36 Seventeenth Memoir on the Law of Storms. [Jan. 



The Balcarras* log we leave out of the consideration of the track of 

 this Cyclone altogether, as though she was doing all she could to get to 

 the Northward, the Cyclone had passed on ahead of her, its passage he- 

 ing faintly indicated by the fall and rise of her barometer. 



From the Guess's log however we can distinctly trace that it was one 

 coming down upon her from the E. b. N., the wind being nearly steady 

 at N. b. W. for a long time, till between 2 p. m. and 8 p. m. of the 

 20th, we find it veering from N. b. "W. to S. W., or 11 points of the 

 storm circle (Cyclone points) in 6 hours, or not far from 2 points per 

 hour. It is thus clear that the vessel was drifted by the Northerly gale 

 just out of the centre, though close upon its Southern border. 



If, as is very probable (for mistakes in newspaper accounts of gales 

 and hurricanes are constantly occurring) the height of the Barometer at 

 midnight 19th, — 20th, was 28.80 instead of 29.50, we may then, allow- 

 ing it to have fallen regularly from 29.00 at 8 p. m. on the 19th to 28. 

 50 at noon of the 20th, or 0.50 in 16 hours, say that its average fall 

 was .031 per hour, and that at the mean time of this 16 hours, or at 4 

 a. m. on the 20th, the centre was thus about 225 miles from the vessel : 

 and we find it was then " a hard gale." 



From this time, 4 a. m. to 6 p. m. of the same day when the wind 

 was West and the centre therefore bearing due North of the Brig, are 

 14 hours. And if our calculation of the distance at 4 a. m. is correct 

 it had then travelled the 225 miles in this time, or at about 16 miles 

 per hour, which is not an excessive rate for the Cyclones of the China Sea. 

 It will be observed however that this calculation depends on the typo- 

 graphical error we have supposed for the height of the Barometer at 

 midnight. If at that hour it had really fallen to 28.50, as set down, 

 this would place the centre at 10 p. m. of the 19th within 80 miles of the 

 Brig, but we can barely suppose it moving so slow (for we have as yet 

 I think nothing below seven miles per hour ascertained for the rates of 

 travelling in the China Sea) that it would only reach the vessel at 6 

 p. m. on the 20th. If we calculate from the fall of 0.20 (29.00 to 28.80) 

 which I suppose to be the true correction of the error in the midnight 

 figures for the Barometer, this will give the mean distance of the centre 

 at 10 p. m. on the 19th to be 175 miles. And as it reached the meridian 

 of the vessel at 6 p. m. or in 20 hours, this was not quite at the rate of 9 

 miles per hour. Either calculation it will be seen is a sufficient ap- 



