174 
MR. LLOYD ON THE DIFFERENCE OF LEVEL BETWEEN 
and yet the most accurate, I examined the whole of the front of the Dock Yard, 
and selected the corner of the boat basin adjoining the ordnance basin, as the 
only spot indeed at all eligible for the erection of a tide-gauge. (The spot is 
shown on the plan of the Yard.) 
By the friendly and prompt assistance of His Majesty’s Commissioner at the 
Dock Yard (J. Lewis, Esq.), I was enabled to have my tide-gauge quickly and 
substantially erected, under the excellent superintendence of Mr. Mitchell, 
the master millwright at the Yard. 
Description of the Tide-Gauge. 
The model is on a scale of three quarters of an inch to a foot.* The flat board 
on which the house stands, represents the Wharf at Sheerness ; it is made long 
at the back, and balanced so as to be placed on a table, to show the trunk in 
the actual position of the gauge. The top or cap to the covering of the staff 
is left unfixed, in order to be taken off, and allow the house to be lifted over 
it, and show the gauge alone. 
The slide rods in the model are of iron wire, and out of proportion ; but no 
smaller was at that time to be found in the Dock Yard ; in the original they 
are ^ copper bolts. 
The slides or pointers have springs to tighten them to the 'rods, but they are 
too minute to act in the model. The lower end of the tube in the model is 
nearly filled up with wood, in order to secure it to the trunk, leaving only a 
part for the gauge-rod to pass ; but in the original the tube is left open below, 
there being sufficient strength in the timber to allow of its being bolted to the 
trunk and platform. There are three small friction-wheels at the upper end of 
the rod, to steady it. 
There is a distance of fifteen feet between the top catch or point on the rod 
which brings the slide down to indicate low water, and the point on the middle 
of the rod which takes the other slide up to indicate high water. Therefore 
allowing an eighteen-feet tide, the top catch will bring the slide down to four 
on the index, and the middle catch on the rod will raise the slide to seven on 
the other index, the difference of which, three added to fifteen (the length be- 
tween the points), gives eighteen. Therefore it will be observed that the dif- 
* The model is deposited at the Royal Society’s Apartments in Somerset House. 
