The secret of the Bessler wheel

Recently I wrote about a modern "perpetual motion" machine, a bicycle wheel that revolves for years without any apparent source of power. Of course it is not really a perpetual motion machine. It was built by a scientist as a challenge for those who saw it to work out how it was powered,  a challenge that 40 years later still baffled Adam Savage in a YouTube video.

I was fascinated by the reference in that video to the Orffyreus wheel, a similar machine from the 18th century. The name was code for the real name of the inventor, Johann Bessler. His wheel (or wheels, actually, as he built several of different sizes) would start moving from stationary with a slight push and would run at 25-50rpm for up to 54 days without any obvious energy source. They could do real work, lifting 5-40lb, depending on the size. Even today there is speculation that he may actually have discovered a source of perpetual motion.

I think the secret is quite simple however. The machine had to have a source of energy, and how would you power a machine like this? Gravity. There were clocks powered by gravity from the period like this one:

A heavy weight on a rope wound round the cylinder visible in the picture would have rotated the cylinder, with the torque converted to movement of the hands by a train of gears. It was obviously situated in a tower or high up on the face of a building or in a high space.

A simple falling weight would not work to power a wheel because it could not pass through the axle. Most probably there was a weight (or weights) attached to a shaft around the axle, powering the mechanism again through a gear train.  A couple of large lead weights falling from the top of the machine around the inner circumference towards the base could have powered a hollow wheel on bearings for many days, or easily contained enough energy to explain the work the machine did. (Yes, they did have bearings in the early 18th century.)

So there you have it. The wheel was a clock. There are actually a couple of very large clues: the pendulum on the front of the wheel controlling an escapement, and the fact that Bessler was an apprentice watchmaker.

Some witnesses of the Bessler machine stated that they could hear falling weights in the wheel, leading to speculation that it was a weighted wheel machine. Such a machine can work, if there is an input of energy, giving weights at the top of the wheel a nudge upwards (and increasing their potential energy). The power source I have described could have been used to do this.

I suppose it's possible that with a complex mechanism of large weights and smaller weights moving in the machine Bessler genuinely thought he was getting something for nothing and failed to realise he was supplying the machine with potential energy in setting up the machine in a state where some of those weights could fall over time, supplying the machine with the kinetic energy it needed to keep running. I'd somehow rather believe that he wasn't an outright fraud.

The secret of the Dreadco perpetual motion machine

Back in 1981 I was an A Level science student. Suggested reading was the New Scientist magazine, which at the time was a serious academic publication. (It seems to be more general interest science now.) Being a fairly lazy A Level science student, I would read the first third of a few articles before getting lost in the detail, skip the middle of the magazine, which was just job adverts, and read the page inside the back cover, a humorous page written by Dr David Jones under the pseudonym Daedalus. 

I don't remember much of what I read, to be honest, but I do remember that in one issue David Jones issued a challenge to readers to work out how a "perpetual motion" machine he had built worked, with the answer and the names of those to guess correctly to be published in the magazine in the next issue. Of course, this being a serious scientific magazine, there was no suggestion that it was a real perpetual motion machine.

I thought about it for a while, and had an idea as to how the wheel was supplied with energy to keep turning. I wrote to David Jones and he wrote back to say my suggestion was correct. Unfortunately my letter just missed the deadline. The names of two other people who had guessed correctly were published in the magazine. I seem to remember that he wrote that he had decided not to reveal how the machine worked for a while longer, to keep people guessing...

I didn't think about it again until a few days ago when a YouTube suggestion for a video about the very machine appeared while I was watching something else. I never thought that over 40 years later it would still be a source of mystery and debate.

I wish I had kept my letter from David Jones, but as far as I knew he was going to reveal how the machine worked in a week or so, so I chucked it in the bin. Apparently all David Jones' letters about the machine are archived, so my letter could be in there!

So what is the secret? Well, I would hate to spoil a 40 year old mystery. It's not really that difficult to guess. A number of people in the YouTube comments have suggested the answer I came up with. As Virginia Mills intimates in the video, look for a mundane explanation, rather than an exotic one. She also gives a huge clue in talking about Orffyreus' weighted wheel perpetual motion machine. The idea of falling weights adding impetus to a wheel is initially attractive until you remember that there is actually no net input of energy because the momentum of the wheel has to drag the weight upwards from a lower level on the way up. Without a source of energy it won't work.

But with a source of energy?