The height of the thermometer at the tents, as observed at noon, varied between 80° and 64°. On board the ship, it never exceeded 70½°, nor was below 60°. The range of the barometer was from 29,42 inches in a gale of wind from the westward, to 30,28 inches in a moderate breeze from south-west.
Mean Dip of the S. end of the needle, taken onshore, 64° 1'
On board, upon the cabin table, 64° 52'.
The increase being probably occasioned by the iron ballast in the bread room underneath.
The Variation given by three compasses at the observatory was 6° 22½' west, by Walker's meridional compass 5° 25', and by the surveying theodolite 8° 17'; but upon the eastern part of the flat granite rock, on the south side of the sound, two theodolites gave only 4° 1' west. On board the ship, at anchor off Point Possession, the variation from the three compasses on the binnacle., when the head was southeastward, was 9° 28'; or, corrected to the meridian, 7° 12' west. It seems not easy to say what ought to be considered as the true variation; but the mean of the observations at the tents being 6° 42', and on board the ship 7° 12', I conceive it will not be far wrong if taken at 7° 0' west.
This is what I allowed in tracing a base line upon the beach between the two harbours; and the back bearings from different stations did not vary more than a degree from it, except at the west end of Michaelmas Island, where the variation, in one spot, was greater by 3°.
The above different variations show that the needle was affected by the rocks; and there will be frequent occasion, in the course of the voyage, to point out similar anomalies in the observations on land; for they were found to take place upon almost all those parts of Terra Australis, where the basis stone is of granite, as here; and also in those where green-stone, porphyry, basaltes, or iron-stone prevail; whereas in the lime, or grit-stone countries, the needle did not appear to suffer any derangement. In the Appendix No. II. to the second volume, where the changes on ship board, which arose from altering the direction of the head, are explained, this subject of the differences on shore is mentioned; for they also were not without a certain degree of regularity.
No set of Tide was perceived on board, either whilst the ship was in the Sound or in Princess-Royal Harbour; nevertheless it was sometimes found to run with considerable strength in the narrow entrances of both harbours. According to lieutenant Flinders' observations on shore during sixteen days there was only one high water in twenty-four hours, which always took place between six and twelve at night; for after, by gradually becoming later, it had been high water at twelve, the next night it took place soon after six o'clock; and then happened later by three-quarters of an hour each night as before. The greatest rise observed was three feet two inches, and the least two feet eight inches. The accumulation was made in this manner: After low water it rose for several hours; then ceased, and became stationary, or perhaps fell back a little. In a few hours it began to rise again; and in about twelve from the first commencement was high water. It was observed by Captain Cook upon the east coast of this country*, and since by many others, including myself, that the night tide rose considerably higher than that of the day; which is conformable to our observations in King George's Sound; but with this difference, that in the day we had scarcely any tide at all.
[* See Hawkesworth's Voyages, Vol. III. p. 224.]
The base line for my survey of the Sound was of 2.46 geographic miles, measured round the curve of the long beach between the two harbours. The other stations whence bearings were taken with the theodolite were--in the Sound, four; at the entrance of and within Princess-Royal Harbour, three; and in Oyster Harbour, four; at each of which a point with a circle is marked in the plan. The soundings were either taken in the ship, with simultaneous cross bearings, or in boats, generally accompanied with notices of known objects in a line, or the angles between them taken with a sextant.
There are many small but no very essential differences between my plan and that of captain Vancouver. The most important to navigation is that in the soundings going into Oyster Harbour; I could find only thirteen feet over the bar, whereas he marked seventeen; a difference, however, which may not improbably have taken place between 1791 and 1801.