Geodesy and Cartography in the 18th Century

In Cassini de Thury's influential book on the measurement of the Paris meridian, published in 1744, questions relating to the shape of the earth and to the "geometrical description of the kingdom" were treated separately.^[1] The division existed only on paper. These fields had developed side by side, ever since Jean Picard surveyed a degree of the Paris meridian in the years 1668–70. Picard's triangulation prepared for a national cartographic venture, desired by Jean Baptiste Colbert; it also produced data for calculating the size of the earth, if not its shape. Throughout the 18th century, most advanced geodetical measurements had to do with mapping projects.

Cassini de Thury and Europe

The French survey was begun in 1683 and, after frequent lengthy intermissions, produced in 1718 its first major accomplishment, the triangulation of over seven degrees of a meridian line through Paris. Operations resumed after political support for the project was regained in 1730. Prompted by Pierre Louis Moreau de Maupertuis' measurement of an arc of meridian in Scandinavia in 1736–7, members of the Paris Academy of Sciences resurveyed the Paris meridian.^[2] The Cassinis had claimed that their measurements showed

[1] César François Cassini de Thury, La meridienne de l'Observatoire royale de Paris (Paris: H.L. Guerin & J. Guerin, 1744), 26, quote, and Relation des deux voyages faits en Allemagne par ordre du roi (Paris, 1765), 1–2: "le seul moyen de perfectionner la géographie, étoit de suivre pour la description d'un pays la même méthode que l'on avoit employée pour la détermination de la figure de la terre."

[2] Josef W. Konvitz, Cartography in France 1660–1848 (Chicago: University of Chicago Press, 1987), 3–13.

the earth to have an oblong shape. But Maupertuis' result suggested otherwise; the remeasurement of the Paris meridian and a survey of an arc of meridian in South America made between 1735 and 1744 confirmed that the earth has an oblate shape. Thus measurements outside of France served to calibrate the geodetic work in France. The triangulation of the whole of France now went ahead, under the direction of César-François Cassini de Thury (third in the astronomer dynasty), although it was Nicolas-Louise Lacaille who did most of the fieldwork.^[3] Between 1739 and 1744 almost 800 triangles, from Dunkerque to Perpignan, were measured, along with nineteen bases. The triangles, printed on eighteen sheets, provided a "geometrical skeleton" rather than a map. This was considered to be sufficient for their intended users, namely, engineers involved in public construction works.^[4]

In the 1750s several projects were begun or completed in Europe to complement the measurements sponsored by the French in France, Lapland, and Peru. A leading promoter of these projects was the Jesuit Roger Boscovich, who obtained the support of the pope to measure an arc of meridian between Rome and Rimini. The survey, which ran from 1750 to 1752, had the dual purpose of adding to knowledge of the shape of the earth and updating maps of the papal state. A copy of the "toise of Peru," borrowed from Paris, allowed comparison of Boscovich's geodesy with French results. Boscovich persuaded the king of Sardinia, Carlo Emanuele III, to sponsor a measurement in Piedmont, which Giovanni Battista Beccaria, a Scolopian priest and professor of physics at the University of Turin, carried out between 1760 and 1764. Beccaria's result did not confirm the oblate shape deduced by the French and so contributed to debate about gravitational irregularities and the reliability of geodesy.^[5] This

[3] Charles C. Gillispie, Science and polity in France at the end of the Old Regime (Princeton: Princeton University Press, 1980), 113–5; Lloyd A. Brown, The story of maps ([1949] New York: Dover, 1977), 252.

[4] Konvitz, Cartography in France , 15–28.

[5] Antonio Marussi, "Italian pioneers in the physics of the universe. III: Geodesy," Cahiers d'histoire mondiale, 7:2 (1963), 473–5; Elizabeth Hill, "Roger Boscovich: A biographical essay," in Lancelot Law Whyte, ed., Roger Joseph Boscovich: Studies of his life and work on the 250th anniversary of his birth (London: George Allen and Unwin, 1961), 42–6.

was true also of the first measurement of an arc of meridian in North America, for which Boscovich was also in some measure responsible. It was carried out between 1764 and 1768 by Jeremiah Dixon and Charles Mason.

Another Jesuit, Father Joseph Liesganig, director of the Observatory at the University of Vienna, began his survey of an arc of meridian between Vienna and Brün in 1759. Maria Theresa ordered this measurement following suggestions from Boscovich, and probably also from Cassini de Thury, who worked on a triangulation to connect the Paris meridian with Vienna, one purpose of which was to correct the military maps of France's ally, Austria. Cassini de Thury participated in Liesganig's work, which was calibrated with his own by means of a copy of the toise of Peru. In 1762 Maria Theresa authorized an extension of this arc and provided Liesganig with instruments and engineers from the military academy in Vienna.^[6]

Boscovich and others, including Bouguer, had supposed that irregularities in the earth's mass distribution drew plumb bobs from the perpendicular and introduced serious error into geodetic measurements. His view was widely accepted by the 1770s. In 1775 Etienne Bonnot de Condillac made public a severe critique of existing geodetic investigations, and, in agreement with d'Alembert and later also Laplace, he judged that the different measurements of arcs of meridian were too contradictory to demonstrate that the earth has a regular ellipsoid shape. In particular, measurements in France and in Piedmont around the same degree of latitude did not agree. In Condillac's view measurements should conform to theory or else theory should be modified.^[7]

[6] Cassini de Thury, Relation des deux voyages , 3–4; Ernst Bernleithner, "Oesterreichs Kartographie zur Zeit des Grafen Ferraris," La cartographie au XVIIIe siècle et l'oeuvre du comte de Ferraris (1726–1814) , Collection histoire pro civitate, no. 54 (1978), 139–42; Johannes Dörflinger, Österreichichsche Karten des 18. Jahrhunderts (Vienna: Österreichische Akademie der Wissenschaften, 1984), 61–2.

[7] Volker Bialas, Erdgestalt, Kosmologie und Weltanschaung: Die Geschichte der Geodäsie als Teil der Kulturgeschichte der Menschheit (Stuttgart: Konrad Wittwer, 1982), 158–9, 166–7, 181–7; Condillac, Cours d'étude pour l'instruction du prince du Parme, III: De l'art de raisonner (1775; Deux-Ponts: [Bodoni], 1782), 217, 275–8. Laplace later changed his mind and advocated the view that the earth is a true ellipsoid. Pierre Simon Laplace, Oeuvres , 7 vols. (Paris: Imprimerie Royale), 5 (1846), 14–6 (text of 1823).

The conflict that Condillac and others pointed out may be characterized as one of quantification versus geometric simplicity. Possessing only a few measurements of meridianal arcs and a theoretical model authorized by the Principia , scientists could maintain that the earth had a regular shape. By the 1780s, however, it had become possible to be a Newtonian and still entertain novel shapes for the earth. The Newtonian theory flowed from the hypothesis that the earth had once been in a fluid state. With the decreasing interest in hypotheses about first causes, which characterized the late 18th-century instrumentalist attitude to science, one could choose any curve that fit the data.^[8] The work of William Roy offers an example.

Meanwhile, Cassini de Thury had created the first nationwide topographical map based on extensive triangulations. A team of draftsmen and engineers worked on the project between 1750 and its conclusion thirty-nine years later under Cassini de Thury's son, Jacques Dominique.^[9] French geodesy had a lasting influence on European cartography. As early as 1736–7, when Maupertuis visited "Lapland," the Swedish Surveying Office made an inspired but, as it happened, premature attempt to appropriate the new technology for the benefit of Swedish cartography. In Denmark, the Scientific Society of Copenhagen was commissioned to carry out a national triangulation on the French model in 1762. The Austrian military surveys by Joseph Jean Ferraris in the 1770s drew on Cassini's example in the choice of scale (1:86,400) and in the triangulation methods. Other European states and Russia did not introduce large-scale triangulations until the early 19th century.^[10]

In sum, French cartography and geodesy led European practices in both field and office. Meridianal arcs were triangulated as backbones for exact cartography; geodesists computed distances in terms of the

[8] J.L. Heilbron, Electricity in the 17th and 18th centuries: A study of early modern physics (Berkeley: University of California Press, 1979), 71–3.

[9] Gillispie, Science and polity , 480–1; Konvitz, Cartography in France , 16–21.

[10] J. Svärdson, "Lantmäteriteknik," Svenska lantmäteriet 1628–1928, 1 (Stockholm, 1928), 223; Asger Lomholt, Det Kongelige Danske Videnskabernes Selskab, 1742–1942: Samlingar til Selskabets historie, 4 (Copenhagen: E. Munksgaard, 1961), 90–104; Bernleithner, "Oesterreichs Kartographie," 132–8; Brown, Story of maps , 270.

Peruvian toise, and draftsmen used the scale of the Cassini maps, sometimes even when cartographic methods remained traditional, as in Henri Mallet's maps of Switzerland.^[11] This calibration and standardization owed much to Cassini de Thury. He envisaged a Europe geometricized to a uniform scale; to this end he extended the French triangulation to Flanders and to Austria, and tried unsuccessfully to win support for a similar extension into Italy.^[12]

Britain kept outside the sphere of Cassini de Thury's influence until 1783. Then, about a month after the end of the American war of independence, he proposed to the British government that a triangular connection should be made between London and Paris. The resulting measurement became the starting point for the Ordnance Survey, a cartographic venture undertaken by military engineers.

British Military and Scientific Engineers

British military cartography before the Ordnance Survey was poorly developed. The only important surveys outside England had been conducted in response to emergencies, like the measurements in Scotland as part of the pacification of the Highlands after the 1745 rebellion. The young draftsman William Roy led the fieldwork of the Scottish survey and later became director of the whole operation.^[13] After completing the work in 1755, he joined the corps of engineers under the Board of Ordnance and became a lieutenant in the army. Throughout his career Roy held double ranks in the engineers and in the army, the latter always being the higher.^[14] This elevated him to a higher social as well as military position than that of mere engineers, who did not acquire military rank before 1757. The status of the mere engineers rose in the 1770s, partly as a result of a new policy of

[11] M.-A. Borgeaud, "Cartographie genevoise de XVIe au XIXe siècle," Archives internationales d'histoire des sciences , no. 6 (1949), 363–74.

[12] Marussi, "Italian pioneers," 475.

[13] J.B. Harley and Yolande O'Donaghue, "Introductory notes," in The old series Ordnance Survey maps of England and Wales, 1 (Lynpne Castle: Harry Margary, 1975), xi; R.A. Skelton, "The military survey of Scotland 1747–1755," The Scottish geographical magazine, 83:1 (1967), 1–15.

[14] R.A. Gardiner, "William Roy, surveyor and antiquary," The geographical journal, 143 (1977), 441–50, on 443–4.

the Board of Ordnance that required cadets in the corps of engineers to have had some formal technical education; the requirement functioned as a social filter, favoring sons of army officers. At the same time the American war gave rise to a greater recognition of the importance of cartographic skills and to the acceptance of engineers as staff officers.^[15] By the 1780s the engineers had achieved the same social status as army officers.

Because of their specialist abilities, members of the corps of engineers (and of the artillery) saw themselves as a part of the scientific community. Some achieved membership in the Royal Society. They figured among the opposition during the so-called dissensions of 1783–4, when Sir Joseph Banks, who had been president of the Society since 1778, was attacked by practically or mathematically oriented Fellows for favoring antiquarianism and natural history—that is, "gentlemen's science."^[16] Banks' forces managed to defeat their opposition. It might therefore come as a surprise that the Banksians in the Royal Society, not the mathematical practitioners, effected the cooperation with Cassini de Thury.^[17] The key figure in their mobilization was William Roy, who belonged

[15] Douglas W. Marshall, The British military engineers 1741–1783: A study of organization, social origin, and cartography (Ph.D. dissertation, University of Michigan, Ann Arbor, 1976), 1–7, 119–24, 130, 317, 343–4.

[16] David Philip Miller, The Royal Society of London 1800–1855: A study in the cultural politics of scientific organization (Ph.D. dissertation, University of Pennsylvania, 1981), 6–14, 36–104, 115, 120, 135; W.A. Seymour, ed., A history of the Ordnance Survey (Folkestone: William Dawson, 1980), 3, 29, 67; Charles Richard Weld, A history of the Royal Society , 3 (London: J.W. Parker, 1848), 151–70; Hector C. Cameron, Sir Joseph Banks (Sydney: Angus and Robertson, 1966), 128–34; Henry Lyons, The Royal Society 1660–1940 (Cambridge: Cambridge University Press, 1944), 202–5, 211–4, 342. There is no evidence that Banks suppressed mathematically oriented science in the Philosophical transactions .

[17] These Banksians on the triangulation included Charles Blagden, Henry Cavendisch, John Lloyd, and John Smeaton, as well as Roy; all were members of the Royal Society Club, a center of Banksian sympathies. Letters of Blagden to Banks, 1783–4, as listed in W.R. Dawson, ed., The Banks letters: A calendar of the manuscript correspondence of Sir Joseph Banks (London: British Museum, 1958), 61–2, 64–5; Archibald Geike, Annals of the Royal Society Club (London: Macmillan, 1917), 174–5; Seymour, A history of the Ordnance Survey , 134.

socially and intellectually to both the Banksian and the mathematical camps.^[18]

In the 1760s Roy had settled in London and had become a Fellow of the Royal Society and a firm friend of Joseph Banks. Roy's strong interest in antiquities resulted in a major work on Roman Britain, published after his death; thus he qualified as a member of the "Banksian Learned Empire." By the early 1780s, Roy had also established a scientific reputation through painstaking work in the field of barometric hypsometry. As a major-general in the army and a lieutenant-colonel in the corps of engineers, he was an influential proponent of a national military survey, the realization of which was his main objective in the Paris-Greenwich triangulation.^[19]