The eccentric engineer

With all the futility of trying to invent a perpetuum mobile, there's still something to be gained from perpetual motion.

I don't know why I didn't think of it before. It could put an end to our dependence on fossil fuels and solve global warming. All we need to do is crack perpetual motion.

There is a long and generally less than illustrious history of perpetual motion engineering which, despite many centuries of failed experiments in the face of the  unforgiving laws of thermodynamics, shows no sign of abating.

The earliest known attempt to describe a machine that would run forever was made by the 12th-century Indian mathematician Bhaskara II. His perpetual wheel had mercury or hinged weights around its rim and, as the wheel turned, the weights moved further from or nearer to the centre of the wheel under the influence of gravity. This, supposedly, would ensure that one side of the wheel was always heavier than the other and thus the 'overbalance wheel' would turn of its own accord. Except it didn't.

Not everyone thought the idea was impossible, and the overbalance wheel became a huge hit with mediaeval inventors. The greatest Renaissance engineer of them all, Leonardo Da Vinci, sketched such devices but, crucially, realised that they were not feasible. He reasoned that as each weight moved further from the rotational axis, the gravitational torque is greater but the moment of inertia is simultaneously increased, and the net gain to the system is zero. He said:

"Oh, ye seekers after perpetual motion, how many vain chimeras have you pursued? Go and take your place with the alchemists."

However, few have been put off, and the vain chimera hunt was soon back on. Most of these 'chimeras' were variations on the overbalance wheel using weights or magnets, although Mark Anthony Zimara did invent the 'self-blowing windmill' - a handy device by which the turning of the sails powered bellows which produced the wind. Cornelius Van Drebbel also invented a 'perpetual motion drive' for a clock which was not a perpetual motion machine and worked. Although it appeared to have no energy input, this perpetual winding mechanism was driven by changes in atmospheric pressure. It was perfected by James Cox in the 1760's with the development of Cox's timepiece.

'Overunity'

After 1635, there was a flood of other designs as patenting took off using the movement of magnets, water, mercury, or in one case cannonballs, through a closed system. Some believed that they might be able to make some money from pretending they could create a machine that ran without an external energy input. John Ernest Worrell Keely liberated $5m from investors in the late 19th century for a machine that, on his death, was found to operate using hidden air pressure tubes.

The scientific community soon acted and as early as 1775 the Royals Academy in Paris refused to deal with perpetual motion. Not that this stopped people trying. The simple desire to get more out than you put in ('overunity') has meant that these machines are still with us. The idea of creating such a machine has, strangely, had a positive effect on science. Just hypothesizing these impossible engines has helped us examine the laws of nature. The great bongo-playing physicist and Nobel laureate Richard Feynman imagined such a machine, although in the face of the immutable First Law of Thermodynamics, he decided to have a crack at the second.

His Brownian Ratchet consisted of a ratcheted cog in a box connected by a massless and frictionless spindle to a paddle in another closed box. The Brownian motion ensured that gas molecules were randomly hitting the paddle, but as the ratcheted gear could only turn one way, only those collisions which pushed the paddle in the same direction pushed it round. And so, the ratchet turned. Except, it wouldn't. For the Brownian ratchet to work, the ratchet mechanism itself would have to be so small that Brownian motion would affect it too, knocking the pawl off the gear and hence allowing it to slip back the other way as often as the collisions with the paddle moved it the correct way. The ratchet would not turn but just randomly oscillate.

Feynman watched a demonstration by Joseph Papp of a car engine that apparently put out far more energy than was put in. As far as Feynman could see, this was a trick, and the 'measuring equipment' which was connected to the mains supply was powering the engine. Papp pulled the plug and the engine continued to run, but Feynman reasoned that there were probably batteries in the 'engine'. So he asked to hold the plug despite Papp's urgent requests for its return. Feynman hoped that the batteries would drain and he would have uncovered the deception. But, sadly, the engine exploded, killing one onlooker.

What happened remains a mystery. Feynman thought that Papp, who had promised to hand his device over to the Stanford Research Institute for testing, had deliberately blown it up. Papp, however, sued Feynman.

Astonishingly Caltech, Feynman's employer, settled out of court and paid up, proving that there is still something to be made from perpetual motion.

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