Irish company Steorn made headlines around the world when it took out a full page advert in The Economist claiming to have developed a device that produced "free energy".
Throughout early July, the company planned to display the device to the public for the first time.
Professor Sir Eric Ash, electrical engineer and former rector of Imperial College London, visited the demonstration for the BBC News website.
Marvellous things can happen in this world.
Sean MacCarthy does not know where the energy comes from
As an engineer, whenever I look at a new baby I say categorically that there can be no such thing - it's far too complicated to work.
Yet we know this lack of faith in the marvellous is misplaced.
So, the fact that a device or an invention looks too marvellous to be true is not conclusive evidence that it isn't.
I believe that it is thinking on such lines that encourages inventors - and there have been many since the 12th Century - to pursue what would be a true marvel: a perpetual motion machine.
The most recent attempt is from Mr Sean McCarthy, the Chief Executive Officer of an Irish company called Steorn.
His invention, known as the "Orbo", is a mechanical device which uses powerful magnets on the rim of a rotor and further magnets on an outer shell.
Mr McCarthy is convinced that it is working. He took a full page advertisement in the Economist last year to say so, and to attract volunteer scientists to check the authenticity of his claims.
They are still in the process of doing so.
In the meantime Mr McCarthy was hoping to demonstrate the machine to the public at the London Kinetica Museum, which is devoted to displaying dynamic art, particularly of artefacts at the interface of science and art.
The demonstration was to run over 10 days starting on 6 July. Unfortunately, there was a technical defect, attributed by Mr McCarthy to the excessive heat produced by lights used to illuminate the device so that cameras could stream pictures of it in action across the web.
He hopes to be able to demonstrate the machine at a later date.
Mr McCarthy appreciates that if the device really works it is in contradiction of the law of conservation of energy, which he sees as a dogma of science.
There is an implied reference to religious dogmas, and it is just here that one can see the source of the misunderstanding.
Most religions feature a multiplicity of dogmas.
A person who is an adherent of that religion may not necessarily believe each and every one of the dogmas. Beliefs cannot of course be chosen a la carte - but there is a degree of flexibility which can accommodate quite significant differences.
The law of conservation of energy is not like this.
It states that the total amount of energy in an isolated system remains constant, although it may change forms, into heat or kinetic energy for example.
In short, law states that energy cannot be created or destroyed.
Denying its validity would undermine not just little bits of science - the whole edifice would be no more. All of the technology on which we built the modern world would lie in ruins.
There is no flexibility in the acceptance of the law as true - at all times, and in all circumstances.
It is the failure to appreciate the difference between this scientific law and a law of religion or of society which is why we know - without having to examine details of a particular device - that Orbo cannot work.
So, last Friday a number of people turned up at the museum and were told that the demonstration would have to be postponed, indefinitely.
The public demonstration has been postponed indefinitely
I was fortunate, however, in that Mr McCarthy kindly agreed to see me.
He is a very friendly person aged just over 40, trained originally as a mechanical engineer.
He has also worked in software engineering and on control systems for the oil industry.
He came across his invention by chance whilst developing an independent power system for CCTV cameras. The company, founded in 2000 and supported privately, is now wholly devoted to developing Orbo.
When asked about the conservation of energy Mr McCarthy says quite frankly that he does not know where the energy that provides perpetual motion comes from. He wonders whether he is somehow harnessing so-called "zero point" energy, a type of residual energy found in a system and first proposed by Einstein.
Zero point energy is the lowest possible energy a system can have and therefore cannot be removed.
He also points out that cosmologists believe in the presence of dark matter and dark energy. Might they somehow help his cause?
I believe that Mr McCarthy is truly convinced of the validity of his invention. It is, in my view, a case of prolonged self deception.
I ended our conversation by giving totally unsolicited advice: to drop Orbo and get back to software engineering.
It would not have been unreasonable had he then grabbed me by the collar and thrown me out of the window. He did none of these things and was totally genial.
Might I have convinced him? I do hope so.
Professor Sir Eric Ash is an electrical engineer. He is a fellow of the Royal Society, the Royal Academy of Engineering and the Institution of Engineering and Technology.