Engines of Our Ingenuity

No. 33:
PERPETUAL MOTION

by John H. Lienhard

Click here for audio of Episode 33.

Today, we look for perpetual motion. 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.

When we talk about a perpetual motion machine, we usually mean a machine that produces power without being fed an even greater amount of power in a different form -- say an engine that produces electrical energy without eating up even more energy in the form of coal. For 140 years we've all agreed on thermodynamic laws that tell us that that sort of machine can't exist.

But think for a moment like a medieval engineer. For years you've harnessed the motions of wind and water. You've harnessed a lot of power, and you're hungry to harness still more. You watch a water wheel turn, and turn, and turn. You watch a wind mill turn, and stop for a while, and then turn some more.

Your eyes tell you that perpetual motion obviously is possible. Besides, the science of your day doesn't discriminate very clearly between physics and magic. The medieval engineer saw more magic than physics in the way windmills induced breezes to grind grain for him. And maybe we're the losers today for failing to see more magic than we do in such a process.

In any event, the Hindu mathematician Bhaskara suggested a machine that would produce continuous power in AD 1150. It was simple enough -- a wheel with weights mounted around its rim in such a way that they swung radially outward on one side and inward on the other. This wheel was supposed to stay forever out of balance and to turn forever.

The Moslems picked the idea up around AD 1200, and it showed up again in France by 1235. For the next 500 years many writers recommended the use of this ingenious -- if impossible -- little device. You wonder, did they ever try to make one? Well, yes they did, but it always seemed that they'd failed to get the proportions just quite right.

17th and 18th-century science eventually made it clear that the overcentered wheel wouldn't work. But then, after that, as each new physical phenomenon was discovered, people invented new ways of using it to produce power without consuming energy. People suggested perpetual motion machines based on static electricity, surface tension, magnetism, hydrostatic forces, and so on.

Today we still look for perpetual motion. Some people do it in the face of the physics that says it's impossible, but others look for as-yet-unthought-of ways to keep producing power. But whatever we concoct, I think that we -- like the medieval engineer -- should be willing to see some element of magic in what we do.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)


Ord-Hume, A.W.J.G., Perpetual Motion: the History of an Obsession. London: George Allen & Unwin Ltd., 1977.

For more on perpetual motion, see Episodes 438, 527, 528, and 614.




Image courtesy of the University of Kentucky's Special Collections Library

A late 17th-century version of Fludd's perpetual motion machine grinding grain as shown in Böckler's Theatre of New Machines




Image courtesy of the University of Kentucky's Special Collections Library

A late 17th-century pump driven by an "overcentered wheel perpetual motion machine" as shown in Böckler's Theatre of New Machines



The Engines of Our Ingenuity is Copyright © 1988-1997 by John H. Lienhard.
Previous Episode | Search Episodes | Index | Home | Next Episode