circulation of the wind in a Hurricane, North of the Equator, than any 

 written description. The spiral Unes in that for low latitudes show the 

 course of the wind around the vortex, its direction at any point on this 

 diagram being the same as the curve at that point. By plotting arrows at 

 all points having the wind from the same direction. North for example, 

 and joining them by a dotted line, it will be found that this line curves 

 towards the centre. The angle of bearing of the centre therefore, supposing 

 the Cyclone to be of a normal character, gradually decreases from about 

 10 points (or it may be 11, 12, or 13 points, or even more) of the compass 

 at the margin to about 8 points nearer the vortex, where the " Eight 

 Point Eule," hereafter given, becomes correct. 



(159.) Form, &c. — A Cyclonic area is rarely circular, but usually more 

 or less oval, seldom perfectly symmetrical, and the vortex or centre ^'s 

 often displaced towards one side. The vortex also sometimes oscillates or 

 moves from one side of the area to the other. The longer axis of the oval 

 usually lies in a line with the path of the Storm, and its effect is as if the 

 circle had been distorted, thus giving a much greater preponderance of the 

 winds due to the longer sides of the oval. An irregular motion of the vortex, 

 as above described, will cause great perplexity and apparent want of regu- 

 larity, yet the Storm itself may be strictly a revolving one. Another cause 

 of complexity in revolving Storms is, that they have been known to separate 

 into two, and in other cases two or more Storms encountering each other 

 have coalesced. 



The vortex or focus of a Cyclone, where reigns a calm accompanied by 

 heavy and confused seas, with a blue sky in the Tropics (known as the 

 " bull's eye "), may be of considerable size, from 10 to 30 miles in diameter 

 in some Storms, and in others, it is thought, may be next to nothing. 

 Here the barometer may read 2 inches or more below the normal. This 

 is the most dangerous part of a revolving Storm, as in its passage the wind 

 suddenly shifts from one point to the other, and here it is generally most 

 violent. Around this the wind circulates in an ever widening circle as it 

 progresses on its course, until the disturbance may cover an area of 1,000 

 miles or more in diameter. 



