A simple dry magnetic pocket compass

A smartphone that can be used as a compass because of the magnetometer inside

A compass is a navigational instrument that measures directions in a frame of reference that is stationary relative to the surface of the earth. The frame of reference defines the four cardinal directions (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 azimuths or bearings, which are commonly stated in this notation.

There are two widely used and radically different types of compass. The magnetic compass contains a magnet that interacts with the earth's magnetic field and aligns itself to point to the magnetic poles. The gyrocompass (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 magnetic compass was invented as a device for divination as early as the Chinese Han Dynasty,^[1][2] and was used "in the search for gems and the selection of sites for houses."^[3] The compass was used in Song Dynasty China by the military for navigational orienteering by 1040-1044,^[4][5][6] and was used for maritime navigation by 1117.^[7] The use of a compass is recorded in Western Europe between 1187 and 1202 ^[8][9][10] and in Persia in 1232.^[11] The dry compass was invented in Europe around 1300.^[12] This was supplanted in the early 20th century by the liquid-filled magnetic compass.^[13]

Types of compasses[link]

There are two widely used and radically different types of compass. The magnetic compass contains a magnet that interacts with the earth's magnetic field and aligns itself to point to the magnetic poles.^[14] 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 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 true south, respectively.

There are other devices which are not conventionally called compasses but which do allow the true cardinal directions to be determined. They are said to work "like a compass", or "as a compass", without actually being a compass. For example, a Global Positioning System (GPS) satellite receiver determines its own position on the ground, as true latitude and true longitude. 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 thence the directions of the cardinal points relative to its direction of movement. Some GPS receivers have two antennas, fixed some distance apart to the structure of a vehicle, usually an aircraft. 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. 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.

The earth's magnetic poles do not coincide with the rotational poles, and the positions of the magnetic poles change over time on a time-scale that is not extremely long by human standards. Significant movements happen in a few years. (Over millions of years, the directions of the true poles also shift, because of continental drift.) For an observer at any point on the earth's surface, there is an angle, called the magnetic declination (or magnetic variation), between the directions of magnetic north and true north. The magnetic declination is different at different points on the earth, and changes with time. Close to the equator, the magnetic declination is no more than a few degrees, but in arctic and Antarctic latitudes it can be much greater. Some magnetic compasses include means to compensate for the magnetic declination, so that the compass shows true directions, relative to the earth's rotational poles. The user of such a compass has to know the local value of the magnetic declination, and adjust the compass accordingly.

Magnetic compass[link]

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 magnetic north of a planet's magnetosphere. The face of the compass generally highlights the cardinal points of north, south, east and west. Often, compasses are built as a stand alone sealed instrument with a magnetized bar or needle turning freely upon a pivot, or moving in a fluid, thus able to point in a northerly and southerly direction.

The compass greatly improved the safety and efficiency of travel, especially ocean travel. A compass can be used to calculate heading, used with a sextant to calculate latitude, and with a marine chronometer to calculate longitude. It thus provides a much improved navigational capability that has only been recently supplanted by modern devices such as the Global Positioning System (GPS).

The compass was invented during the Chinese Han Dynasty between the 2nd century BC and 1st century AD.^[1] The dry compass was invented in medieval Europe around 1300.^[12] This was supplanted in the early 20th century by the liquid-filled magnetic compass.^[13]

Other, more accurate devices have been invented for determining north that do not depend on the Earth's magnetic field for operation (known in such cases as true north, as opposed to magnetic north). A gyrocompass or astrocompass can be used to find true north, while being unaffected by stray magnetic fields, nearby electrical power circuits or nearby masses of ferrous metals. A recent development is the electronic compass, either a magnetometer or a fibre optic gyrocompass, which detects the magnetic directions without potentially fallible moving parts. A magnetometer frequently appears as an optional subsystem built into hand-held GPS receivers. However, magnetic compasses remain popular, especially in remote areas, as they are relatively inexpensive, durable, and require no power supply.^[15]

How a magnetic compass works[link]

A compass functions as a pointer to "magnetic north" because the magnetized needle at its heart aligns itself with the lines of the 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.

A magnet or compass needle's "north" pole is defined as the one which is attracted to the North magnetic pole of the Earth, in northern Canada. 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.^[16][17][18] The compass needle's north pole is always marked in some way: with a distinctive color, luminous paint, or an arrowhead.

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 the cardinal points 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.

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 magnetic poles are near, but are not at the same locations as its geographic poles, a compass does not point to true north. The direction a compass points is called magnetic north, the direction of the North magnetic pole, located in northeastern Canada. 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.

In geographic regions near the magnetic poles, in northeastern Canada and Antarctica, 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.

History[link]

The first compasses were made of lodestone, a naturally magnetized ore of iron.^[3] 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.^[3] Later compasses were made of iron needles, magnetized by stroking them with a lodestone.

Navigation prior to the compass[link]

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 birefringent crystal to determine the sun's direction and elevation from the polarization of daylight; their astronomical knowledge was sufficient to let them use this information to determine their proper heading.^[19] 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.

Geomancy and feng shui[link]

Magnetism was originally used, not for navigation, but for geomancy and fortune-telling by the Chinese. The earliest 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 using lodestone, a special form of the mineral magnetite that aligns itself with the Earth’s magnetic field.^[20]

Based on Krotser and Coe's discovery of an Olmec hematite artifact in Mesoamerica, 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.^[21] Carlson speculates that the Olmecs used similar artifacts as a directional device for astronomical or 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.^[22][7] Several other hematite or magnetite artifacts have been found at pre-Columbian archaeological sites in Mexico and Guatemala.^[23][24]

Navigational compass[link]

The invention of the navigational compass is credited by scholars to the Chinese, who began using it for navigation sometime between the 9th and 11th century, "some time before 1050, possibly as early as 850."^[25] A common theory by historians^[25][26], 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.^[4]

China[link]

Model of a Han Dynasty (206 BC–220 AD) south-indicating ladle or sinan. It is theorized that the south-pointing spoons of the Han dynasty were magnetized lodestones.^[27]

There is disagreement as to exactly when the compass was invented. These are noteworthy Chinese literary references in evidence for its antiquity:

• The earliest Chinese literature reference to magnetism lies in the 4th century BC writings of Wang Xu (鬼谷子): "The lodestone attracts iron."^[28] 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.^[29][3]
• 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."^[30] Within the text, the author Wang Chong describes the spoon as a phenomenon that he has personally observed.^[31] Although the passage does not explicitly mention magnetism,^[32] according to Chen-Cheng Yih, the "device described by Wang Chong has been widely considered to be the earliest form of the magnetic compass."^[27]
• The first clear account of magnetic declination occurs in the Kuan Shih Ti Li Chih Meng ("Mr. Kuan's Geomantic Instructor"), dating to 880.^[33] 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.^[33]
• 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."^[34]
• 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 carriage, or the south-pointing fish."^[5] This was achieved by heating of metal (especially if steel), known today as thermoremanence, and would have been capable of producing a weak state of magnetization.^[5] While the Chinese achieved magnetic remanence and induction by this time, a similar discovery was not made in Europe until about 1600, when William Gilbert published his De Magnete.^[35]
• The first incontestable reference to a magnetized needle in Chinese literature appears in 1088.^[36] The Dream Pool Essays, written by the Song Dynasty polymath scientist Shen Kuo, contained a detailed description of how geomancers magnetized a needle by rubbing its tip with lodestone, and hung the magnetic needle with one single strain of silk with a bit of wax attached to the center of the needle. Shen Kuo pointed out that a needle prepared this way sometimes pointed south, sometimes north.
• The earliest explicit recorded use of a magnetic compass for maritime navigation is found in Zhu Yu's book Pingzhou Table Talks (萍洲可談; Pingzhou Ketan) and dates from 1117:^[7] 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.

Thus, the use of a magnetic compass by the military for 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.

The typical Chinese navigational compass was in the form of a magnetic needle floating in a bowl of water.^[37] 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.^[38] 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.^[38] 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.^[38] Although the European compass-card in box frame and dry pivot needle was adopted in China after its use was taken by Japanese pirates in the 16th century (who had in turn learned of it from Europeans),^[39] the Chinese design of the suspended dry compass persisted in use well into the 18th century.^[7][40] 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.^[37]

Diagram of a Ming Dynasty mariner's compass

The first recorded use of a 48 position mariner's compass on sea navigation was noted in a book titled “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 ]}, the mariner took "Kun Shen needle", or 52.5 degree SW.^[41] Zheng He's Navigation Map, also known as "The Mao Kun Map", contains a large amount of detail "needle records" of Zheng He's travel.^[42]

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.^[4] 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)^[8] than in the Muslim world (1232, 1242, and 1282).^[43][11] 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.^[8][44] 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.^[11] 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.^[43] 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 word for compass, is also used as evidence for the lack of Arabic diffusion. However, evidence to the contrary includes the argument that the Persian compass is described as fish-like, which is a characteristic of early Chinese compasses from the 11th century, suggesting transmission.^[45]

Medieval Europe[link]

Pivoting compass needle in a 14th century copy of Epistola de magnete of Peter Peregrinus (1269)

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,^[9] written between 1187 and 1202, after he returned to England from France^[46] and prior to entering the Augustinian abbey at Cirencester.^[47] 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.^[9] In the Mediterranean, the introduction of the compass, at first only known as a magnetized pointer floating in a bowl of water,^[48] 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.^[49] 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.^[50] The additional few months were of considerable economic importance. For instance, it enabled Venetian convoys to make two round trips a year to the Levant, instead of one.^[51]

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.^[52] However, critics like Kreutz feel that it was later in 1410 that anyone really started steering by compass.^[53]

Navigational sailor's compass rose.

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."^[4] 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)^[8] than in the Muslim world (1232, 1242, and 1282).^[43][11] 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.^[8]

Islamic world[link]

The earliest reference to an iron fish-like compass in the Islamic world occurs in a Persian talebook from 1232.^[11] This fish shape was from a typical early Chinese design.^[7] The earliest Arabic reference to a compass — in the form of magnetic needle in a bowl of water — comes from the Yemeni sultan and astronomer Al-Ashraf in 1282.^[43] He also appears to be the first to make use of the compass for astronomical purposes.^[54] 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.^[11]

In 1300, another Arabic treatise written by the Egyptian 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.^[9] In the 14th century, the Syrian astronomer and timekeeper Ibn al-Shatir (1304–1375) invented a timekeeping device incorporating both a universal sundial and a magnetic compass. He invented it for the purpose of finding the times of Salah prayers.^[55] Arab navigators also introduced the 32-point compass rose during this time.^[56]

India[link]

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.^[57]

Medieval Africa[link]

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 African center of trade in Somalia and the Swahili city-state kingdoms. There is evidence that Swahili maritime merchants and sailors acquired the compass at some point and used them for navigation of Swahili versions of dhows.^{[58][not in citation given]}

Later developments[link]

Dry compass[link]

Early modern dry compass suspended by a gimbal (1570)

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".^[12] 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.

While pivoting needles in glass boxes had already been described by the French scholar Peter Peregrinus in 1269,^[59] and by the Egyptian scholar Ibn Simʿūn in 1300,^[9] traditionally Flavio Gioja (fl. 1302), an Italian 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.^[60] 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),^[61] supporting the notion that the dry compass was known in Europe by then.^[37]

Bearing compass[link]

Bearing compass (18th century).

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.^[62] A surveyor's compass is a specialized compass made to accurately measure heading of landmarks and measure horizontal angles to help with map making. These were already in common use by the early 18th century and are described in the 1728 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 prismatic compass.^[63] 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.^[64][65] This arrangement enabled the user to align the compass with an objective while simultaneously viewing its bearing in the mirror.^[64][66]

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, Alvid, and Alvar Kjellström, who were selling basic compasses, and the four men modified Tillander's design.^[67] In December 1932, the Silva Company was formed with Tillander and the three Kjellström brothers, and the company began manufacturing and selling its Silva orienteering compass to Swedish orienteers, outdoorsmen, and army officers.^{[68][69][70][67]}

Liquid compass[link]

A flush mount, liquid-filled compass on a boat

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.^[71] 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.^[72][73] Liquid-damped marine compasses for ships and small boats were occasionally used by the British Royal Navy from the 1830s through 1860, but the standard Admiralty compass remained a dry-mount type.^[74] 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.^[75]

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:

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...^[13][76]

Typical aircraft-mounted magnetic compass

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.^[13]

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.^[77][78] After the success of this invention, Capt. Creagh-Osborne adapted his design to a much smaller pocket model^[79] for individual use^[80] by officers of artillery or infantry, receiving a patent in 1915.^[81]

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.^[67] The liquid-damped Silva took only four seconds for its needle to settle in comparison to thirty seconds for the original version.^[67]

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.^[82] 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.^[82]

History of non-navigational uses[link]

Building orientation[link]

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 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.^[83] Most of these churches were built in the 12th century, indicating a fairly common usage of magnetic compasses in Europe by then.^[84]

Mining[link]

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 determining tunneling and defining the claims of the various mining companies as early as the 13th century.^[85] In the second half of the 15th century, the compass became standard equipment for Tyrolian miners. Shortly afterwards the first detailed treatise dealing with the underground use of compasses was published by a German miner Rülein von Calw (1463–1525).^[86]

Astronomy[link]

Three astronomical compasses meant for establishing the meridian were described by Peter Peregrinus in 1269 (referring to experiments made before 1248)^[87] In the 1300s, an Arabic treatise written by the Egyptian 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.^[9] In the 14th century, the Syrian astronomer and timekeeper Ibn al-Shatir (1304–1375) invented a timekeeping device incorporating both a universal sundial and a magnetic compass. He invented it for the purpose of finding the times of Salah prayers.^[55] Arab navigators also introduced the 32-point compass rose during this time.^[56]

Modern compasses[link]

A liquid-filled protractor or orienteering compass with lanyard

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.^[88] 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, photoluminescent, or self-luminous materials^[89] 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.

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.^[90] The capsule is mounted in a transparent baseplate containing a direction-of-travel (DOT) indicator for use in taking bearings directly from a map.^[90]

Liquid filled lensatic compass

Cammenga air filled lensatic compass

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 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 clinometers for measuring gradients.^[90] 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.^[91]

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.^[90][92]

The U.S. M-1950 military lensatic compass does not use a liquid-filled capsule as a dampening 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.^[93] 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.^[94]

Some military compasses, like the U.S. M-1950 (Cammenga 3H) military lensatic compass, the Silva 4b Militaire, and the Suunto M-5N(T) contain the radioactive material tritium (3H) and a combination of phosphors.^[95] 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 for the compass, via radioluminescent tritium illumination, which does not require the compass to be "recharged" by sunlight or artificial light.^[96]

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 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.

Thumb compass[link]

Thumb compass on left

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 transparent so that an orienteer can hold a map in the hand with the compass and see the map through the compass.

Gyrocompass[link]

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 ships. They have two main advantages over magnetic compasses:

• they find true north, i.e., the direction of Earth's rotational axis, as opposed to magnetic north,
• 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.)

Large ships typically rely on a gyrocompass, using the magnetic compass only as a backup. Increasingly, electronic fluxgate compasses are used on smaller vessels. However 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.

Solid state compasses[link]

Small compasses found in clocks, mobile phones, and other electronic devices are 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.

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 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.

GPS receivers using two or more antennae can now achieve 0.5° in heading accuracy (e.g.^[97]) 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.

Specialty compasses[link]

A standard Brunton Geo, used commonly by geologists

Apart from navigational compases, other specialty compasses have also been designed to accommodate specific uses. These include:

• Qibla compass, which is used by Muslims to show the direction to Mecca for prayers.
• Optical or prismatic hand-bearing compass, most often used by surveyors, but also by cave explorers, foresters, and geologists. This compasses ordinarily uses a liquid-damped capsule^[98] 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.^[90] 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.^[90]
• 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.

Limitations of the magnetic compass[link]

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 bearings may get stuck because of this and therefore indicate a wrong direction.

All magnetic devices are subject to fields other than Earth's, which is not particularly strong. Local environments may contain mineral deposits and human sources such as MRIs. Vehicles may contain ferrous metals, which may pick up their own fields. Cars may be mostly steel, and render simple compasses useless after time. While ships, submarines, and spacecraft may be built from carefully controlled materials, and later degaussed, drivers rarely take such a step.

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 the indicated heading or decrease the indicated heading.

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.

Construction of a compass[link]

Magnetic needle[link]

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, often by being painted red.

Needle-and-bowl device[link]

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.

Points of the compass[link]

Wrist compass of the Soviet Army with counterclockwise double graduation: 60° (like a watch) and 360°.

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 compass points.

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" (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.

Most military forces have adopted the French "millieme" 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, GDR etc.), often counterclockwise (see picture of wrist compass). This is still in use in Russia.

Compass balancing (magnetic dip)[link]

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.

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 counter balancing the needle against the dip caused by inclination if the compass is taken to a zone with a higher or lower dip.

Compass correction[link]

A binnacle containing a ship's steering compass, with the two iron balls which correct the effects of ferromagnetic materials. This unit is on display in a museum.

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 pitons, etc.) as that can affect their accuracy.^[90] 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.

At sea, a ship's compass must also be corrected for errors, called 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 ferromagnetic materials in the compass's environment can be corrected by two iron balls mounted on either side of the compass binnacle. The coefficient Failed to parse (Missing texvc executable; please see math/README to configure.): a_0

representing the error in the lubber line, while Failed to parse (Missing texvc executable; please see math/README to configure.): a_1,b_1
the ferromagnetic effects and Failed to parse (Missing texvc executable; please see math/README to configure.): a_2,b_2
the non-ferromagnetic component.

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.

Using a compass[link]

Turning the compass scale on the map (D - the local magnetic declination)

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).

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. Variation is defined as the angle between the direction of true (geographic) north and the direction of the meridian between the magnetic poles. Variation values for most of the oceans had been calculated and published by 1914.^[99] 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.

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.^[90]

Soldier using a prismatic compass to get an azimuth.

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.^[90] 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.^[90] 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.

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.

Compasses are to be laid down on a leveled surface so the needle could point to the magnetic north more accurately, as to that the needle only rests or hangs on a bearing fused to the compass casing, if used at a tilt, the needle might hit the casing on the compass, and hence, not move. This will give 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 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.

See also[link]

• Absolute bearing
• Astrocompass
• Beam compass
• Boxing the compass
• Brunton compass
• Coordinates
• Earth Inductor Compass
• Fibre optic gyrocompass
• Fluxgate compass
• Gyrocompass
• Hand compass
• Inertial navigation system
• Magnetic dip
• Marching line
• Magnetic Declination
• Pelorus (instrument)
• Radio compass
• Radio direction finder
• Relative bearing
• Wrist compass

Notes[link]

References[link]

• 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.
• 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
• Carlson, John B. (1975) "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, DOI 10.1126/science.189.4205.753
• 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
• Gubbins, David, Encyclopedia of Geomagnetism and Paleomagnetism, Springer Press (2007), ISBN 1-4020-3992-1, ISBN 978-1-4020-3992-8
• Gurney, Alan (2004) Compass: A Story of Exploration and Innovation, London : Norton, ISBN 0-393-32713-2
• Johnson, G. Mark, The Ultimate Desert Handbook, 1st Ed., Camden, Maine: McGraw-Hill (2003), ISBN 0-07-139303-X
• King, David A. (1983). "The Astronomy of the Mamluks". Isis 74 (4): 531–555. DOI:10.1086/353360 
• Kreutz, Barbara M. (1973) "Mediterranean Contributions to the Medieval Mariner's Compass", Technology and Culture, 14 (3: July), p. 367–383
• Lane, Frederic C. (1963) "The Economic Meaning of the Invention of the Compass", The American Historical Review, 68 (3: April), p. 605–617
• Li Shu-hua (1954) "Origine de la Boussole 11. Aimant et Boussole", Isis, 45 (2: July), p. 175–196
• Ludwig, Karl-Heinz and Schmidtchen, Volker (1997) Metalle und Macht: 1000 bis 1600, Propyläen Technikgeschichte, Berlin : Propyläen-Verl., ISBN 3-549-05633-8
• 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
• 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
• 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
• Seidman, David, and Cleveland, Paul, The Essential Wilderness Navigator, Ragged Mountain Press (2001), ISBN 0-07-136110-3
• Taylor, E.G.R. (1951) "The South-Pointing Needle", Imago Mundi, 8, p. 1–7
• Temple, Robert. (1986). The Genius of China: 3,000 Years of Science, Discovery, and Invention. With a foreword by Joseph Needham. New York: Simon and Schuster, Inc. ISBN 0-671-62028-2.
• Williams, J.E.D. (1992) From Sails to Satellites: the origin and development of navigational science, Oxford University Press, ISBN 0-19-856387-6
• 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
• 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

External links[link]

Wikimedia Commons has media related to: Compass

• How to Make a Compass Audio slideshow from the National High Magnetic Field Laboratory
• Science Friday, "The Riddle of the Compass" (interview with Amir Aczel, first broadcast on NPR on May 31, 2002).
• Paul J. Gans, The Medieval Technology Pages: Compass
• The Tides By Sir William Thomson (Lord Kelvin)
• Evening Lecture To The British Association At The Southampton Meeting on Friday, August 25, 1882 [1]. Refers to compass correction by Fourier series.
• Arrick Robots. Robotics.com Example implementation for digital solid-state compass. ARobot Digital Compass App Note
• How a tilt sensor works. David Pheifer [2]
• The Gear Junkie - review of two orienteering thumb compasses
• The good compass video - A video about important abilities a compass should have
• COMPASSIPEDIA, the great virtual Compass Museum gives comprehensive information about all sorts of compasses and how to use them.
• Geography fieldwork
• Travel Island
• Compass whistles Seven types and subgroups.

Jamie Lidell
Jamie Lidell performing live at Metro, Chicago on October 27, 2006
Background information
Born	(1973-09-18) 18 September 1973 (age 38) Huntingdon, Cambridgeshire, England
Genres	Soul, funk, electronica, experimental
Occupations	Musician
Labels	Warp Records
Associated acts	Super Collider

Jamie Lidell (birth name Jamie Lidderdale;^[1] born 18 September 1973 in Huntingdon, Cambridgeshire, England) is an English musician and soul singer living in Nashville, United States. He also has a group with Cristian Vogel called Super Collider.

Career[link]

Lidell is known for layering tracks made with his voice into a microphone and performing the percussion and melody as a sequenced, beatboxing one-man band. Then over his augmented voices, he sings soul-inspired songs. This exercise makes for energetic live performances. Lidell has become renowned for his diverse range of genre-exploration. Following the release of his 2008 album, Jim, Lidell commented,^[2]

I want it to be about music, I think every musician does. But I think inevitably it ends up becoming about personality, which is what gives rise to the music, so people want to make sure that they get a bit of both. The more things do well, the more people want to know why it does well.

His song "Multiply" was used on the television show Grey's Anatomy, and was also included on its second soundtrack. Another song from his album Multiply, "A Little Bit More", was featured in a series of commercials for the U.S. retailer Target.

He often collaborates with Canadian musicians such as Gonzales, Feist and Mocky. He has also recently collaborated with British electronic duo Simian Mobile Disco for the song "Off The Map". In 2006, he was part of a live performance collaboration with David Link and F. M. Einheit, which was released on CD as 'Echohce'.

In early 2009, Lidell's Jim won in The 8th Annual Independent Music Awards for Best Pop/Rock Album.^[3]

In 2009 he contributed a cover of Grizzly Bear's song "Little Brother" to the Warp20 (Recreated) compilation, as well as having his song "A Little Bit More" covered by Tim Exile.

In March 2010, Lidell announced that he is releasing a new album entitled Compass which is being produced by fellow musician and occasional collaborator Beck. The album was released in May 2010.^[4] The title track is featured in the Rockstar video game Red Dead Redemption, and is one of only four songs in the game to include vocals.

Lidell was the co-writer and vocalist for the Simian Mobile Disco track "Put Your Hands Together", from their 2012 album Unpatterns.^[5]

Discography[link]

• Freekin The Frame EP (1997)
• Muddlin Gear (2000, Spymania)
• Multiply (2005, Warp)
• Multiply Additions (2006, Warp)
• Jim (2008, Warp) #183 US
• Compass (2010, Warp) released May 18

References[link]

External links[link]

• Official website
• Jamie Lidell on Myspace

Ai Kawashima 川嶋あい
Ai Kawashima performing at Japan Day 2009 in Central Park, New York
Background information
Birth name	川島 愛
Born	(1986-02-21) February 21, 1986 (age 26)
Origin	Sawara-ku, Fukuoka, Japan
Genres	J-pop
Occupations	Singer-songwriter, pianist
Years active	1999–present
Labels	Tsubasa, Sony Music Japan
Associated acts	I WiSH
Website	www.kawashimaai.com

Ai Kawashima (川嶋 あい, Kawashima Ai^?, February 21, 1986) is a Japanese pop singer-songwriter and pianist. Overcoming her tragic childhood, she released her debut single Asueno tobira (Door to Tomorrow) as the duo I WiSH in 2003. She is well known for her numerous street performances. She is also known for her devotion to help children under circumstances similar to hers in Japan and all over the world.

Early life[link]

Kawashima was born and raised in Fukuoka, Japan.^[1] After her birth, her mother's health deteriorated and she died when Kawashima was only 3 years old. Because her father had been missing before she was born, she was taken to an orphanage and eventually adopted by the Kawashima family, owners of a construction company. Her foster father died when she was 10. After graduating from middle school, she moved to Tokyo.^[1] Her foster mother died when she was 16. She started playing the piano at the age of 3 and eventually began to think about a career as a singer.^[1]

Career[link]

Kawashima started her career as an enka singer. At around the age of 10, she performed on stage at the Carnegie Hall in New York. In 1999, she released her debut single, Juu-roku Koi Gokoro / Anata ni Kataomoi. However, the enka project was crippled by poor sales and was abandoned entirely within a few months.

After this initial failure, she began to sing her own songs on the busy street corners in Shibuya, Tokyo with a microphone and a radio cassette player.^[1] To become famous, she set herself the goal of performing 1,000 times on the street.^[1] Nobody paid attention to her songs at first, but the crowd gradually grew as she kept performing on streets and she met people who gave her support, culminating her major debut and the 2003 hit single Asueno tobira (Door to Tomorrow), which sold more than 900,000 copies.^[1] She sang the song as the vocalist of the duo I WiSH. She has been performing solo since the duo broke up in 2005.^[1] Her second solo single 12-ko no Kisetsu (12 Seasons) ranked 10th on the Billboard Hits of the world, Japan.^[2] Even after her major debut, she kept performing on streets and, in 2005, she accomplished 1,000 times of street performances, which, according to Kawashima, became the foundation of her music.^[1] In 2009, she performed at Japan Day at Central Park, New York.^[3]

Personal life[link]

Kawashima has devoted her time and money to a project to build schools in developing countries. 3 schools have been finished so far and her goal is to build 100 schools.^[4]

Every year since her mother's death, she has held a memorial concert on August 20.

On the night of March 11, 2011, 20 elementary school students who was able to flee the devastating tsunami after Tohoku earthquake comforted each other by singing the song Tabidachi no hi ni (On the day of departure) together at a local Shinto shrine where they spent the night.^[5] The students had been practicing the song for their graduation ceremony, which was only a week away.^[5] Having heard the story, Kawashima visited the students in a shelter on April 6 and sang the same song together.^[6] On August 21, she visited the students one more time to attend their belated graduation ceremony and sang the song together.^[7] The song ends with the words, "Let us bloom from this bud."

Discography[link]

Kawashima's songs have been featured in various anime and video games. Zetsubou to Kibou (絶望と希望^?) is the theme song of Shining Force Neo; Compass is the theme song of the eighth One Piece movie Episode of Alabasta: The Desert Princess and the Pirates, and Kimi no Koe is the ending theme song of The Place Promised in Our Early Days. One of her newest songs, Door Crawl, is the theme song of Final Fantasy Fables: Chocobo's Dungeon.

Singles[link]

1. [2003.08.21] Tenshitachi no Melody / Tabidachi no Asa (「天使たちのメロディー/旅立ちの朝」)
2. [2004.02.18] 12-ko no Kisetsu ~4 Dome no Haru~ (「12個の季節～4度目の春～」)
3. [2004.05.25/06.02] Page 525 (525ページ)
4. [2004.08.04] Mermaid (「マーメイド」)
5. [2004.11.17] 'Sayonara' 'Arigatō' ~Tatta Hitotsu no Basho~ (「さよなら」「ありがとう」～たった一つの場所～)
6. [2005.04.06] Zetsubō to Kibō (「絶望と希望」)
7. [2005.08.24] ...Arigatō... (「・・・ありがとう．．．」)
8. [2006.02.01] Dear / Tabidachi no Hi ni... (Dear/旅立ちの日に…)
9. [2006.04.19] Mienai Tsubasa (「見えない翼」)
10. [2006.10.11] Taisetsu na Yakusoku / Mou Hitotsu no Yakusoku (「大切な約束/もう１つの約束」)
11. [2007.02.14] My Love
12. [2007.03.14] compass
13. [2007.05.30] Kimi ni..... (「君に･････」)
14. [2007.10.03] Shiawase Desu ka / Suitcase (「幸せですか/スーツケース」)
15. [2007.12.12] Door Crawl (「ドアクロール」)
16. [2008.08.20] Kakera (「カケラ」)
17. [2009.04.08] Daijōbu da yo (「大丈夫だよ」)
18. [2009.12.16] Daisuki da yo (「大好きだよ」)
19. [2010.04.07] haru no yume (「春の夢」)
20. [2010.12.16] I Remember feat. Joe Sample

Mini albums[link]

1. [2002.07.13] Kono Basho Kara... (「この場所から・・・」)
2. [2002.10.18] Habatakeru Hi Made... (「はばたける日まで・・・」)
3. [2002.12.26] Ayumi Tsuzukeru Tame ni... (「歩みつづけるために・・・」)
4. [2003.03.08] Yuki ni Saku Hana no yō ni... (「雪に咲く花のように・・・」)
5. [2003.05.23] Ashita o Shinjite... (「明日を信じて・・・」)
6. [2003.08.02] Utai Tsuzukeru Kara... (「歌いつづけるから・・・」)

Albums[link]

1. [2005.05.18] 12-ko no Uta (Message) (12個の歌(メッセージ))
2. [2005.09.28] Rojoushuu 1 Gou (「路上集Ⅰ号」)
3. [2006.05.24] Thank You! (サンキュー!)
4. [2006.08.23] Piano Songs ~Rojoushuu 2 Gou~ (Piano Songs～路上集2号～)
5. [2007.06.27] Ashiato (足あと)
6. [2008.04.23] Café & Musique ~Rojoushuu 3 Gou~ (Café & Musique ～路上集3号～)
7. [2008.06.04] SINGLE BEST
8. [2008.06.04] COUPLING BEST
9. [2009.06.03] Simple Treasure
10. [2010.05.26] 24/24

DVD[link]

1. [2004.12.01] 道の途中で...。 (Michi no Tochuu de...)
2. [2005.06.08] ライブ1000回達成記念～1136日の記録～ (LIVE 1000-kai Tassei Kinen ~1136 Nichi no Kiroku~)
3. [2005.12.21] PV Collection +α
4. [2006.11.01] ドラマ (大切な約束) (Drama (Taisetsu na Yakusoku))
5. [2006.11.29] つばさ祭'06～秘密の陣～ (Tsubasa-Sai '06 ~Himitsu no Jin~)
6. [2006.12.20] 川嶋あいConcert Tour2006 ～サンキュー！～ (Kawashima Ai Concert Tour 2006 ~Thank You~!)
7. [2007.04.11] 2003.8.20 渋谷公会堂 ～旅立ちの朝～ (2003.8.20 Shibuya Kōkaidō ~Tabidachi no Asa~)
8. [2007.06.27] つばさ祭'07～春の陣～ (Tsubasa-Sai '07 ~Haru no Jin~)
9. [2007.12.26] Ai Kawashima Concert 2007 足あと (Ai Kawashima Concert 2007 Ashi Ato)
10. [2009.04.08] The BEST -seventeenfivetwentyto- Ai Kawashima Concert Tour 2008
11. [2010.01.13] What's your Simple Treasure? SPECIAL Ai Kawashima Concert Tour 2009 渋谷C.C.Lemonホール (What's your Simple Treasure? SPECIAL Ai Kawashima Concert Tour 2009 Shibuya C.C.Lemon Hall)

Books[link]

• 16-sai no Shiroi Chizu (16歳の白い地図^?). Gakken. July 25, 2003. ISBN [[Special:BookSources/978-4-05-402205-7|978-4-05-402205-7]]. 
• Aoi Tabi no Tsuzuki (蒼い旅の続き^?). Gentosha. September 2, 2004. ISBN 978-4-344-00669-0. 
• Saigo no Kotoba (最後の言葉^?). Goma Books. September 1, 2005. ISBN 978-4-7771-0209-9. 

References[link]

External links[link]

Wikimedia Commons has media related to: Ai Kawashima

• Official website

James Randi
Born	Randall James Hamilton Zwinge (1928-08-07) August 7, 1928 (age 83) Toronto, Ontario, Canada
Nationality	Canadian American
Occupation	Magician, illusionist, writer, skeptic
Religion	None (atheist)[1]
Website
www.randi.org

James Randi (born Randall James Hamilton Zwinge; August 7, 1928^[2]) is a Canadian-American stage magician and scientific skeptic^[3][4] best known as a challenger of paranormal claims and pseudoscience. Randi is the founder of the James Randi Educational Foundation (JREF). Randi began his career as a magician named The Amazing Randi, but after retiring at age 60, he began investigating paranormal, occult, and supernatural claims, which he collectively calls "woo-woo".^[5]

Although often referred to as a "debunker", Randi rejects that title owing to its perceived bias, instead describing himself as an "investigator".^[6] He has written about the paranormal, skepticism, and the history of magic. He was a frequent guest on The Tonight Show Starring Johnny Carson and was occasionally featured on the television program Penn & Teller: Bullshit!. The JREF sponsors The One Million Dollar Paranormal Challenge offering a prize of US$1,000,000 to eligible applicants^[7] who can demonstrate evidence of any paranormal, supernatural or occult power or event under test conditions agreed to by both parties.^[8]

Early life[link]

Randi was born in Toronto, Ontario, Canada, and has a younger brother and sister.^[9] He took up magic after seeing Harry Blackstone, Sr^[10] and reading magic books while spending 13 months in a body cast following a bicycle accident. He confounded doctors who expected he would never walk again.^[11] Although a brilliant student, Randi often skipped school, and he dropped out of high school at 17 to perform as a conjurer in a carnival roadshow.^[12] In his twenties, Randi posed as a psychic to establish that they were actually doing simple tricks and briefly wrote an astrological column in the Canadian tabloid Midnight under the name "Zo-ran," by simply shuffling up items from newspaper astrology columns and pasting them randomly into a column.^[13][14] In his thirties, Randi worked in Philippine night clubs and all across Japan.^[15] He witnessed many tricks that were presented as being supernatural. One of his earliest reported experiences is that of seeing an evangelist using a version of the "one-ahead"^[16] routine to convince churchgoers of his divine powers.^[17]

Career[link]

Magician[link]

Randi worked as a professional stage magician, or "conjurer" as he prefers to be called,^[18] and escapologist beginning in 1946, initially under his birth name, Randall Zwinge, and then as The Amazing Randi. Early in his career, Randi was part of numerous stunts involving his escape from jail cells and safes. On February 7, 1956, he appeared live on The Today Show, remaining in a sealed metal coffin submerged in a hotel swimming pool for 104 minutes, breaking what was said to be Houdini's record of 93 minutes.^[19][20]

Randi was the host of The Amazing Randi Show on New York radio station WOR in the mid 1960s.^[21] This radio show, which filled Long John Nebel's old slot with similar content after Nebel went to WNBC in 1962, had frequent pro-paranormal guests, including Randi's then-friend James Moseley. Randi, in turn, spoke at Moseley's 1967 Fourth Congress of Scientific Ufologists in New York City,^[22] stating, "Let's not fool ourselves. There are some garden variety liars involved in all this. But in among all the trash and nonsense perpetrated in the name of Ufology, I think there is a small grain of truth."^[23]

Randi also hosted numerous television specials and went on several world tours. Then Randi appeared as "The Amazing Randi" on a television show titled Wonderama from 1967 to 1972,^[24] and as host of a failed revival of the 1950s children's show The Magic Clown in 1970.^[25] In the February 2, 1974, issue of Abracadabra (a British conjuring magazine), Randi defined the magic community, saying, "I know of no calling which depends so much upon mutual trust and faith as does ours." In the December 2003 issue of The Linking Ring, the monthly publication of The International Brotherhood of Magicians, Points to Ponder: Another Matter of Ethics, p. 97, it is stated, "Perhaps Randi's ethics are what make him Amazing" and "The Amazing Randi not only talks the talk, he walks the walk."

During Alice Cooper's 1973–1974 tour, Randi performed as the dentist and executioner on stage,^[26] and designed and built several of the stage props, including the guillotine.^[27][28] Shortly after that, in February 1975, Randi escaped from a straitjacket while suspended upside-down over Niagara Falls in the winter on the Canadian TV program World of Wizards.^[29]

Randi was once accused of actually using "psychic powers" to perform acts such as spoon bending. James Alcock relates this incident, which occurred at a meeting where Randi was duplicating the performances of Uri Geller: A professor from the University at Buffalo shouted out that Randi was a fraud. Randi said, "Yes, indeed, I'm a trickster, I'm a cheat, I'm a charlatan, that's what I do for a living. Everything I've done here was by trickery." The professor shouted back: "That's not what I mean. You're a fraud because you're pretending to do these things through trickery, but you're actually using psychic powers and misleading us by not admitting it."^[30] The famous author and believer in spiritualism Arthur Conan Doyle had years earlier made a similar accusation against the magician Harry Houdini.^[31] A similar event involved Senator Claiborne Pell. Pell believed in psychic phenomena. When Randi demonstrated viewing a hidden drawing by using trickery, Pell refused to believe that it was a trick, saying, "I think Randi may be a psychic and doesn't realize it." Randi has consistently denied having any paranormal powers or abilities.^[32]

Author[link]

Randi is author of Conjuring (1992), a biographical history of noted magicians. The book is subtitled: Being a Definitive History of the Venerable Arts of Sorcery, Prestidigitation, Wizardry, Deception, & Chicanery and of the Mountebanks & Scoundrels Who have Perpetrated these Subterfuges on a Bewildered Public, in short, MAGIC!. The book selects the most influential magicians and explains their history in the context of strange deaths and careers on the road. This work expanded on the 1976 book Houdini, His Life and Art, co-authored with Bert Randolph Sugar, which focused on Houdini and his cohorts. Randi also wrote a children's book in 1989 titled The Magic World of the Amazing Randi, which introduced children to magic tricks. In addition to his magic books, he has written several educational works about the paranormal and pseudoscientific. These include biographies of Uri Geller and Nostradamus as well as reference material on other major paranormal figures. He is currently working on A Magician in the Laboratory, which recounts his application of skepticism to science,^[33] though in January 2011, he expressed doubts as to whether it would be finished. James Randi has since confirmed the that the book will be sent to publishers by May 20, 2012.^[34] He is a member of the all-male literary banqueting club the Trap Door Spiders, which served as the basis of Isaac Asimov's fictional group of mystery solvers the Black Widowers.^[35]

Skeptic[link]

Randi entered the international spotlight in 1972 when he publicly challenged the claims of Uri Geller. Randi accused Geller of being nothing more than a charlatan and a fraud who used standard magic tricks to accomplish his allegedly paranormal feats, and he supported his claims in the book The Truth About Uri Geller.^[17][36] Geller sued Randi for $15 million in 1991 and lost.^[37] Geller's suit against the Committee for Scientific Investigation of Claims of the Paranormal (CSICOP) was thrown out in 1995, and he was ordered to pay $120,000 for filing a frivolous lawsuit.^[38]

Randi was a founding fellow and prominent member of CSICOP.^[39] During the period when Geller was filing numerous civil suits against him, CSICOP's leadership, wanting to avoid becoming a target of Geller's litigation, requested that Randi refrain from commenting on Geller. Randi refused and resigned. However, he still maintains a respectful relationship with the group and frequently writes articles for its magazine.

Randi has gone on to write several books criticizing beliefs and claims regarding the paranormal.^[40] He has also demonstrated flaws in studies suggesting the existence of paranormal phenomena; in his Project Alpha hoax, Randi revealed that he had been able to orchestrate a three-year-long compromise of a privately funded psychic research experiment.^[41] The hoax became a scandal and demonstrated the shortcomings of many paranormal research projects at the university level.