A brief history of magnetism

With us to start the metaphorical magnetic ball rolling is physicist Michael Coey from Trinity College Dublin, who’s devoted his career to the study of magnetism and magnetic materials, and their history…

Michael - That's a great layman's question. But when one of the great theoretical physicists of the last century, Richard Feynman was asked why magnets attract, he struggled to respond. What he said boiled down to we would need to have a common language gained by studying physics for a few years. And it's really best to accept that they just do and go on from there. In fact, many young people, including the young Albert Einstein, were amazed to discover that you can make a magnet move by just waving another one nearby without them even touching. We just became familiar with magnetic fields and continued from there.

Chris - I think Richard Feynman also said science is like sex: both have practical results, that's not why we do it, though. When did people first become familiar with the idea that this thing you can't explain was a phenomenon? It was a real thing, it was there, it was an entity and that we could see it in action.

Michael - Long, long ago, we found natural magnets, which are rocks called lodestones, that are rich in iron oxide. They have been magnetised, believe it or not, by the enormous electrical current in a lightning strike. They attract and repel each other and they strongly attract metallic iron. So it is maybe about the beginning of the Iron Age.

Chris - So that's how lodestones work. It's nothing to do with the planet's magnetic field. They'd already been magnetised by lightning and then they interact with the earth's magnetic field?

Michael - That's correct.

Chris - And when would people have realised that? Because it's a bit of an intuitive leap to go from you dangle a piece of rock up in the air and realise that it always points the same way. When would they have begun to realise this was a useful thing they could deploy?

Michael - Apart from play things, the first good use of them was made by the Chinese over 2000 years ago. What they did was they carved a lodestone into the shape of a spoon that you sometimes see in Chinese restaurants. They placed it on a polished surface and, lo and behold, the handle turned to point South. Their application was geomancy or feng shui. And it was only about a thousand years later that people realised the effect with a suspended iron needle, or a floating fish, could enable navigation far from land across the trackless ocean. It was the invention of the compass. That was the first time that magnetism really changed the world. It was the first magnetic revolution. It led to the great voyages of discovery in the 15th century when the Chinese Admiral Zheng He discovered Africa in 1415, and Christopher Columbus discovered America in 1492.

Chris - It's amazing to think that feng shui predates navigation, isn't it? But what about the next intuitive leap, which is that magnetism and electricity are tightly bound together? How was that or how did that come to be?

Michael - Well, the similarities were really quite striking, but people for years and years were trying to pin down the link and nobody succeeded until Hans Christian Orsted, who loved to give public lectures in Denmark, was repeating his demonstration that there was no connection between the two using a long copper wire and lots of tiny compasses. But then, in 1820, somebody had already connected the other end of the wire when he connected it to the voltaic pile. And when the current flowed, the magnets began to swing perpendicular to the current. It was that spark that ignited the electromagnetic revolution. Within weeks, the information reached Paris were Ampere and Arago showed that if you wind the current into a coil, it behaved just like a magnet. And a few weeks later, the news reached London and Michael Faraday makes the first rudimentary electric motor. The electromagnetic revolution spreads like wildfire.

Chris - And what about the question of radio? Because radio is also electromagnetic radiation. How was the connection made between electricity, magnetism, and then transmitting invisible waves and information that way?

Michael - That was really thanks to Maxwell who developed a unified theory of electricity, magnetism, and light, where the electric and magnetic fields are perpendicular based on the ideas of Faraday. But the point is that radio is an alternating wave where we have electric and magnetic fields perpendicular: light, radio, microwaves - they all propagate at the speed of light. But what also we got were motors, dynamos, electrical distribution networks banishing the tyranny of day and night, banishing candles, banishing horses from the streets. And in the 19th century, really the world was utterly, utterly changed.

Chris - So there you go. From feng shui right through to how we now have electric cars along our streets. Thanks very much, that's Michael Coey from Trinity College, Dublin.