Michael Faraday received the Rumford Medal in 1846 for his magneto-optical discoveries.
The Royal Society awarded the medal for Faraday’s discovery of optical phenomena produced by magnets and electric currents in transparent media. This work included the rotation of polarized light by a magnetic field, now called the Faraday effect, demonstrating a deep connection between light and electromagnetism.
A common source of confusion is that Faraday also received a Royal Medal in 1846. That award recognized his 20th and 21st series of experimental researches on electricity, including new magnetic actions and the magnetic condition of matter. The Rumford Medal specifically matched his optical and magnetic discoveries.
The Rumford Medal was established for important work involving the thermal or optical properties of matter. Faraday’s award therefore reflected the optical side of his research, rather than his better-known work on electromagnetic induction.