COMPASS encyclopedia topics

compass plant or rosinweed, large, coarse North American perennial herb (Silphium laciniatum) of the family Asteraceae (aster family), found chiefly in open grasslands. The deeply cut leaves tend to point north and south. It has been used medicinally and is sometimes cultivated. Other plants that have a similar leaf orientation are sometimes called compass plants. Compass plant is classified in the division Magnoliophyta, class Magnoliopsida, order Asterales, family Asteraceae.

The Columbia Electronic Encyclopedia Copyright © 2004.
Licensed from Columbia University Press

compass
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compass

compass. 1 In mathematics, an instrument for making circles and measuring distances. Frequently called a pair of compasses, it consists of two metal legs with one end of each attached to a pivot to form a V-shaped device. The free ends are pointed; a pen or pencil may be substituted for one of the points. 2 In navigation, an instrument for determining direction. The mariner's compass consists of a magnetic needle freely suspended so that in the earth's magnetic field it turns until aligned with the magnetic north and south poles. Declination is the angle between the magnetic needle and the geographical meridian. Use of the compass by the early Chinese is probably legendary. The first known reference in European literature dates from the 12th cent. Another more accurate form of navigational compass is the gyrocompass. It consists essentially of a rapidly spinning, electrically driven rotor, suspended in such a way that its axis automatically points along the geographical meridian. The gyrocompass is unaffected by magnetic influences. This compass came into wide use in warships and aircraft during the Second World War. See gyroscope.

The Columbia Electronic Encyclopedia Copyright © 2004.
Licensed from Columbia University Press

compass

In navigation or surveying, the chief device for direction finding on the Earth's surface. Compasses may operate on magnetic or gyroscopic (see gyroscope) principles or by determining the direction of the Sun or a star. The oldest and most familiar type is the magnetic compass, used in different forms in aircraft, ships, and land vehicles and by surveyors. Magnetic compasses work as they do because the Earth itself is a magnet with a north-south field (see geomagnetic field) that causes freely moving magnets to align themselves with the field.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.