Metre

==== International prototype metre bar ====
[[File:US National Length Meter.JPG|thumb|Closeup of National Prototype Metre Bar No. 27, made in 1889 by the International Bureau of Weights and Measures (BIPM) in collaboration with [[Johnson Matthey|Johnson Mattey]] and given to the United States, which served as the standard for American cartography from 1890 replacing the Committee Meter, an authentic copy of the ''Mètre des Archives'' produced in 1799 in Paris, which [[Ferdinand Rudolph Hassler]] had brought to the United States in 1805|left]]

After the [[French Revolution]], [[Napoleonic Wars]] led to the adoption of the metre in [[Latin America]] following [[decolonization|independence]] of [[Empire of Brazil|Brazil]] and [[Hispanic America]], while the [[American Revolution]] prompted the foundation of the [[United States Coast and Geodetic Survey|Survey of the Coast]] in 1807 and the creation of the [[National Institute of Standards and Technology|Office of Standard Weights and Measures]] in 1830. In [[continental Europe]], Napoleonic Wars fostered German nationalism which later led to [[unification of Germany]] in 1871. Meanwhile, most European countries had adopted the metre. In the 1870s, [[German Empire]] played a pivotal role in the unification of the metric system through the [[International Association of Geodesy|European Arc Measurement]] but its overwhelming influence was mitigated by that of neutral states. While the German astronomer [[Wilhelm Julius Foerster]], director of the [[Berlin Observatory]] and director of the German Weights and Measures Service boycotted the Permanent Committee of the International Metre Commission, along with the Russian and Austrian representatives, in order to promote the foundation of a permanent [[International Bureau of Weights and Measures]], the German born, Swiss astronomer, [[Adolphe Hirsch]] 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 disadventage of the [[Conservatoire national des arts et métiers|''Conservatoire national des Arts et Métiers'']].<ref name="Quinn-2019" /><ref name="Von Wild-1903" /><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>

At that time, [[Unit of measurement|units of measurement]] were defined by primary [[Standard (metrology)|standard]]s, and unique artifacts made of different [[alloy]]s with distinct coefficients of [[Thermal expansion|expansion]] were the legal basis of units of length. A wrought iron ruler, the Toise of Peru, also called ''Toise de l'Académie'', was the French primary standard of the toise, and the metre was officially defined by an artifact made of platinum kept in the National Archives. Besides the latter, another platinum and twelve iron standards of the metre were made by [[Étienne Lenoir (instrument maker)|Étienne Lenoir]] in 1799. One of them became known as the ''Committee Meter'' in the United States and served as standard of length in the [[United States Coast and Geodetic Survey|United States Coast Survey]] until 1890. According to geodesists, these standards were secondary standards deduced from the Toise of Peru. In Europe, except Spain, surveyors continued to use measuring instruments calibrated on the Toise of Peru. Among these, the toise of Bessel and the apparatus of Borda were respectively the main references for geodesy in [[Prussia]] and in [[France]]. These measuring devices consisted of bimetallic rulers in platinum and brass or iron and zinc fixed together at one extremity to assess the variations in length produced by any change in temperature. The combination of two bars made of two different metals allowed to take [[thermal expansion]] into account without measuring the temperature. A French scientific instrument maker, [[Jean Nicolas Fortin]], had made three direct copies of the Toise of Peru, one for [[Friedrich Georg Wilhelm von Struve]], a second for [[Heinrich Christian Schumacher]] in 1821 and a third for Friedrich Bessel in 1823. In 1831, [[Henri-Prudence Gambey]] also realized a copy of the Toise of Peru which was kept at [[Altona Observatory]].<ref name="Wolf 1882 20, 32">{{Cite book |last=Wolf |first=M. C |url=https://www.worldcat.org/oclc/16069502 |title=Recherches historiques sur les étalons de poids et mesures de l'observatoire et les appareils qui ont servi a les construire. |date=1882 |publisher=Gauthier-Villars |location=Paris |pages=7–8, 20, 32 |language=French |oclc=16069502}}</ref>{{sfn|Bigourdan|1901|pp=8,158–159,176–177}}<ref name="Quinn-2012">{{Cite book |last=Quinn |first=T. J. |url=https://www.worldcat.org/oclc/861693071 |title=From artefacts to atoms : the BIPM and the search for ultimate measurement standards |date=2012 |isbn=978-0-19-990991-9 |location=Oxford |pages=20, 37–38, 91–92, 70–72, 114–117, 144–147, 8 |oclc=861693071}}</ref><ref name="Clarke-1867">{{Cite journal |last1=Clarke |first1=Alexander Ross |last2=James |first2=Henry |date=1867-01-01 |title=X. Abstract of the results of the comparisons of the standards of length of England, France, Belgium, Prussia, Russia, India, Australia, made at the ordnance Survey Office, Southampton |url=https://royalsocietypublishing.org/doi/10.1098/rstl.1867.0010 |journal=Philosophical Transactions of the Royal Society of London |volume=157 |page=174 |doi=10.1098/rstl.1867.0010 |s2cid=109333769}}</ref><ref name="NIST Special Publication">{{Cite book |url=https://play.google.com/store/books/details?id=NiEEAQAAIAAJ |title=NIST Special Publication |date=1966 |publisher=U.S. Government Printing Office |pages=529 |language=en}}</ref><ref>{{Cite web |title=Borda et le système métrique |url=https://mesurelab.fr/wp/metrologie/histoire-de-la-metrologie/borda-et-le-systeme-metrique/ |access-date=2023-08-29 |website=Association Mesure Lab |language=fr-FR}}</ref><ref name="Viik-2006" /><ref name="Clarke-1873" /><ref name="Brunner-1857" />

[[File:Metric standards Rijksmuseum.jpg|thumb|Historic Dutch replicas of metric standards in the collection of Rijksmuseum, Amsterdam: iron metre with case constructed by Étienne Lenoir in 1799, copper grave kilogram with case (1798), copper volume measures (1829)]]

In the second half of the 19th century, the creation of the [[International Association of Geodesy|International Geodetic Association]] would mark the adoption of new scientific methods.<ref>{{Cite journal |last=Zuerich |first=ETH-Bibliothek |date=1892 |title=Exposé historique des travaux de la commission géodésique suisse de 1862 à 1892 |url=https://doi.org/10.5169/seals-88335 |language=de |doi=10.5169/seals-88335 |access-date=2023-08-29 |website=E-Periodica}}</ref> It then became possible to accurately measure parallel arcs, since the difference in longitude between their ends could be determined thanks to the invention of the [[electrical telegraph]]. Furthermore, advances in [[metrology]] combined with those of [[gravimetry]] have led to a new era of [[geodesy]]. If precision metrology had needed the help of geodesy, the latter could not continue to prosper without the help of metrology. It was then necessary to define a single unit to express all the measurements of terrestrial arcs and all determinations of the [[gravitational acceleration]] by means of pendulum.<ref>Carlos Ibáñez e Ibáñez de Ibero, ''Discursos leidos ante la Real Academia de Ciencias Exactas Fisicas y Naturales en la recepcion pública de Don Joaquin Barraquer y Rovira'', Madrid, Imprenta de la Viuda e Hijo de D.E. Aguado, 1881, p. 78</ref><ref name="Clarke-1867" />

In 1866, the most important concern was that the Toise of Peru, the standard of the toise constructed in 1735 for the [[French Geodesic Mission to the Equator]], might be so much damaged that comparison with it would be worthless, while Bessel had questioned the accuracy of copies of this standard belonging to [[Altona Observatory|Altona]] and [[Koenigsberg Observatory|Koenigsberg]] Observatories, which he had compared to each other about 1840. This assertion was particularly worrying, because when the primary Imperial [[yard]] standard had partially been destroyed in 1834, a new standard of reference was constructed using copies of the "Standard Yard, 1760", instead of the pendulum's length as provided for in the Weights and Measures Act of 1824, because the pendulum method proved unreliable. Nevertheless [[Ferdinand Rudolph Hassler]]'s use of the metre and the creation of the Office of Standard Weights and Measures as an office within the Coast Survey contributed to the introduction of the [[Metric Act of 1866]] allowing the use of the metre in the United States, and preceded the choice of the metre as international scientific unit of length and the proposal by the [[International Association of Geodesy|European Arc Measurement]] (German: ''Europäische Gradmessung'') to establish a "European international bureau for weights and measures".<ref name="Wolf 1882 20, 32" /><ref name=":5">{{Cite web |title=Metric Act of 1866 – US Metric Association |url=https://usma.org/laws-and-bills/metric-act-of-1866#locale-notification |access-date=2021-03-15 |website=usma.org}}</ref><ref name="BEG-1868" /><ref name="Quinn-2019">{{Cite journal |last=Quinn |first=Terry |date=2019 |title=Wilhelm Foerster's Role in the Metre Convention of 1875 and in the Early Years of the International Committee for Weights and Measures |journal=Annalen der Physik |language=en |volume=531 |issue=5 |pages=2 |bibcode=2019AnP...53100355Q |doi=10.1002/andp.201800355 |issn=1521-3889 |s2cid=125240402|doi-access=free }}</ref><ref name="Clarke-1867" /><ref>{{Cite journal |last=Bessel |first=Friedrich Wilhelm |date=1840-04-01 |title=Über das preufs. Längenmaaß und die zu seiner Verbreitung durch Copien ergriffenen Maaßregeln. |url=https://ui.adsabs.harvard.edu/abs/1840AN.....17..193B |journal=Astronomische Nachrichten |volume=17 |issue=13 |pages=193 |bibcode=1840AN.....17..193B |doi=10.1002/asna.18400171302 |issn=0004-6337}}</ref><ref>{{Cite book |last=Britain |first=Great |url=https://books.google.com/books?id=qKZFAAAAcAAJ&q=yard+pendulum&pg=PA759 |title=The Statutes of the United Kingdom of Great Britain and Ireland |date=1824 |language=en}}</ref><ref name="Guillaume-1916">{{Cite journal |last=Guillaume |first=Ed. |date=1916-01-01 |title=Le Systeme Metrique est-il en Peril? |url=https://ui.adsabs.harvard.edu/abs/1916LAstr..30..242G |journal=L'Astronomie |volume=30 |pages=244–245 |bibcode=1916LAstr..30..242G |issn=0004-6302}}</ref><ref name=":4" />

[[File:Metre alloy.jpg|thumb|Creating the metre-alloy in 1874 at the Conservatoire des Arts et Métiers. Present Henri Tresca, George Matthey, Saint-Claire Deville, and Debray.|left]]

In 1867 at the second General Conference of the International Association of Geodesy held in Berlin, the question of an international standard unit of length was discussed in order to combine the measurements made in different countries to determine the size and shape of the Earth.<ref name="Hirsch-1891">{{Cite web |last=Hirsch |first=Adolphe |date=1891 |title=Don Carlos Ibanez (1825–1891) |url=http://www.bipm.org/utils/common/pdf/obituaries/1891_CIPM_ES_IBANEZ-Don-Carlos.pdf |access-date=2017-05-22 |website=Bureau International des Poids et Mesures |pages=4, 8}}</ref><ref>{{Cite web |title=BIPM – International Metre Commission |url=http://www.bipm.org/en/measurement-units/history-si/international-metre-commission.html |access-date=2017-05-26 |website=www.bipm.org}}</ref><ref name="IAG">{{Cite web |title=A Note on the History of the IAG |url=http://www.iag-aig.org/index.php?tpl=text&id_c=80&id_t=143 |access-date=2017-05-26 |website=IAG Homepage}}</ref> According to a preliminary proposal made in [[Neuchâtel]] the precedent year, the General Conference recommended the adoption of the metre in replacement of the toise of Bessel, the creation of an International Metre Commission, and the foundation of a World institute for the comparison of geodetic standards, the first step towards the creation of the [[International Bureau of Weights and Measures]].<ref name="Ross-James">{{Cite journal |last1=Ross |first1=Clarke Alexander |last2=James |first2=Henry |date=1873-01-01 |title=XIII. Results of the comparisons of the standards of length of England, Austria, Spain, United States, Cape of Good Hope, and of a second Russian standard, made at the Ordnance Survey Office, Southampton. With a preface and notes on the Greek and Egyptian measures of length by Sir Henry James |journal=Philosophical Transactions of the Royal Society of London |volume=163 |pages=445–469 |doi=10.1098/rstl.1873.0014 |doi-access=free}}</ref><ref name="Hirsch-1891" /><ref name="IAG" /><ref name="Brunner">{{Cite web |last=Brunner |first=Jean |date=1857 |title=Comptes rendus hebdomadaires des séances de l'Académie des sciences / publiés... par MM. les secrétaires perpétuels |url=https://gallica.bnf.fr/ark:/12148/bpt6k3001w |access-date=2019-05-15 |website=Gallica |pages=150–153 |language=FR}}</ref><ref>{{cite book |last=Guillaume |first=Charles-Édouard |title=La Création du Bureau International des Poids et Mesures et son Œuvre |publisher=Gauthier-Villars |year=1927 |location=Paris |page=321 |trans-title=The creation of the International Bureau of Weights and Measures and its work}}</ref>

Hassler's metrological and geodetic work also had a favourable response in Russia.<ref name="Parr-2006">{{Cite journal |last=Parr |first=Albert C. |date=2006-04-01 |title=A Tale About the First Weights and Measures Intercomparison in the United States in 1832 |url=https://www.nist.gov/publications/tale-about-first-weights-and-measures-intercomparison-united-states-1832 |journal=Journal of Research of the National Institute of Standards and Technology |language=en |volume=111 |issue=1 |pages=31–32, 36 |doi=10.6028/jres.111.003 |pmc=4654608 |pmid=27274915 |via=NIST}}</ref><ref name="Cajori-1921">{{Cite journal |last=Cajori |first=Florian |date=1921 |title=Swiss Geodesy and the United States Coast Survey |url=https://www.jstor.org/stable/6721 |journal=The Scientific Monthly |volume=13 |issue=2 |pages=117–129 |bibcode=1921SciMo..13..117C |issn=0096-3771}}</ref> In 1869, the [[Russian Academy of Sciences|Saint Petersburg Academy of Sciences]] sent to the French Academy of Sciences a report drafted by [[Otto Wilhelm von Struve]], [[Heinrich von Wild]] and [[Moritz von Jacobi]], whose theorem has long supported the assumption of an ellipsoid with three unequal axes for the figure of the Earth, inviting his French counterpart to undertake joint action to ensure the universal use of the [[metric system]] in all scientific work.<ref name="Guillaume-1916" /><ref name="Earth-1911" />

In the 1870s and in light of modern precision, a series of international conferences was held to devise new metric standards. When a conflict broke out regarding the presence of impurities in the metre-alloy of 1874, a member of the Preparatory Committee since 1870 and Spanish representative at the [[Metre Convention|Paris Conference]] in 1875, [[Carlos Ibáñez e Ibáñez de Ibero]] intervened with the [[French Academy of Sciences]] to rally France to the project to create an International Bureau of Weights and Measures equipped with the scientific means necessary to redefine the units of the [[metric system]] according to the progress of sciences.<ref name="NIST-2003">[[#nistmetre|National Institute of Standards and Technology 2003; Historical context of the SI: Unit of length (meter)]]</ref><ref name="Pérard-1957" /><ref name="Quinn-2012" /><ref>{{Citation |last=Dodis |first=Diplomatische Dokumente der Schweiz {{!}} Documents diplomatiques suisses {{!}} Documenti diplomatici svizzeri {{!}} Diplomatic Documents of Switzerland {{!}} |title=Bericht der schweizerischen Delegierten an der internationalen Meterkonferenz an den Bundespräsidenten und Vorsteher des Politischen Departements, J. J. Scherer |date=1875-03-30 |url=https://dodis.ch/42045 |access-date=2021-09-20 |publisher=Diplomatische Dokumente der Schweiz {{!}} Documents diplomatiques suisses {{!}} Documenti diplomatici svizzeri {{!}} Diplomatic Documents of Switzerland {{!}} Dodis |language=fr}}</ref>

The [[Metre Convention]] (''Convention du Mètre'') of 1875 mandated the establishment of a permanent International Bureau of Weights and Measures (BIPM: ''{{lang|fr|Bureau International des Poids et Mesures}}'') to be located in [[Sèvres]], France. This new organisation was to construct and preserve a prototype metre bar, distribute national metric prototypes, and maintain comparisons between them and non-metric measurement standards. The organisation distributed such bars in 1889 at the first [[General Conference on Weights and Measures]] (CGPM: ''{{lang|fr|Conférence Générale des Poids et Mesures}}''), establishing the ''[[International Prototype Metre]]'' as the distance between two lines on a standard bar composed of an alloy of 90% [[platinum]] and 10% [[iridium]], measured at the melting point of ice.<ref name="NIST-2003" />