xxu 



INTRODUCTION. 



two hemifphcres. But however plaufible this theory may 

 feem, at firft fight, experience has abundantly deceded its 



fallacy. 



in thefe feas, the variation of the needle at Cape Circumclfion muft have been lo" 

 Wefterly : whereas, in the moil Wefterly point of Captain Cook's traft, where he 

 was fuificiently near the parallel of 54.° South, to have feen land Tituated in it, the 

 v.-xriation was 1 3" { Wefterly. This difference of 3" |, in the variation, anfvvcrs to 

 about 7° of longitude, in this part of the parallel of 54.° South : and by fo much did 

 Captain Cook fall in with this parallel to the Eaftward of what he ought to have done 

 to fee the land in queftion. " Hence (M. Le Monier infers), that it is not furpriz- 

 " ing the Britifh navigator fliould not find Cape Circumcifion under a meridian 

 " which is 28'' I to the Eaftward of Ferro, when it is really fituated under a meridian 

 " which is but 21" | to the Eaftward of it." 



In replying to thefe allegations, I fliall, firft, fhew, that, granting the depend- 

 ence v/hich M. Le Monier fuppofes may be placed on obfervations of the variation 

 made at fea, hehasftated the quantity of the variation, obferved on board the Refolu- 

 tion, very erroneoufly. 



Secondly, I fliall prove, beyond contraditSlion, that obfervations of the variation, 

 made at fea, cannot be depended on, for the purpofes to which M. Le Monier has ap- 

 plied them. 



And, laftly, that no material error had crept into M. Bouvtt's reckoning ; but that 

 if any error did exift, it muft have been of a contrary nature to that which M. Le Mo' 

 titer fuppofes. 



That A^. Le Monier has not given altogether a true reprefentation of the matter, 

 will appear from hence. On the 16th of February, at noon *, the Refolution was in 

 latitude 54.'^ 31!' South, which is fufficiently near the parallel of 54° South, to fee 

 higii land, the Northern extremity of which lies to the Southward of that parallel ; 

 and at that time we were in 6° Eaft of Greenwich, or 23'^ J Eaft of the ifland of 

 Ferro : that is, 4" l lefs than is aiTigned for our fituation by M. Le Monier. On the 

 evening of the fame day, the fhip being in latitude 54° 24', and longitude 6° 30', or 

 24° i Eaft of Ferro, the variation was no more than i2~' 7 Weft, which alfo is near a 

 degree and half lefs than AL Le Monier fays it was, when we firft arrived in a proper 

 parallel for feeing Cape Circumcifion. It is true, the next morning, in latitude 

 54° 2ii' South, longitude 8" 6' Eaft, we had 13" 42' Weft variation ; biit this was 

 after we had run more than two degrees within fight of the parallel of 54° South. It 

 is, moreover, highly probable, that both thefe variations were too great ; for, on the 

 *7th, in the evening, latitude 54° 25' South, and longitude 9° 20' Eaft ; that is, .1° \ 



more 



* I here go by the dates in " The Original Aftronomical Obfervations," printed by or- 

 der of the Board of Longitude; which, after the 14th of February 1775, diiFer one day 

 from Captain Cook's date;» 



