HUKKICANES. 219 



Storms which were more than double that height. If there be a close 

 analogy between Cyclones and these smaller whirls, it may be inferred that 

 the gigantic whirls composing the former are greatly higher, or perhaps 

 several miles in height, and consequently the direction of the wind expe- 

 rienced during a Cyclone may not always agree with the direction of the 

 progress of the scud above, which may be accounted for by the spiral 

 column not rising perpendicularly in the air. This will be referred to again 

 later on. 



(155.) Incurvature of Wind — It is now considered that the wind only 

 blows circularly round the vicinity of the centre or vortex, while at parts 

 of the Storm farther away it does not blow in a strictly circular course 

 round the centre, but spirally or incurving towards it, as shown in the 

 illustrative diagrams. The curve which the wind describes is in reality 

 a spiral around the focus. If these were drawn, that for the Northern 

 Hemisphere would be curved in the same direction as the figure 6 ; for the 

 Southern it would be this figure reversed, or like the figure 6 on the back 

 of the paper, both beginning at the top. 



This indraft or incurvature of the wind varies according to the latitude 

 and also the quadrant of the Storm. Padre Viiies found that, in the West 

 Indian Hurricanes which he had studied, in the front part of the Storm 

 the winds blew almost in a circle, while in the rear the inclination, or in- 

 draft, was so great that the winds blew almost towards the centre. When 

 in latitudes higher than 30°, however, the Hurricane may cover so great 

 an area as to render the indraft imperceptible. This indraft of course 

 affects the problem of finding the bearing of the centre, discussed hereafter. 



(156.) Similes. — Perhaps the idea of an ascending spiral whirl may be 

 the simplest simile to which to compare the circulation of the winds in a 

 Cyclone. In a paper by D. M. Holme, LL.D., published in the Journal of 

 the Scottish Meteorological Society, 1669, pages 305 — 322, it was pointed 

 out that the whirls which frequently occur in the atmosphere, known as 

 Waterspouts, Whirlwinds, and Dust Storms, often originate in the upper 

 regions of the atmosphere, and descend in the form of an inverted cone to 

 the earth's surface. They are also formed by currents of air ascending 

 from the earth's surface spirally and rotating at the came time. These 

 ascending currents have been distinctly noticed, by various articles (such 

 as hay, straw, branches of trees, and in some cases animals) being seen 

 carried up in the interior of the whirling cylinder. If it were possible to 

 have an aneroid in the interior of it, a depression indicating diminished 

 atmospheric pressure would most probably be observable.- In this paper 

 it is attempted to prove that Cyclones have many features in common with 

 Waterspouts, Dust Storms, and Whirlwinds. 



(157.) Origin.— The most difficult part of the Cyclone theory remains to 

 be mentioned. What causes the suction to which the indraught of air may 

 be attributed ? What determines the course which all these West India 

 Cyclones take in their passage over the earth's surface ? The latter question 

 is the less difficult of the two. If the Cyclones are formed, as they appear 

 to be m the Atlantic Ocean, a httle to the North of the Equator, it is 

 evident that they must move in the first instance to the Westward, because 

 the general atmospheric current is in that direction. When they reach the 



