Zhang Sixun, although innovative, builds upon the …

Years: 976 - 976

Zhang Sixun, although innovative, builds upon the efforts of those before him.

The Han Dynasty era scientist and engineer Zhang Heng (CE 78-139) had invented the first hydraulic-powered (i.e.

with waterwheel and clepsydra) armillary sphere.

In addition, the Tang Dynasty era Buddhist monk and engineer Yi Xing (683-727) had invented the first hydraulic-powered armillary sphere that incorporated the escapement mechanism, yet Zhang Sixun has applied some innovative ideas of his own in order for his hydraulic-powered armillary sphere to function.

His astronomical armillary sphere and clock is much like that of the later statesman Su Song (1020-1101), incorporating the scoop-bearing driving-wheel and gearing, together with 19 clock jacks to report and sound the hours.

His device also employs the use of liquid mercury in the closed circuit of the clepsydra and waterwheel instead of water, because water would freeze easily during winter, while mercury could assure smooth and continual function and timekeeping during the cold season.

Later Ming Dynasty clocks will have the same concern in mind when they employ the use of falling sand grains to push the wheel drive.

The later Su Song will write that after Zhang's death, no one could replicate what he had achieved, much like with Su Song himself and his astronomical clock tower after his own death.

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