Georg Simon Ohm

Georg Simon Ohm: The Schoolteacher Who Measured Resistance

In March 1828, a few months after publishing the book that would eventually put his name on every circuit diagram in the world, Georg Simon Ohm resigned his post at the Jesuit Gymnasium in Cologne. The reason was not scandal or illness. It was that nobody there had noticed. *Die galvanische Kette, mathematisch bearbeitet* had appeared the previous year and had been, in the polite formula, coldly received. Ohm had expected the book to lift him out of secondary-school teaching. Instead he spent the next five years without a proper position at all.

A Locksmith's Curriculum

He was born in Erlangen on 16 March 1789, in the margravate of Brandenburg-Bayreuth. His father Johann Wolfgang Ohm was a locksmith who had educated himself to a startlingly high level, and his mother Maria Elizabeth Beck was a tailor's daughter. Of the couple's seven children only three lived to adulthood — Georg Simon, his sister Elizabeth Barbara, and his brother Martin, who became a mathematician in his own right. Their mother died when Georg was ten.

The education that mattered happened at home. Johann Wolfgang taught both sons mathematics, physics, chemistry and philosophy himself. Georg attended the Erlangen Gymnasium from the age of eleven, and by every account learned almost nothing there: rote drill, minimal science, a system markedly worse than the one his father was running in the workshop. It is a detail worth holding on to, because Ohm's entire scientific life was conducted by a man who had been taught how to teach himself.

Three Semesters and a Dismissal

He entered the University of Erlangen in 1805 and promptly discovered the social side of student life. His father, unimpressed, forced him out after three semesters. In September 1806 he took a mathematics post in Gottstadt bei Nydau in Switzerland; in March 1809 he moved to Neuchâtel as a private tutor for two years. Before he left, the Erlangen professor Karl Christian von Langsdorf gave him the advice that shaped everything after: stop looking for a curriculum and read Euler, Laplace and Lacroix on your own. Ohm did exactly that, and returned to Erlangen in April 1811 to take his doctorate that October.

The Wandering Teacher

The doctorate bought him almost nothing. He lectured in mathematics at Erlangen briefly and left because the salary would not support him. From January 1813 he taught mathematics and physics in Bamberg, first at a poor school and then, from 1816, at an overcrowded one. He was, in the phrase of one biographical account, overburdened with students, finding little appreciation for his conscientious efforts, and resigned to the likelihood that he would never marry — which is why he turned to research at all, partly to prove himself and partly to build a case for a job somewhere more stimulating. Ohm's law was, in origin, a job application.

The Cologne Laboratory

His luck turned in September 1817 when he joined the Jesuit Gymnasium in Cologne, which possessed a well-equipped physics laboratory. He worked through Lagrange, Legendre, Laplace, Biot, Poisson, Fourier and Fresnel. When word reached him of Ørsted's 1820 discovery that a current deflects a compass needle, he had both the apparatus and the mathematics to do something with it.

His first paper, in 1825, examined how the electromagnetic force produced by a wire falls off as the wire is made longer. Two further papers in 1826 supplied the mathematical treatment, and here Ohm made his decisive intellectual move: he modelled the flow of electricity through a conductor on Fourier's analysis of the flow of heat through a solid. Heat, in Fourier's hands, moved from high temperature to low at a rate set by the material's conductivity. Ohm proposed that electricity behaved the same way — a driving difference, a resisting medium, a proportional flow.

Die galvanische Kette

The complete theory appeared in 1827 as *Die galvanische Kette, mathematisch bearbeitet* — the galvanic circuit worked out mathematically. Its central result is now taught to every schoolchild: the current through a conductor is directly proportional to the potential difference applied across it, with resistance as the constant of proportionality. Before Ohm, electrical strength was a vague quality; after him it was a quantity with an equation.

The book failed. Part of the problem was Ohm himself — introverted, poorly connected, holding no university chair. Part of it was method: a heavily mathematical treatment of a physical problem was unfashionable in the German physics of the day, where a more speculative, philosophical style held sway. And part of it was personal, in the shape of hostile influential figures including Georg Friedrich Pohl and Johannes Schultz. Ohm resigned in Cologne in March 1828 and waited.

The Ear, and a Chair at Last

Recognition arrived from abroad first. The Royal Society awarded him the Copley Medal in 1841 and elected him a foreign member in 1842; the Bavarian Academy made him a full member in 1845; Berlin and Turin took him as a corresponding member. He had by then been at the Polytechnic School of Nuremberg since 1833. In 1849 he became curator of the Bavarian Academy's physical cabinet and a lecturer at Munich, and only in 1852 — two years before he died — did he receive the chair of physics there.

His late work turned to sound. In 1843 he proposed a principle of physiological acoustics: that the ear perceives a musical tone as a set of constituent pure harmonic components. The idea, known as Ohm's acoustic law, was a real contribution and is also, as later work established, not quite true. The physicist August Seebeck exposed unjustified assumptions in Ohm's account of combination tones, and Ohm conceded the point. *Beiträge zur Molecular-Physik* followed in 1849.

Why Georg Is Called a Genius

The specific quality on display is analogical transfer — recognising that a solved problem in one domain is structurally the same as an unsolved problem in another. Fourier had already worked out heat conduction. Ohm's insight was that electricity in a wire is the same mathematical animal: a flow driven by a difference and impeded by a property of the medium. Making that identification required him to hold two things at once that his contemporaries mostly kept apart — the delicate experimental work of measuring feeble currents through wires of varying length, and the continental analytic mathematics he had taught himself from Euler and Laplace on Langsdorf's advice. German physics of the 1820s was not doing this. That is precisely why the book landed with a thud.

The counter-case deserves its weight. Ohm's law is not a law of nature in the way Newton's are; it is an empirical regularity that holds for a large and useful class of materials and fails for many others, and Ohm's own formulation rested on a fluid model of electricity that was superseded. He was wrong about combination tones and had to admit it publicly. His career was, by any ordinary measure, a long stretch of mediocre schoolmastering interrupted by two productive years in a Cologne laboratory. What survives is not a body of work but a single relation — though it happens to be the relation on which the whole of electrical engineering was subsequently built, and being right once at that scale is not a small thing.

Legacy

Ohm died in Munich on 6 July 1854 and was buried in the Alter Südfriedhof. His name became a unit: the ohm, symbol Ω, is the SI measure of electrical resistance, and there is a fair argument that no other physicist's name is invoked so often by so many people who could not tell you anything else about him. The self-taught son of a self-taught locksmith ended as the standard against which every conductor on earth is measured.

Achievements

• Copley Medal — 1841
• Foreign Member of the Royal Society — 1842
• Notable work: Ohm's law
• Held posts at Dreikönigsgymnasium, Kaiser-Heinrich-Gymnasium and Ludwig-Maximilians-Universität München
• Educated at Gymnasium Fridericianum Erlangen and University of Erlangen–Nuremberg
• Fields of research: physics