Today, we talk about the last water wheels. 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.
Around 1750, Louis XV's
mistress, Madame de Pompadour, wanted a water
supply for her chateau at Crécy. The job of
providing it fell to the noted French mathematician
Antoine de Parcieux.
Why a mathematician? Well, 18th-century rationalism
was just catching up with the medieval water wheel
in 1750. Power-producing water wheels took many
forms, but the field had narrowed to two types by
then -- overshot and undershot wheels. A stream was
directed beneath an undershot wheel, so the water's
velocity forced it to turn. A stream entered above
an overshot wheel. That way the weight of water
falling through its blades forced the wheel to
turn. The 18th century was marked by a maniacal
drive to harness more and more power for industrial
use. So people badly wanted to know which water
wheel would give the most power.
Parcieux correctly saw that the overshot wheel
would produce more power for the pumps at
Crécy, but his calculations were in error,
and his experiments were pretty crude.
Isaac Newton had given us the intellectual
apparatus for analyzing the water wheel in 1687,
and the people who undertook to do these analyses
form a roll call of the great mathematicians and
scientists in the mid 18th century -- people like
Euler and Bernoulli.
But it was finally the towering figure of John
Smeaton who put the question to rest. Smeaton was
the prototype of the 18th-century engineer. He
designed the first successful Eddystone Lighthouse,
he greatly improved Newcomen's steam engine, he
designed windmills. And, in 1754, he ran a
systematic set of scientific experiments that made
it clear the overshot wheel was better. About the
same time, Euler's son Johann came to the same
conclusion using a correct analysis.
This was just 15 years before Watt patented a
superior steam engine in 1769. It's been argued
that Smeaton slowed the spread of steam power with
his fine work on the water wheel. But that was like
slowing the advance of a Sherman tank with a
cardboard barricade. The steam engine soon made the
water wheel obsolete.
But the body of theory these people gave us
reappeared in the 19th century -- in modern
power-producing water-turbines. They never did slow
the spread of steam power. But today water turbines
give us a nice part of the energy we use, by
cleanly and cheaply taking it from rivers and
waterways.
So the next time you visit Grand Coulee or Hoover
Dam, try not to think about King Louis XV indulging
Madame de Pompadour with running water for their
love-nest.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
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