“... the comparison of the rotary movements... will show no discrepancy or contradiction...."
Su Song, The Rotation of an Armillary Sphere (1092)
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 achievement, however, was an ingenious escapement mechanism that converted this energy discreetly from a pendulum to the gears in a concept vital in the construction of clocks, and a technology unknown to Europeans until late in the thirteenth century. This technology was a precursor to the mechanical escapement, which enabled the manufacture of all-mechanical clocks that could tell time with far greater precision.
