190 
MR. LLOYD ON THE DIFFERENCE OF LEVEL BETWEEN 
The next spot levelled to where any tidal observations were made, was St. 
Catherine’s Docks, where a brass standard was placed close to the south-west 
side of the Dock -gates at the entrance. 
This standard is 4.3143 above the north standard at Sheerness, and 6.2563 
above the index mark xxvm, upon a level with which is a — I — denoting Tri- 
HW 
nity 1S00 
A 
Therefore 4.3143 + 4.0661 — 6.2563 = 2.1241, the height of this index or 
Trinity mark above mean spring tide high-water mark at Sheerness. 
After passing along the Tower Wharf, and placing a standard mark in one of 
the large blocks of granite lately put down near the Traitor’s Arch (see Level- 
lings, page 28), I arrived (not without much vexatious interruption and annoy- 
ance in passing along Thames-street and Billingsgate) at the starlings of Old 
London Bridge, where I had some difficulty in making observations, owing to 
the tremor caused by the vehicles above. I levelled up to the Trinity mark on 
the western side of the bridge, and found as follows (see page 29) : 
No. 443 was 4.1047 below the north standard mark at Sheerness, and the 
HW 
Trinity >800 was 1.9426 above No. 443. 
Therefore 4.1047 — 1.9426 = 2.1621, the height of Trinity mark below north 
standard mark at Sheerness. 
And 4.0661 — 2.1621 = 1.9040 gives the height of Trinity mark above the 
mean spring tide high-water mark at Sheerness. 
Having now made all the observations that time and means afforded me, I 
concluded my levellings at a standard mark sunk in the large plinth of the 
landing-place (near the wall) of the stairs on the north-east side of the New 
London Bridge. 
This standard was (page 29) 2.3967 below the north standard mark at 
Sheerness. 
I have subjoined a list of the different Trinity marks I have observed, and 
their respective heights, and also of the brass standards placed by me, as well 
as various substantial points passed over in the levellings. 
