MADE ON THE COASTS OF EUROPE AND AMERICA IN JUNE 1835. 
303 
arrives along the coast of the Netherlands predominant at another period. The short 
series of observations which we have now before us, does not by any means enable us 
to determine how far this change in the influence of the two tide-waves is constant 
and regular. On the coast of the Netherlands, also, this inequality seems to offer a 
peculiarity ; for it vanishes on the 24th, but increases again without missing a tide. 
In the northern part of Norway it increases from the 12th, vanishes on the 20th, and 
exists but irregularly afterwards. 
The evidence of these statements is seen most clearly by an inspection of the curves 
of which I have spoken ; and the eye catches from these the course of the facts far 
more distinctly than from any numbers. But it is not necessary to publish all these 
curves, and I have therefore only annexed a specimen in Plate XXVII., and, for the 
rest, stated the results of them in numbers in Table XI. The means there given are 
obtained by a graphical interpolation, such as I have already described, and the 
other columns exhibit the effects which are mainly due to the diurnal inequality. 
26. In these tables the differences of heights are arranged according as the tide oc- 
curs a.m. or p.m. But it will be seen at once that this is not, in fact, the circumstance 
on which the distinction depends ; for at most of the places the p.m. tides are greatest 
till about the 12th, then the a.m. tides are the greatest till the 18th, and afterwards 
the p.m. tides are again the highest. Hence we see that it is impossible to give the 
law of this inequality, as is sometimes attempted, by saying that at one season of the 
year the a.m. tides are greatest, and at another season the p.m. tides are greatest. The 
real rule, on the coast of America, is, that the tide which follows the superior transit 
of the moon when she has south declination, and the inferior transit when she has 
north declination, is the greatest. And hence we see that the sign of this inequality 
in the tables must change when we come to the half-day without a tide in each semi- 
lunation, as it will be seen, by inspecting the tables, that it does : for if the tide 
which happens at ll h 50 m a.m. today be the one which follows a superior transit, the 
tfde which happens at 0 h 20 m p.m. tomorrow will also follow a superior transit ; and 
therefore the + sign of the diurnal inequality must pass from the a.m. to the p.m. 
column. 
On the west coasts of Portugal, Spain, France, and Ireland, and in the South-west 
of England, the rule is the same, except that we must state two days after the moon’s 
crossing the equator to the south as the times when the inferior transit gives an increase 
to the next succeeding tide, and vice versd. Thus on the coast of Cornwall the p.m. 
tide was greater from the 9th to the 19th (the day of full moon), because the moon 
had gone south of the equator on the 4th, and the p.m. tide followed the inferior 
transit. On the 20th the a.m tides began to follow the inferior transit, and the sign 
of the inequality would on this account change ; but as the moon went north of the 
equator on the 19th, the tide following the superior transit must become the greatest 
on the 21st, that is, the p.m. tide : and thus the p.m. tides continue the greatest almost 
