The magnetic compass is the oldest navigation instrument for sea travelers. During the 15th century, mariners discovered that the needle of a compass sometimes differed from true north based on surrounding magnetism. In the 17th century, scientist and astronomer Edmond Halley confirmed that there were different magnetic variations present depending on a navigator's geographic position.
Iron and steel ships became common in the 19th century and affected the accuracy of a magnetic compass. Sir G.B. Airy attempted to neutralize the ship's magnetism by placing magnets and unmagnetized iron near the compass.
Mounting the magnetized needle under a sharp pin or card slightly improved the accuracy of the magnetic compass. The cards showed 32 points, each representing a familiar wind direction or one of the four cardinal points: north, south, east and west. The magnetic compass never became truly accurate, however, and the gyroscopic magnet replaced it in 1908.
