Ch.I. south AMERICA. 15 



and true north of the world but alfo as, by repeated 

 obfervations of this kind, the longitude may be found, 

 and we may know within a degree, or a degree and a . 

 half, the real place of the fhip; and this is the neareft 

 approximation to which this has been carried by thofe 

 who revived it at the beginning of this century. Among 

 thefe the chief was, that celebrated Englifhman, Dr. 

 Edmund Halley : in emulation of whom, many others 

 of the fame nation, as alfo feveral Frenchmen, applied 

 themfelves to the improvement of it. We already en- 

 joy the fruits of their labours in the variation charts 

 lately publifhed, though they are principally ufeful only 

 in long voyages ; where the difference of two or of 

 even three degrees is not accounted a confiderable er- 

 ror, when there is a certainty that it cannot exceed that 

 number. This fyfhem, though new with regard to the 

 ufe it is now applied to, is far from being fo among the 

 Spaniards and Portuguefe, very plain vefliges of it re- 

 maining in their old treatifes of navigation. Maniel de 

 Figueyredo, cofmographer to the king of Portugal, in 

 his Hydrographia, or Examin de Pilotos, printed at 

 Lifbon, in 1608, chap. ix. and x. propofes a method 

 for finding, from the variation of the needle, the dif- 

 tance run in failing eaft and weft. And Don Lazaro de 

 Fiores, in his Arte deNavegar, printed in 1 672, chap. i. 

 part ii. quotes this author, as an authority to confirm 

 the fame remark made by himfelf •, adding (chap, ix.) 

 that the Portuguefe, in all their regulations concerning 

 navigation, recommend it as a certain method. It 

 muft hovv'ever be acknowledged, that thofe ancient 

 writers have not handled this point with the penetration 

 and accuracy of the Englifh and P'rench, affifted by a 

 greater number of more recent obfervations. And that 

 the obfervations made in this voyage may be of the 

 mod general ufe, I (hall infert them in the two follow- 

 ing tables ; previoufly informing the reader, that the 

 longitudes correfponding with each are true, the 

 error of the courfe with regard to the difference of me- 

 ridians 



