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{{Infobox person
|name        = 蘇頌 (Sū Sòng)
|birth_date  = 1020
|birth_place = near [[Quanzhou]]
|death_date  = {{death year and age|1101|1020}}
|other_names = 子容 (Zirong)
|occupation  = [[Scholar-bureaucrat]], [[engineer]] and [[diplomat]]
|nationality = Chinese
}}
[[Image:Clock Tower from Su Song's Book.JPG|thumb|right|200px|The original diagram of Su's book showing the inner workings of his clocktower, for more information, click this thumbnail picture.]]
'''Su Song''' ({{zh|t=蘇頌|s=苏颂|p=Sū Sòng}}; [[Chinese style name|style name]]: '''Zirong''' 子容)<ref>Harrist, 239, footnote 9.</ref> (1020–1101 AD) was a renowned [[Chinese people|Chinese]] [[polymath]] who specialized himself as a [[Scholar-bureaucrat|statesman]], [[Chinese astronomy|astronomer]], [[History of cartography#China|cartographer]], [[horology|horologist]], [[Traditional Chinese medicine|pharmacologist]], [[mineralogy|mineralogist]], [[zoology|zoologist]], [[botany|botanist]], [[mechanics|mechanical]] and [[Chinese architecture|architectural engineer]], [[Chinese poetry|poet]], [[antiquarian]], and [[Foreign relations of Imperial China|ambassador]] of the [[Song Dynasty]] (960–1279).

Su Song was the engineer of a [[Hydraulics|water-driven]] [[Astronomical clock|astronomical]] [[clock tower]] in medieval [[Kaifeng]], which employed the use of an early [[escapement]] mechanism.<ref name="needham volume 4 445">Needham, Volume 4, 445.</ref><ref name="needham volume 4 448">Needham, Volume 4, 448.</ref><ref name="bodde 140">Bodde, 140.</ref><ref name="fry 10">Fry, 10.</ref> The escapement mechanism of Su's clock tower had previously been invented by [[Buddhist]] [[monk]] [[Yi Xing]] and government official Liang Lingzan in 725 AD to operate a water-powered [[armillary sphere]], although Su's armillary sphere was the first to be provided with a mechanical clock drive.<ref name="fry 10"/><ref name="needham volume 3 351">Needham, Volume 3, 351.</ref><ref name="bowman 105"/> Su's clock tower also featured the oldest known endless power-transmitting [[chain drive]], called the ''tian ti'' (天梯), or "celestial ladder", as depicted in his horological treatise.<ref name="needham volume 4 111">Needham, Volume 4, 111.</ref> The clock tower had 133 different clock jacks to indicate and [[Striking clock|sound the hours]].<ref>Needham, Volume 4, Part 2, 165.</ref> Su Song's treatise about the clock tower, ''Xinyi Xiangfayao'' (新 儀 . 象 法 要), has survived since its written form in 1092 and official printed publication in 1094. The book has been analyzed by many historians, such as [[Joseph Needham]]. However, the clock itself was dismantled by the invading [[Jin Dynasty (1115–1234)|Jurchen]] army in AD 1127, and although attempts were made to reassemble the clock tower, it was never successfully reinstated. Although the ''Xinyi Xiangfayao'' was his best known treatise, the polymath had other works compiled as well. He completed a large [[celestial atlas]] of several [[star map]]s, several [[Earth|terrestrial]] maps, as well as a treatise on pharmacology. The latter discussed related subjects on mineralogy, zoology, botany, and [[metallurgy]].

Although later European [[Jesuit]] travelers to [[China]] such as [[Matteo Ricci]] and [[Nicolas Trigault]] would briefly mention Chinese clocks with wheel drives in their writing,<ref name="needham volume 4 438">Needham, Volume 4, 438.</ref> early European visitors to China mistakenly believed that the Chinese had never advanced beyond the stage of the [[Water clock|clepsydra]], [[incense clock]], and [[sundial]].<ref name="needham volume 4 435-440"/> They believed that advanced mechanical clockworks were new to China, and were something valuable which Europe could offer.<ref name="needham volume 4 435-440">Needham, Volume 4, 435–440.</ref>  Although not as prominent as in the Song period, contemporary Chinese texts of the [[Ming Dynasty]] (1368–1644) describe a relatively unbroken history of designs of mechanical clocks in China from the 13th to the 16th century.<ref name="needham volume 4 part 2 509 512"/>

==Life and works==
[[Image:SuSongClock1.JPG|thumb|left|220px|A [[scale model]] of Su Song's Astronomical Clock Tower]]
===Career as a scholar-official===
Su Song was born in modern-day [[Fujian]], near medieval [[Quanzhou]].<ref name="needham volume 4 446"/> Like his contemporary [[Shen Kuo]] (1031–1095), Su Song was a [[polymath]]. It was written by his junior colleague and [[Hanlin Academy|Hanlin]] scholar [[Ye Mengde]] (1077–1148)<ref name="liu 593">Liu, 593.</ref> that in Su's youth, he mastered the [[Imperial examination|provincial exams]] and rose to the top of the examination list for writing the best essay on general principles and structure of the [[Chinese calendar]].<ref name="needham volume 4 447"/> From an early age, his interests in astronomy and calendrical science would lead him onto a distinguished path as a [[Scholar-bureaucrat|state bureaucrat]]. In his spare time he was fond of writing poetry, which he used to praise the works of artists such as the painter [[Li Gonglin]] (1049–1106).<ref name="edwards 175 176">Edwards, 175–176.</ref><ref name="harrist 269">Harrist, 269.</ref> He also was an antiquarian and [[Song Dynasty#Archaeology|collector of old artworks from previous dynasties]].<ref name="harrist 269"/>

In matters of administrative government, he had attained the rank of Ambassador and President of the [[Three Departments and Six Ministries|Ministry of Personnel]] at the capital of Kaifeng, and was known also as an expert in administration and finance.<ref name="needham volume 4 32">Needham, Volume 4, 32.</ref> After serving in the Ministry of Personnel, he became a [[Three Departments and Six Ministries|Minister of Justice]] in 1086.<ref name="harrist 269"/> He was appointed as a distinguished editor for the Academy of Scholarly Worthies, where in 1063 he edited, redacted, commented on, and added a preface for the classic work ''[[Huainanzi]]'' of the [[Han Dynasty]] (202 BC–220 AD).<ref name="roth 224">Roth, 224 & 226.</ref> Eventually, Su rose to the post of Vice President of the [[Chancellor of China|Chancellery]] [[wikt:secretariat|Secretariat]]. Among many honorable positions and titles conferred upon him, Su Song was also one of the 'Deputy Tutors of the Heir Apparent'. At court, he chose to distance himself from the political rivalries of the Conservatives, led by Prime Minister [[Sima Guang]] (1019–1086), and the Reformists, led by Prime Minister [[Wang Anshi]] (1021–1086); although many of his associates were of the Conservative faction.<ref name="needham volume 4 446"/> In 1077 he was dispatched on a diplomatic mission to the [[Liao Dynasty]] of the [[Khitan people]] to the north,<ref name="needham volume 4 446 447">Needham, Volume 4, 446–447.</ref> sharing ideas about calendrical science, as the Liao state had created its own calendar in 994 AD.<ref name="bowman 105">Bowman, 105.</ref> In an embarrassing event, Su Song admitted to the emperor that the calendar of the Khitan people was in fact a bit more accurate than their own, resulting in the fining and punishment of officials in the Bureau of Astronomy and Calendar.<ref name="needham volume 4 447">Needham, Volume 4, 447.</ref> Su was supposed to travel north to Liao and arrive promptly for a birthday celebration and feast on a day which coincided with the [[winter solstice]] of the Song calendar, but was actually a day behind the Liao calendar.<ref name="wittfogel feng 599">Wittfogel & Feng, 599.</ref> Historian Liu Heping states that [[Emperor Zhezong of Song]] sponsored Su Song's clocktower in 1086 in order to compete with the Liao for "scientific and national superiority."<ref name="liu 577">Liu, 577.</ref> In 1081, the court instructed Su Song to compile into a book the diplomatic history of Song-Liao relations, an elaborate task that, once complete, filled 200 volumes.<ref name="Breslin 14">Breslin, 14.</ref> With his extensive knowledge of [[cartography]], Su Song was able to settle a heated border dispute between the Song and Liao dynasties.<ref name="Wright 213">Wright, 213.</ref>

===Astronomy===
[[Image:Su Song Star Map 1.JPG|thumb|right|230px|A [[star map]] with equidistant cylindrical projection, from Su Song's ''Xinyi Xiangfayao'', 1092<ref name="needham volume 3 208">Needham, Volume 3, 208.</ref>]]
Su Song also created a celestial atlas (in five separate maps), which had the hour circles between the xiu ([[lunar mansion]]s) forming the [[Meridian (astronomy)|astronomical meridians]], with stars marked in an equidistant cylindrical projection on each side of the [[equator]],<ref name="Miyajima">Miyajima, Kazuhiko (1997). ''Projection Methods in Chinese, Korean and Japanese Star Maps'' from "Highlights of Astronomy" vol. 11B p. 714. Ed. J. Andersen. Norwell: Kluwer Academic Publishers.</ref> and thus, was in accordance to their north polar distances.<ref name="needham volume 4 part 3 569">Needham, Volume 4, Part 3, 569.</ref> Furthermore, Su Song must have taken advantage of the astronomical findings of his political rival and contemporary astronomer Shen Kuo.<ref name="needham volume 3 278">Needham, Volume 3, 278.</ref> This is so because Su Song's fourth star map places the position of the [[pole star]] halfway between Tian shu (−350 degrees) and the current [[Polaris]]; this was the more accurate calculation (by 3 degrees) that Shen Kuo had made when he observed the pole star over a period of three months with his width-improved sighting tube.<ref name="needham volume 3 278"/> There were many star maps written before Song's book, but the greatest significance of these star maps by Su Song is, that they represent the oldest existent star maps in [[printing|printed]] form.<ref name="sivin III 32">Sivin, III, 32.</ref>

===Pharmacology, botany, zoology, and mineralogy===
[[Image:Realgar, 1Rumunia1, Baia Sprie.jpg|thumb|right|200px|Su categorized and accurately described the attributes of many minerals, including the red, pitted surface of [[realgar]] seen above.]]
In 1070, Su Song and a team of scholars compiled and edited the ''Bencao Tujing'' ('Illustrated Pharmacopoeia', original source material from 1058–1061), which was a groundbreaking treatise on pharmaceutical [[botany]], [[zoology]], and [[mineralogy]].<ref name="Wu 5">Wu, 5.</ref> In compiling information for pharmaceutical knowledge, Su Song worked with such notable scholars as Zhang Yuxi, Lin Yi, Zhang Dong, and many others.<ref name="Unschuld 60">Unschuld, 60.</ref> This treatise documented a wide range of pharmaceutical practices, including the use of [[ephedrine]] as a drug.<ref name="needham volume 4 446">Needham, Volume 4, 446.</ref> It includes valuable information on metallurgy and the [[steel]] and [[iron]] industries during 11<sup>th</sup> century China. He created a systematic approach to listing various different minerals and their use in medicinal concoctions, such as all the variously known forms of [[mica]] that could be used to cure ills through [[digestion]].<ref name="needham volume 3 648">Needham, Volume 3, 648.</ref> He wrote of the [[subconchoidal]] fracture of native [[cinnabar]], signs of [[ore]] beds, and provided description on crystal form.<ref name="needham volume 3 649">Needham, Volume 3, 649.</ref> Similar to the ore channels formed by circulation of ground water written of by the later [[Germany|German]] scientist [[Georgius Agricola]], Su Song made similar statements concerning [[copper carbonate]], as did the earlier ''Rihua Bencao'' of 970 with copper [[sulphate]].<ref name="needham volume 3 649"/> Su's book was also the first pharmaceutical treatise written in China to describe the [[flax]], ''[[Urtica thunbergiana]]'', and ''Corchoropsis tomentosa'' (crenata) plants.<ref name="needham volume 6 part 1 174 175">Needham, Volume 6, Part 1, 174, 175.</ref> According to Edward H. Schafer, Su accurately described the translucent quality of fine [[realgar]], its origin from pods found in rocky river gorges, its matrix being pitted with holes and having a deep red, almost purple color, and that the mineral varied in sizes ranging from the size of a pea to a walnut.<ref name="schafer 81">Schafer, 81.</ref> Citing evidence from an ancient work by [[Zheng Xuan]] (127–200), Su believed that physicians of the ancient [[Zhou Dynasty]] (1046–256 BC) used realgar as a remedy for [[peptic ulcer|ulcer]]s.<ref name="schafer 83">Schafer, 83.</ref> As believed in Su's day, the "five poisons" used by Zhou era physicians for this purpose were thought to be cinnabar, realgar, [[chalcanthite]], [[alum]], and [[magnetite]].<ref name="schafer 83"/> Su made systematic descriptions of animals and the environmental regions they could be found, such as different species of freshwater, marine, and shore [[crab]]s.<ref name="west 606">West, 606.</ref> For example, he noted that the freshwater crab species ''Eriocher sinensis'' could be found in the [[Huai River]] running through [[Anhui]], in waterways near the capital city, as well as reservoirs and marshes of [[Hebei]].<ref name="west 606"/> Su's book was preserved and copied into the ''[[Bencao Gangmu]]'' of the [[Ming Dynasty]] (1368–1644) physician and pharmacologist [[Li Shizhen]] (1518–1593).<ref name="west 605">West, 605.</ref>

===Horology and mechanical engineering===
[[Image:SuSongClock2.JPG|thumb|left|Armillary sphere on roof]]
Su Song compiled one of the greatest Chinese [[horological]] treatises of the [[Middle Ages]], surrounding himself with an entourage of notable engineers and astronomers to assist in various projects. ''Xinyi Xiangfayao'' (lit. "Essentials of a New Method for Mechanizing the Rotation of an Armillary Sphere and a Celestial Globe"), written in 1092, was the final product of his life's achievements in horology and clockwork. Fortunately, this book of Su's that was handed down included 47 different illustrations of great detail of the mechanical workings for his [[astronomical clock|astronomical]] [[clocktower]].<ref name="ceccarelli 58">Ceccarelli, 58.</ref>

Su Song's greatest project was the 40-foot-tall water-powered astronomical clocktower constructed in Kaifeng, the wooden pilot model completed in 1088, the bronze components cast by 1090, while the wholly finished work was completed by 1094 during the reign of [[Emperor Zhezong of Song]].<ref name="fry 9">Fry, 9.</ref><ref name="needham volume 4 part 2 495">Needham, Volume 4, Part 2, 495.</ref>  The emperor had previously commissioned [[Han Gonglian]], Acting Secretary of the Ministry of Personnel, to head the project, but the leadership position was instead handed down to Su Song. The emperor ordered in 1086 for Su to reconstruct the ''hun yi'', or "armillary clock", for a new clock-tower in the capital city. Su worked with the aid of Han Gong-lian, who applied his extensive knowledge of mathematics to the construction of the clock-tower.<ref name="needham volume 4 39">Needham, Volume 4, 39.</ref> A small-scale wooden model was first crafted by Su Song, testing its intricate parts before applying it to an actual full-scale clock tower.<ref name="needham volume 4 465">Needham, Volume 4, 465.</ref> In the end, the clock-tower had many impressive features, such as the water-powered, rotating armillary sphere crowning the top-level and weighing some 10 to 20 tons,<ref name="needham volume 4 465"/> a bronze celestial globe located in the middle that was 4.5 feet in diameter,<ref name="needham volume 4 465"/> mechanically-timed and rotating [[manikin]]s dressed in miniature [[Han Chinese clothing|Chinese clothes]] that would exit miniature opening doors to announce the time of day by presenting designated reading plaques, ringing bells and gongs, or beating drums,<ref name="needham volume 4 455">Needham, Volume 4, 455.</ref> a sophisticated use of oblique gears and an escapement mechanism,<ref name="needham volume 4 456">Needham, Volume 4 456.</ref> as well as an exterior [[facade]] of a fanciful [[Chinese pagoda]]. Upon its completion, the tower was called the ''Shui Yun Yi Xiang Tai'', or "Tower for the Water-Powered Sphere and Globe". Joseph Needham writes:

[[Image:Su Song Star Map 2.JPG|thumb|right|200px|Star map of the [[map projection|south polar projection]] for Su's celestial globe, ''Xin Yi Xiang Fa Yao'', 1092]]
{{quote|After the invention of the escapement in ~AD 725 ([[Tang Dynasty]]), there was a great flourishing of gear-wheels in clockwork and jackwork, culminating in the bronze and iron of Su Song's elaborate masterpiece in ~AD 1088.<ref name="needham volume 4 89">Needham, Volume 4, 89.</ref>}}

Years after Su's death, the capital city of Kaifeng was besieged and captured in 1127 by the [[Jurchens]] of the [[Manchurian]]-based [[Jin Dynasty, 1115–1234|Jin Dynasty]].<ref name="ceccarelli 58"/><ref name="Wright 96">Wright, 96.</ref> The clock-tower was dismantled piece by piece by the Jurchens, who carted its components back to their own capital in modern-day [[Beijing]]. However, due to the complexity of the tower, they were unable to successfully piece it back together. The new [[Emperor Gaozong of Song]] instructed Su's son, Su Xie, to construct a new astronomical clock-tower in its place, and Su Xie set to work studying his father's texts with a team of other experts. However, they were also unsuccessful in creating another clock tower, and Su Xie was convinced that Su Song had purposefully left out essential components in his written work and diagrams so that others would not steal his ideas.

As the [[sinologist]] historian [[Derk Bodde]] points out, Su Song's astronomical clock did not lead to a new generation of mass-produced clockworks throughout China since his work was largely a government-sponsored endeavor for the use of astronomers and [[astrologer]]s in the imperial court.<ref name="bodde 362">Bodde, 362.</ref> Yet the mechanical legacy of Su Song did not end with his work. In about 1150, the writer Xue Jixuan noted that there were four types of clocks in his day, the basic [[waterclock]], the [[incense clock]], the [[sundial]], and the clock with 'revolving and snapping springs' ('gun tan').<ref name="needham volume 4 part 2 462">Needham, Volume 4, Part 2, 462.</ref> The rulers of the continuing [[Yuan Dynasty]] (1279–1368 AD) had a vested interest in the advancement of mechanical clockworks.<ref name="fry 12">Fry, 12.</ref>  The astronomer [[Guo Shoujing]] helped restore the [[Beijing Ancient Observatory]] beginning in 1276, where he crafted a water-powered armillary sphere and clock with clock jacks being fully implemented and sounding the hours.<ref name="needham volume 4 part 2 504 505">Needham, Volume 4, Part 2 504–505.</ref>  Complex gearing for uniquely Chinese clockworks were continued in the [[Ming Dynasty]] (1368–1644), with new designs driven by the power of falling sand instead of water to provide motive power to the wheel drive, and some Ming clocks perhaps featured reduction gearing rather than the earlier escapement of Su Song.<ref name="needham volume 4 part 2 509 512">Needham, Volume 4, Part 2, 509–512.</ref>  The earliest such design of a sand-clock was made by Zhan Xiyuan around 1370, which featured not only the scoop wheel of Su Song' device, but also a new addition of a [[Dial (measurement)|stationary dial face]] over which a pointer circulated, much like new European clocks of the same period.<ref name="needham volume 4 part 2 511">Needham, Volume 4, Part 2, 511.</ref>

==Su Song's escapement mechanism==
[[Image:Chain drive, Su Song's book of 1092.jpg|thumb|200px|The oldest known illustration of an endless power-transmitting [[chain drive]], from Su's book of 1092; it was called the "celestial ladder" and was used for coupling the main driving shaft of his clock tower to the armillary sphere gear box (which was mounted at the top of the tower).]]
In Su Song's waterwheel linkwork device the action of the escapement's arrest and release are achieved by gravity exerted periodically as the continuous flow of liquid would fill containers of limited size.<ref name="needham volume 4 462">Needham, Volume 4, 462.</ref> In a single line of evolution, Su Song's clock therefore united the concept of the clepsydra and the mechanical clock into one device run by mechanics and hydraulics. In his memorial, Su Song wrote about this concept:

{{quote|According to your servant's opinion there have been many systems and designs for astronomical instruments during past dynasties all differing from one another in minor respects. But the principle of the use of water-power for the driving mechanism has always been the same. The heavens move without ceasing but so also does water flow (and fall). Thus if the water is made to pour with perfect evenness, then the comparison of the rotary movements (of the heavens and the machine) will show no discrepancy or contradiction; for the unresting follows the unceasing.<ref name="needham volume 4 466"/>}}

In his writing, Su Song credited, as the predecessor of his working clock, the hydraulic-powered armillary sphere of [[Zhang Heng]] (78–139 AD), an earlier Chinese scientist.<ref name="needham volume 4 466">Needham, Volume 4, 466.</ref> Su Song was also strongly influenced by the earlier armillary sphere created by [[Zhang Sixun]] (976 AD), who also employed the escapement mechanism and used liquid [[mercury (element)|mercury]] instead of water in the waterwheel of his astronomical clock tower (since liquid mercury would not freeze during winter and would not corrode and rust metal components over time).<ref name="needham volume 4 469 471">Needham, Volume 4, 469–471.</ref> However, Su Song stated in his writing that after Zhang's death, no one was able to replicate his device, much like his own.<ref name="needham volume 4 470">Needham Volume 4, 470.</ref>

The mechanical clockworks for Su Song's astronomical tower featured a great driving-wheel that was 11 feet in diameter, carrying 36 scoops on its circumference, into each of which water would pour at uniform rate from the 'constant-level tank' (Needham, Fig. 653). The main driving shaft of iron, with its cylindrical necks supported on iron crescent-shaped bearings, ended in a pinion which engages with a gear-wheel at the lower end of the main vertical transmission-shaft.<ref name="needham volume 4 451">Needham, Volume 4, 451.</ref>

Joseph Needham gives a general description of the clock-tower itself:

{{quote|(Su Song's) clockwork, driven by a water-wheel, and fully enclosed within the tower, rotated an observational armillary sphere on the top platform and a celestial globe in the upper story. Its time-announcing function was further fulfilled visually and audibly by the performances of numerous jacks mounted on the eight superimposed wheels of a time-keeping shaft and appearing at windows in the pagoda-like structure at the front of the tower. Within the building, some 40 ft. high, the driving-wheel was provided with a special form of escapement, and the water was pumped back into the tanks periodically by manual means. The time-annunciator must have included conversion gearing, since it gave 'unequal' as well as equal time signals, and the sphere probably had this. Su Sung's treatise on the clock, the ''Hsin I Hsiang Fa Yao'', constitutes a classic of horological engineering.<ref name="needham volume 4 449">Needham, Volume 4, 449.</ref>}}

[[Image:SuSongClock3.JPG|thumb|right|Celestial globe on third floor]]
[[Image:SuSongClock4.JPG|thumb|right|Time display panel]]
[[Image:SuSongClock5.JPG|thumb|right|Water wheel with water tank and [[escapement]] mechanism]]
That was figure Fig. 650, while Fig. 656 displays the upper and lower [[noria]]s with their tanks and the manual wheel for operating them.

Fig. 657 displays a rather miniature and scaled-down pic for the basics of the escapement mechanism in an illustration (from Su's book), with Needham's caption here in this quote: "The 'celestial balance' or escapement mechanism of Su Sung's clockwork (Xinyi Xiangfayao, ch. 3, p. 18b),".<ref name="needham volume 4 458">Needham, Volume 4, 458.</ref> The latter figure carefully labels:

*a right upper lock
*upper link
*left upper lock
*axle or pivot
*long chain
*upper counterweight
*sump
*checking fork of the lower balancing lever
*coupling tongue
*main (i.e. lower) counterweight.<ref name="needham volume 4 458"/>

Figure 658. displays a more intricate and most-telling half-page scale drawing of Su Song's large escapement mechanism, labeling these individual parts as they interact with one another:

*arrested spoke
*left upper lock
*scoop  being filled by
*water jet from constant-level tank
*small counterweight
*checking fork  tripped by a projection pin on the scoop, and forming the near end of
*the lower balancing lever  with
*its lower counterweight
*coupling tongue, connected by
*the long chain with
*the upper balancing lever, which has at its far end
*the upper counterweight, and at its near end
*a short length chain connecting it with the upper lock beneath it;
*right upper lock <ref name="needham 460">Needham, volume 4 460.</ref>

==The endless chain drive==

[[Image:Chain.gif|frame|right|An endless roller chain and [[sprocket]], used in Su Song's clock tower to operate the rotation of the [[armillary sphere]]]]
The world's oldest illustrated depiction of an endless power-transmitting chain drive is from Su Song's horological treatise.<ref name="needham volume 4 111"/> It was used in the clockworks for coupling the main drive shaft to the armillary sphere gearbox (rotating three small pinions),<ref name="needham volume 4 457">Needham, Volume 4, 457.</ref> as seen in Needham's Fig. 410 and Fig. 652.<ref name="needham volume 4 111"/> This belonged to the uppermost end of the main vertical transmission shaft, incorporating right angle gears and oblique gears connected by a short idling shaft.<ref name="needham volume 4 456"/> The toothed ring gear called the diurnal motion gear ring  was fit around the shell of the armillary sphere along the declination parallel near the southern pole.<ref name="needham volume 4 456 457">Needham, Volume 4, 456–457.</ref> Although the ancient [[History of Greece|Greek]] [[Philo of Byzantium]] (3rd century BC) featured a sort of endless belt for his magazine [[ballista|arcuballista]], which did not transmit continuous power,<ref name="needham volume 4 457"/> the influential source for Su Song's chain drive is most likely the continuously-driven [[chain pump]] known in China since the [[Han Dynasty]] (202 BC–220 AD).<ref name="needham volume 4 457"/> From his horological treatise, Su Song states:

{{quote|The chain drive (lit. celestial ladder) is {{convert|19.5|ft|m|abbr=on|adj=mid|long}}. The system is as follows: an iron chain with its links joined together to form an endless circuit hangs down from the upper chain-wheel which is concealed by the tortoise-and-cloud (column supporting the armillary sphere centrally), and passes also round the lower chain-wheel which is mounted on the main driving-shaft. Whenever one link moves, it moves forward one tooth of the diurnal motion gear-ring and rotates the Component of the Three Arrangers of Time, thus following the motion of the heavens.<ref name="needham volume 4 457"/>}}

In addition, the motion gear rings and the upper drive wheel both had 600 teeth, which by Su's mathematical precision carefully calculated measured units of the day in a division of 1/600.<ref name="fry 11">Fry, 11.</ref> These gears having 600 teeth would thus ensure the division the day into basic unit measurements of 2 minutes and 24 seconds.<ref name="fry 11"/>

==Su Song's armillary sphere==

[[Image:Ancient Beijing observatory 04.jpg|thumb|right|230px|A modern replica of a [[Ming Dynasty]] era armillary sphere found at the Beijing Ancient Observatory]]
In Joseph Needham's third volume of ''Science and Civilization in China'', the drawing for Fig. 159 displays a drawing of Su Song's armillary sphere (as depicted in his 11<sup>th</sup> century treatise), complete with three 'nests' or layers of mechanically-rotated rings. It was the earlier Chinese astronomer Li Chun-feng of the Tang Dynasty who in 633 AD created the first armillary sphere with three layers to calibrate multiple aspects of astronomical observation.<ref name="needham volume 3 343">Needham, Volume 3, 343.</ref> Zhang's armillary sphere has often been compared to that of the 13<sup>th</sup> century monarch [[Alfonso X of Castile]] in [[Islamic]]-era [[Spain]]. The chief difference was that Alfonso's instrument featured an arrangement for making measurements of the [[azimuth]] and [[altitude]], which was present in the [[Arabic]] tradition, while Su Song's armillary sphere was duly graduated.<ref name="needham volume 3 353">Needham, Volume 3, 353.</ref> For the drawing of Su's armillary sphere, the listing of components are:

*The Outer Nest <ref name="needham volume 3 351">Needham, Volume 3, 351.</ref>
**meridian circle
**horizon circle
**outer equator circle

*The Middle Nest<ref name="needham volume 3 351"/>
**solstitial colure circle
**ecliptic circle
**diurnal motion gear-ring, connecting with the power-drive

*The Inner Nest <ref name="needham volume 3 351"/>
**polar-mounted declination ring or hour-angle circle, with
**sighting tube attached to it and strengthened by a
**diametral brace

*Other Parts<ref name="needham volume 3 351"/>
**vertical column concealing the transmission shaft
**supporting columns in the form of dragons
**cross-piece of the base, incorporating water-levels
**south polar pivot
**north polar pivit

==Transmission of Su's text and his legacy==

When Su Song's ''Xinyi Xiangfayao'' was written in 1092 and the horological monograph finalized and presented in 1094, his work was published and widely [[printing|printed]] in the north (see [[woodblock printing]] and [[movable type]] of [[Bi Sheng]]). In the south, printing and circulation of his work was not widely distributed until Shi Yuanzhi of [[Jiangsu]] had it printed there in 1172.<ref name="needham volume 4 448"/>

When presenting his clocktower design to the Emperor Zhezong, Su Song equated the constant flow of water with the continuous movements of the heavens, the latter of which symbolized the unceasing power of the emperor.<ref name="liu 578 585">Liu, 578, 585.</ref> This appealed to emperor, who featured artwork representing the clocktower on vehicles of major imperial processions, as illustrated in the ''Illustration of the Imperial Grand Carriage Procession'' of 1053.<ref name="liu 578">Liu, 578.</ref>

The later [[Ming Dynasty]]/[[Qing Dynasty]] scholar Qian Zeng (1629–1699) held an old volume of Su's work, which he faithfully reproduced in a newly-printed edition. He took special care in avoiding any rewording or inconsistencies with the original text as well.<ref name="needham volume 4 448"/> Again, it was later reprinted by Zhang Xizu (1799–1844).<ref name="needham volume 4 448"/>

Interestingly enough, Su Song's treatise on astronomical clockwork was not the only one made in China during his day, as the ''[[Song Shi]]'' (compiled in 1345) records the written treatise of the ''Shuiyunhun Tianjiyao'' (Wade-Giles: ''Shui Yun Hun Thien Chi Yao''; lit. Essentials of the [Technique of] making Astronomical Apparatus revolve by Water-Power), written by Juan Taifa. However, this treatise no longer survives.<ref name="needham volume 4 450">Needham, Volume 4, 450.</ref>

In the realm of modern research, the late British [[biochemist]] and historian of Chinese science [[Joseph Needham]] (1900–1995) (known as Li Yuese in China) did extensive research and analysis of Su Song's texts and various achievements in his ''Science and Civilization in China'' book series. Joseph Needham also related many detailed passages from Su's contemporary medieval Chinese sources on the life of Su and his achievements known in his day. In 1956, John Christiansen reconstructed a model of Su Song's clocktower in a famous drawing, which garnered attention in the West towards 11<sup>th</sup> century Chinese engineering.<ref name="liu 577 579">Liu, 577–579.</ref> A miniature model of Su Song's clock was reconstructed by John Cambridge and is now on display at the [[Science Museum (London)|National Science Museum]] at [[South Kensington]], [[London]].<ref name="liu 593"/> In China, the clocktower was reconstructed to one-fifth its actual scale by Wang Zhenduo, who worked for the Chinese Historical Museum in [[Beijing]] in the 1950s.<ref name="xi 466">Xi, 466.</ref>

==See also==
{{Portal|Atlas}}
*[[List of Chinese writers]]
*[[List of mineralogists]]
*[[List of cartographers]]
*[[Clock tower]]
*[[Water clock]]
*[[Pin-pallet escapement]]
*[[Grasshopper escapement]]
*[[Technology of the Song Dynasty]]
*[[Richard of Wallingford]]
*[[Villard de Honnecourt]]
*Giovanni [[de Dondi]]
*[[John Harrison]]
*[[Thomas Tompion]]
*[[George Graham (clockmaker)|George Graham]]
*[[Jean Froissart]]
*[[Dante Alighieri]]
*[[Zhang Heng]]

==Notes==
{{Reflist|2}}

==References==
<div class="references-small">
*Bodde, Derk (1991). ''Chinese Thought, Society, and Science''. Honolulu: University of Hawaii Press.
*Bowman, John S. (2000). ''Columbia Chronologies of Asian History and Culture''. New York: Columbia University Press.
*Breslin, Thomas A. (2001). ''Beyond Pain: The Role of Pleasure and Culture in the Making of Foreign Affairs''. Westport: Praeger Publishers.
*Ceccarelli, Marco (2004). ''International Symposium on History of Machines and Mechanisms''. New York: Kluwer Academic Publishers.
*Edwards, Richard. "Li Gonglin's Copy of Wei Yan's 'Pasturing Horses'," ''Artibus Asiae'' (Volume 53, Number 1/2, 1993): 168–181; 184–194.
*Fry, Tony (2001). ''The Architectural Theory Review: Archineering in Chinatime''. Sydney: University of Sydney.
*Harrist, Robert E., Jr. "The Artist as Antiquarian: Li Gonglin and His Study of Early Chinese Art," Artibus Asiae (Volume 55, Number 3/4, 1995): 237–280.
*Liu, Heping. ""The Water Mill" and Northern Song Imperial Patronage of Art, Commerce, and Science," ''The Art Bulletin'' (Volume 84, Number 4, 2002): 566–595.
*Needham, Joseph (1986). ''Science and Civilization in China: Volume 3, Mathematics and the Sciences of the Heavens and the Earth''. Taipei: Caves Books, Ltd.
*Needham, Joseph (1986). ''Science and Civilization in China: Volume 4, Physics and Physical Technology, Part 2: Mechanical Engineering''. Taipei: Caves Books, Ltd.
*Needham, Joseph (1986). ''Science and Civilization in China: Volume 4, Physics and Physical Technology, Part 3, Civil Engineering and Nautics''. Taipei: Caves Books, Ltd.
*Needham, Joseph (1986). ''Science and Civilization in China: Volume 6, Biology and Biological Technology, Part 1, Botany''. Taipei: Caves Books Ltd.
*Roth, Harold D. "Text and Edition in Early Chinese Philosophical Literature," ''Journal of the American Oriental Society'' (Volume 113, Number 2, 1993): 214–227.
*Schafer, Edward H. "Orpiment and Realgar in Chinese Technology and Tradition," ''Journal of the American Oriental Society'' (Volume 75, Number 2, 1955): 73–89.
*Sivin, Nathan (1995). ''Science in Ancient China: Researches and Reflections''. Brookfield, Vermont: VARIORUM, Ashgate Publishing.
*Unschuld, Paul U. (2003). ''Nature, Knowledge, Imagery in an Ancient Chinese Medical Text''. Berkeley: University of California Press.
*West, Stephen H. "Cilia, Scale and Bristle: The Consumption of Fish and Shellfish in The Eastern Capital of The Northern Song," ''Harvard Journal of Asiatic Studies'' (Volume 47, Number 2, 1987): 595–634.
*Wittfogel, Karl A. and Feng Chia-Sheng. "History of Chinese Society Liao (907–1125)," Transactions of the American Philosophical Society (Volume 36, 1946):  i–xv; 1–752.
*Wright, David Curtis (2001) ''The History of China''. Westport: Greenwood Press.
*Wu, Jing-nuan (2005). ''An Illustrated Chinese Materia Medica''. New York: Oxford University Press.
*Xi, Zezong. "Chinese Studies in the History of Astronomy, 1949–1979," ''Isis'' (Volume 72, Number 3, 1981): 456–470.
</div>

==External links==
{{Commons category|Su Song}}
*[http://www.thenagain.info/WebChron/China/SongClock.html Su Song's Clock 1088]
*[http://concise.britannica.com/ebc/article-9379947/Su-Song Su Song in the Britannica Encyclopedia]
*[http://thenagain.info/webchron/Technology/SongClock.html Miniature working replica by the Japanese Tanseisha Company]
*[http://www.jameslindlibrary.org/trial_records/11th_Century/ben_cao_tu_jing/ben_cao_tu_jing_tp.html The Ben Cao Tu Jing at the James Lind Library]
*[http://www.bookrags.com/history/imperial-china-science-technology-health/sub16.html Su Song at Bookrags.com]

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