Zhang Heng's earthquake detector was mocked until a messenger galloped in
When Zhang Heng's new seismoscope signalled a quake to the northwest, nobody in the Han capital of Luoyang had felt a thing, and his rivals at court enjoyed the apparent failure. Then a messenger arrived reporting an earthquake roughly 400 to 500 kilometres away in Gansu. The device, presented in 132, was the first of its kind.
Zhang was born in AD 78 at Xi'e in Nanyang, into a respected but not wealthy family; his grandfather had helped restore the Han dynasty, and his father died when Zhang was ten. He left home in 95 to study in Chang'an and Luoyang, writing an early rhapsody on hot springs he passed on the way, and modestly turned down offers of government posts. He did not take up astronomy until he was 30.
Emperor An summoned him in 112 for his mathematical skill, and he served two terms as Chief Astronomer. The job went well beyond stargazing: he kept the calendar, flagged lucky and unlucky days, and set a literacy exam requiring candidates to know at least 9,000 characters. For all this he was paid at the 600-bushel grain rank, the lowest the emperor could appoint directly in a scale that ran from 100 to 10,000. He built the first water-driven armillary sphere, added a second tank to the water clock, catalogued about 2,500 stars, refined earlier Chinese values for pi, and argued that the Moon shines by reflected sunlight.
His stubbornness cost him. He opposed a 123 proposal to reform the calendar using apocryphal texts, and his views on those texts and on the Gengshi Emperor's role in the Han restoration kept him off the committee writing the dynastic history, ending hopes of becoming court historian. Later, as Palace Attendant on 2,000 bushels, he urged Emperor Shun to curb the palace eunuchs, who slandered him in return; he answered with a rhapsody on whether good men should flee a corrupt world.
He eventually left for a provincial post in Hejian, was recalled to the capital in 138 and died there the following year. His poetry was prized for centuries, and some modern scholars compare his astronomy to Ptolemy's.
Source: Zhang Heng
