260 Seventeenth Memoir on the Law of Storms. [March, 



The Barometer we find was on the 16th at 29.71, and had fallen to 

 29.39 at Noon of the 17th, and at 3 a. m. of the 18th, it was at 29.04 

 before and during the calm, and rose again to 29.29 at Noon, shewing 

 that though the wind was rapidly veering from N.N. W. to West, by 

 S. W. to South, and the vessel therefore in the Southern and Eastern 

 verges of the calm centre, yet the Cyclone itself was travelling out to 

 the Westward. On the 19th, the Bar. is noted as at 29.45, which 

 shews, so far as the Barometer enables us to form any judgment when 

 so near the centre, that for this day and a half, or two days, the Cyclone 

 was running up with the ship, and its fall again from 29.45 at Noon to 

 29.25 at midnight of the 20th — 21st shews also that it was again ap- 

 proaching the vessel and curving off to the Eastward past the South 

 point of Formosa, so as to bring the Easurain again into the calm centre. 



During this remarkable track the centre of the Cyclone must have 

 been to the Westward of the ship throughout, and it must have been 

 also travelling at a slow rate, since the vessel's drift when hove too was 

 sufficient to keep the wind alwa}^s about South, and it is only during 

 her first run that she brought the wind as far as S. E. ; her subsequent 

 bearing up being only for about five hours at six knots per hour. We 

 may infer however from this that the Cyclone was of some considerable 

 extent, and its centre at some distance, for had it been small and the 

 centre close, the wind would necessarily have been more variable, and 

 its direction have altered quickly with the vessel's position within the 

 storm circle. On this account then, I conceive that we cannot allow 

 the centre to have been on an average at less than 75 miles to the West 

 of the ship, giving to the whole Cyclone a diameter of 150 miles. 



The track, as I have said before, must be one nearly parallel to the 

 vessel's course and then curving rapidly over to the Eastward towards 

 midnight, 21st, — 22nd. Capt. Shire having carefully given on his Chart 

 the position of the vessel at midnight as being in Lat. 21° 16'; Long. 

 120° 38/ we are enabled to estimate the rate of travelling of the Cyclone 

 with some degree of accuracy, for as the distance from this point to day- 

 light of the 18th, is about 270 miles in a strait line, with allowance for 

 the curving of the storm as I have marked its track, we may call it 300 

 miles. This distance it took 90 hours, from 6 a. m. 18th to midnight of 

 21st, — 22nd, to travel, so that its rate of progress did not exceed per 

 hour 3.3 miles. 



