178 
MR. LLOYD ON THE DIFFERENCE OF LEVEL BETWEEN 
These results agree so very nearly, that they may be safely taken as correct. 
I have given them at length, to afford the data for finding the true level of the 
sea. It will be seen that the mean level taken from spring tides differs 0.556 
from the mean level deduced from neap tides. I shall, however, assume the 
mean level as 1 7 • 27 , differing only 0.04 from the same of the whole year’s ob- 
servations of 1827- 
At the north-western end of the caisson I caused a small cross (+) to be 
cut in the granite, which corresponded exactly with the xxxi feet of the indices 
cut in the masonry at the side of the caisson. This cross is situated as follows, 
with regard to the standard marks in the yard. (See page 3 of Levelling 
Book.) 
The northern standard, which is my zero point, is 0.5789 below the cross. 
The southern standard at the other end of the Dock Yard wall is 0.0259 above 
the cross ; therefore 0.0259 + 0.5789 = 0.6048 gives the height of the south 
standard above the northern one, although they are set equally beneath the 
surface of the granite. 
The standard at the eastern edge of the great basin is 0.6735 above the 
northern, and 0.6735 — 0.6048=0.0687 above the southern standard, and 
0.6735 -0.5789=0.0946 above the +. 
The standard at the navy well is 6.0656 below eastern standard. 
5.9968 below south standard. 
5.3920 below north standard, 
and *5.9710 below the cross. 
Now, the mean level of the sea being 17-27 feet, the + or xxxi feet of the 
indices is 13.73 above the mean level of the sea, and 4.645 above the mean 
spring tide high-water mark. And 
North standard ] 
or zero is . J 
f 13.73— 0.5789=13.1511 above the level of the sea, and 4.0661 -j 
I - above 
[ high- 
spring tide 
■water mark. 
South do . 
13.73 + 0.0259-13.7559 . . 
. . . 4.6709 
. 
do. 
East do . 
13.73 + 0.0946 — 13.8246 . 
. . . 4.7396 
. 
do. 
Navy well 
13.73-5.9710- 7.7590 . , 
below 
do. 
Tide-gauge 
standard . j 
J. 13.73-0.0946-13.6354 . 
above 
do. 
‘ In page 4 of Levellings there will be observed a difference of 0.0001 in the two sets of levels, the 
first set taken in March, the last in June. 
