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10. Payment - ready to pay for your Compass, then use your credit card or PayPal! Be aware of companies that don't accept them, there may be genuine reasons but given the huge amount of choice you have when buying online there is no reason at all not to buy via credit card or PayPal.



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's magnetic field, which is of great assistance in navigation. The face of the compass generally highlights the cardinal points of north, south, east and west. A compass can be used in conjunction with a marine chronometer to calculate longitude) and a sextant to calculate latitude, providing a very accurate navigation capability. This device greatly improved maritime trade by making travel safer and more efficient. An early form of the compass was invented in China in the 11th century. The familiar mariner's compass was invented in Europe around 1300, from whence later originated the liquid compass and the gyrocompass.

More technically, a compass is a magnetic device using a needle to indicate the direction of the North Magnetic Pole of a planet's magnetosphere. Any Measuring instrument with a magnetized bar or needle turning freely upon a pivot and pointing in a northerly and southerly direction can be considered a compass. A compass dial is a small pocket compass with a sundial. A variation compass is a specific instrument of a delicate type of construction. It is used by observing variations of the needle. A gyrocompass or astrocompass, which does not depend on the earth's magnetic field for its operation, can also be used to find true north.

History of the navigational compass 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. 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 made extensive use of soundings. The astrolabe, originally invented in the Hellenistic civilization, was significantly improved upon by later medieval Islamic astronomy and Islamic Golden Age#Age of discovery who used it to aid in navigation.

Mesoamerica The find of an Olmec hematite artifact, fitted with a sighting mark and found in experiment as fully operational as a compass, has led the American astronomer John Carlson after radiocarbon dating to conclude that "the Olmec may have discovered and used the geomagnetic lodestone compass earlier than 1000 BC".Carlson, p. 753–760 Carlson suggests that the Olmecs may have used such devices for directional orientation of the dwellings of the living and the interments of the dead.

Needle-and-bowl device By rubbing a needle on silk, the needle becomes magnetized and when placed in a straw and put in a puddle of water it becomes a compass. This device was universally used as a compass until the introduction of the box-like compass with a pivoting 'dry' needle around 1300.

China Due to disagreement as to when the compass was invented, it may be appropriate to list some noteworthy History of China literary references offered as possible evidence for its antiquity, in chronological order:



Thus, the first clear instance of a magnetic direction finder, a compass, appeared ca. 1044. However, it should be pointed out that the compass remained in use by the Chinese in the form of a magnetic needle floating in a bowl of water.Kreutz, p. 373

According to 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.Needham p. 255 Evidence of this is found in the Shilinguangji ('Guide Through the Forest of Affairs'), first published in 1325 by Chen Yuanjing, although its compilation had taken place between 1100 and 1250 AD. 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 loadstone sealed in by wax, and if rotated, the needle at the tail would always point in the northern cardinal direction. Although the 14th century European compass-card in box frame and dry pivot needle was adopted in China after its use was taken by Japanese people pirates in the 16th century (who had in turn learned of it from Europeans),Needham, p. 289. the Chinese design of the suspended dry compass persisted in use well into the 18th century.Needham, p. 290

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, but there is no indication that Chinese mariners ever used anything but the floating needle in a bowl until the 16th-century European contacts.Kreutz, p. 373

Additionally, it must be pointed out that, unlike Needham, other experts on the history of the compass make no mention of an indigenous dry compass in China and reserve the term for the European form which became later worldwide standard.Kreutz, p. 367–383LaneLi Shu-hua, p. 175-196

Later developments in China

Question of diffusion image:Compass thumbnail.jpg's compass rose. There is much debate on what happened to the compass after its first appearance with the Chinese. Different theories include:

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.Kreutz, p. 368 Other evidence for this includes the Arabic word for "Compass" (al-konbas), possibly being a derivation of the old Italian language 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.Kreutz, p. 369 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.Kreutz, p. 370.

Question of independent European invention (1269)There have been various arguments put forward whether the European compass was an independent invention or not:

Arguments pro independent invention:

Arguments contra independent invention:

Impact in the Mediterranean In the Mediterranean, the introduction of the mariner's compass, at first only known as a magnetized pointer floating in a bowl of waterKreutz, p. 368–369, went hand in hand with improvements in dead reckoning methods, and the development of Portolan charts, leading to more navigation during winter months in the second half of the 13th century.Lane, p. 606f. 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.Lane, p. 608 The additional few months were of considerable economic importance. For instance, it enabled Venice convoys to make two round trips a year to the Levant, instead of one.Lane, p. 608 & 610

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.Lane, p. 608 & 613

Although critics like Kreutz feels that it was later in 1410 that anyone really started steering by compass. Kreutz, p. 372–373

Mining The use of a compass as a direction finder underground was pioneered by the Tuscan mining town Massa where floating magnetic needles were employed for determing tunneling and defining the claims of the various mining companies as early as the 13th century.Ludwig and Schmidtchen, p. 62–64 In the second half of the 15th century, the compass belonged to the standard equipment of Tyrol miners, and shortly afterwards a first detailed treatise dealing with the underground use of compasses was published by the Germany miner Rülein von Calw (1463-1525).Ludwig and Schmidtchen, p. 64

Dry compass The familiar dry compass was invented in Europe around 1300. The true 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".Lane, p. 615 While pivoting needles in glass boxes had already been described by the French scholar Peter Peregrinus in 1269,Taylor there is an inclination to honour tradition and credit Flavio Gioja (fl. 1302), an Italian pilot (harbour) from Amalfi, with perfecting the sailor's compass by suspending its needle over a compass card, giving thus the compass its familiar appearance.Lane, p. 616 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),Kreutz, p. 374 supporting the notion that the dry compass was known in Europe by then.Kreutz, p. 373

Liquid compass In 1936 Tuomas Vohlonen invented the first successful portable liquid-filled compass designed for individual use.http://www.prh.fi/en/tietoaprhsta/innogalleria/vohlonen_takes_a_bearing.html

Construction of a simple compass 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. 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, often by being painted red.

Modern compasses image:liquid filled compass.jpgModern hand-held navigational compasses use a magnetized needle or dial inside a fluid-filled (oil, kerosene, or alcohol is common) capsule; the fluid causes the needle to stop quickly rather than oscillate back and forth around magnetic north. Most modern recreational and military compasses integrate a protractor with the compass, using a separate magnetized needle. In this design the rotating capsule containing the magnetized needle is fitted with orienting lines and an outlined orienting arrow, then mounted in a transparent baseplate containing a direction-of-travel (DOT) indicator for use in taking bearings directly from a map. Other features found on some modern handheld compasses are map and romer scales for measuring distances and plotting positions on maps, luminous markings or bezels for use at night or poor light, various 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 inclinometers for measuring gradients.

The military forces of a few nations, notably the United States Army, continue to utilize older lensatic card compass designs with magnetized compass dials instead of needles. A lensatic card compass permits reading the bearing off of the compass card with only a slight downward glance from the sights (see photo), but requires a separate protractor for use with a map. The official U.S. military lensatic compass does not use fluid to dampen needle swing, but rather electromagnetic induction. A 'deep-well' design is used to allow the compass to be used globally with little or no effect in accuracy caused by a tilting compass dial. As induction forces provide less damping than fluid-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 humid environments.

A range of specialty compasses would include a Qibla compass which is used by Muslims to show the direction to Mecca for prayers. Similarly a Jerusalem compass http://www.jewishsoftware.com/products/The_Incredible_Jerusalem_Compass_813.asp?bhcd2=1177746874is used by Jews to point the direction of Jerusalem for prayers.

Other specialty compasses include the optical or prismatic hand-bearing compass, often used by surveyors, cave explorers, or mariners. This compass uses an oil-filled capsule and magnetized compass dial with an integral optical or prismatic sight, often fitted with built-in photoluminescent or battery-powered illumination. 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 solid metal housings, and many are fitted for tripod mounting for additional accuracy.

Mariner's compasses can have two or more magnetic needles 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 rhumbs), 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 gyrocompass, using the more reliable magnetic compass for back-up. Increasingly, electronic fluxgate compass are used on smaller vessels. However compasses are widely in use as they can be small, use simple technology, 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.

Some modern military compasses, like the SandY-183 (the one pictured) contains the radioactive material Tritium (3H) 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).

Solid state compasses Small compasses found in clocks, cell phones (e.g. the Nokia 5140i) and other electronic gear are Solid-state (electronics) devices usually built out of two or three magnetic field sensors that provide data for a microprocessor. Using trigonometry the correct heading relative to the compass is calculated.

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 or microprocessor and used either internally, or sent to a display unit. An example implementation, including parts list and circuit schematics, shows one design of such electronics.The sensor uses precision magnetics and highly calibrated internal electronics to measure the response of the device to the Earth's magnetic field. The electrical signal is then processed or digital electronics.

Bearing compass A bearing compass is a magnetic compass mounted in such a way that it allows the taking of bearings of objects by aligning them with the lubber line of the bearing compass.

Compass correction containing a ship's steering compass, with the two iron balls which correct the effects of ferromagnetism materials

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 never be used in close proximity to ferrous metal objects or electromagnetic fields (batteries, car bonnets, engines, steel pitons, wristwatches, etc.)

Compasses used in or near trucks, cars or other mechanized vehicles are particularly difficult to use accurately, 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.

At sea, a ship's compass must also be corrected for errors, called Magnetic 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 materials in the compass's environment can be corrected by two iron balls mounted on either side of the compass binacle. The coefficient a_0 representing the error in the lubber line, while a_1,b_1 the ferromagnetic effects and a_2,b_2 the non-ferromagnetic component.

Fluxgate compasses can be calibrated automatically, and can also be programmed with the correct local compass variation so as to indicate the true heading.

Using a compass

The simplest way of using a compass is to know that the arrow always points in the same direction, magnetic North, which is roughly similar to 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 or even opposite direction than expected over short distances, provided the terrain is fairly flat and visibility is not impaired. In fact, 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.

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 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 Silva 1-2-3 System, after Silva Compass, manufacturers of the first protractor compasses.

A dynamic rotating draggable Silva compass is available online to practice setting compass and map bearings: http://geographyfieldwork.com/UsingCompass.htm



Compass balancing Because the Earth's magnetic field's inclination and intensity vary at different latitudes, compasses are often balanced during manufacture. 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 balancing prevents excessive dipping of one end of the needle which can cause the compass card to stick and give false readings. Suunto has recently introduced two-zone compasses that can be used in one entire hemisphere, and to a limited extent in another without significant loss of accuracy.

Some different compass systems:Image:Boussole_en_grades_table_conversion.jpg|Compass with 400 grads division and conversion tableImage:RECTA_full_syst.jpg|Swiss army compass with mils divisionImage:Boussole à prisme échelles gros plan.jpg|Compass with prism (inverted graduation)Image:Boussole prisme groupe.jpg|Compass with prism (bearing 220° through eyepiece)image:Boussole_fantassin_russe.jpg|Wrist compass of the Soviet Army with double graduation: 60° (like a watch) and 360° (below the figures for 15°, 30° and 45° of the outer graduation are the cyrillic letters "" ( = west), ""( = south) and "" ( = east)Image:Boussole_avec_inclinomètre.jpg|Land surveyor compass with clinometerImage:Stratum_compass-clar_hg.jpg|Stratum compass after Prof. ClarImage:Compass_boussole_Bézard_AF_+_visée.jpg|German Bézard compass (Company Lufft) formerly utilized in many European armies (bearing is taken through slots in lid)

Points of the compass Originally, many compasses were marked only as to the direction of magnetic north, or to the four cardinal points (north, south, east, west). Later, mariners divided the compass card into thirty-two equally spaced points divided from the cardinal points. For a table of the thirty-two points, see Boxing the compass#Compass points.

The 360-degree system later took hold, which is still in use today for civilian navigators. The degree dial spaces the compass markings with 360 equidistant points. Other nations adopted the 'grad' system, which spaces the dial into 400 grads or points.

Most military defense forces have adopted the 'mil' system, in which the compass dial is spaced into 6400 units (some nations use 6000) or 'mils' for additional precision when measuring angles, laying artillery, etc. The value to the military is that one mil subtends approximately one metre at a distance of one kilometer.

Former Warsaw Pact countries (Soviet Union, GDR etc.) used a 60° graduation, often counterclockwise (see picture of wrist compass). This is still in use in Russia.

See also

Gallery Image:Compass_Fitted_To_A_Yacht.jpg|A simple compass typical to a small yachtImage:Silva_Sighting_Compass.jpg] in the night

Notes

References

External links





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's magnetic field, which is of great assistance in navigation. The face of the compass generally highlights the cardinal points of north, south, east and west. A compass can be used in conjunction with a marine chronometer to calculate longitude) and a sextant to calculate latitude, providing a very accurate navigation capability. This device greatly improved maritime trade by making travel safer and more efficient. An early form of the compass was invented in China in the 11th century. The familiar mariner's compass was invented in Europe around 1300, from whence later originated the liquid compass and the gyrocompass.

More technically, a compass is a magnetic device using a needle to indicate the direction of the North Magnetic Pole of a planet's magnetosphere. Any Measuring instrument with a magnetized bar or needle turning freely upon a pivot and pointing in a northerly and southerly direction can be considered a compass. A compass dial is a small pocket compass with a sundial. A variation compass is a specific instrument of a delicate type of construction. It is used by observing variations of the needle. A gyrocompass or astrocompass, which does not depend on the earth's magnetic field for its operation, can also be used to find true north.

History of the navigational compass 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. 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 made extensive use of soundings. The astrolabe, originally invented in the Hellenistic civilization, was significantly improved upon by later medieval Islamic astronomy and Islamic Golden Age#Age of discovery who used it to aid in navigation.

Mesoamerica The find of an Olmec hematite artifact, fitted with a sighting mark and found in experiment as fully operational as a compass, has led the American astronomer John Carlson after radiocarbon dating to conclude that "the Olmec may have discovered and used the geomagnetic lodestone compass earlier than 1000 BC".Carlson, p. 753–760 Carlson suggests that the Olmecs may have used such devices for directional orientation of the dwellings of the living and the interments of the dead.

Needle-and-bowl device By rubbing a needle on silk, the needle becomes magnetized and when placed in a straw and put in a puddle of water it becomes a compass. This device was universally used as a compass until the introduction of the box-like compass with a pivoting 'dry' needle around 1300.

China Due to disagreement as to when the compass was invented, it may be appropriate to list some noteworthy History of China literary references offered as possible evidence for its antiquity, in chronological order:



Thus, the first clear instance of a magnetic direction finder, a compass, appeared ca. 1044. However, it should be pointed out that the compass remained in use by the Chinese in the form of a magnetic needle floating in a bowl of water.Kreutz, p. 373

According to 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.Needham p. 255 Evidence of this is found in the Shilinguangji ('Guide Through the Forest of Affairs'), first published in 1325 by Chen Yuanjing, although its compilation had taken place between 1100 and 1250 AD. 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 loadstone sealed in by wax, and if rotated, the needle at the tail would always point in the northern cardinal direction. Although the 14th century European compass-card in box frame and dry pivot needle was adopted in China after its use was taken by Japanese people pirates in the 16th century (who had in turn learned of it from Europeans),Needham, p. 289. the Chinese design of the suspended dry compass persisted in use well into the 18th century.Needham, p. 290

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, but there is no indication that Chinese mariners ever used anything but the floating needle in a bowl until the 16th-century European contacts.Kreutz, p. 373

Additionally, it must be pointed out that, unlike Needham, other experts on the history of the compass make no mention of an indigenous dry compass in China and reserve the term for the European form which became later worldwide standard.Kreutz, p. 367–383LaneLi Shu-hua, p. 175-196

Later developments in China

Question of diffusion image:Compass thumbnail.jpg's compass rose. There is much debate on what happened to the compass after its first appearance with the Chinese. Different theories include:

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.Kreutz, p. 368 Other evidence for this includes the Arabic word for "Compass" (al-konbas), possibly being a derivation of the old Italian language 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.Kreutz, p. 369 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.Kreutz, p. 370.

Question of independent European invention (1269)There have been various arguments put forward whether the European compass was an independent invention or not:

Arguments pro independent invention:

Arguments contra independent invention:

Impact in the Mediterranean In the Mediterranean, the introduction of the mariner's compass, at first only known as a magnetized pointer floating in a bowl of waterKreutz, p. 368–369, went hand in hand with improvements in dead reckoning methods, and the development of Portolan charts, leading to more navigation during winter months in the second half of the 13th century.Lane, p. 606f. 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.Lane, p. 608 The additional few months were of considerable economic importance. For instance, it enabled Venice convoys to make two round trips a year to the Levant, instead of one.Lane, p. 608 & 610

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.Lane, p. 608 & 613

Although critics like Kreutz feels that it was later in 1410 that anyone really started steering by compass. Kreutz, p. 372–373

Mining The use of a compass as a direction finder underground was pioneered by the Tuscan mining town Massa where floating magnetic needles were employed for determing tunneling and defining the claims of the various mining companies as early as the 13th century.Ludwig and Schmidtchen, p. 62–64 In the second half of the 15th century, the compass belonged to the standard equipment of Tyrol miners, and shortly afterwards a first detailed treatise dealing with the underground use of compasses was published by the Germany miner Rülein von Calw (1463-1525).Ludwig and Schmidtchen, p. 64

Dry compass The familiar dry compass was invented in Europe around 1300. The true 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".Lane, p. 615 While pivoting needles in glass boxes had already been described by the French scholar Peter Peregrinus in 1269,Taylor there is an inclination to honour tradition and credit Flavio Gioja (fl. 1302), an Italian pilot (harbour) from Amalfi, with perfecting the sailor's compass by suspending its needle over a compass card, giving thus the compass its familiar appearance.Lane, p. 616 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),Kreutz, p. 374 supporting the notion that the dry compass was known in Europe by then.Kreutz, p. 373

Liquid compass In 1936 Tuomas Vohlonen invented the first successful portable liquid-filled compass designed for individual use.http://www.prh.fi/en/tietoaprhsta/innogalleria/vohlonen_takes_a_bearing.html

Construction of a simple compass 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. 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, often by being painted red.

Modern compasses image:liquid filled compass.jpgModern hand-held navigational compasses use a magnetized needle or dial inside a fluid-filled (oil, kerosene, or alcohol is common) capsule; the fluid causes the needle to stop quickly rather than oscillate back and forth around magnetic north. Most modern recreational and military compasses integrate a protractor with the compass, using a separate magnetized needle. In this design the rotating capsule containing the magnetized needle is fitted with orienting lines and an outlined orienting arrow, then mounted in a transparent baseplate containing a direction-of-travel (DOT) indicator for use in taking bearings directly from a map. Other features found on some modern handheld compasses are map and romer scales for measuring distances and plotting positions on maps, luminous markings or bezels for use at night or poor light, various 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 inclinometers for measuring gradients.

The military forces of a few nations, notably the United States Army, continue to utilize older lensatic card compass designs with magnetized compass dials instead of needles. A lensatic card compass permits reading the bearing off of the compass card with only a slight downward glance from the sights (see photo), but requires a separate protractor for use with a map. The official U.S. military lensatic compass does not use fluid to dampen needle swing, but rather electromagnetic induction. A 'deep-well' design is used to allow the compass to be used globally with little or no effect in accuracy caused by a tilting compass dial. As induction forces provide less damping than fluid-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 humid environments.

A range of specialty compasses would include a Qibla compass which is used by Muslims to show the direction to Mecca for prayers. Similarly a Jerusalem compass http://www.jewishsoftware.com/products/The_Incredible_Jerusalem_Compass_813.asp?bhcd2=1177746874is used by Jews to point the direction of Jerusalem for prayers.

Other specialty compasses include the optical or prismatic hand-bearing compass, often used by surveyors, cave explorers, or mariners. This compass uses an oil-filled capsule and magnetized compass dial with an integral optical or prismatic sight, often fitted with built-in photoluminescent or battery-powered illumination. 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 solid metal housings, and many are fitted for tripod mounting for additional accuracy.

Mariner's compasses can have two or more magnetic needles 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 rhumbs), 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 gyrocompass, using the more reliable magnetic compass for back-up. Increasingly, electronic fluxgate compass are used on smaller vessels. However compasses are widely in use as they can be small, use simple technology, 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.

Some modern military compasses, like the SandY-183 (the one pictured) contains the radioactive material Tritium (3H) 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).

Solid state compasses Small compasses found in clocks, cell phones (e.g. the Nokia 5140i) and other electronic gear are Solid-state (electronics) devices usually built out of two or three magnetic field sensors that provide data for a microprocessor. Using trigonometry the correct heading relative to the compass is calculated.

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 or microprocessor and used either internally, or sent to a display unit. An example implementation, including parts list and circuit schematics, shows one design of such electronics.The sensor uses precision magnetics and highly calibrated internal electronics to measure the response of the device to the Earth's magnetic field. The electrical signal is then processed or digital electronics.

Bearing compass A bearing compass is a magnetic compass mounted in such a way that it allows the taking of bearings of objects by aligning them with the lubber line of the bearing compass.

Compass correction containing a ship's steering compass, with the two iron balls which correct the effects of ferromagnetism materials

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 never be used in close proximity to ferrous metal objects or electromagnetic fields (batteries, car bonnets, engines, steel pitons, wristwatches, etc.)

Compasses used in or near trucks, cars or other mechanized vehicles are particularly difficult to use accurately, 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.

At sea, a ship's compass must also be corrected for errors, called Magnetic 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 materials in the compass's environment can be corrected by two iron balls mounted on either side of the compass binacle. The coefficient a_0 representing the error in the lubber line, while a_1,b_1 the ferromagnetic effects and a_2,b_2 the non-ferromagnetic component.

Fluxgate compasses can be calibrated automatically, and can also be programmed with the correct local compass variation so as to indicate the true heading.

Using a compass

The simplest way of using a compass is to know that the arrow always points in the same direction, magnetic North, which is roughly similar to 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 or even opposite direction than expected over short distances, provided the terrain is fairly flat and visibility is not impaired. In fact, 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.

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 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 Silva 1-2-3 System, after Silva Compass, manufacturers of the first protractor compasses.

A dynamic rotating draggable Silva compass is available online to practice setting compass and map bearings: http://geographyfieldwork.com/UsingCompass.htm



Compass balancing Because the Earth's magnetic field's inclination and intensity vary at different latitudes, compasses are often balanced during manufacture. 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 balancing prevents excessive dipping of one end of the needle which can cause the compass card to stick and give false readings. Suunto has recently introduced two-zone compasses that can be used in one entire hemisphere, and to a limited extent in another without significant loss of accuracy.

Some different compass systems:Image:Boussole_en_grades_table_conversion.jpg|Compass with 400 grads division and conversion tableImage:RECTA_full_syst.jpg|Swiss army compass with mils divisionImage:Boussole à prisme échelles gros plan.jpg|Compass with prism (inverted graduation)Image:Boussole prisme groupe.jpg|Compass with prism (bearing 220° through eyepiece)image:Boussole_fantassin_russe.jpg|Wrist compass of the Soviet Army with double graduation: 60° (like a watch) and 360° (below the figures for 15°, 30° and 45° of the outer graduation are the cyrillic letters "" ( = west), ""( = south) and "" ( = east)Image:Boussole_avec_inclinomètre.jpg|Land surveyor compass with clinometerImage:Stratum_compass-clar_hg.jpg|Stratum compass after Prof. ClarImage:Compass_boussole_Bézard_AF_+_visée.jpg|German Bézard compass (Company Lufft) formerly utilized in many European armies (bearing is taken through slots in lid)

Points of the compass Originally, many compasses were marked only as to the direction of magnetic north, or to the four cardinal points (north, south, east, west). Later, mariners divided the compass card into thirty-two equally spaced points divided from the cardinal points. For a table of the thirty-two points, see Boxing the compass#Compass points.

The 360-degree system later took hold, which is still in use today for civilian navigators. The degree dial spaces the compass markings with 360 equidistant points. Other nations adopted the 'grad' system, which spaces the dial into 400 grads or points.

Most military defense forces have adopted the 'mil' system, in which the compass dial is spaced into 6400 units (some nations use 6000) or 'mils' for additional precision when measuring angles, laying artillery, etc. The value to the military is that one mil subtends approximately one metre at a distance of one kilometer.

Former Warsaw Pact countries (Soviet Union, GDR etc.) used a 60° graduation, often counterclockwise (see picture of wrist compass). This is still in use in Russia.

See also

Gallery Image:Compass_Fitted_To_A_Yacht.jpg|A simple compass typical to a small yachtImage:Silva_Sighting_Compass.jpg] in the night

Notes

References

External links





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