laid down from theodolite bearings taken on shore, combined with the
observed latitudes; and consequently the accuracy in longitude of the
first portion depends upon that of Port Jackson and the time keepers, and
of the last, upon Upper Head and the survey. These two unconnected
longitudes meet at Port Curtis, and the difference between them is there
no more than 5".

From observations with the theodolite upon the top of Upper Head, the
_variation_ was 8 deg. 37' east; but on moving the instrument ten yards to
the south-west, it was 45' less. At two other stations on the west side
of the sound, it was 8 deg. 15', and 8 deg. 0'; and on board the ship 7 deg. 17' and
7 deg. 46', corrected. On the east side of the sound it differed at six
stations on shore, from 8 deg. to 6 deg.; and on board the ship was 6 deg. 44'
corrected. As general results, therefore, but subject to many small
deviations, the variation may be taken,

On the west side of Broad Sound at 8 deg. 0' E.
On the east side 7 0
At the head of the sound it was,
at one station 12 deg., at another 10 deg.;
the mean, 11 0

The differences between the two sides of the sound, both on shore and on
board, are nearly similar to what took place in Shoal-water Bay.

The rise of _tide_ and time of high water have been mentioned; but it may
be proper to say what I conceive to be the cause of the extraordinary
rise in Broad Sound. From Cape Howe, at the southern extremity of the
East Coast, to Port Curtis at the edge of the tropic, the time of high
water falls between seven and nine hours after the moon's passage, and
the rise does not exceed nine feet; but from thence to the northward,
commencing with Keppel Bay, the time becomes later, and the rise
augments, till, at Broad Sound, they reach eleven hours, and between
thirty and thirty-five feet. The principal flood tide upon the coast is
supposed to come from the south-east, and the ebb from the north, or
north-west; but from the particular formation of Keppel and Shoal-water
Bays, and of Broad Sound, whose entrances face the north, or north-west,
this ebb tide sets into them, and accumulates the water for some time,
becoming to them a flood. This will, in some degree, account for the
later time and greater rise of the tide; and is conformable to what
captain Cook says upon the same subject (Hawkesworth, III. 244); but I
think there is still a super-adding cause. At the di