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Houfeng didongyi (seismoscope)

Type Object Region China Time 132–200

Earthquake-detecting instrument created by Zhang Heng in 132 CE, indicating quake direction via triggered dragon-mouth pellets, one of the earliest d…

Timeline

  1. 132Lingtai, Luoyang · HenanZhang Heng made the houfeng didongyi, shaped like a large vessel, with eight dragons cast around it, each holding a copper pellet; toads below caught them in their mouths, with an internal trigger sensing quakes, installed at the Lingtai for observing earthquakes.
  2. c. 138Luoyang · HenanHistorical records state that one day the northwest dragon mouth of the didongyi released a pellet, and days later a relay reported an earthquake in Longxi; capital officials then believed in its efficacy, making this the instrument's most famous recorded observation.
  3. c. 200–500China · ChinaThe original instrument was lost in wartime, with only textual records surviving through the ages; modern scholars have proposed various reconstruction models based on the Book of the Later Han and principles of mechanics, with the underlying principle still subject to academic discussion.

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