While older designs commonly incorporated a flexible rubber diaphragm or airspace inside the capsule to allow for volume changes caused by temperature or altitude, some modern liquid compasses use smaller housings and/or flexible capsule materials to accomplish the same result. Modern compasses usually use a magnetized needle or dial inside a capsule completely filled with a liquid (lamp oil, mineral oil, white spirits, purified kerosene, or ethyl alcohol are common). Design A liquid-filled protractor or orienteering compass with lanyard This was supplanted in the early 20th century by the liquid-filled magnetic compass. Dry compasses began to appear around 1300 in Medieval Europe and the Islamic world. Later compasses were made of iron needles, magnetized by striking them with a lodestone, which appeared in China by 1088 during the Song dynasty, as described by Shen Kuo. The first compasses in ancient Han dynasty China were made of lodestone, a naturally magnetized ore of iron. History Model of a lodestone compass from Han dynasty Some magnetic compasses include means to manually compensate for the magnetic declination, so that the compass shows true directions. The effect of this means a map with the latest declination information should be used.

The locations of the Earth's magnetic poles slowly change with time, which is referred to as geomagnetic secular variation. The local magnetic declination is given on most maps, to allow the map to be oriented with a compass parallel to true north. Depending on where the compass is located on the surface of the Earth the angle between true north and magnetic north, called magnetic declination can vary widely with geographic location. In navigation, directions on maps are usually expressed with reference to geographical or true north, the direction toward the Geographical North Pole, the rotation axis of the Earth. When the compass is held level, the needle turns until, after a few seconds to allow oscillations to die out, it settles into its equilibrium orientation. The needle is mounted on a low-friction pivot point, in better compasses a jewel bearing, so it can turn easily. The magnetic field exerts a torque on the needle, pulling the North end or pole of the needle approximately toward the Earth's North magnetic pole, and pulling the other toward the Earth's South magnetic pole. It functions as a pointer to ' magnetic north', the local magnetic meridian, because the magnetized needle at its heart aligns itself with the horizontal component of the Earth's magnetic field. The magnetic compass is the most familiar compass type. The first usage of a compass recorded in Western Europe and the Islamic world occurred around 1190. 206 BC), and later adopted for navigation by the Song dynasty Chinese during the 11th century. If local variation between magnetic north and true north is known, then direction of magnetic north also gives direction of true north.Īmong the Four Great Inventions, the magnetic compass was first invented as a device for divination as early as the Chinese Han dynasty (since c. These numbers allow the compass to show azimuths or bearings which are commonly stated in degrees. Other methods may be used, including gyroscopes, magnetometers, and GPS receivers.Ĭompasses often show angles in degrees: north corresponds to 0°, and the angles increase clockwise, so east is 90°, south is 180°, and west is 270°. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with magnetic north. For other uses, see Compass (disambiguation).Ī modern military compass, with included sight device for aligningĪ compass is a device that shows the cardinal directions used for navigation and geographic orientation. This article is about the direction finding instrument used in navigation.

Protractor military