The Uses of a Compass as a Navigation Instrument

HIstory

• By the 10th century, Arab traders had brought magnetic compasses to Europe. Throughout the middle ages, compasses were widely used for navigation, although they were not reliable and little was known about why they worked. 15th century mariners such as Columbus knew the needle of a compass didn't point true north. They realized that it made an angle with magnetic north that varied at different places on the globe. In the 19th century, compasses became unreliable on ships built from iron, but in 1908, the gyroscopic compass was invented. It was unaffected by the fabric of its surroundings and is similar to compasses used today.

Magnetic

• The ancient Chinese discovered that the magnetic field around the Earth caused a magnetized needle hung from a thread to swing into alignment with the north and south magnetic poles. Needles were magnetized by being stroked with a lodestone made from magnetic rock. In early compasses, the needles were mounted on a pin and swung over a card marked with points that matched the direction of the winds. The four main points, or cardinal points, are north, south, east and west. But these compasses were affected by motion, especially at sea. Later ships' compasses were hung from gimbals to improve reliability.

Sun

• A basic sun compass is a needle set in a disc. The shadow from the needle will describe a different arc at different times of the year. It is possible to navigate using the shadow of the needle if the point at which the needle's shadow hits the arc is kept constant. According to Franck Petterson of the Northern Lights Planetarium in Norway, the Vikings used a primitive sun compass to navigate to the North American continent and back across the Atlantic.

Solar

• In 1836, William Austin Burt was required by the state of Wisconsin to survey large tranches of land for settlers. He found that large deposits of iron ore in the earth made his magnetic compass erratic, so he invented a solar compass which fixed the position of true north by astronomical observation. It could make accurate records of swamps, rugged terrain and landmarks that aided navigation. Versions of his compass are still used by surveyors today.

Gyroscopic

• The gyroscopic compass was patented by inventor Elmer Ambrose Sperry in 1908. Fellow American G. M. Hopkins had invented the first electrically driven gyroscope, and Sperry realized its potential as navigation device in steel and iron ships, where magnetic compasses were unreliable. His compass was adopted by the U.S. Navy in 1911 and played a large part in navigating ships during WWI. He also created the "Metal Mike," which was a gyroscopic autopilot system. The gyroscopic compass was used to navigate the Queen Mary and all war ships in WWII.