AT SOUTHAMPTON AND AT IPSWICH. 
51 
therefore, in which the mean level of the sea in different places is compared, I con- 
ceive it is not sufficient to take the mean of high and low water, but it is necessary 
to express the depression by the formula A + B sin phase + b cos phase -f- C sin 2 phase 
-f- &c., and to adopt the constant A as determining the mean level. The difference, 
at Southampton, is about nine inches, by which quantity the mean level , as defined 
above, is higher than the mean of high and low waters. 
The singularity of the results obtained at Southampton induced me to take mea- 
sures for observing the tides in another estuary ; and for this purpose I selected 
Ipswich as a good station. The positions of these places are not exactly similar : 
Southampton is nearly at the head of its gulf ; Ipswich may be considered as being 
absolutely at the head of its gulf. The length of the Orwell does not differ materially 
from that of the Southampton water ; and in depth, breadth, magnitude of tide, &c., 
it resembles it closely. Nevertheless, it will appear from the following results that 
the laws of the tides at these two places are extremely different. 
An application made by me to Charles May, Esq. of Ipswich, was by him laid 
before the Dock Committee ; and I received from that body a most courteous offer 
of every assistance which could be required for the observation of the tides. The 
immediate superintendence of the observations was undertaken by James Jones, 
Esq., Dockmaster ; and to the talent and spirit with which this gentleman undertook 
the troublesome business, I am entirely indebted for the opportunity of presenting 
the Royal Society with trustworthy results. 
The observations commenced on 1842, May 24, 23 h 40 m (astronomical reckoning), 
and finished on May 27, 3 h 35 m ; embracing four complete tides. The height of the 
water was observed at every five minutes. The zero of the scale is the Lock Sill. 
Great attention was given to the determination of time. No irregularity appears on 
the face of the observations except about May 25, 19 h , after a heavy squall from the 
S.S.E. with violent rain. 
The times and intervals of high water are as follows : — 
May 25. . . 
h m 
1 5 
h 
m 
. . Interval . 
12 
15 
25. . . 
13 20 
12 
30 
26. . . 
1 50 
. 12 
10 
26. . . 
14 0 
, 12 
34 
27. . . 
2 34 
The times and intervals of low water are, — 
h m 
May 25. . . 
6 55 
h m 
25. . . 
. 18 35 
. Interval . 
11 40 
26. . 
. 7 30 

12 55 
26, . 
19 45. 
12 15 
