The earth sciences crusades of the 1830s and 1840s

In the 1830s a new regime of observation, involving simultaneously organized observation campaigns, emerged and restructured the developing fields of meteorology and geomagnetism. The term ‘regime of observation’ designates an ideal-typical set of practices and discourses structuring a certain kind of scientific observation. These campaigns mobilized observers who carried out series of simultaneous observations. These observations were short, typically lasting a few days, but intensive, being conducted once every hour or every five minutes, for example. In 1834 the German physicists Carl Friedrich Gauss and Wilhelm Weber organized a vast observation programme, the Magnetischer Verein. They simultaneously introduced an original measurement device for magnetic intensity derived from Coulomb's torsion balance. They called on observers to take part in simultaneous observations of the terrestrial magnetic field. In 1838 they observed the direction and the intensity of the field every five minutes during twenty-four hours on the last Saturday of the month. Dörries has explained how from 1836 to 1840 magnetometric expertise was transferred from Germany to Britain. From 1835 a group of British scientists promoted the study of geomagnetism throughout the empire. This group emerged from the first circle of the British Association for the Advancement of Science (BAAS); Edward Sabine, Humphrey Lloyd and John Herschel all belonged to it. Herschel was at Cape Town until 1838; on his return to Britain he became enthusiastic about the Magnetischer Verein campaigns. He then used his political and academic connections to promote the British ‘magnetic crusade’. That ‘crusade’ implied the organization of simultaneous magnetic observation campaigns and the creation of a network of permanent magnetic stations. The British magnetic campaigns were to be continued until 1848, while Gauss and Weber abandoned the field of geomagnetism at the start of the 1840s. The Paris Observatory took part in neither the British nor the German campaigns. Between 1835 and 1840 the Paris Observatory indeed lost the leadership it had held in the field. French geomagnetic observations, made during the course of scientific expeditions with Gambey's compasses, were becoming obsolete in comparison with the Anglo-German simultaneous campaigns, which used Gauss and Weber's magnetometer set-up in fixed observatories.

Adolphe Quetelet, the Brussels Observatory and the meteorological simultaneous campaigns

Simultaneous observation campaigns also occurred at the same time in the field of meteorology. During his first year in Cape Town in 1834,Footnote ² Herschel planned simultaneous meteorological observation campaigns within the framework of a local learned society, the South African Literary and Scientific Institution.Footnote ³ Herschel invited its members to observe the barometer and the thermometer every hour at solstices and equinoxes. Herschel was inspired by Humphrey Lloyd, who on those same days carried out intensive series of magnetic observation in his Dublin Observatory.Footnote ⁴ In May 1835 Herschel wanted to get observations related to the Northern Hemisphere. He wrote to the director of the Brussels Observatory, Adolphe Quetelet, to ask him to take part in the meteorological campaigns.Footnote ⁵ Quetelet agreed and began observing at the 1835 summer solstice.

Quetelet is known as one of the most important figures of the nineteenth-century statistical sciences.Footnote ⁶ Yet his importance in the development of earth sciences from the middle of the 1830s to the beginning of the 1860s has been neglected. Quetelet was the director of the Brussels Observatory from its effective creation in 1832.Footnote ⁷ From 1835 to 1845 he devoted himself almost entirely to ‘his’ observatory. He promoted what he called the Physique du globe. This included studies related to meteorological, magnetic and electrometric observations, and studies of physical meteors, tides and marine currents. In the same decade, after the publication of his major work in social statistics, Quetelet published fifty-seven papers of which thirty-nine are related to his programme of Physique du globe.Footnote ⁸ He published only five articles on astronomy, four of which were notes concerning astronomical ‘events’, and but four articles on geodesy. He devoted only three short articles to social statistics in that decade.

After 1840 Quetelet succeeded John Herschel as coordinator of simultaneous meteorological observation campaigns. Once he returned to England in May 1838 Herschel gradually disengaged himself from the campaigns he had organized. On 25 October 1838 he wrote to Quetelet asking him to halt his simultaneous observations. Herschel was overwhelmed by the amount of observations he was collecting. In June 1836 he had already written to Quetelet that those campaigns would soon exceed his individual capacities due to ‘the quantity of calculations’ and ‘the huge correspondence’ they required.Footnote ⁹ He was also disappointed by how little he was able to deduce from the observations. Before 1840 Quetelet merely recruited the Brussels Observatory and some Belgian volunteers to Herschel's meteorological observation campaigns. In addition, in January 1840 he joined the German and British magnetic campaigns. A magnetometer was installed in a wooden shed in the gardens of the Brussels Observatory.Footnote ¹⁰ The observations were carried out in accordance with the instructions of Gauss and Weber's journal, the Resultate des Magnetischen Vereins. Taking part in simultaneous observation campaigns, Quetelet wanted firmly to place the Brussels Observatory within the European scientific landscape. However, his ambitions could at that stage only remain modest. His involvement in geomagnetic and meteorological studies was to some extent a choice by default. The Belgian observatory had neither financial, nor technical, nor human means to become a first-rank astronomical observatory. In that context, Quetelet saw Herschel's withdrawal from the field as an unexpected opportunity.

With the British astronomer's agreement, Quetelet sought to replace him in managing the centralization of the observations made at the solstice of December 1840. In previous years, Quetelet had extended the initial network of observers: in 1842 there were forty-one, spread throughout Belgium (three), France (eleven), Italy (six), Holland (six), Switzerland (four), Austria (four), the United Kingdom (three), Prussia and Bavaria (two), Luxembourg (one) and Spain (one). The observations were published in the Bulletin and the Mémoires de l'Académie Royale des Sciences de Bruxelles. Quetelet supervised them until 1844, when he decided to withdraw from their organization.Footnote ¹¹ He then asked his correspondents to send their observations to Johann von Lamont, director of the Munich Observatory. But the transition was difficult and the campaigns were quickly thrown into disarray.

Auguste Bravais, Charles Martins and the expedition of La Recherche

The Paris Observatory took part in neither the British nor the German geomagnetic campaigns of the 1830s and 1840s. Nor did it take part in the meteorological campaigns. I have found no mention of an explicit request from Quetelet to Arago in the archives of the Paris Observatory nor in the correspondence of the Belgian scientist. The director of the Paris Observatory presumably simply ignored Quetelet's calls to observers in the same spirit that Sabine summarized in a letter to Lloyd in January 1840 about the geomagnetic campaigns: ‘Arago either has not or pretends not to have much notion of what our system is.’Footnote ¹² In France it was instead a scientific expedition organized by the Navy that prompted the renewal of the earth sciences in the 1830s and 1840s. In spring 1838 the corvette La Recherche left the port of Le Havre for the north of Lapland. This was the second expedition of the corvette into the Arctic. In 1835 and 1836 La Recherche had sailed the same seas looking for the barque La Lilloise, which had disappeared in August 1833. At the time of this initial expedition the marine surgeon and naturalist Paul Gaimard recruited two scientists, two artists and a littérateur to study polar regions. On his return to France Gaimard sought to set up a second expedition of La Recherche, this time with a purely scientific goal. He met King Louis-Philippe, who supported the project. A second expedition was planned by the French Navy. Among the six members of the first expedition was the lieutenant de vaisseau Victor Lottin of the French Navy. Lottin had already taken part in many scientific expeditions. Notably, he circumnavigated the globe with Jules Dumont D'Urville and Louis Duperrey aboard La Coquille in between 1822 and 1825. In 1835 and 1836 he had supervised the astronomical, meteorological and geomagnetic observations of the first La Recherche expedition. The team for the second expedition also included Gaimard, the painters Bevalet and Mayer, the geologist Eugène Robert and the littérateur Xavier Marmier.Footnote ¹³ Paul Gaimard also supplemented his team with a physicist, Auguste Bravais, and a naturalist, Charles Martins.

Auguste Bravais was born in Annonay.Footnote ¹⁴ After a preparatory class in Paris, in 1829 he entered the Ecole polytechnique. At the end of the polytechnic curriculum he chose to join the Navy. Assigned to a non-scientific position, he pursued his personal research. He spent his vacations in the family house where he maintained intense botanical activity in collaboration with his brother Louis. Bravais was especially interested in studies concerning the terrestrial environment (including meteorology, geomagnetism and hydrography) and in astronomy. He thus busied himself during his vacation at the start of 1837 in following the course taught by François Arago at the Paris Observatory. Bravais had an exceptional mastery of analytical and geometrical techniques, due to his studies at the Ecole polytechnique. In the 1830s Simon-Denis Poisson was his academic protector. Bravais and Poisson shared the same scientific style, characterized by major use of analytical developments.Footnote ¹⁵ At the beginning of 1837 both Bravais's father and brother pressed him to apply for a position in the second expedition of La Recherche; they thought this participation would help his scientific career. Gaimard agreed in March 1837.Footnote ¹⁶

In a letter to Gaimard, Bravais recommended one of his friends, Charles Martins, for the expedition.Footnote ¹⁷ Martins spent his first twenty years in Switzerland and was fluent in both French and German. He had then come to Paris to study medicine and completed his doctorate in 1834. Martins was especially interested in natural sciences and was assistant to the botany chair at the Paris Medical School. Charles Martins and Auguste Bravais first met in the middle of the 1830s through Auguste's older brother, the naturalist Louis Bravais. They often collected plant specimens together around Annonay. In 1837 Bravais recommended Martins to Gaimard by praising his bilingualism and his medical skills. A follower of Alexander von Humboldt and Augustin-Pyramus De Candolle, Martins was in 1837 finishing an important work on the botanical geography of the Mont Ventoux. This work was to be published the following year in the Annales des sciences naturelles. Footnote ¹⁸ Martins had studied the limits in altitude of several vegetal species and systematically used the barometer to determine the altitude of each plant collected or observed; hypsometry was thus one of his concerns. These practical skills were another argument in his favour. Bravais suggested that Martins and he could work together on hypsometric measurements.Footnote ¹⁹

La Recherche left Le Havre on 13 June 1838 with Bravais and Martins on board; five Scandinavian scientists joined the team en route.Footnote ²⁰ After a stop in the port of Hammerfest, La Recherche reached Bell Sound on the west coast of Spitzbergen on 25 July 1838. However, on 5 August La Recherche had to leave the bay and dropped anchor in Hammerfest on 12 August. The corvette came back to France at the end of the month, but five members of the scientific team spent the autumn and winter of 1838 near Hammerfest in a scientific residence. The group was composed of three Navy officers familiar with the physical and hydrographic sciences (Lottin, Bravais and the Swedish Carl Bertil Lilliehöök), a member of the Stockholm Observatory (Per Adam Siljeström) and a French painter of natural history (Bevalet). Settling in at the end of August 1838, they occupied the small trading post of Bossekop in the fjord of Alten. There they set up a permanent site of scientific observation mainly dedicated to meteorology and geomagnetism.

The Bossekop ‘land-based ship’ and the meteorological campaigns

The scientific team carried out meteorological simultaneous observation campaigns at Bossekop and on board La Recherche. Bravais and Martins planned them under their own initiative, relying upon instructions written by Herschel.Footnote ²¹ These instructions prescribed observation on the hour during a day and a half, at solstices and equinoxes, as well as on the first and third Saturday of the month. On 12 June 1838, just before boarding, Bravais and Martins wrote to Jean-François Delcros, a retired military engineer–geographer, to ask him to carry out observations in Paris.Footnote ²² They wanted to ensure, at the very least, a corresponding series in France. Bravais and Martins met Delcros during the preparations for the trip. Delcros had a special relationship with the instrument-maker Ernst, who provided barometers for La Recherche. He was something of a relay between the maker and the scientific community. An expert on hypsometry, he testified to the quality of the Ernst barometer. Delcros accepted the request and observed throughout the expedition.

At Bossekop the campaigns were carried out at the times prescribed by Herschel and a continuous observation series was also pursued. Thirty years later, in a funeral eulogy of Bravais, the geologist Léonce Elie de Beaumont described that continuous activity. He wrote that the men worked ‘with the same regularity as in a warship’.Footnote ²³ From 1 September 1838 until 6 April 1839 all the settlers except Bevalet observed the meteorological instruments every two hours by rotation.Footnote ²⁴ When onboard La Recherche Bravais had already made observations, together with Lottin and Martins. The series was started during the trip from Le Havre to Bell Sound and pursued until La Recherche returned to France. The meteorological observations formed part of a social practice specific to the marine world: the regular maintenance of the systematic naval watch. This kind of practice was to be pursued on land at the Bossekop observatory. From this perspective, the observatory therefore resembled a ‘land-based ship’: a place where domestic and work spaces were largely merged in a context of strict discipline and with the existence of what might be called a ‘(meteorological) watch’. This ‘meteorological watch’ was part of a regime of observation that can be characterized as ‘hypso-meteorological’. It emerged in the 1810s in the context of the hypsometric researches then undertaken by Pierre-Simon Laplace and Louis-François Ramond de Carbonnières. In 1811 Ramond described a hypsometric protocol in a section entitled ‘Instruction élémentaire et pratique sur l'application du baromètre au calcul des hauteurs’ of his Mémoires sur la formule barométrique.Footnote ²⁵ This text was mainly concerned with field operations, but it also included a section devoted to sedentary practices and summarized the hypso-meteorological regime.

Under this regime observers conducted long series of meteorological observations. They observed for months or years, each day at midday, and in the morning, afternoon and evening, at Ramond's three ‘critical times’. One of the essential functions of these observations was their use as permanent hypsometric references. In order to permit comparisons, the sedentary observers systematically provided the scientific community with all the details of the barometer they used: its constitution and its conditions of use; its site, reduction protocols and computing methods; and the state of the atmosphere around the instrument. The measurements had also to be reduced to a virtual common environment. Reduction of pressures to a common temperature provided the third main characteristic of the hypso-meteorological regime of observation, together with time regularity and instrumental transparency.

This regime was disseminated to all French observatories during the 1810s. In 1816 meteorological observations were reorganized on this basis at the Paris Observatory by Arago.Footnote ²⁶ Earlier observations organized in 1785 by Cassini IV, resumed in 1798 under Louis Cotte's supervision, included barometric and thermometric readings carried out irregularly.Footnote ²⁷ They aimed to record the ‘meteorological events’ of the day, the absolute maximum and minimum of pressure and temperature.Footnote ²⁸ From 1816 observations were performed at noon and at Ramond's fixed critical times at the Paris Observatory. In contrast with earlier practice, pressures were systematically reduced to a common temperature. This series was to be pursued until 1855. Laplace made use of it in the 1820s to evaluate the gravitational action of the Moon on the atmosphere.Footnote ²⁹ It was this kind of observation which was transferred onboard scientific exploration ships during the Restoration and the July Monarchy.Footnote ³⁰ But in an expeditionary context, the temporal regularity of the meteorological observations was uniform in order to determine the times of barometric extremes.

In Bossekop the settlers kept a ‘meteorological watch’, characteristic of the ‘hypso-meteorological’ regime of observation, and at the same time they carried out the new meteorological simultaneous observation campaigns. The same syncretism prevailed in geomagnetic observations. In June 1838, when La Recherche left Le Havre, the French model of geomagnetic observation, which included low-precision measurements performed in the context of a scientific expedition by means of Gambey's compasses, was in clear competition with the Anglo-German model, which included precision observations using Gauss and Weber's magnetometers installed within fixed observatories. The geomagnetic work of the expedition of La Recherche was a synthesis of these two models. At Bossekop the scientists used both compasses and magnetometers. Both types of instrument were used in a ‘geomagnetic watch’ and in the simultaneous observation campaigns of the Magnetischer Verein, conducted on the final Saturday of the month every five minutes during 24 hours.Footnote ³¹ The organization of the over-wintering also compromised between the French and the Anglo-German models of practice. Bossekop was not a permanent observatory, but the over-wintering lasted several months and took place in wooden sheds – semi-permanent constructions. Observations produced in the ‘land-based ship’ of Bossekop then appear as somewhat intermediary between maritime observations or at a temporary landing, as in the French model, and observations in fixed sites, as suggested by the Anglo-German precedent. The Bossekop scientific team sent its observations both to Arago and to Gauss, who published them in his Resultate des Magnetischen Vereins.

European barometers and Quetelet's network

After the end of their over-wintering, Bravais and Martins carried out the Herschelian meteorological campaigns during their trip overland from Bossekop to Paris.Footnote ³² This trip was also an opportunity to inspect the barometers of Germanic and Scandinavian Europe. This investigation was published in 1841 in the Mémoires de l'Académie Royale des Sciences de Bruxelles. Footnote ³³ Bravais and Martins gave Quetelet an inventory of observation conditions in this region of Europe. The Belgian astronomer then used this information when in 1842 and 1843 he published all the details concerning the origin, construction, installation and use of instruments in his simultaneous meteorological observation campaigns. During their journey Bravais and Martins brought with them two of the six Ernst–Fortin barometers from La Recherche. They observed in Uppsala and Stockholm observatories (October and November 1839), in the Copenhagen Polytechnic School (at the end of November 1839), in the Altona and Berlin observatories (during December 1839), in the Dresden ‘mathematical salon’ (at the end of December 1839), in Ludwig Kaëmtz's house in Halle (at the beginning of January 1840), in the Göttingen and Brussels observatories (January 1840) and finally in the Paris Observatory (at the beginning of February 1840). This investigation was also an opportunity to be introduced into the erudite society of these European territories. They met Humboldt in Berlin, the meteorologist Ludwig Kaëmtz in Halle and Quetelet in Brussels.

Bravais and Martins took note of all the characteristics of the barometers they inspected. Essential was the maker's name and the instrument's serial number, because this ensured its traceability. Reference to a maker could itself be a criterion of precision and reliability. A small number of makers were of high repute: Ernst in Paris, Pistor and Schieck in Berlin, Buzengeiger in Tübingen, Hoffmann in Leipzig. In their article Bravais and Martins gave very detailed descriptions of the barometers, in particular the dimensions of the barometric tubes, cisterns and scales. They directly measured the instruments to an accuracy of one millimetre or a tenth of a millimetre. They also carried out systematic comparisons between their Ernst–Fortin barometers and those they inspected, in order to evaluate the ‘imperfections des baromètres’ and the ‘erreurs d'observation’.Footnote ³⁴

This latter expression designated individual observational error.Footnote ³⁵ Bravais's and Martins's programme was also an investigation into the observers of Germanic and Scandinavian Europe. On at least four occasions they carried out their barometric comparisons using a two-stage procedure. First the local observer read his own barometer; at the same time either Bravais or Martins read one of their two Ernst–Fortin instruments. Then, immediately after the Frenchmen, the local observer read the level indicated by the Ernst–Fortin barometer. Bravais and Martins concluded that the mean excess in the observation of their Ernst–Fortin device in comparison with their own readings was 0.09 mm (Uppsala), 0.08 mm (Halle), 0.031 mm (Göttingen) and 0.005 mm (Altona).Footnote ³⁶ They identified the evaluation of the point of contact of the ivory tip with the mercury surface of the barometric cistern as the cause of these differences.Footnote ³⁷ In 1841, in their article in the Mémoires de l'Académie Royale des Sciences de Bruxelles, they were to suggest that microscopes be added to the barometric devices to eliminate this problem.

In these efforts to improve the barometric system, Bravais and Martins's aim was then to study the existence of small barometric oscillations, observed simultaneously in distant sites during the course of Quetelet's observation campaigns.Footnote ³⁸ Bravais and Delcros had been involved in these campaigns since spring 1840 after their return to France. Quetelet then wrote to Bravais to ask for his participation. He began observing at the spring equinox of 1841.Footnote ³⁹ Quetelet also asked Delcros, who in turn recruited some users of Ernst–Fortin barometers. Five were to contribute to the campaigns. Delcros sent them a description of Quetelet's meteorological programme and a specimen observation form.Footnote ⁴⁰ Thus Bravais and Delcros participated in an important way in the extension of Quetelet's campaigns in France.

An avalanche of graphs and maps

The meteorological and geomagnetic campaigns of the 1830s and 1840s contributed to the ‘avalanche of printed numbers’ described by Ian Hacking as taking place during the second quarter of the nineteenth century.Footnote ⁴¹ This massive production of numbers was accompanied by the development of new ways of treating bodies of numerical data using graphs and maps. These graphical techniques were central at Bossekop, where Bravais and Lottin plotted graphs of meteorological and geomagnetic parameters, producing bar graphs and smoothed curves.Footnote ⁴² The Resultate des Magnetischen Vereins published graphs of magnetic declination and intensity in the stations participating in the German campaigns. With respect to the meteorological campaigns, from 1840 Quetelet systematically plotted series of barometric curves representing pressure variations over intervals of thirty-six hours at the sites where observations were carried out.Footnote ⁴³ He was deeply influenced by the graphic culture that existed among British scientists such as James David Forbes, John Herschel and William Whewell. This production of graphs was aimed at the visual comparison of pressure variations to study the synchronicity of the barometric oscillations in different places.Footnote ⁴⁴

In order to pursue analysis of his meteorological observations, at the end of the 1840s Quetelet developed a new method of presenting and analysing observational data and simultaneously suggested an interpretative theory of atmospheric evolutions. Quetelet drew his inspiration from a research programme carried out in the 1840s by William Radcliffe Birt under the influence of John Herschel.Footnote ⁴⁵ According to Birt a range of pressure waves propagated permanently on the Earth's surface; through mutual interference some of these waves were at the origin of storms. His theory was based on the analysis of graphs representing the variation of pressure over time in different places. In 1851 Quetelet gave his own version of this atmospheric-wave theory, initiating an important innovation in terms of cartographic representation.Footnote ⁴⁶ He collected all the barometric observations available for Europe and Asia for June, July and August 1841. He plotted the curves representing the variations of the barometric pressures in about twenty stations from Brussels to Beijing. He used these graphs to work out the days and hours of extreme pressure in these stations. Then Quetelet plotted continuous lines on a geographical map of Eurasia. These isolines linked places where the barometer was at a maximum for a given day and hour. He identified these lines as the crests of the atmospheric waves. With these isochronic lines, Quetelet took part in Humboldt's wake in the development of a fundamental tool of scientific culture, the isoline, by extending its use to the analysis of temporal variations.

Conclusion

In the 1830s and 1840s a spectacular development of geomagnetic and meteorological studies took place on a European level. This development was multi-centred. In Germany, at the end of the 1830s, Gauss and Weber conceived new devices of measurement of the terrestrial magnetic field and promoted the first simultaneous observation campaigns, in the framework of their Magnetischer Verein. In Great Britain a group of scientists involved in the creation of the BAAS organized a programme of data accumulation about the terrestrial environment, which included a massive production of magnetic and meteorological observations. The British ‘magnetic crusade’ led to a modification of Gauss and Weber's geomagnetic devices, the organization of simultaneous magnetic observation campaigns and the creation of magnetic stations in the British colonies. The meteorological simultaneous campaigns were envisioned and promoted by John Herschel, before Quetelet replaced him in the project of the centralization of observations. In the 1840s William Radcliffe Birt exploited the enormous amount of observations available by using graphical representations of the variations of pressure, in the context of his atmospheric-wave theory.Footnote ⁴⁷

Geomagnetic and meteorological observation campaigns recruited observers in France, in both sedentary and expeditionary contexts. The paper has identified a group of scientists (such as Bravais, Martins, Lottin) who were peculiarly receptive to the new ethos of production and use of data concerning the terrestrial environment. As regards Bravais, one can partly explain this tendency by reference to his identity as scientific serviceman. He had real experience and interest in exploration and field sciences, partly due to his service as marine officer. But at the same time, he was trained at the Polytechnique and was Poisson's follower. He shared his master's ideal of mathematization and his passion for precision in measurement. This might explain his interest in new forms of observation in the 1830s and 1840s, at the time when Arago refused to take them into account. In addition, his opposition to the director of the Paris Observatory reflected the old disputes between Arago and Poisson, one of his main academic competitors. This was also in accordance with the context of the second expedition of La Recherche, through which Gaimard sought to impose his own authority against Arago in the business of scientific exploration.

At Bossekop the settlers adopted a model of scientific over-wintering that represented a synthesis between the ‘classical’ French observations and the new regime of simultaneous observation campaigns. After their return to France, they participated in Quetelet's meteorological campaigns and on one occasion in a geomagnetic one. On 18 March 1840 Lottin, Bravais and Martins met in a house at Vaujours near Paris. Using a magnetometer from the expedition of La Recherche, they performed observations on behalf of the British magnetic crusade. This initiative remained unique, but it revealed once again the desire to take part in the geomagnetic campaigns despite Arago's opposition. Bravais sent these observations to Quetelet, who published them in the Bulletin de l'Académie Royale des Sciences de Bruxelles. Footnote ⁴⁸ In doing so, Bravais and Martins avoided calling upon Arago, without directly publishing in a British periodical. Bravais and Martins also published their works relating to earth sciences in the Mémoires of the Brussels academy. In France the main scientific publications, the Comptes rendus de l'Académie des sciences and the Annales de chimie et de physique, controlled by Arago, did not then publish texts relating to the earth science crusades of the 1830s and 1840s. Belgian publications offered Bravais and Martins an opportunity to contribute to these crusades without the need to publish in Germany or in Great Britain, but instead in French, in periodicals controlled by Quetelet.

Between 1840 and 1844 Quetelet organized European meteorological campaigns structured, in term of convergence and publication of observations, around the Brussels Observatory. After succeeding Herschel, the Belgian astronomer used his personal connections to promote the meteorological campaigns in France. He was in touch with Bravais and Martins: they observed and recruited for him and he published their scientific articles and their data. Thus the Brussels Observatory constituted a buffer zone between the British, French and German scientific communities, matching the position of Belgium at the intersection of these three national and linguistic spaces. That function was to be essential in the creation of the intellectual and material culture of dynamic meteorology. Quetelet's version of the atmospheric-wave theory was to inspire the activity of the meteorological service of the Paris Observatory after Arago's death.Footnote ⁴⁹ It was to be at the basis of the development, in the 1860s, of the synoptic forecast, which involved plotting isobaric curves and wind observations in so-called ‘synoptic’ charts, then predicting the weather by looking for deformations in the isobaric patterns. The history of nineteenth-century meteorology largely involved processes of interaction, competition, cooperation and hybridization between national scientific groups and institutions. Quetelet and the Belgian scientific institutions mainly played the role of interface in those processes. It made Brussels one of the capitals of the earth sciences from the middle of the 1830s to the beginning of the 1860s.