Skip to main content
No. 438:
Redheffer's PMM-I

Today, let's place bets on a perpetual motion 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.

In 1812 Charles Redheffer showed up in Philadelphia with a perpetual motion machine. He set it up and charged a viewing fee. The public was fascinated. We didn't yet have physical laws to deny perpetual motion, but common sense ran against it. So Redheffer's machine drew people in. A confederate stirred things up in the Philadelphia Gazette. He offered a huge bet that no one could debunk the machine.

Redheffer also asked the state of Pennsylvania for money to develop his device. When state inspectors arrived, they found they had to view the machine through a barred window.

What they saw was a gravity-driven pendulum affair. The output gear drove a vertical shaft. Then a member of the team noticed something very small and very subtle. The gear teeth were worn on the wrong side. Apparently the output shaft drove the machine. The machine didn't drive the shaft.

So the inspector went back and made his own perpetual motion machine. He used hidden clockwork to drive it. It looked like Redheffer's machine, but you could walk right up to it. Next he arranged a showing, and he invited Redheffer.

Redheffer took the bait, the hook, the line, and the sinker. He was so astonished that he cornered the fellow and offered to buy the secret for a huge sum.

And so Redheffer was unmasked in Philadelphia. He had to take his scam to New York. This time some friends of Robert Fulton took him to see it. Fulton noticed the motion wasn't steady -- the speed kept varying. Redheffer surely didn't use hidden clockwork, but Fulton realized what was driving it.

Encouraged by the crowd, Fulton knocked away some structure behind the table. Sure enough, there was a hidden catgut belt. He traced it back to where an old man was locked in an upper room. Redheffer was feeding the poor fellow bread and water and forcing him to turn the crank drive all day long.

Back in Philly, newspapers kept the issue alive. Had the city missed a chance to drive its water pumps free of charge? Redheffer was far from the last to waken dreams of something for nothing. The public likes to be fooled, but only for a little while. How often have you read about impossibly efficient engines suppressed by dark forces of "the establishment"?

The game goes on today -- sometimes deliberate, but more often sincere. The will-o-the-wisp of cold fusion draws us in just as surely as ESP and UFO's do. We drink in the magic that invention promises, because it's so exciting when invention actually delivers.

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, Chapter 8.

For more on perpetual motion, see Episodes 33527528, and 614.


Smithsonian Institution photo provided by Charles Redheffer's descendent, Nancy Redheffer

Redheffer Perpetual Motion Machine replica at the Franklin Institute