Zhang Heng Designs an Instrument to Report Distant Earthquakes

In 132, the Han imperial court at Luoyang received a new mechanical device presented by the scholar and official Zhang Heng. Historical accounts describe the device as indicating the direction of a distant earthquake, rather than measuring its strength. Skepticism greeted the apparatus at court, particularly on an occasion when it indicated a shock originating from the northwest while residents in the capital noticed no movement. According to the historical account, a messenger subsequently reported an earthquake in the region of present-day Gansu.

Zhang's achievement took place within an imperial system that viewed earthly and heavenly occurrences through an intensely political lens. Han cosmological beliefs interpreted natural disasters as severe portents of Heaven's displeasure with earthly administration. When a series of earthquakes shook the empire a year after the seismoscope appeared, Emperor Shun solicited official commentary on these occurrences. Zhang submitted a memorial linking the calamities to systemic administrative flaws, criticizing recent changes in civil service recruitment that concentrated authority under the Three Excellencies and imposed a minimum age limit of forty on candidates.