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A Small Compass: A small compass (sometimes with a handle) designed to be easily held in front of your face is called a band bearing compass. As its name implies, it is ordinarily used for determining the direction of distant objects.
Within a limited arc of forward visibility, bearings can be taken by sighting across the steering compass. The extent to which this can be done is determined by the layout of the helm position and the compass installation. A hand-bearing compass will normally allow observations to be taken essentially all around the horizon.
The earth has a magnetic field, much as if it had a giant bar magnet inside it. A compass consists of several small bar magnets beneath a card that has a scale around its perimeter, graduated in degrees. These magnets align themselves with the horizontal component of the earth's field, and the direction is read from the scale on the card that is opposite an index mark, the lubber's line, fixed on the case of the compass. To make compasses more sensitive, the card is supported on a needle-sharp bearing and floated in or on a non-freezing liquid. A top, usually spherical in shape, covers the compass to contain the liquid. The entire assembly is often mounted in gimbals, pivots and brackets that allow the compass to remain as nearly level as possible as the vessel pitches and rolls. |
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