8 
THE REV. W. WHEWELL ON THE TIDES OF THE PACIFIC, 
without observation) and the time at which the high water follows the moon’s transit 
{the lunitidal interval) ; for the comparison of such intervals in successive half-days 
would immediately show whether the observations give any consistent result : and if 
they do not, they must be of little value. This test I have accordingly applied to the 
observations hereafter quoted. Where the lunitidal intervals on successive half-days 
differ very much (by two or three hours, for instance), or follow some progression 
inconsistent with the usual laws of the tides, the results of those observations can be 
of no immediate value, either for drawing cotidal lines, or for any other purpose. 
21. But besides the irregularities in the observed tides arising from inaccurate or 
confused processes, there are others arising from the phenomena themselves. For 
instance, there are some places where the tides are regulated by the sun as much as 
they are by the moon, or even more. At these places we should obtain no intelligible 
result by referring them to the moon alone. Again, in other places the lunitidal 
interval is affected by a large inequality which makes it alternately greater and less : 
for instance, in successive tides it is, (in minutes,) 
30, 150, 60, 180, 30, 210, 
and so on. Now what shall we say is the ‘‘establishment” in such a case? If we 
take the “ corrected establishment,” as I have defined it (the mean interval), it is 110“; 
but this is not an approximate value for any single tide. If we take the three smaller 
intervals, which may happen to be the day tides, we have, for the mean, 40“ ; if we 
take the three others, we have 1 80“, or three hours. And if w'e use the common 
“ establishment,” the confusion is still greater. The fact is, that in such cases the 
term “establishment” loses all definite meaning, as I have already observed*. It 
cannot be of use, either in expressing the laws of the tides at any one place, or the 
mode of transmission of the tide from one place to another. The former subject, the 
law of the diurnal inequality of the tides at a particular place, I have been able to 
assign for several places, and in some degree, in general. The latter, the mode in 
which the diurnal and the semidiurnal wave are transmitted and continued, is a 
more difficult question. I shall however add a few words on each of these points. 
22. Before I quit the subject of cotidal lines, I may remark, that Capt. FitzRoy 
has pointed out the difficulties which attend the representation of the tides of the 
Atlantic and Pacific by means of cotidal lines, and has suggested a “ libration or 
oscillation” of the ocean as better explaining the phenomena-f'. I had already, in 
4836:}:, pointed out other difficulties which belong to the case of the Atlantic, accord- 
ing to the series of observations then made. 
We must recollect, however, that there are other ways besides the two which I 
have noticed (a stationary undulation and a revolving tide-wave) which will give us 
* Philosophical Transactions, 1840, Part I., p. 164. 
t Voyages of the Adventure and Beagle. Appendix, p. 277. 
]: Philosophical Transactions, 1836, Part II., p. 304. 
