Swiss Geodetic Commission

The Swiss Geodetic Commission is a commission of the Swiss Academy of Sciences, founded in 1861 within the framework of the Central European Arc Measurement, which later became the International Geodetic Association, and then the International Association of Geodesy.[1]

It initiates and coordinates geodetic research in Switzerland. It plays an advisory role in the development of Swiss geodetic policies. It contributes to disseminating geodetic knowledge to the general public. It supports the expansion of Swiss geodetic infrastructure, including the introduction of innovative methodologies and technologies. It maintains links with international institutions such as the International Association of Geodesy and the International Union of Geodesy and Geophysics.[1]

Early history

In the 19th century in particular, learned societies contributed to the emergence of national consciousness and the emancipation of the bourgeoisie. Their members, who often held influential positions, formed a link between citizens and the administration. The societies carried out public tasks and brought together people of different faiths and backgrounds. They offered scholars the opportunity to freely exchange their ideas outside of academia.[2] During the period of Geneva's annexation to France (1798-1813), the Société des Naturalistes took the name of Société de Physique et d'Histoire Naturelle (SPHN). Respectively since 1801 and 1805, Alessandro Volta and Alexander von Humboldt were honorary members of the SPHN. Henri-Albert Gosse, its founder in 1791,[3] was also behind the creation of the Swiss Academy of Natural Sciences, the first of its kind in Europe, in 1815.[4][5] In the same year, Switzerland expanded from 19 to 22 cantons with the accession of the cantons of Geneva, Neuchâtel and Valais. Guillaume-Henri Dufour, cantonal engineer in Geneva since 1817 and commissioned by the Federal Diet to superintend land surveying of Switzerland,[6][7] founded in 1838 in Carouge (canton of Geneva) a topographic office (the future Federal Office of topography),[8] which published under his direction, from 1845 to 1864, the first official map of Switzerland, on the basis of new cantonal measurements.[9][10] The map of the canton of Geneva, which can be considered Dufour's masterpiece, had been published in 1842.[11] After the Sonderbund War, the country pacified by Guillaume-Henri Dufour adopted a new Swiss Federal Constitution, inspired by the Constitution of the United States,[12] founding the federal state in 1848.[13]

The Swiss Geodetic Commission was created during the publication of the Dufour map, and its initial work contributed to the design of the Topographic Atlas of Switzerland. In 1861, Johan Jacob Baeyer proposed the creation of the Central European Arc Measurement, whose objective was to redetermine anomalies in the shape of the Earth using precise arc measurements combined with gravimetry. The aim was to figure out the geoid using gravimetric and leveling measurements to derive an accurate understanding of the Earth ellipsoid while taking vertical deflections into account.[14]

On July 7, 1861, the Prussian delegation in Bern submitted Baeyer's project to the Federal Council. The Federal Department of the Interior submitted it to Guillaume Henri Dufour, head of the Swiss Federal Office of Topography. At the 1861 session of the Swiss Society of Natural Sciences in Lausanne, the project discussed by the physics section of the Society was strongly supported by Élie Ritter and Adolphe Hirsch. On their proposal, the Society decided to give a favorable opinion on Switzerland's accession to the Central European Arc Measurement and to establish the Swiss Geodetic Commission. Its founding members were Rudolf Wolf, president (canton of Zurich), Guillaume Henri Dufour, honorary president and Élie Ritter, soon replaced by Émile Plantamour (canton of Geneva), Adolphe Hirsch (canton of Neuchâtel) and Hans Heinrich Denzler (canton of Bern).[14]

Baeyer's goal was a new determination of anomalies in the shape of the Earth using precise triangulations, combined with gravity measurements. This involved determining the geoid by means of gravimetric and leveling measurements, in order to deduce the exact knowledge of the Earth spheroid while taking into account local deflections of the plumb line due to gravity anomalies affecting gravity of Earth. To resolve this problem, it was necessary to carefully study considerable areas of land in all directions. Baeyer developed a plan to coordinate geodetic surveys in the space between the parallels of Palermo and Christiana (Oslo) and the meridians of Bonn and Trunz (German name for Milejewo in Poland). This territory was covered by a triangle network and included more than thirty observatories or stations whose position was determined astronomically. Bayer proposed to remeasure ten arcs of meridians and a larger number of arcs of parallels, to compare the curvature of the meridian arcs on the two slopes of the Alps, in order to determine the influence of this mountain range on vertical deflection. Baeyer also planned to determine the curvature of the seas, the Mediterranean Sea and Adriatic Sea in the south, the North Sea and the Baltic Sea in the north. In his mind, the cooperation of all the States of Central Europe could open the field to scientific research of the highest interest, research that each State, taken in isolation, was not able to undertake.[14][15]

In 1875, Charles Sanders Peirce conducted experiments at the Geneva Observatory with his reversible pendulum, and commissioned the Société genevoise d'instruments physiques (SIP) a vacuum chamber for his pendulum.[16][17] The former Geneva Observatory was located on the Saint-Antoine bastion, now the Promenade de l’Observatoire, opposite the main entrance of the Musée d'Art et d'Histoire (1910).[18][19] Built in 1772 at the initiative of Jacques-André Mallet, the Geneva Observatory was the first in Switzerland. In addition to astronomical observations, the institution carried out meteorological surveys and organized chronometer competitions.[20] The role of observatories in assessing the accuracy of mechanical watches was crucial in driving the mechanical watchmaking industry toward ever-higher levels of precision. As a result, high-quality mechanical watch movements today achieve extremely high accuracy. The building was demolished in 1829 and rebuilt on the same site the following year by Guillaume Henri Dufour.[20]

Charles Sanders Peirce's work promoted the advent of American science at the forefront of global metrology. Alongside his intercomparisons of artefacts of the metre and contributions to gravimetry through improvement of the reversible pendulum, Peirce was the first to tie experimentally the metre to the wave length of a spectral line. According to him the standard length might be compared with that of a wave of light identified by a line in the solar spectrum. Albert Abraham Michelson soon took up the idea and improved it.[21][22]

Significant improvements in gravity measuring instruments must also be attributed to Friedrich Wilhelm Bessel. He devised a gravimeter constructed by Adolf Repsold which was first used in Switzerland by Emile Plantamour, Charles Sanders Peirce and Isaac-Charles Élisée Cellérier (1818–1889), a Genevan mathematician soon independently discovered a mathematical formula to correct systematic errors of this device which had been noticed by Plantamour and Adolphe Hirsch.[23][24] In 1875, the Conference of the European Arc Measurement dealt with the best instrument to be used for the determination of gravitational acceleration. After an in-depth discussion in which Charles Sanders Peirce took part, the association decided in favor of the reversion pendulum, which was used in Switzerland, and it was resolved to redo in Berlin, in the station where Friedrich Wilhelm Bessel made his famous measurements, the determination of gravity by means of devices of various kinds employed in different countries, to compare them and thus to have the equation of their scales.[25] This work led in 1901 to the Earth ellipsoid proposed by Friedrich Robert Helmert, whose parameter values were remarkably close to reality. Helmert determined a value of ⁠1/298.3⁠ for the flattening of the Earth to be compared with that of ⁠1/298.25⁠ obtained from the analysis of the first satellites measurements.[26][27]

The European Arc Measurement also decided the creation of an international geodetic standard at the General Conference held in Paris in 1875. Thus, the Commission resolved to acquire, at common expense, a measuring instrument which was to be used either to measure new bases in countries which did not have their own device or to repeat previous measurements. The comparisons of the new results with those provided by the old national standards would make it possible to obtain their equation. The apparatus would to be calibrated at the International Bureau of Weights and Measures (BIPM), using the international prototype metre. The system with a microscope and bimetallic rulers, which had given such brilliant results in Spain, was proposed.[25]

When Spain decided the creation of a large-scale map of Spain in 1852, 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 Wilhelm Bessel simply joined measuring the intervals by means of vernier callipers 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, and which Ibáñez ameliorated using a single standard with lines marked on the bar.[30][a][b]

The creative side of Ferdinand Rudolph Hassler was seen in the design of new surveying instruments. Most original was Hassler's baseline apparatus which involved an idea worked out by him in Switzerland and perfected in America. Instead of bringing different bars in actual contact during the process of baseline measurements, he used four two-metre (6 ft 7 in) iron bars fastened together totaling eight metres (26 ft) in length and optical contact.[32][41] As early as February–March 1817, Hassler standardized the bars of his device which were actually calibrated on the Committee meter (an authentic copy of the Mètre des Archives) which was the property of the American Philosophical Society, to whom it had been presented by Hassler himself, who had received it from Tralles, a foreign member of the French Committee charged with the construction of the standard metre by comparison with the Toise of Peru, which had served as unit of length in the measurement of the meridional arcs in France and Peru. The Committee meter possessed all the authenticity of any original metre extant, bearing not only the stamp of the committee, but also the original mark by which it was distinguished from the other bars during the operation of standardising.[42][41]

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.[43][44] However, the baselines for this map had been 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.[45][46][c] One of these baselines, which extended from Walperswil to Sugiez, had already been measured twice in 1791 and 1797 by Hassler and Tralles, first with a chain such as the one Jesse Ramsden made for the Anglo-French Survey (1784–1790), then with an apparatus of four toise bars calibrated on a toise of Jacques Canivet.[49][50]

In Europe, surveyors continued to use measuring instruments calibrated on the Toise of Peru.[45][51] Ibáñez and Frutos Saavedra Meneses went to Paris to supervise the production by Jean Brunner of a measuring instrument calibrated against the metre which they had devised. In 1856, the length of the rulers was determined by comparison with Borda's double-toise N°1 which was the main reference for measuring all geodetic baselines in France and whose length was by definition 3.8980732 metres at a specified temperature.[52][51] From 1865 to 1868, Carlos Ibáñez e Ibáñez de Ibero added the survey of the Balearic Islands with that of the Iberian Peninsula.[53] For this work, he devised a new instrument.[54][42] This device, called the Ibáñez apparatus, was calibrated on the Spanish standard and would be used in Switzerland to measure the geodetic bases of Aarberg, Weinfelden and Bellinzona. In June 1886, following these operations, the Ibáñez apparatus was recalibrated on Brunner's international bimetallic device (itself calibrated on the international prototype metre) at the International Bureau of Weights and Measures (BIPM).[55][25]

The International Statistical Institute was founded in 1885 during the Jubilee of the Royal Statistical Society, coinciding with the 25th anniversary of the Société de statistique de Paris.[56][d] Its origins can be traced back to a series of international statistical congresses, the first of which was chaired by Adolphe Quetelet and held in Brussels in 1853, following the Great Exhibition of 1851 organized in London at the initiative of Prince Albert of Saxe-Coburg-Gotha, husband of Queen Victoria.[57][59] Alongside the 1855 Universal Exhibition and the second Statistical Congress held in Paris, an International Association for Obtaining a Uniform Decimal System of Measures, Weights and Coins was created in 1855.[60] Under the impetus of this association, a Comité des poids mesures et monnaies was established at the 1867 Universal Exhibition in Paris,[61] which called for the international adoption of the metric system.[62][38]

In the 19th century, statisticians knew that scientific observations were subject to two types of error: constant errors and random errors. The effects of the latter could be corrected using the least squares method. Constant errors, on the other hand, had to be carefully avoided, as they were caused by various factors that consistently altered the results of observations in the same direction. These errors thus tended to render the results they affected worthless. Consider, for example, measuring a straight line to determine its length in metres. If a metal ruler is used for this measurement, and an error is made in determining the temperature at which its length corresponds to that of a metre, all observations will be affected by a consistent error stemming from this error, and no matter how many times the operation is repeated, it will be impossible to obtain an accurate result. If, on the contrary, we know exactly the temperature at which the ruler is equivalent to the metre and if the error affects the actual temperature of the ruler in the different observations, each observation will be affected by a random error, but these errors will occur sometimes in one direction and sometimes in the other, and by repeating the operation a large number of times we can hope to eliminate their effect by compensating for them.[63]

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.[45][64] It had been the consideration of the divergences between the different toises used by geodesists that had led the Central European Arc Measurement (German: Mitteleuropäische 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 BIPM.[65][54][e] Careful comparisons with several standard toises showed that the international metre calibrated on the Mètre des Archives was not exactly equal to the legal metre or 443.296 lines of the toise, but, in round numbers, ⁠1/75 000⁠ of the length smaller.[73][f]

Thus, a difference of ⁠1/65 000⁠ between the French and Spanish triangulations appeared when the French triangulation, which until then, like the Spanish triangulation, was based on measurements taken with instruments calibrated on Borda's double-toise N°1,[51] was reduced to the International prototype metre, itself referred to the Mètre des Archives.[75][g] By contrast, in 2007, a comparison of the American Committee meter and its Swiss counterpart was carried out at NIST and METAS. The two metre standards can be considered perfectly equivalent, with a difference of only (0.96 ±3.0) micrometres. The poor quality of the measuring surfaces explained the significant uncertainty in the measurements compared to today's standards.[76]

As Carlos Ibáñez e Ibáñez de Ibero stated, the International prototype metre would form the basis of the new international system of units, but it would no longer have any relation to the dimensions of the Earth that geodesists were trying to determine. It would be no more than the material representation of the unity of the system.[23] In his 2002 book The measure of all things, Ken Alder recalled that the metre is about 0.2 millimetres shorter than it should be according to its original proposed definition. However, the error in measuring the length of Paris meridian represented less than 2% of the total error, and the error due to a flawed assumption about the shape of the Earth contributed to approximately 3% of the total error. If the meticulous work of Pierre Méchain and Jean Baptiste Delambre were the only source of error, the current metre would be too long by less than 4 μm instead of being too short by 197 μm. The 95% of the missing length of the metre is due to the failure to account for vertical deflections; this was beyond the scope of Delambre and Méchain because the Earth's gravitational field had not yet been studied.[79][80]

Current work

The commission continues its work today, combining fundamental research with stimulating its practical application.[1]

See also

Notes

  1. ^ The American Revolution, in which the United States was supported by France and Spain,[31] led to the founding of the Survey of the Coast in 1807 and the creation of the Office of Standard Weights and Measures in 1830.[32] In 1830, Ferdinand Rudolph 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 coefficients of expansion to assess temperature effects on the measurements.[33] In 1834, Hassler, measured at Fire Island the first baseline of the Survey of the Coast,[34] 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 meridian arc measurement, which had been used to determine the length of the metre.[35] Nevertheless, 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.[36]
  2. ^ Heinrich von Wild is another example illustrating the role played by Swiss scientists in 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, the Swiss born director of the Central Geophysical Observatory in Saint Petersburg,[37] and Moritz von Jacobi inviting his French counterpart to undertake joint action to ensure the universal use of the metric system in all scientific work.[38] The Swiss physicist and meteorologist was delegated by Russia to the International Metre Commission in 1870, to the Diplomatic Conference of 1875, and, after the signing of the Metre Convention, to the International Committee for Weights and Measures. 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,[39] 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.[40]
  3. ^ The Helvetic Republic adopted the metric system by law in 1801. However this was never applied, because in 1803 the competence for weights and measures returned to the cantons. On the territory of the current canton of Jura, then annexed to France (Mont-Terrible), the metre was adopted in 1800. The Canton of Geneva adopted the metric system in 1813, the canton of Vaud in 1822, the canton of Valais in 1824 and the canton of Neuchâtel in 1857. In 1835, twelve cantons of the Swiss Plateau and the north-east adopted a concordat based on the federal foot (exactly 0.3 m) which entered into force in 1836. The cantons of central and eastern Switzerland, as well as the Alpine cantons, continued to use the old measures. According to the 1848 Constitution the federal foot was to come into force throughout the country. In Geneva, a committee chaired by Guillaume Henri Dufour militated in favor of maintaining the decimal metric system in the French-speaking cantons and against the standardization of weights and measures in Switzerland on the basis of the metric foot. In 1868 the metric system was legalized alongside the federal foot, which was a first step towards its definitive introduction. Cantonal calibrators were supervised by a Federal Bureau of Verification created in 1862, whose management was entrusted to Heinrich von Wild from 1864. In 1875, the responsibility for weights and measures was transferred back from the cantons to the Confederation, and Switzerland (represented by Adolphe Hirsch) joined the Metre Convention. The same year a federal law imposed the metric system from 1 January 1877.[47][48]
  4. ^ The 81 founding members of the International Statistical Institute constituted the elite of statisticians of that era within government administrations and scientific academies.[57] In Rome, in 1887, the International Geodetic Association and the International Committee for Weights and Measures were represented at the first session of the International Statistical Institute (now the ISI World Statistics Congress), notably by their president and delegate from Spain, Carlos Ibáñez e Ibáñez de Ibero.[58]
  5. ^ In 1866 Spain, represented by Carlos Ibáñez e Ibáñez de Ibero, joined the Central European Arc Measurement at the Permanent Commission meeting in Neuchâtel.[66][67] Ibáñez announced that Spain would collaborate in remeasuring and extending the French meridian arc and presented two of his works, translated into French by Aimé Laussedat, to the Permanent Commission of the Central European Arc Measurement. These were Expériences faites avec l'appareil à mesurer les bases appartenant à la commission de la carte d'Espagne, which relates the comparison of Borda's double-toise with the Spanish ruler,[51] and Base centrale de la triangulation géodésique d'Espagne, which contains the report of the comparison of the Spanish ruler and the Egyptian ruler.[68][67] From 1870 to 1894, François Perrier, then Jean-Antonin-Léon Bassot proceeded to a new survey.[69] In 1879 Ibáñez and François Perrier completed the junction between the geodetic networks of Spain and Algeria and thus completed the measurement of a meridian arc which would extend from Shetland to the Sahara.[70] This connection was a remarkable enterprise where triangles with a maximum length of 270 km were observed from mountain stations (Mulhacén, Tetica, Filahoussen, M'Sabiha) over the Mediterranean Sea.[71][72]
  6. ^ The metre according to the older relation was called the “legal metre,” according to the new relation the “international metre.” The values were: Legal metre＝3·28086933 ft., International metre＝3·2808257 ft.[73] Since 1959, the yard has officially been defined as exactly 0.9144 metre.[74]
  7. ^ Assuming a linear thermal expansion coefficient of 11.6·10−6 °C-1 for steel,[76] the difference between the Spanish metre (or legal metre defined as 443.296 lines of the Toise of Peru) and the international metre (defined as the length of the Mètre des Archives) must be related to a temperature error of approximately 1.3 °C during the calibration of Borda apparatus, which was used for baseline measurements of the Arc measurement of Delambre and Méchain.[77][78]

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