380 
MR. LUBBOCK ON THE TIDES IN THE PORT OF LONDON. 
the day, (which I was not aware of until lately,) because the persons in 
attendance at night have nothing else to do than to look out for high water ; 
but in the day, owing to the press of business at the top of the tide, the water 
has fallen an inch or two at times before it has been noticed. The water 
remains stationary for some little time at high water, and therefore it is diffi- 
cult to fix the time of that phenomenon precisely, without the aid of some 
mechanical contrivance ; this will however I hope soon be supplied both at 
the London and St. Katherine Docks. 
I have also to present to the Society some observations of the tides made 
during one year at the East India Docks, under the superintendence of Captain 
Eastfield, and which were kindly undertaken at my suggestion : these obser- 
vations were made with great care, and may, I believe, generally be depended 
upon to the minute. 
When the variations in the time and height of high water due to changes in 
the parallax and declination of the luminaries are neglected, the theories of 
Bernoulli and of Laplace lead to the same results, and these results agree 
most remarkably with observation. The same agreement is manifested in the 
circumstance that the variations of the interval between the time of the moon’s 
transit and the time of high water, and the variations of the height of high 
water from the mean height, are greatest at the equinoxes, and least at the 
solstices, or soon after ; and also that the height of high water increases as 
the distance of the moon decreases, that is, as her parallax increases. The 
difference between the heights when her parallax is greatest and least may 
be considered nearly a foot at the London Docks. 
The changes in the declinations of the sun and moon, and in the parallax of 
the moon, have a sensible effect both on the time and on the height of high 
water ; the law however of these changes is so complicated, and the observa- 
tions are so imperfect, that for the present I think it will be necessary to have 
recourse to empirical tables for their calculation. They are not in conformity 
with the theory of Bernoulli, which has, I believe, never before been com- 
pared with observation ; nor can I reconcile them to the theory of Laplace. 
The constants which might be supposed the same for this port and for Brest, 
determined by means of these observations, do not agree with those determined 
by Laplace from the observations at Brest. The comparison would be ex- 
