The mirror. (Stillwater, Minn.) 1894-1925, 1916-06-29
The Mariners Compass
An Interesting and Descriptive Outline of the
Mysteries and Workings of the Compass
By Mr.. NJ.

vessel or other cause. Liquid
compasses are used by nearly all
the leading navies of the world.
The compass used in the United
States navy, is known as the navy
service liquid compass. 1t consists
of a skeleton card = inches in di-
ameter, made of timed brass, rest
ing on pivot in liquid, with
provisions for two pairs of mag
nets symmetrically placed.
The magnet system of the card
is made up of four cylindrical
bundles of steel wires, these wires
are placed side by side and mag
netized as a bundle between the
poles of powerful electro magnet.
They are then put in cylindrical
case, sealed and attached to the
compass card. Bundles of steel
wires are used because they are
more homogeneous, can be more
perfectly tempered, and give
greater magnetic power than a
solid steel bar of the same weight.
Two of the magnets are placed
parallel to the north and south
diameter Of the card, and on chords
of about Is degrees of a circle
passing through their extremities.
These two magnets penetrate the
air vessel, to which they are SOL
dered, and are further secured to
the bottom of the ring of the card.
The other two magnets are some
what shorter than the two just
mentfoneds They are placed paral-
lei to the two longer magnets or
Of about 45 degrees of a circle
passing through their extremities
and are secured to the bottom of
the ring of the compass card.
The card is of curved annular
type; the outer ring being convex
on the upper and inner side, and is
graduated to read to one-quarter
point, card circle being adjusted
to its outer edge and divided to
half degrees is used in reading
bearings by an azimuth circle or
in laying the course to degrees.
The card is provided with a con-
centric spheroidal air vessel which
buoys its own weight and that of
the magnets, allowing a pressure
of about 80 grains on the pivot.
The weight of the card in air is
5000 grains. The air vessel is
provided with hollow cone. open
at its lower end, and provided with
the pivot bearing or cap, contain
ing sapphire which rests upon
the pivot and thus supports the
card. The pivot is fastened to the
center of the bottom of the bowl
by a fanged plate; through this
plate are two small holes which
communicate with the expansion
chamber and permit the liquid to
circulate between it and the bowl.
The pivot is made of gun metal
and has an iridium cap.
The card is mounted in bronze
bowl which is closely fitted with a
glass cover, the bearing edges of
which are packed with rubber to
prevent the evaporation or leak
age of the liquid which entirely
fills the bowl.
Beneath the bowl is a metallic,
self-adjusting expansion chamber
of elastic metal, by means of which
the bowl is kept constantly full
without the show of bubbles or the
development of undue pressure
caused by changes in temperature.
The dry compass, of which the
Lord Kelvin compass is considered
the standard, consists of a strong
paper card with its central portion
cut away, and has it's outer edges
stiffened by Thin aluminium ring.
The pivot is provided with an
iridium point. upon which rests a