INTRODUCTION. 
XI 
between two observations, the mean of the reckoning, worked 
backwards and forwards, was taken, to fix the ship’s place. In the 
selection of angles for the construction of the charts, those have, for 
obvious reasons, been preferred, which were most easterly or westerly, 
when an observation for latitude was made ; and those which were 
most northerly or southerly, at the time of an actual observation 
for determining the longitude. When angles only were taken, that 
is, when the sun was obscured so as to prevent the possibility of ob- 
taining his altitude and azimuth, the angles were used by laying them 
off from one or more points, whose geographical position had been 
previously fixed ; and by this means, in many instances, the former 
angles have been found to correspond and intersect accurately, when 
there would otherwise have been considerable doubt as to the exact 
place of the ship. The observations for latitude and longitude have 
been seldom or never made by less than two, and frequently by 
three or four, observers, and a mean of these used in the con- 
struction of the chart. The observers were generally Captain 
Sabine, Lieutenant Beechey, Mr. Hooper, and myself; the angles 
were taken with a sextant; sometimes by myself, and sometimes by 
Lieutenant Beechey, to whose skill and industry in this depart- 
ment of my duty, I am happy to acknowledge myself very materially 
indebted. 
A detailed account having been given by Captain Sabine in the 
Appendix, of the chronometers used in obtaining the longitudes for 
the survey, and of the mode of correcting their rates, it is unne- 
cessary for me to add any thing on that subject, the care which has 
been bestowed upon them being sufficiently apparent on an inspection 
of the tables. In the daily winding of the chronometers. Captain 
