Image: EastHanSeismograph

Description: A replica of an ancient Chinese Seismograph from Eastern Han Dynasty (25-220 CE). This picture is taken from an exhibition at Chabot Space & Science Center in Oakland, California. The plaque of the exhibit said: Detecting a Quake In 132 CE, after several earthquakes in China, astronomer Zhang Heng invented this instrument to warn people of the next one. When the ground shook, it moved a pendulum inside the jug. The pendulum pushed a lever that opened one dragon's mouth. A ball rolled out and into the toad's mouth below, sounding an alarm. The open dragon mouth pointed in the direction of the earthquake, notifying the Emperor.
Title: EastHanSeismograph
Credit: en:File:EastHanSeismograph.JPG
Author: en:user: Kowloonese
Usage Terms: Creative Commons Attribution-Share Alike 3.0
License: CC-BY-SA-3.0
License Link: http://creativecommons.org/licenses/by-sa/3.0/
Attribution Required?: Yes