DOCKS.
particularly for closing wide entrances, and
therefore has increased in favour.
The floating caisson closely resembles a ship
in cross section. It floats into and out of posi-
tion, and its immersion is decreased or in-
creased by means of water ballast. In the side
walls and bottom of a dry dock designed to be
closed by a floating caisson there are grooves.
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The caisson is floated across the entrance,
and when in position is filled with water
until it sinks tightly into place, projec-
tions from its sides engaging with the grooves
mentioned. It is slower to handle than
gates, and is somewhat in the way when a
dock is open ; but for big docks it serves
admirably.
WARSHIP ENTERING A DOCK.