WhereIsAtlas · Timekeeping
Su Song's Escapement
The clock tower at Kaifeng was dismantled and hauled north in 1127 — and the mechanism it used is running, right now, in every watch on every wrist
Transformed — Two objects share this name and they did not share a fate. The tower at Kaifeng was dismantled when the Jin took the city in 1127 and hauled north to Yanjing, where it was never successfully reassembled [5][6]. No original part survives: as a physical object it is defunct, and this entry says so plainly. The escapement inside it is a different matter. The principle — hold back a continuous force, release it one tooth at a time, count the releases — is the operating principle of every mechanical clock made anywhere since. Filed as transformed because the object is gone and the idea is not.
An escapement is the part of a mechanical clock that converts a continuous supply of energy into discrete, equal, countable steps. Water falls, a weight descends, a spring unwinds — all of it smooth, all of it useless for counting. The escapement interrupts that smoothness, letting the mechanism advance one tooth at a time, and the interruption is the tick [1][3].
The mechanism is older than this entry's subject. The first escapement in the record is credited to Yi Xing (一行) and Liang Lingzan, whose water-driven astronomical instrument of 725 is described as its origin [6]. What Su Song (蘇頌, Sū Sòng) and Han Gonglian (韩公廉) built at Kaifeng between 1086 and 1092 is the version that survives on paper [4].
That distinction is the whole point of the entry. Su Song's tower — the 水运仪象台, a compound astronomical instrument regulated by a water-wheel escapement — is not the earliest escapement. It is the earliest one described in enough engineering drawings to be reconstructed [4][5]. The knowledge, not the machine, is the surviving achievement.
Timeline
- 725 — The first escapement: Yi Xing (一行) and Liang Lingzan build a water-driven astronomical instrument described as the origin of the escapement [6] (China)
- 1086 — The commission: Su Song and Han Gonglian are set to work on the instrument at Kaifeng [4] (Kaifeng)
- 1092 — The tower is completed: The 水运仪象台 is finished, regulated by a water-wheel escapement [4] (Kaifeng)
- 1092-1094 — The treatise: 新仪象法要 records the design in text and drawings, which is what makes reconstruction possible [4][5] (Kaifeng)
- 1127 — Dismantled and taken north: The Jin take Kaifeng; the tower is dismantled and hauled to Yanjing, where it is never successfully reassembled [5][6] (Kaifeng and Yanjing)
- Later — Lost: The machine does not survive in any part; only modern reconstructions exist [6] (China)
- Now — Every watch: The escapement principle runs in every mechanical clock in the world (Worldwide)
Quick facts
- What it is
- a mechanism that turns continuous force into countable, equal ticks
- Built into
- the water-powered astronomical clock tower at Kaifeng (水运仪象台)
- Who
- Su Song (蘇頌), with Han Gonglian (韩公廉)
- Commissioned 1086, completed
- 1092 [4] — some accounts give 1088 for the wooden model [1]
- First escapement in the record
- Yi Xing (一行) and Liang Lingzan, 725 [6]
- Dismantled
- 1127, taken north to Yanjing, never successfully reassembled [5][6]
- Preserved as
- 新仪象法要 (*Xīnyí Xiàngfǎyào*), the treatise with its drawings [4][5]
- Filed as
- transformed — object lost, principle universal
Sources
- Su Song — Wikipedia (2026-10-25) ↩
- Heavenly Clockwork (Needham, Wang & Price) — Cambridge University Press, via Google Books (2026-10-25)
- World's Oldest Astronomical Clock Tower — Science and Technology Daily (2026-10-25) ↩
- 水运仪象台：11世纪世界科技明珠 — 科普中国 (China Association for Science and Technology) (2026-10-25) ↩
- 有人说达·芬奇是"西方的苏颂" — 新华社 (Xinhua) (2026-10-25) ↩
- سو سونغ (Su Song) — ويكيبيديا (Arabic Wikipedia) (2026-10-25) ↩