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| {{About|the direction finding instrument used in navigation}}
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| [[File:Kompas Sofia.JPG|thumb|right|A simple dry magnetic portable compass.]]
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| [[File:Smartphone Compass.jpg|thumb|A [[smartphone]] that can be used as a compass because of the [[magnetometer]] inside.]]
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| A '''compass''' is a [[navigational instrument]] that shows directions in a frame of reference that is stationary relative to the surface of the Earth. The frame of reference defines the four ''[[cardinal direction]]s'' (or ''points'') – [[north]], [[south]], [[east]], and [[west]]. Intermediate directions are also defined. Usually, a diagram called a [[compass rose]], which shows the directions (with their names usually abbreviated to initials), is marked on the compass. When the compass is in use, the rose is aligned with the real directions in the frame of reference, so, for example, the "N" mark on the rose really points to the north. Frequently, in addition to the rose or sometimes instead of it, angle markings in degrees are shown on the compass. North corresponds to zero degrees, and the angles increase clockwise, so east is 90 degrees, south is 180, and west is 270. These numbers allow the compass to show [[azimuth]]s or [[Bearing (navigation)|bearing]]s, which are commonly stated in this notation.
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| The magnetic compass was first invented as a device for [[divination]] as early as the [[History of Science and Technology in China|Chinese]] [[Han Dynasty]] (since about 206 BC).<ref name=merrill>{{cite book|last=Merrill|first=Ronald T.|title=The Earth's magnetic field: Its history, origin and planetary perspective|year=1983|publisher=Academic press|location=San Francisco|isbn=0-12-491242-7|page=1|edition=2nd printing|coauthors=McElhinny, Michael W.}}</ref><ref name="Li Shu-hua, p. 176">Li Shu-hua, p. 176</ref><ref name="cambridge1"/> The compass was used in [[Song Dynasty]] China by the military for [[Land navigation (military)|navigational orienteering]] by 1040-1044,<ref name="Barbara M. Kreutz 367" /><ref name="needham volume 4 part 1 252">Needham, p. 252</ref><ref name="Li Shu-hua, p. 182f">Li Shu-hua, p. 182f.</ref> and was used for maritime navigation by 1111 to 1117.<ref name="Ronan">{{cite book|author1=Colin A. Ronan|author2=Joseph Needham|title=The Shorter Science and Civilisation in China|url=http://books.google.com/books?id=CjRAiqGSJ50C&pg=PA27|date=25 July 1986|publisher=Cambridge University Press|isbn=978-0-521-31560-9|pages=28–29}}</ref> The use of a compass is recorded in Western Europe between 1187 and 1202,<ref name="Barbara M. Kreutz 368"/><ref name=Schmidl>{{Cite journal|title=Two Early Arabic Sources On The Magnetic Compass|first=Petra G.|last=Schmidl|journal=Journal of Arabic and Islamic Studies|year=1996–1997|volume=1|pages=81–132|ref=harv|postscript=<!--None-->}} http://www.uib.no/jais/v001ht/01-081-132schmidl1.htm#_ftn4</ref><ref name="Lanza 2006 255">{{cite book | last= Lanza | first=Roberto | last2=Meloni | first2=Antonio | title=The earth's magnetism an introduction for geologists | year=2006 | publisher=Springer | location=Berlin | page=255 | isbn=978-3-540-27979-2}}</ref> and in Persia in 1232.<ref name="Barbara M. Kreutz 370"/> The dry compass was invented in Europe around 1300.<ref name="Lane, p. 615">Lane, p. 615</ref> This was supplanted in the early 20th century by the liquid-filled magnetic compass.<ref name="W. H. Creak 238-239"/>
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| ==Types of compasses==
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| [[File:Military Compass of J. Lindsay Brough.jpg|thumb|A military compass that was used during [[World War I]].]]
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| There are two widely used and radically different types of compass. The [[Compass#Magnetic compass|magnetic compass]] contains a magnet that interacts with the [[earth's magnetic field]] and aligns itself to point to the [[Geomagnetic Pole|magnetic poles]].<ref>The Earth's magnetic field is approximately that of a tilted dipole. If it were exactly dipolar, the compass would point to the [[geomagnetic poles]], which would be identical to the [[North Magnetic Pole]] and [[South Magnetic Pole]]; however, it is not, so these poles are not equivalent and the compass only points 360' off at the [[geomagnetic poles]].</ref> Simple compasses of this type show directions in a frame of reference in which the directions of the magnetic poles are due north and south. These directions are called ''magnetic north'' and ''magnetic south''. The [[Gyrocompass|gyro compass]] (sometimes spelled with a hyphen, or as one word) contains a rapidly spinning wheel whose rotation interacts dynamically with the rotation of the earth so as to make the wheel precess, losing energy to friction until its axis of rotation is parallel with the earth's. The wheel's axis therefore points to the earth's rotational poles, and a frame of reference is used in which the directions of the rotational poles are due north and south. These directions are called ''[[true north]]'' and ''[[South|true south]]'', respectively. The [[astrocompass]] works by observing the direction of stars and other celestial bodies.
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| There are other devices which are not conventionally called compasses but which do allow the true cardinal directions to be determined. Some [[Global Positioning System|GPS]] receivers have two or three antennas, fixed some distance apart to the structure of a vehicle, usually an aircraft or ship. The exact latitudes and longitudes of the antennas can be determined simultaneously, which allows the directions of the cardinal points to be calculated relative to the heading of the aircraft (the direction in which its nose is pointing), rather than to its direction of movement, which will be different if there is a [[crosswind]]. They are said to work "like a compass", or "as a compass".
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| Even a GPS device or similar can be used as compass, since if the receiver is being moved, even at walking pace, it can follow the change of its position, and hence determine the [[compass bearing]] of its direction of movement, and hence the directions of the cardinal points relative to its direction of movement. A much older example was the Chinese [[south-pointing chariot]], which worked like a compass by directional [[dead reckoning]]. It was initialized by hand, possibly using astronomical observations e.g. of the [[Pole Star]], and thenceforth counteracted every turn that was made to keep its pointer aiming in the desired direction, usually to the south. [[Watch]]es and [[sundial]]s can also be used to find compass directions. See their articles for details.
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| A recent development is the electronic compass which detects the direction without potentially fallible moving parts. This may use a [[fibre optic gyrocompass]] or a [[magnetometer]]. The magnetometer frequently appears as an optional subsystem built into hand-held GPS receivers and mobile phones. However, magnetic compasses remain popular, especially in remote areas, as they are relatively inexpensive, durable, and require no power supply.<ref>Seidman, David, and Cleveland, Paul, ''The Essential Wilderness Navigator'', Ragged Mountain Press (2001), ISBN 0-07-136110-3, p. 147: Since the magnetic compass is simple, durable, and requires no separate electrical power supply, it remains popular as a primary or secondary navigational aid, especially in remote areas or where power is unavailable.</ref>
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| ===Magnetic compass===
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| The magnetic compass consists of a magnetized pointer (usually marked on the North end) free to align itself with [[Earth's magnetic field]]. A compass is any magnetically sensitive device capable of indicating the direction of the [[North Magnetic Pole|magnetic north]] of a planet's [[magnetosphere]]. The face of the compass generally highlights the [[Cardinal direction|cardinal points]] of north, south, east and west. Often, compasses are built as a stand alone sealed [[Measuring instrument|instrument]] with a magnetized bar or needle turning freely upon a [[Lever|pivot]], or moving in a fluid, thus able to point in a northerly and southerly direction.
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| The compass greatly improved the safety and efficiency of travel, especially ocean travel. A compass can be used to calculate [[Course (navigation)|heading]], used with a [[sextant]] to calculate [[latitude]], and with a [[marine chronometer]] to calculate [[longitude]]. It thus provides a much improved [[navigation]]al capability that has only been recently supplanted by modern devices such as the [[Global Positioning System]] (GPS).
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| === How a magnetic compass works ===
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| [[Image:Compass align.jpg|thumb|An inexpensive compass, aligned so that its needle points through the "North" mark on its compass card.]]
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| A compass functions as a pointer to "[[magnetic north]]" because the [[magnetize]]d needle at its heart aligns itself with the lines of the [[Magnetic field of earth|Earth's magnetic field]]. The [[magnetic field]] exerts a [[torque]] on the needle, pulling one end or ''pole'' of the needle toward the Earth's [[North magnetic pole]], and the other toward the [[South magnetic pole]]. The needle is mounted on a low-friction pivot point, in better compasses a [[jewel bearing]], so it can turn easily. When the compass is held level, the needle turns until, after a few seconds to allow oscillations to die out, one end points toward the North magnetic pole.
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| A magnet or compass needle's "north" pole is defined as the one which is attracted to the [[North magnetic pole]] of the Earth. Since opposite poles attract ("north" to "south") the North magnetic pole of the Earth is actually the ''south'' pole of the Earth's magnetic field.<ref>{{cite book
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| | last = Serway
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| | first = Raymond A.
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| | coauthors = Chris Vuille
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| | title = Essentials of college physics
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| | publisher = Cengage Learning
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| | year = 2006
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| | location = USA
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| | page = 493
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| | url = http://books.google.com/books?id=8n4NCyRgUMEC&pg=PA493&dq=magnet+%22north+pole%22+earth#v=onepage&q=magnet%20%22north%20pole%22%20earth&f=false
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| | doi =
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| | isbn = 0-495-10619-4}}</ref><ref>{{cite book
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| | last = Emiliani
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| | first = Cesare
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| | coauthors =
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| | title = Planet Earth: Cosmology, Geology, and the Evolution of Life and Environment
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| | publisher = Cambridge University Press
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| | year = 1992
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| | location = UK
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| | page = 228
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| | url = http://books.google.com/books?id=MfAGpVq8gpQC&pg=PA228&dq=magnet+%22north+pole%22+earth#v=onepage&q=magnet%20%22north%20pole%22%20earth&f=false
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| | doi =
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| | isbn = 0-521-40949-7}}</ref><ref>{{cite book
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| | last = Manners
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| | first = Joy
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| | authorlink =
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| | coauthors =
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| | title = Static Fields and Potentials
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| | publisher = CRC Press
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| | year = 2000
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| | location = USA
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| | page = 148
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| | url = http://books.google.com/books?id=vJyqbRPsXYQC&pg=PA148&dq=magnet+%22north+pole%22+earth#v=onepage&q=magnet%20%22north%20pole%22%20earth&f=false
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| | doi =
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| | isbn = 0-7503-0718-8}}</ref> The compass needle's north pole is always marked in some way: with a distinctive color, luminous paint, or an arrowhead.
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| Instead of a needle, professional compasses usually have bar magnets glued to the underside of a disk pivoted in the center so it can turn, called a "compass card", with a "[[compass rose]]" showing the [[cardinal point]]s and degrees marked on it. Better compasses are "''liquid-filled''"; the chamber containing the needle or disk is filled with a liquid whose purpose is to damp the oscillations of the needle so it will settle down to point to North more quickly, and also to protect the needle or disk from shock.
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| In navigation, directions on maps are expressed with reference to ''geographical'' or ''[[true north]]'', the direction toward the [[Geographical North Pole]], the rotation axis of the Earth. Since the Earth's [[Geomagnetic Pole|magnetic poles]] are near, but are not at the same locations as its [[geographic pole]]s, a compass does not point to true north. The direction a compass points is called ''[[magnetic north]]'', the direction of the North magnetic pole. Depending on where the compass is located on the surface of the Earth the angle between [[true north]] and [[magnetic north]], called ''[[magnetic declination]]'' can vary widely, increasing the farther one is from the prime meridian of the Earth's magnetic field. The local magnetic declination is given on most maps, to allow the map to be oriented with a compass parallel to true north. Some magnetic compasses include means to manually compensate for the magnetic declination, so that the compass shows true directions.
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| In geographic regions near the [[Geomagnetic Pole|magnetic poles]], in the Arctic and Antarctic, variations in the Earth's magnetic field cause magnetic compasses to have such large errors that they are useless, so other instruments must be used for navigation.
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| The positions of the magnetic poles change over time, on a time-scale that is not extremely long by human standards. They wander over time-periods of only a few years, leading to corresponding changes of the directions of magnetic north and south as observed everywhere on the planet.
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| ==History==
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| The compass was invented in China, during the [[Han Dynasty]] between the 2nd century BC and 1st century AD.<ref name=merrill/> The first compasses were made of [[lodestone]], a naturally magnetized ore of iron.<ref name="cambridge1">{{cite book|last=Lowrie|first=William|title=Fundamentals of Geophysics|year=2007|publisher=Cambridge University Press|location=London|isbn=9780521675963|pages=281|quote=Early in the Han Dynasty, between 300-200 BC, the Chinese fashioned a rudimentary compass out of lodestone... the compass may have been used in the search for gems and the selection of sites for houses... their directive power led to the use of compasses for navigation}}</ref> Ancient Chinese people found that if a lodestone was suspended so it could turn freely, it would always point in the same direction, toward the magnetic poles. Early compasses were used for geomancy "in the search for gems and the selection of sites for houses," but were later adapted for navigation during the [[Song Dynasty]] in the 11th century.<ref name="cambridge1"/> Later compasses were made of iron needles, magnetized by striking them with a lodestone. The dry compass was invented in [[Middle Ages|medieval]] Europe around 1300.<ref name="Lane, p. 615" /> This was supplanted in the early 20th century by the liquid-filled magnetic compass.<ref name="W. H. Creak 238-239"/>
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| ===Navigation prior to the compass===
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| {{see also|Polynesian navigation}}
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| Prior to the introduction of the compass, position, destination, and direction at sea were primarily determined by the sighting of landmarks, supplemented with the observation of the position of celestial bodies. On cloudy days, the Vikings may have used [[cordierite]] or some other [[birefringence|birefringent crystal]] to determine the sun's direction and [[Horizontal coordinate system|elevation]] from the [[Polarization (waves)|polarization]] of daylight; their astronomical knowledge was sufficient to let them use this information to determine their proper heading.<ref>{{cite journal |author= Gábor Horváth|year= 2011|title= On the trail of Vikings with polarized skylight|journal= Philosophical Transactions of the Royal Society B |volume= 366 |pages= 772–782 |doi= 10.1098/rstb.2010.0194 |issue= 1565 |author-separator= , |display-authors= 1 |last2= Barta |first2= A. |last3= Pomozi |first3= I. |last4= Suhai |first4= B. |last5= Hegedus |first5= R. |last6= Akesson |first6= S. |last7= Meyer-Rochow |first7= B. |last8= Wehner |first8= R.}}</ref> For more southerly Europeans unacquainted with this technique, the invention of the compass enabled the determination of heading when the sky was overcast or foggy. This enabled mariners to navigate safely far from land, increasing sea trade, and contributing to the [[Age of Discovery]].{{citation needed|date=October 2013}}
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| ===Geomancy and feng shui===
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| Magnetism was originally used, not for navigation, but for [[geomancy]] and [[fortune-telling]] by the [[China|Chinese]]. The earliest [[China|Chinese]] [[magnetic]] compasses were probably not designed for navigation, but rather to order and harmonize their environments and buildings in accordance with 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="NHMFL Early Chinese Compass">{{cite web|url=http://www.magnet.fsu.edu/education/tutorials/museum/chinesecompass.html|title=National High Magnetic Field Laboratory: Early Chinese Compass|publisher=Florida State University|accessdate=2009-02-05}}</ref>
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| 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]] (lodestone) bar with a groove at one end (possibly for sighting). The artifact now consistently points 35.5 degrees west of north, but may have pointed north-south when whole. 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 |coauthors=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">A. P. Guimarães, "Mexico and the early history of magnetism", ''Revista Mexicana de Fisica'', Vol. 50, pp. 51-53 (2004)</ref><ref>http://www.dartmouth.edu/~izapa/CS-MM-Chap.%203.htm</ref>
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| ===Navigational compass===
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| A number of ancient cultures used [[lodestone]]s, suspended so they could turn, as magnetic compasses for navigation. Early mechanical compasses are referenced in written records of the [[China|Chinese]], who began using it for navigation sometime between the 9th and 11th century, "some time before 1050, possibly as early as 850."<ref name="needhamb">{{cite book|last=Needham|first=Joseph|title=The Shorter Science and Civilisation in China, Volume 3|year=1986|publisher=Cambridge University Press|pages=176|isbn=9780521315609|quote=the introduction of the mariner's compass on Chinese ships some time before 1050, possibly as early as 850}}</ref> A common theory by historians,<ref name="needhamb">{{cite book|last=Needham|first=Joseph|title=Cambridge University Press|publisher=University of California Press|pages=173|quote=Thus the possibility presents itself that... it may have formed part of one of those transmissions from Asia which we find in so many fields of applied science}}</ref><ref name="mceachren">{{cite book|last=McEachren|first=Justin W.|title=General Science Quarterly, Volumes 5-6|publisher=University of California Press|pages=337|quote=From the Chinese, the Arabs in all probability learned to use the magnetic needle, and in this round-about fashion it was brought to Europe}}</ref> suggests that the Arabs introduced the compass from China to Europe, although current textual evidence only supports the fact that Chinese use of the navigational compass preceded that of Europe and the Middle East.<ref name="Barbara M. Kreutz 367">Kreutz, p. 367</ref>
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| ====China====
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| {{Further|Four Great Inventions|List of Chinese inventions|History of science and technology in China}}
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| [[File:Model Si Nan of Han Dynasty.jpg|thumb|right|Model of a [[Han Dynasty]] (206 BC–220 AD) south-indicating ladle or ''sinan''. It is theorized{{By whom|date=June 2013}} that the south-pointing spoons of the Han dynasty were magnetized lodestones.<ref name=en1>{{cite book|last=Selin|first=Helaine|page=541|title=Encyclopaedia of the History of Science, Technology, and Medicine in Non-Western Cultures|year=1997|publisher=Springer|isbn=9781402045592|quote=The device described by Wang Chong has been widely considered to be the earliest form of the magnetic compass}}</ref>]]
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| There is disagreement as to exactly when the compass was invented. These are noteworthy [[History of China|Chinese]] literary references in evidence for its antiquity:
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| * The magnetic compass was first invented as a device for [[divination]] as early as the [[History of Science and Technology in China|Chinese]] [[Han Dynasty]] (since about 206 BC).<ref name=merrill>{{cite book|last=Merrill|first=Ronald T.|title=The Earth's magnetic field: Its history, origin and planetary perspective|year=1983|publisher=Academic press|location=San Francisco|isbn=0-12-491242-7|page=1|edition=2nd printing|coauthors=McElhinny, Michael W.}}</ref><ref name="Li Shu-hua, p. 176"/><ref name="cambridge1"/> The compass was used in [[Song Dynasty]] China by the military for [[Land navigation (military)|navigational orienteering]] by 1040-1044,<ref name="Barbara M. Kreutz 367" /><ref name="needham volume 4 part 1 252">Needham, p. 252</ref><ref name="Li Shu-hua, p. 182f">Li Shu-hua, p. 182f.</ref> and was used for maritime navigation by 1111 to 1117.<ref name="Ronan">{{cite book|author1=Colin A. Ronan|author2=Joseph Needham|title=The Shorter Science and Civilisation in China|url=http://books.google.com/books?id=CjRAiqGSJ50C&pg=PA27|date=25 July 1986|publisher=Cambridge University Press|isbn=978-0-521-31560-9|pages=28–29}}</ref>
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| * The earliest [[Chinese literature]] reference to '''magnetism''' lies in the 4th century BC writings of [[Guiguzi|Wang Xu]] (鬼谷子): "The lodestone attracts iron."<ref>http://www.gutenberg.org/cache/epub/7209/pg7209.html</ref> The book also notes that the people of the state of Zheng always knew their position by means of a "south-pointer"; some authors suggest that this refers to early use of the compass.<ref name="cambridge1"/><ref name="needham volume 4 part 1 190">Needham p. 190</ref>
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| * The first mention of a spoon, speculated to be a lodestone, observed '''pointing in a [[cardinal direction]]''' is a Chinese work composed between 70 and 80 AD (''[[Lunheng]]''), which records that "But when the south pointing spoon is thrown upon the ground, it comes to rest pointing at the south."<ref name="Needham18">Needham p. 18</ref> Within the text, the author Wang Chong describes the spoon as a phenomenon that he has personally observed.<ref name="Needham182">Needham p. 18 "''here the author is contrasting a fable which he did not believe with actual events he has seen with his own eyes''"</ref> Although the passage does not explicitly mention magnetism,<ref name="Li Shu-hua 180">Li Shu-hua, p. 180</ref> according to Chen-Cheng Yih, the "device described by Wang Chong has been widely considered to be the earliest form of the magnetic compass."<ref name=en1/>
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| * The first clear account of '''[[magnetic declination]]''' occurs in the ''Kuan Shih Ti Li Chih Meng'' ("Mr. Kuan's Geomantic Instructor"), dating to 880.<ref name="clerks">{{cite book|last=Needham|first=Joseph|title=Clerks and Craftsmen in China and the West|year=1970|pages=243–244|isbn=9780521072359|publisher=Cambridge University Press|quote=The geomantic book Kuan Shih Ti Li Chih Meng... has the first account of it... the Chiu Thien Hsuan Nu Chhing Nang Hai Chio Ching... includes an implicit reference to declination}}</ref> Another text, the ''Chiu Thien Hsuan Nu Chhing Nang Hai Chio Ching'' ("Blue Bag Sea Angle Manual") from around the same period, also has an implicit description of magnetic declination. It has been argued that this knowledge of declination requires the use of the compass.<ref name="clerks"/>
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| * A reference to a magnetized needle as a "'''mysterious needle'''" appears in 923-926 in the ''Chung Hua Ku Chin Chu'' text written by Ma Kao. The same passage is also attributed to the 4th century AD writer Tshui Pao, although it is postulated that the former text is more authentic. The shape of the needle is compared to that of a tadpole, and may indicate the transition between "lodestone spoons" and "iron needles."<ref name="Needham273-274">Needham p. 273-274</ref>
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| * The earliest reference to a specific magnetic '''direction finder''' device for land navigation is recorded in a [[Song Dynasty]] book dated to 1040-44. There is a description of an iron "south-pointing fish" floating in a bowl of water, aligning itself to the south. The device is recommended as a means of orientation "in the obscurity of the night." The ''[[Wujing Zongyao]]'' (武經總要, "Collection of the Most Important Military Techniques") stated: "When troops encountered gloomy weather or dark nights, and the directions of space could not be distinguished...they made use of the [mechanical] [[South Pointing Chariot|south-pointing carriage]], or the south-pointing fish."<ref name="needham volume 4 part 1 252">Needhamn, p. 252</ref> This was achieved by heating of metal (especially if steel), known today as [[Thermoremanent magnetization|thermoremanence]], and would have been capable of producing a weak state of magnetization.<ref name="needham volume 4 part 1 252"/> While the Chinese achieved magnetic [[remanence]] and induction by this time, in both Europe and Asia the phenomenon was attributed to the supernatural and occult, until about 1600 when [[William Gilbert (astronomer)|William Gilbert]] published his ''[[De Magnete]]''.<ref name="Elman">{{cite book|author=Benjamin A. Elman|title=On Their Own Terms: Science in China, 1550-1900|url=http://books.google.com/books?id=qm57OqARqpAC&pg=PA24|date=30 June 2009|publisher=Harvard University Press|isbn=978-0-674-03647-5|page=242}}</ref>
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| * The first incontestable reference to a '''magnetized needle''' in Chinese literature appears in 1088.<ref name="Li Shu-hua, p. 182f"/> The ''[[Dream Pool Essays]]'', written by the [[Song Dynasty]] [[polymath]] scientist [[Shen Kuo#Magnetic needle compass|Shen Kuo]], contained a detailed description of how [[geomancer]]s magnetized a [[Dial (measurement)|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 Kuo pointed out that a needle prepared this way sometimes pointed south, sometimes north.
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| *The earliest explicit recorded use of a magnetic compass for '''maritime navigation''' is found in [[Zhu Yu (author)|Zhu Yu]]'s book ''Pingchow Table Talks'' (萍洲可談; Pingzhou Ketan) and dates from 1111 to 1117: ''The ship's pilots are acquainted with the configuration of the coasts; at night they steer by the stars , and in the daytime by the sun. In dark weather they look at the south pointing needle''.<ref name="Ronan"/>
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| Thus, the use of a magnetic compass by the military for [[Land navigation (military)|land navigation]] occurred sometime before 1044, but incontestable evidence for the use of the compass as a maritime navigational device did not appear until 1117.
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| The typical Chinese navigational compass was in the form of a magnetic needle floating in a bowl of water.<ref name="Kreutz, p. 373">Kreutz, p. 373</ref> According to [[Joseph Needham|Needham]], the Chinese in the [[Song Dynasty]] and continuing [[Yuan Dynasty]] did make use of a dry compass, although this type never became as widely used in China as the wet compass.<ref name="needham volume 4 part 1 255">Needham p. 255</ref> Evidence of this is found in the ''Shilin guangji'' ("Guide Through the Forest of Affairs"), published in 1325 by Chen Yuanjing, although its compilation had taken place between 1100 and 1250.<ref name="needham volume 4 part 1 255"/> The dry compass in China was a dry suspension compass, a wooden frame crafted in the shape of a turtle hung upside down by a board, with the lodestone sealed in by wax, and if rotated, the needle at the tail would always point in the northern cardinal direction.<ref name="needham volume 4 part 1 255"/> Although the European compass-card in box frame and dry pivot needle was adopted in China after its use was taken by [[Wokou|Japanese pirates]] in the 16th century (who had in turn learned of it from Europeans),<ref name="needham volume 4 part 1 289">Needham, p. 289.</ref> the Chinese design of the suspended dry compass persisted in use well into the 18th century.<ref name="needham volume 4 part 1 290">Needham, p. 290</ref> However, according to Kreutz there is only a single Chinese reference to a dry-mounted needle (built into a pivoted wooden tortoise) which is dated to between 1150 and 1250, and claims that there is no clear indication that Chinese mariners ever used anything but the floating needle in a bowl until the 16th-century.<ref name="Kreutz, p. 373"/>
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| [[File:Ming-marine-compass.jpg|thumb|Diagram of a Ming Dynasty mariner's compass]]
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| The first recorded use of a 48 position mariner's compass on sea navigation was noted in ''The Customs of Cambodia'' by Yuan Dynasty diplomat [[Zhou Daguan]], he described his 1296 voyage from [[Wenzhou]] to [[Angkor Thom]] in detail; when his ship set sail from Wenzhou, the mariner took a needle direction of “ding wei” position, which is equivalent to 22.5 degree SW. After they arrived at [[Baria]],{{disambiguation needed|date=October 2011}} the mariner took "Kun Shen needle", or 52.5 degree SW.<ref>Zhou</ref> [[Zheng He]]'s Navigation Map, also known as "The Mao Kun Map", contains a large amount of detail "needle records" of [[Treasure voyages|Zheng He's expeditions]].<ref name="Ma, Appendix 2">Ma, Appendix 2</ref>
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| There is a debate over the diffusion of the compass after its first appearance with the Chinese. At present, according to Kreutz, scholarly consensus is that the Chinese invention predates the first European mention by 150 years.<ref name="Barbara M. Kreutz 367" /> However, there are questions over diffusion, because of the apparent failure of the Arabs to function as possible intermediaries between East and West because of the earlier recorded appearance of the compass in Europe (1190)<ref name="Barbara M. Kreutz 368"/> than in the Muslim world (1232, 1242, and 1282).<ref name="Barbara M. Kreutz 370"/><ref name="Barbara M. Kreutz 369"/> The first European mention of a magnetized needle and its use among sailors occurs in [[Alexander Neckam]]'s ''De naturis rerum'' (On the Natures of Things), written in 1190.<ref name="Barbara M. Kreutz 368">Kreutz, p. 368</ref><ref name="Lanza 2006 255"/> The earliest reference to a compass in the Middle East is attributed to the Persians, who describe an iron fish-like compass in a talebook dating from 1232.<ref name="Barbara M. Kreutz 370">Kreutz, p. 370</ref> In the Arab world, the earliest reference comes in ''The Book of the Merchants' Treasure'', written by one Baylak al-Kibjaki in Cairo about 1282.<ref name="Barbara M. Kreutz 369">Kreutz, p. 369</ref> Since the author describes having witnessed the use of a compass on a ship trip some forty years earlier, some scholars are inclined to antedate its first appearance accordingly. That the [[Arabic]] word for "Compass" (''al-konbas'') may be a derivation of the old [[Italian language|Italian]] word for compass, is also used as evidence for the lack of diffusion from China to Europe. However, the Persian compass is described as fish-like, which is a characteristic of early Chinese compasses from the 11th century, suggesting transmission from China to Persia.<ref name="Needham12-13">Needham p. 12-13 "''...that the floating fish-shaped iron leaf spread outside China as a technique, we know from the description of Muhammad al' Awfi just two hundred years later''"</ref>
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| ==== Medieval Europe ====
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| [[File:Epistola-de-magnete.jpg|thumb|Pivoting compass needle in a 14th-century copy of ''Epistola de magnete'' of [[Peter Peregrinus]] (1269).]]
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| Alexander Neckam reported the use of a magnetic compass for the region of the English Channel in the texts ''De utensilibus'' and ''De naturis rerum'',<ref name=Schmidl>{{Cite journal|title=Two Early Arabic Sources On The Magnetic Compass|first=Petra G.|last=Schmidl|journal=Journal of Arabic and Islamic Studies|year=1996–1997|volume=1|pages=81–132|ref=harv|postscript=<!--None-->}} http://www.uib.no/jais/v001ht/01-081-132schmidl1.htm#_ftn4</ref> written between 1187 and 1202, after he returned to England from France<ref name="alxn">{{cite book|last=Neckam|first=Alexander|title=Alexandri Neckam De Naturis Rerum Libri Duoi|year=1863|publisher=Longman, Roberts, and Green|page=xi}}</ref> and prior to entering the Augustinian abbey at Cirencester.<ref name="brill1">{{cite book|last=Gutman|first=Oliver|title=Liber Celi Et Mundi|year=2003|publisher=BRILL|page=xx|isbn=9789004132283|quote=probably whilst teaching theology at Oxford before entering the Augustinian abbey at Cirencester in 1202}}</ref>
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| In 1269 Petrus Peregrinus of Maricourt described a floating compass for astronomical purposes as well as a dry compass for seafaring, in his well-known Epistola de magnete.<ref name=Schmidl>{{Cite journal|title=Two Early Arabic Sources On The Magnetic Compass|first=Petra G.|last=Schmidl|journal=Journal of Arabic and Islamic Studies|year=1996–1997|volume=1|pages=81–132|ref=harv|postscript=<!--None-->}}</ref>
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| In the Mediterranean, the introduction of the compass, at first only known as a magnetized pointer floating in a bowl of water,<ref>Kreutz, p. 368–369</ref> went hand in hand with improvements in [[dead reckoning]] methods, and the development of [[Portolan chart]]s, leading to more navigation during winter months in the second half of the 13th century.<ref>Lane, p. 606f.</ref> While the practice from ancient times had been to curtail sea travel between October and April, due in part to the lack of dependable clear skies during the Mediterranean winter, the prolongation of the sailing season resulted in a gradual, but sustained increase in shipping movement; by around 1290 the sailing season could start in late January or February, and end in December.<ref>Lane, p. 608</ref> The additional few months were of considerable economic importance. For instance, it enabled [[Venice|Venetian]] convoys to make two round trips a year to the [[Levant]], instead of one.<ref>Lane, p. 608 & 610</ref>
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| At the same time, traffic between the Mediterranean and northern Europe also increased, with first evidence of direct commercial voyages from the Mediterranean into the English Channel coming in the closing decades of the 13th century, and one factor may be that the compass made traversal of the [[Bay of Biscay]] safer and easier.<ref>Lane, p. 608 & 613</ref> However, critics like Kreutz feel that it was later in 1410 that anyone really started steering by compass.<ref>Kreutz, p. 372–373</ref> [[File:Compass thumbnail.jpg|thumb|right|Navigational [[sailor]]'s compass rose.]]
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| At present, according to Kreutz, "barring the discovery of new evidence, it seems clear the first Chinese reference to" the compass "antedates any European mention by roughly 150 years."<ref name="Barbara M. Kreutz 367"/> However, there are questions over diffusion, because of the apparent failure of the Arabs to function as possible intermediaries between East and West because of the earlier recorded appearance of the compass in Europe (1190)<ref name="Barbara M. Kreutz 368"/> than in the Muslim world (1232, 1242, and 1282).<ref name="Barbara M. Kreutz 370"/><ref name="Barbara M. Kreutz 369"/> This is countered by evidence of the temporal proximity of the Chinese navigational compass (1117) to its first appearance in Europe (1190) and the common shape of the early compass as a magnetized needle floating in a bowl of water.<ref name="Barbara M. Kreutz 368"/>
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| ==== Islamic world ====
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| The earliest reference to an iron fish-like compass in the [[Muslim world|Islamic world]] occurs in a [[Persian language|Persian]] talebook from 1232.<ref name="Barbara M. Kreutz 370"/> This fish shape was from a typical early Chinese design.<ref name="Needham12-13"/> The earliest [[Arabic language|Arabic]] reference to a compass — in the form of magnetic needle in a bowl of water — comes from the [[Yemen]]i sultan and [[Islamic astronomy|astronomer]] Al-[[Ashraf]] in 1282.<ref name="Barbara M. Kreutz 369"/> He also appears to be the first to make use of the compass for [[Islamic astronomy|astronomical purposes]].<ref>Emilie Savage-Smith (1988), "Gleanings from an Arabist's Workshop: Current Trends in the Study of Medieval Islamic Science and Medicine", ''[[Isis (journal)|Isis]]'' '''79''' (2): 246-266 [263]</ref> Since the author describes having witnessed the use of a compass on a ship trip some forty years earlier, some scholars are inclined to antedate its first appearance in the [[Arab world]] accordingly.<ref name="Barbara M. Kreutz 370"/>
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| In 1300, another Arabic treatise written by the [[Egypt]]ian astronomer and [[muezzin]] Ibn Simʿūn describes a dry compass for use as a "[[Qibla (Kabba)]] indicator" to find the direction to [[Mecca]]. Like Peregrinus' compass, however, Ibn Simʿūn's compass did not feature a compass card.<ref name="Schmidl"/> In the 14th century, the [[Syria]]n astronomer and timekeeper [[Ibn al-Shatir]] (1304–1375) invented a [[time]]keeping device incorporating both a universal [[sundial]] and a magnetic compass. He invented it for the purpose of finding the times of [[salat]] prayers.<ref name=King-1983>{{Harv|King|1983|pp=547–8}}</ref> [[Islamic geography|Arab navigators]] also introduced the 32-point [[compass rose]] during this time.<ref name=Tibbetts>G. R. Tibbetts (1973), "Comparisons between Arab and Chinese Navigational Techniques", ''Bulletin of the School of Oriental and African Studies'' '''36''' (1): 97-108 [105-6]</ref>
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| ==== India ====
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| The compass was used in India for navigational purposes and was known as the matsya yantra, because of the placement of a metallic fish in a cup of oil.<ref>{{cite book|url=http://books.google.com/?id=HUAPAAAAIAAJ&dq=%22matsya+yantra%22+%2B+compass&q=%22matsya+yantra%22 |title=The American journal of science - Google Books |publisher=|date= |accessdate=2009-06-30|year=1919}}</ref>
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| ==== Medieval Africa ====
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| There is evidence that the distribution of the compass from China likely also reached eastern Africa by way of trade through the end of the Silk Road that ended in [[East Africa]]n center of trade in [[Somalia]] and the [[Swahili people|Swahili]] city-state kingdoms.<ref>{{cite book|last=Stockwell|first=Foster|title=Westerners in China : a history of exploration and trade, ancient times through the present|year=2003|publisher=McFarland & Co. Publishers|location=Jefferson, NC|isbn=9780786414048|page=14}}</ref> There is evidence that Swahili maritime merchants and sailors acquired the compass at some point and used them for navigation of Swahili versions of [[dhow]]s.<ref>{{cite book|last=Bulliet ''et al.''|first=Richard W.|title=The earth and its peoples : a global history|publisher=Wadsworth Cengage Learning|location=Boston|isbn=9780538744386|page=381|edition=5th, Student}}</ref>
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| ==Later developments==
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| === Dry compass ===
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| [[File:Kardanischer-Kompass.jpg|thumb|[[Early modern period|Early modern]] dry compass suspended by a [[gimbal]] (1570).]]
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| The dry mariner's compass was invented in Europe around 1300. The dry mariner's compass consists of three elements: A freely pivoting needle on a pin enclosed in a little box with a glass cover and a [[wind rose]], whereby "the wind rose or compass card is attached to a magnetized needle in such a manner that when placed on a pivot in a box fastened in line with the keel of the ship the card would turn as the ship changed direction, indicating always what course the ship was on".<ref name="Lane, p. 615"/> Later, compasses were often fitted into a [[gimbal]] mounting to reduce grounding of the needle or card when used on the pitching and rolling deck of a ship.
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| While pivoting needles in glass boxes had already been described by the French scholar [[Peter Peregrinus]] in 1269,<ref>Taylor</ref> and by the Egyptian scholar Ibn Simʿūn in 1300,<ref name=Schmidl/> traditionally [[Flavio Gioja]] (fl. 1302), an Italian [[pilot (harbour)|pilot]] from [[Amalfi]], has been credited with perfecting the sailor's compass by suspending its needle over a compass card, thus giving the compass its familiar appearance.<ref name="Frederic C. Lane 616">Lane, p. 616</ref> Such a compass with the needle attached to a rotating card is also described in a commentary on [[Dante]]'s ''[[Divine Comedy]]'' from 1380, while an earlier source refers to a portable compass in a box (1318),<ref>Kreutz, p. 374</ref> supporting the notion that the dry compass was known in Europe by then.<ref name="Kreutz, p. 373"/>
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| === Bearing compass ===
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| [[File:Bearing compass.jpg|thumb|upright|Bearing compass (18th century).]]
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| A ''bearing compass'' is a magnetic compass mounted in such a way that it allows the taking of [[bearing (navigation)|bearing]]s of objects by aligning them with the lubber line of the bearing compass.<ref>{{cite web |url=http://www.westmarine.com/webapp/wcs/stores/servlet/WestAdvisorDisplayView?storeId=30003&langId=-1&catalogId=10001&advisor=bearing.htm |title=Hand Bearing Compass |year=2004 |publisher=West Marine |accessdate=2007-12-28}}</ref> A ''[[surveyor's compass]]'' is a specialized compass made to accurately measure heading of landmarks and measure horizontal angles to help with [[Cartography|map making]]. These were already in common use by the early 18th century and are described in the 1728 [[Cyclopaedia, or an Universal Dictionary of Arts and Sciences|Cyclopaedia]]. The bearing compass was steadily reduced in size and weight to increase portability, resulting in a model that could be carried and operated in one hand. In 1885, a patent was granted for a [[hand compass]] fitted with a viewing prism and lens that enabled the user to accurately sight the heading of geographical landmarks, thus creating the ''[[sighting compass|prismatic compass]]''.<ref>Frazer, Persifor, ''A Convenient Device to be Applied to the Hand Compass'', Proceedings of the American Philosophical Society, Vol. 22, No. 118 (Mar., 1885), p. 216</ref> Another sighting method was by means of a reflective mirror. First patented in 1902, the ''Bézard compass'' consisted of a field compass with a mirror mounted above it.<ref name="Article">The Compass Museum, ''The Bézard Compass'', [http://www.compassmuseum.com/hand/bezard.htm Article]</ref><ref>Barnes, Scott, Churchill, James, and Jacobson, Cliff, ''The Ultimate Guide to Wilderness Navigation'', Globe Pequot Press (2002), ISBN 1-58574-490-5, ISBN 978-1-58574-490-9, p. 27</ref> This arrangement enabled the user to align the compass with an objective while simultaneously viewing its bearing in the mirror.<ref name="Article"/><ref>Barnes, p. 27</ref>
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| In 1928, Gunnar Tillander, a Swedish unemployed instrument maker and avid participant in the sport of [[orienteering]], invented a new style of bearing compass. Dissatisfied with existing field compasses, which required a separate protractor in order to take bearings from a map, Tillander decided to incorporate both instruments into a single instrument. It combined a compass with a protractor built into the base. His design featured a metal compass capsule containing a magnetic needle with orienting marks mounted into a transparent protractor baseplate with a lubber line (later called a ''direction of travel indicator''). By rotating the capsule to align the needle with the orienting marks, the course bearing could be read at the lubber line. Moreover, by aligning the baseplate with a course drawn on a map - ignoring the needle - the compass could also function as a protractor. Tillander took his design to fellow orienteers [[Björn Kjellström|Björn]], Alvid, and Alvar Kjellström, who were selling basic compasses, and the four men modified Tillander's design.<ref name="LIT">Litsky, Frank, ''Bjorn Kjellstrom, 84, Orienteer and Inventor of Modern Compass'', Obituaries, The New York Times, 1 September 1995</ref> In December 1932, the Silva Company was formed with Tillander and the three Kjellström brothers, and the company began manufacturing and selling its [[Silva compass|Silva orienteering compass]] to Swedish orienteers, outdoorsmen, and army officers.<ref name="LIT"/><ref>Seidman, p. 68</ref><ref>Kjellström, Björn, ''19th Hole: The Readers Take Over: Orienteering'', Sports Illustrated, 3 March 1969</ref><ref>Silva Sweden AB, ''Silva Sweden AB and Silva Production AB Become One Company: History'', Press Release 28 April 2000</ref>
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| === Liquid compass ===
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| [[File:Flush mount compass.jpg|thumb|A surface mount, liquid-filled compass on a boat.]]
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| The liquid compass is a design in which the magnetized needle or card is damped by fluid to protect against excessive swing or wobble, improving readability while reducing wear. A rudimentary working model of a liquid compass was introduced by Sir [[Edmund Halley]] at a meeting of the [[Royal Society]] in 1690.<ref>Gubbins, David, ''Encyclopedia of Geomagnetism and Paleomagnetism'', Springer Press (2007), ISBN 1-4020-3992-1, ISBN 978-1-4020-3992-8, p. 67</ref> However, as early liquid compasses were fairly cumbersome and heavy, and subject to damage, their main advantage was aboard ship. Protected in a [[binnacle]] and normally [[gimbal]]-mounted, the liquid inside the compass housing effectively damped shock and vibration, while eliminating excessive swing and grounding of the card caused by the pitch and roll of the vessel. The first liquid mariner's compass believed practicable for limited use was patented by the Englishman Francis Crow in 1813.<ref>Fanning, A.E., ''Steady As She Goes: A History of the Compass Department of the Admiralty'', HMSO, Department of the Admiralty (1986), pp. 1-10</ref><ref>Gubbins, p. 67</ref> Liquid-damped marine compasses for ships and small boats were occasionally used by the [[United Kingdom|British]] [[Royal Navy]] from the 1830s through 1860, but the standard Admiralty compass remained a dry-mount type.<ref>Fanning, A.E., pp. 1-10</ref> In the latter year, the American physicist and inventor [[Edward Samuel Ritchie]] patented a greatly improved liquid marine compass that was adopted in revised form for general use by the [[United States Navy]], and later purchased by the Royal Navy as well.<ref>Warner, Deborah, ''Compasses and Coils: The Instrument Business of Edward S. Ritchie'', Rittenhouse, Vol. 9, No. 1 (1994), pp. 1-24</ref>
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| Despite these advances, the liquid compass was not introduced generally into the Royal Navy until 1908. An early version developed by RN Captain Creak proved to be operational under heavy gunfire and seas, but was felt to lack navigational precision compared with the design by Lord Kelvin:
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| <blockquote>Captain Creak's first step in the development of the liquid compass was to introduce a "card mounted on a float, with two thin and relatively short needles, fitted with their poles at the scientifically correct angular distances, and with the centre of gravity, centre of buoyancy, and the point of suspension in correct relation to each other...The compass thus designed rectified the defects of the Admiralty Standard Compass...with the additional advantage of considerable steadiness under heavy gunfire and in a seaway... The one defect in the compass as developed by Creak up to 1892 was that "for manoeuvring purposes it was inferior to Lord Kelvin's compass, owing to comparative sluggishness on a large alteration of course through the drag on the card by the liquid in which it floated...<ref name="W. H. Creak 238-239"/><ref>Gubbins, p. 67: The use of parallel or multiple needles was by no means a new development; their use in dry-mount marine compasses was pioneered by navigation officers of the [[Dutch East India Company]] as early as 1649.</ref></blockquote>
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| [[File:Aero Magnetic Compass.jpg|thumb|left|Typical aircraft-mounted magnetic compass.]]
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| However, with ship and gun sizes continuously increasing, the advantages of the liquid compass over the Kelvin compass became unavoidably apparent to the Admiralty, and after widespread adoption by other navies, the liquid compass was generally adopted by the Royal Navy as well.<ref name="W. H. Creak 238-239">W. H. Creak: "The History of the Liquid Compass", ''The Geographical Journal'', Vol. 56, No. 3 (1920), pp. 238-239</ref>
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| Liquid compasses were next adapted for aircraft. In 1909, Captain [[F.O. Creagh-Osborne]], Superintendent of Compasses at the British Admiralty, introduced his ''Creagh-Osborne'' aircraft compass, which used a mixture of alcohol and distilled water to damp the compass card.<ref>Davis, Sophia, ''Raising The Aerocompass In Early Twentieth-century Britain'', British Journal for the History of Science, published online by Cambridge University Press, 15 Jul 2008, pp. 1-22</ref><ref>Colvin, Fred H., ''Aircraft Mechanics Handbook: A Collection of Facts and Suggestions from Factory and Flying Field to Assist in Caring for Modern Aircraft'', McGraw-Hill Book Co. Inc. (1918), pp. 347-348</ref> After the success of this invention, Capt. Creagh-Osborne adapted his design to a much smaller pocket model<ref>The Compass Museum, [http://www.compassmuseum.com/wrist/wrist_1.htm#C-O Article]: Though the ''Creagh-Osborne'' was offered in a wrist-mount model, it proved too bulky and heavy in this form.</ref> for individual use<ref>Hughes, Henry A., ''Improvements in prismatic compasses with special reference to the Creagh-Osborne patent compass'', Transactions of The Optical Society 16, London: The Optical Society (1915), pp. 17-43: The first liquid-damped compass compact enough for pocket or pouch was the ''Creagh-Osborne'', patented in 1915 in Great Britain.</ref> by officers of artillery or infantry, receiving a patent in 1915.<ref>Hughes, Henry A., pp. 17-43</ref>
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| In December 1932, the newly founded Silva Company of Sweden introduced its first baseplate or bearing compass that used a liquid-filled capsule to damp the swing of the magnetized needle.<ref name="LIT"/> The liquid-damped Silva took only four seconds for its needle to settle in comparison to thirty seconds for the original version.<ref name="LIT"/>
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| In 1933 [[Tuomas Vohlonen]], a surveyor by profession, applied for a patent for a unique method of filling and sealing a lightweight [[celluloid]] compass housing or capsule with a petroleum distillate to dampen the needle and protect it from shock and wear caused by excessive motion.<ref name="december2001">Suunto Oy, ''Suunto Company History'', December 2001 [http://www.suunto.com/suunto/Worlds/outdoor/main/outdoor_article_normal.jsp? Article]</ref> Introduced in a wrist-mount model in 1936 as the [[Suunto]] Oy ''Model M-311'', the new capsule design led directly to the lightweight liquid field compasses of today.<ref name="december2001"/>
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| == History of non-navigational uses ==
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| === Building orientation ===
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| Evidence for the orientation of buildings by the means of a magnetic compass can be found in 12th century [[Denmark]]: one fourth of its 570 [[Romanesque architecture|Romanesque churches]] are rotated by 5-15 degrees clockwise from true east-west, thus corresponding to the predominant magnetic declination of the time of their construction.<ref>N. Abrahamsen: "Evidence for Church Orientation by Magnetic Compass in Twelfth-Century Denmark", ''Archaeometry'', Vol. 32, No. 2 (1992), pp. 293-303 (293)</ref> Most of these churches were built in the 12th century, indicating a fairly common usage of magnetic compasses in [[Europe]] by then.<ref>N. Abrahamsen: "Evidence for Church Orientation by Magnetic Compass in Twelfth-Century Denmark", Archaeometry, Vol. 32, No. 2 (1992), pp. 293-303 (303)</ref>
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| === Mining ===
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| The use of a compass as a direction finder underground was pioneered by the [[Tuscany|Tuscan]] mining town [[Massa]] where floating magnetic needles were employed for determining tunneling and defining the claims of the various mining companies as early as the 13th century.<ref>Ludwig and Schmidtchen, p. 62–64</ref> In the second half of the 15th century, the compass became standard equipment for [[German Tyrol|Tyrol]]ian miners. Shortly afterwards the first detailed treatise dealing with the underground use of compasses was published by a [[Germany|German]] miner [[Rülein von Calw]] (1463–1525).<ref>Ludwig and Schmidtchen, p. 64</ref>
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| === Astronomy ===
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| Three astronomical compasses meant for establishing the [[Meridian (astronomy)|meridian]] were described by [[Peter of Maricourt|Peter Peregrinus]] in 1269 (referring to experiments made before 1248)<ref>Taylor, p. 1f.</ref> In the 1300s, an Arabic treatise written by the [[Egypt]]ian astronomer and [[muezzin]] Ibn Simʿūn describes a dry compass for use as a "[[Qibla]] indicator" to find the direction to [[Mecca]]. Ibn Simʿūn's compass, however, did not feature a compass card nor the familiar glass box.<ref name=Schmidl/> In the 14th century, the [[Syria]]n astronomer and timekeeper [[Ibn al-Shatir]] (1304–1375) invented a [[time]]keeping device incorporating both a universal [[sundial]] and a magnetic compass. He invented it for the purpose of finding the times of [[salat]] prayers.<ref name=King-1983/> [[Islamic geography|Arab navigators]] also introduced the 32-point [[compass rose]] during this time.<ref name=Tibbetts/>
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| ==Modern compasses==
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| [[File:walkers compass arp.jpg|thumb|right|upright|A liquid-filled protractor or orienteering compass with lanyard.]]
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| Modern compasses usually use a magnetized needle or dial inside a capsule completely filled with a liquid (lamp oil, mineral oil, white spirits, purified kerosene, or ethyl alcohol is common). While older designs commonly incorporated a flexible rubber diaphragm or airspace inside the capsule to allow for volume changes caused by temperature or altitude, some modern liquid compasses utilize smaller housings and/or flexible capsule materials to accomplish the same result.<ref>''Gear Review: Kasper & Richter Alpin Compass'', OceanMountainSky.Com</ref> The liquid inside the capsule serves to dampen the movement of the needle, reducing oscillation time and increasing stability. Key points on the compass, including the north end of the needle are often marked with [[phosphorescent paint|phosphorescent]], [[photoluminescent]], or self-luminous materials<ref>Nemoto & Co. Ltd., [http://www.nemoto.co.jp/en/products/luminova/luminova.html Article]: In addition to ordinary phosphorescent luminous paint ([[zinc sulfide]]), brighter photoluminescent coatings which include radioactive [[isotope]]s such as [[Strontium-90]], usually in the form of [[strontium aluminate]], or [[tritium]], which is a radioactive isotope of [[hydrogen]] are now being used on modern compasses. Tritium has the advantage that its radiation has such low energy that it cannot penetrate a compass housing.</ref> to enable the compass to be read at night or in poor light. As the compass fill liquid is noncompressible under pressure, many ordinary liquid-filled compasses will operate accurately underwater to considerable depths.
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| Many modern compasses incorporate a baseplate and [[protractor]] tool, and are referred to variously as "[[orienteering]]", "baseplate", "map compass" or "protractor" designs. This type of compass uses a separate magnetized needle inside a rotating capsule, an orienting "box" or gate for aligning the needle with magnetic north, a transparent base containing map orienting lines, and a bezel (outer dial) marked in degrees or other units of angular measurement.<ref name=des>{{cite book | author = Johnson, G. Mark | date = 2003-03-26 | title = The Ultimate Desert Handbook | publisher = McGraw-Hill Professional | isbn = 0-07-139303-X | page = 110}}</ref> The capsule is mounted in a transparent baseplate containing a ''direction-of-travel'' (DOT) indicator for use in taking bearings directly from a map.<ref name=des/>
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| [[File:Cammenga-lensatic-compass-model-27.jpg|thumb|left|Cammenga air filled lensatic compass.]]
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| Other features found on modern orienteering compasses are map and [[romer]] scales for measuring distances and plotting positions on maps, luminous markings on the face or bezels, various [[sighting compass|sighting mechanisms]] (mirror, prism, etc.) for taking bearings of distant objects with greater precision, "global" needles for use in differing hemispheres, adjustable declination for obtaining instant true bearings without resort to arithmetic, and devices such as [[inclinometer|clinometer]]s for measuring gradients.<ref name=des>{{cite book | author = Johnson, G. Mark | date = 2003-03-26 | title = The Ultimate Desert Handbook | publisher = McGraw-Hill Professional | isbn = 0-07-139303-X | pages = 110–111}}</ref> The sport of orienteering has also resulted in the development of models with extremely fast-settling and stable needles for optimal use with a topographic map, a land navigation technique known as ''terrain association''.<ref>Kjernsmo, Kjetil, '[www.learn-orienteering.org/old/buying.html How to use a Compass]'', retrieved 8 April 2012</ref>
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| The military forces of a few nations, notably the United States Army, continue to issue field compasses with magnetized compass dials or cards instead of needles. A magnetic card compass is usually equipped with an optical, lensatic, or prismatic sight, which allows the user to read the bearing or azimuth off the compass card while simultaneously aligning the compass with the objective (see photo). Magnetic card compass designs normally require a separate protractor tool in order to take bearings directly from a map.<ref name=des>{{cite book | author = Johnson, G. Mark | date = 2003-03-26 | title = The Ultimate Desert Handbook | publisher = McGraw-Hill Professional | isbn = 0-07-139303-X | page = 112}}</ref><ref>U.S. Army, ''Map Reading and Land Navigation'', FM 21-26, Headquarters, Dept. of the Army, Washington, D.C. (7 May 1993), ch. 11, pp. 1-3: Any 'floating card' type compass with a straightedge or centerline axis can be used to read a map bearing by orienting the map to magnetic north using a drawn magnetic azimuth, but the process is far simpler with a protractor compass.</ref>
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| The U.S. M-1950 military lensatic compass does not use a liquid-filled capsule as a [[damping]] mechanism, but rather [[electromagnetic induction]] to control oscillation of it magnetized card. A "deep-well" design is used to allow the compass to be used globally with a card tilt of up to 8 degrees without impairing accuracy.<ref>'[http://landnavigation.org/Documents/Compass%20Mil%20Specs.pdf Article MIL-PRF-10436N]'', rev. 31 October 2003, Washington, D.C.: U.S. Dept. of Defense</ref> As induction forces provide less damping than liquid-filled designs, a needle lock is fitted to the compass to reduce wear, operated by the folding action of the rear sight/lens holder. The use of air-filled induction compasses has declined over the years, as they may become inoperative or inaccurate in freezing temperatures or extremely humid environments due to condensation or water ingress.<ref>Kearny, Cresson H., ''Jungle Snafus...And Remedies'', Oregon Institute Press (1996), ISBN 1-884067-10-7, pp. 164-170: In 1989, one U.S. Army jungle infantry instructor reported that about 20% of the issue lensatic compasses in his company used in a single jungle exercise in [[Panama]] were ruined within three weeks by rain and humidity.</ref>
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| Some military compasses, like the U.S. M-1950 ([[Cammenga]] 3H) military lensatic compass, the [[Silva compass|Silva 4b ''Militaire'']], and the [[Suunto|Suunto M-5N(T)]] contain the radioactive material [[tritium]] (<small><sub>1</sup></small>H<sup>3</sup>) and a combination of phosphors.<ref>Ministry of Defence, ''Manual of Map Reading and Land Navigation'', HMSO Army Code 70947 (1988), ISBN 0-11-772611-7, ISBN 978-0-11-772611-6, ch. 8, sec. 26, pp. 6-7; ch. 12, sec. 39, p. 4</ref> The U.S. M-1950 equipped with self-luminous lighting contains 120 mCi (millicuries) of tritium. The purpose of the tritium and phosphors is to provide [[Illumination (lighting)|illumination]] for the compass, via [[radioluminescence|radioluminescent]] [[tritium illumination]], which does not require the compass to be "recharged" by sunlight or artificial light.<ref>{{cite web|url=http://www.orau.org/PTP/collection/radioluminescent/armycompass.htm |title=Military Compass |publisher=Orau.org |date= |accessdate=2009-06-30}}</ref> However, tritium has a [[half-life]] of only about 12 years,<ref>[[CRC Handbook of Chemistry and Physics]]. page B247</ref> so a compass that contains 120 mCi of tritium when new will contain only 60 when it is 12 years old, 30 when it is 24 years old, and so on. Consequently, the illumination of the display will fade.
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|
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| Mariner's compasses can have two or more gimbaled magnets permanently attached to a compass card. These move freely on a pivot. A ''lubber line'', which can be a marking on the compass bowl or a small fixed needle indicates the ship's heading on the compass card. Traditionally the card is divided into thirty-two points (known as ''rhumb''s), although modern compasses are marked in degrees rather than cardinal points. The glass-covered box (or bowl) contains a suspended [[gimbal]] within a [[binnacle]]. This preserves the horizontal position.
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| ===Thumb compass===
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| {{Main|Thumb compass}}
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| [[File:Compasses orienteering.jpg|thumb|right|Thumb compass on left.]]
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| A '''thumb compass''' is a type of compass commonly used in [[orienteering]], a sport in which map reading and terrain association are paramount. Consequently, most thumb compasses have minimal or no degree markings at all, and are normally used only to orient the map to magnetic north. Thumb compasses are also often [[transparency (optics)|transparent]] so that an orienteer can hold a [[Orienteering map|map]] in the hand with the compass and see the map through the compass.
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| ===Gyrocompass===
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| {{Main|Gyrocompass}}
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| A ''gyrocompass'' is similar to a [[gyroscope]]. It is a non-magnetic compass that finds [[true north]] by using an (electrically powered) fast-spinning wheel and friction forces in order to exploit the rotation of the Earth. Gyrocompasses are widely used on [[ship]]s. They have two main advantages over magnetic compasses:
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| * they find ''true north'', i.e., the direction of [[Earth]]'s rotational axis, as opposed to [[Magnetic North Pole#Magnetic north and magnetic declination|magnetic north]],
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| * they are not affected by [[ferromagnetic]] metal (including iron, steel, cobalt, nickel, and various alloys) in a ship's hull. (No compass is affected by nonferromagnetic metal, although a magnetic compass will be affected by any kind of wires with [[electric current]] passing through them.)
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| Large ships typically rely on a gyrocompass, using the magnetic compass only as a backup. Increasingly, electronic [[fluxgate compass]]es are used on smaller vessels. However, magnetic compasses are still widely in use as they can be small, use simple reliable technology, are comparatively cheap, often easier to use than [[GPS]], require no energy supply, and unlike GPS, are not affected by objects, e.g. trees, that can block the reception of electronic signals.
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| ===Solid state compasses===
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| {{Main|Magnetometer}}
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| Small compasses found in clocks, [[mobile phone]]s, and other electronic devices are [[Solid-state (electronics)|solid-state]] compasses, usually built out of two or three [[magnetic field sensors]] that provide data for a microprocessor. The correct heading relative to the compass is calculated using [[trigonometry]].
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| Often, the device is a discrete component which outputs either a digital or analog signal proportional to its orientation. This signal is interpreted by a [[microcontroller|controller]] or [[microprocessor]] and used either internally, or sent to a display unit. The sensor uses highly calibrated internal electronics to measure the response of the device to the Earth's magnetic field.
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| [[GPS receiver]]s using two or more antennae can now achieve 0.5° in heading accuracy and have startup times in seconds rather than hours for gyrocompass systems. Manufactured primarily for maritime applications, they can also detect pitch and roll of ships.
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| === Specialty compasses ===
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| [[File:Brunton.JPG|thumb|A standard Brunton Geo, used commonly by geologists.]]
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| Apart from navigational compasses, other specialty compasses have also been designed to accommodate specific uses. These include:
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| * [[Qibla compass]], which is used by Muslims to show the direction to Mecca for prayers.
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| * Optical or [[Prism (optics)|prismatic]] [[hand bearing compass|hand-bearing compass]], most often used by surveyors, but also by cave explorers, foresters, and geologists. This compasses ordinarily uses a liquid-damped capsule<ref>Kramer, Melvin G., U.S. Patent No. 4175333, ''Magnetic Compass'', Riverton, Wyoming: The Brunton Company, pub. 27 November 1979: The ''Brunton Pocket Transit'', which uses magnetic induction damping, is an exception.</ref> and magnetized floating compass dial with an integral optical (direct or lensatic) or prismatic sight, often fitted with built-in photoluminescent or battery-powered illumination.<ref name=des>{{cite book | author = Johnson, G. Mark | date = 2003-03-26 | title = The Ultimate Desert Handbook | publisher = McGraw-Hill Professional | isbn = 0-07-139303-X | pages = 113–114}}</ref> Using the optical or prism sight, such compasses can be read with extreme accuracy when taking bearings to an object, often to fractions of a degree. Most of these compasses are designed for heavy-duty use, with high-quality needles and jeweled bearings, and many are fitted for tripod mounting for additional accuracy.<ref name=des/>
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| * Trough compasses, mounted in a rectangular box whose length was often several times its width, date back several centuries. They were used for land surveying, particularly with plane tables.
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| === Limitations of the magnetic compass ===
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| The compass is very stable in areas close to the equator, which is far from "magnetic north". As the compass is moved closer and closer to one of the magnetic poles of the Earth, the compass becomes more sensitive to crossing its magnetic field lines. At some point close to the magnetic pole the compass will not indicate any particular direction but will begin to drift. Also, the needle starts to point up or down when getting closer to the poles, because of the so-called [[magnetic inclination]]. Cheap compasses with bad [[bearing (mechanical)|bearings]] may get stuck because of this and therefore indicate a wrong direction.
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| Magnetic compasses are influenced by any fields other than Earth's. Local environments may contain magnetic mineral deposits and artificial sources such as [[MRI]]s, large iron or steel bodies, electrical engines or strong permanent magnets. Any electrically conductive body produces its own magnetic field when it is carrying an electric current. Magnetic compasses are prone to errors in the neighborhood of such bodies. Some compasses include magnets which can be adjusted to compensate for external magnetic fields, making the compass more reliable and accurate.
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| A compass is also subject to errors when the compass is accelerated or decelerated in an airplane or automobile. Depending on which of the Earth's hemispheres the compass is located and if the force is acceleration or deceleration the compass will increase or decrease the indicated heading. Compasses that include compensating magnets are especially prone to these errors, since accelerations tilt the needle, bringing it closer or further from the magnets.
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| Another error of the mechanical compass is turning error. When one turns from a heading of east or west the compass will lag behind the turn or lead ahead of the turn. Magnetometers, and substitutes such as gyrocompasses, are more stable in such situations.
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| == Construction of a compass ==
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| === Magnetic needle ===
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| A magnetic rod is required when constructing a compass. This can be created by aligning an iron or steel rod with Earth's magnetic field and then tempering or striking it. However, this method produces only a weak magnet so other methods are preferred. For example, a magnetised rod can be created by repeatedly rubbing an iron rod with a magnetic [[lodestone]]. This magnetised rod (or magnetic needle) is then placed on a low friction surface to allow it to freely pivot to align itself with the magnetic field. It is then labeled so the user can distinguish the north-pointing from the south-pointing end; in modern convention the north end is typically marked in some way.
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| === Needle-and-bowl device ===
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| If a needle is rubbed on a [[lodestone]] or other magnet, the needle becomes magnetized. When it is inserted in a cork or piece of wood, and placed in a bowl of water it becomes a compass. Such devices were universally used as compass until the invention of the box-like compass with a 'dry' pivoting needle sometime around 1300.
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| ===Points of the compass===
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| {{Main|Boxing the compass}}
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| [[File:Boussole fantassin russe.jpg|thumb|Wrist compass of the Soviet Army with counterclockwise double graduation: 60° (like a watch) and 360°.]]
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| Originally, many compasses were marked only as to the direction of magnetic north, or to the four cardinal points (north, south, east, west). Later, these were divided, in China into 24, and in Europe into 32 equally spaced points around the compass card. For a table of the thirty-two points, see [[Boxing the compass#Compass points|compass points]].
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| In the modern era, the 360-degree system took hold. This system is still in use today for civilian navigators. The degree system spaces 360 equidistant points located clockwise around the compass dial. In the 19th century some European nations adopted the "[[grad (angle)|grad]]" (also called grade or gon) system instead, where a right angle is 100 grads to give a circle of 400 grads. Dividing grads into tenths to give a circle of 4000 decigrades has also been used in armies.
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| Most military forces have adopted the French "[[Angular mil|mil]]lieme" system. This is an approximation of a milli-radian (6283 per circle), in which the compass dial is spaced into 6400 units or "mils" for additional precision when measuring angles, laying artillery, etc. The value to the military is that one [[angular mil]] subtends approximately one metre at a distance of one kilometer. Imperial Russia used a system derived by dividing the circumference of a circle into chords of the same length as the radius. Each of these was divided into 100 spaces, giving a circle of 600. The [[Soviet Union]] divided these into tenths to give a circle of 6000 units, usually translated as "mils". This system was adopted by the former [[Warsaw Pact]] countries ([[Soviet Union]], [[East Germany|GDR]] etc.), often counterclockwise (see picture of wrist compass). This is still in use in Russia.
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| ===Compass balancing (magnetic dip)===
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| Because the Earth's magnetic field's inclination and intensity vary at different latitudes, compasses are often balanced during manufacture so that the dial or needle will be level, eliminating needle drag which can give inaccurate readings. Most manufacturers balance their compass needles for one of five zones, ranging from zone 1, covering most of the [[Northern Hemisphere]], to zone 5 covering [[Australia]] and the southern oceans. This individual zone balancing prevents excessive dipping of one end of the needle which can cause the compass card to stick and give false readings.<ref name=globalcompass>[http://www.mapworld.co.nz/global.html Global compasses], MapWorld.</ref>
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| Some compasses feature a special needle balancing system that will accurately indicate magnetic north regardless of the particular magnetic zone. Other magnetic compasses have a small sliding counterweight installed on the needle itself. This sliding counterweight, called a 'rider', can be used for counterbalancing the needle against the dip caused by inclination if the compass is taken to a zone with a higher or lower dip.<ref name=globalcompass/>
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| ===Compass correction===
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| {{Main|Magnetic deviation}}
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| [[File:MuseeMarine-compas-p1000468.jpg|thumb|upright|A [[binnacle]] containing a ship's standard compass, with the two iron balls which correct the effects of [[ferromagnetism|ferromagnetic]] materials. This unit is on display in a museum.]]
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| Like any magnetic device, compasses are affected by nearby ferrous materials, as well as by strong local electromagnetic forces. Compasses used for wilderness land navigation should not be used in proximity to ferrous metal objects or electromagnetic fields (car electrical systems, automobile engines, steel [[piton]]s, etc.) as that can affect their accuracy.<ref name=des>{{cite book | author = Johnson, G. Mark | date = 2003-03-26 | title = The Ultimate Desert Handbook | publisher = McGraw-Hill Professional | isbn = 0-07-139303-X | page = 122}}</ref> Compasses are particularly difficult to use accurately in or near trucks, cars or other mechanized vehicles even when corrected for deviation by the use of built-in magnets or other devices. Large amounts of ferrous metal combined with the on-and-off electrical fields caused by the vehicle's ignition and charging systems generally result in significant compass errors.
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| At sea, a ship's compass must also be corrected for errors, called [[Magnetic deviation|deviation]], caused by iron and steel in its structure and equipment. The ship is ''swung'', that is rotated about a fixed point while its heading is noted by alignment with fixed points on the shore. A compass deviation card is prepared so that the navigator can convert between compass and magnetic headings. The compass can be corrected in three ways. First the [[lubber line]] can be adjusted so that it is aligned with the direction in which the ship travels, then the effects of permanent magnets can be corrected for by small magnets fitted within the case of the compass. The effect of [[ferromagnetism|ferromagnetic]] materials in the compass's environment can be corrected by two iron balls mounted on either side of the compass binnacle. The coefficient <math>a_0</math> representing the error in the lubber line, while <math>a_1,b_1</math> the ferromagnetic effects and <math>a_2,b_2</math> the non-ferromagnetic component{{Elucidate|date=December 2012}}.
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| A similar process is used to calibrate the compass in light general aviation aircraft, with the compass deviation card often mounted permanently just above or below the magnetic compass on the instrument panel. Fluxgate electronic compasses can be calibrated automatically, and can also be programmed with the correct local compass variation so as to indicate the true heading.
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| == Using a compass ==
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| [[File:CompassUseMapMarked.jpg|thumb|Turning the compass scale on the map (D - the local magnetic declination).]]
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| [[File:CompassUseTargetMarked.jpg|thumb|When the needle is aligned with and superimposed over the outlined orienting arrow on the bottom of the capsule, the degree figure on the compass ring at the direction-of-travel (DOT) indicator gives the magnetic bearing to the target (mountain).]]
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| A magnetic compass points to magnetic north pole, which is approximately 1,000 miles from the true geographic North Pole. A magnetic compass's user can determine true North by finding the magnetic north and then correcting for variation and deviation. [[Magnetic declination|Variation]] is defined as the angle between the direction of true (geographic) north and the direction of the [[meridian (geography)|meridian]] between the magnetic poles. Variation values for most of the oceans had been calculated and published by 1914.<ref>Wright, Monte, Most Probable Position, University Press of Kansas, Lawrence, 1972, p.7</ref> [[Magnetic deviation|Deviation]] refers to the response of the compass to local magnetic fields caused by the presence of iron and electric currents; one can partly compensate for these by careful location of the compass and the placement of compensating magnets under the compass itself. Mariners have long known that these measures do not completely cancel deviation; hence, they performed an additional step by measuring the compass bearing of a landmark with a known magnetic bearing. They then pointed their ship to the next compass point and measured again, graphing their results. In this way, correction tables could be created, which would be consulted when compasses were used when traveling in those locations.
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| Mariners are concerned about very accurate measurements; however, casual users need not be concerned with differences between magnetic and true North. Except in areas of extreme magnetic declination variance (20 degrees or more), this is enough to protect from walking in a substantially different direction than expected over short distances, provided the terrain is fairly flat and visibility is not impaired. By carefully recording distances (time or paces) and magnetic bearings traveled, one can plot a course and return to one's starting point using the compass alone.<ref name=des>{{cite book | author = Johnson, G. Mark | date = 2003-03-26 | title = The Ultimate Desert Handbook | publisher = McGraw-Hill Professional | isbn = 0-07-139303-X | page = 149}}</ref>
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| [[File:Measuring azimuth with a compass.png|left|thumb|Soldier using a prismatic compass to get an azimuth.]]
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| Compass navigation in conjunction with a map (''terrain association'') requires a different method. To take a map bearing or ''true bearing'' (a bearing taken in reference to true, not magnetic north) to a destination with a [[protractor compass]], the edge of the compass is placed on the map so that it connects the current location with the desired destination (some sources recommend physically drawing a line). The orienting lines in the base of the compass dial are then rotated to align with actual or true north by aligning them with a marked line of longitude (or the vertical margin of the map), ignoring the compass needle entirely.<ref name=des>{{cite book | author = Johnson, G. Mark | date = 2003-03-26 | title = The Ultimate Desert Handbook | publisher = McGraw-Hill Professional | isbn = 0-07-139303-X | pages = 134–135}}</ref> The resulting ''true bearing'' or map bearing may then be read at the degree indicator or direction-of-travel (DOT) line, which may be followed as an ''[[azimuth]]'' (course) to the destination. If a ''magnetic'' north bearing or ''compass bearing'' is desired, the compass must be adjusted by the amount of magnetic declination before using the bearing so that both map and compass are in agreement.<ref name=des/> In the given example, the large mountain in the second photo was selected as the target destination on the map. Some compasses allow the scale to be adjusted to compensate for the local magnetic declination; if adjusted correctly, the compass will give the true bearing instead of the magnetic bearing.
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| The modern hand-held [[protractor compass]] always has an additional direction-of-travel (DOT) arrow or indicator inscribed on the baseplate. To check one's progress along a course or azimuth, or to ensure that the object in view is indeed the destination, a new compass reading may be taken to the target if visible (here, the large mountain). After pointing the DOT arrow on the baseplate at the target, the compass is oriented so that the needle is superimposed over the orienting arrow in the capsule. The resulting bearing indicated is the magnetic bearing to the target. Again, if one is using "true" or map bearings, and the compass does not have preset, pre-adjusted declination, one must additionally add or subtract [[magnetic declination]] to convert the ''magnetic bearing'' into a ''true bearing''. The exact value of the magnetic declination is place-dependent and varies over time, though declination is frequently given on the map itself or obtainable on-line from various sites. If the hiker has been following the correct path, the compass' corrected (true) indicated bearing should closely correspond to the true bearing previously obtained from the map.
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| A compass should be laid down on a level surface so that the needle only rests or hangs on the bearing fused to the compass casing - if used at a tilt, the needle might touch the casing on the compass and not move freely, hence not pointing to the magnetic north accurately, giving a faulty reading. To see if the needle is well leveled, look closely at the needle, and tilt it slightly to see if the needle is swaying side to side freely and the needle is not contacting the casing of the compass. If the needle tilts to one direction, tilt the compass slightly and gently to the opposing direction until the compass needle is horizontal, lengthwise. Items to avoid around compasses are magnets of any kind and any electronics. Magnetic fields from electronics can easily disrupt the needle, avoiding it from pointing with the earth's magnetic fields, causing interference. The earth's natural magnetic forces are considerably weak, measuring at 0.5 [[Gauss]] and magnetic fields from household electronics can easily exceed it, overpowering the compass needle. Exposure to strong magnets, or magnetic interference can sometimes cause the magnetic poles of the compass needle to differ or even reverse. Avoid iron rich deposits when using a compass, for example, certain rocks which contain magnetic minerals, like [[Magnetite]]. This is often indicated by a rock with a surface which is dark and has a metallic luster, not all magnetic mineral bearing rocks have this indication. To see if a rock or an area is causing interference on a compass, get out of the area, and see if the needle on the compass moves. If it does, it means that the area or rock the compass was previously at/on is causing interference and should be avoided.
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| ==See also==
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| * [[Absolute bearing]]
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| * [[Aircraft compass turns]]
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| * [[Astrocompass]]
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| * [[Beam compass]]
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| * [[Binnacle]] - nautical compass incorporating magnetic correction
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| * [[Boxing the compass]]
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| * [[Brunton compass]]
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| * [[Coordinate]]s
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| * [[Earth Inductor Compass]]
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| * [[Fibre optic gyrocompass]]
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| * [[Fluxgate compass]]
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| * [[Geological compass]]
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| * [[Gyrocompass]]
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| * [[Hand compass]]
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| * [[Inertial navigation system]]
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| * [[Magnetic dip]]
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| * [[Marching line]]
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| * [[Magnetic Declination]]
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| * [[Magnetic deviation]]
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| * [[Pelorus (instrument)]]
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| * [[Radio compass]]
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| * [[Radio direction finder]]
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| * [[Relative bearing]]
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| * [[Wrist compass]]
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| ==Notes==
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| {{reflist|colwidth=30em}}
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| ==References==
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| * Admiralty, Great Britain (1915) ''Admiralty manual of navigation, 1914'', Chapter XXV: "The Magnetic Compass (continued): the analysis and correction of the deviation", London : HMSO, 525 p.
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| * [[Amir Aczel|Aczel, Amir D.]] (2001) ''The Riddle of the Compass: The Invention that Changed the World'', 1st Ed., New York : Harcourt, ISBN 0-15-600753-3
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| *Carlson, John B. (1975) [http://www.sciencemag.org/cgi/content/abstract/189/4205/753 "Lodestone Compass: Chinese or Olmec Primacy?]: Multidisciplinary analysis of an Olmec hematite artifact from San Lorenzo, Veracruz, Mexico”, ''Science'', '''189''' (4205 : 5 September), p. 753-760, [[Digital object identifier|DOI]] 10.1126/science.189.4205.753
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| * [[Frances Gies and Joseph Gies|Gies, Frances and Gies, Joseph]] (1994) ''Cathedral, Forge, and Waterwheel: Technology and Invention in the Middle Age'', New York : HarperCollins, ISBN 0-06-016590-1
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| *Gubbins, David, ''Encyclopedia of Geomagnetism and Paleomagnetism'', Springer Press (2007), ISBN 1-4020-3992-1, ISBN 978-1-4020-3992-8
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| * Gurney, Alan (2004) ''Compass: A Story of Exploration and Innovation'', London : Norton, ISBN 0-393-32713-2
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| * Johnson, G. Mark, ''The Ultimate Desert Handbook'', 1st Ed., Camden, Maine: McGraw-Hill (2003), ISBN 0-07-139303-X
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| * {{Cite journal |last=King |first=David A. |year=1983 |title=The Astronomy of the Mamluks |journal=[[Isis (journal)|Isis]] |volume=74 |issue=4 |pages=531–555 |doi=10.1086/353360 |ref=harv |postscript=<!--None--> }}
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| * Kreutz, Barbara M. (1973) "Mediterranean Contributions to the Medieval Mariner's Compass", ''Technology and Culture'', '''14''' (3: July), p. 367–383
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| * Lane, Frederic C. (1963) "The Economic Meaning of the Invention of the Compass", ''The American Historical Review'', '''68''' (3: April), p. 605–617
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| * Li Shu-hua (1954) "Origine de la Boussole 11. Aimant et Boussole", ''Isis'', '''45''' (2: July), p. 175–196
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| * Ludwig, Karl-Heinz and Schmidtchen, Volker (1997) ''Metalle und Macht: 1000 bis 1600'', Propyläen Technikgeschichte, Berlin : Propyläen-Verl., ISBN 3-549-05633-8
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| * Ma, Huan (1997) ''Ying-yai sheng-lan'' [The overall survey of the ocean's shores (1433)], Feng, Ch'eng-chün (ed.) and Mills, J.V.G. (transl.), Bangkok : White Lotus Press, ISBN 974-8496-78-3
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| * Needham, Joseph (1986) ''Science and civilisation in China'', Vol. 4: "Physics and physical technology", Pt. 1: "Physics", Taipei: Caves Books, originally publ. by Cambridge University Press (1962), ISBN 0-521-05802-3
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| * Needham, Joseph and Ronan, Colin A. (1986) ''The shorter Science and civilisation in China : an abridgement of Joseph Needham's original text'', Vol. 3, Chapter 1: "Magnetism and Electricity", Cambridge University Press, ISBN 0-521-25272-5
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| *Seidman, David, and Cleveland, Paul, ''The Essential Wilderness Navigator'', Ragged Mountain Press (2001), ISBN 0-07-136110-3
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| *Taylor, E.G.R. (1951) "The South-Pointing Needle", ''Imago Mundi'', '''8''', p. 1–7
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| * Williams, J.E.D. (1992) ''From Sails to Satellites: the origin and development of navigational science'', Oxford University Press, ISBN 0-19-856387-6
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| * Wright, Monte Duane (1972) ''Most Probable Position: A History of Aerial Navigation to 1941'', The University Press of Kansas, Library of Congress Catalog Card Number 72-79318
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| * Zhou, Daguan (2007) ''The customs of Cambodia'', translated into English from the French version by Paul Pelliot of Zhou's Chinese original by J. Gilman d'Arcy Paul, Phnom Penh : Indochina Books, prev publ. by Bangkok : Siam Society (1993), ISBN 974-8298-25-6
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| ==External links==
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| {{Commons}}
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| * [http://www.magnet.fsu.edu/mediacenter/slideshows/compass/index.html How to Make a Compass] Audio slideshow from the National High Magnetic Field Laboratory
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| * Paul J. Gans, [http://scholar.chem.nyu.edu/tekpages/compass.html The Medieval Technology Pages: Compass]
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| * Evening Lecture To The British Association At The Southampton Meeting on Friday, August 25, 1882 [http://zapatopi.net/kelvin/papers/the_tides.html]. Refers to compass correction by [[Fourier series]].
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| * Arrick Robots. Robotics.com Example implementation for digital solid-state compass. ''[http://www.robotics.com/arobot/compass.html ARobot Digital Compass App Note]''
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| * How a tilt sensor works. David Pheifer ''[http://www.sensorsmag.com/articles/0500/120/main.shtml]''
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| *[http://thegearjunkie.com/the-thumb-compass The Gear Junkie] - review of two orienteering thumb compasses
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| *[http://www.odoo.tv/The-good-Compass.62.0.html?&L=1 The good compass video] - A video about important abilities a compass should have (narration in German)
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| *[http://www.compassmuseum.com/ COMPASSIPEDIA, the great virtual Compass Museum] gives comprehensive information about all sorts of compasses and how to use them.
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| *[http://geographyfieldwork.com/UsingCompass.htm Geography fieldwork]
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| {{Flight instruments}}
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| {{Aircraft components}}
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| {{aviation lists}}
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| {{Orienteering|type=collapsed}}
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| [[Category:Chinese inventions]]
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| [[Category:Magnetic devices]]
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| [[Category:Navigational equipment]]
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| {{Link GA|es}}
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