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The south-pointing chariot (or carriage) was an ancient Chinese two-wheeled vehicle that carried a movable pointer to indicate the
south South is one of the cardinal directions or compass points. The direction is the opposite of north and is perpendicular to both east and west. Etymology The word ''south'' comes from Old English ''sūþ'', from earlier Proto-Germanic ''*sunþa ...
, no matter how the chariot turned. Usually, the pointer took the form of a
doll A doll is a model typically of a human or humanoid character, often used as a toy for children. Dolls have also been used in traditional religious rituals throughout the world. Traditional dolls made of materials such as clay and wood are foun ...
or figure with an outstretched arm. The chariot was supposedly used as a
compass A compass is a device that shows the cardinal directions used for navigation and geographic orientation. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with ...
for
navigation Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation ...
and may also have had other purposes. The ancient Chinese invented a mobile-like armored cart in the 5th century BC called the Dongwu Che (). It was used for the purpose of protecting warriors on the battlefield. The Chinese war wagon was designed as a kind of mobile protective cart with a shed-like roof. It would serve to be rolled up to city fortifications to provide protection for
sappers A sapper, also called a pioneer or combat engineer, is a combatant or soldier who performs a variety of military engineering duties, such as breaching fortifications, demolitions, bridge-building, laying or clearing minefields, preparing fie ...
digging underneath to weaken a wall's foundation. The early Chinese war wagon became the basis of technologies for the making of ancient Chinese south-pointing chariots. There are legends of earlier south-pointing chariots, but the first reliably documented one was created by the Chinese mechanical engineer Ma Jun ( – 265) of
Cao Wei Wei ( Hanzi: 魏; pinyin: ''Wèi'' < : *''ŋjweiC'' < Three Kingdoms The Three Kingdoms () from 220 to 280 AD was the tripartite division of China among the dynastic states of Cao Wei, Shu Han, and Eastern Wu. The Three Kingdoms period was preceded by the Eastern Han dynasty and was followed by the West ...
. No ancient chariots still exist, but many extant ancient Chinese texts mention them, saying they were used intermittently until about 1300. Some include information about their inner components and workings. There were probably several types of south-pointing chariot which worked differently. In most or all of them, the rotating road wheels mechanically operated a
gear A gear is a rotating circular machine part having cut teeth or, in the case of a cogwheel or gearwheel, inserted teeth (called ''cogs''), which mesh with another (compatible) toothed part to transmit (convert) torque and speed. The basic ...
ed mechanism to keep the pointer aimed correctly. The mechanism had no magnets and did not automatically detect which direction was south. The pointer was aimed southward by hand at the start of a journey. Subsequently, whenever the chariot turned, the mechanism rotated the pointer relative to the body of the chariot to counteract the turn and keep the pointer aiming in a constant direction, to the south. Thus the mechanism did a kind of directional
dead reckoning In navigation, dead reckoning is the process of calculating current position of some moving object by using a previously determined position, or fix, and then incorporating estimates of speed, heading direction, and course over elapsed time. ...
, which is inherently prone to cumulative errors and uncertainties. Some chariots' mechanisms may have had differential gears.


Historical texts


Earliest sources

The south-pointing chariot, a mechanical-geared, wheeled vehicle used to discern the southern cardinal direction (without magnetics), was given a brief description by Ma's contemporary Fu Xuan.Needham, Volume 4, Part 2, 40. The contemporary 3rd century source of the ''
Weilüe The ''Weilüe'' () was a Chinese historical text written by Yu Huan between 239 and 265. Yu Huan was an official in the state of Cao Wei (220–265) during the Three Kingdoms period (220–280). Although not a formal historian, Yu Huan has been h ...
'', written by the East Han dynasty politician
Yuan Huan Yuan Huan ( 190s–210s), courtesy name Yaoqing, was an official who lived during the late Eastern Han dynasty of China. During the 190s, he served under the warlords Liu Bei, Yuan Shu and Lü Bu. After the fall of Lü Bu in 198, Yuan Huan join ...
also described the south-pointing chariot of belonging to the Chinese mechanical engineer and politician Ma Jun. The
Jin dynasty (266–420) The Jin dynasty (; ) or the Jin Empire, sometimes distinguished as the (司馬晉) or the (兩晉), was an imperial dynasty of China that existed from 266 to 420. It was founded by Sima Yan (Emperor Wu), eldest son of Sima Zhao, who had p ...
era text of the ''Shu Zheng Ji'' (Records of Military Expeditions), written by Guo Yuansheng, recorded that south-pointing chariots were often stored in the northern
gatehouse A gatehouse is a type of fortified gateway, an entry control point building, enclosing or accompanying a gateway for a town, religious house, castle, manor house, or other fortification building of importance. Gatehouses are typically the mo ...
of the Government Workshops (Shang Fang) of the capital city. However, the later written ''
Song Shu The ''Book of Song'' (''Sòng Shū'') is a historical text of the Liu Song Dynasty of the Southern Dynasties of China. It covers history from 420 to 479, and is one of the Twenty-Four Histories, a traditional collection of historical records. ...
'' (''Book of Song'') (6th century) recorded the south-pointing chariot's design and use in further detail, as well as creating the background legend of the device's (supposed) use long before Ma's time, in the
Western Zhou dynasty The Western Zhou ( zh, c=, p=Xīzhōu; c. 1045 BC – 771 BC) was a royal dynasty of China and the first half of the Zhou dynasty. It began when King Wu of Zhou overthrew the Shang dynasty at the Battle of Muye and ended when the Quanrong n ...
(1050–771 BC). The book also provided a description of the south-pointing chariot's re-invention and use in times after Ma Jun and the Three Kingdoms. The 6th century text, translated by the British scientist and historian
Joseph Needham Noel Joseph Terence Montgomery Needham (; 9 December 1900 – 24 March 1995) was a British biochemist, historian of science and sinologist known for his scientific research and writing on the history of Chinese science and technology, i ...
, reads as follows (the south-pointing chariot is referred to as the south-pointing carriage): The last sentence of the passage is of great interest for navigation at sea, since the magnetic
compass A compass is a device that shows the cardinal directions used for navigation and geographic orientation. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with ...
used for seafaring navigation was not used until the time of
Shen Kuo Shen Kuo (; 1031–1095) or Shen Gua, courtesy name Cunzhong (存中) and pseudonym Mengqi (now usually given as Mengxi) Weng (夢溪翁),Yao (2003), 544. was a Chinese polymathic scientist and statesman of the Song dynasty (960–1279). Shen wa ...
(1031–1095). Although the ''Song Shu'' text describes earlier precedents of the south-pointing chariot before the time of Ma Jun, this is not entirely credible, as there are no pre-Han or Han dynasty era texts that describe the device.Needham, Volume 4, Part 2, 287–288. In fact, the first known source to describe stories of its legendary use during the Zhou period was the ''Gu Jin Zhu'' book of Cui Bao (c. 300), written soon after the Three Kingdoms era.Needham, Volume 4, Part 2, 288 Cui Bao also wrote that the intricate details of construction for the device were once written in the ''Shang Fang Gu Shi'' (''Traditions of the Imperial Workshops''), but the book was lost by his time.


Japan

The invention of the south-pointing chariot also made its way to
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...
by the 7th century. The '' Nihon Shoki'' (The Chronicles of Japan) of 720 described the earlier Chinese
Buddhist Buddhism ( , ), also known as Buddha Dharma and Dharmavinaya (), is an Indian religion or philosophical tradition based on teachings attributed to the Buddha. It originated in northern India as a -movement in the 5th century BCE, and ...
monk A monk (, from el, μοναχός, ''monachos'', "single, solitary" via Latin ) is a person who practices religious asceticism by monastic living, either alone or with any number of other monks. A monk may be a person who decides to dedic ...
s Zhi Yu and Zhi You constructing several south-pointing Chariots for
Emperor Tenji , also known as Emperor Tenchi, was the 38th emperor of Japan,Imperial Household Agency (''Kunaichō'')天智天皇 (38)/ref> according to the traditional order of succession.Ponsonby-Fane, Richard. (1959). ''The Imperial House of Japan'', p. 52 ...
of Japan in 658.Needham, Volume 4, Part 2, 289. This was followed up by several more chariot devices built in 666 as well.


''Song Shi''

The south-pointing chariot was also combined with the earlier Han dynasty era invention of the
odometer An odometer or odograph is an instrument used for measuring the distance traveled by a vehicle, such as a bicycle or car. The device may be electronic, mechanical, or a combination of the two ( electromechanical). The noun derives from ancient G ...
, a mechanical device used to measure distance traveled, and found in all modern
automobile A car or automobile is a motor vehicle with wheels. Most definitions of ''cars'' say that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people instead of goods. The year 1886 is regarded ...
s. It was mentioned in the
Song dynasty The Song dynasty (; ; 960–1279) was an imperial dynasty of China that began in 960 and lasted until 1279. The dynasty was founded by Emperor Taizu of Song following his usurpation of the throne of the Later Zhou. The Song conquered the res ...
(960–1279) historical text of the ''Song Shi'' (compiled in 1345) that the engineers
Yan Su Yan Su (; 9 May 1930 – 12 February 2016) was a Chinese playwright and lyricist who served as vice-president of China Theatre Association. He held the civilian rank equivalent to general in the PLA Air Force Political Department Song and Dance T ...
(in 1027) and Wu Deren (in 1107) both created south-pointing chariots, which it details as follows.Needham, Volume 4, Part 2, 291. (In Needham's translation, inches and feet (ft) are used as units of distance. 1 inch is 25.4 millimetres. 1 ft is 12 inches or 304.8 mm.) After this initial description of Yan Su's device, the text continues to describe the work of Wu Deren, who crafted a wheeled device that would combine the odometer and south-pointing chariot:


Chariots with differential gears


Background and explanation

The English engineer
George Lanchester George Herbert Lanchester (1874 – 13 February 1970) was an English engineer. He was one of three brothers who played a leading role in the early development of the UK auto-industry. In 1909, following the departure from full-time involvement ...
proposed that some south-pointing chariots employed differential gears.
Joseph Needham Noel Joseph Terence Montgomery Needham (; 9 December 1900 – 24 March 1995) was a British biochemist, historian of science and sinologist known for his scientific research and writing on the history of Chinese science and technology, i ...
(1986). ''Science and Civilization in China: Volume 4, Part 2'', page 296. Taipei: Caves Books, Ltd.
A differential is an assembly of gears, nowadays used in almost all automobiles except some electric and hybrid-electric ones, which has three shafts linking it to the external world. They are conveniently labelled A, B, and C. The gears cause the rotation speed of Shaft A to be proportional to the ''sum'' of the rotation speeds of Shafts B and C. There are no other limitations on the rotation speeds of the shafts. In an automobile, Shaft A is connected to the engine (through the transmission), and Shafts B and C are connected to two road wheels, one on each side of the vehicle. When the vehicle turns, the wheel going around the outside of the turning curve has to roll further and rotate faster than the wheel on the inside. The differential permits this to happen while both wheels are being driven by the engine. If the sum of the speeds of the wheels is constant, the speed of the engine does not change. In a south-pointing chariot, according to the hypothesis, Shaft B was connected to one road wheel and Shaft C was connected ''through a direction-reversing gear'' to the other road wheel. This made Shaft A rotate at a speed that was proportional to the ''difference'' between the rotation speeds of the two wheels. The pointing doll was connected (possibly through intermediate gears) to Shaft A. When the chariot moved in a straight line, the two wheels turned at equal speeds, and the doll did not rotate. When the chariot turned, the wheels rotated at different speeds (for the same reason as in an automobile), so the differential caused the doll to rotate, compensating for the turning of the chariot. The hypothesis that there were south-pointing chariots with differential gears originated in the 20th century. People who were familiar with modern (e.g. automotive) uses of differentials interpreted some of the ancient Chinese descriptions in ways that agreed with their own ideas. Essentially, they re-invented the south-pointing chariot, as it had previously been re-invented several times in antiquity. Working chariots that use differentials have been constructed in recent decades. Whether any such chariots existed previously is not known with certainty. Although the
Antikythera mechanism The Antikythera mechanism ( ) is an Ancient Greek hand-powered orrery, described as the oldest example of an analogue computer used to predict astronomical positions and eclipses decades in advance. It could also be used to track the four-y ...
is believed to have used differential gears, the first true differential gear definitely known to have been used was by Joseph Williamson in 1720.Needham, Volume 4, Part 2, 298. He used a differential for correcting the
equation of time In mathematics, an equation is a formula that expresses the equality of two expressions, by connecting them with the equals sign . The word ''equation'' and its cognates in other languages may have subtly different meanings; for example, in F ...
for a
clock A clock or a timepiece is a device used to measure and indicate time. The clock is one of the oldest human inventions, meeting the need to measure intervals of time shorter than the natural units such as the day, the lunar month and ...
that displayed both
mean There are several kinds of mean in mathematics, especially in statistics. Each mean serves to summarize a given group of data, often to better understand the overall value ( magnitude and sign) of a given data set. For a data set, the '' ar ...
and solar time.


Geometrical properties

If the south-pointing chariot were built perfectly accurately, using a differential gear, and if it travelled on an Earth that was perfectly smooth, it would have interesting properties. It would be a mechanical compass that transports a direction, given by the pointer, along the path it travels. Mathematically the device performs
parallel transport In geometry, parallel transport (or parallel translation) is a way of transporting geometrical data along smooth curves in a manifold. If the manifold is equipped with an affine connection (a covariant derivative or connection on the tangent b ...
along the path it travels. The chariot can be used to detect straight lines or
geodesics In geometry, a geodesic () is a curve representing in some sense the shortest path ( arc) between two points in a surface, or more generally in a Riemannian manifold. The term also has meaning in any differentiable manifold with a connection. ...
. A path on a surface the chariot travels along is a geodesic if and only if the pointer does not rotate with respect to the base of the chariot. Because of the
curvature In mathematics, curvature is any of several strongly related concepts in geometry. Intuitively, the curvature is the amount by which a curve deviates from being a straight line, or a surface deviates from being a plane. For curves, the can ...
of the Earth's surface (due to it being curved around as a globe), the chariot would generally not continue to point due south as it moves. For example, if the chariot moves along a geodesic (as approximated by any
great circle In mathematics, a great circle or orthodrome is the circular intersection of a sphere and a plane passing through the sphere's center point. Any arc of a great circle is a geodesic of the sphere, so that great circles in spherical geome ...
) the pointer should instead stay at a fixed angle to the path. Also, if two chariots travel by different routes between the same starting and finishing points, their pointers, which were aimed in the same direction at the start, usually do not point in the same direction at the finish. Likewise, if a chariot goes around a closed loop, starting and finishing at the same point on the Earth's surface, its pointer generally does not aim in the same direction at the finish as it did at the start. The difference is the holonomy of the path, and is proportional to the enclosed area. If the journeys are short compared with the radius of the Earth, these discrepancies are small and may have no practical importance. Nevertheless, they show that this type of chariot, based on differential gears, would be an imperfect compass even if constructed exactly and used in ideal conditions.


Lack of precision, and implications

Real machines are never built perfectly accurately. Simple geometry shows that if the chariot's mechanism is based on a differential gear and if, for example, the width of the track of the chariot (the separation between its wheels) is three metres, and if the wheels are intended to be identical but actually differ in diameter by one part in a thousand, then if the chariot travels one kilometre in a straight line, the "south-pointing" figure will rotate nearly twenty degrees. If it initially points exactly to the south, at the end of the one-kilometre trip it will point almost to the
south-southeast The points of the compass are a set of horizontal, radially arrayed compass directions (or azimuths) used in navigation and cartography. A compass rose is primarily composed of four cardinal directions—north, east, south, and west—each ...
or
south-southwest The points of the compass are a set of horizontal, radially arrayed compass directions (or azimuths) used in navigation and cartography. A compass rose is primarily composed of four cardinal directions—north, east, south, and west—each ...
, depending on which wheel is the larger. If the chariot travels nine kilometres, the figure will end up pointing almost due north. Obviously, this would make it useless as a south-pointing compass. To be a useful navigational tool, the figure would have to rotate no more than a couple of degrees over a journey of a hundred kilometres, but this would require the chariot's wheels to be equal in diameter to within one part in a million. Even if the process of manufacturing the wheels were capable of this precision (which would not be possible with ancient Chinese methods), it is doubtful that the equality of the wheels could be maintained for long as they are subjected to the wear and tear of travelling across open country. Irregularity of the ground would add further errors to the device's functioning. Considerable scepticism is therefore warranted as to whether this type of south-pointing chariot, using a differential gear for the whole time, was used in practice to navigate over long distances. Conceivably, the south-pointing doll was fixed to the body of the chariot while it was travelling in straight lines, and coupled to the differential only when the chariot was turning. The charioteer could have operated a control to do this just before and after making each turn, or maybe shouted commands to someone inside the chariot who connected and disconnected the doll and the differential. This could have been done without stopping the chariot. If turns were brief and rare, this would have greatly reduced the pointing errors, since they would have accumulated only during the short periods when the doll and differential were connected. However, it raises the problem of how the chariot could have been kept travelling in straight lines with sufficient accuracy without using the pointing doll. If the real purposes of the chariot and the accounts of it were amusement and impressing visiting foreigners, rather than actual long-distance navigation, then its inaccuracy might not have been important. Considering that a large mechanical wagon or chariot would be obligated to travel on roads, the destination in question would typically not be in an unknown direction. The fact that the sources cited above mention that the chariot was placed at the front of processions, its high level of mechanical complexity and fragility, and that it was 'reinvented' several times contribute to the conclusion that it was not used for navigation, as a truly practical and useful navigational tool would not be forgotten or left unused.


Chariots without differential gears

Although the hypothesis that the south-pointing chariot used differential gears has gained wide acceptance, it should be recognized that functional south-pointing chariots without differential gears are possible. The ancient descriptions are often unclear, but they suggest that the Chinese implemented several different designs, at least some of which did not include differentials.


Mechanical designs

Some of the ancient descriptions suggest that some south-pointing chariots could move in only three ways: straight ahead, or turning left or right with a fixed radius of curvature. A third wheel might have been used to fix the turning radius. If the chariot was turning, the pointing doll was connected by gears to one or other of the two main road wheels (e.g. whichever was on the outside of the curve around which the chariot was moving) so the doll rotated at a fixed speed, relative to the rate of the chariot's movement, to compensate for the predetermined rate of turn. The doll turned in opposite directions depending on which road wheel was connected to it, so its rotation compensated for the chariot turning left or right. This design would have been simpler than using a differential gear. The chariots of Yan Su and Wu Deren appear to have used this type of mechanism. (See descriptions quoted from the ''Song Shi'', above.) Apart from the presence of components in Wu Deren's vehicle to make it function as an
odometer An odometer or odograph is an instrument used for measuring the distance traveled by a vehicle, such as a bicycle or car. The device may be electronic, mechanical, or a combination of the two ( electromechanical). The noun derives from ancient G ...
, there were only minor differences between them. In each chariot, the two main road wheels were attached to vertical gear wheels. A large horizontal gear wheel was linked (possibly via intermediate gearing) to the pointing doll, and was positioned so a diameter almost spanned the space between the uppermost points of the vertical gear wheels. When the chariot was moving straight ahead, there was no connection between these gears, but when the chariot turned, a small gear wheel was lowered into contact with the horizontal gear and one of the vertical gears, thus linking the doll to one of the road wheels. Two small gear wheels were available, one to connect the horizontal gear to each of the vertical ones. Of course, they were not used simultaneously. The small gear wheels were raised and lowered by an arrangement of weights, pulleys and cords which were attached to the pole to which the horses that pulled the chariot were harnessed. When the horses moved to one side or the other, in order to turn the chariot, the pole moved and the cords lowered the appropriate small gear wheel into its working position. When the horses returned to walking straight ahead, the small gear wheel was raised out of contact with the main horizontal and vertical gears. Thus the system functioned automatically. The mirror-symmetry of the vertical gears being linked by the small gears to the horizontal gear at diametrically opposite points caused the horizontal gear to rotate in opposite directions depending on which road wheel was linked to it, thus rotating the pointing doll in opposite directions when the chariot turned left and right. The description does not mention a third road wheel to fix the turning radius, but it is possible that such a wheel was present. No gears would have been attached to it, so perhaps the author of the description did not mention it because he did not realize that it was an important part of the mechanism. Putting such a wheel on the chariot and making it function properly would not have been difficult. It might have been attached to the pole to which the horses were harnessed. Stops would have been provided to limit the motions of the pole to left and right. If a third road wheel was included, this type of south-pointing chariot could have worked quite accurately as a compass when used for short journeys under good conditions, but if used for long journeys it would have been subject to cumulative errors, like chariots using the differential mechanism. If in fact there was no third road wheel, the chariot might have functioned as a compass if turns were always made so that one of the two wheels was stationary and only the other rotated, with the pointing doll connected to it by gears. The charioteer could have kept the stationary wheel from turning by controlling the horses appropriately. (A
brake A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction. Backgroun ...
would have helped, but there is no mention of one in the description.) The radius of the curve around which the rotating wheel moved would have equalled the track-width of the chariot, and the gears turning the doll would have been chosen accordingly. This design would have worked as a compass for short journeys, but would have suffered from cumulative errors if used for long ones. Also, the chariot would have been slow and awkward to turn. This might not have mattered if turns were rarely executed. The ''Song Shi'' description of the gears in Yan Su's chariot, and the numbers of teeth on them, suggests that it worked this way, without a third road wheel. The gear ratios would have been correct if the pointing doll was attached directly to the large horizontal gear wheel, and the track-width of the chariot equalled the diameter of the road wheels. Wu Deren's chariot also appears to have been designed to work this way. The width of the chariot, and therefore presumably the track-width, was greater than the diameter of the wheels. The gear ratios were appropriate for these dimensions. The charioteer would have had to use great skill to ensure that the radius of each turn of the chariot was correct to make one of the wheels exactly stop rotating. Unless he did this correctly, the pointing doll would not have kept aiming to the south. He would have been able to adjust the direction in which it aimed by making turns that were more or less sharp. This would sometimes have given him opportunities to use the chariot dishonestly. If it was being demonstrated to spectators, for example, and was being driven around in front of them, making many turns, the charioteer, who would have known which way was south, would have been able to make the chariot ''appear to'' work extremely accurately as a compass for long periods. The spectators could have been shown the machinery, and would have seen that the charioteer could not manipulate the doll. They would presumably have been impressed by the apparent accuracy of the mechanism. It is possible that this type of chariot was sometimes constructed with the prime purpose of fraudulently impressing spectators. Possibly, people who built these chariots deceived their own employers with them, which could have gained them fame and fortune provided nobody tried using the chariots for real navigation. Other mechanical designs for the south-pointing chariot are also possible, including ones that employ a device that is used today, the
gyrocompass A gyrocompass is a type of non-magnetic compass which is based on a fast-spinning disc and the rotation of the Earth (or another planetary body if used elsewhere in the universe) to find geographical direction automatically. The use of a gyroc ...
. However, there is no indication that the ancient Chinese knew of these.


Non-mechanical possibilities

Some south-pointing chariots may not have been purely mechanical devices. Someone riding inside the chariot may have used some non-mechanical method of determining the compass directions, and turned the doll on top of the chariot accordingly. There are several methods that could have been used, for example: * By using a magnetic compass. The Chinese were using this for navigation by the 11th century, when south-pointing chariots were still being made and used. * By using astronomical observations of the Sun and/or stars, e.g. the
Pole Star A pole star or polar star is a star, preferably bright, nearly aligned with the axis of a rotating astronomical body. Currently, Earth's pole stars are Polaris (Alpha Ursae Minoris), a bright magnitude-2 star aligned approximately with its ...
. Chinese astronomical knowledge was extensive. * By using local knowledge. The person in the chariot may have known the area or had a map or description of it. * By observing the polarization of light from the sky. Vikings used
birefringent Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are said to be birefringent (or birefractive). The birefring ...
crystals of Iceland spar to navigate across the Atlantic Ocean by this method at about the same time. Iceland spar is found in China, as well as in Iceland and some other places. Insects such as bees can respond to sky polarization and use it to find their way home. Whether the Chinese used it is hypothetical, but it is certainly possible. * By observing light that had been refracted by the Earth's atmosphere. This is one of the techniques that were used by Polynesian navigators to steer ships among Pacific islands. When the surface of the Earth, ocean or ground, is colder than the air above it, a dense layer of air is formed near the surface, which refracts light downward. The result is that light can go around the curvature of the Earth, allowing things to be seen at much greater distances than simple geometry would predict. The images are very distorted, but they can be recognized by skilled navigators. Certain other Polynesian techniques can also be used on land and may have been employed by the Chinese. Unlike mechanisms that rely on the rotation of road wheels, most of these methods can be used at sea. This may account for the mention (see "Earliest sources" above) that a marine version of the south-pointing chariot existed. These methods can work accurately over long distances, unlike the mechanical designs for the chariot.


Necessity of non-mechanical orientation

Some non-mechanical method of finding the south must have been used when a mechanical south-pointing chariot was initialized, aiming its pointer to the south at the start of a journey. Any of the methods mentioned above in "Non-mechanical possibilities" could have been used. If any south-pointing chariot was really used for long-distance navigation, it must have relied (after initialization) on a non-mechanical direction-finding method. It might have been operated non-mechanically by someone riding in it, as outlined above. Alternatively, if it had a mechanical mechanism, it must have been frequently re-initialized non-mechanically to eliminate accumulated errors and uncertainties. The only chariots that might not have needed non-mechanical methods of finding the south would have been those that were never used for long-distance navigation. If some chariots were used only for amusement or fraud, they could have worked purely mechanically. Even initialization could have been avoided by simply declaring some arbitrary direction to be "south".


Modern replicas

While none of the historic south-pointing chariots remain, full sized replicas can be found. The History Museum in
Beijing } Beijing ( ; ; ), Chinese postal romanization, alternatively romanized as Peking ( ), is the Capital city, capital of the China, People's Republic of China. It is the center of power and development of the country. Beijing is the world's Li ...
,
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
, holds a replica based on the mechanism of Yen Su (1027). The
National Palace Museum The National Palace Museum (; Pha̍k-fa-sṳ: Kwet-li̍p kù-kiung pok-vu̍t-yèn), is a museum in Taipei, Republic of China (Taiwan). It has a permanent collection of nearly 700,000 pieces of Chinese artifacts and artworks, many of which w ...
in
Taipei Taipei (), officially Taipei City, is the capital and a special municipality of the Republic of China (Taiwan). Located in Northern Taiwan, Taipei City is an enclave of the municipality of New Taipei City that sits about southwest of the ...
,
Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the no ...
, holds a replica based on the Lanchester mechanism of 1932. Referred to as the "southern pointing man", two replicas can also be seen (and physically experimented with) at the
Ontario Science Centre The Ontario Science Centre, formally the Centennial Museum of Science and Technology, is a science museum in Toronto, Ontario, Canada. It is located near the Don Valley Parkway about northeast of downtown on Don Mills Road just south of ...
in Toronto, Canada.


See also

* Chariots in ancient China * Chinese war wagon * History of science and technology in China *
List of Chinese inventions China has been the source of many innovations, scientific discoveries and inventions. This includes the '' Four Great Inventions'': papermaking, the compass, gunpowder, and printing (both woodblock and movable type). The list below contains th ...
*
Mechanical engineering Mechanical engineering is the study of physical machines that may involve force and movement. It is an engineering branch that combines engineering physics and mathematics principles with materials science, to design, analyze, manufacture, ...


Notes


References


The Chinese South-Seeking chariot: A simple mechanical device for visualizing curvature and parallel transport
M. Santander, American Journal of Physics – September 1992 – Volume 60, Issue 9, pp. 782–787 *Needham, Joseph (1986). ''Science and Civilization in China: Volume 4, Part 2''. Taipei: Caves Books, Ltd. *
Kit Williams Christopher "Kit" Williams (born 28 April 1946) is an English artist, illustrator and author best known for his 1979 book '' Masquerade'', a pictorial storybook which contains clues to the location of a golden (18 carat) jewelled hare created ...
, ''Engines of Ingenuity'', Gingko Press (February 2002),


External links

{{Commonscat, South-pointing chariot
South Pointing Things
– Useful site with lot of info, images an

for building chariots
RLT
– Fully functional model kit
A video of a 3D model of an open differential
Chariots Chinese inventions Chinese mythology Human-powered vehicles Mechanical engineering Military vehicles of China Vehicle technology Warhorses