It
consists of a small reservoir, A, Fig. 4, placed at one side of the
ship, in the cabin, or other convenient locality, communicating by a
tube with the glass gauge, B, secured at the opposite side, the whole
being half filled with glycerine, which is the fluid recommended by Mr.
Wm. Denny, though water or any other liquid will answer the purpose.
At one side of the gauge is the circular scale, C, capable of being
revolved round its vertical axis, as well as adjusted up and down, so
as to bring the zero pointer exactly to the top of the fluid when the
vessel is without list. Round the top of the scale, at D, are engraved
four different draughts, and under these are the metacentric heights.
Test tanks of known capacity are placed at each side of the vessel, but
in no way connected with the reservoir or gauge. The metacentric height
is found as follows: The ship being freed from bilge water, the roller
scale is turned round to bring to the front the mark corresponding with
the mean draught of the vessel at the time, and the zero pointer is
placed opposite the surface of the liquid in the gauge. One of the test
tanks being filled with a known weight of water, the vessel is caused
to list, and in consequence the liquid in the tube takes a new position
corresponding with the degree of heel, the disturbance being greater
according as the vessel has been more or less overbalanced.
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