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Compass (Instrument used to indicate)

an instrument used to indicate the magnetic meridian or the position of objects with respect to that meridian, and employed especially on ships, and by surveyors and travelers.

Its origin is unknown, but it is supposed to have been brought from China to Europe about the middle of the 13th century. As now generally used it consists of three parts: namely, the box, the card COMPASS or fly, and the needle the latter being the really essential part, and consisting of a small magnet SO suspended that it may be able to move freely in a horizontal direction. The box, ox, which contains the card and needle, is, in the case of the common mariner's compass, a circular brass receptacle hung within a wooden one by two concentric rings called gimbals, so fixed by the cross centers to the box that the inner one, or compass-box, shall retain a horizontal position in all motions of the ship. The circular card is divided into 32 equal parts by lines drawn from the center NNW NW by N COMPASS bar of magnetized steel. It is fixed on the under side of the card, and in the center is placed a conical socket, which is poised on an upright pointed pin fixed in the bottom of the box; so that the card, hanging on the pin, turns freely round its center, and one of the points, by the property of the needle, will always be directed toward the North Pole. The needle, however, is liable to a certain deviation owing to the magnetism of the ship itself, and this is especially strong in iron ships. To obviate this defect Sir William Thomson invented a compass, having a number of needles arranged in N Nbyw Noy E NNE NE ZN NE

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The four principal are called cardinal points: viz., North, South, East and West. The names of the rest are compounded of these. The needle is a small In a particular manner instead of one. this compass quadrantal errors are corrected by means of two iron globes fixed on opposite sides of the binnacle; while the various components of the ship's magnetic force are neutralized by a series of bar-magnets so arranged as to act as correctors. In the compass used by land-surveyors and others the needle is not fixed to the card, but plays alone, the card being drawn on the bottom of the box.

COMPASSES