Editing Metre Convention (section)

== Cartography and the metre ==
The [[American Revolution]], in which the [[United States]] was supported by [[France]] and [[Spain]],<ref>{{Cite web |last=Ferreiro |first=Larrie D. |date=December 2024 |title=The Rise and Fall and Rise of Spain in the Historiography of the American Revolution |url=https://institutofranklin.net/sites/default/files/revistas/%5B2024-12/The%20Rise%20and%20Fall%20and%20Rise%20of%20Spain%20in%20the%20Historiography%20of%20the%20American%20Revolution_Larrie%20D.%20Ferreiro.pdf |website=Instituto Franklin-UAH}}</ref> led to the founding 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.<ref name="Cajori-1921" /> During the mid-19th century, the metre was adopted in [[Khedivate of Egypt]] an autonomous tributary state of the [[Ottoman Empire]] for [[cadastral surveying]].<ref name="Jamʻīyah al-Jughrāfīyah al-Miṣrīyah-1876">{{Cite book |last=Jamʻīyah al-Jughrāfīyah al-Miṣrīyah |url=http://archive.org/details/bulletindelasoc00almgoog |title=Bulletin de la Société de géographie d'Égypte |date=1876 |publisher=[Le Caire] |others=University of Michigan |pages=5–16}}</ref><ref>{{Cite book |author=Ismāʿīl-Afandī Muṣṭafá |url=https://gallica.bnf.fr/ark:/12148/bpt6k840511v |title=Notes biographiques de S.E. Mahmoud Pacha el Falaki (l'astronome), par Ismail-Bey Moustapha et le colonel Moktar-Bey |date=1886 |pages=10–11 |language=EN}}</ref><ref name="Ismāʿīl-Afandī Muṣṭafá-1864">{{Cite book |author=Ismāʿīl-Afandī Muṣṭafá |url=https://gallica.bnf.fr/ark:/12148/bpt6k62478474 |title=Recherche des coefficients de dilatation et étalonnage de l'appareil à mesurer les bases géodésiques appartenant au gouvernement égyptien / par Ismaïl-Effendi-Moustapha, ... |date=1864 |language=EN}}</ref> In [[continental Europe]], adoption of the [[metric system]] and a better [[standardisation]] of units of measurement marked the [[Second Industrial Revolution|Technological Revolution]], a period in which [[German Empire]] would challenge [[United Kingdom]] as the foremost industrial nation in Europe. This was accompanied by development in [[cartography]] which was a prerequisite for both military operations and the creation of the infrastructures needed for industrial development such as [[Rail transport|railways]]. During the process of [[unification of Germany]], [[Geodesy|geodesists]] called for the establishment of an [[International Bureau of Weights and Measures]] in [[Europe]].<ref name="Alder-2015">{{Cite book |last1=Alder |first1=Ken |title=Mesurer le monde: l'incroyable histoire de l'invention du mètre |last2=Devillers-Argouarc'h |first2=Martine |date=2015 |publisher=Flammarion |isbn=978-2-08-130761-2 |series=Libres Champs |location=Paris |pages=499–520, 517-518}}</ref><ref name="BEG-1868">{{Cite book |url=http://gfzpublic.gfz-potsdam.de/pubman/item/escidoc:108187:4/component/escidoc:272449/Generalbericht.mitteleurop%C3%A4ische.Gradmessung%201867.pdf |title=Bericht über die Verhandlungen der vom 30. September bis 7. October 1867 zu BERLIN abgehaltenen allgemeinen Conferenz der Europäischen Gradmessung |publisher=Central-Bureau der Europäischen Gradmessung |year=1868 |location=Berlin |pages=123–134 |language=german}}</ref>

=== Swiss, American, Spanish and Egyptian cartography ===
[[File:HasslerCollection 001.jpg|thumb|Triangulation near [[New York City]], 1817|left]]

The [[Helvetic Republic]] adopted the [[metric system]] by law in 1801.<ref>{{Cite web |title=Système métrique |url=https://hls-dhs-dss.ch/fr/articles/013754/2014-05-22/ |access-date=2025-04-08 |website=hls-dhs-dss.ch |language=fr}}</ref> In 1805, a Swiss immigrant [[Ferdinand Rudolph Hassler]] brought copies of the French metre and kilogram to the United States. In 1830 the [[United States Congress|Congress]] decided to create uniform standards for length and weight in the United States.<ref name=":3">{{Cite web |title=e-expo: Ferdinand Rudolf Hassler |url=https://www.f-r-hassler.ch/en/weights/index.html |access-date=2025-04-07 |website=www.f-r-hassler.ch}}</ref> Hassler was mandated to work out the new standards and proposed to adopt the metric system. The United States Congress opted for the [[Yard#Physical standards|British Parliamentary Standard Yard of 1758]] and the British [[Imperial units#Mass and weight|Troy Pound of 1824]] as length and weight standards.<ref name=":3" /> Nevertheless Ferdinand Rudolph Hassler's use of the metre and the creation of the [[National Institute of Standards and Technology|Office of Standard Weights and Measures]] as an office within the [[United States Coast and Geodetic Survey|Coast Survey]] contributed to the introduction of the [[Metric Act of 1866]] allowing the use of the metre in the United States.<ref name="Metric Act of 1866">{{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>

In 1816, Ferdinand Rudolph Hassler was appointed first Superintendent of the [[United States Coast and Geodetic Survey|Survey of the Coast]].<ref>{{cite web |url=https://celebrating200years.noaa.gov/historymakers/hassler/welcome.html |title=NOAA 200th Top Tens: History Makers: Ferdinand Rudolph Hassler |publisher=National Oceanic and Atmospheric Administration |location=US |date=2024-03-19 |access-date=2024-10-17}}</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> Trained in geodesy in Switzerland, France and [[Germany]], Hassler had brought a standard metre made in Paris to the United States in October 1805. He designed a baseline apparatus which instead of bringing different bars in actual contact during measurements,<ref name="Cajori-1921" /> used only one bar calibrated on the Committee meter, an authenthic copy of the {{Lang|fr|Mètre des Archives}},<ref>{{Cite book |url=https://play.google.com/store/books/details?id=NiEEAQAAIAAJ |title=National Bureau of Standards Miscellaneous Publication |date=1966 |publisher=U.S. Government Printing Office |pages=529 |language=en}}</ref><ref name=":10">{{Cite journal |last=Clarke |first=Alexander Ross |last2=James |first2=Henry |date=1873 |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 |url=https://royalsocietypublishing.org/doi/10.1098/rstl.1873.0014 |journal=Philosophical Transactions of the Royal Society of London |volume=163 |pages=445–469 |doi=10.1098/rstl.1873.0014}}</ref> and optical contact.<ref name="Cajori-1921" /><ref>{{Cite book |last1=American Philosophical Society. |url=https://www.biodiversitylibrary.org/item/26092 |title=Transactions of the American Philosophical Society |last2=Society |first2=American Philosophical |last3=Poupard |first3=James |date=1825 |volume=new ser.:v.2 (1825) |location=Philadelphia [etc.] |pages=234–278}}</ref> In 1830, Hassler became head of the Office of Weights and Measures, which became a part of the Survey of the Coast. He compared various units of length used in the [[United States]] at that time and measured [[Thermal expansion|coefficients of expansion]] to assess temperature effects on the measurements.<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> In 1834, Hassler, measured at [[Fire Island]] the first [[Baseline (surveying)|baseline]] of the Survey of the Coast,<ref name=":5">{{Cite book |last1=Hassler |first1=Harriet |url=http://archive.org/details/ferdinandrudolph1068hass |title=Ferdinand Rudolph Hassler (1770–1843) |last2=Burroughs |first2=Charles A. |date=2007 |others=NIST Research Library |pages=51–52}}</ref> shortly before [[Louis Puissant]] declared to the French Academy of Sciences in 1836 that Jean Baptiste Joseph Delambre and Pierre Méchain had made errors in the [[Arc measurement|meridian arc measurement]], which had been used to determine the length of the metre.<ref name="Lebon-1899">{{Cite book |last=Lebon |first=Ernest |url=https://gallica.bnf.fr/ark:/12148/bpt6k949666 |title=Histoire abrégée de l'astronomie / par Ernest Lebon,... |date=1899 |pages=168–171 |language=EN}}</ref><ref>{{Cite book |last=Puissant |first=Louis |url=https://gallica.bnf.fr/ark:/12148/bpt6k5323385b |title=Nouvelle détermination de la distance méridienne de Montjouy à Formentera, dévoilant l'inexactitude de celle dont il est fait mention dans la base du système métrique décimal, par M. Puissant,... lu à l'Académie des sciences, le 2 mai 1836 |language=EN}}</ref>[[File:Appareil_Ibáñez.jpg|thumb|313x313px|Ibáñez apparatus calibrated on the metric Spanish standard and used at [[Aarberg]], in [[canton of Bern]], [[Switzerland]] in 1880.<ref>{{Cite book |last1=Hirsch |first1=A. |title=Le Réseau de Triangulation suisse |last2=Dumur |first2=J. |publisher=Commission géodésique suisse |year=1888 |volume=Troisième volume. La Mensuration des Bases |pages=3–4 |language=fr}}</ref>]]
In 1855, the Dufour map (French: ''Carte Dufour''), the first [[Topographic Map of Switzerland|topographic map of Switzerland]] for which the metre was adopted as the unit of length, won the gold medal at the Exposition Universelle.<ref>{{Cite news |last=Abplanalp |first=Andrej |date=2019-07-14 |title=Henri Dufour et la carte de la Suisse |url=https://blog.nationalmuseum.ch/fr/2019/07/dufour-le-cartographe/ |archive-url=https://web.archive.org/web/20241225163218/https://blog.nationalmuseum.ch/fr/2019/07/dufour-le-cartographe/ |archive-date=25 December 2024 |access-date=2025-01-25 |work=Musée national - Blog sur l'histoire suisse |language=de-DE |url-status=live }}</ref><ref>{{Cite journal |last=Dufour |first=G.-H. |date=1861 |title=Notice sur la carte de la Suisse dressée par l'État Major Fédéral |url=https://www.persee.fr/doc/globe_0398-3412_1861_num_2_1_7582 |journal=Le Globe. Revue genevoise de géographie |volume=2 |issue=1 |pages=5–22 |doi=10.3406/globe.1861.7582}}</ref> However, the baselines for this map were measured in 1834 with three toises long measuring rods calibrated on a toise made in 1821 by [[Jean Nicolas Fortin]] for [[Friedrich Georg Wilhelm von Struve]].<ref>{{Cite journal |last=Seligmann |first=A. E. M. |date=1923 |title=La Toise de Belgique |journal=Ciel et Terre, Bulletin of the Société Belge d'Astronomie |volume=39 |page=25}}</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> The Spanish standard, a geodetic measuring device calibrated on the metre devised by [[Carlos Ibáñez e Ibáñez de Ibero]] and [[Frutos Saavedra Meneses]], was also displayed by [[Jean Brunner]] at the Exhibition.<ref>{{Cite periodical |last=Brenni |first=Paolo |date=1996 |title=19th Century French Scientific Instrument Makers XI: The Brunners and Paul Gauher |url=https://www.unav.es/gep/TheBrunnersCartaParis.pdf |archive-url=https://web.archive.org/web/20241203014633/https://www.unav.es/gep/TheBrunnersCartaParis.pdf |archive-date=3 December 2024 |access-date=2025-01-25 |periodical=Bulletin of the Scientific Instrument Society |number=49 |url-status=live }}</ref><ref>{{Cite journal |last=Brenni |first=Paolo |date=1996 |title=19th Century French Scientific Intrument Makers |url=https://www.unav.es/gep/TheBrunnersCartaParis.pdf |journal=Bulletin of the Scientific Instrument Society |issue=49 |page=4 |archive-url=https://web.archive.org/web/20241203014633/https://www.unav.es/gep/TheBrunnersCartaParis.pdf |archive-date=3 December 2024}}</ref> Carlos Ibáñez e Ibáñez de Ibero recognized that the end standards with which the most perfect devices of the eighteenth century and those of the first half of the nineteenth century were still equipped, that [[Jean-Charles de Borda]] or [[Friedrich Bessel|Friedrich Wilhelm Bessel]] simply joined measuring the intervals by means of screw tabs or glass wedges, would be replaced advantageously for accuracy by microscopic measurements, a system designed in [[Switzerland]] by Ferdinand Rudolph Hassler and [[Johann Georg Tralles]],<ref>{{Cite web |last=Wolf |first=Rudolf |date=1891-01-01 |title=Histoire de l'appareil Ibañez-Brunner in Comptes rendus hebdomadaires des séances de l'Académie des sciences / publiés... par MM. les secrétaires perpétuels |url=https://gallica.bnf.fr/ark:/12148/bpt6k3068q |access-date=2023-08-31 |website=Gallica |pages=370–371 |language=FR}}</ref> and which Ibáñez ameliorated using a single standard with lines marked on the bar. Regarding the two methods by which the effect of temperature was taken into account, Ibáñez used both the bimetallic rulers, in platinum and brass, which he first employed for the central base of Spain,<ref name="Brunner-18572">{{Cite web |last=Brunner |first=Jean |date=1857-01-01 |title=Appareil construit pour les opérations au moyen desquelles on prolongera dans toute l'étendue de l'Espagne le réseau trigonométrique qui couvre la France in 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=2023-08-31 |website=Gallica |pages=150–153 |language=FR}}</ref> and the simple iron ruler with inlaid mercury thermometers which was used in Switzerland.<ref name=":6" /><ref name=":11">{{Cite EB1911 |wstitle= Geodesy |volume = 11 |last1= Clarke |first1= Alexander Ross |author-link1= Alexander Ross Clarke |last2= Helmert |first2= Friedrich Robert |author-link2= Friedrich Robert Helmert |pages= 607-615 |short=1}}</ref> On the sidelines of the [[Exposition Universelle (1855)]] and the second [[International Statistical Institute|Congress of Statistics]] held in Paris, an association with a view to obtaining a uniform decimal system of measures, weights and currencies was created in 1855.<ref name=":4" /> Under the impetus of this association, a Committee for Weights and Measures and Monies (French: ''Comité des poids, mesures et monnaies'') would be created during the [[Exposition Universelle (1867)]] in Paris and would call for the international adoption of the metric system.<ref name=":8">{{Cite web |title=History – The BIPM 150 |url=https://thebipm150.org/history/ |access-date=2025-04-08 |language=fr-FR}}</ref><ref name=":4" />

[[Egyptian astronomy]] has ancient roots which were revived in the 19th century by the modernist impetus of [[Muhammad Ali of Egypt|Muhammad Ali]] who founded in Sabtieh, [[Boulaq]] district, in [[Cairo]] an Observatory which he was keen to keep in harmony with the progress of this science still in progress.<ref name="Ismāʿīl-Afandī Muṣṭafá-1864" /><ref name="Jamʻīyah al-Jughrāfīyah al-Miṣrīyah-1876" /> In 1858, a Technical Commission was set up to continue [[cadastral surveying]] inaugurated under Muhammad Ali. This Commission suggested to Viceroy [[Sa'id of Egypt|Mohammed Sa'id Pasha]] to buy geodetic devices which were ordered in France. While [[Mahmud Ahmad Hamdi al-Falaki]] was in charge, in Egypt, of the direction of the work of the general map, the viceroy entrusted to [[Ismail Mustafa al-Falaki]] the study, in Europe, of the precision apparatus calibrated against the metre intended to measure the geodesic bases and already built by [[Jean Brunner]] in Paris. Ismail Mustafa had the task to carry out the experiments necessary for determining the expansion coefficients of the two platinum and brass bars, and to compare the Egyptian standard with a known standard. The Spanish standard designed by Carlos Ibáñez e Ibáñez de Ibero and Frutos Saavedra Meneses was chosen for this purpose, as it had served as a model for the construction of the Egyptian standard.<ref name="Jamʻīyah al-Jughrāfīyah al-Miṣrīyah-1876" /><ref name="Ismāʿīl-Afandī Muṣṭafá-1864" /> In addition, the Spanish standard had been compared with [[Jean-Charles de Borda|Borda]]'s double-toise N°&nbsp;1, which served as a comparison module for the measurement of all geodesic bases in France,<ref name="Soler-1997">{{Cite journal |last=Soler |first=T. |date=1997-02-01 |title=A profile of General Carlos Ibáñez e Ibáñez de Ibero: first president of the International Geodetic Association |journal=Journal of Geodesy |language=en |volume=71 |issue=3 |pages=176–188 |bibcode=1997JGeod..71..176S |citeseerx=10.1.1.492.3967 |doi=10.1007/s001900050086 |issn=1432-1394 |s2cid=119447198}}</ref><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> and was also to be compared to the Ibáñez apparatus.<ref name=":10" /><ref name="Soler-1997" /> In 1954, the connection of the southerly extension of the [[Struve Geodetic Arc]] with an arc running northwards from [[South Africa]] through [[Egypt]] would bring the course of a major [[meridian arc]] back to land where [[Eratosthenes]] had founded [[geodesy]].<ref>{{Cite news |title=Nomination of the STRUVE GEODETIC ARC for inscription on the WORLD HERITAGE LIST |url=https://whc.unesco.org/uploads/nominations/1187.pdf |pages=40, 143–144}}</ref>

=== European geodesy ===
In Europe, except Spain,<ref name="Brunner-18572" /> surveyors continued to use measuring instruments calibrated on the Toise of Peru.<ref name="Quinn-2012">{{Cite book |last=Quinn |first=T. J. |title=From artefacts to atoms: the BIPM and the search for ultimate measurement standards |date=2012 |publisher=Oxford University Press |isbn=978-0-19-990991-9 |location=Oxford |pages=9, 11, 20, 37–38, 91–92, 70–72, 114–117, 144–147, 8 |oclc=861693071}}</ref> 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.<ref>{{Cite web |title=Borda et le système métrique |url=https://mesurelab.fr/wp/metrologie/histoire-de-la-metrologie/borda-et-le-systeme-metrique/ |archive-url=https://web.archive.org/web/20230829055653/https://mesurelab.fr/wp/metrologie/histoire-de-la-metrologie/borda-et-le-systeme-metrique/ |archive-date=29 August 2023 |access-date=2023-08-29 |website=Association Mesure Lab |language=fr-FR}}</ref><ref name="Viik-2006">{{Cite news |last=Viik |first=T |date=2006 |title=F. W. Bessel and geodesy |work=Struve Geodetic Arc, 2006 International Conference, The Struve Arc and Extensions in Space and Time, Haparanda and Pajala, Sweden, 13–15 August 2006 |pages=10, 6 |citeseerx=10.1.1.517.9501}}</ref> A French scientific instrument maker, [[Jean Nicolas Fortin]], 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 Wilhelm Bessel in 1823. In 1831, [[Henri-Prudence Gambey]] also realised a copy of the Toise of Peru which was kept at [[Altona Observatory]].<ref>{{Cite book |last=Wolf |first=M. C |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><ref>{{Cite book |last=Baeyer |first=Johann Jacob |title=Grösse und Figur der Erde |publisher=Georg Reimer |year=1861 |location=Berlin |publication-date=1861 |pages=87–94 |language=de}}</ref>

In the second half of the 19th century, the creation of the [[International Association of Geodesy|Central European Arc Measurement]] ({{Langx|de|Mitteleuropäische Gradmessung}}) would mark, following [[Carl Friedrich Gauss]],<ref>{{Cite book |last=Tardi |first=Pierre (1897-1972) Auteur du texte |url=https://gallica.bnf.fr/ark:/12148/bpt6k3355272d/f74.item |title=Traité de géodésie / par le capitaine P. Tardi ; préface par le général G. Perrier |date=1934 |pages=34 |language=EN}}</ref><ref name="Quinn-20122" /> Friedrich Wilhelm Bessel and Friedrich Georg Wilhelm von Struve examples,<ref name=":9">{{Cite EB1911|wstitle=Earth, Figure of the|volume=8|last1=Clarke|first1=Alexander Ross|author-link1=Alexander Ross Clarke|last2=Helmert|first2=Friedrich Robert|author-link2=Friedrich Robert Helmert|pages=801-813|short=1}}</ref> the systematic adoption of more rigorous methods among them the application of the [[least squares]] in geodesy.<ref>{{Cite web |title=Mesure du 1er mètre: une erreur qui changea le monde |url=https://www.techniques-ingenieur.fr/actualite/articles/mesure-du-1er-metre-une-erreur-qui-changea-le-monde-2715/ |access-date=December 30, 2020 |website=Techniques de l'Ingénieur |language=fr-FR}}</ref><ref name="Lebon-1899" /> It 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]].<ref name="Clarke-1867" /> 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>

In 1866, an 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,<ref name="Clarke-1867" /> 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.<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 |page=193 |bibcode=1840AN.....17..193B |doi=10.1002/asna.18400171302 |issn=0004-6337}}</ref> In fact, the length of Bessel's Toise, which according to the then legal ratio between the metre and the Toise of Peru, should be equal to 1.9490348 m, would be found to be 26.2·10<sup>-6</sup> m greater during measurements carried out by [[Justin-Mirande René Benoit|Jean-René Benoît]] at the International Bureau of Weights and Measures. It was the consideration of the divergences between the different toises used by geodesists that led the [[International Association of Geodesy|European Arc Measurement]] ({{langx|de|links=no|Europäische Gradmessung}} ) to consider, at the meeting of its Permanent Commission in Neuchâtel in 1866, the founding 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>Guillaume, Charles-Édouard (1927). ''La Création du Bureau International des Poids et Mesures et son Œuvre'' [''The creation of the International Bureau of Weights and Measures and its work'']. Paris: Gauthier-Villars. p. 129-130.</ref><ref name="Pérard-1957" /> [[Spain]] joined the [[International Association of Geodesy|European Arc Measurement]] at this meeting.<ref>{{Cite web |date=2013-06-22 |title=El General Ibáñez e Ibáñez de Ibero, Marqués de Mulhacén {{!}} Revista e-medida |url=https://www.e-medida.es/numero-4/el-general-ibanez-e-ibanez-de-ibero-marques-de-mulhacen/ |access-date=2025-04-08 |language=es}}</ref> In 1867 at the second General Conference of the European Arc Measurement held in [[Berlin]], the question of international standard 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=":0">{{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 |url-status=live |archive-url=https://web.archive.org/web/20170722002232/http://www.iag-aig.org/index.php?tpl=text&id_c=80&id_t=143 |archive-date=22 July 2017 |access-date=16 May 2017 |website=IAG Homepage}}</ref> The conference recommended the adoption of the metric system (replacing [[Friedrich Bessel|Bessel]]'s toise) and the creation of an International Metre Commission.<ref name=":0" />

=== Saint Petersburg Academy ===
[[Ferdinand Rudolph Hassler]]'s metrological and geodetic work also had a favourable response in Russia.<ref name="Parr-2006" /><ref name="Cajori-1921" /> 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]], who secured, in 1860, the co-operation of Prussia, Belgium, France and England to the measurement of the European arc of parallel in 52° latitude,<ref name=":11" /><ref name="Clarke-1867" /> [[Heinrich von Wild]], the Swiss born director of the Central Geophysical Observatory in [[Saint Petersburg]],<ref>{{Cite web |date=2015-12-08 |title=History of IMO |url=https://public-old.wmo.int/en/about-us/who-we-are/history-IMO |url-status=dead |archive-url=https://web.archive.org/web/20231218170901/https://public-old.wmo.int/en/about-us/who-we-are/history-IMO |archive-date=December 18, 2023 |access-date=2023-10-12 |website=public.wmo.int |language=en}}</ref> and [[Moritz von Jacobi]], whose theorem has long supported the assumption of an ellipsoid with three unequal axes for the figure of the Earth,<ref name=":9" /> 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" /> The [[French Academy of Sciences]] and the [[Bureau des Longitudes]] in Paris drew the attention of the French government to this issue. In November 1869, [[Napoleon III]] issued invitations to join the International Metre Commission in Paris.<ref name=":8" /><ref>{{Cite web |title=BIPM – International Metre Commission |url=https://www.bipm.org/en/measurement-units/history-si/international-metre-commission.html |url-status=dead |archive-url=https://web.archive.org/web/20180109182826/https://www.bipm.org/en/measurement-units/history-si/international-metre-commission.html |archive-date=9 January 2018 |access-date=9 January 2018 |website=bipm.org}}</ref>

=== The International Metre Commission (1870/1872) ===
Prior to the 1870 conference, French politicians had feared that the British might reject the existing metre and would prefer to have new value of its theoretical length. However, [[James Clerk Maxwell]] wrote in 1865 that no scientist could become famous proposing a metre deduced from new measurements of the size of the Earth,<ref>{{Cite book |last=Maxwell |first=James Clerk |url=https://archive.org/details/electricandmagne01maxwrich/page/n39/mode/2up |title=A treatise on electricity and magnetism |date=1873 |publisher=Oxford : Clarendon Press |others=University of California Libraries |pages=3}}</ref> while [[Adolphe Hirsch]] would recall, in his 1891 [[obituary]] of Carlos Ibáñez e Ibáñez de Ibero, that the International Metre Commission had decided not to propose a new length for the metre.<ref name=":6">{{Cite book |last=Hirsch |first=Adolphe |url=https://play.google.com/store/books/details?id=M1PnAAAAMAAJ |title=Comptes-rendus des séances de la Commission permanente de l'Association géodésique internationale réunie à Florence du 8 au 17 octobre 1891 |date=1892 |publisher=De Gruyter, Incorporated |isbn=978-3-11-128691-4 |pages=101-109 |language=fr}}</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>

In July 1870, two weeks before the conference was due to start, the [[Franco-Prussian War]] broke out. Although the delegates did meet (without a German delegation), it was agreed that the conference should be recalled once all the delegates (including the German delegation) were present.<ref name="Adler" /> Following the war, which resulted in Napoleon III's exile, Germany and Italy, now unified nations, adopted the metric system as their national system of units, but with the prototype copy of the kilogram and metre under the control of the [[French Third Republic]].<ref name=":7" /> In 1872 the new republican government reissued the invitations and the same year scientists from thirty European and American countries met in Paris.<ref name=":7">
{{cite book
 |title = The Measure of all Things – The Seven-Year-Odyssey that Transformed the World
 |last= Alder
 |first= Ken
 |year= 2002
 |pages = 348–354
 |publisher= Abacus
 |location= London
 |isbn= 0-349-11507-9
}}</ref>

When the International Metre Commission was reconvened in 1872, it was proposed that new prototype metre and kilogram standards be manufactured to reproduce the values of the existing artifacts as closely as possible.<ref name="Adler">{{cite book |last=Alder |first=Ken |title=The Measure of all Things – The Seven-Year-Odyssey that Transformed the World |publisher=Abacus |year=2002 |isbn=0-349-11507-9 |location=London |page=354}}</ref> Indeed, since its origin, the metre had kept a double definition; it was both the ten-millionth part of the quarter meridian and the length represented by the ''Mètre des Archives''. The first was historical, the second was metrological. There was much discussion, considering the opportunity either to keep as definitive the units represented by the metre and kilogram standards of the Archives, or to return to the primitive definitions, and to correct the units to bring them closer to them. The first solution prevailed, in accordance with common sense and in accordance with the advice of the French Academy of Sciences. Abandoning the values represented by the standards, would have consecrated an extremely dangerous principle, that of the change of units to any progress of measurements; the [[Metric system|Metric System]] would be perpetually threatened with change, that is to say with ruin.<ref name="Guillaume-1916" /> The Commission decided the maintenance of new international standards rather than using French existing standards which, at that time, were 70 years old and which, through wear and tear, might not be exactly the same as when they had been adopted in 1799.<ref name="Adler" />  Thus the Commission called for the creation of a new international prototype metre which length would be as close as possible to that of the ''Mètre des Archives'' and the arrangement of a system where national standards could be compared with it.<ref name="Guillaume-1916" />

=== The 1874 metre-alloy ===
[[File:Metre alloy.jpg|thumb|Preparing the first metre-alloy in May 1874, at the Conservatoire des Arts et Métiers, Paris]]
On 6 May 1873 during the 6th session of the French section of the Metre Commission, [[Henri Étienne Sainte-Claire Deville]] cast a 20-kilogram platinum-iridium ingot from Matthey in his laboratory at the [[École normale supérieure (Paris)]]. On 13 May 1874, 250 kilograms of platinum-iridium to be used for several national prototypes of the metre was cast at the [[Conservatoire national des arts et métiers]].<ref name="BIPM-150" /> 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 president of the Permanent Committee of the International Metre Commission,<ref>{{Cite book |last=Bigourdan |first=Guillaume |url=https://archive.org/details/lesystmemtri00bigo/page/n345/mode/2up |title=Le système métrique des poids et mesures ; son établissement et sa propagation graduelle, avec l'histoire des opérations qui ont servi à déterminer le mètre et le kilogramme |date=1901 |publisher=Paris : Gauthier-Villars |others=University of Ottawa |pages=313}}</ref> [[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="Pérard-19572">{{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> In fact, the chemical analysis of the alloy produced in 1874 by the French section revealed contamination by [[ruthenium]] and [[iron]] which led the [[General Conference on Weights and Measures|International Committee for Weights and Measures]] to reject, in 1877, the prototypes produced by the French section from the 1874 alloy. It also seemed at the time that the production of prototypes with an X profile was only possible through the [[extrusion]] process, which resulted in iron contamination. However, it soon turned out that the prototypes designed by [[Henri Tresca]] could be produced by [[Milling (machining)|milling]].<ref name="Quinn-20122">{{Cite book |last=Quinn |first=T. J. |title=From artefacts to atoms: the BIPM and the search for ultimate measurement standards |date=2012 |publisher=Oxford University Press |isbn=978-0-19-990991-9 |location=Oxford |pages=3-10, 14, 90-91, 56-57, 72, 108, 56-57 |oclc=861693071}}</ref>