Mat-. 9, 1888,] 



SCIENTIFIC NEWS. 



225 



STORMS.— II. 



( Continued from page 197.^ 



THE tropical cyclones or hurricanes, which are smaller 

 and have much stronger winds, move only from 50 

 to 300 miles a day. At the actual centre there is a 

 calm and usually blue sky which is swept clear of 

 clouds by the uprushing air ; this is called the " eye of 

 the storm " or the " bull's eye." A still smaller atmo- 

 spheric whirl of two or three hundred yards diameter is 

 produced by the most violent winds that are known, 

 and is called a tornado. The pressure is so greatly 

 diminished that trees, fragments of ruined buildings, and 

 even human beings are caught up from the ground and 

 carried to considerable distances. It is very remarkable 

 that such a storm does not disturb the higher regions of 

 the air, and the central spout does not extend higher 

 than the lowest layer of clouds. Tornadoes travel 

 usually to the north-east in the northern hemisphere, 



storms which have travelled towards our shores. Our 

 newspapers often give a message from America to say 

 that a storm may be expected at about a certain date, 

 and there are persons who place such confidence in 

 these warnings that they put down casual showers of 

 rain, snowstorms, frosts or even fogs to the credit of the 

 prophesy ! The number of storms which actually cross 

 the Atlantic in a year is given by Mr. Abercromby as 

 from eight to twenty. The chart before us shows nine- 

 teen tracks crossing long. 60 degs., which lies between 

 Newfoundland and Nova Scotia ; and of these, six appear 

 to reach long. 10 degs., which lies on the west coast of 

 Ireland. Some of them have become spent in mid 

 ocean, others have turned to the north or the south. A 

 cyclone takes from four to ten days to make the passage. 

 The West Indian hurricanes are fortunately as regu- 

 lar in their movements as they are disastrous in their 

 effects. The circular published by the U.S. Hydro- 

 graphic Office on this subject recommends that when a 



rotating in a direction opposite to that of the hands of a 

 watch, and moving at about thirty miles an hour. On 

 a still smaller scale, the violence of the wind is fortu- 

 nately less, as in the case of water-spouts, which are 

 produced in an exactly similar way ; and creating as 

 they do a vacuum sufficiently great to draw up water to 

 the clouds, would do great damage to a ship ; but they 

 are the effect of a whirlwind of only ten or twelve feet 

 in diameter. And lastly we have the eddy on a dusty 

 road, a few inches, perhaps, in diameter. Such a minia- 

 ture whirlwind may be artificially produced by means of 

 the apparatus described in Scientific News, p. 67, vol. i.. 

 No. 3, First Series. 



The large cyclones of the temperate zones not only 

 move with such rapidity, and are of so large an extent 

 that it would be impossible for a vessel at sea to avoid 

 them, but they are very uncertain in their movements. 

 A large number have been traced across the Atlantic, 

 and among the admirable publications of the United 

 States Bureau of Navigation is a chart of the North 

 Atlantic Ocean, showing the tracks of more than twenty 



hurricane is evidently approaching, the captain should 

 heave-to and carefully make and record observations of 

 the barometer, thermometer, wind and weather, every 

 half hour or even more frequently, with the view of 

 finding the direction of the centre of the storm, the 

 direction in which it is moving, and the position of the 

 ship with regard to it. The two diagrams which are 

 reduced from those given in the circular show the direc- 

 tion of the wind and the state of the barometer. The 

 curved lines in Fig. 3 show the direction of the wind. 

 The air is drawn to the centre of the circle where 

 the barometer is lowest, and the path becomes more 

 circular as its velocity increases, and finally it whirls 

 round with hurricane force. At the centre is the calm 

 spot from 10 to 30 miles in diameter, the diameter of 

 the whole area represented being from 100 to 800 miles, 

 being generally less in low latitudes. The direction of 

 the wind at any point on the diagram is the same as the 

 direction of the curve at that point, and the arrows show 

 the direction at the points where they are plotted. By 

 placing arrows at all points having the wind in the same 



