The ancient Chinese Earthquake detector was invented by Zhang Heng (A.D. 78-139) around A.D. 132. The instrument was a copper-domed urn with dragons' heads circling the outside. Each dragon head contained a bronze ball. A pendulum hung from the top of the dome, which would swing when the Earth shook. The swinging pendulum would knock a ball from the mouth of a dragon into the waiting open mouth of a bronze toad below. The ball made a loud noise and signaled the occurrence of an earthquake. By observing which ball had been released, one could determine the direction of the earthquake's epicenter (the point on the Earth's surface directly above the quake's point of origin).Ancient Chinese Earthquake Detector Papercraft
