MR. LUBBOCK ON THE TIDES. 
55 
present time, with great precision, but the establishment is subject to change, 
and the determination of this quantity will probably require to be repeated 
after several years. 
With respect to the determination of the influence of the parallax and decli¬ 
nation of the moon, it is desirable to employ more observations than I have 
done; I contented myself with about 5000, in order to spare M. Dessiou’s 
time. A similar discussion of observations of the tides at Brest or some other 
favourable situation is greatly to be wished for, in order to ascertain how far 
these effects are the same in different ports. 
The discussion of the observations of the times and heights of low water at 
the London Docks also remains, which I have been obliged to postpone. 
The height of the water at any given time and place may be calculated when 
the requisite constants have been determined. At the London Docks the height 
of the water expressed in feet is 
16-68-1- 4-448 {cos 2 (0, - X) + -3/88 cos 2 {6 - X) } 
which formula affords results agreeing nearly with observation, and which may 
be compared with the curves given by Mr. Palmer, (see Phil. Trans. 1831, 
Part I.). According to this expression the mean rise of the tide is 12 ft. 3 in. 
When X — X t = 0, (that is, at the London Docks when the moon passes the 
meridian at 2 o’clock,) the curve in question is the curve of sines. 
According to M. Baussy, (Memoire sur les Marees des Cotes de France, 
Connaissance des Temps 1834,) the height of high water varies with the atmo¬ 
spheric pressure, being highest when the barometer is lowest. This paper did 
not come to my knowledge until after these pages were in the press; but the 
determination by M. Daussy of the establishment of the port of Brest coincides 
with that which I have given, namely 3 h 48 m . 
