October 28, 1831

Faraday disc

Faraday produces continuous current with a rotating copper disc

The generator was a copper plate about the size of a dinner plate, turned by hand on a brass axle near a pair of magnets.

A copper plate on a brass axle

Working in London on 28 October 1831, Michael Faraday recorded experiments with a copper plate approximately twelve inches in diameter and a fifth of an inch thick, mounted on a brass axle and rotated near concentrated magnetic poles.

The concentrating magnets were each about six or seven inches long, an inch wide and half an inch thick.

He ran collectors from the rotating plate to a galvanometer.

The needle that stayed put

The galvanometer needle remained deflected for as long as the plate kept turning — evidence of a continuous current rather than the momentary pulse he had seen before.

Reversing the plate's rotation reversed the deflection, and moving the plate away from the magnet made the effect disappear.

His later published account explained that the moving plate produced currents across the direction of its motion, and described the revolving copper plate as a new kind of electrical machine.

What this day was not

It was not the discovery of electromagnetic induction. The ring-coil experiment that produced transient induction had come on 29 August.

It was not a Royal Society demonstration either: this was laboratory work, and Faraday's first "Experimental Researches in Electricity" paper was read there on 24 November 1831.

"Dynamo" is a later label for a rotating-disc or homopolar generator, and Faraday's own account conceded that the current could not yet heat a fine wire, make a spark, or do useful work.

Sources

Researched 24 Aug 2026 8 sources not yet audited

How this was checked

Researched from the web into a fact sheet and rewritten from that sheet. This article has not yet had an independent model audit. How the pipeline works →

What the sources leave uncertain

The date and apparatus are documented in Faraday's laboratory diary.
The term 'dynamo' is a later label. Faraday's apparatus is more precisely a rotating-disc or homopolar generator.
A different surviving Royal Institution object also called 'Faraday's generator' uses a moving bar magnet and wire coil. That should not be confused with the rotating copper disc documented on October 28.