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[[Image:Compass in a wooden frame.jpg|thumb|Compass in a wooden box]] | [[Image:Compass in a wooden frame.jpg|thumb|Compass in a wooden box]] | ||
A '''compass''' (or '''mariner's compass''') is a navigational instrument for finding directions on the earth. It consists of a magnetized pointer free to align itself accurately with [[Earth's magnetic field|Earth]]'s | A '''compass''' (or '''mariner's compass''') is a navigational instrument for finding directions on the earth. It consists of a magnetized pointer free to align itself accurately with [[Earth's magnetic field|Earth]]'s magnetic field, which is of great assistance in [[navigation]]. The [[cardinal points]] are [[north]], south, east and west. A compass can be used in conjunction with a [[chronometer]] and a [[sextant]] to provide a very accurate [[navigation]] capability. This device greatly improved maritime trade by making travel safer and more efficient. An early form of compass was invented in China in the 11th century. The familiar mariner's compass was invented in Europe around 1300. | ||
More technically, a ''compass'' is a magnetic device using a needle to indicate the direction of the magnetic north of a planet's [[magnetosphere]]. Any [[Measuring instrument|instrument]] with a magnetized bar or needle turning freely upon a pivot and pointing in a [[north]]erly and | More technically, a ''compass'' is a magnetic device using a needle to indicate the direction of the magnetic north of a planet's [[magnetosphere]]. Any [[Measuring instrument|instrument]] with a magnetized bar or needle turning freely upon a pivot and pointing in a [[north]]erly and southerly direction can be considered a compass. A '''compass dial''' is a small pocket compass with a [[sundial]]. A '''variation compass''' is a specific instrument of a delicate type of construction. It is used by observing variations of the needle. A gyrocompass or astrocompass can also be used to ascertain [[True north]]. | ||
== History of the navigational compass == | == History of the navigational compass == | ||
=== Pre-history === | === Pre-history === | ||
Prior to the introduction of the compass, direction at sea was primarily determined by the position of celestial bodies. Navigation was supplemented in some places by the use of [[Sounding line|soundings]]. Difficulties arose where the sea was too deep for soundings and conditions were continually overcast or foggy. Thus the compass was not of the same utility everywhere. For example, the Arabs could generally rely on clear skies in navigating the [[Persian Gulf]] and the [[Indian Ocean]] (as well as the predictable nature of the | Prior to the introduction of the compass, direction at sea was primarily determined by the position of celestial bodies. Navigation was supplemented in some places by the use of [[Sounding line|soundings]]. Difficulties arose where the sea was too deep for soundings and conditions were continually overcast or foggy. Thus the compass was not of the same utility everywhere. For example, the Arabs could generally rely on clear skies in navigating the [[Persian Gulf]] and the [[Indian Ocean]] (as well as the predictable nature of the monsoons). This may explain in part their relatively late adoption of the compass. Mariners in the relatively shallow [[Baltic Sea|Baltic]] made extensive use of soundings. | ||
=== Developments in China === | === Developments in China === | ||
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* The earliest Chinese literary reference to '''magnetism''' lies in a [[4th century BC]] book called ''Book of the Devil Valley Master'' (鬼谷子): "The [[lodestone]] makes iron come or it attracts it."<ref>Li Shu-hua, “Origine de la Boussole 11. Aimant et Boussole,” ''Isis'', Vol. 45, No. 2. (Jul., 1954), p.175</ref> | * The earliest Chinese literary reference to '''magnetism''' lies in a [[4th century BC]] book called ''Book of the Devil Valley Master'' (鬼谷子): "The [[lodestone]] makes iron come or it attracts it."<ref>Li Shu-hua, “Origine de la Boussole 11. Aimant et Boussole,” ''Isis'', Vol. 45, No. 2. (Jul., 1954), p.175</ref> | ||
* The first mention of the '''magnetic attraction of a needle''' is to be found in a Chinese work composed between 20 and 100 AD (''Louen-heng''): "A lodestone attracts a needle."<ref>Li Shu-hua, “Origine de la Boussole 11. Aimant et Boussole,” ''Isis'', Vol. 45, No. 2. (Jul., 1954), p.176</ref> In 1948, the scholar Wang Tchen-touo tentatively constructed a 'compass' in the form of south-indicating spoon on the basis of this text. However, it should be noted that "there is no explicit mention of a magnet in the ''Louen-heng''" and that "beforehand it needs to assume some hypotheses to arrive at such a conclusion".<ref>Li Shu-hua, “Origine de la Boussole 11. Aimant et Boussole,” ''Isis'', Vol. 45, No. 2. (Jul., 1954), p.180</ref> | * The first mention of the '''magnetic attraction of a needle''' is to be found in a Chinese work composed between 20 and 100 AD (''Louen-heng''): "A lodestone attracts a needle."<ref>Li Shu-hua, “Origine de la Boussole 11. Aimant et Boussole,” ''Isis'', Vol. 45, No. 2. (Jul., 1954), p.176</ref> In 1948, the scholar Wang Tchen-touo tentatively constructed a 'compass' in the form of south-indicating spoon on the basis of this text. However, it should be noted that "there is no explicit mention of a magnet in the ''Louen-heng''" and that "beforehand it needs to assume some hypotheses to arrive at such a conclusion".<ref>Li Shu-hua, “Origine de la Boussole 11. Aimant et Boussole,” ''Isis'', Vol. 45, No. 2. (Jul., 1954), p.180</ref> | ||
* The earliest reference to a magnetic device as a '''direction finder''' is recorded in a | * The earliest reference to a magnetic device as a '''direction finder''' is recorded in a Song dynasty book dated to 1040-44. Here we find 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." There is, however, no mention of a use for navigation, nor how the fish was magnetized.<ref>Li Shu-hua, “Origine de la Boussole 11. Aimant et Boussole,” ''Isis'', Vol. 45, No. 2. (Jul., 1954), p.181</ref> | ||
* The first incontestable reference to a '''magnetized needle''' in Chinese literature appears as late as 1086.<ref>Li Shu-hua, “Origine de la Boussole 11. Aimant et Boussole,” ''Isis'', Vol. 45, No. 2. (Jul., 1954), p.182f.</ref> The ''Dream Pool Essay'' written by | * The first incontestable reference to a '''magnetized needle''' in Chinese literature appears as late as 1086.<ref>Li Shu-hua, “Origine de la Boussole 11. Aimant et Boussole,” ''Isis'', Vol. 45, No. 2. (Jul., 1954), p.182f.</ref> The ''Dream Pool Essay'' written by Song Dynasty scholar [[Shen Kua]] 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 Kua pointed out that a needle prepared this way sometimes pointed south, sometimes north. | ||
* The earliest recorded actual use of a '''magnetized needle for navigational purposes''' then is to be found in Zhu Yu's book ''Pingzhou Table Talks'' (Pingzhou Ke Tan) of AD [[1117]]: ''The navigator knows the geography, he watches the stars at night, watches the sun at day; when it is dark and cloudy, he watches the compass.'' | * The earliest recorded actual use of a '''magnetized needle for navigational purposes''' then is to be found in Zhu Yu's book ''Pingzhou Table Talks'' (Pingzhou Ke Tan) of AD [[1117]]: ''The navigator knows the geography, he watches the stars at night, watches the sun at day; when it is dark and cloudy, he watches the compass.'' | ||
*A pilot's compass handbook titled Shun Feng Xiang Song (Fair Winds for Escort) in the Oxford [[Bodleian Library]] contains great details about the use of compass in navigation. | *A pilot's compass handbook titled Shun Feng Xiang Song (Fair Winds for Escort) in the Oxford [[Bodleian Library]] contains great details about the use of compass in navigation. | ||
=== Question of Diffusion === | === Question of Diffusion === | ||
[[image:Compass thumbnail.jpg|thumb|right|Navigational | [[image:Compass thumbnail.jpg|thumb|right|Navigational mariner's compass]] There is much debate on what happened to the compass after its first appearance with the Chinese. Different theories include: | ||
* Travel of the compass from China to the Middle East via the [[Silk Road]], and then to Europe | * Travel of the compass from China to the Middle East via the [[Silk Road]], and then to Europe | ||
* Direct transfer of the compass from China to Europe, and then later from Europe to the Middle East | * Direct transfer of the compass from China to Europe, and then later from Europe to the Middle East | ||
* Independent creation of the compass in the Europe and then its transfer thereafter to the Middle East. | * Independent creation of the compass in the Europe and then its transfer thereafter to the Middle East. | ||
The latter two are supported by evidence of the earlier mentioning of the compass in European works rather than Arabic. The first European mention of a magnetized needle and its use among sailors occurs in | The latter two are supported by evidence of the earlier mentioning of the compass in European works rather than Arabic. 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), probably written in Paris in 1190.<ref>Barbara M. Kreutz, “Mediterranean Contributions to the Medieval Mariner's Compass,” ''Technology and Culture'', Vol. 14, No. 3. (Jul., 1973), p.368</ref> Other evidence for this includes the Arabic word for "Compass" (''al-konbas''), possibly being a derivation of the old Italian word for compass. | ||
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>Barbara M. Kreutz, “Mediterranean Contributions to the Medieval Mariner's Compass,” ''Technology and Culture'', Vol. 14, No. 3. (Jul., 1973), 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. There is also a slightly earlier non-Mediterranean Muslim reference to an iron fish-like compass in a Persian talebook from 1232.<ref>Barbara M. Kreutz, “Mediterranean Contributions to the Medieval Mariner's Compass,” ''Technology and Culture'', Vol. 14, No. 3. (Jul., 1973), 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>Barbara M. Kreutz, “Mediterranean Contributions to the Medieval Mariner's Compass,” ''Technology and Culture'', Vol. 14, No. 3. (Jul., 1973), 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. There is also a slightly earlier non-Mediterranean Muslim reference to an iron fish-like compass in a Persian talebook from 1232.<ref>Barbara M. Kreutz, “Mediterranean Contributions to the Medieval Mariner's Compass,” ''Technology and Culture'', Vol. 14, No. 3. (Jul., 1973), p.370</ref> | ||
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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. | 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. | ||
Large ships typically rely on a | Large ships typically rely on a gyrocompass, using the more reliable magnetic compass for back-up. Increasingly electronic [[fluxgate]] compasses are used on smaller vessels. | ||
Some modern military compases, like the [SandY-183 http://www.orau.org/PTP/collection/radioluminescent/armycompass.htm](the one pictured) contains the radioactive material [[Tritium]] (<small>3</small>H) and a combination of Phosphorous. The SandY-183 contained 120mCi (millicuries) of tritium. The name SandY-183 is derived from the name of the company, Stocker and Yale (SandY). | Some modern military compases, like the [SandY-183 http://www.orau.org/PTP/collection/radioluminescent/armycompass.htm](the one pictured) contains the radioactive material [[Tritium]] (<small>3</small>H) and a combination of Phosphorous. The SandY-183 contained 120mCi (millicuries) of tritium. The name SandY-183 is derived from the name of the company, Stocker and Yale (SandY). | ||
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However, compass navigation used in conjunction with a map (''terrain association'') requires a different compass 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. 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. In the given example, the large mountain in the second photo was selected as the target destination on the map. | However, compass navigation used in conjunction with a map (''terrain association'') requires a different compass 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. 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. In the given example, the large mountain in the second photo was selected as the target destination on the map. | ||
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 | 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 not, any local walker club should know it. 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. | ||
This method is sometimes known as the '''[http://www.silva.se/outdoor/misc/123.htm Silva 1-2-3 System]''', after [[Silva Compass]], manufacturers of the first protractor compasses. | This method is sometimes known as the '''[http://www.silva.se/outdoor/misc/123.htm Silva 1-2-3 System]''', after [[Silva Compass]], manufacturers of the first protractor compasses. | ||
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== See also == | == See also == | ||
* | * Azimuth | ||
* Beam compass | * Beam compass | ||
* | * coordinates | ||
* fluxgate compass | * fluxgate compass | ||
* [[global positioning system|global positioning system (GPS)]] | * [[global positioning system|global positioning system (GPS)]] | ||
* | * gyrocompass | ||
* | * Gyrosin compass | ||
* | * gyrostatic compass | ||
* inertial navigation system | * inertial navigation system | ||
* [[Marching line]] | * [[Marching line]] | ||
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* [[Silva Compass]] | * [[Silva Compass]] | ||
* [[Suunto]] | * [[Suunto]] | ||
* | * surveyor's compass, or circumferentor | ||
* | * Thumb compass | ||
* [[Wrist compass]] | * [[Wrist compass]] | ||
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[[br:Nadoz-vor]] | [[br:Nadoz-vor]] | ||
[[bg:Компас]] | [[bg:Компас]] | ||
bs:Kompas | |||
ca:Brúixola | ca:Brúixola | ||
[[el:Πυξίδα]] | [[el:Πυξίδα]] | ||
[[fa:قطبنما]] | [[fa:قطبنما]] | ||
[[gl:Compás]] | [[gl:Compás]] | ||
ko:나침반 | |||
id:Kompas | id:Kompas | ||
[[he:מצפן]] | [[he:מצפן]] | ||
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[[yi:קאמפאס]] | [[yi:קאמפאס]] | ||
[[zh:指南针]] | [[zh:指南针]] | ||
[[Category:Hiking equipment]] | [[Category:Hiking equipment]] | ||
[[Category:Orientation]] | [[Category:Orientation]] | ||
[[ar:بوصلة]] | |||
[[da:Kompas]] | |||
[[de:Kompass]] | [[de:Kompass]] | ||
[[es:Brújula]] | |||
[[fi:Kompassi]] | [[fi:Kompassi]] | ||
[[fr:Boussole]] | [[fr:Boussole]] | ||
[[it:Bussola]] | |||
[[nl:Kompas]] | [[nl:Kompas]] | ||
[[pt:Bússola]] | [[pt:Bússola]] | ||
[[scout-o-wiki:Kompass]] | |||
[[sv:Kompass]] | [[sv:Kompass]] | ||