No. 520 therefore differed very little to the east of the lunar observations, and the first day's rate was almost exactly the same as that with which we had quitted Upper Head; whilst No. 543 differed greatly, both in longitude and rate. A similar discordance had been noticed at the Cumberland Island, marked l2, twenty days after leaving Upper Head; No. 520 then differed only 1' 1.2" from the survey, but No. 543 erred 7' 2.2" to the east. I have therefore been induced to prefer the longitude given by No. 520, to the mean of both time keepers; and accordingly, the positions of places before mentioned or laid down in the charts, between Upper Head and Sweers' Island, including Torres' Strait, are from this time keeper alone; with such small correction equally proportioned; as its error from the lunars, 2' 50.2" to the east in fifty-two days, made necessary.
No. 543 had undergone some revolution on the passage, but seemed at this time to be going steadily; whereas No. 520, which had kept its rate so well, now varied from 18.79" to 25.39", and ceased to be entitled to an equal degree of confidence.
Mean dip of the south end of the needle, observed upon the west point of Sweers' Island, 44° 27'.
Variation of the theodolite in the same place, 4° 7' E.
Variation of the surveying compass in the Road, 2° 28' with the ship's head E. N. E, and 4° 30' with the head northward; the mean corrected to the meridian, will be 4° 31' E.
In bearings taken on the east side of Bentinck's Island, the variation appeared to be a full degree greater than on the west side of Sweers' Island.
The tides in the Investigator's Road ran N. N. E. and S. S. W., as the channel lies, and their greatest rate at the springs, was one mile and a quarter per hour; they ran with regularity, but there was only one flood and one ebb in the day. The principal part of the flood came from N. N. E.; but according to lieutenant Fowler's remarks on shore, between the 23rd and 27th, it was high water three hours after the opposite tide had set in; or about three hours and a quarter before the moon came to the meridian. At the Prince of Wales' Islands, and at Coen River, it had also appeared that the tide from south-west made high water. The time here happened between 8½h and 11½h at night, from the 23rd to the 27th; but whether high water will always take place at night, as it did at King George's Sound on the South Coast, I cannot be certain. About twelve feet was the greatest rise, which I apprehend would be diminished to eight, at the neap tides.
CHAPTER VII.
Departure from Sweers' Island.
South side of C. Van Diemen examined.
Anchorage at Bountiful Island: turtle and sharks there.
Land of C. Van Diemen proved to be an island.
Examination of the main coast to Cape Vanderlin.
That cape found to be one of a group of islands.
Examination of the islands; their soil, etc.
Monument of the natives.
Traces of former visitors to these parts.
Astronomical and nautical observations.