A schoolteacher with a well-equipped lab
Georg Ohm, working as a schoolteacher in Germany with access to a well-equipped physics laboratory, spent 1825 and 1826 conducting a systematic series of experiments on how electrical current related to the wires and materials it passed through, publishing his results in 1827 in a treatise titled Die galvanische Kette, mathematisch bearbeitet, or The galvanic circuit investigated mathematically. What he described was a simple, generalisable relationship: for most conductive materials, the voltage across a section of circuit equals the current flowing through it multiplied by that section’s resistance, a relationship now written as voltage equals current times resistance, or equivalently as current equalling voltage multiplied by conductance, the reciprocal of resistance.
Cavendish got there first, quietly
Ohm was not, in fact, the first person to notice this relationship. Henry Cavendish had carried out very similar experiments as early as January 1781, decades before Ohm’s own work, but Cavendish never published his results, and they remained essentially unknown to the wider scientific community until James Clerk Maxwell brought them to light in 1879, long after Ohm’s law had already taken Ohm’s name and become the standard way of describing the relationship. Had Cavendish published at the time, the same physics might well be known under an entirely different name today.
Dismissed as fanciful speculation
Ohm’s own publication met with open hostility rather than acceptance when it first appeared. German critics dismissed the work as little more than fanciful speculation dressed up in mathematics, and one government minister reportedly declared that a professor teaching such ideas was unfit to teach science at all, reflecting a prevailing view within German academic circles at the time that genuine scientific truths ought to be derived through pure reasoning rather than established through experimental measurement. The hostility was severe enough that Ohm resigned from his teaching position at a Jesuit gymnasium in Cologne, and broader acceptance of his result did not arrive until the 1840s, more than a decade after the original publication.
Not a law of nature, but a good approximation
What has held up is the relationship itself, though its status is more limited than the word law might suggest. Ohm’s law is an empirical generalisation drawn from experimental observation rather than a fundamental principle that must hold everywhere, and it works extremely well across most conductive materials over a wide range of currents without being universally true. A range of materials and devices, most notably semiconductor components like p-n junction diodes, do not keep a constant resistance as the voltage across them changes, and are accordingly described as non-ohmic, following a more complicated relationship between current and voltage than Ohm’s simple proportional rule.
A theory arrives decades later
Despite that limitation, by the 1850s Ohm’s law was widely accepted as an established, well-proven relationship, and it became one of the foundational tools of electrical engineering and circuit analysis, a status it has never lost. A proper theoretical explanation for why the law holds so well for ordinary conductors came only much later, through the Drude model developed around 1900 and further refined by subsequent quantum mechanical treatments of how electrons move through a conducting material, work that finally explained, rather than simply confirmed, the relationship Ohm had originally found through careful measurement alone.
Vindication, decades late
Ohm himself lived to see at least some of that vindication: the Royal Society awarded him the Copley Medal in 1841, elected him a foreign member the following year, and he was admitted to the Bavarian Academy of Sciences and Humanities in 1845, before finally securing a full professorship at the University of Munich in 1852, two years before his death in 1854. The SI unit of electrical resistance, the ohm, now carries his name into every circuit diagram and electronics textbook. This is worth an hour for how sharply it separates the fate of an idea from the fate of the person who published it, a genuinely useful, largely correct empirical relationship met first with open scientific hostility before eventually becoming one of the most basic tools in electrical engineering.