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    China Chronology

    Su Song's Clock



    Su Song, a Chinese expert in the calculation of calendars, built an advanced astronomical clock in 1088. The clock was a precise apparatus used for astronomical observations and time keeping during the reign of Zhezong (Bulliet 333). Recent interests in the clock led to the building of a replica for the National Museum of Natural Science in China. This reconstruction revealed the intricacies of the clock and proved the greatness of the intellectual capacities of its creator.

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    Su Song led a team of skilled mathematicians and artisans in building the clock tower. It was the most advanced astronomical instrument of its day. Unfortunately, only 39 years after the clock tower was completed, the Jin army invaded the Song's capital (Taiwan's Biggest Cuckoo Clock?). They completely dismantled the clock and carried it off to their capital which is modern day Beijing. The Jin army was unable, however, to reassemble the clock due to the complexity of its construction (Taiwan's Biggest Cuckoo Clock?).

    Under the leadership of Gazong (1132-1162) China returned to its splendor. However it was still missing its clock tower. Gazong sent an edict to Su Song's son Su Xie commanding him to duplicate the Yuanyou armillary sphere and celestial globe that his father built. Upon receiving the imperial command to re-create the clock, Su Xie went home to search for his father's old texts which described the clock's assembly. Despite several years of work, he was never able to create a working replica of this masterpiece. Eventually, Su Xie and his colleagues concluded that key sections of the plans, concerning the clock's construction had been excised to keep their contents secret.

    The clock tower consisted of three levels. The upper level contained an armillary sphere. This represented "the great circles of the heavens" which allowed astrologers to make accurate astronomical observations. On the middle level, there was a celestial globe which displayed the movements of celestial bodies, and the bottom level had wooden mannequins which struck the time of day. The whole tower formed a single mechanism which was turned by water power, without any human effort. The clock's precision was comparable to a sundial (Bulliet 333). The sphere was comprised of 12 rings in three layers, each of the rings being marked with a scale. From the sphere one could directly read off the positions of the 24 Solar Terms, and could find a star or planet by looking through a sighting tube (How the Astronomical Clock Tower worked).

    In 1990 the desire to unearth the secrets of Song's clock tower resurfaced. Han Pao-te , director of the National Museum of Natural Science, received a proposal from the Japanese company Tanseisha to build a replica of Song's clock tower. The replica was to be placed in the museum's new Chinese Science Hall.

    This was scaled down version was the outcome of hundreds of hours of work

    This scaled down replica was the outcome of the Tanseisha's project.

    Courtesy of the National Museum of Natural Sciences

    Many problems occurred while recreating the clock. Had the team of researchers led by Han Pao-Te been allowed to use the technology of today, recreating a working clock tower would have been easy. However, Han Pao-te insisted that they use only technology available at the time of its original construction. Also, the only surviving plans for the tower were written for the emperor; hence there was no need to go into scientific details in describing it (How the Astronomical Clock Tower worked). Thus, it was extremely important for the crew to get a clear understanding of the original design. Wang Yung-hsin, one of engineers working on the wheel said "We had to infer the unknown from the known." "The hardest part was when we started reading [the text]. I recognized every character, but when putting them together I couldn't make heads or tails of it" said Kuo Mei-fang, a former student of Pao-te (Taiwan's Biggest Cuckoo Clock?).

    Because of the enormous span of time between the Song dynasty and the present day, creating a 100% replica is next to impossible. When the time came for the clock to be assembled, there were several technical difficulties. Eventually, they worked out the glitches in the clock and placed the exhibit in the museum. Many visitors to the museum do not understand the ingenuity of the clock, but everyone can appreciate the originality of the idea. Han Pao-Te hopes to one day complete the exhibit by describing in detail the problems they came across in building the clock with the purpose of enhancing the phenomenal piece of ancient Chinese technology (Taiwan's Biggest Cuckoo Clock?).


    Bulliet Richard, The Earth and its People. (Boston; Houghton Mifflin, 1997).

    Encyclopedia Britannica ,15th edition, 1992.

    How the Astronomical Clock Tower worked:

    Taiwan's Biggest Cuckoo Clock?-Recreating an Astronomical Timepiece:

    Edited by: Anthony A. Ragona
    Researched by: Andrew J. Newlin
    Written by: Vanessa R. Ahmed
    September 23, 1997

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