Zhang Heng

Zhang Heng studied in Luoyang and Chang'an, then worked his way from minor civil servant in Nanyang to Chief Astronomer at the imperial court. His refusal to bend on calendrical disputes kept him from becoming Grand Historian, and a feud with palace eunuchs under Emperor Shun drove him out to administer Hejian Kingdom in present-day Hebei. He invented a water-powered armillary sphere to track the stars, refined the inflow water clock, and cataloged twenty-five hundred stars while theorizing that the Moon was a sphere lit by reflected sunlight. His poetry circulated widely; his mechanical ingen…