AND ON THE DIURNAL INEQUALITY. 
11 
we note that the interval of three hours intervenes between high water at Payta 
and at Callao ; no one can maintain that the question of the tides is exhausted, 
or even that there is not a great deal to be done, in order to decide in what manner 
invisible obstacles, as the inequalities of the bottom of the sea, act upon the velocity 
of propagation of the tide-wave and upon its height. In the age in which we live, 
to propose a scientific question in a distinct form is half its solution.” 
I may remark that the object of the present memoir is mainly to give additional 
distinctness to the problem thus proposed, in order that further observations and cal- 
culations may help us on to the solution. 
27 . In Captain FitzRoy’s “Narrative of the Surveying Voyages of H.M.S. Ad- 
venture and Beagle, between 1826 and 1836,” there are in the Appendix, two articles 
on the tides; one, containing the time and rise of the tide at a great number of places, 
the other containing some general remarks, to which I have already referred. Cap- 
tain FitzRoy notices the features in the tides of the Pacific partly as Admiral Du 
Petit-Thouars does. Thus he says (p. 281), — 
“ It is high water at Cape Pillar and at Chiloe, including the intermediate coast, 
almost at one time : from Valdivia to the Bay of Mexillones (differing eighteen de- 
grees in latitude) there is not an hour’s difference in the time of high water: from 
Arica to Payta the times vary gradually as the coast trends westward : from Panama 
to California, the times also change gradually as the coast trends westward : and 
from forty to sixty north, high water takes place at one time.” 
Captain FitzRoy combines these and many other facts respecting the tides into a 
hypothetical general view of the movement of the ocean, which may be of service in 
provoking further inquiry, though it can hardly be considered tenable in detail, as 
perhaps the present memoir may serve to show. 
28. In the Philosophical Transactions for 1840*, I mentioned and discussed certain 
remarkable tide observations made at Petropaulofsk in Kamtschatka, which I had 
received from Admiral Lutke. That officer has since combined several tide obser- 
vations of his own and others, in a “Notice sur les Maries Periodiques dans le Grand 
Ocean Boreal et dans la Mer Glaciale,” and has, in a chart of the North Pacific 
attached to this notice, drawn the cotidal lines belonging to that ocean. I will place 
here an extract from this Notice, pointing out the grounds on which he proceeds, and 
the difficulty in which he finds himself involved. 
“ In examining the order of sequence of the tide-hours on the west coast of 
America and in the Aleutian Isles, we see clearly that the tide coming from the 
south runs along this shore to the north-west ; and then to the west along the chain 
of the Aleutians to the coast of Kamtschatka, employing twelve hours in passing 
from San Bias to Petropaulofsk. Proceeding from this point, we can no longer 
follow it with the same certainty, having no data for the tides at the Kurile Isles 
and on the eastern coast of Japan. Further to the south we again have some obser- 
* Part I., p. 161. 
