Standardization of the Ohm as a Unit of Electrical Resistance, 1861–1867 [Scanning Our Past]

The first working telegraphs were built by several individuals in the 1830s and they began to be adopted into practical use in the 1840s prior to the laying of the first undersea telegraphic cable across the English Channel, before attempting to cross the Atlantic Ocean. A string of subsequent failures on undersea cables led to an acceptance of a need to measure, accurately, the resistance of both the wire and insulation. Prior to 1860, there was no widely accepted system of electrical units or standards. This article gives an overview of the historical development of the Ohm as a unit. In Section I, we discuss the telegraphic communication. Section II considers electrical resistance, Section III reports on the work of the British Association (BA) Committee, and Sections IV and V discuss the recognition and subsequent developments. This month's history article takes a look at how the British Association Committee on Electrical Standards built the first internationally recognized material resistance standard, the BA unit of Resistance, subsequently called the Ohm.