Today, a story about 19th-century science and
21st-century technology. The University of
Houston's College of Engineering presents this
series about the machines that make our
civilization run, and the people whose ingenuity
Here comes a wild new idea
for meeting our energy needs. And it leads us right
back to the Victorian scientist Lord Kelvin. In
1851, Kelvin wrote our modern system of
thermodynamics. Up to then, the things we knew
about heat seemed to disagree. He made sense of it
all. Once he did, we could design engines that'd
draw power from any natural temperature gradient.
So we look for natural gradients. The Gulf Stream
provides one. Engineers have worked on a floating
engine to generate electric power from warm water
flowing over colder water below.
There's a much larger temperature gradient right
under our feet. In many places, Earth's temperature
rises 150 degrees each mile you drill downward. And
here we run into Lord Kelvin again.
In 1862 the deeply religious and anti-evolutionist
Kelvin shocked both fundamentalists and geologists.
He calculated that Earth was a hundred million
years old. If we began as molten lava, he said, it
would've taken that long to cool down and establish
Earth's temperature gradient.
Kelvin didn't know that radioactivity sustains the
gradient. His result was low by a factor of 50. And
it kicked off a fight that lasted into this
century. Yet the fight itself finally gave us
better mathematics as well as better physics.
Now engineers want to tap into Earth's temperature
gradient. They're drilling test holes into the
earth. They mean to pump cold water down into the
rock, 12,000 feet below. They should be able to
bring it back under pressure at 460 degrees. The
hot water can then supply a power plant on the
We Americans are so hungry for energy. We use 80
quadrillion BTUs a year. But Earth is vast. The
energy stored in subsurface rock could supply that
energy for a hundred thousand years.
Still, it's a new technology. And new technologies
always harbor troubles. We'll have to force water
down through cracks in the hot, dry rock. Then we
have to find the water after it's heated and pump
it back up. And, like coal or oil, Earth's heat can
be used up. When it's gone, it's gone for a long,
As we drill downward I hope we do the right thing.
And I look back at quiet, scholarly Lord Kelvin.
There he sits behind it all. He wasn't thinking
about 21st-century power. He was thinking about
Watt's steam engine -- and about a debate between
geologists and fundamentalists that's now grown
So honest 19th-century thought is still feeding
21st century life. Kelvin's lucid mind set forces
in motion that've reached beyond his comprehension
-- and beyond his dreams.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
Nahin, P.J., Kelvin's Cooling Sphere: Heat Transfer
Theory in the 19th Century Debate over the
Age-of-the-Earth. History of Heat Transfer:
Essays in Honor of the 50th Anniversary of the ASME
Heat Transfer Division. (E.T. Layton and J.H.
Lienhard, eds.) New York: ASME, 1988, pp. 65-85.
Wald, M.W., Mining Deep Underground for Energy.
The New York Times, Sunday, November
3, 1991, pg. 16 F.
Some might object when I credit Kelvin for setting
up the means for drawing power from a temperature
gradient. Carnot had already given us the
underlying idea in 1824. But he did so without
understanding what heat was. It wasn't until 1851
that Kelvin made a proper separation of the first
and second laws of thermodynamics. Only then could
we really relate the power output of a heat engine
to a temperature gradient, quantitatively.
The Engines of Our Ingenuity is
Copyright © 1988-1997 by John H.
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