1849.] Seventeenth Memoir on the Law of Storms. 43 



this time in about Lat. 14° 30' N. ; Long. 118° 17' East; and from 

 this time to Noon of the 8th, when Capt. Francis places her in about 

 Lat. 15° 12' ; Long. 119° 10', she may have made an E. N. E. course 

 good, or one directly towards the centre of the Cyclone, which, when 

 close upon her, veered first to N. "W. and then at 4 p. m. became more 

 moderate, the centre having reached her so far as to place her as it were 

 on its S. E. border with a S. Westerly breeze. She then ran up 1 1 

 miles to the N. E. but reached that part at which the wind was at 

 South and blowing a hurricane. 



This gives us an idea of what the size of the central space may have 

 been. For if we suppose an octagon (S. West to South, being one- 

 eighth of the wind circle) of eleven miles on each side, this will require 

 a circle of 25 miles to include it. And we may take the Rob Roy's run 

 to the N. E. as having been across one side of such an octagon. I have 

 made no allowance in this for the motion of the Cyclone itself, which 

 unless the ship was carried with it, would at least add ten miles more 

 to this estimate.* 



But be this as it may, we can account very fairly for the wind's shift- 

 ing now to a hurricane at South, by this run of 1 1 miles, and we must 

 take the first shift of N. W. to S. W., though the last was not of full 

 force, for the true index to the track at that time. If the ship had been 

 lying to, the full tyfoon would doubtless have returned at S. W. or there- 

 abouts. 



But we have seen before that from the steadiness of the wind at 

 N. N. W. till nearly Noon, it was at first coming down upon the vessel 

 from the E. N. E. to W. S. W. It therefore by this time (Noon to 

 4 p. m.) was altering its track to the Westward. And as we find that 

 the wind very soon became S. S. E., at which point the vessel being 

 disabled drifting only, it ended also at S. S. E. we must allow that it 

 now travelled away nearly to the W. N. W. or thereabouts. 



The Swallow appears to have been at Noon of the 9th at about 400 

 miles to the N. W. b. W. of the Rob Roy's position of the 8th, with 

 her Cyclone beginning only from the N. E., or we may say with the 



* Though 35 miles is a large estimate, we must recollect this was not the calm 

 space, but the verge of it, when there was still a fresh S. W. gale. The large calm 

 spaces are perhaps not so rare as we may suppose, and they account for ships lying 

 so long in them, which occurs also when the Cyclone is a slow moving one. 



G 2 



