The magic of magnets
A French magician helped Napoleon win his Algerian campaign by using magnets in his act. Jason England explains.
“Any sufficiently advanced technology is indistinguishable from magic.” These words from science-fiction author Sir Arthur C. Clarke have a special resonance for a magician: we have always been early adopters of advanced technology.
Let me share one example of a scientific principle that was recruited for magic and that simultaneously ended an armed conflict in North Africa.
Jean Eugène Robert-Houdin is considered the father of modern magic. Born in 1805 and trained as a watchmaker, a chance encounter with a technical book on stage-illusions altered his life – it mistakenly arrived by mail in place of a book on watchmaking. Fascinated with the methods he’d stumbled upon and able to deploy his mechanical expertise to improve upon them, he became the most celebrated magician of the 19th century – and inspired a young Erik Weisz to take the stage name Houdini.
In 1856 Robert-Houdin had retired from the stage when the French government ordered him to give a series of performances in Algeria. Napoleon’s army had been unable to subdue Algerian warriors emboldened by faith in their tribal chieftains’ magical abilities. These ‘marabouts’ were using simple tricks to convince the local warriors they would be invincible to French guns. One involved surreptitiously plugging the gun’s ‘vent’ – the pathway from the spark of the blasting cap to the powder charge – preventing it from firing. The marabouts would hand the tampered French pistol to one of their soldiers, wave their hands in a mysterious manner and the gun would flash and fizzle but not fire. Robert-Houdin’s objective was to beat the wizards at their own game with a demonstration of superior French magic.
Then with a magical gesture, the great conjuror proceeded to rob the man of all of his strength.
At a gathering of some 30 tribal marabouts, Robert-Houdin demonstrated the best stage illusions of the day. As the evening drew to a close, he performed his grand finale. He invited one of the largest and strongest of the local marabouts to join him on stage and asked him to lift a small wooden chest. The confident warrior had no trouble doing so. Then with a magical gesture, the great conjuror proceeded to rob the man of all of his strength. When the marabout tried to lift the chest a second time he was unable to do so. The assembled marabouts were stunned.
The secret was the application of the (then) little-known science of electromagnetism. Robert-Houdin’s chest contained an iron bottom, while a powerful magnetic field generated underneath the stage kept the box firmly in place whenever the performer desired. I’ve been fortunate enough to examine Robert-Houdin’s original prop in a private collection and can personally attest to its “magical” immobility when the magnetic field was engaged.
These days we’re so familiar with magnets few would be taken in by this trick. Yet magnetism is still a fundamental part of the magician’s toolkit – and you don’t have to be a magician to demonstrate its fascinating effects. There’s a simple experiment you can try at home that appears magical – even when your audience knows magnets are being used.
Find a short piece of copper pipe, a ball bearing and a strong spherical magnet that fits inside it. In my own demonstrations I use a pipe 75 centimetres long and 1.5 centimetres in diameter, a one centimetre steel ball bearing and a matching one centimetre spherical neodymium magnet.
When you drop the regular ball bearing down the pipe, it falls out the bottom in far less than a second. But what happens when you drop the magnetic sphere? Magnets don’t stick to copper. No matter how strong the magnet, it will not stick when held against the copper pipe. So the magnetic sphere should fall straight through like the ball bearing, right? Wrong!
My magnet takes a whole six seconds to pass through the pipe! If you look down the pipe, you’ll see it slowly oscillate from side to side as it floats down. It looks magical.
This eerie phenomenon results from the inseparable nature of electricity and magnetism. Soon after 19th century English chemist Michael Faraday and contemporaries began experimenting with simple batteries, they noticed this link. A flowing electric current always generates a companion magnetic field and, likewise, a moving magnet placed near a conductive material will induce an electric current in it.
So as my magnet falls, its motion induces a current in the copper pipe. This current creates its own magnetic field – in the opposite direction to the fall. That repels the falling magnet, slowing its descent. Stronger magnets produce more powerful fields and more pronounced resistance to falling.
Heinrich Lenz reported the principles behind this effect in 1834. Known as Lenz’s Law, it is put to use in a range of modern gadgets including the braking system in spinning industrial rotors, induction cooktops and metal-detectors – which are useful if my ball bearing rolls off stage.
So you could say magic helped Napoleon in Africa – and science played its part too.