Compass (Instrument used to indicate)

Collier's New Encyclopedia (1921)

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 or fly, and the needle the latter being the really essential part, and consisting that it of a small magnet so suspended 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 N NNW Nbyw NW by N 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 85 80 75 70 Wibyn Woys M MSM swby.w M'S SAMS MAS MSS to the circumference, called points or rhumbs; the intervals between the points are also divided into halves and quarters, and the whole circumference into equal parts or degrees, 360 of which complete the circle; and consequently, the distance or angle comprehended between any two rhumbs is equal to 114°. 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 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 65 60 55 50 45 40 35 30 25 20 15 10 505 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 85 80 75 William Thomson invented a compass, having a number of needles arranged in NNE Noy E NE ZN NE SE by E SS 35 ass S COMPASS a particular manner instead of one. In 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.