A seismoscope is an instrument that indicates the shaking of the earth during an earthquake.
It should not be confused with a seismometer or a seismograph that also records the movement.
Its naive to believe that such instruments didnt exist before Zhang Hengs invention.
A replica of Zhang Hengs seismoscope.
On the outside of the vessel there were eight dragon-heads, facing the eight principal directions of the compass.
The direction from which the ball dropped indicated from whence the tremors came.
Zhang Heng called his invention Houfeng Didong Yi, or earthquake weathervane.
Because no one felt any shaking in the capital, his critics wrote the instrument off as a failure.
Photo credit: Science & Society Picture Library via Endgadget.
A possible mechanism of the seismoscope.
Photo credit: Science & Society Picture Library via Endgadget.
Contemporary writers have described the nature of the instrument, but the inner workings of it is a mystery.
This ball was delicately balanced atop of a thin pedestal at the center of the instrument.
Directly above the ball was a suspended pendulum lightly touching the ball.
Pendulum-based seismometers were used until the 19th century.
Some instruments use springs instead of pendulums.
