tJLLOA*S VOYAGE TO St)UTH AMERICA. 



3^5 



ternible, the diftance is not lefs than one hundred and eighty leagues. This track of 

 water is a certain mark for directing one's courfe ; becaufe, after leaving it, we have 

 the fatisfadion of knowing the remaining diftance ; it is not deleniated on any map, 

 except the new one lately publifhed in France j though it would doubtlefs be of great 

 ufe in them all. 



Nothing farther remains, than to give an account of the variation of the needle 

 in different parts in which we found the fhip by her latitude and longitude; a 

 point of the utmoft confequence in navigation, not only with regard to the ge- 

 neral advantage to mariners in knowing the number of degrees intercepted be- 

 between the magnetic and true north of the world, but alfo as, by repeated obferva- 

 tions 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 approxi- 

 mation 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 French- 

 men, appHed themfelves to the improvement of it. We already enjoy the fruits 

 of their labours in the variation charts lately publifhed, though they are prin- 

 cipally ufeful only in long voyages ; where the difference of two or of even three 

 degrees is not accounted a confiderable error, when there is a certainty that it 

 cannot exceed that number. This fyflem, though new with reward to the ufe 

 it is now applied to, is far from being fo among the Spaniards and Portuguefe, 

 very plain vefliges of it remaining in their old treatifes of navigation. Maniel de Fi- 

 gueyredo, 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 diflance run in failing eall and weft. And Don Lazaro 

 de Flores, in his Arte de Navegar, printed in 1672, 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 cer- 

 tain method. It muft, however, be acknowledged, that thofe ancient writers have not 

 handled this point with the penetration and accuracy of the Englifh and French, 

 aflifted by a greater number of more recent obfervations. And that the obfervations . 

 made in this voyage may be of the- moft general ufe, I fhall infert them in the two fol- 

 lowing tables ; previoufly informing the reader, that the longitudes correfponding with 

 each are true, the error of the courfe, with regard to the difference of meridians, being 

 correded from the obfervations of the fathers Laval and Feuillee : — 



Variations ohferved by Don George Juan, the Longitude being reckoned wejifrom Cadiz* 



Variations 



