China's researchers to resurrect 2,000-year-old earthquake sensor

Chinese researchers are working to reconstruct Zhang Heng’s ancient seismoscope, the Houfeng Didong Yi, originally invented in 132 AD and considered the world’s first earthquake detector. The device reportedly consisted of a bronze jar with eight dragons facing different compass directions, each holding a ball above a toad’s mouth. When an earthquake occurred, the dragon facing the quake’s direction would release its ball into the toad’s mouth, indicating the quake’s direction. Although historically celebrated, the device’s existence and functionality have been questioned, leading to its removal from Chinese textbooks in 2017. Xu Guodong, a researcher at China’s Institute of Disaster Prevention, has re-examined historical texts and developed a realistic reconstruction using modern engineering principles. His model uses a central pendulum that swings during an earthquake, triggering a lever system to release a ball from the corresponding dragon, with a locking mechanism ensuring only one ball drops per event. Xu’s calculations suggest the device could detect ground movements as small