DIURNAL INEQUALITY WAVE ALONG THE COASTS OF EUROPE. 
231 
Comparing the diurnal wave, which brings the diurnal inequality of high and of 
low water, with the semidiurnal wave, which brings every tide, we find that 
At Ferrol, the diurnal wave is about 2§ hours earlier. 
At Port Magee, about 4 hours earlier. 
At Doonkeghan, about 2 hours earlier. 
At Sligo, about 1| hour earlier. 
At Ballynass, about 1 hour later. 
At Scrabsters, about 4 hours earlier. 
At Buckie, about 4 hours earlier. 
At Uzon, about 5 hours earlier. 
At North Berwick, about 3 hours earlier. 
At Berwick-upon-Tweed, about 4 hours earlier. 
At Clay Hole, about 2 hours earlier. 
These quantities are unavoidably somewhat vague ; for the place of the summit 
of the wave, as determined by four points of the curve, is necessarily liable to uncer- 
tainty, arising from its form not being known ; besides which it is affected by acci- 
dental causes. And it may be seen by the diagrams that the distance of the summit 
from high or low water often differs considerably on different days. The curve at 
Ballynass, where the diurnal wave differs most from the general average, is very 
irregular. The above quantities, therefore, do not afford us any clear evidence of a 
progressive separation of the diurnal from the semidiurnal wave. And the varia- 
tions which lake place in the diurnal inequality at different places, may be referred 
to a partial acceleration or retardation of the diurnal wave. Thus on the east coast 
of Scotland (at Uzon, near Montrose), the diurnal wave shoots on before the semi- 
diurnal, so as to arrive five hours sooner than that ; consequently it nearly coincides 
with low water, and the diurnal inequality of low water is great, while that of high 
water almost vanishes. But at North Berwick, in the Frith of Forth, this displace- 
ment of the diurnal wave is almost corrected, the diurnal inequality affecting high 
and low waters almost equally. 
We appear to be led by this course of investigations to the conclusion, that 
the differences of diurnal inequality at different places are governed by local circum- 
stances, and do not form a progressive series. We need the less be surprised at this, 
having already seen (in the Sixth Series of these Researches,) that the amount of the 
rise of the tide differs very much even within small distances along the coast, or 
across the sea, and follows no progressive course of increase or decrease. And we 
may hence explain the cases, many of which occur, in which places having no diurnal 
inequality are interposed in a line of coast along which the inequality prevails : for 
example, at Baltimore, near the south-west point of Ireland, the diurnal inequality is 
not perceptible, either at high or low water, in the observations of June 1835, (which 
were carefully made,) although it is very conspicuous both on the west and on the 
south coast of the island. 
