Su Song's astronomical clock tower with escapement mechanism

Date

1088 CE (completed 1092)

Category

Science, technology & invention

Region

Song China (Kaifeng)

Era

Post-Classical / Medieval

Significance

Between 1088 and 1092 the Song official and engineer Su Song (1020-1101) directed the construction at Kaifeng of a roughly ten-metre water-powered astronomical clock tower.

Its great wheel was regulated by a water-driven escapement, a device that releases energy in regular, measured steps and is the conceptual heart of all later mechanical clocks. The tower also incorporated the earliest known endless chain drive, the so-called celestial ladder, which rotated an armillary sphere on the roof to track the heavens, while jacks rang bells and displayed plaques to mark the hours and watches of the night. Su Song documented the whole machine in an illustrated treatise, the Xin Yi Xiang Fa Yao, one of the finest surviving records of medieval engineering. The original tower was dismantled after the Jin captured Kaifeng in 1127 and could not be rebuilt. Although there is no direct line of transmission, Su Song's escapement predates the first weight-driven mechanical clocks of Europe by roughly two centuries, illustrating the sophistication of Song-era timekeeping and mechanical technology.

Empires active in 1088 CE (completed 1092)

• Almoravid Empire
  1056 CE – 1147 CE
• Song Dynasty
  960 CE – 1279 CE
• Abbasid Caliphate
  750 CE – 1258 CE
• Byzantine Empire
  330 CE – 1453 CE
• Kanem-Bornu Empire
  700 CE – 1900 CE
• Ghaznavid Empire
  977 CE – 1186 CE

Related science, technology & invention events

• Ibn al-Haytham Completes the Book of Optics
  c. 1021 CE
• First recorded use of the magnetic compass for navigation
  c. 1088-1117 CE
• Wujing Zongyao records the first gunpowder formulas
  1044 CE
• Bi Sheng invents movable-type printing in Song China
  c. 1040–1048 CE
• Ibn Sina completes the Canon of Medicine
  c. 1025 CE
• Al-Biruni Measures the Earth's Radius
  c. 1017 CE

Further reading

A Little History of Science

The wider story

A Little History of Science

William Bynum

Warm, jargon-free tour of discovery from Babylonian stargazers to the genome.

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