Engines of Our Ingenuity

No. 527:
COX'S PERPETUAL-MOTION MACHINE

by John H. Lienhard

Click here for audio of Episode 527.

Today, we make an impossible machine. 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.

Perpetual-motion machines have been an ongoing dream for about a thousand years. Here's a strange windmill. It drives a bellows that blows the air that turns it. There's a water wheel that pumps its own water supply. Always something for nothing!

Now I gaze at a photo of a beautiful machine. It is exquisite. It's tall like a grandfather clock. The polished wood and brass is a work of art. High up is a clock face. The body contains a huge blown-glass barometer. It has the noble lines of classic architecture.

This is James Cox's perpetual-motion machine. Not only is it beautiful, but it also works. This is no sham. Of course, it isn't really a perpetual-motion machine. But Cox, who built it in London during the 1760's, thought it was.

What it is is a clock that never has to be wound. As the weather changes, the barometer drives a ratchet mechanism. It keeps the clock wound. The whole action runs on jewelled bearings. It's a stunningly delicate and sophisticated heat engine.

Cox was a well-known clockmaker. He showed his self-winding clock in a private museum along with other fine clocks. When he died in 1788, a museum owner named Thomas Weeks bought the clock. It ticked away in his museum until the 1830s.

After that it was sold off again. This time, it vanished until it turned up on public display in 1898. It finally came to rest in the Victoria and Albert Museum.

Cox's clock writes an odd chapter in the history of human ingenuity. For he seemingly succeeded in creating that great will-o-the-wisp, perpetual motion. 18th-century science hadn't yet written laws that would tell us it was impossible. But Cox saw where that science was going, and he worked around it. He saw how nature could provide energy and make it look like something for nothing.

A contemporary writer said Cox's engine was like a water wheel. That, he said, was perpetual motion of a similar kind. And he was right. Cox's clock was actually kin to the windmill.

Like the windmill, it took energy from the sun. The warming of air causes winds and pressure changes. Machines that tap that reservoir don't violate physical laws. What they do is create the illusion of magic by accepting a gift from nature.

This strange clock is a fit reminder of the most magical source of energy for our energy-hungry world. That source is the sun. The sun brings us as close as we'll ever get to realizing the age-old hope -- of perpetual motion.

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., Chapter 7, 1977.

For a contemporary claim to having created a perpetual motion machine, see:

http://en.wikipedia.org/wiki/User:Perpetual_motion_machine

For more on perpetual motion, see Episodes 33, 438, 528, and 614.


The Engines of Our Ingenuity is Copyright © 1988-1997 by John H. Lienhard.

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