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The powerful magnetism of James Clerk Maxwell

The great Victorian physicist not only unravelled the mystery of electromagnetism but was also funny, charming and a master of comic verse

16 February 2019

9:00 AM

16 February 2019

9:00 AM

Professor Maxwell’s Duplicitous Demon: How James Clerk Maxwell Unravelled the Mystery of Electromagnetism and Matter Brian Clegg

Icon Books, pp.293, £16.99

Chances are, you are reading these words in some room or other. Build a wall down the middle of it, and in the middle of the wall, insert a tiny shutter. Conjure up a tiny critter who can open and shut this little door at will. When a hotter-than-average air molecule careers towards it, the creature opens the shutter and lets the molecule pass to the other side of the room. Colder-than-average molecules are allowed to pass in the other direction. Soon enough, one half of the room is sweltering, while the other half is distinctly nippy. Magic?

Not yet. A fridge performs exactly this trick, pumping heat out of its interior through that dinky radiator at the back. The refrigerator only becomes magical if it carries on running after you unplug it. Fighting entropy is expensive. It takes energy. Us living types cock a spectacular snook at the forces of entropy, but we too are in a sense plugged in. Snuff out the sun and you snuff out all life.

This ‘finite being’ of James Clerk Maxwell’s imagination — the ‘demon’ conjured up in a typically charming and flippant letter to his friend Peter Tait in 1867 — needs no power source, because it exists to demonstrate that there is no actual mechanical reason why the air in one half of an enclosed space should not grow hotter than the air in the other half. It could happen, but luckily for us it’s unimaginably unlikely. Our existence depends, moment to moment, on the innate conservatism of big numbers.

Brian Clegg would have it that his short, charming scientific biography of the Victorian Scottish physicist James Clerk Maxwell is not all his own work, but a collaboration with Maxwell’s demon. At any rate, the demon interrupts Clegg’s narrative at several points to explain the scientific work of his creator.


Is this framing device necessary? No one picking up this book is going to want to avoid its helpfully bracketed science bits. And for newcomers to the territory, that demon narrator is bound to disappoint. Clegg gets as close as he dares to suggesting that it may be real, but it isn’t (and thank goodness for that, because time itself is among the casualties that would flow from its appearance).

Clegg’s whimsy proves singularly appropriate, not so much for what it contributes to the argument, as for what it implies about his hero. Maxwell was funny and flippant and charming. Never mind that his laws of thermodynamics underpin spacetime, Maxwell — unique among scientists — wrote comic verse that is actually good. His mind moved 50-to-the-dozen. Tait once recalled how ‘his extempore lectures exhibited, in a manner most aggravating to the listener, the extraordinary fertility of his imagination’.

Maxwell was born in 1831, a gentleman whose rural lowland accent got him teased, and whose easy relations with working men shaped a lifetime’s commitment to public education. His academic career took him to Edinburgh, Cambridge, Aberdeen, London, and back to Cambridge where, as the first Cavendish professor of physics, he equipped and developed the world-renowned Cavendish laboratory.

Clegg makes a loose and entertaining unity of a scientific career that embraced everything from colour photography to making architectural models out of jelly. Maxwell understood the physics of particles better than anyone. He understood how bodies, be they lumps of rock or gas molecules, behave en masse, and he described their collective action through statistics. He used his fertile mechanical imagination to explore problems that, on the face of it, weren’t mechanical at all. Most famously, he constructed an entirely mechanical model of the relationship between magnetism and electricity which predicted the electromagnetic nature of light.

Clegg reveals with a conjuror’s confidence how Maxwell moved ‘from simply explaining observations through mathematics to building mathematical models that took on a life of their own’. It’s a matter of interpretation whether the scientist truly entered the modern era; for that, he would have had to accept his models of electrical and magnetic force as something totally isolated from the reality they reflected. The next stage in the physical sciences’ march towards abstraction was to remove Maxwell’s mechanical analogies for things, leaving their mathematics hovering in the air like the smile on the Cheshire cat.

Since Maxwell, those of us who wish to become leading figures in physics have no choice but to grasp high-level mathematics, while the rest need writers like Clegg to make any sense at all of what’s going on behind the doors of labs like the Cavendish.

Clegg’s huge backlist of popular science covers everything from quantum entanglement to climate change. He has yet to write a break-out book. Nor will he, I suspect: he’s one of that curiously egoless cohort of excellent writers — Philip Ball and Oliver Morton also spring to mind — who quietly, steadily, run rings around their flashier peers. Like them, Clegg doesn’t make science delightful. He delights in science. It shows.


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