Seismoscope by Chang Heng, c 132 AD. Model.
© Science Museum / Science & Society Picture Library
Seismoscope by Chang Heng, c 132 AD. Model. The Chinese astronomer, mathematician and seismologist, Chang Heng (78-139 AD) described the earliest known seismoscope in about 132 AD. Shock waves displace a pendulum linked to a mechanism which opens the jaws of the dragon facing the direction of the earthquake. A ball falls from the dragon's teeth into the mouth of a toad below to record the event.