Eager to distract Louis from going to war, and receptive to the lobbying of France’s leading astronomers, Colbert enthusiastically endorsed the creation of the Académie, paying 6,000 livres for the site on which the observatory would be built, and more than 700,000 livres to complete it. Colbert even granted its members annual pensions of up to 3,000 livres, as was given to Cassini upon his arrival in 1668.11 The pensions acknowledged a change in the social status of experimental scientists, who were now being incorporated into the apparatus of state power at the highest level.
Like Ptolemy’s Alexandria and Palermo, Colbert’s Paris Observatory became a centre of calculation, a place where diverse information could be gathered, processed and disseminated to a wider audience in the interests of the state authorities,12 but it would operate on a scale and with a level of precision of which Ptolemy and could only dream. Initially, the appearance of a series of comets, as well as eclipses of the sun and moon earlier in 1666, ensured that the astronomers dominated the new observatory. But Colbert’s ambitions required that the Académie’s remit extended beyond astronomy, and that this would be a very different place for organizing scientific knowledge from those that had gone before it like Alexandria, Palermo or the Casa de la Contratación in Seville.
As Fontenelle observed, Colbert’s interest in supporting the Académie derived from his programme for bureaucratic management of the royal state. Even before the Académie’s foundation, Colbert was anxious to commission a large-scale, up-to-date map of the entire kingdom to assess its resources. He requested that provincial officials submit every available map of the regions, to assess ‘whether they are inclined to war or agriculture, to commerce or manufacture – and also of the state of roads and waterways, the rivers in particular, and of possible improvements to them’.13 These would then be collated and corrected by Nicolas Sanson. In theory it was a great plan, but the responses revealed the formidable political and logistical problems that would have to be overcome to complete such a project. Only eight provinces bothered to respond to Colbert’s request. The rest remained silent, either lacking the cartographic resources or being anxious that the results might lead to higher taxation. Despite his interest in marking political boundary lines, Sanson was more at home making handcoloured maps of the ancient world, and was unsurprisingly intimidated by the physical scale of the project. In a memorandum written in 1665, he acknowledged the need for two related projects: the creation of one general map of France, and another of regional maps showing their administrative divisions. These regional maps would show Colbert every feature, ‘including the smallest hamlets and assarts [land cleared for cultivation], even châteaux, farms and single private houses that stand alone and away from the parishes’. Considering the size of France and the variety of terrain, this would be a physically daunting, technically challenging and very expensive operation. If traditional surveying methods were used – pacing the land with measuring rods, consulting the locals and deferring to ancient statutes – then ‘the task would never be ended were one to employ all the surveyors and geometers in the world’.14 There had to be another way, so Colbert asked his new Académie to develop a new method of surveying large swathes of territory; he was so impatient that its members even discussed the matter during their first meeting in December 1666.
Their recommendations proposed a novel fusion of astronomy and geography. The expertise used in making scientific instruments for mapping the heavens would be applied to the tools used in topographical surveying, and Cassini’s astronomical observations could be applied in the determination of longitude. Funding was provided to refine established scientific instruments, including quadrants, used to measure the altitude of celestial bodies, and their navigational equivalent, the sextant, as well as the alidade, used in surveying to determine direction and orientation. The Académie decided to apply their new principles and instruments in a series of ‘observations’. First Paris then the entire country would be surveyed and mapped using the latest scientific innovations. The Académie’s methods brought together two strands of scientific measurement. Cassini provided astronomical observations that offered the most accurate calculation of longitude. Abbé Jean Picard, a French priest, astronomer, surveyor and founding member of the Académie, provided topographical precision based on practical surveying techniques. When these two were combined they would offer a powerful method for undertaking a countrywide survey of France.
Picard was already well known for his adaption of measuring instruments to enable much greater precision in the observation of celestial phenomenon and topographical surveying. His primary interest was in solving a scientific conundrum which was at least as old as Eratosthenes: how to calculate the earth’s diameter accurately. Whereas Cassini was interested in calculating longitude from east to west, Picard was concerned with measuring an arc of the meridian from north to south. Such an arc (or line) could be drawn due north–south anywhere on the planet, tracing an imaginary arc from pole to pole right around the earth’s circumference. Such an arc could ascertain the latitude of any particular place, as well as the diameter and circumference of the earth.
Picard’s method of surveying involved two kinds of measurement: the first, a celestial measurement to establish the surveyor’s latitude; the second, a series of angular terrestrial measurements which made possible accurate triangulation. A new micrometer (a gauge used to measure the angular size of a celestial object) allowed Picard to calculate planetary dimensions more accurately, while his telescopic quadrant replaced the usual method of using pinholes for sighting, enabling unprecedented accuracy in measuring both celestial altitudes and terrestrial angles. Armed with these new instruments, he was now ready to conduct the first modern geodetic survey of the earth’s surface and in 1669 he set out to measure a meridian line between Malvoisine, south of Paris, and Sordon near Amiens, which he calculated were on the same meridian. He used 4 metre long wooden rods in calculating the distance of just over 100 kilometres, and his results were impressive. Picard computed that one degree of latitude was 57,060 toises. One toise was 6 French feet, or just under 2 metres, giving a final estimate of 111 kilometres (69.1 miles). Using these figures as a multiplier he also calculated that the earth’s diameter was 6,538,594 toises, or 12,554 kilometres (7,801 miles). The actual figure is today calculated at 12,713 kilometres (7,899 miles).
Fig. 24 Diagram of triangles, from Jean Picard, Le Mesure de la terre, 1671.
Fig. 25 ‘Carte particulière des environs de Paris’, 1678.
The implications of Picard’s survey for astronomy were sensational. His calculation of the earth’s size verified Isaac Newton’s hypothesis of universal gravitation, encouraging the Englishman to finally publish his arguments in the Philosophiae Naturalis Principia Mathematica (1687).15 The practical impact of Picard’s methods on mapmaking was also substantial. To establish his meridional arc, Picard had measured a base line along which it was also now possible to ‘triangulate’ distances and directions. Knowing the exact length between two points on his base line, Picard could identify a third point in the landscape and, using trigonometrical tables, precisely calculate its distance. The result looked like a triangulated snake moving across the base line. The method was used in Picard’s Mesure de la terre (1671) and in the Académie’s first ‘observation’, the ‘Carte particulière des environs de Paris’, completed by Picard in the late 1660s and first published in 1678. On its scale 1 ligne (the smallest unit of pre-revolutionary measurement, one-twelfth of an imperial inch, or approximately 2.2 millimetres), represented 100 toises on the ground, giving a scale of 1:86,400. This would become the standard scale for all subsequent regional maps produced by the Cassinis. Both examples show that at this stage the Académie’s main aim was to provide a new geometrical framework for the subsequent mapping of the country. Distances were measured according to the mathematics of triangulation, allowing the correct location of places to be plotted across empty spa
ce. The result resembles a chain of abstract geometry rather than a depiction of a chaotic, thriving country.
The Académie’s next ‘observation’ gave a much better indication of the political power of the new methods. Picard was again chosen to lead the project, which would involve mapping the entire coastline of France. Having established the principles of a meridian line from which a triangulation survey could map the interior, Picard agreed with Cassini that an outline of the whole country would require a different method. This time Cassini’s observations of the eclipses of Jupiter’s moons would be used to calculate longitude. In 1679 Picard went back into the field. With the help of Philippe de la Hire, another member of the Académie, Picard spent the next three years calculating positions along the coastline. Previous maps of France had calculated positions according to a prime meridian running through the Canary Islands, a hangover from the sixteenth-century methods of calculating longitude inherited from the Greeks. But longitudinal distance between the meridian through the Canary Islands and any meridian in France had yet to be established. Picard now based observations on a prime meridian through Paris. He gradually moved down the coast and over to the Mediterranean, taking measurements in Brittany (1679), La Rochelle (1680) and Provence (1682).16
The finished map, entitled the Carte de France corrigée, was finally presented to the Académie in February 1684. The Academicians, not to mention the king himself, were shocked. As if to emphasize the modernity of their calculations, Picard and La Hire plotted their new coastline in bold over the top of the traditional outline estimated by Sanson. The new map showed the meridian of Paris for the very first time, but it also dramatically reduced the size of France from Sanson’s calculation of over 31,000 square leagues (150,000 square kilometres) to just over 25,000 square leagues (120,000 square kilometres).17 The whole Atlantic coast was shifted eastwards, while the Mediterranean coast retreated northwards. The map showed that strategically important naval ports like Cherbourg and Brest had been plotted several kilometres out to sea on Sanson’s earlier map. Fontenelle captured the mixture of scientific excitement and political concern created by the map’s unveiling. ‘They effected a very substantial correction to the coast of Gascony,’ he recalled, ‘making it straight where before it had been curved, and bringing it closer in; so that the King [Louis XIV] had occasion to say, jokingly, that their journey had brought him nothing but loss. It was a loss that enriched geography, and rendered navigation more certain and safe.’18 The message was daunting but clear: the traditional map of France had to be torn up and calculated again by a new kind of geometrical measurement.
Fig. 26 Jean Picard and Philippe de la Hire, Carte de France corrigée,1693 edition.
By the mid-1680s, everything was in place for a comprehensive survey of the entire country. The combination of Cassini’s astronomical observations and Picard’s methods of triangulation had established a general geodetic framework from which a detailed survey of the country’s interior could now be undertaken. But Colbert’s demand for geographical information from the regions had still not been satisfied, and as far as the Academicians were concerned the main purpose of their work up to the 1680s was still the larger measurement of the earth’s size and shape. Even as the surveyors completed their work, Louis’s armies were on the march, invading part of the Spanish Netherlands and sparking war (1683–4). Together with the deaths of first Picard (1682) and then Colbert (1683), Louis’s military expenditures meant that lack of money put paid to any immediate support for extending the work Cassini and Picard had begun. In 1701 Louis’s dynastic ambitions embroiled him in yet another European conflict, this time over hereditary rights to the vacant Spanish throne. Horrified at the spectre of Spain and France united under the Bourbon monarchy, England, Holland and Portugal launched a long and bloody war against them that stretched across Europe, North America and even the Caribbean. By the time the twelve-year War of the Spanish Succession had come to a bitter and inconclusive end in 1713, Louis’s territorial ambitions remained unfulfilled, and his treasury was massively depleted. With Cassini I’s death in 1712, there was little political appetite or intellectual leadership for ambitious surveying and mapmaking projects.
Work continued intermittently on extending the measurement of the Paris meridian across the length of the country from north to south, but this was regarded as a geodetic project designed to answer the question consuming late seventeenth-century scientists: what was the earth’s definitive size and shape? Isaac Newton’s theory of gravity assumed that the earth could not be a perfect sphere because its force seemed to vary between the equator and the poles. Newton concluded that the earth was not a perfect sphere but an oblate spheroid, slightly bulging at the equator and flattened at the poles. Cassini I and his son Jacques (Cassini II) were unconvinced, and followed the theories of René Descartes (1596–1650). Revered across Europe as the great philosopher of the mind, Descartes was also renowned as a ‘geometer’, or applied mathematician, who put forward the argument that the earth was a prolate ellipsoid, bulging at the poles but flatter at the equator, like an egg. His theory was widely accepted by the Académie, and the resolution of the controversy soon became a matter of national pride on both sides of the English Channel.19
Neither group had much empirical evidence to support its claims. Newton’s supporters pointed to unverified reports that the effect of gravity on pendulum measurements increased towards the poles. Jacques Cassini attempted to assert his authority as his father’s successor as head of the Paris Observatory in 1712 by endorsing the Cartesian position. Delivering a paper to the Académie in 1718, Cassini II argued that the surveys supervised by his father and Picard in the 1680s revealed that degrees of latitude shortened towards the North Pole, confirming Descartes’s prolate ellipsoid.20 In a reversal of national stereotypes, English speculative theory was pitted against French empirical observation. In an attempt to resolve the dispute, the Academicians lobbied the new king, Louis XV, and his naval minister, to support scientific expeditions along the equator and near the poles to measure their respective degrees of latitude. As well as offering to resolve a scientific debate in France’s favour, the Academicians also pointed to the commercial and colonial benefits of such adventures. Louis agreed, providing financial backing to two expeditions, ‘not only for the progress of the sciences, but also for commerce, in making navigation more exact and easier’.21 The precise astronomical observations and surveying practices developed by Cassini and Picard would now be tested in distant parts of the globe to solve one of science’s great foundational questions. The Académie’s original surveying mission had suddenly become international, in pursuit of the resolution of a dispute that overshadowed its previous preoccupations with the borders and regions of France.
In 1735 the first expedition set off to the Spanish colony of equatorial Peru, followed by the second the following year to Lapland in the Arctic Circle. Only the comparative measurement of the length of a degree at the equator and in the Arctic Circle could resolve the controversy, because if the earth was oblate (as Newton claimed) the length would increase, but if it was prolate (as Descartes claimed) it would decrease. Both teams intended to reproduce Cassini’s surveying methods of determining latitude through astronomical observations and measuring distance by triangulation. The Peruvian mission was beset with disasters, from earthquakes and volcanic eruptions to civil wars, and took eight years to return. The Lapland venture was more successful, and in August 1737 its leader, Pierre-Louis Moreau de Maupertuis, was back in Paris.22 Maupertuis reported his findings three months later to the Académie, as well as to Louis and his ministers. Cassini II’s horror was undisguised: Maupertuis’s estimates of the degree of latitude confirmed Newton’s belief that the earth bulged very slightly at the equator. Picard’s measurements in 1669 had strengthened Newton’s thesis concerning universal gravity, and the Cassini family’s methods now also provided irrefutable empirical evidence, against themselves, of
Newton’s theory that the earth was an oblate spheroid. The French Newtonians were triumphant. They included none other than Voltaire, who wrote to congratulate Maupertuis, mischievously addressing him as ‘My dear flattener of worlds and the Cassinis’.23
Fig. 27 Pierre-Louis Moreau de Maupertuis, ‘A Map of the country where the arc of the meridian was measured’, The Figure of the Earth, 1738.
The Peruvian expedition returned in 1744 and also confirmed Newton’s theory. Despite the blow to the Académie’s prestige, the controversy over the earth’s shape proved that the Cassini surveying method could be exported and practised anywhere in the world. The fact that it disproved the Cassinis’ own belief in Descartes’s shape of the earth only strengthened the growing realization that this was a scientific method that could present a verifiable, disinterested representation of the world, regardless of faith and ideology. A further consequence of the debate over the earth’s shape now presented itself. Initially Cassini I and Picard had undertaken their first surveys based on the assumption of a perfectly spherical earth. Now that Newton’s theory had been verified, all their calculations needed to be revised.
The appointment in 1730 of Philibert Orry (1689–1747) as Louis XV’s controller-general renewed Colbert’s original interest in a countrywide survey ‘for the good of the State and the convenience of the public’.24 Orry had little interest in what he considered esoteric debates over the earth’s shape: he was more concerned that the Department of Public Works (the Ponts et Chaussées) lacked accurate maps to develop France’s transport network, and in 1733 he ordered Cassini II to resume triangulation of the whole country. Unlike Colbert, Orry wanted to establish the state’s control over the recruitment and training of engineers and surveyors (or ‘geometers’). Louis XIV and Colbert had patronized a group of savants chosen for their family connections and individual brilliance. Orry, by contrast, understood that the state needed to establish scientific colleges to recruit and educate students in the requisite skills of surveying and mapmaking. He wanted standardized maps to provide the navy with accurate charts and allow the army to build its fortifications and fix the kingdom’s boundaries. He would later issue a proclamation calling for the survey to trace ‘road plans following a uniform type in all the kingdom’s généralités’.25 The aims and even the language associated with the survey were beginning to change. The role of the state, the public interest and the importance of standardization were now replacing royal patronage, elite scientific speculation and astronomy in supporting its completion. But until a new generation of trained geometers emerged, Orry had no other choice but to turn to Cassini II to complete the survey.
A History of the World in 12 Maps Page 38
