234 OBSEEVATIONS ON THE WINDS. 



By the diagrams it will be seen that the winds of the Dangerous and 

 Navigable Semicircles of a Eevolving Storm depend much upon the latitude ; 

 at any given position in the Dangerous Semicircle, with a vessel hove-to, 

 the winds will be found to veer, while they back in the Navigable Semi- 

 circle. It is especially dangerous to encounter a Hurricane during its re- 

 curve, as it then slows down and sometimes remains almost stationary for 

 several days, the spirally in-blowing winds tending to involve a vessel 

 deeper and deeper in the Storm. 



Cool weather is characteristic, in extra-tropical regions, of the Navigable 

 Semicircle, owing to the indraught from the North- Westward. Warm 

 weather, on the contrary, indicates the Dangerous Semicircle where the air 

 is drawn from the South-Eastward. 



The Hon. E. Abercromby remarks : — The so-called Dangerous Semicircle 

 owes part of its bad reputation to the fact that the weather is usually 

 more severe on that side than the other. The reason ordinarily assigned 

 for the epithet " dangerous " is that a ship running before the wind in 

 that semicircle will cross the path of the Storm in front of the vortex ; 

 while a scudding ship in the other semicircle will cross behind the vortex. 

 This is perfectly true ; but the whole character of the weather is also more 

 severe, because the highest pressure, strongest wind, and worst weather are 

 usually found on the side of the Dangerous Semicircle.* 



Mr. Meldrum, the well-known meteorologist, has established the fact that 

 when a Hurricane occurs in the Trade Wind area, a belt of intensified wind 

 is usually formed on its Polar side, in which there is a falling barometer 

 with increasing wind, making it difficult to discover whether the vessel is 

 really involved in the Storm. In this case, not until the barometer has 

 fallen at least six-tenths of an inch, is it safe to assume that, because the 

 Trade Wind increases in force and remains steady in direction, you are on 

 the Une of advance of the Storm. By attempting, under this impression, 

 too early to cross its track, nmning free as soon as the wind begins to 

 freshen, you are liable to plunge directly into the vortex. 



(173.) In order to simplify the remarks concerning the shifts of wind 

 which a vessel hove-to will experience during the progress of a Cyclone, 

 and to render them perfectly clear, a copy of the figure on page 235, by 

 the late Lieutenant Evans, who wrote on this subject under the name of 

 " Stormy Jack," may be drawn on thick paper or card-board. The outer 

 circle, to be fixed, represents the points of the horizon ; the inner circle, 

 to be movable, and attached, with a button in the centre, so as to revolve 

 on the outer or under circle; thus the inner circle may represent the 

 phases of the wind, as it gyrates round a centre, the arrows showing the 

 revolution of the aerial current from right to left. The movable circle is 

 sub-divided into four quadrants, with the phases of the wind marked on 

 the rim, for the purpose of facilitating the mode of operation. 



(174.) To use the instrument, formed as above, place the movable circle 

 upon the under one, East in juxtaposition with the North point of the 

 horizon. «"- The vessel's position may be marked as a stationary spot on the 

 outer circle — say under the N.N.W. verge, where the wind, as shown by 



Journal of the Scottish Meteorological Society," 1888, pages 316 — 317. 



