COMPASS

a magnetized needle balanced on a fine point above a card. The needle will set itself so as always to point in the same direction—to the magnetic N. and 8S. Owing to this property, it is of great value to the navigator. In a modern ship’s ec. the needle consists of eight light magnetized strips of steel, placed parallel to each other like the steps of a ladder, and fastened together by silk threads. Such a compound ni e is more reliable, and is also steadier in a heavy sea than is a single needle. The card is frequently a thin aluminum rim, on which a paper scale divided into the 32 points of the c. is fixed. The c. (consisting of needle and card) is contained in a copper bowl, supported on gimbals (concentric rings), which keep it horizontal no matter how the ship pitches. The iron and steel of which the ship is built affect the c.; this is corrected by. @ proce known as ‘swinging the ship,’ as a result of which ma es of soft iron or magnets are distributed near the c. so as to counteract — the ship’s magnetic effects. In the Liquid or Spirit c., the card floats on a mixture of water and alcohol. Card and needle turn together. Very great steadine is obtained with this form of instrument. In the latest form of c.—the Gyro c.— the gyrostatic principle is applied. By means of a gyro wheel the axis of the whole combination is kept parallel to the earth’s axis, and the instrument thus shows both latitude and the ship’s course. The c. is unafiected by the ship magnetism or by surrounding ma es of iron, and may be used to control a number of suitably placed dials. The c. is supposed to have been used in China about 3,000 years ago, but it was not heard of in Europe until the XII. cent. About the beginning of the XIV. cent. Flavio Gioja, an Italian, invented a c. of eight points. Columbus discovered the magnetic declination (1492) of the c.