Zhang Heng (78CE-139CE) was a polymath who worked in fields as diverse as astronomy and poetry, who rose to scholarly and political prominence in ancient China’s Eastern Han Dynasty.
As Chief Astronomer in the Imperial Court he was responsible for both observing and recording celestial events, as well as preparing the calendar. He was also responsible for a literary test used to filter out potential appointees to select sections of the Imperial civil service, demonstrating a level of influence that may seem surprising to modern eyes.
He is especially remembered for being among the individuals to independently create a water-powered armillary sphere. These devices used a series of moving concentric rings to accurately mimic the movement of celestial bodies, allowing for their prediction without the need for continuous direct observation.
He is credited for the invention of the seismoscope; a machine able to determine the direction and occurrence of an earthquake. Reconstructions of his work have suggested that his machine operated using a pendulum on top of a ball. When a shockwave moved the seismoscope, the pendulum at first instant would not move, allowing the ball to fall down a channel in the opposite direction of the shockwave, thus indicating the direction of the focus.
Some articles written about his work include “The Review Of Reconstruction Designs Of Zhang Heng’s Seismoscope” by Kuo-Hung Hsiao and Hong-Sen Yan (2009), and “Zhang Heng’s Seismograph: Earthquake Measuring and Forecasting in Ancient China” by Zhichao Li (2021)