The stone of the hill had in it specks of quartz or feldtspath, and was not much unlike that of Pier Head; but it had a more basaltic appearance. A piece of it applied to the theodolite, drew the needle two degrees out of its direction, and yet the bearings did not show any great difference from the true variation; for an amplitude taken on board the ship by Mr. Flinders, when the head was N. N. E, gave 6° 18', or corrected to the meridian, 7° 17' east, and the variation on the eastern side of the hill was 8° 15', according to the back bearing of Pier Head.
From an observation of the sun's upper and lower limbs in an artificial horizon, the latitude was 21° 50' 18", and the ship bore from thence S. 68° E. two miles and a half; the latitude of the ship should therefore have been 21° 51' 14"; but a meridian altitude observed to the north by lieutenant Flinders, gave 21° 49' 54"; and I believe that altitudes from the sea horizon can never be depended on nearer than to one minute, on account of the variability of the horizontal refraction. From this cause it was that, when possible, we commonly observed the latitude on board the ship both to the north and south, taking the sun's altitude one way and his supplement the other, and the mean of the two results was considered to be true; separately, they often differed 1', 2', and even 3', and sometimes they agreed. The observation to the north most commonly gave the least south latitude, but not always, nor was there any regular coincidence between the results and the heights of the barometer or thermometer; though in general, the more hazy the weather, the greater were the differences. At this time, the wind was light from the eastward and weather hazy; the thermometer stood at 72°, and barometer at 30.15 inches.
At two o'clock we got under way to go up Broad Sound, it being then near low water. After steering south-east one mile, the depth rapidly diminished and we tacked; but the ship was set upon a bank of sand, where she hung five minutes and then swung off. I afterwards steered nearer to the shore, in deeper water; and at dusk the anchor was dropped in 5 fathoms, sandy bottom, between the Flat Isles and the main, West Hill bearing N. 35° W. three leagues; the master sounded towards the coast, which was five miles off, and found the deepest water to be on that side. In the morning [FRIDAY 10 SEPTEMBER 1802] the wind had shifted to south, and we beat up in a channel formed by the Flat Isles and the shoals attached to them, on one side, and the shelving banks from the main coast, on the other. We had the assistance of a strong flood tide till eleven o'clock; at which time the anchor was let go, one mile from the north end of the 4th Flat Island.
I landed immediately, with the botanists; and at the south-east end of the island, which is a little elevated, took bearings and the meridian altitude of both limbs of the sun from an artificial horizon. The latitude deduced was 22° 8' 33"; and the ship bearing N. 19° 30' W., two miles, it should have been for her, 22° 6' 40"; but lieutenant Flinders' observation to the north gave 22° 5' 19", or 1' 21" less, nearly as on the preceding day; and it was ascertained that the difference arose neither from the eye nor the instrument. Amongst the bearings were,
West Hill, the top, N. 16° 40' W.
Northumberland Isles. the peak marked 'h', N. 25 15 E.
Long Island, extreme of the north point, N. 73 35 E.
Upper Head, on the west shore up Broad Sound, S. 39 55 E.
The 4th Flat Isle is about one mile long, and there is a smaller lying off its south-east end; they are a little elevated, and bear grass and small trees; but the shores are covered with mangroves, and surrounded with extensive flats of mud and sand. The main coast, from which they lie two or three miles, is also low, with mangroves and shelving mud banks; but there is a deep channel between, of a mile in width. In the evening, when the flood made, we steered into this channel with a light sea-breeze; but not having time to clear it before dark, the anchor was dropped in 4 fathoms at six o'clock.
My attention was attracted this evening by the vast extent of mud left dry on each side of the channel, and I ordered particular attention to be paid to the tides during the night. At eleven o'clock, when the flood had ceased running, the depth was sounded and the lead line measured, and the same at half past five in the morning [SATURDAY 11 SEPTEMBER 1802] when it was low water; the difference was no less than thirty-two feet, and it wanted a day of being full moon; so that the springs may reach two or three feet higher. The flood set S. by E., but its greatest rate did not exceed one mile and three quarters an hour.
At daylight the wind was south-east, directly against us. We backed and filled, drifting up with the flood between the shoals on each side, and having the Lady Nelson and a boat ahead; but on approaching the end of the channel, our passage into the sound was blocked up by a bank running across, upon which there was not water enough for the ship by a fathom, and we therefore anchored. At nine the tide had risen a fathom. and we passed over into the open sound; the depth immediately increasing to 4 and 7 fathoms, reduced to low water. So long as the flood continued running we worked up the sound; and when it ceased, anchored three miles from a shallow opening in the low western shore, the second which had been observed. We again proceeded upwards with the evening's tide until dusk; and at nine next morning [SUNDAY 12 SEPTEMBER 1802] passed a fifth opening, and anchored abreast of the hilly projection on its east side, which I have named Upper Head, in 4 fathoms, soft bottom, two-thirds of a mile from the shore. This was the first place on the main where there was any prospect of being able to land; for the western shore, thus far up, was equally low, and as much over-run with mangroves and defended by muddy flats, as the shores of Keppel Bay.
It being my intention to explore the head of Broad Sound with the brig and whale boat, a situation where tents could be fixed and an easy communication held with the ship during my absence, was the object now sought; and I immediately went with a party of the gentlemen, to ascertain how far Upper Head was calculated for our purpose. We landed at half flood, without difficulty; and on ascending the hill, obtained a view of the Sound which exceeded my expectations. Amongst the many bearings taken, were the following fixed points in the survey.
Pine Mount, of Shoal-water Bay, S. 84° 38' E.
Pier Head, the western part, N. 36 7 E.
West hill, the top, N. 28 5 W.
Flat Isles, the 4th, station there, N. 39 53 W.