MADE ON THE COASTS OF EUROPE AND AMERICA IN JUNE 1835. 301 
1 inch ; at Christiansund 6 feet 8 inches ; at Lofoden 7 feet 7 inches ; and at Trom- 
soe, in latitude 69° 38', it is 8 feet 8 inches. At Peterhead, on the coast opposite 
Norway, it is 12 feet. 
I shall not here attempt to reduce these changes to any general rules, but shall 
proceed to another branch of our results. 
Sect. V. The Diurnal Inequality. 
22. The Diurnal Inequality of the tides is only now beginning to be attended to as it 
deserves ; for it is a regular change, considerable in its amount, and almost universal 
in its prevalence. It would be easy to enumerate many actual cases in which the 
safety or loss of a ship has been determined by this inequality. Though the existence 
of such an inequality in particular places has long been known, its laws have been 
misunderstood: for example, it has been supposed always to affect the morning and 
evening tides in opposite ways, which is only an accidental and local expression of its 
rule. Mr. Lubbock* has published the mode in which he has obtained it for Liver- 
pool, while Mr. Bywater, who has introduced it into his Tide-Tables for that port, 
and Mr. Bunt, who is constructing Tide-Tables for Bristol, have also collected this 
inequality from observations. But the connexion of the inequality, as it exists in 
different parts of the world, was never brought into view till the discussion of the 
European and American observations of last June. The laws which the inequality 
follows when thus considered on an extensive plan appear to me to be very curious, 
as they result from this examination of the facts ; and I now proceed to explain 
them. 
23. The inequality is most clearly seen in the heights of high water. I exhibited 
the results in curves, by erecting a series of ordinates at equal distances to represent 
the heights of the successive high waters above a fixed point at each place ; and the 
curves which were thus produced showed, in most places, a series of parallel zigzags 
(the tides being alternately higher and lower) ; and these curves were so regular, and 
so exactly accompanied each other, as to prove both the goodness of the observations 
and the existence of the diurnal inequality. This was the case, in the most marked 
manner, on the coast of America, where scarcely any exception occurred. Next to 
this, the inequality was conspicuous, especially during a portion of the series of obser- 
vations, on the coasts of Spain and Portugal ; then on the west coast of France, the 
coast of Cornwall, and parts of the west coast of Ireland : on the shores of the Ger- 
man Ocean, although the operation of the inequality was obvious, it was less steady 
and regular. 
24. The diurnal inequality depends upon the moon being north or south of the 
equator ; its maximum corresponds to (but is not necessarily simultaneous with) the 
moon’s greatest declination ; and the period of its vanishing corresponds in like 
manner with the time of the moon passing the equator. Between periods corre- 
* Philosophical Transactions, 1836, Part I., page 57. 
