What did the original seismometer look like?
Cheng Heng s original seismometer was lost. Luckily, its description survived. It was a cast bronze vessel with a domed lid, resembling a wine jar. The working innards, of “toothed machinery and ingenious constructions,” were hidden. The surface of the vessel was decorated with motifs of mountains, tortoises, birds, animals and antique writing. Around the vessel were eight dragons whose mouths held a ball. Round the base of the vessel sat eight corresponding toads with their mouths open, looking upwards. The sign for an earthquake was the falling of a ball from the dragon into the mouth of a toad. The direction of the earthquake is indicated by the position of the toad which swallowed the ball. This instrument was most remarkable: On one occasion one of the dragons let fall a ball from its mouth though no perceptible shock could be felt. All the scholars at the capital were astonished at this strange effect occurring without any evidence of an earthquake to cause it. But several days l
