The m ain part of a compass is its magnetic system (card). The
compass card consists of th in brass or a lu m in iu m disk 1 graduated
by degree divisions up to 360°. This disk carries empty
float 2. Secured to disk 1 sym m etrically under the float is a pair
of magnets 3, whose axes are parallel to the 0-180° line on disk /.
Like poles of magnets 3 point in the same direction. W ith its
pin 5 the compass card rests on a cup of hard stone, fitted into
column 4 of the compass and called the compass cap. C olum n 4
serves as the support for the compass card and is arranged inside
compass bowl 6, which is an a lu m in iu m vessel closed by watertig
h t glass cover 7. Under the glass is course line 8 in the form
of a th in wire, arranged above disk 1 and serving as an index
in reading off the compass heading. Compass bowl 6 is filled
w ith a liq u id for dam ping oscillations of the card. Bowl 6 is
connected to membrane chamber 9. Chamber 9 serves to compensate
for the change in volume of the liq u id upon changes
in temperature.
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