Today, we visit a wonderful Chinese clock. 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.
Water clocks were used from
remote antiquity until mechanical clocks finally
replaced them -- only about 700 years ago. You
might know them by their Greek name,
clepsydra, which means "a stealer of
water." That's because all water clocks -- one way
or another -- used a steady flow of water to
measure time. Second-century Egyptian engineers
added a clever kind of self-regulation to water
clocks. Their version was picked up by Arab
artisans; and the Moors of medieval Spain finally
brought it to a very high state of development in
the West.
The Chinese, of course, had their own version of
the water clock, and the Sung dynasty improved on
it during the 11th century. Finally, in 1086, the
emperor charged an official named Su-Sung to create
what was to be the finest water clock up to that
time. Su-sung put together a team that finished the
clock 8 years later.
Most ancient clocks tried to do a lot more than
just tell people how much time had passed. They
tended to have bells and dials and displays of
planetary motions. But it was hard for water clocks
to do all these things, because a float indicator
riding on a water surface didn't exert enough force
to drive a lot of extra machinery.
Su-Sung got around that problem. His huge clock
stood 40 feet high and was powered by a special
water wheel. Buckets around its rim were filled,
one at a time, by a steady flow of water. When each
bucket was heavy enough to trip a mechanism, it
fell forward -- carrying the bucket behind it into
place under the water spout. And the process
repeated. The weight of the buckets exerted enough
force to activate all sorts of displays. Su-Sung's
wonderful clock, with its tick-tock motion, was
quite accurate. It looked a little like the
mechanical clock which wasn't invented for another
200 years in Europe.
Su-Sung's clock was stolen when invading Tatars put
an end to the Sung dynasty in 1126. The Tatars
weren't able to get it running again, and the high
art of Chinese clock-making completely disappeared.
But even before the Tatar invasion, Taoistic
reformers had come into power. They saw fancy
clock-building as part of the older regime and did
little to sustain it. Su-Sung's book on the
operation of his clock didn't surface in the West
until the 17th century. By then, of course, the
Western mechanical clock was light-years ahead of
it.
But the West didn't always hold a monopoly on
time-keeping. It's sobering to know that the state
of the art in the 11th century was, in fact,
Su-Sung's marvelous water clock.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
