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cylinder carries a pulley at each end, working in a carriage 
traversing suitable guides ; each- of these pulleys carries a 
chain, secured at one end to the brickwork, and carrying at 
its other a second pulley, over which a second chain passes, 
the pulley traversing similar guides to the first. The effect of 
a stroke of the piston is to produce a shortening of one of 
the last-mentioned chains to the extent of four times the length 
of the stroke, while the corresponding chain at the opposite 
end is lengthened by an equal quantity. These two chains 
are connected together by a line of rods lying in a groove 
under the pavement, and by means of chains passing 
round large pulleys at each end of the locks, so that any point 
in the line of rods and chains traverses in either direction a 
distance of four times the length of the stroke of the cylin- 
ders. This motion is communicated by means of a toothed 
wheel to each of the crabs which wind up the chains attached 
to the gates, and thus opens or closes them. One boy can 
manoeuvre each cylinder, by means of levers governing the 
inlet and exhaust valves, and the gates can be opened or 
closed in the space of about two minutes on an average. 
All the above machinery lies beneath the pavement, and no 
part of it, except the crabs, occupies any space on the quays. 
The shuttles of the sluices mentioned above can be raised or 
lowered with the greatest facility by means of a hydrostratic 
cylinder fixed vertically in a well above them, to the piston-rod 
of which the shuttle is attached. The accumulator for working 
the above system of machinery consists of a stand-pipe, 
forming a continuation of the main from the engine, which 
rises to the height of nearly 200 feet, and is surmounted 
by a large iron tank. This stand-pipe and tank are supported 
upon a lofty and handsome brick tower, whose total height 
from the pavement of the wharf is 300 feet, it being about 
28 feet square at the level of the pavement, and having a 
slight taper. The style of architecture adopted in this tower 
