The Off-Key Bard
History

This Day in History — Michael Faraday Discovers Electromagnetic Induction

On this day in 1831

On August 29, 1831, Faraday watched a galvanometer needle twitch twice — once connecting, once disconnecting the battery. Those two twitches power the modern world.

The Off-Key Bard watches a needle twitch beside two coils of wire — an almost insignificant movement revealing a principle that would eventually power cities…

"Electricity and magnetism were already known. Faraday discovered how to make one create the other."

On this day in 1831, Michael Faraday sat in his laboratory at the Royal Institution in London and wrote in his diary: "Have had an iron ring made (soft iron), iron round and 7/8 inches thick and ring 6 inches in external diameter."

What followed those words was the most consequential experiment in the history of electrical science.

Faraday was, by any conventional measure, an unlikely person to make it. Born in 1791 to a poor London blacksmith, he had almost no formal education. As a teenager he was apprenticed to a bookbinder, and it was there — surrounded by books he was bound but permitted to read — that he began educating himself in science. He attended a series of lectures by the celebrated chemist Humphry Davy at the Royal Institution, sent Davy his meticulous notes, and was hired as Davy's chemical assistant in 1813. By 1831, Faraday was one of Britain's most respected experimental scientists — a man whose genius for physical intuition and careful observation had already produced the discovery of electromagnetic rotation (the principle behind the electric motor) in 1821. But the deeper question had nagged at him for a decade: if an electric current could produce a magnetic field, as Hans Christian Ørsted had shown in 1820, could a magnetic field be made to produce an electric current?

He had tried and failed repeatedly. Then he spent ten days of intensive work in August 1831 and built the apparatus that answered the question.

The Induction Ring

The device was almost comically simple. Faraday wound coils of copper wire — wire of the type normally used for ladies' bonnets, insulated with cotton and twine — around opposite sides of a soft iron ring six inches in external diameter. He called one side A and connected it to a voltaic battery through a switch. He called the other side B and connected it to a galvanometer, a sensitive instrument that detects even tiny flows of current.

He closed the switch.

The galvanometer needle deflected briefly — a small, rapid kick — and returned to zero.

He held the connection steady. Nothing. No current flowed in the B coil while the battery ran continuously through the A coil. The needle sat still.

He opened the switch.

The needle kicked again — this time in the opposite direction — and returned to zero.

He described what he had seen as a "wave of electricity" propagated through the iron. What he had actually discovered was something more fundamental: a static magnetic field produces no current. Only a changing magnetic field — the instant of formation when the circuit closed, the instant of collapse when it opened — induces current in a neighboring conductor. Change in magnetic flux is the essential trigger.

When he connected a more powerful battery — one hundred pairs of plates rather than a handful — the galvanometer needle didn't just twitch. It spun around rapidly four or five times before finally settling into mere oscillations.

What Followed

Faraday spent the autumn of 1831 working through the implications, finding other manifestations of the same principle — he showed that moving a bar magnet in and out of a coil of wire induced a current without any battery at all, and built a device he called the Faraday Disk: a copper disc rotating between the poles of a horseshoe magnet, generating a continuous steady current from nothing but mechanical rotation. It was the world's first electric generator.

The iron ring itself — still on display in the Royal Institution's Faraday Museum — is one of the most important surviving scientific objects in history. It took Faraday approximately ten working days to wind the coils by hand, insulating each layer with twine and calico. It looks like something a careful craftsman might produce in an afternoon. It is the direct ancestor of every transformer, generator, motor, and induction charger in existence.

James Clerk Maxwell later translated Faraday's visual concept of "lines of force" — which Faraday sketched rather than calculated, not being a trained mathematician — into the four equations of classical electromagnetism that still govern the field today.

"A needle moved, then moved once more,
And opened an electric door…
From changing fields and coils wound tight,
Would someday rise a world of light."

History reminds us: Faraday's experiment didn't light a city that afternoon. But the two small kicks of that galvanometer needle revealed the fundamental mechanism that powers every electric grid, every motor, every transformer, and every wireless charging pad on Earth. It began with a bookbinder's apprentice, a 6-inch iron ring, and some wire made for ladies' bonnets.

Sources

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