Ohm's Law Published
In 1827, the German physicist Georg Simon Ohm published Die galvanische Kette, mathematisch bearbeitet (The Galvanic Circuit Investigated Mathematically), a work that set out a precise mathematical relationship between voltage, current and resistance in electrical circuits. The principle, now known as Ohm's law, states that the current through a conductor is proportional to the voltage across it, with resistance as the constant of proportionality. It remains the first tool every student of electricity learns, and it underpins the design of everything from household wiring to microchips.
The background lay in the decades after Alessandro Volta's invention of the battery around 1800. Scientists could now produce steady electric currents, but they had no agreed way to measure or predict them. Ohm, a mathematics teacher working in Cologne, was influenced by Joseph Fourier's analysis of heat flow, and he drew an analogy between the movement of heat along a bar and the movement of electricity along a wire. In this picture, differences in electrical "tension" drove a flow, much as temperature differences drove heat.
Ohm tested his ideas experimentally. His early measurements, published in 1825, were complicated by the unstable batteries of the time, whose output drifted as they were used. He improved his results by using thermocouples, which provided a steadier source, and by measuring current through a torsion balance that detected the magnetic effect of the current on a needle. He then varied the length and material of wires to see how they affected the flow. His 1827 book combined these results with a theoretical treatment. Historians also note that Henry Cavendish had found similar relationships decades earlier, but his work remained unpublished until later in the nineteenth century.
Ohm's work was not welcomed at first. Some German critics found his mathematical approach too abstract and speculative, and the reception reportedly hurt his career prospects, leaving him in modest teaching posts for years. Recognition came gradually from abroad. The Royal Society of London awarded him its Copley Medal in 1841, and he later obtained a professorship at Munich, where he spent his final years.
The legacy of Ohm's law is both practical and conceptual. It made electrical circuits calculable, paving the way for the telegraph networks, power systems and electronics of the following centuries. In 1881 the international electrical community honored him by naming the unit of electrical resistance the ohm, symbolized by the Greek letter omega. Although many materials and devices do not obey the law exactly, and are called non-ohmic, it remains an essential approximation and a model of how careful measurement and mathematics can turn a puzzling natural phenomenon into a usable science.