 "From myth to reality: Scientists recreate 2000-year-old Chinese quake sensor")
About 2,000 years ago, a Chinese scholar named Zhang Heng reportedly created a groundbreaking device called the Houfeng Didong Yi, a seismoscope that allegedly could detect distant earthquakes and even point to their direction.
Though mentioned in ancient texts like The Book of the Later Han, some scholars doubt its existence, calling it a myth, and it was dropped from China’s school curriculum in 2017.
Now, a team of researchers in China is working to prove this ancient invention was real by rebuilding it with the help of modern science.
The device
Imagine a decorative wine jar with eight dragons around it, each holding a bronze ball in its mouth, and toads below waiting to catch them.
When an earthquake’s tremors hit, a hidden mechanism would make one dragon drop its ball into a toad’s mouth with a loud clang, showing the quake’s direction.
According to The Book of the Later Han, it was “as accurate as the gods.”
Built in 132 AD during the Eastern Han dynasty, this device was allegedly far ahead of its time—Europe didn’t have a similar tool until 1856, when Italian scientist Luigi Palmieri made one.
Challenges and determination
Sceptics argue that ancient technology couldn’t be that advanced, but others believe it was a remarkable engineering achievement.
Efforts to recreate the device based on old texts have failed to fully match its described abilities.
Xu Guodong, an associate professor at the Institute of Disaster Prevention in Hebei, is leading a team to change that.
Using modern seismic knowledge, they’ve designed a model with three parts: an excitation structure, a transmission structure, and a shutdown system.
Impact Shorts
More ShortsHistorical texts describe a “capital pillar” with eight channels as the device’s core.
Xu’s team believes this pillar wasn’t an unstable rod, as some thought, but a pendulum-like cantilever, similar to a giant chopstick fixed in the ground.
When the ground moved just 1mm, the pendulum’s tip would swing at least 5mm, amplifying the tremor. This motion triggered an L-shaped lever system, releasing a bronze ball from a dragon’s mouth. Even a tiny 0.5mm tremor could tip the delicate balance, sending the ball into a toad’s mouth below.
A clever locking system ensured only one ball fell. When the first ball dropped, it activated levers that locked the other seven, so only one direction was recorded, matching the historical claim that “one dragon triggering while seven remained silent.”
Xu calls this design almost prophetic for its time.
The device was built to detect quakes reliably without false triggers, responding to ground movements as small as 0.5mm. However, pinpointing the exact direction of an earthquake’s epicentre was tricky and only accurate under specific conditions, like when the device aligned with certain fault lines.
Xu’s research, published in Progress in Geophysics in March, aims to restore the Houfeng Didong Yi’s place as a marvel of ancient engineering.
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