Zhang Heng's seismometer
A bronze vessel drops a ball in the direction of an earthquake hundreds of kilometres away.
- When
- Known to
- ± 2 years
- Era
- Classical, Holocene
In 132 CE the astronomer Zhang Heng presents an instrument with eight dragon heads holding bronze balls above eight toads; a tremor causes one ball to fall, indicating the direction. It reportedly detected a distant earthquake that nobody in the capital had felt, and was disbelieved until a messenger arrived days later. Zhang also produced a water-driven armillary sphere and a strikingly accurate value for pi.