44 Seventeenth Memoir on the Law of Storms. [J4tf. 



centre at least 120 miles to the S. E. of her, and as at Noon of the 8th,, 

 we may call the centre of the Rob Roy's Cyclone about 30 or 40 miles 

 to the West of her position, it follows that the actual distance between 

 the positions of the two centres on these days was not more than 290 

 miles, which would allow a rate of 12.1 miles per hour for its progress 

 on a W. N. W. course, which being both usual and probable, we may 

 fairly and safely assume that it was the same Cyclone which, curving 

 up to the "W. N. W. as it cleared the mountains of Luconia, between 

 Pt. Capones and Cape Bolinao, reached and dismasted the Swallow 

 in consequence of her ill judged run to the Southward, travelling then, 

 as will be seen by her shift of wind, to the N. W. 



On the 10th, at 10 a. m. by the Swallow's log, its centre reached 

 that vessel when she was about in Lat. 16° 42 ; Long. 111° 03 ; , so that it 

 had not travelled up more than 130 miles in this 22 hours, or our pre- 

 vious estimate of the distance of the centre on the 9th was too small, or 

 the storm was of larger dimensions, or it had slackened its rate of motion 

 on approaching the high land of Hainam. If we take the whole time (46 

 hours) between the passage of the centre over the Rob Roy on the 8th, 

 and this estimated position on the 10th, the entire distance between the 

 two positions is 7 degrees, or 420 miles, which for 46 hours will 

 give an average of 9.2 per hour, and if we adopted this rate throughout, 

 it would place the centre so as to make the wind at Noon on the 9fch, to 

 have been about N. E. b. N. instead of N. E., which it may well have 

 been, since the winds are rarely marked on board of merchant ships at 

 busy and anxious times like the approach of a tyfoon in the China Sea, 

 with any especial care. We may also suppose, as this has been well 

 authenticated in other instances, that as above stated, the rate of the 

 Cyclone's motion to have been checked on its approach to the Coast of 

 Hainam. 



What is important however to our investigation is, that the Cyclone, 

 which had probably a double curving, though the track is made strait 

 on the Chart, is fairly traceable across the China Sea. 



The log of the General Wood is too imperfectly given to afford any 

 fair ground for comment. She was evidently to the Northward of the 

 Swallow, and felt the N. E. quadrants of her Cyclone, but we cannot 

 say at what distance, as her position is omitted. 



The Ardaseer was evidently close to the Rob Roy, but we have not 



