Editing Joule (section)

== History ==
{{Multiple image
| image1            = Sir William Siemens by Rudolph Lehmann.jpg
| image2            = James-Prescott-Joule.png
| footer            = In an 1882 [[British Science Association]] meeting, Chairman [[Carl Wilhelm Siemens|Siemens]] (left) proposed naming the unit after [[James Prescott Joule]] (right).
| total_width       = 250
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The [[CGS system]] had been declared official in 1881, at the first [[International Electrical Congress]].
The [[erg]] was adopted as its unit of energy in 1882. [[Carl Wilhelm Siemens|Wilhelm Siemens]], in his inauguration speech as chairman of the [[British Association for the Advancement of Science]] (23 August 1882) first proposed the ''joule'' as unit of [[heat]], to be derived from the electromagnetic units [[ampere]] and [[ohm]], in cgs units equivalent to {{val|e=7|u=erg}}.
The naming of the unit in honour of [[James Prescott Joule]] (1818–1889), at the time retired and aged 63, followed the recommendation of Siemens:

{{quote|Such a heat unit, if found acceptable, might with great propriety, I think, be called the Joule, after the man who has done so much to develop the dynamical theory of heat.<ref>{{cite conference | quote=The unit of heat has hitherto been taken variously as the heat required to raise a pound of water at the freezing-point through 1°&nbsp;Fahrenheit or Centigrade, or, again, the heat necessary to raise a kilogramme of water 1°&nbsp;Centigrade. The inconvenience of a unit so entirely arbitrary is sufficiently apparent to justify the introduction of one based on the electro-magnetic system, viz. the heat generated in one second by the current of an Ampère flowing through the resistance of an Ohm. In absolute measure its value is 10<sup>7</sup> C.G.S. units, and, assuming Joule's equivalent as 42,000,000, it is the heat necessary to raise 0.238&nbsp;grammes of water 1°&nbsp;Centigrade, or, approximately, the {{frac|1|1000}}th part of the arbitrary unit of a pound of water raised 1°&nbsp;Fahrenheit and the {{frac|1|4000}}th of the kilogramme of water raised 1°&nbsp;Centigrade. Such a heat unit, if found acceptable, might with great propriety, I think, be called the Joule, after the man who has done so much to develop the dynamical theory of heat. |first = Cal Wilhelm |last=Siemens |author-link=Carl Wilhelm Siemens |url=http://gallica.bnf.fr/ark:/12148/bpt6k781656 |title=Report of the Fifty-Second Meeting of the British Association for the Advancement of Science |pages=1–33 |quote-pages=6-7 |date= August 1882 |location=Southampton}}</ref>}}

At the second International Electrical Congress, on 31 August 1889, the joule was officially adopted alongside the [[watt]] and the ''quadrant'' (later renamed to [[Henry (unit)|henry]]).<ref>Pat Naughtin: [http://www.metricationmatters.com/docs/MetricationTimeline.pdf ''A chronological history of the modern metric system''], metricationmatters.com, 2009.</ref>
Joule died in the same year, on 11 October 1889.
At the fourth congress (1893), the "international ampere" and "international ohm" were defined, with slight changes in the specifications for their measurement, with the "international joule" being the unit derived from them.<ref>{{cite book |author=<!--Staff writer(s); no by-line.--> |title= Proceedings of the International Electrical Congress|url=https://archive.org/details/proceedingsinte01chicgoog|location=New York |publisher=American Institute of Electrical Engineers |date=1894 }}</ref>

In 1935, the [[International Electrotechnical Commission]] (as the successor organisation of the International Electrical Congress) adopted the "[[Giovanni Giorgi|Giorgi]] system", which by virtue of assuming a defined value for the [[magnetic constant]] also implied a redefinition of the joule. The Giorgi system was approved by the [[International Committee for Weights and Measures]] in 1946. The joule was now no longer defined based on electromagnetic unit, but instead as the unit of [[Work (physics)|work]] performed by one unit of force (at the time not yet named [[Newton (unit)|newton]]) over the distance of 1 [[metre]]. The joule was explicitly intended as the unit of energy to be used in both electromagnetic and mechanical contexts.<ref>[http://www.bipm.org/en/CIPM/db/1946/2/ ''CIPM, 1946, Resolution 2, Definitions of electric units'']. ''bipm.org''.</ref> The ratification of the definition at the ninth [[General Conference on Weights and Measures]], in 1948, added the specification that the joule was also to be preferred as the unit of [[heat]] in the context of [[calorimetry]], thereby officially deprecating the use of the [[calorie]].<ref>[http://www.bipm.org/en/CGPM/db/9/3/ ''9th CGPM, Resolution 3: Triple point of water; thermodynamic scale with a single fixed point; unit of quantity of heat (joule).''], ''bipm.org.''</ref>  This is the definition declared in the modern [[International System of Units]] in 1960.<ref>{{SIbrochure|pp=165–166}}</ref>

The definition of the joule as J&nbsp;=&nbsp;kg⋅m<sup>2</sup>⋅s<sup>−2</sup> has remained unchanged since 1946, but the joule as a derived unit has inherited changes in the definitions of the   [[second]] (in 1960 and 1967), the [[metre]] (in 1983) and the [[kilogram]] ([[2019 revision of the SI|in 2019]]).<ref>{{Cite journal |date=11 May 2018 |title=SI Redefinition |url=https://www.nist.gov/si-redefinition |journal=NIST |language=en}}</ref>