236 THE REV. W. WHEWELL ON THE DETERMINATION OF THE 



our labours were conducted, as I have already stated, with a peculiar view to several 

 questions respecting the connection of tide phenomena at different times and places ; 

 and I will now state the answers to these questions, which our results supply. 



I. To which transit of the moon ought we to refer the tide ? 

 \ It has been well shown by Mr. Lubbock that the agreement between the empirical 

 laws of the tides and the equilibrium theory is much improved, by referring the tides 

 to a transit anterior to their occurrence by two or three days. He denotes the suc- 

 cessive transits of the moon (at intervals of about twelve hours) by the letters A, B, 

 C, D, E, F ; F being the transit which immediately precedes (by about two hours) the 

 high water at London : and he finds that the laws of the tides at London and Liver- 

 pool agree best with theory when they are referred to the transit B. The tide which 

 reaches London at two hours after the transit F, was at Plymouth about six hours 

 after the transit E; and as from transit B to transit E is about thirty-eight hours, if 

 we refer the Plymouth tides to transit B, we take a transit about forty-four hours 

 before the tide. Transits A and C are about fifty-six and thirty-two hours anterior 

 to the tide. Nearly the same may be said of Bristol, for the tide there is nearly 

 contemporaneous with that at Plymouth. I have, therefore, referred the Bristol 

 tides of 1834 and 1835 to each of the three transits A, B, C, and have compared 

 the results. 



The general result is, that the ti'ansit B gives the best tables. This is shown both 

 by the unaccounted-for residue of the observed quantities, which is smallest when 

 transit B is used ; and by the form of the curves for the parallax and declination 

 corrections, which is most regular for this transit. 



We may therefore, it would seem, assume, at least for our own coasts, that the 

 tides are to be referred to a transit of the moon, which takes place a day and a half 

 before the tide reaches the coasts of Europe. 



We may, however, observe that we do not in this way obtain an exact agreement 

 of observation and theory, even with regard to the semimenstrual inequality. It has 

 appeared from Mr. Lubbock's researches respecting the Liverpool tides*, that while 

 the transit A gives a very exact agreement of the theoretical and observed times, we 

 must take a still earlier transit if we would obtain this agreement with respect to the 

 heights. Nor does that selection of a transit which best represents the semimen- 

 strual inequality, bring about an agreement with theory in the parallax and declina- 

 tion corrections, as we shall see. We must allow, therefore, that though there 

 appear to be, in the actual laws of the tides, inequalities corresponding to all these 

 which arise from the supposition of the equilibrium-tide of an anterior epoch trans- 

 mitted along the ocean to our shores, we cannot so assume the epochs to produce 

 all the inequalities at once. The epoch is of one value for the times, of another for 

 the heights; different again for the parallax correction, and again different for the 

 effect of declination. 



* Philosophical Transactions, 1836, Part II. 



