Standardization of the Ohm as a Unit of Electrical Resistance, 1861-1867

This discusses the historical developments that led to the standardisation of the Ohm. Following developments in early electrical telegraphy systems, particularly those involving undersea cable international communication, the British Association (BA) set up a committee in 1861 to propose electrical units of resistance, which were ultimately based on the metric system. This committee, which comprised many prominent scientists from this period such as William Thomson, Fleeming Jenkin, James Clerk Maxwell, etc., considered the many wire material resistance standards as well as the mercury column artifact standard proposed by Werner Siemens. The committee finally proposed adoption of "The BA Unit of Resistance" which was adjusted in magnitude to meet closely to the needs of telegraphic engineers. The committee coordinated the fabrication of a set of wire coil standard resistors in 1865, based on precious metals, with copies being offered for sale. The set of original standards exist today in the London Science Museum archives. In 1872 the unit of resistance was named the "Ohm" after the German physicist Georg Simon Ohm. The committee produced essentially the standard units of Ohms, Amps, and Volts that we use today, with a far reaching effect on virtually all later work on precision electrical measurement. Their early resistance units, which were specified by material resistance standards, were subsequently replaced, in 1990, by definitions based on the high precision quantum Hall effect standard.