South Pointing Chariot - AbsoluteAstronomy.com

The south-pointing chariot (or carriage) was an ancient Chinese two-wheeled vehicle that carried a movable pointer to indicate the south

South

South is a noun, adjective, or adverb indicating direction or geography.South is one of the four cardinal directions or compass points. It is the opposite of north and is perpendicular to east and west.By convention, the bottom side of a map is south....

, no matter how the chariot turned. Usually, the pointer took the form of a doll

Doll

A doll is a model of a human being, often used as a toy for children. Dolls have traditionally been used in magic and religious rituals throughout the world, and traditional dolls made of materials like clay and wood are found in the Americas, Asia, Africa and Europe. The earliest documented dolls...

or figure with an outstretched arm. The chariot was supposedly used as a compass

Compass

A compass is a navigational instrument that shows directions in a frame of reference that is stationary relative to the surface of the earth. The frame of reference defines the four cardinal directions – north, south, east, and west. Intermediate directions are also defined...

for navigation

Navigation

Navigation is the process of monitoring and controlling the movement of a craft or vehicle from one place to another. It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks...

, and may also have had other purposes.

There are legends of earlier south-pointing chariots, but the first reliably documented one was created by Ma Jun

Ma Jun

Ma Jun , style name Deheng , was a Chinese mechanical engineer and government official during the Three Kingdoms era of China...

(c. 200–265 CE) of Cao Wei

Cao Wei

Cao Wei was one of the states that competed for control of China during the Three Kingdoms period. With the capital at Luoyang, the state was established by Cao Pi in 220, based upon the foundations that his father Cao Cao laid...

during the Three Kingdoms

Three Kingdoms

The Three Kingdoms period was a period in Chinese history, part of an era of disunity called the "Six Dynasties" following immediately the loss of de facto power of the Han Dynasty rulers. In a strict academic sense it refers to the period between the foundation of the state of Wei in 220 and the...

, about eight hundred years before the first navigational use of a magnetic compass. No ancient chariots still exist, but many extant ancient Chinese texts mention them, saying they were used intermittently until about 1300 CE. 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

Gear

A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine....

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, then, 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

Dead reckoning

In navigation, dead reckoning is the process of calculating one's current position by using a previously determined position, or fix, and advancing that position based upon known or estimated speeds over elapsed time, and course...

, which is inherently prone to cumulative errors and uncertainties. Some chariots' mechanisms may have had differential gears. If so, it was probably the first use of differentials anywhere in the world.

Legend

Legend has it that Huangdi, credited as being the founder of the Chinese nation, lived in a magnificent palace in the Kunlun Mountains

Kunlun Mountains

The Kunlun Mountains are one of the longest mountain chains in Asia, extending more than 3,000 km. In the broadest sense, it forms the northern edge of the Tibetan Plateau south of the Tarim Basin and the Gansu Corridor and continues east south of the Wei River to end at the North China Plain.The...

.

There was also at this time another tribal leader, Chi You

Chi You

Chi You was a tribal leader of the ancient nine Li tribe . He is best known as the tyrant who fought against the then-future Yellow Emperor during the Three Sovereigns and Five Emperors era in Chinese mythology. For the Hmong people, Chi You was a sagacious mythical king...

, who was skilled at making weapons and waging war. He attacked the tribe of Yandi, driving them into the lands of Huangdi. Huangdi was angered by this and went to war with Yandi, initially suffering several defeats. At some stage in the fighting Chi You conjured up a thick fog to confound Huangdi's men. They used the south-pointing chariot to find their way and they were ultimately victorious.

History

It was recorded in the Sanguo Zhi (Records of the Three Kingdoms

Three Kingdoms

) that the 3rd century CE mechanical engineer Ma Jun

Ma Jun

Ma Jun , style name Deheng , was a Chinese mechanical engineer and government official during the Three Kingdoms era of China...

from the Kingdom of Wei was the inventor of the south-pointing chariot (also called the south-pointing carriage). After being mocked by Permanent Counsellor Gaotang Long and the Cavalry General Qin Lang that he could not reproduce what they deemed a non-historical and nonsensical pursuit, Ma Jun retorted "Empty arguments with words cannot (in any way) compare with a test which will show practical results". After inventing the device and proving those who were doubtful wrong, he was praised by many, including his contemporary Fu Xuan

Fu Xuan

Fu Xuan was a Chinese poet of the Western Jin Dynasty. An impoverished orphan, he became rich due to his literary fame...

, a noted poet of his age.

After Ma Jun the south-pointing chariot was re-invented by Zu Chongzhi

Zu Chongzhi

Zu Chongzhi , courtesy name Wenyuan , was a prominent Chinese mathematician and astronomer during the Liu Song and Southern Qi Dynasties.-Life and works:...

(429–500 CE), after the details of its instructions had been lost temporarily in China. During the Tang Dynasty

Tang Dynasty

The Tang Dynasty was an imperial dynasty of China preceded by the Sui Dynasty and followed by the Five Dynasties and Ten Kingdoms Period. It was founded by the Li family, who seized power during the decline and collapse of the Sui Empire...

(618–907 CE) and Song Dynasty

Song Dynasty

The Song Dynasty was a ruling dynasty in China between 960 and 1279; it succeeded the Five Dynasties and Ten Kingdoms Period, and was followed by the Yuan Dynasty. It was the first government in world history to issue banknotes or paper money, and the first Chinese government to establish a...

(960–1279 CE) the south-pointing chariot was combined with another mechanical wheeled vehicle, the distance-measuring odometer

Odometer

An odometer or odograph is an instrument that indicates distance traveled by a vehicle, such as a bicycle or automobile. The device may be electronic, mechanical, or a combination of the two. The word derives from the Greek words hodós and métron...

.

Some early historical records state that the south-pointing chariot was invented around the first millennium BCE, but such evidence is obscure.

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

Fu Xuan

Fu Xuan was a Chinese poet of the Western Jin Dynasty. An impoverished orphan, he became rich due to his literary fame...

. The contemporary 3rd century CE source of the Weilüe

Weilüe

The Weilüe written by Yu Huan between CE 239, the end of Emperor Ming’s reign, and 265 CE, the end of the Cao Wei . Although not an "official historian," Yu Huan has always been held in high regard amongst Chinese scholars....

, written by Yuan Huan

Yuan Huan

Yuan Huan, style name Yaoqing , was an official during the Han Dynasty period of Chinese history. During the 190s, he served the warlords Liu Bei, Yuan Shu and Lü Bu. After the fall of Lü Bu in 198, Yuan joined Cao Cao as an advisor. He was involved in a number of policy decisions, including the...

also described the south-pointing chariot of Ma Jun. The Jin Dynasty (265–420 CE) 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

Gatehouse

A gatehouse, in architectural terminology, is a building enclosing or accompanying a gateway for a castle, manor house, fort, town or similar buildings of importance.-History:...

of the Government Workshops (Shang Fang) of the capital city. However, the later written Song Shu

Book of Song

The Book of Song , also called "The History of the Song," 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. It was authored by Shen Yue from...

(Book of Song) (6th century CE) recorded the south-pointing chariot's design and use in further detail, as well as created background legend of the device's (supposed) use long before Ma's time, in the Western Zhou Dynasty (1050–771 BCE). The book also provided description of the south-pointing chariot's re-invention and use in times after Ma Jun and the Three Kingdoms. The 6th century CE text reads as follows. (In this translation, by Needham, the south-pointing chariot is referred to as the south-pointing carriage. Also, he uses "AD" to denote dates in the Common Era, and "BC" for dates Before the Common Era.):

The last sentence of the passage is of great interest for navigation at sea, since the magnetic compass

Compass

used for seafaring navigation was not used until the time of Shen Kuo

Shen Kuo

Shen Kuo or Shen Gua , style name Cunzhong and pseudonym Mengqi Weng , was a polymathic Chinese scientist and statesman of the Song Dynasty...

(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. 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 CE), written soon after the Three Kingdoms era. 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

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

by the 7th century. The Nihon Shoki

Nihon Shoki

The , sometimes translated as The Chronicles of Japan, is the second oldest book of classical Japanese history. It is more elaborate and detailed than the Kojiki, the oldest, and has proven to be an important tool for historians and archaeologists as it includes the most complete extant historical...

(The Chronicles of Japan) of 720 CE described the earlier Chinese Buddhist monk

Monk

A monk is a person who practices religious asceticism, living either alone or with any number of monks, while always maintaining some degree of physical separation from those not sharing the same purpose...

s Zhi Yu and Zhi You constructing several south-pointing Chariots for Emperor Tenji

Emperor Tenji

, also known as Emperor Tenchi, was the 38th emperor of Japan, according to the traditional order of succession.Tenji's reign spanned the years from 661 through 671.-Traditional narrative:...

of Japan in 658 CE. This was followed up by several more chariot devices built in 666 CE as well.

South-pointing chariot in Song Shi

The south-pointing chariot was also combined with the earlier Han Dynasty era invention of the odometer

Odometer

(also Greco-Roman), a mechanical device used to measure distance traveled, and found in all modern automobile

Automobile

An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...

s. It was mentioned in the Song Dynasty

Song Dynasty

(960–1279 CE) historical text of the Song Shi (compiled in 1345) that the engineers Yan Su (in 1027 CE) and Wu Deren (in 1107 CE) both created south-pointing chariots, which it details as follows. (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:

Background and explanation

There is a widely believed hypothesis that most, if not all, south-pointing chariots worked by means of differential gears. 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.

If the hypothesis is true, then the Chinese probably knew about differentials centuries before Europeans. There has been speculation that the ancient Greeks knew about them in about 100 BCE, but this is now considered unlikely. The first true differential gear definitely known to have been used in the Western world was by Joseph Williamson in 1720. He used a differential for correcting the equation of time

Equation of time

The equation of time is the difference between apparent solar time and mean solar time. At any given instant, this difference will be the same for every observer...

for a clock

Clock

A clock is an instrument used to indicate, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell". A silent instrument missing such a mechanism has traditionally been known as a timepiece...

that displayed both mean

Local mean time

Local mean time is a form of solar time that corrects the variations of local apparent time, forming a uniform time scale at a specific longitude...

and solar time

Solar time

Solar time is a reckoning of the passage of time based on the Sun's position in the sky. The fundamental unit of solar time is the day. Two types of solar time are apparent solar time and mean solar time .-Introduction:...

. Even then, the differential was not fully appreciated in Europe until James White emphasized its importance and provided details for it in his Century of Inventions (1822).

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

Parallel transport

In geometry, parallel transport is a way of transporting geometrical data along smooth curves in a manifold. If the manifold is equipped with an affine connection , then this connection allows one to transport vectors of the manifold along curves so that they stay parallel with respect to the...

along the path it travels.

The chariot can be used to detect straight lines or geodesics. 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 non-Euclidean geometry of the Earth's surface (due to it being curved

Curvature

In mathematics, curvature refers to any of a number of loosely related concepts in different areas of geometry. Intuitively, curvature is the amount by which a geometric object deviates from being flat, or straight in the case of a line, but this is defined in different ways depending on the context...

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

Great circle

A great circle, also known as a Riemannian circle, of a sphere is the intersection of the sphere and a plane which passes through the center point of the sphere, as opposed to a general circle of a sphere where the plane is not required to pass through the center...

) 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

Holonomy

In differential geometry, the holonomy of a connection on a smooth manifold is a general geometrical consequence of the curvature of the connection measuring the extent to which parallel transport around closed loops fails to preserve the geometrical data being transported. For flat connections,...

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

Cardinal direction

The four cardinal directions or cardinal points are the directions of north, east, south, and west, commonly denoted by their initials: N, E, S, W. East and west are at right angles to north and south, with east being in the direction of rotation and west being directly opposite. Intermediate...

or south-southwest

Boxing the compass

Boxing the compass is the action of naming all thirty-two points of the compass in clockwise order. Such names are formed by the initials of the cardinal directions and their intermediate ordinal directions, and are very handy to refer to a heading in a general or colloquial fashion, without...

, 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, say, 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.

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

Odometer

, 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

Brake

A brake is a mechanical device which inhibits motion. Its opposite component is a clutch. The rest of this article is dedicated to various types of vehicular brakes....

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. Maybe it is not surprising that the chariots were "lost" when conflicts flared up!

Other mechanical designs for the south-pointing chariot are also possible, including ones that employ a device that is used today, the gyro compass

Gyrocompass

A gyrocompass is a type of non-magnetic compass which bases on a fast-spinning disc and rotation of our planet to automatically find geographical direction...

. 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 CE, 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
Pole star
The term "Pole Star" usually refers to Polaris, which is the current northern pole star, also known as the North Star.In general, however, a pole star is a visible star, especially a prominent one, that is approximately aligned with the Earth's axis of rotation; that is, a star whose apparent...

. Chinese astronomical knowledge
Chinese astronomy
Astronomy in China has a very long history, with historians considering that "they [the Chinese] were the most persistent and accurate observers of celestial phenomena anywhere in the world before the Arabs."...

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. At about the same time, the Vikings are thought to have used birefringent crystals of Iceland Spar
Iceland spar
Iceland spar, formerly known as Iceland crystal, is a transparent variety of calcite, or crystallized calcium carbonate, originally brought from Iceland, and used in demonstrating the polarization of light . It occurs in large readily cleavable crystals, easily divisible into rhombs, and is...

to navigate across the Atlantic Ocean by this method. 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".

Timeline

The south-pointing chariot has been invented and reinvented at many times throughout Chinese history. Below is a partial timeline of the major events;

Year	Event
2634 BCE	According to Legend, the Yellow Emperor Yellow Emperor The Yellow Emperor or Huangdi1 is a legendary Chinese sovereign and culture hero, included among the Three Sovereigns and Five Emperors. Tradition holds that he reigned from 2697–2597 or 2696–2598 BC... designs the south-pointing chariot. It is built for him by the craftsman Fang Bo.
1115 BCE	During the reign of the Duke of Chou, the duke gives five such devices (called Zhinan) to ambassadors of Yueshang to get them back home.
120 .. 139 CE	Zhang Heng Zhang Heng Zhang Heng was a Chinese astronomer, mathematician, inventor, geographer, cartographer, artist, poet, statesman, and literary scholar from Nanyang, Henan. He lived during the Eastern Han Dynasty of China. He was educated in the capital cities of Luoyang and Chang'an, and began his career as a... might have reinvented the vehicle.
233 .. 237	Ma Jun Ma Jun Ma Jun , style name Deheng , was a Chinese mechanical engineer and government official during the Three Kingdoms era of China... constructs a working vehicle for Emperor Ming of Wei.
300	Cui Bao reports that the construction is described in a book (not preserved) named Shang Fang Ku Shih.
334 .. 349	Xie Fei Xie Fei (inventor) Xiè Fēi was a Jie state Later Zhao scholar who occupied a position as Head of the Healing Department in the State Chancellery... makes one for Later Zhao Later Zhao The Later Zhao was a state of the Sixteen Kingdoms during the Jin Dynasty in China. It was founded by the Shi family of the Jie ethnicity... Jie Jie Jie might refer to:* Jie of Xia, last ruler of the Xia Dynasty of China* Jie , tribe in the Xiongnu Confederation in the 4th and 5th centuries* Jie , an ethnic group of Ugandan pastoralists.... state Emperor Shi Jilong Shi Hu Shi Hu , courtesy name Jilong , formally Emperor Wu of Zhao , was an emperor of the Chinese/Jie state Later Zhao... (石季龍, aka Shi Hu Shi Hu Shi Hu , courtesy name Jilong , formally Emperor Wu of Zhao , was an emperor of the Chinese/Jie state Later Zhao... )
394 .. 416	Linghu Sheng makes one for Emperor Xiaowu of Jin China.
417	Linghu Sheng's vehicle is captured by Emperor An of Jin Emperor An of Jin Emperor An of Jin , personal name Sima Dezong , was an emperor of the Eastern Jin Dynasty in China. He was described as so developmentally disabled that he was unable to speak, clothe himself, or be able to express whether he was hungry or full... . It is reported that, at this time, there is no machinery, but only a man inside who turns the figure.
423 .. 452	Guo Shanming fails to make one for Emperor Taiwu of Northern Wei Emperor Taiwu of Northern Wei Emperor Taiwu of Northern Wei , personal name Tuoba Tao , nickname Foli , was an emperor of the Chinese/Xianbei dynasty Northern Wei... .
423 .. 452	Ma Yue Ma Yue Ma Yue was born in 1959 to a Muslim Hui family in Hebei whose association with martial arts goes back six generations.As a five year old, his father Ma Xianda took him to train with his grandfather, Ma Fengtu where he learned his family styles Tongbeiquan, Piguaquan, Fanziquan, Bajiquan, and Cuojiao... succeeds, but he is killed by Guo Shanming.
478	Zu Chongzhi Zu Chongzhi Zu Chongzhi , courtesy name Wenyuan , was a prominent Chinese mathematician and astronomer during the Liu Song and Southern Qi Dynasties.-Life and works:... makes a new improved (bronze gears) vehicle for Emperor Shun of Liu Song Emperor Shun of Liu Song Emperor Shun of Liu Song , personal name Liu Zhun , courtesy name Zhongmou , nickname Zhiguan , was an emperor of the Chinese dynasty Liu Song... .
658	Buddhist monk Chiyu constructs vehicle for Japanese Emperor Tenji Emperor Tenji , also known as Emperor Tenchi, was the 38th emperor of Japan, according to the traditional order of succession.Tenji's reign spanned the years from 661 through 671.-Traditional narrative:...
666	Monk Chiyu constructs another vehicle for Japanese Emperor Tenji Emperor Tenji , also known as Emperor Tenchi, was the 38th emperor of Japan, according to the traditional order of succession.Tenji's reign spanned the years from 661 through 671.-Traditional narrative:... .
806 .. 821	Jin Gongli presents a south-pointing carriage to Emperor Xianzong of Tang Emperor Xianzong of Tang Emperor Xianzong of Tang , personal name Li Chun , né Li Chun , was an emperor of the Chinese Tang Dynasty... .
1027	Engineer Yan Su (member of the "Board of Works") describes his construction (5 cogged, 4 non-cogged gear wheels, 18 soldier-drivers).
1107	Chamberlain Wu Deren presents a specification (24 cogged, 4 non-cogged gear wheels), which is successfully built twice.
1341	Chu Tê-Jun describes a jade figure as part of a miniature south-pointing carriage.
1720	Joseph Williamson uses a differential gear in a clock.
1834	Julius Klaproth Julius Klaproth Julius Heinrich Klaproth , German linguist, historian, ethnographer, author, Orientalist and explorer. As a scholar, he is credited along with Jean-Pierre Abel-Rémusat, with being instrumental in turning East Asian Studies into scientific disciplines with critical methods.-Chronology:Klaproth was... writes to Alexander von Humboldt Alexander von Humboldt Friedrich Wilhelm Heinrich Alexander Freiherr von Humboldt was a German naturalist and explorer, and the younger brother of the Prussian minister, philosopher and linguist Wilhelm von Humboldt... , noting the south-pointing chariot chih-nan-ch´ê, but assumes that a magnetic compass is hidden in the little doll.
1879	James Starley James Starley James Starley was an English inventor and father of the bicycle industry. He was one of the most innovative and successful builders of bicycles and tricycles. His inventions include the differential gear and the perfection of chain-driven bicycles.-Early life:Starley was born in 1831 at Albourne,... first uses a differential gear in a vehicle.
1909	Professor Giles Herbert Giles Herbert Allen Giles was a British diplomat and sinologist, educated at Charterhouse. He modified a Mandarin Chinese Romanization system earlier established by Thomas Wade, resulting in the widely known Wade-Giles Chinese transliteration system... points out that the directional property of the south-pointing chariot was effected by a mechanical system, and not by magnetism.
1909	Professor Bertram Hopkinson (Cambridge Professor of Engineering, Cambridge University The Professorship of Engineering is a professorship at the University of Cambridge. Founded in 1875 as a chair in 'Mechanism and Applied Mechanics', it was renamed to 'Mechanical Sciences' in 1934, and to 'Engineering' in 1966.... ) remarks that some mechanism would have been required to ensure that the gears connected to the chariot wheels at right and left were engaged or disengaged when the chariot turned right or left. After some years of study, he declares that Yen Su's specification is insufficient to build a working model.
1910	The first mechanical navigation aide, "Jones Live Map", is invented. Like in the south-pointing chariot, the movement of the road wheels is geared down, but this time to show the relative position of the vehicle on a map.
1924	Rev. A. C. Moule (Cambridge) proposes a realization of Wu Tê-Jen's specification, where the chariot is allowed to drive only in straight lines. For each turn it is stopped, a gear connected and the turn done on the spot, the pointer now being corrected automatically.
1924	K. T. Dykes is the first to propose a differential gearing, arguing that the clutch Clutch A clutch is a mechanical device which provides for the transmission of power from one component to another... mechanism proposed by Moule is "slow and complicated to drive".
1932	Dr. J.B.Kramer discovers references to the mechanical nature of the south-pointing chariot and declares that the Chinese therefore did not invent the magnetic compass, unaware that the magnetic compass had been described by Shen Kuo about 200 years before its (re)invention in Europe.
1932	George Lanchester (chief engineer at Lanchester Motor Company Lanchester Motor Company The Lanchester Motor Company Limited was a car manufacturer based until 1930 at Armourer Mills, Montgomery Street, Sparkbrook, Birmingham, England. It operated from 1895 to 1955.... ) proposes that the ancient machines (Ma Jun notably) embodied some kind of differential gear. He builds a working model to prove his concept.
1937	Wang Zhenduo proposes a realization of Yan Su's specification and builds a working model from it.
1948	Bao Sihe proposes another reconstruction.
1955	F.W. Cousins introduces the Lanchester reconstruction to a broader public, namely the Meccano Meccano Meccano is a model construction system comprising re-usable metal strips, plates, angle girders, wheels, axles and gears, with nuts and bolts to connect the pieces. It enables the building of working models and mechanical devices.... fans.
1956	J. Coales points out that by hanging a carrot from the emperor's hand, the south-pointing chariot would become self-steering!
1977	Professor André Wegener Sleeswyk publishes a scientific essay on the historic chariots. He proves their feasibility exactly to the words in the ancient texts.
1978	Dr. Alan Partridge starts a contest in Meccano Magazine Meccano Magazine Meccano Magazine was an English monthly hobby magazine published by Meccano Ltd between 1916 and 1963, and by other publishers between 1963 and 1981. The magazine was initially created for Meccano builders, but it soon became a general hobby magazine aimed at "boys of all ages"... for the design with the fewest gears. It is shown subsequently that no gears are necessary at all!
1979	Dr. Noel C. Ta'Bois (LDS RCS Eng) publishes a concise treatise on the theoretical aspects. Working specimens are shown, which do not adhere to the "width equals wheel diameter" rule.
1979	Lu Zhiming produces three reconstructions based on differential gears.
1980	Mr. Don Frantz from New York re-discovers the south-pointing chariot, builds models along the Lanchester path and manages to place them in the Museum of the Province of Xian Shaanxi History Museum Shaanxi History Museum, which located to the northwest of the Giant Wild Goose Pagoda in the ancient city Xi'an, in the Shaanxi province of China, is one of the first huge state museums with modern facilities in China. The museum houses over 300,000 items including murals, paintings, pottery,... .
1982	Yan Zhiren builds another model, stressing that only differential gears provide the accuracy reported by the old writings.
1991	Mr. M. Santander from Spain proposes to use the chariot to teach students the basic concepts of parallel transport Parallel transport In geometry, parallel transport is a way of transporting geometrical data along smooth curves in a manifold. If the manifold is equipped with an affine connection , then this connection allows one to transport vectors of the manifold along curves so that they stay parallel with respect to the... and curvature Curvature In mathematics, curvature refers to any of a number of loosely related concepts in different areas of geometry. Intuitively, curvature is the amount by which a geometric object deviates from being flat, or straight in the case of a line, but this is defined in different ways depending on the context... . En passant a mathematical model is given for Mr. Nuttall's design.

Where they can be seen

While none of the historic south-pointing chariots remain, full sized replicas can be found.

The History Museum in Beijing

Beijing

Beijing , also known as Peking , is the capital of the People's Republic of China and one of the most populous cities in the world, with a population of 19,612,368 as of 2010. The city is the country's political, cultural, and educational center, and home to the headquarters for most of China's...

, China

China

Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

holds a replica based on the mechanism of Yen Su (1027).
The National Palace Museum

National Palace Museum

The National Palace Museum is an art museum in Taipei. It is the national museum of the Republic of China, and has a permanent collection of over 677,687 pieces of ancient Chinese artifacts and artworks, making it one of the largest in the world. The collection encompasses over 8,000 years of...

in Taipei

Taipei

Taipei City is the capital of the Republic of China and the central city of the largest metropolitan area of Taiwan. Situated at the northern tip of the island, Taipei is located on the Tamsui River, and is about 25 km southwest of Keelung, its port on the Pacific Ocean...

, Taiwan

Taiwan

Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...

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 in Toronto Canada.

External links

South Pointing Things – Useful site with lot of info, images and plans for building chariots
RLT – Fully functional model kit
A video of a 3D model of an open differential

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Legend

History

Earliest sources

Japan

South-pointing chariot in Song Shi

Background and explanation

Geometrical properties

Lack of precision, and implications

Chariots without differential gears

Mechanical designs

Non-mechanical possibilities

Necessity of non-mechanical orientation

Timeline

Where they can be seen

See also

External links