6g8 PHILOSOPHICAL TRANSACTIONS. [anNO 1 763. 



book intitled * Certain errors in navigation detected and corrected,' published 

 about the year 15QQ. In chap. 2d, he tells us, ' that the errors in the plain 

 chart had been complained of by divers, as namely by Martin Cortese, Petrus 

 Nonius, and even Gerardus Mercator seemeth to have corrected them, in his 

 Universal Map of the World; yet none of them had taught any certain way how 

 to amend such gross faults :' And in his Preface he declares, * that by occasion 

 of Mercator's map, he first thought of correcting so many and great absurdities 

 in the common Sea Chart, but the way how this was by him done, he neither 

 learnt of Mercator, nor of any man else.' Wright's method (erroneously called 

 Mercator's) was at this time then adopted; has continued ever since in use; and 

 has been improved by some of the greatest mathematicians who have flourished 

 since that time; and though sometimes attacked, yet it has been found im- 

 pregnable. 



The first person who charged Mr. Wright with errors in his tables of rhumbs, 

 is Simon Stevins, in his large volume of mathematical remembrances, which 

 Wright himself plainly confutes in a subsequent edition of his book: now Stevins 

 does not condemn the principles, but only asserts that his tables have some 

 faults in them, and endeavours to prove that the 4th rhumb, at 78° of longi- 

 tude, ought to have 6i° 26' of latitude, whereas Wright makes it only 61*^ 14'. 

 Hence the great difference is no more than 12 minutes ; and what inconveni- 

 ence hence can arise to the mariner in such a run, were this the fact } But it 

 turns out otherwise ; for this difference is reduced to less than one minute (even 

 according to Stevins's own way) as evidently appears from Wright's answer in 

 page 214. If every rhumb is then found to possess its true latitude in this 

 chart, at every degree and minute of longitude, without any sensible or ex- 

 plicable error (to make use of our author's own words) it follows, that the 

 degrees of latitude are duly encreased, or that the table of meridional parts is 

 true. 



Doctor Halley has given a curious method of dividing the nautical meridian, 

 and of performing the problems in sailing according to the true chart, in the 

 Philos. Trans., N'* 219, by a method different from Mr. Wright's, but so nearly 

 corresponding in practice, that this alone is a sufficient testimony in favour of 

 this author. Our worthy brother Mr. John Robertson, in his excellent Ele- 

 ments of Navigation, Vol.2, page 358, expresses himself thus: " Now though 

 a table thus made (Wright's table of meridional parts constructed to minutes) 

 be abundantly sufficient for all nautical purposes ; yet had the secants of smaller 

 parts than minutes been taken, the table would have been more correct ; and 

 therefore Mr. Oughtred, Sir Jonas Moore, Doctor Wallis, Doctor Halley, and 

 others, have been induced to find methods of constructing those tables with 

 more accuracy, than by the addition of secants to every minute. But a table 



