The world's first water-driven astronomical clock tower was by far the most advanced astronomical instrument of its day,Its designer was Su Song(1020-1101),who oversaw the project with the aid of mathematician Han Gong-lian.The elaborate,40-foot (12 m),.water-powered,mechanically driven clock had bronze castings,precision gears,gear rings,and pinions.A bronze armillary sphere with a celestial globe mounted below allowed the sun,moon, and selected stars to be seen through a sighting tube.
The tower was a three-level,pagoda-like structure powered by thirty-six buckets attached to a central wheel,each of which would trip a lever and tilt forward at a predetermined point to engage the clock's complex system of gears and counterweights.Song's greatest achievment,however,was an ingenious escapement mechanmism that converted this energy discrteetly from a pendulum to a gears in a concept vital in the construction of clocks,and technology was a precursor to the mechanical; escapement,which enabled the manufacture of all-mechanical clocks that could tell time with far greater precision.
