176 
MR. LLOYD ON THE DIFFERENCE OF LEVEL BETWEEN 
standard in the vicinity of the tide-gauge, so that future observations might 
be easily connected with the standard, I selected a large block of granite in 
the southern pier of the entrance to the boat basin, the position of which is 
shown in the plan of the Yard. I caused a block of gun-metal (cast for the 
purpose), two inches and a half square and eight inches long, to be sunk in the 
centre of the granite, about an inch below the surface, thereby allowing a brass 
box and cover to be placed over the standard, to protect it from injury. 
In order that there should be a sufficient number of checks to the stability 
of this standard mark, I caused three more to be placed in the Yard ; viz. one 
near the southern extremity on the wall of the Dock Yard, one at the eastern 
side of the great hasin, and one in a large block of stone resting on the brick- 
work of the navy well 330 feet deep. 
But however satisfied I might be that these standards were sufficiently firm, 
1 thought it advisable to seek some spot more unquestionable in its foundation 
than Sheerness Dock Yard. I found a place that possessed this advantage ; it 
was a slight eminence about two miles and a half to the southward of the Dock 
Yard, and surrounded by a moat. 
On this eminence formerly stood the old castle of Queenborough, within a 
short distance of the present town of Queenborough. The castle, which was 
in the form of a pentagon, was some years ago pulled down, but a very small 
part of the foundation was left. On this foundation, which is rubble and chalk, 
some feet under the surface a very large block of granite was placed for me, 
by order of the commanding officer of engineers, and into which was let one 
of the brass standards. The place is now covered over, but marked by a small 
mound of earth near it, and reference can be easily made to it if required. 
Having now standard marks enough to ensure, by comparison, the know- 
ledge of any alteration (if any should occur) in the zero point, I commenced 
levelling. 
My first business was to ascertain the difference of the several standards in 
the Dock Yard above the level of the sea. 
From a series of observations made at the caisson at the entrance to the 
great basin, in the years 182/, 1828, 1829, the mean of the tides was as 
follows : 
