24 INTRODUCTION TO THE 



of the state of the southern hemisphere, and can 

 pronounce with certainty, that the equilibrium of 



54" south, when she crossed the meridian which is 21 to the 

 eastward of Ferro, that is, 3f east of Greenwich, the longitude 

 which M. Le Monier assigns for Cape Circumcision, to see if it 

 had been in that situation, yet her consort, the Adventure, was 

 for several degrees on each side of that meridian ; and especially 

 when she had 10^ of west variation, full as near to the parallel 

 of 54? south as M. Bouvet was to the land when he saw it*; and 

 on the day that she actually passed that meridian, had fine clear 

 weather, f Hence, therefore, granting M. Le Monier his own 

 arguments, which, however, I have proved to be erroneous, and 

 that observations made at sea, for the variation of the compass, 

 may be depended on for the purpose of finding the longitude, 

 it is utterly impossible that both the Resolution and Adventure 

 could have passed Cape Circumcision without seeing it. But J 

 shall now show, that these observations are liable to a much greater 

 error than the whole quantity, so vigorously insisted on by this 

 gentleman. 



I will not here run the risk of incurring M. Le Monier's dis- 

 pleasure, by calling the accuracy of M. Bouvet's observations in 

 question; but will admit every thing that he himself can think 

 due to the instruments and observations of that deserving naviga- 

 tor. It is enough for my argument, and it is but too evident 

 from the observations themselves, that ours were by no means 

 capable of determining the variation to so small a quantity as that 

 which M. Le Monier rests his whole cause upon ; and if so, his argu- 

 ments, which depend wholly on a supposition, that not only they, 

 but M. Bouvefs also, were capable of determining it with the 

 utmost exactness, must fall to the ground. 



1st, It appears, from various instances, that the variations ob- 

 served by the same compass would differ 3 to 5, 6, and sometimes 

 even 10, from no other cause whatever, but putting the ship's 

 head a contrary way. X 



2d, That the same compass, in the same situation in every 

 respect, within a few miles, but at two different times of the same 

 day, would give variations differing from one another, 3, 4, 5, 

 6, and even 7$. 



See The Original Astronomical Observations, p. 185., and Bouvet's Voyage, 

 published by Mr. Dalrymple, p. 4. and 11. 



f See the Observations, p. 218. 



X See the Original Astronomical Observations, made in the second voyage, 

 March 11. 1775, p. 572., January 24. 1774, p. 375.. and July 28. p. 578. 



Observations in the second voyage, February 2. 1775, p. 571., and January 

 J 9. 1775, p. 382. Also observations in last voyage, July 17- 1776, p. 179 

 August 50. }. 1 SI., January 21. 1777, p. 192., and September 15. 1778 

 p. 205. 



