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{{short description|none}} <!-- "none" is preferred when the title is sufficiently descriptive; see [[WP:SDNONE]] -->
[[File:Southern Song Figure Holding Land Compass (9872744925).jpg|thumb|[[Song dynasty]] figurine of a man holding a compass]]
The [[compass]] is a [[magnetometer]] used for [[navigation]] and orientation that shows direction in regards to the [[Cardinal direction|geographic cardinal points]]. The structure of a compass consists of the compass rose, which displays the four main directions on it: [[East]] (E), [[South]] (S), [[West]] (W) and [[North]] (N). The angle increases in the clockwise position. North corresponds to 0°, so east is 90°, south is 180° and west is 270°.
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== Geomancy and Feng Shui ==
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The compass was invented in China during the [[Han dynasty]] between the 2nd century BC and 1st century AD where it was called the '''"south-governor"'''(''sīnán'' {{lang|zh|司南}}) or '''"South Pointing Fish"''' ({{lang|zh|指南魚}}).<ref name=merrill /> The magnetic compass was not, at first, used for navigation, but for [[geomancy]] and [[fortune-telling]] by the [[China|Chinese]]. The earliest [[China|Chinese]] [[magnetic]] compasses were possibly used to order and harmonize buildings by the geomantic principles of ''[[feng shui]]''. These early compasses were made with [[lodestone]], a form of the mineral [[magnetite]] that is a naturally occurring [[magnet]] and aligns itself with the Earth's magnetic field.<ref name="Guarnieri 7-1"/> People in ancient China discovered that if a lodestone was suspended so it could turn freely, it would always point toward the magnetic poles. Early compasses were used to choose areas suitable for building houses, growing crops, and to search for rare gems. Compasses were later adapted for navigation during the [[Song dynasty]] in the 11th century.<ref name="cambridge1" />
Based on Krotser and Coe's discovery of an [[Olmec]] [[hematite]] artifact in [[Mesoamerica]], [[radiocarbon dating|radiocarbon dated]] to 1400–1000 BC, astronomer John Carlson has hypothesized that the Olmec might have used the geomagnetic [[lodestone]] earlier than 1000 BC for [[geomancy]], a method of [[divination]], which if proven true, predates the Chinese use of magnetism for [[feng shui]] by a millennium.<ref name="John B. Carlson 1975">John B. Carlson, "Lodestone Compass: Chinese or Olmec Primacy? Multidisciplinary Analysis of an Olmec Hematite Artifact from San Lorenzo, Veracruz, Mexico", ''Science'', New Series, Vol. 189, No. 4205 (5 September 1975), pp. 753-760 (1975)</ref> Carlson speculates that the Olmecs used similar artifacts as a directional device for astronomical or [[geomancy|geomantic]] purposes but does not suggest navigational usage. The artifact is part of a polished [[hematite]] bar with a groove at one end, possibly used for sighting. Carlson's claims have been disputed by other scientific researchers, who have suggested that the artifact is actually a constituent piece of a decorative ornament and not a purposely built compass.<ref>{{cite book|last=Needham|first=Joseph |author2=Lu Gwei-Djen|title=Trans-Pacific Echoes and Resonances: Listening Once Again |publisher=World Scientific |year=1985 |page=21}}</ref> Several other hematite or magnetite artifacts have been found at pre-Columbian archaeological sites in Mexico and Guatemala.<ref name="A. P. Guimarães 2004">{{cite journal | last1 = Guimarães | first1 = A. P. | year = 2004 | title = Mexico and the early history of magnetism | journal = Revista Mexicana de Fisica | volume = 50 | pages = 51–53 | bibcode = 2004RMxFE..50...51G }}</ref><ref>{{cite web |url=http://www.dartmouth.edu/~izapa/CS-MM-Chap.%203.htm |title=Chapter 3 |publisher=Dartmouth.edu |access-date=2015-06-06 |archive-date=2012-07-16 |archive-url=https://web.archive.org/web/20120716191610/http://www.dartmouth.edu/~izapa/CS-MM-Chap.%203.htm |url-status=dead }}</ref>
== Early navigational compass ==
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