Seismometer

Seismometer

Machines; Natural hazard prevention

The seismometer was made of fine copper, and looked like a big cup with a lid. The instrument was cast with eight dragons on the surface (whose heads pointed in eight directions), and each dragon had a copper ball in the mouth. On the ground below the dragons there were eight copper toads raising their heads and opening their mouths opposite the dragons' mouths. When an earthquake occurred, the dragon facing that direction would open its mouth, and the ball would fall into the toad's mouth, automatically indicating the direction of the earthquake.

Zhang Heng

Han Dynasty

Armillary sphere

Round-shaped with dragons and toads to represent directions

Physical object

Chinese geography