Zhang Heng, Chinese seismologist, c 120 AD.
© Science Museum / Science & Society Picture Library
Porcelain statuette of the Chinese astronomer, mathematician and seismologist, Zhang Heng (78-139 AD), who described the earliest seismoscope known in about 132 AD. His description has been used as the basis for the Science Museum's reconstruction of this object, which shows four dragons holding balls in their mouths, suspended over four toads. Arriving shock waves displaced 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.