%Z INTRODUCTION TO THE 



But however plausible this theory may seem at first 

 sight, experience has abundantly detected its fallacy. 



were not unattended to at that time, from what the Captain 

 has said, p. 236. Vol. II. of his account of the voyage. And 

 it may be proper to observe here, that what fell from Captain 

 Cook on this subject, was to show that this circumstance was then 

 attended to, and not to throw blame on M. Bouvet, for whose 

 memory and abilities Captain Cook entertained great respect : nor 

 is it incompatible with the utmost respect, for a man to have a 

 favourable opinion of his own labours ; or to endeavour to show 

 why he thinks the disagreement between them and those of another 

 person, when there is one, does not arise from an error committed 

 by himself. There could, therefore, be no occasion for M. Le 

 Monier to express himself as he has done in several parts of his 

 second Memoir. 



The substance of M. Le Monier 's argument is this. In 1739, 

 when M. Bouvefs, discovery is supposed to have been made, the 

 methods for determining the longitude of a ship at sea were very 

 defective ; and, of course, the longitude of any land which hap- 

 pened accidentally to be seen by one, was equally uncertain. On 

 a presumption that this was the case with respect to Cape Circum- 

 cision, M. Le Monier enquires into the quantity of the variation 

 of the magnetic needle, observed by M. Bouvet at that place, and 

 also into observations of the same kind, made at other places in the 

 neighbourhood of it, about the same time, as well as both before 

 and since. And by comparing these observations together, he 

 concludes, that at the time when Captain Cook was in these seas, 

 the variation of the needle at Cape Circumcision must have been 

 10 westerly : whereas, in the most westerly point of Captain 

 Cook's track, where he was sufficiently near the parallel of 54 

 south, to have seen land situated in it, the variation was 13 

 westerly. This difference of 3, in the variation, answers to 

 about 7 of longitude, in this part of the parallel of 54 south : and 

 by so much did Captain Cook fall in with this parallel to the east- 

 ward of what he ought to have done to see the land in question. 

 " Hence (M. Le Monier infers), that it is not surprising the British 

 " navigator snould not find Cape Circumcision under a meridian 

 " which is 28 to the eastward of Ferro, when it is really situated 

 ** under a meridian which is but 21 to the eastward of it." 



In replying to these allegations, I shall first show, that, grant- 

 ing the dependence which M. Le Monier supposes may be placed 

 on observations of the variation made at sea, he has stated the 

 quantity of the variation observed on board the Resolution, very 

 erroneously. 



Secondly, I shall prove, beyond contradiction, that observations 

 of the variation, made at sea, cannot be depended on for the pur- 

 poses to which M. Le Monier has applied them. 



And, lastly, that no material error had crept into M. Bouvefs 



4, 



