PREFACE. 
T he publication in 1814, of a voyage commenced in 1801, and of 
which all the essential parts were concluded within three years, 
requires some explanation. Shipwreck and a long imprisonment 
prevented my arrival in England until the latter end of 1810; 
much had then been done to forward the account, and the charts 
in particular were nearly prepared for the engraver ; but it was de- 
sirable that the astronomical observations, upon which so much 
depended, should undergo a re-calculation, and the lunar distances 
have the advantage of being compared with the observations made 
at the same time at Greenwich; and in July 1811, the necessary 
authority was obtained from the Board of Longitude. A consider- 
able delay hence arose, and it was prolonged by the Greenwich 
observations being found to differ so much from the calculated 
places of the sun and moon, given in the Nautical Almanacks of 
1801, 2 and 3, as to make considerable alterations in the longitudes 
of places settled during the voyage ; and a reconstruction of all 
the charts becoming thence indispensable to accuracy, I wished also 
to employ in it corrections of another kind, which before had been 
adopted only in some particular instances. 
A variety of observations with the compass had shown the mag- 
netic needle to differ from itself sometimes as much as six, and even 
seven degrees, in or very near the same place, and the differences 
appeared to be subject to regular laws ; but it was so extraordinary 
