In 1861 the British Association (BA) for the Advancement of Science formed a committee to establish a new standard in electrical science, by defining an internationally recognised unit of resistance. The committee comprised some leading figures in electrical science, including James Clerk Maxwell, William Thomson (later Lord Kelvin), and Henry Fleeming Jenkin. Their work in Glasgow and Edinburgh was supported by experiments conducted by Maxwell and Sir Charles Wheatstone with a team at King’s College London, who tested various forms of apparatus that could be used by standards laboratories around the world to calibrate resistive devices.
The motivation for the British Association’s initiative stemmed from the emerging technology of long distance submarine telegraphy cables in the 1860s, notably the transatlantic cables linking Great Britain and the United States. It was known that the signalling speed of messages in Morse code was limited by the cable resistance and capacitance so that precise knowledge of the conductor quality was important.
Maxwell’s team worked for several years and, under Thomson’s direction, eventually devised a method of calibration using a spinning coil immersed in a magnetic field, that was adopted in 1867 for the experimental determination of the value of the new unit of resistance, which became known as the Ohm (after the German scientist Georg Ohm).
During his 53 years as a professor at Glasgow University, Thomson taught some 7,000 students from all over the world, and established an advanced class in mathematical physics and a laboratory in which they could undertake experimental work. The laboratory students worked mainly on problems derived from Kelvin’s own scientific and engineering research in electricity, establishing a “school of electrical engineering”.
On 17th September 2019 we celebrated the work on the standardisation of the unit of resistance with an IEEE Milestone Plaque unveiling at the Hunterian Museum at Glasgow University.
The plaque unveiling was performed by IEEE 2019 President Professor Jose Moura with IEEE UK and Ireland Section Chair Mike Hinchey and Professor Peter Grant from the University of Edinburgh. The unveiling was followed by a Technical Symposium on ‘The Standardisation of Electrical Measurement Units’. The technical symposium covered the work done to standardise the units used for electrical measurements, at a time when there were different and incompatible standards that were not internationally recognised.
Watch the Ohm Milestone Unveiling Event