View source for Biography:Yi Xing

'''Yi Xing''' ({{zh|c=一行|p=Yī Xíng|w='''I-Hsing'''}}, 683–727), born '''Zhang Sui''' ({{zh|t=張遂}}), was a {{wipe|China}} [[Astronomy:Astronomer|astronomer]], [[Biography:Mathematician|mathematician]], [[Engineering:Mechanical engineering|mechanical engineer]] and [[Philosophy:Bhikkhu|Buddhist monk]] of the Tang dynasty (618&ndash;907). His astronomical [[Globe#celestial|celestial globe]] featured a clockwork [[Engineering:Escapement|escapement]] mechanism, the first in a long tradition of Chinese [[Astronomy:Astronomical clock|astronomical clock]]works.

==Science and technology==

===Terrestrial-astronomical survey===
In the early 8th century, the Tang court put Yi Xing in charge of a [[Engineering:Surveying|terrestrial-astronomical survey]].<ref name="hsu 98">Hsu, 98.</ref> This survey had many purposes. It was established in order to obtain new astronomical data that would aid in the prediction of [[Earth:Solar eclipse|solar eclipse]]s.<ref name="hsu 98"/> The survey was also initiated so that flaws in the calendar system could be corrected and a new, updated calendar installed in its place.<ref name="hsu 98"/> The survey was also essential in determining the measurement of the length of [[Earth:Meridian arc|meridian arc]].<ref name="hsu 98"/> This would resolve the confusion created by the earlier practice of using the difference between shadow lengths of the sun observed at the same time at two places to determine the ground distance between them.<ref name="hsu 98"/> This was the same process used by the ancient Greek [[Biography:Eratosthenes|Eratosthenes]] (276&ndash;196 BC).<ref name="hsu 98"/>

Yi Xing had thirteen test sites established throughout the empire, extending from Jiaozhou in Vietnam — at [[Earth:Latitude|latitude]] 17°N — to the region immediately south of [[Earth:Lake Baikal|Lake Baikal]] — latitude 50°N.<ref name="hsu 99">Hsu, 99.</ref> There were three observations done for each site, one for the height of [[Astronomy:Polaris|polaris]], one for the shadow lengths of summer, and one for the shadow lengths of winter.<ref name="hsu 99"/> The latitudes were deciphered from this data, while the Tang calculation for the length of one degree of meridian was fairly accurate compared to modern calculations.<ref name="hsu 99"/> Yi Xing understood the variations in the length of a degree of meridian, and criticized earlier scholars who permanently fixed an estimate for shadow lengths for the duration of the entire year.<ref name="hsu 99"/>

===The escapement and celestial globe===
Yi Xing was famed for his genius, known to have calculated the number of possible positions on a [[Software:Go (game)|go]] board game (though without a symbol for zero he had difficulties expressing the number). He, along with his associate Liang Lingzan (a government official), is best known for applying the earliest-known escapement mechanism to a water-powered celestial globe. However, Yi Xing's mechanical genius and achievements were built upon the knowledge and efforts of previous Chinese mechanical engineers, such as the statesman and master of gear systems [[Biography:Zhang Heng|Zhang Heng]] (78–139) of the Han Dynasty, the equally brilliant engineer Ma Jun (200–265) of the [[History:Three Kingdoms|Three Kingdoms]], and the Daoist Li Lan (c. 450) of the Southern and Northern Dynasties period.

It was the earlier Chinese inventor Zhang Heng who was the first to apply hydraulic power (i.e. a waterwheel and [[Physics:Water clock|water clock]]) in mechanically-driving and rotating his equatorial [[Astronomy:Armillary sphere|armillary sphere]]. The arrangement followed the model of a water-wheel using the drip of a clepsydra (see [[Physics:Water clock|water clock]]), which ultimately exerted force on a lug to rotate toothed-gears on a polar-axis shaft.<ref name="needham volume 4 532">Needham, Volume 4, 532.</ref> With this, the slow computational movement rotated the armillary sphere according to the recorded movements of the planets and stars. Yi Xing also owed much to the scholarly followers of Ma Jun, who had employed horizontal jack-wheels and other mechanical toys worked by waterwheels.<ref name="needham volume 4 532"/> The Daoist Li Lan was an expert at working with water clocks, creating steelyard balances for weighing water that was used in the tank of the clepsydra,<ref name="needham volume 4 532"/> providing more inspiration for Yi Xing. Like the earlier water-power employed by Zhang Heng and the later escapement mechanism in the astronomical [[Engineering:Clock tower|clock tower]] engineered and erected by [[Biography:Su Song|Su Song]] (1020–1101), Yi Xing's celestial globe employed water-power in order for it to rotate and function properly.<ref name="needham volume 4 470">Needham, Volume 4, 470.</ref> The historian [[Biography:Joseph Needham|Joseph Needham]] states (Wade–Giles spelling):

{{quote|When the first escapement came, in +725 (AD), I-Hsing and Liang Ling-tsan arranged for two jacks to strike the hours, standing on the horizon surface of their sphere or globe.<ref name="needham volume 4 165">Needham, Volume 4, 165.</ref>}}

In regards to mercury instead of water (as noted in the quote above), the first to apply liquid mercury for motive power of an armillary sphere was Zhang Sixun in 979 AD (because mercury would not freeze during winter).<ref name="needham volume 3 350">Needham, Volume 3, 350.</ref><ref name="needham volume 4 471">Needham, Volume 4, 471.</ref> During his age, the Song dynasty (960–1279) era historical text of the ''Song Shi'' mentions Yi Xing and the reason why his armillary sphere did not survive the ages after the Tang (Wade–Giles spelling):

{{quote|A jade balancing mechanism (yu heng)(ie. the escapement) is erected behind (lit. outside) a curtain, holding and resisting (chhih o) the main scoops (shu tou). Water pours down rotating the wheel (chu shui chi lun). Lower, there is a cog-wheel (chi lun) with 43 (teeth). There are also hooks, pins, and interlocking rods one holding another (kou chien chiao tsho hsiang chhih). Each (wheel) moves the next without reliance on any human force. The fastest wheel turns round each day through 2928 teeth (chhih), the slowest one moves by 1 tooth in every 5 days. Such a great difference is there between the speed of the wheels, yet all of them depend on one single driving mechanism. In precision, the engine can be compared with Nature itself (lit. the maker of all things; tsao wu che). As for the rest, it is much the same as the apparatus made (long ago) by I-Hsing. But that old design employed mainly bronze and iron, which corroded and rusted so that the machine ceased to be able to move automatically. The modern plan substitutes hard wood for these parts, as beautiful as jade...<ref name="needham volume 4 499">Needham, Volume 4, 499.</ref>}}

Earlier Tang era historical texts of the 9th century have this to say of Yi Xing's work in astronomical instruments in the 8th century (Wade–Giles spelling):
{{quote|One (of these) was made in the image of the round heavens (yuan thien chih hsiang) and on it were shown the lunar mansions (hsiu) in their order, the equator and the degrees of the heavenly circumference. Water, flowing (into scoops), turned a wheel automatically (chu shui chi lun, ling chhi tzu chuan), rotating it (the sphere) one complete revolution in one day and night. Besides this, there were two rings (lit. wheels) fitted round the celestial (sphere) outside, having the sun and moon threaded on them, and there were made to move in circling orbit (ling te yun hsing). Each day as the celestial (sphere) turned one revolution westwards, the sun made its way one degree eastwards, and the moon 13 and 7/19 degrees (eastwards). After 29 and a fraction rotations (of the celestial sphere) the sun and moon met. After it made 365 rotations the sun accomplished its complete circuit. And they made a wooden casing the surface of which represented the horizon, since the instrument was half sunk in it. This permitted the exact determinations of the times of dawns and dusks, full and new moons, tarrying and hurrying. Moreover there were two wooden jacks standing on the horizon surface, having one a bell and the other a drum in front of it, the bell being struck automatically to indicate the hours, and the drum being beaten automatically to indicate the quarters.<ref name="needham volume 4 473 474">Needham, Volume 4, 473-474.</ref>}}

{{quote|All these motions were brought about (by machinery) within the casing, each depending on wheels and shafts (lun chu), hooks, pins and interlocking rods (kou chien chiao tsho), coupling devices and locks checking mutually (kuan so hsiang chhih)(ie. the escapement). Since (the clock) showed good agreement with the Tao of Heaven, everyone at that time praised its ingenuity. When it was all completed (in +725) it was called the 'Water-Driven Spherical Bird's-Eye-View Map of the Heavens (Shui Yun Hun Thien Fu Shih Thu) or 'Celestial Sphere Model Water-Engine' and was set up in front of the Wu Chheng Hall (of the Palace) to be seen by the multitude of officials. Candidates in the [[Social:Imperial examination|imperial examination]]s (in +730) were asked to write an essay on the new armillary (clock). But not very long afterwards the mechanism of bronze and iron began to corrode and rust, so that the instrument could no longer rotate automatically. It was therefore relegated to the (museum of the) College of All Sages (Chi Hsien Yuan) and went out of use.<ref name="needham volume 4 475">Needham, Volume 4, 475.</ref>}}

==Buddhist Scholarship==
Yi Xing wrote a commentary on the ''Mahavairocana Tantra''. This work had a strong influence on the Japanese monk [[Biography:Kūkai|Kūkai]] and was key in his establishment of Shingon Buddhism.<ref name="Rethinking Japan">Rethinking Japan p.330</ref>

==In his honor==
[[File:Guoqing Temple, 2014-12-27 51.JPG|thumb|right|180px|Memorial Pagoda of Monk Yi Xing]]
At the Tiantai-Buddhist Guoqing Temple of Mount Tiantai in Zhejiang Province, there is a Chinese pagoda erected directly outside the temple known as the Memorial Pagoda of Monk Yi Xing. His tomb is also located on Mount Tiantai.

== See also ==
*List of Chinese people
*[[Biography:List of inventors|List of inventors]]
*[[Engineering:List of mechanical engineers|List of mechanical engineers]]
*[[Engineering:Verge escapement|Verge escapement]]
*Villard de Honnecourt

==Notes==
{{Reflist|20em}}

==References==
*Hsu, Mei-ling. "The Qin Maps: A Clue to Later Chinese Cartographic Development," ''Imago Mundi'' (Volume 45, 1993): 90-100.
*Ju, Zan, [https://web.archive.org/web/20070929105000/http://203.72.198.245/web/Content.asp?ID=63185 "Yixing"]. ''Encyclopedia of China'' (Religion Edition), 1st ed.
*Needham, Joseph (1986). ''Science and Civilization in China: Volume 3''. Taipei: Caves Books, Ltd.
*Needham, Joseph (1986). ''Science and Civilization in China: Volume 4, Part 2''. Taipei: Caves Books, Ltd.
*Boscaro, Adriana (2003) ''Rethinking Japan: Social Sciences, Ideology and Thought''. Routledge. 0-904404-79-x p.&nbsp;330

==External links==
*[https://web.archive.org/web/20070415085348/http://www.chinaculture.org/gb/en_madeinchina/2005-09/02/content_72419.htm Yi Xing at Chinaculture.org]
*[https://web.archive.org/web/20070928212309/http://www.topren.net/travel/sights/tiantaishan/main.html Yi Xing's Tomb Tiantai Mountain]
*[http://hua.umf.maine.edu/China/astronomy/tianpage/0015H_YiXing_9275_man683727bw.html Yi Xing at the University of Maine]


{{DEFAULTSORT:Yi, Xing}}
category:8th-century mathematicians
[[Category:Ancient Chinese astronomers]]
[[Category:Hydraulic engineering]]

{{Sourceattribution|Yi Xing|1}}