British Asociation Standard Ohm resistor, 1865.
© Science Museum / Science & Society Picture Library
A British Asociation Standard Ohm resistor purchased by the English physicist Michael Faraday (1791-1867) in 1865. Instructions for using the device are on the inside of the lid of its box. The British Asociation Committee on Standards of Electrical Resistance produced a set of one ohm standard resistances, in 1865. They were the first electrical standards in the world. Copies were also made for distribution and for sale. Faraday, at the Royal Institution in London, was the first purchaser. The ohm is the standard unit of electrical resistivity, and is named after the German physicist Georg Ohm (1789-1854), who formulated the law which states that the current flowing in a conductor is directly proportional to the potential difference acros it.