A study on ancient Chinese time laws and the time-telling system of Su Song's clock tower

Abstract

The ancient Chinese time laws showed a historical progress about how people started to recognize time and use time-keeping instruments. Dividing the celestial sphere into 12 sections and the indicator-arrow's scale of the clepsydra into one hundred parts established an equal time concept, which was a guide to divide a day into several equal parts. This also provided an objective condition for the development of astronomical clock in ancient China. Su Song and Han Gong-Lian built a clock tower ( Water-Powered Armillary Sphere and Celestial Globe) in 1088 A.D. during the Northern Song Dynasty. This was the greatest achievement of the development of astronomical clock in ancient China. The time-telling system of Su Song's clock tower was composed of the day and night time-keeping wheel and the five-storey wooden pagoda. By the use of concrete image and sound, it was to present three different time laws during that period, which were the Duodecimal Time Law, the Clepsydra Time Law and the Geng Dian Time Law. This outstanding mechanical structure included four types of percussion instruments (large bell, drum, small bell, and gong), four striking wooden puppets with active arms, and 158 time-reporting wooden puppets wearing particular signs and three variant colored clothes (scarlet, purple, and green). Multi-cam striking mechanism perfectly worked and created correspondent musical interaction between image and sound within each storey of the five-storey wooden pagoda. It was regarded as a clever engineering design with great scientific and artistic value.