th pure india-rubber, and a
corrugated expansion chamber is attached to the bottom to allow for the
expansion and contraction of the liquid. The card is a mica disk, either
painted as in fig. 1, or covered with linen upon which the degrees and
points are printed, the needles being enclosed in brass.

[Illustration: FIG. 5.--Liquid Compass.

A, Bowl, partly in section. N, Hole for filling, with screw plug.
B, Expansion chamber. O, O, Magnetic needles.
D, The glass. P, Buoyant chamber.
G, Gimbal ring. Q, Iridium pivot.
L, Nut to expand chamber when R, Sapphire cap.
filling bowl. S, Mica card.]
M, Screw connector.

Great steadiness of card under severe shocks and vibrations, combined
with a minimum of friction in the cap and pivot, is obtained with this
compass. All compasses are fitted with a gimbal ring to keep the bowl
and card level under every circumstance of a ship's motion in a seaway,
the ring being connected with the binnacle or pedestal by means of
journals or knife edges. On the inside of every compass bowl a vertical
black line is drawn, called the "lubber's point," and it is imperative
that when the compass is placed in the binnacle the line joining the
pivot and the lubber's point be parallel to the keel of the vessel.
Thus, when a degree on the card is observed opposite the lubber's point,
the angle between the direction in which the ship is steering and the
north point of the compass or course is at once seen; and if the
magnetic variation and the disturbing effects of the ship's iron are
known, the desired angle between the ship's course and the geographical
meridian can be computed. In every ship a position is selected for the
navigating or standard compass as free from neighbouring iron as
possible, and by this compass all courses are shaped and bearings taken.
It is also provided with an azimuth circle or mirror and a shadow pin or
style placed in the centre of the glass cover, by either of which the
variable angle between the compass north and true north, called the
"total error," or variation and deviation combined, can be observed. The
binnacles or pedestals for compasses are generally constructed of wood
about 45 in. high, and fitted to receive and alter at pleasure the
several magnet and soft iron correctors. They are also fitted with
different forms of suspension in which the compass is mounted to obviate
the mec