260 OBSERVATIONS ON THE WINDS. 



gusts ; whereas, if the wind precedes the rain, the squalls are seldom so 

 furious, and terminate in moderate showers of rain. The general rule, 

 however, is often interrupted by the operation of local causes. 



" The Descending Squall is not so easily discerned as the former, because 

 it issues from clouds which are formed in the lower parts of the atmosphere, 

 near the observer ; and when clouds are thus formed, they generally pro- 

 duce showers of rain, and successive squalls of wind. In the Mexican Sea, 

 heavy and very sudden descending squalls come at times from very small 

 clouds. These are scarcely felt until the cloud is almost right over the 

 ship's masts. 



" The White Squall is not often experienced; but it sometimes happens 

 near to, or within, the Tropics, particularly in the vicinity of mountainous 

 land. This squall generally blows very violently for a short time ; and, as 

 it is liable to happen when the weather is clear, without any appearance 

 in the atmosphere to indicate its approach, it is consequently very dan- 

 gerous. The only mark that accompanies it is the wind." 



(205.) Captain FitzRoy says: — " Undoubtedly the worst wind, next to 

 a Hurricane, which a vessel can encounter, is a violent White Squall, so 

 called because it is accompanied by no cloud or peculiar appearance in the 

 sky, and because of its tearing up the surface of the sea, and sweeping it 

 along so as to make a white sheet of foam. Of Squalls of this description, 

 frequent in the West Indies, and occasionally felt in other parts of the 

 world, no notice will be given much above the horizon ; but, by consulting 

 a good barometer or sympiesometer, and frequently watching the surface 

 of the sea itself, even a White Squall may be guarded against in sufficient 

 time. 



" Dark clouds, hard mixed with soft, and inky fragments in rapid motion 

 beneath them, accompanied, perhaps, by lightning and distant thunder, are 

 the forerunners of a heavy squall. Soft shapeless clouds, Sn which it is 

 impossible to point out a definite edge, usually bring rain, but not wind ; 

 and, generally speaking, the more distinctly defined the edges of the 

 clouds are, the more wind they foretell. A httle attention to these simple 

 observations, so familiar to persons who have been some time at sea, may 

 save young officers unnecessary anxiety in one case, and prompt them to 

 shorten sail at a proper time in the other." — ("Voyage of the Beagle,' 

 vol. ii., page 49.) 



(206.) Mr. F. A. Jahncke,* of St. Thomas, says on this subject : — 

 White Squalls are sometimes terribly destructive to vessels, either capsizing 

 them, or carrying away their masts. They occur with fine weather and a 

 good breeze, but I have not heard that they happen on land, but always 

 at sea. It must be a rapid descent of the Equatorial Wind met below by 

 the Trade Wind, which arrests its circular motion ; that must be the cause, 

 as their duration is only for a few moments. 



Captain Toynbee remarks that he has been struck by the frequency of 

 Squalls from the direction of the upper current of air in parts of the sea 

 where the lower wind was from nearly an opposite direction. In studying 



• General Remarks on West India Cyclones, by F. A. Jahncke, see " Quarterly Journal 

 Oithe Meteorological Society," No. 10, April. 1874. 



