Electromagnetism in the Encyclopaedias

Abstract

“Heat, Electricity and Magnetism… though very different, agree in some general characters” wrote the natural philosopher John Playfair in 1819 in his influential "Dissertation Second" for the Encyclopaedia Britannica. His essay provides little evidence to support the claim of John Leslie, writing a sequel dissertation in the 1820s, that, “[Electricity’s] close connexion, if not identity, with magnetism, had been long suspected.” Leslie, of course, was writing with the benefit of hindsight, informed by Hans Christian Ørsted’s discovery of the effect of an electric current on a magnetised needle in 1820. After a brief overview of Ørsted's life, I investigate what encyclopaedia articles such as these can tell us about electricity and magnetism in the years leading up to Ørsted’s publication, and immediately afterwards.