Editing Metre Convention (section)

== The 1875 conferences in Paris ==

The principal tasks facing the delegates at the 1875 Diplomatic Conference on the Metre was the replacement of the existing metre and kilogram artefacts that were held by the French Government and the setting up of an organization to administer the maintenance of standards around the globe. The conference did not concern itself with other units of measure. The conference had undertones of Franco-German political manoeuvring, particularly since the French had been humiliated by the Prussians during the war a few years previously. Although France lost control of the metric system, they ensured that it passed to international rather than German control and that the international headquarters were in Paris.<ref name=Adler/>

While the German astronomer [[Wilhelm Julius Foerster]] along with the Russian and Austrian representatives had boycotted the Permanent Committee of the International Metre Commission in order to prompt the reunion of the Diplomatic Conference of the Metre and  to promote the foundation of a permanent International Bureau of Weights and Measures,<ref name="Poids-1903">{{Cite book |last=Comité Interational des Poids et Mesures |title=Procès-Verbaux des Séances. Deuxième Série. Tome II. Session de 1903 |publisher=Gauthier-Villars |location=Paris |pages=5–7}}</ref> Adolphe Hirsch, delegate of Switzerland at this Diplomatic Conference in 1875, conformed to the opinion of [[Italy]] and [[Spain]] to create, in spite of French reluctance, the International Bureau of Weights and Measures in France as a permanent institution at the disadvantage of the ''[[Conservatoire national des arts et métiers]]''.<ref>{{Cite web |date=30 March 1875 |title=Bericht der schweizerischen Delegierten an der internationalen Meterkonferenz an den Bundespräsidenten und Vorsteher des Politischen Departements, J. J. Scherer in Erwin Bucher, Peter Stalder (ed.), Diplomatic Documents of Switzerland, vol. 3, doc. 66, dodis.ch/42045, Bern 1986. |url=https://dodis.ch/42045 |website=Dodis}}</ref>

In 1875, the Permanent Commission of the European Arc Measurement would also hold its reunion in Paris and decide the creation of an international geodetic standard for baselines' measurement calibrated against the metre.<ref>{{Cite web |last=Hirsch |first=Adolphe |title=Bulletin de la Société des Sciences Naturelles de Neuchâtel |url=https://www.e-periodica.ch/digbib/view?pid=bsn-001:1874:10#581 |access-date=2025-04-08 |website=E-Periodica |page=255 |language=de}}</ref> [[Second French Empire|French Empire]] had hesitated for a long time before giving in to the demands of the European Arc Measurement, which asked the French geodesists to take part in its work. It was only after the [[Franco-Prussian War]], that [[Charles-Eugène Delaunay]] represented [[France]] at the Congress of [[Vienna]] in 1871. In 1874, [[Hervé Faye]] was appointed member of the Permanent Commission of the European Arc Measurement presided by Carlos Ibáñez e Ibáñez de Ibero who was collaborating with the French on the extension and  remeasurement of the [[Arc measurement of Delambre and Méchain#Extension of Greenwich meridian arc|meridian arc of Delambre and Méchain]] since 1853.<ref name="Lebon-1899" /><ref name="Soler-1997" />

Spain notably supported France for these outcomes and the first president of the International Committee for Weights and Measures,<ref>{{Cite book |last=Comité international des poids et mesures |first= |url=https://play.google.com/books/reader?id=QgkAAAAAMAAJ&pg=GBS.PA3&hl=fr |title=Procès-verbaux des séances de 1875-1876 |date=1876 |publisher=Bureau international des poids et mesures. |pages=3 |language=fr}}</ref> the Spanish geodesist, Carlos Ibáñez e Ibáñez de Ibero received the [[List of foreign recipients of the Légion d'Honneur|Grand Officer medal of the Légion d'Honneur]] for his diplomatic role on this issue and was awarded the [[Poncelet Prize]] for his scientific contributions to metrology and geodesy.<ref>{{Cite web|url=http://www.academie-sciences.fr/fr/|title=Carlos IBAÑEZ DE IBERO (14 avril 1825 – 29 janvier 1891), par Albert Pérard (inauguration d'un monument élevé à sa mémoire)|last=Pérard|first=Albert|date=1957|website=Institut de France Académie des Sciences|archive-url=https://web.archive.org/web/20170517112721/http://www.academie-sciences.fr/fr/|archive-date=17 May 2017|access-date=18 May 2017|url-status=bot: unknown}}</ref> Indeed, Carlos Ibáñez e Ibáñez de Ibero, first president of the [[International Association of Geodesy|International Geodetic Association]], played a pivotal role in reconciling French and German interests.<ref name="Soler-1997" /><ref name="Pérard-1957">{{Cite web |last=Pérard |first=Albert |date=1957 |title=Carlos Ibáñez e Ibáñez de Ibero (14 avril 1825 – 29 janvier 1891), par Albert Pérard (inauguration d'un monument élevé à sa mémoire) |url=https://www.academie-sciences.fr/pdf/eloges/ibanez_notice.pdf |website=Institut de France – Académie des sciences |pages=26–28}}</ref>

=== Reference standards ===
[[Image:Platinum-Iridium meter bar.jpg|right|thumb|220px|Historical ''[[international prototype of the metre]]'', made of an alloy of platinum and iridium, that was the standard from 1889 to 1960.]]Although the new standard metre had the same value as the old metre, it had an "X" cross-section designed by [[Henri Tresca]] rather than a rectangular cross-section as this reduced the flexing when taking measurements. Moreover, the new bar, rather than being exactly one metre in length was a little longer than one metre and had lines engraved on them that were exactly one metre apart.<ref>
{{cite book |first1=Thomas |last1=McGreevy |title=The Basis of Measurement: Volume 1 – Historical Aspects |pages=150–151 |isbn=0-948251-82-4 |year=1995 |publisher=Pitcon Publishing (Chippenham) Ltd}}
</ref> The London firm [[Johnson Matthey]] delivered 30 prototype metres and 40 prototype kilograms. At the first meeting of the [[CGPM]] in 1889 bar No.&nbsp;6 and cylinder No.&nbsp;X were chosen by lot as the international prototypes. The remainder were either kept as BIPM working copies or distributed by lot to member states as national prototypes.<ref>
{{cite journal
 |last1= Jabbour
 |first1= Z.J.
 |last2= Yaniv
 |first2= S.L.
 |year= 2001
 |title= The Kilogram and Measurements of Mass and Force
 |journal= J. Res. Natl. Inst. Stand. Technol.
 |volume= 106
 |issue= 1
 |pages= 25–46
 |url= http://nvl.nist.gov/pub/nistpubs/jres/106/1/j61jab.pdf
 |access-date= 28 March 2011
 |doi= 10.6028/jres.106.003
 |pmid= 27500016
 |pmc= 4865288
 |archive-url= https://web.archive.org/web/20110604144310/http://nvl.nist.gov/pub/nistpubs/jres/106/1/j61jab.pdf
 |archive-date= 4 June 2011
 |url-status= dead
}}</ref>

The comparison of the new prototypes of the metre with each other involved the development of special measuring equipment and the definition of a reproducible temperature scale. The BIPM's [[Temperature measurement|thermometry]] work led to the discovery of special alloys of iron–nickel, in particular [[invar]], whose practically negligible coefficient of expansion made it possible to develop simpler baseline measurement methods,<ref name="Guillaume-1906">{{Cite journal |last=Guillaume |first=C.-H.-Ed |date=1906-01-01 |title=La mesure rapide des bases géodésiques |url=https://zenodo.org/record/2007289 |journal=Journal de Physique Théorique et Appliquée |volume=5 |pages=242–263 |doi=10.1051/jphystap:019060050024200}}</ref> and for which its director, the Swiss physicist [[Charles Édouard Guillaume]], was granted the [[Nobel Prize in Physics]] in 1920. Guillaume's Nobel Prize marked the end of an era in which [[metrology]] was leaving the field of [[geodesy]] to become an autonomous [[Branches of science|scientific discipline]] capable of redefining the metre through [[Technology|technological]] applications of [[physics]].<ref>{{Cite web |title=BIPM – la définition du mètre |url=https://www.bipm.org/fr/measurement-units/history-si/evolution_metre.html |archive-url=https://web.archive.org/web/20170430075245/http://www.bipm.org/fr/measurement-units/history-si/evolution_metre.html |archive-date=30 April 2017 |access-date=2019-05-15 |website=www.bipm.org}}</ref><ref name="BIPM-150">{{Cite web |title=History – The BIPM 150 |url=https://thebipm150.org/history/ |access-date=2025-01-24 |language=}}</ref> On the other hand, the foundation of the United States Coast and Geodetic Survey by Ferdinand Rudolph Hassler paved the way to a new definition of the metre, with [[Charles Sanders Peirce]] being the first to experimentally link the metre to the wavelength of a spectral line. [[Albert A. Michelson]] soon took up the idea and improved it.<ref name="Crease-2009">{{Cite journal |last=Crease |first=Robert P. |date=2009-12-01 |title=Charles Sanders Peirce and the first absolute measurement standard |url=https://pubs.aip.org/physicstoday/article/62/12/39/390647/Charles-Sanders-Peirce-and-the-first-absolute |journal=Physics Today |volume=62 |issue=12 |pages=39–44 |bibcode=2009PhT....62l..39C |doi=10.1063/1.3273015 |issn=0031-9228}}</ref>

The prototype metre was retained as the international standard until 1960 when the metre was redefined in terms of the wavelength of the orange-red line of [[krypton-86]]. The current definition of the metre is "the length of the path travelled by light in vacuum during a time interval of 1/{{val|299792458}} of a second".

On 16 November 2018, the 26th [[General Conference on Weights and Measures]] (CGPM) voted unanimously in favour of revised definitions of some [[SI base unit]]s, in particular the kilogram.<ref>{{Cite news|url=https://www.nist.gov/news-events/news/2018/11/historic-vote-ties-kilogram-and-other-units-natural-constants|title=Historic Vote Ties Kilogram and Other Units to Natural Constants|last=Materese|first=Robin|date=16 November 2018|work=NIST|access-date=17 November 2018|archive-date=18 November 2018|archive-url=https://web.archive.org/web/20181118014932/https://www.nist.gov/news-events/news/2018/11/historic-vote-ties-kilogram-and-other-units-natural-constants|url-status=live}}</ref> The new definitions came into force on 20 May 2019, but did not change the metre.<ref name=SI-statement/><ref name=bipm>[http://www.bipm.org/en/committees/cipm/meeting/105.html "Decision CIPM/105-13 (October 2016)"] {{Webarchive|url=https://web.archive.org/web/20170824095943/http://www.bipm.org/en/committees/cipm/meeting/105.html |date=24 August 2017 }}. The day is the 144th anniversary of the Metre Convention.</ref>

=== International organization ===
The Convention created an [[international organization]] with two governing organs to facilitate the standardization of weights and measures around the world. The first, the CGPM provides a forum for representative of member states, the second, the CIPM is an advisory committee of metrologists of high standing. The Secretariat or Headquarters provides appropriate meeting and laboratory facilities in support of the CGPM and CIPM.<ref name=":2">
{{cite web
 |url=http://www.bipm.org/en/convention/
 |title=The Metre Convention
 |publisher=Bureau International des Poids et Mesures
 |access-date=1 October 2012
 |archive-date=26 September 2012
 |archive-url=https://web.archive.org/web/20120926202046/http://www.bipm.org/en/convention/
 |url-status=live
}}</ref>

The structure may be compared to a [[corporation]], the CIPM is analogous to a [[board of directors]], and the CGPM to a [[shareholders' meeting]].

==== General Conference on Weights and Measures ====
The [[General Conference on Weights and Measures]] ({{lang|fr|Conférence générale des poids et mesures}} or CGPM) is the principal decision-making body put on place by the convention. It is made up of delegates from member states and [non-voting] observers from associate states and economies.<ref>
{{cite web
 |url         = http://www.bipm.org/en/convention/cgpm/
 |title       = General Conference on Weights and Measures
 |year        = 2011
 |publisher   = Bureau International des Poids et Mesures
 |access-date  = 26 September 2012
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20120926233323/http://www.bipm.org/en/convention/cgpm/
 |archive-date = 26 September 2012
}}</ref> The conference usually meets every four years to receive and discuss a report from the CIPM and to endorse new developments in the SI on the advice of the CIPM though at the 2011 meeting, it agreed to meet again in 2014 rather than 2015 to discuss the maturity of the [[New SI definitions|new SI proposals]].<ref name="bipm.org">
{{cite press release
 | url = http://www.bipm.org/utils/en/pdf/Press_release_resolution_1_CGPM.pdf
 | title = General Conference on Weights and Measures approves possible changes to the International System of Units, including redefinition of the kilogram.
 | publisher = [[General Conference on Weights and Measures]]
 | location = Saint-Cloud, France
 | date = 23 October 2011
 | access-date = 25 October 2011
 | archive-date = 9 February 2012
 | archive-url = https://web.archive.org/web/20120209175127/http://www.bipm.org/utils/en/pdf/Press_release_resolution_1_CGPM.pdf
 | url-status = live
}}</ref> It is also responsible for new appointments to the CIPM and decides on major issues concerning the development and financing of the BIPM. According to the Metre Convention (Art. 4) the President of the [[French Academy of Sciences]] is also the President of the General Conference on Weights and Measures.

==== International Committee for Weights and Measures ====
[[File:Metric seal.svg|thumb|200px|Seal of the BIPM]]
The [[General Conference on Weights and Measures#CIPM|International Committee for Weights and Measures]] ({{lang|fr|Comité international des poids et mesures}} or CIPM) is made up of eighteen (originally fourteen)<ref>Convention of the Metre (1875), Appendix 1 (Regulation), Article 8</ref> individuals from a member state of high scientific standing, nominated by the CGPM to advise the CGPM on administrative and technical matters. It is responsible for the running of ten consultative committees (CCs), each of which investigates different aspects of metrology – one CC discusses the measurement of temperature, another the measurement of mass and so on. The CIPM meets annually at Saint-Cloud to discuss annual reports from the various CCs, to submit an annual report to the governments of member states in respect of the administration and finances of the BIPM and to advise the CGPM on technical matters as and when necessary. Each member of the CIPM is from a different member state – with France, in recognition of its work in setting up the convention, always having one seat on the CIPM.<ref>
{{cite web
 |url = http://www.bipm.org/en/committees/cipm/
 |title = CIPM: International Committee for Weights and Measures
 |year = 2011
 |publisher = Bureau International des Poids et Mesures
 |access-date = 26 September 2012
 |archive-date = 24 September 2012
 |archive-url = https://web.archive.org/web/20120924192125/http://www.bipm.org/en/committees/cipm/
 |url-status = live
}}</ref><ref>
{{cite web|url=https://www.bipm.org/en/about-us/member-states/fr/|title=BIPM – France [Member State]|website=bipm.org|access-date=5 January 2018|archive-date=6 January 2018|archive-url=https://web.archive.org/web/20180106072343/https://www.bipm.org/en/about-us/member-states/fr/|url-status=dead}}</ref>

==== Secretariat of the BIPM ====
The Secretariat (or Headquarters) of the [[International Bureau of Weights and Measures]] ({{lang|fr|Bureau international des poids et mesures}} or BIPM) is based at Saint-Cloud, France. It has custody of the now historical [[international prototype of the kilogram]] and provides [[metrology]] services for Member States and hosts  formal meetings. It also has custody of the former [[international prototype of the metre]] which was retired in 1960. Over the years the various prototypes of the metre and of the kilogram were returned to the BIPM laboratories for recalibration services.

Initially it had a staff of 9, falling to 4 once the initial batch of prototypes had been distributed;<ref>Convention of the Metre (1875), Appendix 1 (Regulation), Article 6</ref> in 2012 it had a staff of over 70 people and an annual budget of over €10&nbsp;million.<ref>
{{cite web
 |url = http://www.bipm.org/en/bipm/
 |title = The BIPM headquarters
 |year = 2011
 |publisher = Bureau International des Poids et Mesures
 |access-date = 26 September 2012
 |archive-date = 7 November 2012
 |archive-url = https://web.archive.org/web/20121107000551/http://www.bipm.org/en/bipm/
 |url-status = live
}}</ref> The director of the BIPM is ''ex-officio'' a member of the CIPM and a member of all consultative committees.

=== Headquarters, language and protocol ===
[[File:BIPM courtyard.jpg|thumb|upright=1.35|The [[Pavillon de Breteuil]] in [[Saint-Cloud]], Paris]]
The original treaty was written in French and the authoritative language of all official documents is French. Communication between the BIPM and member states is, in the case of France, via the French Foreign Minister and in the case of all other members, via the members' ambassador to France.<ref>Convention of the Metre, Appendix 1 (Regulations), Articles 16 and 19</ref>

The French government offered the treaty members the [[Pavillon de Breteuil]] in [[Saint-Cloud]] to house the BIPM. The Pavillon was originally built in 1675 on the estate of the Château de Saint-Cloud which was home to, amongst others, [[Napoleon III|Emperor Napoleon III]]. The château was all but destroyed during the [[Franco-Prussian War]] (1870–1) and the Pavillon badly damaged.<ref>
{{cite web
 |title = The BIPM headquarters
 |url = http://www.bipm.org/en/bipm/
 |access-date = 27 September 2012
 |publisher = [[International Bureau of Weights and Measures]]
 |archive-date = 7 November 2012
 |archive-url = https://web.archive.org/web/20121107000551/http://www.bipm.org/en/bipm/
 |url-status = live
}}</ref> The Pavillon has been fully restored and, as headquarters of an [[intergovernmental organization]] enjoys privileges and immunities.<ref>
{{cite web
 |title = Protocol
 |url = http://www.diplomatie.gouv.fr/en/spip.php?page=article_imprim&id_article=15045
 |access-date = 27 September 2012
 |publisher = [[Ministry of Foreign and European Affairs (France)|Ministère Affaires étrangères, Republique Francaise]] [Ministry of Foreign Affairs, Republic of France]
 |date = 10 January 2011
 |archive-date = 3 April 2013
 |archive-url = https://web.archive.org/web/20130403093934/http://www.diplomatie.gouv.fr/en/spip.php?page=article_imprim&id_article=15045
 |url-status = live
}}</ref>