The BIPM has the mandate to provide the basis for a single, coherent system of measurements throughout the world, traceable to theInternational System of Units (SI). This task takes many forms, from direct dissemination of units to coordination through international comparisons of national measurement standards (as in electricity and ionising radiation).[4]
Following consultation, a draft version of the BIPM Work Programme is presented at each meeting of the General Conference for consideration with the BIPM budget. The final programme of work is determined by the CIPM in accordance with the budget agreed to by the CGPM.[5][6]
Scientific and technical activities carried out in its four departments: chemistry, ionising radiation, physical metrology, and time
Liaison and coordination work, including providing the secretariat for the CIPM Consultative Committees and some of their Working Groups and for the CIPM MRA, and providing institutional liaison with the other bodies supporting the international quality infrastructure and other international bodies
Capacity building and knowledge transfer programs to increase the effectiveness within the worldwide metrology community of those Member State and Associates with emerging metrology systems
A resource centre providing a database and publications for international metrology
The BIPM is one of the twelve member organisations of the International Network on Quality Infrastructure (INetQI), which promotes and implements QI activities inmetrology, accreditation, standardisation and conformity assessment.[9]
The BIPM has an important role in maintaining accurate worldwide time of day. It combines, analyses, and averages the official atomic time standards of member nations around the world to create a single, officialCoordinated Universal Time (UTC).[10]
The BIPM is overseen by theInternational Committee for Weights and Measures (French:Comité international des poids et mesures, CIPM), a committee of eighteen members that meet normally in two sessions per year,[11] which is in turn overseen by theGeneral Conference on Weights and Measures (French:Conférence générale des poids et mesures, CGPM) that meets in Paris usually once every four years, consisting of delegates of the governments of the Member States[12][13] and observers from the Associates of the CGPM. These organs are also commonly referred to by their French initialisms.
Replicas of historical metric standards, including an iron copy of themètre des Archives.
In the 19th century,units of measurement were defined by primarystandards, and unique artefacts made of differentalloys with distinct coefficients ofexpansion were the legal basis of units of length. A wrought iron ruler, the Toise of Peru, also calledToise de l'Académie, was the French primary standard of the toise, and the metre was officially defined by an artefact made of platinum kept in the National Archives.[27] Besides the latter, another platinum and twelve iron standards of the metre were made byÉtienne Lenoir in 1799.[28] One of them became known as the Committee Meter in the United States and served as standard of length in theUnited States Coast Survey until 1890.[29][30]
In 1855, the Dufour map (French:Carte Dufour), the firsttopographic map of Switzerland for which the metre was adopted as the unit of length, won the gold medal at the Exposition Universelle.[32][33] However, the baselines for this map were measured in 1834 with three toises long measuring rods calibrated on a toise made in 1821 byJean Nicolas Fortin forFriedrich Georg Wilhelm von Struve.[34][35]
The geodetic measuring device calibrated on the metre devised byCarlos Ibáñez e Ibáñez de Ibero andFrutos Saavedra Meneses, was displayed byJean Brunner at the Exhibition.[36][37] The four-metre-long Spanish measuring instrument, which became known as the Spanish Standard (French:Règle espagnole), was compared withBorda's double-toise N° 1, which served as a comparison module for the measurement of all geodesic bases in France,[38][39] and was also to be compared to the Ibáñez apparatus.[40][38] In order to maintainmeasurement traceability it was important to control the temperature during these intercomparisons in order to avoidsystematic errors.[23][41]
The Earth measurements thus underscored the importance of scientific methods at a time whenstatistics were implemented in geodesy.[24][23] As a leading scientist of his time, Carlos Ibáñez e Ibáñez de Ibero was one of the 81 initial members of theInternational Statistical Institute (ISI) and delegate of Spain to the first ISI session (now called World Statistic Congress) in Rome in 1887.[38][42] On the sidelines of theExposition Universelle (1855) and the secondCongress 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.[16] 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 theExposition Universelle (1867) in Paris and would call for the international adoption of the metric system.[43][16]
In 1858, a Technical Commission was set up to continuecadastral surveying inaugurated underMuhammad Ali. This Commission suggested to buy geodetic devices which were ordered in France.Mohammed Sa'id Pasha entrusted toIsmail Mustafa al-Falaki the study of the precision apparatus calibrated against the metre intended to measure geodetic baselines and built byJean 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.[44][45]
According to geodesists, these standards were secondary standards deduced from the Toise of Peru.[16] In continental Europe, except Spain,[49] surveyors continued to use measuring instruments calibrated on the Toise of Peru.[16] Among these, the toise of Bessel and the apparatus of Borda were respectively the main references for geodesy inPrussia and inFrance. 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 takethermal expansion into account without measuring the temperature.[50][51]
Metric act of 1866 and calls for an international standard unit of length
In 1866,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 theMetric Act of 1866 allowing the use of the metre in the United States,[52] and preceded the choice of the metre as international scientific unit of length and the proposal by the 1867 General Conference of theEuropean Arc Measurement (German:Europäische Gradmessung) to establish the International Bureau of Weights and Measures.[18][15] Moreover, it was asserted that the Toise of Peru, the standard of the toise constructed in 1735 for theFrench Geodesic Mission to the Equator, might be so much damaged that comparison with it would be worthless,[35] while Bessel had questioned the accuracy of copies of this standard belonging toAltona andKoenigsberg Observatories, which he had compared to each other about 1840.[53][28]
This assertion was particularly worrying, because when the primary Imperialyard 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 theWeights and Measures Act 1824,[54] because the pendulum method proved unreliable.[55][56]
The intimate relationships that necessarily existed betweenmetrology andgeodesy explain that theInternational Association of Geodesy, founded to combine the geodetic operations of different countries, in order to reach a new and more exact determination of the shape and dimensions of the Globe, prompted the project of reforming the foundations of themetric system, while expanding it and making it international. Not, as it was mistakenly assumed for a certain time, that the Association had the unscientific thought of modifying the length of the metre, in order to conform exactly to its historical definition according to the new values that would be found for the terrestrial meridian. But, busy combining the arcs measured in the different countries and connecting the neighbouring triangulations, geodesists encountered, as one of the main difficulties, the unfortunate uncertainty which reigned over the equations of the units of length used.Adolphe Hirsch, GeneralBaeyer and ColonelIbáñez decided, in order to make all the standards comparable, to propose to the Association to choose the metre for geodetic unit, and to create an international prototype metre differing as little as possible from themètre des Archives.[21]
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.[21][57] According to a preliminary proposal made inNeuchâtel the precedent year,[22] the General Conference recommended the adoption of the metre in replacement of the toise of Bessel,[57][58] 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.[22][21]
Creating the metre-alloy in 1874 at the Conservatoire des Arts et Métiers. Present Henri Tresca, George Matthey, Saint-Claire Deville, and DebrayCloseup of National Prototype Metre Bar No. 27, made in 1889 by the International Bureau of Weights and Measures (BIPM) in collaboration withJohnson Mattey and given to the United States,[61] which served as the standard for American cartography from 1890 replacing the Committee Meter, an authentic copy of theMètre des Archives produced in 1799 in Paris, whichFerdinand Rudolph Hassler had brought to the United States in 1805.[29]
The French government gave practical support to the creation of an International Metre Commission, which met in Paris in 1870 and again in 1872 with the participation of about thirty countries.[43][14] There was much discussion within this commission, considering the opportunity either to keep as definitive the units represented by the standards of the Archives, or to return to the primitive definitions, and to correct the units to bring them closer to them. Since its origin, the metre has kept a double definition; it is both the ten-millionth part of the quarter meridian and the length represented by theMètre des Archives. The first is historical, the second is metrological. 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; theMetric System would be perpetually threatened with change, that is to say with ruin. Thus the Commission called for the creation of a newinternational prototype metre which length would be as close as possible to that of theMètre des Archives and the arrangement of a system where national standards could be compared with it.[55]
At the session on 12 October 1872 of the Permanent Committee of the International Metre Commission, which was to become theInternational Committee for Weights and Measures,[14] Carlos Ibáñez e Ibáñez de Ibero was elected president. On 19 April 1875, Ibáñez' presidency was confirmed andAdolphe Hirsch was elected secretary of the International Committee for Weights and Measures.[62][63] 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 theÉcole 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 theConservatoire national des arts et métiers.[43] 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,Carlos Ibáñez e Ibáñez de Ibero intervened with theFrench 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 themetric system according to the progress of sciences.[64] In fact, the chemical analysis of the alloy produced in 1874 by the French section revealed contamination byruthenium andiron which led theInternational 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 theextrusion process, which resulted in iron contamination. However, it soon turned out that the prototypes designed byHenri Tresca could be produced bymilling.[16]
The 1875 Metre Convention and the founding of the BIPM
The principal tasks facing the delegates at the 1875 conference was the replacement of the existing metre and kilogram artefacts that were held by the French Government and the setting up of an organisation 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.[17]
Two members of the Permanent Committee of the International Metre Commission, the German astronomer,Wilhelm Julius Foerster, director of theBerlin Observatory and director of the German Weights and Measures Service, and the Swiss geodesist of German origin,Adolphe Hirsch were also among the main architects of the Metre Convention.[15][65] While the German astronomerWilhelm Julius Foerster along with the Russian and Austrian representatives boycotted the Permanent Committee of the International Metre Commission in order to prompt the reunion of theDiplomatic Conference of the Metre and to promote the foundation of a permanent International Bureau of Weights and Measures,[66][15]Adolphe Hirsch, delegate ofSwitzerland at this Diplomatic Conference in 1875, conformed to the opinion ofItaly andSpain to create, in spite of French reluctance, the International Bureau of Weights and Measures in France as a permanent institution at the disadvantage of theConservatoire national des arts et métiers.[67][68]
Spain notably supported France for this outcome and the first president of the International Committee for Weights and Measures, the Spanish geodesist,Carlos Ibáñez e Ibáñez de Ibero received theGrand Officer medal of the Légion d'Honneur for his diplomatic role on this issue and was awarded thePoncelet Prize for his scientific contribution to metrology.[69] Indeed, as Carlos Ibáñez e Ibáñez de Ibero was collaborating with the French on the extension of thearc measurement of Delambre and Méchain since 1853, and was president of both the Permanent Committee of the International Metre Commission since 1872 and the Permanent Commission of theInternational Association of Geodesy since 1874, he was to play a pivotal role in reconciling French and German interests.[38][70] The Metre Convention was signed on 20 May 1875 in Paris and the International Bureau of Weights and Measures was created under the supervision of the International Committee for Weights and Measures, presided by Carlos Ibáñez e ibáñez de Ibero.[63][38]
The 1889 General Conference on Weights and Measures
In 1889, theGeneral Conference on Weights and Measures, presided byAlfred Descloizeaux, met at thePavillon de Breteuil, the seat of the International Bureau of Weights and Measures. It performed the first great deed dictated by the motto inscribed in the pediment of the splendid edifice that is the metric system: "A tous les temps, à tous les peuples" (For all times, to all peoples); and this deed consisted in the approval and distribution, among the governments of the states supporting the Metre Convention, of prototype standards of hitherto unknown precision intended to propagate the metric unit throughout the whole world.[25][71]
For metrology the matter of expansibility was fundamental; as a matter of fact, the temperature measuring error related to the length measurement in proportion to the expansibility of the standard and the constantly renewed efforts of metrologists to protect their measuring instruments against the interfering influence of temperature revealed clearly the importance they attached to the expansion-induced errors. It was common knowledge, for instance, that effective measurements were possible only inside a building, the rooms of which were well protected against the changes in outside temperature, and the very presence of the observer created an interference against which it was often necessary to take strict precautions.[25] Thus, the Contracting States also received a collection of thermometers whose accuracy made it possible to ensure that of length measurements.[72] Theinternational prototype metre would also be a "line standard"; that is, the metre was defined as the distance between two lines marked on the bar, so avoiding the wear problems of end standards.[16]
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'sthermometry work led to the discovery of special alloys of iron–nickel, in particularinvar, whose practically negligible coefficient of expansion made it possible to develop simpler baseline measurement methods, and for which its director, the Swiss physicistCharles-Edouard Guillaume, was granted theNobel Prize in Physics in 1920. Guillaume's Nobel Prize marked the end of an era in whichmetrology was leaving the field ofgeodesy to become an autonomousscientific discipline able of redefining the metre throughtechnological applications ofphysics.[73][26][43] On the other hand, the fondation of the United States Coast and Geodetic Survey byFerdinand Rudolph Hassler paved the way to the actual definition of the metre, withCharles Sanders Peirce being the first to experimentally link the metre to the wavelength of a spectral line.Albert Abraham Michelson soon took up the idea and improved it.[56]
In 1987 the International Bureau of Weights and Measures took over some of the work of theInternational Time Bureau when it was dissolved in 1987. The remaining tasks were assigned to theInternational Earth Rotation and Reference Systems Service (IERS),[74] which replaced theInternational Polar Motion Service and the earth-rotation section of the International Time Bureau.[75] Already in 1936, irregularities in the speed ofEarth's rotation due to the unpredictable movement of air and water masses were discovered through the use ofquartz clocks. They implied that the Earth's rotation was an imprecise way of determining time. In 1967, the second was redefined based onatomic clocks.[76] resulting in theInternational Atomic Time (TAI). The International Bureau of Weights and Measures began to establish atomic clocks world-wide, numbering more than 450 currently.[77]
^abcdefghQuinn, T. J. (2012).From artefacts to atoms: the BIPM and the search for ultimate measurement standards. Oxford: Oxford University Press. pp. 3–10, 14,90–91,56–57, 72, 108,56–57.ISBN978-0-19-990991-9.OCLC861693071.
^abAlder, Ken; Devillers-Argouarc'h, Martine (2015).Mesurer le monde: l'incroyable histoire de l'invention du mètre. Libres Champs. Paris: Flammarion. pp. 499–520,517–518.ISBN978-2-08-130761-2.
^abcGuillaume, Ch.-Éd. (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 et Cie, Éditeur. pp. 18–19, 321.
^abcWolf, M. C (1882).Recherches historiques sur les étalons de poids et mesures de l'observatoire et les appareils qui ont servi a les construire (in French). Paris: Gauthier-Villars. pp. 7–8, 20, 32.OCLC16069502.
^Hirsch, A.; Dumur, J. (1888).Le Réseau de Triangulation suisse (in French). Vol. Troisième volume. La Mensuration des Bases. Commission géodésique suisse. pp. 3–4.
^Abplanalp, Andrej (14 July 2019)."Henri Dufour et la carte de la Suisse".Musée national - Blog sur l'histoire suisse (in German).Archived from the original on 25 December 2024. Retrieved25 January 2025.
^Viik, T (2006). "F. W. Bessel and geodesy".Struve Geodetic Arc, 2006 International Conference, The Struve Arc and Extensions in Space and Time, Haparanda and Pajala, Sweden, 13–15 August 2006. pp. 10, 6.CiteSeerX10.1.1.517.9501.
^Quinn, Terry (2012).From artefacts to atoms: the BIPM and the search for ultimate measurement standards. New York: Oxford University Press. p. 144.ISBN978-0-19-530786-3.
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