Yi Xing

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For the Vietnamese monk with the same Chinese dharma name, see Thich Nhat Hanh

Yi Xing (Yi-xing; Wade-Giles: I-Hsing) (一行) (683 – 727) was a Chinese astronomer, mathematician, mechanical engineer, and Buddhist monk of the Tang Dynasty.

Contents 1 The escapement and celestial globe 2 See also 3 Notes 4 References

[edit] The escapement and celestial globe

Yi Xing was famed for his genius, known to have calculated the number of possible positions on a go board game (though without a sign for zero he had difficulties expressing the number). He, along with his associate Liang Ling-zan (a government official), is best known for applying the earliest known escapement mechanism to a water-powered celestial globe. However, Yi Xing's mechanical genius and achievements were built upon the knowledge and efforts of previous Chinese mechanical engineers, such as the statesman Zhang Heng (78–139) of the Han Dynasty, the engineer Ma Jun (200–265) of the Three Kingdoms, and the Daoist Li Lan (c. 450) of the Southern and Northern Dynasties period.

It was the earlier Chinese inventor Zhang Heng who was the first to apply hydraulic power (ie. a waterwheel) in mechanically-driving and rotating his equatorial armillary sphere). The arrangement followed the model of a water-wheel using the drip of a clepsydra (see water clock), which ultimately exerted force on a lug to rotate toothed-gears on a polar-axis shaft.^[1] With this, the slow computational movement rotated the armillary sphere according to the recorded movements of the planets and stars. Yi Xing also owed much to the scholarly followers of Ma Jun, who had employed horizontal jack-wheels and other mechanical toys worked by waterwheels.^[1] The Daoist Li Lan was an expert at working with water clocks, creating steelyard balances for weighing water that was used in the tank of the clepsydra,^[1] providing more inspiration for Yi Xing. Like the earlier water-power employed by Zhang Heng and the later escapement mechanism in the astronomical clock tower engineered and erected by Su Song (1020–1101), Yi Xing's celestial globe employed water-power in order for it to rotate and function properly.^[2] The historian Joseph Needham states (Wade-Giles spelling):

When the first escapement came, in +725 (AD), I-Hsing and Liang Ling-tsan arranged for two jacks to strike the hours, standing on the horizon surface of their sphere or globe.^[3]

The Song Dynasty (960–1279) era historical text of the Song Shi mentions Yi Xing as well, and the reason why his armillary sphere did not survive the ages after the Tang Dynasty (Wade-Giles spelling):

A jade balancing mechanism (yu heng)(ie. the escapement) is erected behind (lit. outside) a curtain, holding and resisting (chhih o) the main scoops (shu tou). Water pours down rotating the wheel (chu shui chi lun). Lower, there is a cog-wheel (chi lun) with 43 (teeth). There are also hooks, pins, and interlocking rods one holding another (kou chien chiao tsho hsiang chhih). Each (wheel) moves the next without reliance on any human force. The fastest wheel turns round each day through 2928 teeth (chhih), the slowest one moves by 1 tooth in every 5 days. Such a great difference is there between the speed of the wheels, yet all of them depend on one single driving mechanism. In precision, the engine can be compared with Nature itself (lit. the maker of all things; tsao wu che). As for the rest, it is much the same as the apparatus made (long ago) by I-Hsing. But that old design employed mainly bronze and iron, which corroded and rusted so that the machine ceased to be able to move automatically. The modern plan substitutes hard wood for these parts, as beautiful as jade...^[4]

[edit] See also

• List of Chinese people
• Verge escapement
• Villard de Honnecourt
• Su Song

[edit] Notes

[edit] References

• Needham, Joseph (1986). Science and Civilization in China: Volume 4, Part 2. Taipei: Caves Books, Ltd.