Chap. VIII.
309
low water on the shore; by which means a greater number of vessels can be admittedevery high water.
The two steam engines can be separately worked, but are connected by a line of triplecranks, which move six double-action pumps. The pumps are 3 feet in diameter, andhave a stroke of 4 feet 6 inches; these are united to a horizontal iron pipe, 3 feet
6 inches in diameter, bent at one end, where it descends into a well, 8 feet in diameter, thebottom of which is 3 feet below low water mark. Communicating with this well is aculvert, 8 feet wide, 6 feet 6 inches high, and 170 feet in length, formed, as is the well, ofashlar masonry ; the bottom is laid 2 feet below low water, at spring tides; over the outerend is placed a grating, to prevent any matter from entering and entangling the pumpvalves. The water raised by the pumps can be discharged either into the entrancelock or the basin.
At spring tides the depth of water on the sills of the outward lock gates is, at the firsthour after flood, 16 feet; at the second hour, 21 feet 2 inches ; at the third, 24 feet; at thefourth, 26 feet 6 inches; and at the fifth hour after flood, and at high water, 28 feet.
At the first hour after high water it is 24 feet 6 inches ; at the second, 20 feet 10 inches;at the third, 18 feet 2 inches; at the fourth, 15 feet 7 inches; at the fifth, 13 feet 2 inches ;at the sixth, 11 feet 3 inches; and at low water, 10 feet.
During neap tides, the depth of water at the first hour after flood is 13 feet 6 inches;at the second, 16 feet 10 inches; at the third, 20 feet 3 inches; at the fourth, 22 feet
7 inches; and at the fifth hour, and at high water, 24 feet.
And at the first hour after high water, 21 feet 11 inches ; after the second 18 feet; thethird 16 feet 2 inches; the fourth 15 feet 6 inches; the fifth, 14 feet; the sixth, 12 feet10 inches ; and at low water, 12 feet.
The entrance lock is built of grey stock bricks, laid in mortar made with lias lime ; theplatforms, hollow quoins, bond stones, and copings of the lock walls, are of Bramley Fall
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Fig. 309. SIDE OP ENTRANCE LOCK.
stone, and the whole so cemented that they form a solid mass. As the site of the docksand quays is upon a hard stratum of gravel, it was found necessary to line the bottom ofthe docks, and puddle the back of thewalls, as well as to place the counter-forts upon foundations impervious towater.
An artificial concrete, composed ofblue lias lime mixed with eight partsof coarse sand, was kneaded into a thickmortar, and spread over a bed, a footin thickness, of sufficient size to receivethe breadth of the wall of the counter-forts and puddle. A wooden sill waslaid under the front edge of the wall,and a row of sheeting piles, 14 feetin length, and 9 inches in thickness,was driven along the side of it, theirjoints for 3 feet downwards beingclosely caulked.
The facing wall of the whole of Fig. 310 .
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SECTION OP ENTRANCE LOCK.