Su Song was the engineer of a clock tower in medieval Kaifeng, which employed the use of an early escapement mechanism. 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. The clock tower had 133 different clock jacks to indicate and . Su Song's treatise about the clock tower, ''Xinyi Xiangfayao'' , 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 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 maps, several 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, early European visitors to China mistakenly believed that the Chinese had never advanced beyond the stage of the clepsydra clock, incense clock, and sundial. Although not as prominent as in the Song period, contemporary Chinese texts of the Ming Dynasty describe a relatively unbroken history of designs of mechanical clocks in China from the 13th to the 16th centuries. that in Su's youth, he mastered the and rose to the top of the examination list for writing the best essay on general principles and structure of the Chinese calendar. He also was an antiquarian and . After serving in the Ministry of Personnel, he became a in 1086. Eventually, Su rose to the post of Vice President of the 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 , and the Reformists, led by Prime Minister Wang Anshi ; although many of his associates were of the Conservative faction. sharing ideas about calendrical science, as the Liao state had created its own calendar in 994 AD. 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. 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. 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." 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. With his extensive knowledge of cartography, Su Song was able to settle a heated border dispute between the Song and Liao dynasties.
Astronomy
Su Song also created a celestial atlas as well , which had the hour circles between the xiu forming the , with stars marked in quasi-orthomorphic cylindrical projection on each side of the equator, and thus was in accordance to their north polar distances. This cylindrical projection was similar to Mercator projection, the latter innovated by Gerard Mercator in 1569. This is so because Su Song's fourth star map places the position of the pole star halfway between Tian shu and the current Polaris; this was the more accurate calculation that Shen Kuo had made when he observed the pole star over a period of three months with his width-improved sighting tube.
Pharmacology, botany, zoology, and mineralogy
In the year 1070 Su Song and a team of scholars compiled and edited the ''Bencao Tujing'' , which was a groundbreaking treatise on pharmaceutical botany, zoology, and mineralogy. In compiling information for pharmaceutical knowledge, Su Song worked with such notable scholars as Zhang Yuxi, Lin Yi, Zhang Dong, and many others. This treatise documented a wide range of pharmaceutical practices, including the use of ephedrine as a drug. It includes valuable information on metallurgy and the steel and iron industries during 11th 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. He wrote of the subconchoidal fracture of native cinnabar, signs of ore beds, and provided description on crystal form. Similar to the ore channels formed by circulation of ground water written of by the later scientist Georgius Agricola, Su Song made similar statements concerning copper carbonate, as did the earlier ''Rihua Bencao'' of 970 with copper sulphate. According to Edward H. Schafer, Su accurately described the translucent quality of fine realgar, its origin from pods found in rocky river gorges, it's 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. Citing evidence from an ancient work by Zheng Xuan , Su believed that physicians of the ancient Zhou Dynasty used realgar as a remedy for ulcers. 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. 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.
Horology and mechanical engineering
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'' , 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 clocktower.
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. 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. 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. 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, a sophisticated use of oblique gears and an escapement mechanism, 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:
Years after Su's death, the capital city of Kaifeng was besieged and captured in 1127 by the Jurchens of the Manchurian-based . 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' . The rulers of the continuing Yuan Dynasty had a vested interest in the advancement of mechanical clockworks. 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. Complex gearing for uniquely Chinese clockworks were continued in the Ming Dynasty , 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. 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 over which a pointer circulated, much like new European clocks of the same period.
Su Song's escapement mechanism
Su Song's escapement is similar and reminiscent of the anchor escapement found in European clockworks of the 17th century. 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.
In his writing, Su Song accredited the predecessor of his working clock to the hydraulic-powered armillary sphere of Zhang Heng , an earlier Chinese scientist. However, Su Song stated in his writing that after Zhang's death, no one was able to replicate his device, much like his own.
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' . 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.
Joseph Needham gives a general description of the clock-tower itself:
That was figure Fig. 650, while Fig. 656 displays the upper and lower norias 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 , with Needham's caption here in this quote: "The 'celestial balance' or escapement mechanism of Su Sung's clockwork ,". 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 counterweight.
The endless chain drive
The world's oldest illustrated depiction of an endless power-transmitting chain drive is from Su Song's horological treatise. as seen in Needham's Fig. 410 and Fig. 652. Although the ancient Philo of Byzantium featured a sort of endless belt for his magazine , which did not transmit continuous power, These gears having 600 teeth would thus ensure the division the day into basic unit measurements of 2 minutes and 24 seconds. Zhang's armillary sphere has often been compared to the 13th 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. For the drawing of Su's armillary sphere, the listing of components are:
*The Outer Nest
**meridian circle
**horizon circle
**outer equator circle
*The Middle Nest 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.
The later Ming Dynasty/Qing Dynasty scholar Qian Zeng 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.
In the realm of modern research, the deceased British biochemist and historian of Chinese science Joseph Needham has done extensive research and analysis of Su Song's texts and various achievements in his ''Science and Civilization in China'' book series. Joseph Needham had 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 11th century Chinese engineering. A miniature model of Su Song's clock was reconstructed by John Cambridge and is now on display at the at South Kensington, London.
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