The Magnetic Compass
Overview
The magnetic compass was an important advance in navigation because it allowed mariners to determine their direction even if clouds obscured their usual astronomical cues such as the North Star. It uses a magnetic needle that can turn freely so that it always points to the north pole of the Earth's magnetic field. Knowing where north is allows the other directions to be determined as well. The compass was invented by the Chinese, and was widely used for navigation beginning in about the thirteenth century.
Background
The phenomenon of magnetism was known to the ancient Greeks, but the magnetic compass was invented by the Chinese. The thirteenth century explorer Marco Polo (1254-1324) is said to have brought a compass with him when he returned to Venice after his twenty years of service in the court of Kublai Khan (1215-1294). He may indeed have carried home such a souvenir. However, the knowledge that a piece of the naturally magnetic iron ore magnetite (Fe3O4), called a lodestone, would align itself from north to south if allowed to move freely, seems to have arisen at least a century before Marco Polo in Europe and the Arab world.
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