175 
Pellew's Group.] TERRA AUSTRALIS. 
change ; but in No. 520, the rate is more than 8” greater, and the 
longitude was getting per day too much to the east, as well be- 
fore as after it was let down. The coast from Sweers' to Obser- 
vation Island is consequently laid down by No. 543, with the small 
accelerating correction arising from the o",i9 increase of rate in 
16,4 days. 
Variation of the theodolite, observed on the east 
side of South- west Island, - - - 22' east. 
In the bearings taken at different parts within the group, the vari- 
ation seemed to differ from 2 0 30' to r 30'. The largest variations 
were on the east sides of the islands, and the smallest on the west 
sides ; seeming to show an attraction of the land upon the south 
end of the needle. On board the ship, when coasting along the east 
side of Vanderlin’s Island, and the whole group lay to the west, the 
variation appeared from the bearings to be as much as 4 0 east. 
The best observation made on the tide, was on the 23d, during 
my boat excursion to the south end of Vanderlin's Island. On that 
morning the moon passed over the meridian at sixteen minutes past 
ten, and the perpendicular movements of the tide were as follows. 
At seven o’clock, when I left the shore, the tide was falling; on 
landing at nine it was stationary, and appeared to be low water ; at 
noon it rose fast, and at three was still rising, and continued so to 
do, but slowly, until seven in the evening. The tide then began to 
fall; but after subsiding one foot, it rose again until ten o’clock, 
and had then attained its greatest height. Low water took place 
therefore about an hour before, and high water at eleven hours 
and a quarter after the moon passed the meridian : the rise appeared 
to be from four to seven feet. At Wellesley’s Islands high 
water had taken place an hour and a half earlier, which seems 
extroardinary, if, as it necesarily must, the flood come from the 
northward. I think it very probable, that the tide in both places 
will follow what was observed in King George’s Sound on the 
South Coast,- where high water, after becoming gradually later 
1802. 
December. 
