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XXV. Note on the Tides in the Port of London. By J. W. Lubbock, Esq. 
V. P. and Treas. R.S. 
Read June 25, 1832. 
Mr. STRATFORD has favoured me with a comparison of the predicted 
times of high water deduced from Mr. Bulpit’s Tables, White’s Ephemeris, 
and the British Almanac, with the observations at the London Docks. These 
observations are, unfortunately, so imperfect, that the differences must not be 
entirely attributed to the errors of the Tables, which, however, seem suscepti¬ 
ble of much improvement. I subjoin this comparison; and in order to convey 
an idea of the confidence which may be placed in the observations, I also sub¬ 
join a comparison, by Mr. Deacon, of the observations at the London and 
St. Katherine’s Docks, which are made according to the same plan, and of 
which the merit is the same. The differences in the determinations at these 
two places, which are only about a quarter of a mile distant from each other, 
may serve to indicate the reliance which can be placed in either. 
In my paper on the Tides at Brest, I remarked that the retard or the con¬ 
stant is considerably greater as deduced from observation here than at 
Brest. That this must be the case is also evident from the following very 
simple a priori considerations.—The highest high water takes place when the 
moon passes the meridian at a time equal to the retard. The tide is propa¬ 
gated from Brest to London, round Scotland, in about twenty-two hours, that 
is, supposing the tide which takes place in our river to be principally due to 
that branch of the tide which descends along the eastern coast of Great Bri¬ 
tain, which I believe to be the case. The highest tide therefore is propagated 
from Brest to London in about twenty-two hours, and the difference in the 
retard or in the constant X — \ will be nearly the moon’s motion in twenty- 
two hours, or about 11°; I made the difference in the retard from observation 
10°. The tide takes about fifteen hours to reach Brest from the Cape of Good 
Hope; no doubt the retard there is considerably less. 
