The year 2020 marks the 1000th birth anniversary of Su Song, a famous astronomer of the Northern Song Dynasty. His most well-known technological achievement was the construction of the Water-driven Astronomical Clock-tower, which was one of the most outstanding astronomical instruments in ancient China.
Su Song was born in Tong'an County, Quanzhou Prefecture, which is now the Tong'an district in Xiamen, Fujian Province. At age of 70, he applied the most advanced knowledge in astronomy and technology in mechanical engineering at that time, to construct the Water-driven Astronomical Clock-tower that combined the functions of astronomical observation, celestial globes representation, time measurement and timekeeping.
The 12-meter-high Water-driven Astronomical Clock-tower was entirely driven by hydropower. At the top was the "armillary sphere" used for astronomical observation, it was able to track the Sun and stars through a power-transmitting system. The "celestial globe" at the middle recorded the features of the starry sky by the concept of a celestial sphere to demonstrate the movement of celestial bodies. A timekeeping system was installed at the bottom. The mechanism used inside the tower was similar to the escapement in modern clocks. Its marvellous design reveals the advancement in mechanical technology of the Song Dynasty.
After the completion of the Water-driven Astronomical Clock-tower, Su Song recorded the design and operation of the tower in his publication "Xin Yixiang Fayao". Unfortunately, the tower was destroyed after the "Jingkang Incident". The construction technology was lost for a long time as its descendants were not able to master the mechanical principle. The tower was reconstructed not until recent decades.