HUEEICANES. 263 



The Tornado usually follows a day of calm, and of overpowering heat. 

 The South-Westerly breeze, which prevails during the winter season, has 

 given place to calms and light airs from North to N.E. Owing to this 

 direction of the wind, the sky is completely clear of clouds, yet the Southern 

 part of the horizon becomes dark, a small cloudy black mass appears to 

 the South and S.B,, and foretells the formation of a Tornado. After a time, 

 which varies from two to four hours, this black mass begins to move and 

 to approach the zenith. This motion is slow, and I have always seen it 

 in a direction nearly from South to North. When the mass of nimbus has 

 risen to about 25° above the horizon, it forms a regular semicircle there, 

 beneath which the sky can sometimes be seen. The edge of this moving 

 black mass shows sharply on the blue sky, which is mottled by a few white 

 fleecy clouds, moving with the North-Easterly winds which have become 

 rather more energetic in the lower regions of the air. 



When at about 45° from the zenith, this accumulation of clouds pre- 

 sents a most characteristic appearance. It is a vast black circle, a sort of 

 mushroom without a stalk, seen in a three-quarters view from below ; its 

 outline clearly defined in front, and to the right and left edges, but ilJ 

 defined behind in the part which touches the horizon. These clouds are 

 sometimes, but rarely, furrowed by lightning, and in general no thunder 

 is heard. Below the most distant part of this black mass, large white 

 clouds are seen. 



Sometimes the motion of the meteor is so slow, that it takes half an hour 

 to reach the zenith ; sometimes scarcely five minutes elapse from the time 

 when the clouds are seen to begin to move until they are fairly overhead. 

 The meteoric mass seen from below has no longer any definite form, the 

 sky being quickly invaded by clouds which seem to move in complete 

 disorder. 



It is generally at the moment when the front edge of the Tornado reaches 

 the zenith, often a little sooner, and sometimes only when two-thirds of 

 the sky are covered, that a wind of extreme violence comes from a South- 

 Easterly direction. 



This storm lasts at the most for a quarter of an hour, during which time 

 the wind backs to East, then to N.E., North, and finally to N.W. ; it then 

 passes to the S.W., lighter at first, but regaining its energies at S.W. The 

 change of wind is not always so regular as this, for sometimes it freshens 

 up again from S.E. Sometimes it gets lighter and lighter until it becomes 

 N.W., and never goes beyond that quarter. In some Tornados the wind 

 stops at North, the Tornado disappears, calm and rain succeed, and then 

 light steady South- Westerly winds. The only constant thing is, the greater 

 force of the wind at the beginning of the Tornado. Its force is only really 

 dangerous quite at the beginning, and when the wind is from the S.B, 

 Sometimes the meteor disappears in 10 or 15 minutes ; it then only con- 

 sists in this rapid motion of the wind, and this passage of black clouds, 

 without rain, or thunder-storm. This is the least frequent form, and is 

 called a Dry Tornado. 



Generally, when the wind passes to S.W., a thunder-storm bursts, the 

 rain falls with extreme violence for a quarter of an hour, then becomes 

 moderate, and the wind remains light at South or S.W. 



