102 
MR. LUBBOCK ON THE TIDES. 
In consequence of this additional number of observations some of the jumps or irre- 
gularities which the former tables presented have been removed*, but the differences 
are in general less than I anticipated. 
It is evident from the diagrams in Plate III. that a diurnal inequality in the in- 
terval at London is distinct although small. The value of the constant C is different 
from that which obtains for Liverpool. It is evident from Plate III. that the diurnal 
inequality in passing from Liverpool to London becomes reversed, that is to say, if 
a and b denote two successive heights of high water at Liverpool, and a!, V successive 
heights at London caused by the same tides, 
if a > b then generally a < V . 
The character of the diurnal inequality is generally manifest in the observations of 
a single month, as may be seen by those which are laid down in Plate IV. When 
the change is remarked which takes place in the diurnal inequality in passing from 
Plymouth to Portsmouth, it will not excite surprise that this inequality should be so 
different for places more distant from each other, as for London and Liverpool. 
The calculations or predictions of the time of high water at any given place have 
long been made to depend upon what is called the establishment of the port, or a cer- 
tain quantity presumed to be constant and independent of the distances and declina- 
tions of the luminaries, but which may be influenced by local circumstances. It 
seemed to me desirable to ascertain carefully how much this quantity has fluctuated 
during the time the observations were made at Liverpool by Mr. Hutchinson, which 
we have employed, and since the observations at the London Docks were instituted. 
Tables XIV. and XXX., which give these fluctuations, have been computed by 
Mr. Russell. The changes of the Liverpool establishment, and the fluctuations of 
the average height of high water at Liverpool are given in Table XIV., and are 
exhibited in fig. 1. Plate V.: which shows the time and height of high water from 
1802 to 1835 at the London Docks on the full and change of the moon; the moon’s 
parallax being 5 7', and the declinations of the luminaries 15 °, i. e. the establishment 
and the fluctuations in the average height of high water during the same interval. 
All the intervals and heights have been carefully reduced to horizontal parallax 57' 
and declination 15 °. 
The changes of the London establishment, and the fluctuations of the average 
height, are given in Table XXX., and are exhibited in fig. 2. Plate V. These fluctua- 
tions in the interval and in the height present an insuperable obstacle to extreme ac- 
curacy in tide predictions, unless they can be explained. 
“ In 1832 none of the lower portions of old London Bridge, (with the exception 
of two piers,) which prevented the natural flow of the tidal waters, were removed ; 
and in the second year ( 1833 ) almost the whole of that structure was cleared away as 
* See, for instance, the calendar month correction for the interval in January, and the correction for the 
height corresponding to H. P. 56'. 
