South Pointing Chariot

The South Pointing Chariot is widely regarded as one of the most complex geared mechanism of the ancient Chinese civilization, and was continually used throughout the medieval period as well. It was supposedly invented sometime around 2600 BC in China by the Yellow Emperor Huang Di, yet the first valid historical version was created by Ma Jun (c. 200-265 AD) of Cao Wei during the Three Kingdoms. The chariot is a two-wheeled vehicle, upon which is a pointing figure connected to the wheels by means of differential gearing. Through careful selection of wheel size, track and gear ratios, the figure atop the chariot will always point in the same direction, hence acting as a non-magnetic compass vehicle. Throughout history, many Chinese historical texts have mentioned the South Pointing Chariot, while some described in full detail the inner components and workings of the device.

Legend and history

Legend

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

There was also at this time another tribal leader, Chi You, who was skilled at making weapons and waging war. He attacked the tribe of Yan Di, driving them into the lands of Huang Di. Huang Di was angered by this and went to war with Yan Di, initially suffering several defeats. At some stage in the fighting, Chi You conjured up a thick fog to confound Huang Di's men, however the South Pointing Chariot was used to find their way, and they were ultimately victorious.

History

Despite legend, it was recorded in the "Sanguo Zhi" (Records of the Three Kingdoms) that the 3rd century mechanical engineer Ma Jun 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 Caotang 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, a noted poet of his age.

After Ma Jun, the South Pointing Chariot was re-invented by Zu Chongzhi (429-500 AD), after the details of its instructions had been lost temporarily in China. During the Tang Dynasty (618-907 AD) and Song Dynasty (960-1279 AD) the South Pointing Chariot was combined with another mechanical wheeled vehicle, the distance-measuring odometer.

Some early historical records states that the south pointing chariot was invented around the first millenium B.C.E., but such evidence is obscure.

Historical texts for the South Pointing Chariot

Earliest sources

The South Pointing Chariot, a differential 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", written by Yuan Huan also described the South Pointing Chariot of Ma Jun. The Jin Dynasty (265-420 AD) 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 of the Government Workshops (Shang Fang) of the capital city. However, the later written "Song Shu" ("Book of Song") (6th century AD) 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 BC-771 BC). 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 text reads as follows (in Needham's translation, 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 used for seafaring navigation was not used until the time of Shen Kuo (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 AD), 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 by the 7th century. The "Nihon Shoki" (The Chronicles of Japan) of 720 AD described the earlier Chinese Buddhist monks Zhi Yu and Zhi You constructing several South Pointing Chariots for Emperor Tenji of Japan in 658 AD.Needham, Volume 4, Part 2, 289.] This was followed up by several more chariot devices built in 666 AD as well.

outh Pointing Chariot in the "Song Shi"

The South Pointing Chariot was also combined with the earlier Han Dynasty era invention of the odometer (also Greco-Roman), a mechanical device used to measure distance traveled, and found in all modern automobiles. It was mentioned in the Song Dynasty (960-1279 AD) historical text of the "Song Shi" (compiled in 1345) that between the engineers Yan Su (in 1027 AD) and Wu Deren (in 1107 AD) both created South Pointing Chariots, which it details as follows:Needham, Volume 4, Part 2, 291.]

cquote|'...Then below the crossbar at the end of the pole, two small vertical wheels 3 inches in diameter and pierced by an iron axle, to the left 1 small horizontal wheel, 1.2 feet in diameter, with 12 teeth, to the right 1 small horizontal wheel, 1.2 ft. in diameter, with 12 teeth, in the middle 1 large horizontal wheel, of diameter 4.8 ft. and circumference 14.4 ft., with 48 teeth, the teeth at intervals of 3 inches apart; in the middle a vertical shaft piercing the center (of the large horizontal wheel) 8 ft. high and 3 inches in diameter; at the top carrying the wooden figure of the "xian"'.

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:

After the work of these various engineers, to put the device of the South Pointing Chariot into global perspective, the first true differential gear used in the Western world was by Joseph Williamson in 1720.Needham, Volume 4, Part 2, 298.] Joseph Williamson used a differential for correcting the equation of time for a clock that displayed both mean and solar time. 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).

How it works

The South Pointing Chariot is a mechanical compass that transports a direction, given by the pointer, along the path it travels. The differential in the gear system integrates the difference in wheel rotation between the two wheels and thus detects the rotation of the base of the chariot. The mechanism compensates this rotation by rotating the pointer in the opposite direction.

Mathematically the device approximates parallel transport along the path it travels. In the Euclidean plane, the device performs parallel transport. On a curved surface it only approximates parallel transport. In the limit where the distance between the wheels tends to zero, the approximation becomes exact.

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.

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;

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, China holds a replica based on the mechanism of Yen Su (1027).The National Palace Museum in Taipei, Taiwan holds a replica based on the Lanchester mechanism of 1932.

ee also

*List of Chinese inventions
*History of science and technology in China
*Technology of the Song Dynasty
*Mechanical engineering
*Compass

Notes

References

* [http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf&id=AJPIAS000060000009000782000001&idtype=cvips&ident=freesearch&prog=search 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, "Engines of Ingenuity", Gingko Press (February 2002), ISBN-13: 978-1584231066

External links

* [http://www.odts.de/southptr/ South Pointing Things] - Useful site with lot of info, images and [http://www.odts.de/southptr/reposito.htm plans] for building chariots