Zhang Sixun and the Prosperous Astronomy in the Song Dynasty

Deng Meng

Sichuan Changjiang Vocational College

Abstract: Chinese astronomy reached its pinnacle in the Song Dynasty (960-1279)as culture continued to prosper to a new height. The invention of the“Taiping Armillary Sphere” by Zhang Sixun, who was from Bazhong in the Shu area (today’s Sichuan province), marked a milestone in the astronomical development in China. This article delves into the driving forces behind Zhang Sixun’s outstanding contributions to astronomy from the perspectives of the important role of astronomy in the politics of the Song Dynasty, the great attention the imperial court paid to astronomy,and the influence of the Shu culture, which centers on the belief “Tian Shu Zai Shu” (the rule of the universe is best observed in Shu).

Keywords: Song Dynasty, politics, astronomy, Taiping Armillary Sphere, Tian Shu Zai Shu, value

Astronomy and Politics in the Song Dynasty

“Unity of Heaven and Man” has always been an important philosophical thought in Chinese culture. The theory of “mutual correspondence between Heaven and Man” (tian ren gan ying) derived from the thought holds that human physiology and social phenomena such as ethics and politics are all direct reflections of nature, or to put it in another way, are driven and dominated by the forces of nature. Therefore, throughout the Chinese history, astronomy was often an important factor in political activities. The great scholar Qian Mu said in his later years that the greatest contribution of Chinese culture was its close observation of the relationship between “heaven” and“man,” while the concept of “Unity of Heaven and Man” was “the essence of the whole philosophy of Chinese culture.” Chengzhu Lixue (school of rationalist thinking), the dominant school of philosophy in the Song Dynasty, sets “the law of heaven” as the supreme norm and fundamental law that governs all behaviors of human society (“human desires”).

The Song Dynasty is believed to be an era when the Chinese culture became mature and reached its peak, which has often been discussed a lot and is universally acknowledged in the academic circles.For example, Professor Chen Yinque wrote that “the culture of the Chinese nation had evolved over thousands of years before it reached its pinnacle in the Song Dynasty.” Such cultural prosperity is not only reflected in the humanities and social sciences, but also in natural sciences. According toHistory of Song—State Offices, in the 7th year of Yuanfeng (1084), the subjects for the students to study as printed by the central publication department includedJiu Zhang Suan Shu(Nine Chapters on Mathematical Arts),Zhoubi Suanjing(The Arithmetical Classic of the Gnomon and the Circular Paths of Heaven),Haidao(Sea Island Mathematical Manual),Sunzi Suanjing(Master Sun’s Mathematical Manual),Wu cao suan jing(Mathematical Manual of the Five Government Departments),Zhang Qiujian Suanjing(Zhang Qiujian’s Mathematical Manual),Jigu suanjing(Continuation of Ancient Mathematics), andXiahou Yang Suanjing(Xiahou Yang’s Mathematical Manual). Wang Yong from the Southern Song Dynasty also said in hisYan Yi Yi Mou Lu(which records the rules and rituals of the Southern Song Dynasty), “Calligraphy, painting, arithmetic, and law were all as important as literary and military studies in the Song Dynasty.”Mathematical Treatise in Nine Sectionswas completed in 1247 by Qin Jiushao, who was from Anyue County in the Southern Song Dynasty, also made innovative contributions to the mathematical development in the world, such asDa Yan Qiu Yi Shu(which is for solving simultaneous congruence equations), also known as theChinese Remainder Theorem,San Xie Qiu Ji Shu(calculating the area of triangles when the lengths of all sides are given)and Qin Jiushao’s formula (numerical method for finding the positive roots of high-order equations).

Astronomy, one of the basic natural sciences, was also taken to a new height in the Song Dynasty.Astronomical instruments manufactured during this period were sophisticated and innovative,outperforming those of previous times in terms of both quantity and quality—an important milestone in the development of Chinese astronomy in ancient times. Systemic observations of stars were made,and the determinative stars of the 28 mansions were meticulously measured for calendar compilations.A calendar with a more accurate length of the return year was compilations. Among the records of new stars in ancient China, the most important observation was the “Tianguan Guest Star” (SN 1054)discovered and recorded by Yang Weide during the Song Dynasty. This marks a great achievement in star observation in ancient China. In July of the first year of Jiayou of the Song Dynasty (1054), an astronomer named Yang Weide reported to the emperor that a “guest star” appeared in the sky and broke into Taurus. We can still see the nebula of gas and dust from that supernova. It is called the“Crab Nebula” because it looks like a crab. With regards to the institutional systems, in addition to the special government agency Si Tian Jian (bureau of astronomical observation), the Song Dynasty also established an Astronomical Academy in the imperial palace to conduct astronomical observations and check Si Tian Jian’s reports in the early morning of the next day.

The astronomical and calendrical system in ancient China involved astrology and was closely related to politics and military affairs. According toSong Xing Tong(The Criminal Code of the Song Dynasty, 963), the first code of the Song Dynasty, “All the astrological objects, astronomical books,prophetic books, seven-star calendar, Tai Yi and Lei Gong Shi (two forms of Chinese divination)shall not be shared and privately learned by individuals, and any privately-held objects and learning activities must be destroyed and forbidden. Officials of Si Tian Jian and Hanlin Academy are not allowed to let other people read these previously-mentioned books.” Indeed, in Chinese society that was dominated by “mutual correspondence between Heaven and Man.” Abnormal astronomical phenomena could provide strong support for the legitimacy of the emperor’s governance on the one hand, and could also be exploited by rebels to justify their uprising. This is one of the reasons why emperors in ancient China attached great importance to astronomy. Records show that in April of the third year of Jingde in the Song Dynasty (1006), “a bright star appeared in the west of the star of Di (a determinative star of the twenty-eight mansions) and no one could tell what it was. Some said it was a demon star against the emperor and was an omen for military conflicts.” This incident was followed by a public disturbance. According to the explanation of Zhou Keming, who was born into a family of astronomers, “The new star (which was a supernova) is Zhou Bo. It is yellow-colored, and its light is brilliant. It is a star of virtue since it blesses the country to be virtuous and prosperous…Civil and military officials shall be allowed to celebrate so that the people can rest assured.” Rumors thus died down and society was stabilized.

Both the reign of the founding Emperor Taizu of Song and his younger brother Emperor Taizong witnessed officials from astronomical institutions directly involved in the competition for the throne.These officials influenced public opinion by explaining astronomical phenomena in their favor to justify the legitimacy of regime succession. According toThe History of Song, when the founding emperor Zhao Kuangyin was stationed at Chenqiaoyi with his army, Miao Xun, who was “good at astronomy and astrology,” masterminded an astronomical observation event for Zhao since they had a deep friendship. One day, Miao and Chu Zhaofu, a close associate of Zhao, announced the abnormal phenomenon of two suns appearing in the sky in front of the troops by explaining that“there is another sun below the original one and black light has shone around them for a long time.”They continued to explain that the new sun appeared to outshine the other, a sign that there would be a new emperor to whom the Mandate of Heaven would be transferred. In traditional Chinese culture and the astrological system, the sun is the symbol of the sovereign, and two suns appearing at the same time and which are competing with each other indicates that there are two rulers, and a new dynasty will prevail. Miao Xun’s tactic successfully mobilized the public and justified the legitimacy of Zhao Kuangyin’s coup (when Zhao was urged by his soldiers to wear a yellow robe which was exclusive to emperors), which happened the same night. Later during the Kaibao period(968-975), the Prince of Jin Zhao Guangyi, who administered the state capital, once prohibited the“private learning” of astronomy to control public opinion. Moreover, he also participated in planning the “two-sun propaganda” before the “Chenqiao coup,” so he knew well that the interpretation of astronomical phenomena could be used for political revolution. After Prince of Jin ascended to the throne, he placed even more emphasis on the development of astronomy, hoping to get public support for his succession. As a result, under the reign of Prince Jin, who was later known as Emperor Taizong of the Song Dynasty, it was common to see divination specialists holding important posts in the imperial court. According toXu Zizhi Tongjian Changbian—Third Year of Yongxi(Extended Continuation to Comprehensive Mirror to Aid in Government) Volume 27 composed by Li Tao, a person from Chengdu with the surname of “Houmochen” and name “Liyong” “sold medicines in the capital and used sorcery tricks to deceive people. He was later summoned by Emperor Taizong and was appointed to an imperial post. He then served as guard general in the imperial palace, supervisor of Bingzhou garrison, and deputy commander at Zhengzhou. Those who were close to him all held important positions.” Sima Guang told a story in hisShushui Ji Wen(Memoir at Shushui): Li Shun revolted in the Shu area, so Emperor Taizong of Song dispatched Zhao Changyan to lead the troops to suppress the rebellion in Shu. When Zhao left, a monk from Mount Emei “who was appointed to a position in the imperial court because of his divination skills” raised his objection by saying to the emperor, “Zhao Changyan has a sharp angle at the root of his nose, which is a sign of rebellion, so he should not be dispatched to quell the uprising in Shu.” He also cited political division during the period of the Five Dynasties (907-960) and Ten Kingdoms (902-979) prior to the founding of the Song Dynasty and warned, “Changyan had always been admired and praised and had no heirs. Now that he led the army to Shu and held military power, the chances are that he will no longer obey the imperial orders in the future.” The emperor took his words and “sent envoys to stop his progression and let other generals lead the army instead.”

A New System for Selecting Astronomical Talents in the Song Dynasty

In addition to systems such as imperial examinations and conferring, the recommendation was also an important talent selection method, especially for those with special skills in the Song Dynasty.For example, when Shen Kuo, author ofMengxi Bitan(Dream Pool Essays), served in Si Tian Jian, he once “recommended” a grassroots commoner named Wei Pu to a state astronomical institution.

Following the wake of years of war and social turmoil in the late Tang Dynasty and the Five Dynasties and Ten Kingdoms, the new Song Dynasty was confronted with the grim situation of an extreme shortage of astronomical specialists. To address this problem, the government “retained”officials with professional expertise who served the previous regime on the one hand and recruited talents from the whole country on the other. These two approaches of appointing former officials and recruiting freshmen from the country helped to form a stable team of astronomical professionals and laid a solid foundation for the development of astronomy in the Song Dynasty. The characteristics of talent selection in the Song Dynasty were as follows. First, anyone who was informed of astronomical and calendrical knowledge could take examinations organized by the state either by “applying by themselves” or on the “recommendation of others” irrespective of their social status. Those who passed the examination would be able to study and work in the Si Tian Jian after being appointed as government officials. For example, during the years of Chunhuan (990-994) under the reign of Emperor Taizong of Song, Chu Zhilan from Linru, Henan province, who was good at “Liu Ren (a form of calendrical astrology) and Qimen Dunjia (a form of ancient divination),” was “admitted as a student at the imperial court after he recommended himself when the government recruited people with divination knowledge on a large scale.” He was then “appointed to the imperial Hanlin Academy because of his outstanding divination skills and later served in several positions at Si Tian Jian, and the highest post was as a dean in the Ministry of Works under the Department of State Affairs.”According toSong Hui Yao Manuscripts—31 Officials—Si Tian Jian(Song Government Manuscript Compendium), in the fourth year of Jingde under the reign of Emperor Zhenzong (1007), a man named Zhu Shuji from Suzhou “failed the provincial examination several times, but he was well informed of astrological and calendrical knowledge, so he signed up for the professional examination”and finally succeeded in “obtaining the Jinshi degree and became Lingtai Lang at Si Tian Jian.”Another example is Yang Hao, who was from Chengdu. He was well-versed in astronomy and was quite famous in the Shu area. In November of the first year of Jingde under Emperor Zhenzong, “the governor heard about his professional skills and recommended him to the imperial court. Yang was later summoned to sit an examination at Si Tian Jian,” and successfully obtained “the position of Lingtai Lang at Si Tian Jian.” In the Song Dynasty, “those who serve the court with their professional skills” were called “technical officials,” which is similar to how people are identified in modern days.Sixth Chapter of Official Posts Records—Ministry of Internal ServantsofThe History of Song(Volume 166) clearly states that “a person responsible for daily affairs of the Hanlin Academy, who is a Yaban or Duzhi (name of court positions), takes care of the four bureaus of astronomy, calligraphy, painting,and medical officers. All those who practice professional skills serve in these bureaus.”

In the early Northern Song Dynasty, more than half of the astronomical officials in the astronomical institutions of the imperial court were from the grassroots level. They were conferred positions and rewarded because of their professional skills. The government’s promotion of people who were familiar with calendrical knowledge also contributed to the opening-up of imperial astronomical institutions. Those who climbed up the social ladder with specialist knowledge, set examples for ambitious ordinary people. Some scholars pointed out that “officials who entered astronomical institutions because of their special achievements did not have strong technical capabilities. Letting them serve in Si Tian Jian could only be regarded as a disguised form of buying them over. Moreover, those from an astronomical family from the late Tang Dynasty were still not numerous enough for the imperial court and it was not possible to use only the talents cultivated by the government itself. In this case, recruitment from the country became the only way” (Wang,2019). The government reinforced this ruling by recruiting grassroots astronomers on the one hand,and prohibiting professionals working “in the imperial system” from doing part-time work in the other. For example, the ban issued in the fifth year of Kaibao by Emperor Taizu (972) reads, “All the astrological objects, astronomical books, prophetic books, the seven-star calendar, materials about Tai Yi, Lei Gong Shi, Liu Ren, and Dunjia shall not be privately held, or the holder would be punished” (Li, 2004). An edict was issued in the first month of the first year of Jingde under Emperor Zhenzong (1004), saying that “from now on, officials and students at Si Tian Jian and astronomical school of Hanlin Academy are not allowed to perform fortune-telling, or to write planet calendars and information about divination at the home of government officials or commoners. Those who violate the regulation will be severely punished. Whistle-blowing was encouraged and rewarded.Three students formed a team so that they could supervise each other. One violator would make the whole team liable and anyone in the team who reports on others’ misconducts would be rewarded.”Measures such as this type of supervision over others, collective punishment, and encouragement of whistle-blowing all speak to the efforts the Song Dynasty made to prevent private sharing of astronomical achievements. Similar practices can be found inThe History of Song, Li Tao’sXu Zizhi Tongjian Changbian, andSong Hui Yao Manuscriptswritten by Xu Song of the Qing Dynasty, which records stories, calendars, and archives of the court during the Song Dynasty.

In the 9th year of Kaibao (976) and 17 days after Zhao Guangyi ascended to the throne, the new emperor issued a rigorous ban that read, “Prefectures shall send all those who know astronomy and mathematics well to the capital. Those who dare to hide them will be beheaded. Whistleblowers will be rewarded 300,000 taels.” This displayed the government’s resolution to recruit all the astronomical talents from across the country. In October of the following year, or the second year of Taiping Xingguo (977), Emperor Taizong issued a more rigorous decree that read, “Divination practitioners in the country have been summoned to the court. When asked about their professional knowledge, they appeared to be ignorant. It can be inferred that they simply scammed people out of money by telling fortunes at will. From now on, except for Er Zhan (traditional Chinese practice of determining the location of a house, tomb, or other items that are believed to have a vital bearing on the fortunes of a family, owner, or user) and Yi Shi (means of divination), all their books about astronomy, face reading,Liuren, Dunjia, Sanming, and yin yang must be turned over to the government within one month”.①See Li Tao’s Xu Zizhi Tongjian Changbian Volume 13, Guihai entry of November in the 5th year of Kaibao.In December of that year, under the direct order of Emperor Taizong, the government summoned a total of 351 scholars from all over the country who had expertise in astronomy and mathematics to take examinations for further selection. Among them, 68 qualified candidates were recruited and appointed officials at Si Tian Tai. It is noteworthy that the government would never let go of those who failed the national examination because they would become destabilizing factors. This is just as what is said inThe History of Song—Astronomical Records, “Astronomical officials are important, so how can we easily let them go.” In the end, the candidates who failed the selection “all had their face tattooed (a kind of punishment) and were exiled on islands.” In other words, in the early Song Dynasty, such kind of examinations for selecting officials with certain specialized skills was extremely cruel in that those who succeeded would become government officials and lead a better life while those who failed would be subjected to the “tattoo punishment” and have a miserable life on deserted “island.”

We can get a glimpse of this examination fromSong Huiyao Jigang. This is the record of an examination that took place in November of the second year of Xi’ning (1069): Basically,examinations for posts such as Ti Ju Guan, Pan Jian, and Ceyan Guan were held in spring and autumn each year in the evening at the National Planetarium. Examiners would point to stars in the night sky or on the “armillary sphere” and ask candidates questions. “Candidates would be asked about constellations, and those who answered 80 percent of the questions correctly were deemed most proficient.” “If candidates got more than half the questions wrong, they would be demoted to be extra students” (Xu, 1957), but these “extra students” who failed the examination for the first time would still get another chance to sit the examination again and be promoted to “regular students” as long as they worked hard and made progress in their field. That is, “Those who were demoted to be extra students due to illness and lack of proper knowledge about stars would still be granted a chance to take another examination if they recovered and progressed in the astronomical knowledge after more than one year.” If the first national selection of astronomy officials as ordered by Emperor Taizong in the second year of Taiping Xingguo (977) was conducted in this humane way, then it can be inferred that the 283 candidates who failed the examination might be rogues who were ignorant yet hoped to win by a fluke. So, it was not unfair for them to be punished and exiled to a deserted island. The emperor himself did see a lot of “Mr. Nan Guos (who pretended to play the musical instrument ofyuin an ensemble in a Chinese fable)” who were either recommended by local officials or took the initiative to sign up for the examination. Among the 68 candidates who were appointed positions at Si Tian Tai in this national examination as ordered by Emperor Taizong for private practitioners of astronomy and mathematics across the country, there was one named Zhang Sixun from Shu who made outstanding achievements in astronomical and calendrical studies.

According toThe History of Song—Astronomical Records, in late December of the second year of Taiping Xingguo, Zhang Sixun (947-1017) passed the national examinations of astronomy and mathematics and was appointed a professional official at Si Tian Jian. In the first lunar month of the 4th year of Taiping Xingguo (979), less than two years after Zhang took office, he completed the world’s first automatic planetarium. Emperor Taizong was overjoyed and named it “Taiping Armillary Sphere.” Then, the emperor ordered the production of its model which was then “placed in the southeast chamber of the Wenming Hall” after it was finished the following year. It only took a little more than one year for Zhang to finish the model of “Taiping Armillary Sphere,” testifying to the fact that Zhang was already well informed of necessary knowledge and skills to make himself a competent astronomer and astronomical engineer as early as when he was in his hometown.Therefore, it can be inferred that the manufacturing expertise of astronomical instruments was well accepted and developed in the Bashu area and relevant techniques were also mature. The national astronomical observatory Si Tian Jian only provided Zhang with a platform and some equipment.We can learn about the popularity of astronomy in the Shu area from a story that is recorded in bothBook of the Later HanandChronicles of Huayang. At the end of the Eastern Han Dynasty, there was a person from Guanghan in the Shu area named Zhe Xiang with a courtesy name Boshi. He “had a wealth of 200 million taels and 800 servants.” His forefather served the governor of Wuwei and was conferred Marquise Zhe of Nanyang, hence the family name of “Zhe.” However, the wealthy Zhe Xiang regarded his fortune as “misfortune,” so he shared his possessions with neighbors so that everyone could benefit from them. He often joined with people, including lower-class tenant farmers, to discuss astronomy and the Five Classics (refers to the five Confucian classics:The Book of Songs,The Book of History,The Book of Rites,The Book of Changes, andThe Spring and Autumn Annals). People even created a ballad to express their appreciation that goes, “Whom has Zhe invited?Zhu Yunqing and Duan Jieying. There is a tenant named Zhao Zhongping among them, and they happily talk about Astronomy and the Five Classics.” There is another story inThe History of the Northern Dynasties—Biography—Yuan Yanwritten by Li Yanshou in the Tang Dynasty: due to the popularity of astronomy in Shu, Yang Xiu, son of Emperor Wen of the Sui Dynasty and “Prince of Shu,” committed the most serious crime of “making armillary sphere illegally.” This incident points to at least two conclusions: First, the research on astronomy and the production of astronomical instruments in the Shu area were popular among all classes despite their being “illegal”; second, the production and use of armillary spheres were monopolized by the emperor himself, and even those as noble as princes were not allowed to be engaged in making them.

Zhang Sixun’s Opportunity

Zhang Sixun might have hesitated and struggled as to whether he should participate in the national examination for astronomers in question. At that time, Emperor Taizong issued a decree to recruit talents proficient in astronomy and astrology from across the country to join the government, which greatly appealed to Zhang a lot. In the past, people who left the Bashu area and succeeded in their career in the imperial court were all those who had excellent skills, especially in the field of astronomy.In the Han Dynasty (202-220), Luo Xiahong from Langzhong in the Shu area established his fame in the capital Chang’an by making a water-powered armillary sphere. In the Tang Dynasty (618-907),Liang Lingzan from the Shu area also had a successful career at the capital by inventing a copper armillary sphere and making technical breakthroughs in automatic timekeeping devices. They were household names among astronomy practitioners. The chance came to Zhang Sixun when the imperial court started to recruit grassroots astronomers. By taking part in the examination, Zhang could make full use of what he had learned, and he even stood a chance of displaying his unique talents in front of the government officials and the emperor himself. He could also make remarkable achievements and had his name remembered in history. Such a career plan was far more accessible and practical than getting a degree through imperial examinations. Furthermore, the imperial examination had already become a regular event, and each examination would see a considerable number of candidates orJinshidegree holders. For example, more than 17,000 people were qualified for theJurendegree in the imperial examination held in the third year of Chunhua under Emperor Taizong (992). The previous emperor held many imperial examinations during his 16 years of reign, but he never publicly recruited talents in astronomy from across the country. However, the sitting emperor issued the announcement only one year after he ascended to the throne. This was a once-in-a-lifetime chance that should not be missed. Moreover, he was already known in the area for his expertise after years of hard work in astronomical studies, so he could not hide away anyway given that the imperial order clearly stated that those who had astronomical knowledge and relevant skills must take the examination in the capital.“Those who are qualified but refuse to sign up will be sentenced to death.”

What Zhang Sixun worried about, however, was the suppression of the Shu people in the early years of the Song Dynasty. At that time, a poem composed by Madame Huarui of the Later Shu was still circulating: “The king on the rampart flies the white flag. Deep within the palace, how could I know? One hundred forty thousand all disarmed! Among these, was there not a single man?” Worse still, the Later Shu’s Emperor Meng Chang died suddenly when he was arrested in the Song capital after he surrendered, which made the Shu people dissatisfied with the rule of the Song Dynasty. This is what the historical record says: In the early Song Dynasty, although the Bashu area hosted “a lot of schools and scholars,” they expressed the attitude of “non-violent non-cooperation” to the new regime by refusing to become imperial officials under the pretext of “nostalgia” and were not willing to give up the affluent life in their hometown. Zhang Sixun, who grew up in the Shu area, was naturally influenced by the local views on the Song regime. Another example is what the governor of Bashu Zhang Yong (946-1015) did to promote the integration of the Bashu culture into the mainstream.Zhang Yong was from Juancheng, Shandong province. He was appointed to take charge of affairs in Bashu twice under the recommendation of Tian Xi and Su Yijian who were also from the Shu area and were high-ranking officials in the central government. Zhang Yong’s promotion of the Shu culture was deemed by the emperor and the Shu people as a major political achievement. AsThe History of Songgoes, “In the early days, the Shu scholars were eager to learn, but were not happy with serving as government officials. Yong noticed Zhang Ji, Li Tian, and Zhang Kui whose knowledge and skills were praised by neighbors. So, he encouraged them to take the imperial examination. All of them passed the test and became government officials. That was when local scholars started to change their attitude.”

Zhang Sixun, who was in his thirties and was already a well-educated person, likely had many plans for his future career. Studying hard to pass the imperial examination was the most widelyaccepted way for intellectuals to start their career, but the reality was he should not count too much on this approach since he was still a commoner in his thirties. Nevertheless, he was interested inI Ching(the Book of Changes) and mathematics, so he became acquainted with many friends with similar hobbies. He also gathered together with friends to observe stars and often discussed related issues, from which he learned much about astronomy. Then there came the imperial recruitment, and he could do nothing but sign up since there was no way to hide. After all, it was a good opportunity to change his fate by turning his hobbies into a successful career. Zhang Sixun finally decided to take the examination in the capital, and he did, thus advancing Chinese astronomy to a new height.

“Hun Xiang,” or celestial globe, is a spherical coordinate instrument made in ancient China based on the Hun Tian theory (which holds that the earth is floating inside the celestial sphere). It is used to demonstrate the movement of celestial bodies on the celestial sphere and to measure the coordinate differences between the zodiac and the equator by simulating the movement of stars. The instrument looks like a sphere that consists of several concentric rings, a model that simulates what the celestial sphere is like as perceived by human eyes. This is what is said inThe History of Song—Astronomical Recordsabout the armillary sphere created by Zhang Sixun—“Taiping Armillary Sphere” is a combination of a clock and a celestial globe. It has three stories and is more than three meters high. Such a design conforms to the Chinese astronomical theory that believes in “the round sky and square earth” theory. The ceiling of the instrument is designed just as if it were the starry sky on which there are “the moon and the sun which observers can look up at.” Observers can enter the hollow building to observe celestial bodies including the sun, the moon, and stars. “There are various apparatuses that control the movement of the armillary sphere. There is a scale of 365 degrees on which the sun, the moon, the five stars, the Ziwei Gong, the mansions, the Doujian, and the zodiac move. Their movements on the scale point to different seasons.” All the mechanical parts are placed on the second and third floors of the object. There is a supporting pillar and parts that control the movement of different wheels. There is also a puppet time teller that resembles the god. It tells the time by “ringing a bell on the left, striking a chime on the right and beating a drum in the middle.” Such movements “are repeated every day.” The god is named “seven-day god” which points to the seven stars (the Sun, the Moon, Mars, Mercury, Jupiter, Venus, and Saturn) that people used to call seven days in a week in ancient China. What people called the Day of the Sun, the Day of the Moon, the Day of Mars, the Day of Mercury, the Day of Jupiter, the Day of Venus, and the Day of Saturn correspond to Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, and Saturday as we know them today. The armillary sphere also features 12 gods based on the “12 hours” (one hour being equal to two hours in the modern day), with each god in charge of one hour. Time tellers would show up in turn, holding a card of the corresponding hour in their hand and telling the length of the day based on the quarters.” “The old time-telling method relied on human labor, but the new invention is more sophisticated as the movement of the sun, the moon, and the shift of day and night is all based on nature.” “Seven star-days form a cycle,and each day is divided into 12 hours which are announced by corresponding gods in turn. The start and the middle of the hour and quarters are announced by a bell, a chime, and a drum, respectively. This is a set of time-keeping systems that automatically tells the quarters by beating the drum and tells the hour by striking the chime, which marks the origin of automatic time-keeping instruments and watches.

Innovations of “Taiping Armillary Sphere”

Wang Yinglin, a scholar from the Southern Song Dynasty, spoke highly of Zhang Sixun’s outstanding contributions in hisYuhaiVolume 4 under the entry of “Armillary Sphere at Wenming Hall in Taiping Xingguo.” “Zhang Sixun, a student at Si Tian Jian said he was able to make the celestial globe, so he handed in the model he made to the imperial court. The emperor summoned official workers to the court to make one according to the model. The globe was completed in the first lunar month of the fourth year of Taiping Xingguo…Conventional spheres were rather simple in structure and were powered by water, making them not accurate at all in telling time. The accuracy improved when people started to use mercury instead. Old models tracked the movement of the Sun manually, but the present one relies on natural power. The celestial sphere was first made during the Eastern Han Dynasty by Zhang Heng (78-139). During the Kaiyuan years, the monk Yi Xing and Liang Lingzan were ordered by the emperor to make a new armillary sphere, but it was made with copper and iron and stopped running as time went by. The new sphere in question designed by Zhang Sixun resembled the shape of a pavilion that is several meters tall with several floors. It used puppets as time-telling gods that told the time by ringing the bell, striking the chime, and beating the drum.There were also 12 gods, each representing an hour. When it was their turn, they would show up holding the corresponding card. The ceiling featured the Sun, the Moon and stars which one must look up to observe. Its mechanical parts were hidden in the building. It was quite a clever design…Following the death of Zhang Sixun, the Taiping Armillary Sphere was broken, and no one knew its operating mechanism.”

In terms of the armillary sphere made by Liang Lingzan of the Tang Dynasty,shui lun(water wheel) is the gear,shui dou(water bucket) is the tooth, and the scale bar is an escapement. Water is poured into the bucket until the weight exceeds the balance of the scale—this isochronous process is controlled by the escapement. This “instrument made during the Kaiyuan years” was equipped with all the elements of a clock escapement, but the limited development made it not adequately accurate.The most significant improvement made by Zhang Sixun’s “Taiping Armillary Sphere” is that Zhang Sixun uses mercury in place of the water wheel adopted by Liang Lingzan. The reason for that is that the volume of water changes greatly in winter and summer due to different temperatures, which result in inconsistent driving forces for the wheel. Water freezes in winter and slows the movement,making the timekeeping inaccurate. Mercury performs consistently throughout the year irrespective of different temperatures. Therefore, it was quite a breakthrough to replace water with mercury.Zhang Sixun used mercury as a power thanks thanks to his profound understanding of the properties of mercury. He created a pavilion-style timekeeper that featured a bell, chime, and drum based on the prototype invented by Liang Lingzan’s “Kaiyuan instrument” in the Tang Dynasty. His invention also influenced other celestial spheres developed later on. By replacing manual labor with a gear operation and water with mercury as the driving force for the “five wheels,” Zhang eliminated the inaccuracy caused by different temperatures throughout the year. By improving the manipulator, the inertial movement of the “earth wheel” was better controlled. The design of wooden “seven-day gods” and 12 time-telling gods” among others, all marked a milestone of Chinese astronomy.

110 years later, the well-known astronomer Su Song said in hisXin Yixiang Fa Yao(1091), “Following the death of Zhang Sixun, the Taiping Armillary Sphere was broken, and no one knew its operating mechanism,” which seems to suggest his own innovation. In fact, Su Song and Han Gonglian borrowed many terms from Zhang Sixun when making hydro-mechanical astronomical clock towers,so it is hard to say that they never referred to Zhang Sixun’s theory and engineering ideas. For example,Su Song once said, “Sixun followed the designing method of the armillary sphere made during the years of Kaiyuan. The upper cover represents the Ziwei Gong, and the area around represents the celestial sphere which rotates from the east to the west.” Moreover, Su Song should have observed the armillary sphere invented by Zhang Sixun since he once described the instrument in great detail. He said, “Zhang Sixun’s armillary sphere has several stories and is several meters high. It has a rotating shaft in the middle, which is powered by water. It features time-keeping gods who ring the bell, strike the chime, and beat the drum day and night. There are also 12 gods responsible for the 12 hours. When it is their turn, they will sound the hour holding corresponding cards in their hands.” Such mechanical operations are nearly synchronized with the movement of celestial bodies while maintaining a constant speed. It was already the prototype of an astronomical clock as it “synchronizes accurately with the movement of celestial bodies, making it an extremely sophisticated instrument.” He also acknowledged that “Zhang Sixun initiated the design” with respect to the production of astronomical clocks in ancient China (Guan, 1991, p. 481). When Su Song served as the minister of the Ministry of Personnel, he examined the armillary sphere used by the Taishi Bureau under the imperial commission. As a result,he should have learned and inherited the production skills and theories concerning “Taiping Armillary Sphere” invented by Zhang Sixun (which was regarded as a major national project a hundred years ago). More importantly, Su Song made himself an important figure in history because he had the ability and enabling conditions to write the monographXin Yixiang Fa Yao. Historians like Toqto’a in the Yuan Dynasty explained in detail Zhang Sixun’s scientific thinking and the shape, level, functions,and key innovations of “Taiping Armillary Sphere” when editingThe History of Songin “Astronomical Records,” so it can be inferred that Su Song, who lived in the Song Dynasty, didn’t tell the whole story when saying “no one knew its operating mechanism.”

In making the armillary sphere, Zhang Sixun replaced water with mercury to prevent freezing in cold weather. This was 664 years earlier than the mercury barometer created in 1643 by Italian physicist and mathematician, Evangelista Torricelli. Zhang made a significant contribution to the mechanization and automation of armillary spheres in ancient China. As early as in the Warring States Period in the east of the Bashu Basin, a woman named “Qing” was powerful enough to “rival Emperor Qin Shi Huang (the First Emperor of Qin) because of her family business of cinnabar (a kind of ore of mercury) for several generations. The history and scale of this family business can reflect the demand for cinnabar in the Bashu area. Cinnabar mining at that time was mainly to satisfy the needs of the textile industry and cosmetics for women. The cinnabar from the Shu area is what Li Si said of “Xi Shu Dan Qing (cinnabar from the western Shu),” which was the tribute paid to Emperor Qin Shi Huang in his “Letter to Qin Shi Huang.” With the prevalence of the idea of immortality in China since the Han Dynasty, cinnabar had always been the main raw material for cultivation in pursuit of longevity, known as “alchemy” in ancient China. Taoists believed that cinnabar could make people immortal because it was collected from the mineral veins under the nourishment of the Sun and the Moon and thus was full of the energy of nature. Chinese Taoism priests spent their lives by the “alchemy furnace.” After being roasted, cinnabar produced a heavy, silvery liquid, which was called quicksilver (which is mercury as known today). This silvery shiny liquid glittered under the sunlight—it looked just like “the essence of heaven and earth.” Taoism was prevalent in the Bashu area, also the birthplace of Taoism. Body-spirit cultivation for immortality and Taoist practices were popular there for a long time in history. With this background information in mind, it is not difficult for us to understand why Zhang Sixun chose mercury as the driving force for his instrument.

Zhang Sixun’s “Taiping Armillary Sphere” is significant in the following aspects: he was the first to adopt “l(fā)aws of nature” in defining and standardizing seasons, solar terms, time differences,temperature differences, year, month, day, and hour. His epoch-making invention ushered in scientific thinking in the development of astronomy. From then on, the movement of the Sun and the Moon,the shift of the day and night, temperature, and time-keeping could be automatically displayed. The instrument operated day and night and integrated time-keeping, observation, and demonstration into one. This speaks to the astronomical achievement made in the Song Dynasty in terms of theory and technological progress under specific historical conditions. In other words, the invention embodies the achievements of astronomy, calendrical systems, metallurgy, casting, mechanical technology,architecture, and engineering during the prime time of the Song Dynasty. According toThe History of Song—Astronomical Records, “The old time-telling method relied on human labor, but the new invention is more sophisticated as the movement of the Sun, the Moon and the shift of day and night is all based on nature.”The History of Jin—Celestial Spherealso said clearly, “The astronomical bureau of the Song Dynasty did not have any celestial spheres in the early days. During the years of Taiping Xingguo, Sixun followed the designing method of the armillary sphere made during the years of Kaiyuan. The upper cover represents the Ziwei Gong, and the area around represents the celestial sphere which rotates from the east to the west—a great innovation.” With all these achievements,Zhang Sixun is recognized as the founder of astronomical instruments and timekeeping clocks and as a milestone in the history of astronomical development and machinery manufacturing. Historians also said, “Zhang Sixun’s invention built on the achievements of Yi Xing and Liang Lingzan in the Tang Dynasty and influenced the making of armillary sphere later on” (Bai & Chen, 2015, p. 1773).

On the one hand, the essence of the Bashu culture is best captured in the saying that “the rule of the universe is best observed in Shu.” As a result, the astronomical study was quite popular in the Shu area, which explains why there were so many astronomical specialists in the Shu area who made remarkable contributions to the scientific and technological development in ancient China. At the same time, the grassroots talents from the Shu area who were engaged in astronomy in national institutions could have a high-level platform for their career. Having access to advanced scientific thinking, they could make full use of available resources such as technical materials, archives,equipment, and technical and financial support. The success of Zhang Sixun is the best example.