Wreck Reef . ] TERRA AUSTRALIS. 
with the Port Jackson rate, or 14' 3 5", 9 less than the lunar observa- 
tions. 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 com'pass from ob- 
serving the sun’s magnetic azimuth a. m. and/), m., when equal alti- 
tudes were taken, and comparing the mean azimuth at correspond- 
ing 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 g° if east from ten ob- 
servations, and that marked No. 2, 13 0 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 8 k 50' in the morning ; the rise was six feet 
two inches, but the night tide will probably reach to eight, or per- 
haps 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 quar- 
ter, 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 leagueun 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 ; 
but the eastern bank is the most considerable, and most frequented 
by birds ; turtle also land there occasionally, and this bank was not 
improperly called Bird Islet, being now covered with coarse grass, 
331 
1803. 
October. 
\ 
