Compasses

A compass (or mariner's compass) is a navigational instrument for finding directions on the earth. It consists of a magnetised pointer free to align itself accurately with Earth's magnetic field. more...

A compass provides a known reference direction which is of great assistance in navigation. The cardinal points are north, south, east and west. A compass can be used in conjunction with a clock and a sextant to provide a very accurate navigation capability. This device greatly improved maritime trade by making travel safer and more efficient.

A compass can be any magnetic device using a needle to indicate the direction of the magnetic north of a planet's magnetosphere. Any instrument with a magnetized bar or needle turning freely upon a pivot and pointing in a northerly and southerly direction can be considered a compass. A compass dial is a small pocket compass with a sundial. A variation compass is a specific instrument of a delicate type of construction. It is used by observing variations of the needle. A gyrocompass or astrocompass can also be used to ascertain True north.

History of the navigational compass

Compasses were initially used in feng shui in ancient China. The first known use of Earth's magnetic field in this way occurred in ancient China as a spectacle. Arrows were cast similarly to dice. These magnetised arrows aligned themselves pointing north, impressing the audience. The earliest record of use of magnetic lodestone as a direction point was in a 4th century Chinese book: Book of the Devil Valley Master

Dream Pool Essays written by Song Dynasty scholar Shen Kua in AD 1086 contained a detailed description of how geomancer magnetized a needle by rubbing its tip with lodestone, and hung the magnetic needle with one single strain of silk with a bit of wax attached to the center of the needle. Shen Kua pointed out that the needle prepared this way some times pointed south, some times pointed north.

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