““Zhang’s seismometer—Houfeng Didong Yi, or the “instrument for inquiring into the wind and the shaking of the earth”—was reconstructed by a Chinese museum in 2005. The device used a pendulum in the middle of an urn that was lined with eight dragons, each pointing outward in a different direction. When the machine detected a quake, the pendulum dislodged a bronze ball that then dropped out of the mouth of one of the dragons and into the mouth of a metal toad—indicating the direction of the earthquake’s epicenter.””
