AND ON THE DIURNAL INEQUALITY. 
19 
shall I further examine how far the phenomena approach to the cases of fluid motion 
already described, in which there is a marked wave at the outskirts of the mass, and 
an approximate quiescence of the surface in the central parts ; namely, the case of 
a stationary undulation, and of a revolving undulation*. I may remark, however, 
that the latter supposition, that of a revolving undulation by which the tide is carried 
from California northwards along the American shore and to the coast of Kamts- 
chatka, while the cotidal lines converge to some central point in the North Pacific, 
would explain the smallness of the tides at the Sandwich Isles. 
36. When we proceed westward from the central parts of the South Pacific to 
New Zealand and Australia, we again find the feature which we have already noticed 
in the tides ; namely, that the cotidal lines run nearly parallel to the shore in its 
neighbourhood, but that we cannot easily infer the oceanic from the littoral tides ; 
for the tide lines of VI., VII., VIII., IX., X., XI. succeed each other along the coast 
of New Zealand, and apparently double round its northern and southern extremities, 
as we should expect from the laws of fluids. But yet the line of X. recurs again on 
the coast of Australia, and is succeeded by later hours as we proceed northward and 
southward from about lat. 30° south. Cotidal lines may be drawn to accommodate 
themselves to these data ; but of these lines the parts which occupy the ocean be- 
tween New Zealand and Australia must be very doubtful. 
I have been favoured by Sir James Ross with about a month’s observations of the 
tides in the Bay of Islands in New Zealand, which I may refer to hereafter ; but my 
means of tracing the progress of the tides along the coast of New Zealand still depend 
upon Captain Cook’s statements -f-. The longitude of New Zealand is so nearly 12^ 
that the local tide-hour may be considered as coincident with the Greenwich hour. 
At Tobago Bay, near the most easterly point of these islands, the time is O'*. In 
proceeding to Mercury Bay and the Bay of Islands on the north-east coast, it becomes 
7^^ 30*" and 8*^ respectively. And in proceeding southward from Tobago Bay, we have 
also a retardation. At Queen Charlotte’s Sound and Admiralty Sound, in Cook’s 
Strait, which separates the two islands, it is 9*^ 30“* and 10^, the strait producing a 
considerable retardation. At Dusky Bay, the southern point of the island, the time 
is 10^ 57"*. 
Tides of Australia. 
37 . With regard to the coast of Australia, I have been furnished with a consider- 
able quantity of tide observations, resulting principally from the surveys of Captain 
Blackwood and Captain Stokes. These are now to be added to the observations 
formerly collected from Captains Cook, Flinders and King. The earliest tides, as I 
formerly observed, appear to occur between the latitudes 24° and 35° south. I shall 
therefore proceed from this part southwards and northwards. 
* Or rather a revolving cotidal line. See Article 23, 
t Philosophical Transactions, 1772. 
