The creation of the International Bureau of Weights and Measures followed the
Metre Convention of 1875, after the
Franco-Prussian War (1870–1871), These trends culminated in the 1889
General Conference on Weights and Measures, with the distribution of the
metre and
kilogram standards to the States parties to the
Metre Convention. When the metre was adopted as an international unit of length, it was well known that it no longer corresponded to its
historical definition. At that time, mathematicians like
Legendre and
Gauss had developed new methods for processing data, including the
least squares method which allowed to compare experimental data tainted with
observational errors to a mathematical model. Moreover, the International Bureau of Weights and Measures would have a central role for international geodetic measurements as
Charles Édouard Guillaume's discovery of
invar, an especially temperature-stable nickel-iron alloy, minimised the impact of measurement inaccuracies due to temperature
systematic errors. Besides the latter, another platinum and twelve iron standards of the metre were made by
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 Survey until 1890. , in
canton of Bern,
Switzerland in 1880.|left In 1855, the Dufour map (French:
Carte Dufour), the first
topographic map of Switzerland for which the metre was adopted as the unit of length, won the gold medal at the Exposition Universelle. 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. The geodetic measuring device calibrated on the metre devised by
Carlos Ibáñez e Ibáñez de Ibero and
Frutos Saavedra Meneses, was displayed by
Jean Brunner at the Exhibition. The four-metre-long Spanish measuring instrument, which became known as the Spanish Standard (French:
Règle espagnole), was compared with
Borda's double-toise N° 1, which served as a comparison module for the measurement of all geodesic bases in France, and was also to be compared to the Ibáñez apparatus. The Earth measurements thus underscored the importance of scientific methods at a time when
statistics were implemented in geodesy. On the sidelines of the
Exposition Universelle (1855) and the second
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. signatories It was not until 1954 that the connection of the southerly extension of the
Struve Geodetic Arc, a chain of survey
triangulations stretching from
Hammerfest in
Norway to the
Black Sea, 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. The Struve Geodetic arc measurement extended on a period of forty years and initiated an international scientific collaboration between
Russian Empire and the
United Kingdoms of Sweden and Norway with the involvement of proeminent astronomers such as
Friedrich Georg Wilhelm von Struve,
Friedrich Wilhelm Bessel,
Carl Friedrich Gauss and
George Biddell Airy. 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 in
Hamburg. According to geodesists, these standards were secondary standards deduced from the Toise of Peru.
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 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 1867 General Conference of the
European Arc Measurement (German:
Europäische Gradmessung) to establish the International Bureau of Weights and Measures. Moreover, it was asserted 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, because the pendulum method proved unreliable.
International Geodetic Association The intimate relationships that necessarily existed between
metrology and
geodesy explain that the
International 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 the
metric 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, General
Baeyer and Colonel
Ibáñez 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 the 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. According to a preliminary proposal made in
Neuchâtel the precedent year, 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. In 1869, the
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.
The International Metre Commission (1870/1872) and given to the United States, Carlos Ibáñez e Ibáñez de Ibero was elected president. On 19 April 1875, Ibáñez' presidency was confirmed and
Adolphe Hirsch was elected secretary of the International Committee for Weights and Measures. 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. In fact, the chemical analysis of the alloy produced in 1874 by the French section revealed contamination by
ruthenium and
iron which led the
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.
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. While the German astronomer
Wilhelm 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 the
Diplomatic Conference of the Metre and to promote the foundation of a permanent International Bureau of Weights and Measures, 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 the
Grand Officer medal of the Légion d'Honneur for his diplomatic role on this issue and was awarded the
Poncelet Prize for his scientific contribution to metrology. 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. In order to avoid the difficulty in exactly determining the temperature of a bar by the mercury thermometer,
Friedrich Wilhelm Bessel, inspired by
Jean-Charles de Borda, introduced in 1834 near
Königsberg a compound bar which constituted a metallic thermometer. A
zinc bar was laid on an
iron bar two toises long, both bars being perfectly planed and in free contact, the zinc bar being slightly shorter and the two bars rigidly united at one end. As the temperature varied, the difference of the lengths of the bars, as perceived by the other end, also varied, and afforded a quantitative correction for temperature variations, which was applied to reduce the length to standard temperature. During the measurement of the base line the bars were not allowed to come into contact, the interval being measured by the insertion of glass wedges. The results of the comparisons of four measuring rods with one another and with the standards were elaborately computed by the method of
least-squares. These comparisons were essential. Indeed,
thermal expansion, which corresponds to the increase in volume of a body caused by heating, was already well known at the time.
Pierre Bouguer had demonstrated it to a large audience at the
Hôtel des Invalides. This problem has consistently dominated all thinking regarding the measurement of geodetic standards. Geodesists were preoccupied with the constant concern of accurately determining the temperature of the length standards used in the field. Determining this variable, on which the length of measuring instruments depends, has always been considered so complex and so important that one could almost say that the history of geodetic standards corresponds to the history of the precautions taken to avoid temperature errors. In the absence of a standard temperature scale, inconsistencies arose when attempting to link geodetic surveys from different countries to create a European geodetic network. In 1886,
Adolphe Hisch, secretary of the
International Committee for Weights and Measures (CIPM) and of the
International Geodetic Association, proposed that all the toises that had served as geodetic standards in Europe during the 19th century be compared at the BIPM with the Toise of Peru and with the new
international metre so that the measurements made until then could be used to measure the Earth. The result of these comparisons made it possible to reduce the arcs measured in Germany to the metre. The discordance of which remained between the triangles common to the German and French networks could be reduced to which was at the limit of
accuracy of geodetic surveys at the time. 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 26.2·10−6 m greater during measurements carried out by
Jean-René Benoît at the BIPM.
The 1889 General Conference on Weights and Measures In 1889, the
General Conference on Weights and Measures, presided by
Alfred Descloizeaux, met at the
Pavillon 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. 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. Thus, the Contracting States also received a collection of thermometers whose accuracy made it possible to ensure that of length measurements. The
international 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.
Additional roles for standardised time In 1987 the International Bureau of Weights and Measures took over some of the work of the
International Time Bureau when it was dissolved in 1987. The remaining tasks were assigned to the
International Earth Rotation and Reference Systems Service (IERS), which replaced the
International Polar Motion Service and the earth-rotation section of the International Time Bureau. Already in 1936, irregularities in the speed of
Earth's rotation due to the unpredictable movement of air and water masses were discovered through the use of
quartz clocks. They implied that the Earth's rotation was an imprecise way of determining time. In 1967, the second was redefined based on
atomic clocks. resulting in the
International Atomic Time (TAI). The International Bureau of Weights and Measures began to establish atomic clocks world-wide, numbering more than 450 currently.
The 2019 revision of the SI The
International System of Units (SI, abbreviated from the French ''Système international (d'unités)
), the modern form of the metric system was revised in 2019. It is the only system of measurement with an official status in nearly every country in the world. It comprises a coherent system of units of measurement starting with seven base units, which are the second (the unit of time with the symbol s), metre (length, m), kilogram (mass, kg), ampere (electric current, A), kelvin (thermodynamic temperature, K), mole (amount of substance, mol), and candela (luminous intensity, cd). Since 2019, the magnitudes of all SI units have been defined by declaring exact numerical values for seven defining constants
when expressed in terms of their SI units. These defining constants are the hyperfine transition frequency of caesium Δν
Cs, the speed of light in vacuum c
, the Planck constant h
, the elementary charge e
, the Boltzmann constant k
, the Avogadro constant N
A, and the luminous efficacy K''cd. == Directors ==