Zhang Heng

Zhang Heng served the Han dynasty court as an astronomer and mathematician, cataloguing roughly 2,500 stars and building a water powered armillary sphere to track them. In 132 CE he built the first seismoscope, a bronze vessel ringed with eight dragon heads that dropped a ball toward a bronze toad to indicate the direction of a distant earthquake before any human observer felt it, and he independently narrowed the approximation of pi. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/