MR. LUBBOCK ON THE TIDES IN THE PORT OF LONDON. 
389 
The Annuaire du Bureau des Longitudes and various works on navigation 
give 2 h 45 m for the establishment of the Port of London; it seems therefore 
probable that the high water takes place now much earlier than it did formerly. 
It is generally admitted that the constant X — a ; is the same at different ports ; 
this, however, requires to be confirmed by accurate determinations, and is one 
of the most interesting questions in the theory of the tides. Bernoulli makes 
this constant 20° or l h 20 m only in time ; Laplace adopts the same value, 
though not expressly. Bernoulli’s Table for finding the time of high water, 
which is given in the Annuaire du Bureau des Longitudes, and in works on 
navigation, is quite inapplicable to the Port of London on this account, even in 
the mean distances of the moon, as the following comparison will show : 
Time of 
Moon’s 
Transit. 
Interval between the Moon’s Transit 
and the Time of High Water. 
Error 
of 
Calculation. 
Observed. 
Calculated. 
h 
h m 
li m 
m 
0 
1 57 
1 57 
0 
2 
1 26 
1 231 
- H 
4 
56 
55 
— i 
6 
42 
541 
+ 121 
8 
1 23 
2 0 
+ 37 
10 
2 10 
2 20 
+ 10 
The Table in the Annuaire for the year 1829 was made use of ; the Table in 
that for 1831 differs from that only in form. 
If \ — x the greatest tide takes place at new and full moon. 
The quantity X is called by Laplace the fundamental hour of the port. — Ex- 
position du Systbme du Monde, p. 289. 
I shall now compare the heights of high water, calculated by means of the 
same constants with those given by observation column B, Table V. 
According to the preceding theory, the height of high water 
= D + E {cos 2 (0, - A,) + .3788 cos 2 (9 - A) } 
D and E being constants to be determined by observation. 
When the moon passes the meridian at two o’clock, 2d — 2 A / =0, 2d — 2X = 0 
eight o’clock, 2d— 2 X ; = 0, 2d — 2 X =180° 
