atitude_ of Wreck-Reef Bank was ascertained from eight meridian
observations from the sea, and four from an artificial horizon: the mean
of the latter, which are considered the best, is 22 deg. 11' 23" S.

_Longitude_ from sixty sets of lunar distances, of which the individual
results are given in Table VIII. of the Appendix No. I. to this volume,
155 deg. 18' 50.5" E.

The longitude of the bank, as given by Earnshaw's No. 520 on Aug. 28,
eleven days after the shipwreck, was 155 deg. 4' 14.6" with the Port Jackson
rate, or 14' 35.9" less than the lunar observations. In laying down the
Porpoise's track on the chart, this error has been corrected by an equal
proportion, according to the time of each observation for the longitude.

Mr. Flinders deduced the _variation_ of the compass from observing the
sun's magnetic azimuth a. m. and p. m., when equal altitudes were taken,
and comparing the mean azimuth at corresponding altitudes with the true
meridian; this method is probably not the best, and the results from two
compasses differed considerably; Walker's compass, marked No. 1, giving
9 deg. 17' east from ten observations, and that marked No. 2, 13 deg. 54' from
five observations. The first is undoubtedly the best, though possibly not
very correct.

There are here two regular _tides_ daily, and it was high water on the
day of full moon at 8h 50' in the morning; the rise was six feet two
inches, but the night tide will probably reach to eight, or perhaps nine
feet at the height of the springs.

Some account was given of Wreck-Reef Bank before quitting it in the boat,
but I had not then acquired a knowledge of the whole extent of the reef.
It is about twenty miles long, and from a quarter, to one mile and a half
in breadth; and consists of many distinct patches of different
magnitudes, the six principal of which are from four to eight or ten
miles in circuit. They are separated by channels of one mile to near a
league in width; and in the two easternmost I found from 8 to 10 fathoms,
and nothing to prevent a ship passing through in a case of necessity.
Four of the six larger patches have each a sand bank near the middle,
which do not appear to have been lately covered by the tide; and they are
now more or less frequented by sea birds, such as noddies, boobies,
tropic, and man-of-war birds, gannets, and perhaps some others. Of these
four banks, two lie to the west and one to the east of that near which
our ships struck;