Zhang Heng

Zhang Heng was an Eastern Han Chinese polymath whose work spanned astronomy, mathematics, invention, and poetry. He is especially known for devising an early instrument that indicated distant earthquakes.

Eastern Han dynasty: The later period of the Han dynasty in China, conventionally dated 25–220 CE. Zhang Heng served the court during this dynasty.
Houfeng didong yi: An instrument devised by Zhang Heng to indicate the direction of a distant earthquake. It is the invention most closely associated with his name.
Seismoscope: An instrument that indicates the occurrence or direction of an earthquake without necessarily measuring its strength. The Houfeng didong yi is a famous early example of this instrument type.
Emperor An of Han: An emperor of the Eastern Han dynasty who ruled from 106 to 125 CE. Zhang Heng held court offices during An’s reign.
History of seismology: The development of methods and theories for studying earthquakes and seismic waves. Zhang Heng’s device is often discussed as an early milestone, despite its different purpose from modern seismology.
Han dynasty: A Chinese imperial dynasty that ruled from 206 BCE to 220 CE, with an interregnum from 9 to 23 CE. Its institutions and intellectual traditions shaped Zhang Heng’s world.
Armillary sphere: A model of the celestial sphere made from rings that represent circles in the sky. Zhang Heng built an instrument of this kind to represent celestial motions.
Pendulum: A body suspended from a pivot that swings under gravity when displaced. Later explanations of Zhang Heng’s device often invoke a moving mass, though its exact mechanism is unknown.
Ban Gu: A historian and poet of the Eastern Han dynasty, best known for compiling the Book of Han. His historical tradition provides a key context for accounts of Han officials and scholarship.
History of science in China: The historical development of scientific knowledge and practice in China. His varied work illustrates the range of early imperial Chinese scholarship.

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