Astronomer, mathematician and court official, credited in the Hou Hanshu with building the device
Plate 025
132 CE
Luoyang, Han dynasty China
No photograph is shown for this exhibition. The museum displays an image only where it can show the object honestly.
About this date
The date is recorded in the Chinese history Hou Hanshu. No original instrument survives, and modern reconstructions are interpretations of the description.
About credit
The Hou Hanshu credits Zhang Heng. It was written after his lifetime, and how the device worked is known only from a short description.
Chapter II
The world before
Life before the Seismoscope
Earthquakes were noticed only where they were felt. News arrived by messenger days later, if at all.
II
The human achievement
How it came about
According to the Hou Hanshu, in 132 CE Zhang Heng presented a bronze instrument about two metres across. Eight dragons faced the compass directions; a shake in one direction released a ball from the matching dragon. The record says it registered a distant quake that nobody in the capital had felt.
III
Understanding the invention
How it works
The Seismoscope, explained in two steps.
01
Step 01 of 02
A pendulum that stays still
Modern reconstructions often use a heavy inner pendulum that lags when the ground shakes, tripping a release.
A pendulum that stays still
Direction by lever
IV
The transformation
What changed for humanity
Government
Knowing where an earthquake struck helped officials send aid to the right region.
Science
It signals a tradition of building instruments to observe natural events.
It is among the earliest known instruments for detecting earthquakes, reflecting an effort to observe and record natural events rather than treat them only as omens.
V
Before and after
Life before and after The Seismoscope
Before
By messenger after the fact.
After
A recorded signal and direction.
On larger screens, drag the divider (or use the arrow keys) to give more room to the world before or after.
VI
Its legacy
What came after
MHI 025
The Seismoscope
Beyond the collection
The seismograph
Modern seismographs, developed in the 19th century, record ground movement continuously.
