Georg Simon Ohm

Georg Simon Ohm was born in Erlangen in 1789, the son of a self-educated locksmith. His father had taught himself mathematics out of books and drilled it into both his sons at home; neither received the elite university-track education of their peers, but both came out of adolescence fluent in the calculus of their century — a preparation that placed them, quietly, ahead of most of their professorial contemporaries. Georg taught school in Bamberg, Cologne, and finally Berlin: a succession of underpaid Gymnasium posts where he spent evenings doing experiments on the side. The place he did his most important work was a *Gymnasium in Cologne* — a secondary school — because no German university would hire him.

Between 1825 and 1827 he built a torsion-balance galvanometer of his own design, precise enough to detect tiny currents and calibrated against magnetic deflection. He drove currents through wires of precisely measured length and cross-section, each wire connected to a voltaic pile whose EMF he controlled by varying the number of cells. Systematically, patiently, he measured the current as a function of wire length, wire thickness, and applied voltage. The pattern that fell out was brutally simple: for a given conductor, current is proportional to voltage, and the proportionality constant — what he called the *resistance* — is intrinsic to the wire, scaling linearly with length and inversely with cross-section. He wrote it all up in 1827 in *Die galvanische Kette, mathematisch bearbeitet* — "The galvanic circuit, investigated mathematically" — a book that was part experiment, part mathematical theory of electrical conduction. Every electrical engineer in the world still uses the three letters of that result: V = IR.

The book was received coldly, and the story from here is a parable about what German academic physics in the 1820s valued. *Annalen der Physik* published a hostile review. The reigning figures of Berlin natural philosophy — a school more interested in "facts" and *Naturphilosophie* than in mathematical models — dismissed Ohm's work as "unphysical speculation." His own Prussian education ministry demanded he resign his Cologne teaching post for "false doctrine." He spent the next fifteen years in professional exile, scraping by on private tutoring and temporary research assistantships, unable to secure a stable academic position in Germany. The rescue came from abroad: in 1841 the Royal Society of London awarded him the Copley Medal — the highest scientific honour in the world, previously given to Faraday, Ampère, and Berzelius — and cited his voltage-current work as "the most important contribution to electrical physics since Volta." That single act of international recognition restored Ohm to legitimacy in the German-speaking world. He was finally appointed to a chair at Munich in 1852, two years before his death. The SI unit of resistance, one ohm (Ω), was named in his honour in 1881. The shape of the story is the classic one: an idea so obvious in hindsight that the hindsight itself takes decades to arrive.