Volcanoes and Earthquakes

Who invented the ancient Chinese earthquake detector?

The detector, invented by Zhang Heng (78–139C.E.) around 132C.E., was a copper-domed urn with dragons’ heads circling the outside, each containing a bronze ball. Inside the dome was suspended a pendulum that would swing when the ground shook and 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. Knowing which ball had been released, one could determine the direction of the earthquake’s epicenter (the point on Earth’s surface directly above the quake’s point of origin).


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