Yi-Xing (I-Hsing)

SUBJECT AREA: Horology

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b. c. 672/683 China

d. 727 China

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Chinese astronomer and mathematician.

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A Tantric Buddhist monk, Yi-Xing was one of the greatest astronomers and mathematicians in Chinese history. He was much influenced by Indian and therefore Hellenic astronomy. Around 725, he constructed armillary spheres with ecliptically mounted sighting tubes for taking measurements in ecliptic co-ordinates. With these instruments he took many readings of star positions and may even have discovered the proper motion of the stars. Yi-Xing's Da Yan Li Shu calendar was the result of an imperial commission to reform the calendar. It was edited the year after his death, in 728, and was officially adopted the following year. This calendar gave a nearly correct value for the irregularity of the movement of the Sun and came closer than previous attempts to calculate the day of true syzygy. Yi-Xing's method of interpolation was identical to that used by Gauss in the eighteenth century. He was also the inventor of the "water wheel link work escapement" mechanism as used later in the clock of Su Song.

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Further Reading

J.Needham, Science and Civilisation in China, Cambridge: Cambridge University Press, 1959–65, vols III, pp. 37–8; IV.2, pp. 471ff., 532–3.

——1960, Heavenly Clockwork, pp. 17–8, 20–1, 23–5, 62, 72, 74ff., 85, 89, 94, 98, 104–5, 107, 112, 122–3, 132, 139, 151, 153, 154, 166, 175, 177, 180, 182, 187.

LRD