Editing International System of Units (section)

=== Giovanni Giorgi and the problem of electrical units ===

At the close of the 19th century three different systems of units of measure existed for electrical measurements: a [[CGS-based system for electrostatic units]], also known as the Gaussian or ESU system, a [[CGS-based system for electromechanical units]] (EMU), and an International system based on units defined by the Metre Convention<ref>{{cite book |title=Weights, Measures and Units |url=https://archive.org/details/dictionaryofweig0000fenn |url-access=registration |author-first=Donald |author-last=Fenna |at=International unit |isbn=978-0-19-860522-5 |publisher=[[Oxford University Press]] | date=2002}}</ref> for electrical distribution systems. Attempts to resolve the electrical units in terms of length, mass, and time using [[dimensional analysis]] was beset with difficulties – the dimensions depended on whether one used the ESU or EMU systems.<ref name="Maxwell2">{{cite book |title=A treatise on electricity and magnetism |volume=2 |author-first=J. C. |author-last=Maxwell |date=1873 |publisher=Clarendon Press |location=Oxford |url=https://archive.org/stream/electricandmag02maxwrich |pages=242–245 |access-date=12 May 2011}}</ref> This anomaly was resolved in 1901 when [[Giovanni Giorgi]] published a paper in which he advocated using a fourth base unit alongside the existing three base units. The fourth unit could be chosen to be [[electric current]], [[voltage]], or [[electrical resistance]].<ref name="IECGiorgi">{{cite web |url=http://www.iec.ch/about/history/beginning/giovanni_giorgi.htm |title=In the beginning...: Giovanni Giorgi |publisher=[[International Electrotechnical Commission]] | access-date=5 April 2011 |archive-date=15 May 2011 |archive-url=https://web.archive.org/web/20110515134553/http://www.iec.ch/about/history/beginning/giovanni_giorgi.htm |url-status=dead}}</ref>

Electric current with named unit 'ampere' was chosen as the base unit, and the other electrical quantities derived from it according to the laws of physics. When combined with the MKS the new system, known as MKSA, was approved in 1946.<ref name=NIST330/>