DIURNAL INEQUALITY WAVE ALONG THE COASTS OF EUROPE. 
229 
different places exhibit is this : we may suppose that the diurnal wave has the same 
epoch as me semidiurnal wave., but that the former wave travels with a different 
velocity from the latter. The consequence of this would be that the diurnal inequality 
would at one port be thrown entirely upon the high water, at a place at some distance, 
where the diurnal wave had gained (or lost) six (lunar) hours upon the semidiurnal 
wave, the diurnal inequality would fall entirely upon the low water, and would not 
appear in the high water at all ; and at intermediate places it would affect both high 
and low waters. If neither of these cases appear to agree with the facts, there ap- 
pears to be no supposition remaining but that the diurnal wave travels irregularly, so 
as to affect only or principally sometimes high water, sometimes low water, some- 
times both, with no regular progression. And in this case it may be conceived that 
the diurnal wave at some places vanishes or becomes very small, as I have shown in 
the Sixth Series of these Researches that the semidiurnal wave does, even in the near 
neighbourhood of places where it is of considerable magnitude. 
The form of the curve which represents the diurnal wave at a series of ports would 
be modified in the following manner on these different suppositions. If the epoch of 
this wave changes more rapidly than that of the other inequalities, the sinuous curve 
which represents the diurnal wave, will have its zero ordinates, and its maximum or- 
dinates, gradually transferred from one half day to a succeeding one, and so on, as 
we proceed in the direction of its propagation. Each of the sinuous swells , corre- 
sponding to the successive tides, may remain in the same place, but the assemblage 
of them, corresponding to a semimenstrual series of north or of south lunar declina- 
tions, will glide forwards by an alteration of the values of the maximum ordinates in 
these diurnal swells. On the other hand, if the epoch were the same at different 
places, and the velocity of the diurnal wave different from that of the semidiurnal 
wave, each diurnal swell will slide on, separating itself more and more from the cor- 
responding high (or low) water, but undergoing no progressive change in its mag- 
nitude. 
The form of the diurnal wave curve was thus determined for several series of 
places, and I will state the conclusions to which these series respectively led*. 
First Series. — Ferrol, Port Magee (west end of Valentia Island), Doonkeghan 
(Mayo), Sligo, Ballynass (in the north-west of Ireland), Scrabsters (near Thurso), 
Buckie, Uzon (near Montrose), North Berwick (Frith of Forth), Berwick-upon-Tweed, 
and Clay Hole (Lincolnshire). 
This series begins on the west coast of Spain, and proceeding by the west coast of 
Ireland to the north of Scotland, turns round the north-east point of Scotland, and 
goes on along the east coast of Britain. 
It appears, in the first place, by the inspection of these curves, that there is no such 
slow propagation of the diurnal inequality as I had supposed. The inequality vanishes 
at all these places about the 10th and 22nd of June, the moon’s declination having 
* The curves for a series of places on the coasts of the British Channel are given in Plate XIV. 
2 h 2 
