4 SEVENTH REPORT—1837. 
as they go, the question must be considered as perfectly open,—or, 
rather, they indicate that the Dublin circle has, to the present time, 
given consistent results, which have not been disproved. 
Dr. Robinson pointed out the necessity, in such inquiries, of guard- 
ing against the errors proceeding from changes of temperature, which 
may occasion a diurnal change, capable, in some cases, of masking 
the parallax, supposing it given by the instrument. He stated that he 
had examined the index correction of his own circle by observing the 
Pole star and 6 Urse minoris at both culminations on the same days ; 
and that, though the German astronomers were always attentive to 
detect such changes, it was not, as far as he knew, generally practised 
in Britain. 
On Tides. By the Rev. W. WuHEwELL, F..R.S., Se. 
Mr. Whewell observed that his own researches agreed with those of 
Mr. Lubbock, both in giving a very close and remarkable coincidence 
of the laws of observation and theory on most points, and also in dis- 
closing some curious discrepancies of some of the features of the 
observed tides from the theoretical*. In particular, he stated that he 
had satisfied himself, as Mr. Lubbock had done, but by independent 
investigations, founded on quite different facts, that the diurnal in- 
equality was very different at different points of the same coast ; and 
that at places not very distant from each other, he had found cases 
where this inequality was absolutely inverted, making ¢hat the lower of 
two successive tides, which, at a period of their progress a little 
anterior, had been the higher. He stated that this circumstance, 
having attracted his attention, he had, in a postscript to his seventh 
series of Tide Researches, printed in the Philosophical Transactions, 
offered a certain hypothesis as a mode of accounting for it—namely, 
that the tides might be conceived as transmitted by ¢ransverse undula- 
tions; and, he added, that subsequent researches, about to be pub- 
lished in his eighth series, had shown him that he must entirely re- 
tract this hypothesis. He added also, that he was able to say the 
same of another hypothesis, at first sight very plausible—namely, that — 
the diurnal tide travels at a different rate from the common semi- 
diurnal tide. He stated, that having taken sixty of the best-con- 
ditioned places on the coasts of Great Britain and Ireland, for the 
purpose of tracing the progress of this diurnal inequality, he had had 
the requisite calculations made by calculators (Mr. Dessiou and Mr. 
Ross) placed at his disposal by the Admiralty. He had separated the 
diurnal wave from the semi-diurnal tide, by examining the compara- 
tive influence of the diurnal inequality upon high and upon low 
waters. He had pursued this diurnal wave first along the west coast 
of Ireland, round the north of Scotland, and down the east coast of 
Scotland and England; and he had found that the diurnal wave never 
gained or lost much in its rate of progress compared with the semi- 
diurnal. This was generally two or three hours behind, sometimes 
* See p. 103. 
