Today, an earth-shaken invention -- far older than
we'd think. The University of Houston's College of
Engineering presents this series about the machines
that make our civilization run, and the people
whose ingenuity created them.
We face an odd problem when
we look for the origins of our cleverest machines.
So many were invented in China and never plowed
into any mainstream of knowledge. So much
spectacular human ingenuity was poured into the
various Chinese royal courts and then forgotten.
That's the way it was with seismography.
"China has always been plagued with earthquakes."
observes historian Robert Temple. Some of them,
like the great earthquake of 1556, were just awful.
It killed 800,000 people. Down through the
millennia, the Chinese have left very good records
of those disasters.
So it was that Chang Heng, astronomer royal to the
Han Dynasty, invented an accurate seismograph in AD
132 -- 1600 years before anyone in the West did. It
was a large bronze urn with eight dragon heads
gazing outward in eight directions. Each dragon
held a ball in his mouth. Around the base of the
urn, under each dragon, sat a frog with his mouth
A delicate inverted pendulum was hidden in the urn.
The slightest seismic ripple moved it. The swinging
pendulum tapped a mechanism that dislodged one of
the balls. The ball fell from the mouth of the
dragon into the mouth of the frog below. It landed
with a great clang that announced the earthquake.
Knowing which frog had been fed, you could tell the
direction of the quake.
Members of the court thought the device had failed
when the alarm sounded one day and they felt
nothing. Doubt turned to astonishment a few days
later. A messenger arrived from a town 400 miles
away to report that it'd been savaged by an
Chinese writings talked about Chang Heng's
seismograph and ones like it until the Mongols
overran China. After that, it vanished as though it
had never been. The next seismograph was invented
in France in 1703. But seismography really started
up again -- and with pendulum devices -- only 130
Chinese seismography was no flash in the pan from a
one-time inventor. Chang Heng was brilliant. He
described a round earth in infinite space. He
invented lines of longitude and latitude. The
Chinese called that, "throwing a net over the
And why is such brilliance so badly remembered?
It's probably because people like Chang Heng were
tied so tightly to their patrons. They didn't
belong to the same loose, open communities of
freely moving scholars that have diffused knowledge
so effectively in the West.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds