The Discovery of France

by Graham Robb

  The man who stood in the belfry at Dammartin that night in August 1792 was an astronomer from Amiens, which happens to lie close to the meridian. Jean-Baptiste Delambre had been appointed to lead the northern part of the expedition, from Dunkirk to Rodez (seven hundred and fifty kilometres). His colleague, Pierre Méchain, was to survey the shorter but more mountainous and partly uncharted section from Barcelona to Rodez (three hundred and thirty kilometres). They were to determine the meridian by triangulation. The principle is simple: take three clearly visible points – in this case, the Dammartin belfry, a roof in Montmartre and the church of Saint-Martin-du-Tertre. Next, using the repeating circle, find the angles of the triangle. Finally, measure the distance between two of the points using rulers. This provides the baseline, and elementary trigonometry gives the length of the other two sides.24 With the first triangle established, sightings taken from a fourth observation point allow the next, adjacent triangle to be calculated. The triangles can then go marching rigidly along the meridian until, at the other end, a second baseline is measured with rulers to verify the results.

  Unfortunately, as Delambre discovered, Nature cloaked her immutable laws in change and used human beings to cover her tracks. Variables such as altitude, atmospheric refraction and the contraction and expansion of instruments in heat and cold were small matters compared to the human chaos. Delambre’s initial circumambulation of Paris, at a distance of twenty-five to thirty kilometres from the centre, was a sobering glimpse of the struggle ahead. The supposedly unchanging French countryside was in a constant state of flux. Many of the triangulation points set up by earlier expeditions had vanished. Trees had grown up to hide the view; buildings had been moved; staircases in castle towers had crumbled away; churches had been bricked up or demolished.

  The biggest obstacle was the fact that few people understood the fraternal and egalitarian nature of the project. At Montjay, Delambre’s observation platform was torn down by citizens exercising their new democratic right to destroy anything new. In the Orléans forest, he was able to build his platform only because the local people were busy elsewhere in the forest, demolishing ‘a stone pyramid called the Meridian which was built by the former seigneurs as a sign of their greatness’. (It was an obelisk commemorating Cassini’s survey of 1740.) Delambre was forced to give impromptu public talks to explain his mission: he was not a Prussian, his spyglass was not for spying and the letters of accreditation bearing the royal seal were not secret messages from Citizen Capet (formerly known as Louis XVI). At Saint-Denis, where the kings of France were buried, a crowd broke into his carriage and discovered the most suspicious-looking collection of objects they had ever seen.

  The instruments were laid out on the square, and I was forced to recommence my lecture on geodesy . . . The light was failing and it was almost impossible to see. The audience was very large. The front rows heard without understanding; the others, further back, heard less and saw nothing. Impatience was spreading and there were murmurs from the crowd. A few voices proposed one of those expeditious means, so commonly used in those days, which cut through all difficulties and put an end to all doubts.

  Further south, change and decay had swept across the land like a flood. Earlier surveyors had left almost as few traces as Arne Saknussemm in Jules Verne’s Journey to the Centre of the Earth. Some old people remembered seeing Cassini pass through their village many years before, but the platforms and wooden pyramids he had built as triangulation points had been dismantled for the wood or destroyed as enemy signalling devices. The plains around Bourges had been shorn of every eminence: Delambre was told that a representative of the people had ‘demolished all those steeples that elevated themselves arrogantly above the humble dwellings of the sans-culottes’. The Temple of Reason at Rodez – formerly known as the cathedral – was the only original triangulation point that remained in the Aveyron. The more remote the area, the more tenuous the connection with scientific truth. At Bort-les-Orgues, Delambre’s signal, placed on the bizarre organ-pipe escarpment above the town, was said to have caused a landslide that sank the streets waist-deep in mud. This happened almost every year, but, for once, the cause was obvious. On the fog-bound summit of Puy Violent above Salers, the wizard’s straw-covered house made from three twenty-three-foot tree trunks was blamed for the death of several cows and a spate of minor accidents.

  Seven years and thousands of miles later, after suffering atrocious weather, impassable roads and impossible peasants, illness, flimsy platforms that wavered in the wind because the carpenters had skimped on materials, the mental breakdown of Méchain and an attack of wild dogs who scattered the rulers that had been carefully laid along the baseline near Perpignan, Delambre submitted his results at the world’s first international scientific conference, held in Paris on 2 February 1799. A metre-long bar of pure platinum was presented to the National Assembly in April. This was to be the permanent standard metre ‘for all people, for all time’, though it would take another century to persuade the whole country to adopt the decimal system.

  Satellite surveys have since shown that the official metre, which was supposed to be one ten-millionth of the distance from the North Pole to the Equator, is approximately 0.23 millimetres short. Ironically, the provisional metre which the Académie des Sciences had been forced to come up with in 1793 is closer by about 0.1 millimetres, though it was an estimate based on earlier surveys. But the metre of Delambre and Méchain had the authority of experience. That bar of platinum was a monument to one of the great expeditions of the age. Like all great expeditions, the journey along the meridian discovered far more than the explorers set out to find. The eternal values on which the republic was supposed to be founded – liberty, equality, fraternity and mathematical precision – had turned out to be extraordinarily elusive. Two men and their assistants had taken seven years to survey a narrow corridor of land. Instead of reducing the country to the size of a map and a table of logarithms, they had shown how much of France remained to be discovered.

  *

  THE JOURNEY OF Delambre and Méchain was just one episode in a great odyssey which began before they were born and continued long after they were dead. When they returned to Paris in 1799, more than half a century had passed since the young geometer on Cassini’s expedition had been bludgeoned to death by the natives of Les Estables, yet the map of France had still not been fully published. Even the published sheets included areas that only seemed to have been charted. This was hardly surprising. Nothing like it had been attempted before. It was the first detailed map of an entire country to be based on extensive, coordinated surveys. As Cassini III25 wrote in his introduction to the first sheet (Paris), published in 1750,

  When one considers how many years, journeys, exertions, investigations, instruments, operations and observations are required for the exact description of a country, it is no wonder that a work of such scope, which relies on measurements taken in the field, should progress at such a slow and cautious pace.

  The long adventure had begun on a field in Flanders in 1746 during the War of the Austrian Succession. While the French and Austrian armies were laying waste to the land, César-François Cassini de Thury was recording it on beautiful maps of camps and battlefields. To him, this was normal family business. His grandfather and father had surveyed the meridian in 1700. César-François himself had been involved with the work since childhood. He grew up in the Paris Observatory, where his grandfather had discovered four of the moons of Saturn. At the age of eighteen, he joined the expedition that drew a line perpendicular to the meridian, from Saint-Malo in the west to Strasbourg in the east. At nineteen, he lectured at the Académie des Sciences on the importance of geodesic measurements.

  The man who was born at the intersection of the meridian and the west–east line knew the country better than anyone else. No one had undertaken such long journeys across the land, following the invisible line of geometrical truth rather than rivers and roads; no one had surveyed the land from so
many vantage points. From scaffolding erected in forests and plains, Cassini had seen views that no one else had seen. He had heard dialects unknown to lexicographers, and he had an unrivalled knowledge of cheese from the Auvergne (unwholesome) to the Jura (delicious).

  When Louis XV saw Cassini’s battlefield maps, he recognized their military importance. Cassini had been asked to bring along some astronomical instruments to keep His Majesty amused. He not only kept him amused, he also persuaded him to authorize a project so grand and expensive that it makes the seven-year voyage to Saturn of the probe that bears his grandfather’s name seem quite modest. Cassini was officially asked to produce a map of the entire kingdom on a scale that would make the smallest hamlets visible.

  Now that he had funding for a complete map of France, Cassini could begin to recruit a small team of ingénieurs-géographes. They had to be mentally strong, physically fit and, preferably, unattached. They should be familiar with astronomy and trigonometry. They should know how to draw and how to build an observation platform. Since the six-month-long mapping season coincided with the season of military campaigns, they should always be prepared for action. The army’s own geometers were expected ‘to read and write foreign languages and to be able to swim, so that nothing need prevent them from executing urgent and important reconnaissances’. These athletic scientists were the astronauts of the eighteenth century, with certain obvious differences: they were poorly paid and could expect no personal glory; they would be out of contact for long periods; and they could be quite certain that they would encounter hostile aliens.

  *

  FOR THE FIRST EXPEDITION (1748–49), Cassini recruited about a dozen young men in their early twenties. They were equipped with miniature instruments that were less accurate than the full-scale instruments but small enough to be carried to the top of a steeple or a mountain. Though some of the provinces had good maps of their own, much of the land that the Cassini team was to explore had never been charted. Until then, most map-makers had simply copied earlier maps and perpetuated old mistakes. There were maps of the Alps that showed a plain in the middle of the mountains near Chamonix and a giant peak called ‘La Mont Maudite’ (the Cursed Mountain) thirty miles west of its real counterpart, Mont Blanc. Even in 1792, when Savoy was annexed and renamed Département du Mont Blanc, the official government map was more like optimistic science fiction than a record of reality. It showed a road running around the base of Mont Blanc and a carriageway over the 9,068-foot Col de l’Iseran, which was first crossed by road in 1937. Cassini’s geometers were starting with a sheet of paper.

  Their task was far more complicated than Delambre’s triangulation of the meridian. On arriving in a new place, the geometer would seek out the curé, the lord or the syndic who represented the local assembly. This could take all day if the man was out in the fields or away at market. After gaining access to the steeple or the tower, he would survey the land and produce a preliminary sketch. The curé,lord or syndic would then be asked to name – in French – the villages, hamlets and farms, the castles and the abbeys, the rivers and the woods, and to point out the location of roads, bridges, fords, locks, windmills, watermills and gibbets. In featureless regions like Champagne or the Landes, tiny landmarks might be noted: a lonely tree, an abandoned tileworks, even the temporary pyramid from which the measurements were taken.

  In the evening, the geometer would write the names on his chart and sketch the hills and valleys, trying to keep the vellum clean while the local inhabitants peered over his shoulder or held a meeting to decide what to do about him.

  The whole process was a curious mixture of precision and approximation. A priest in the Berry remembered the cartographer’s visit in 1756:

  He set up three stations in my parish and I accompanied him. He wrote down all the objects he could see: hamlets, farms, main roads, trees, towers, steeples, etc. To confirm his calculations he had his servant measure in common feet the distances of certain objects. I remember that his little pedometer one day gave him the exact number of feet from Issoudun to Graçon [sic for Graçay: fifteen miles]. It is true that for certain things that he was unable to see, such as an estate that lay in a valley, he asked its distance from the steeple . . . If all the engineers were as reliable in their operations as the one I saw at work, their scribes must produce very regular maps.

  The naming of all these places and landmarks was a puzzle in itself. There was no complete list of towns and villages, and there were no agreed spellings. Many local names would never be recorded or would survive only in a garbled form. As Cassini explained, some landowners saw the naming process as a splendid opportunity to recreate the landscape in their own image. They saw no reason to identify the obscure farm and the decaying hamlet that were about to be swallowed up by their magnificent new park, or the medieval ruin that would soon be superseded by their new, symmetrical château:

  Names had to be given to these new objects, and lords thought that they had the right to name them. Several seigneurs lumped together under the same appellation various estates or fiefdoms which each had their own name and which the local people continue to use.

  Despite the King’s written orders, some priests refused to unlock the door to the steeple, and some town assemblies refused to cooperate. As the map spread south to Provence and Languedoc, it became apparent that the geometers would have to obtain letters of introduction from authorities more local than a king who lived in Versailles. A man who worked on Sundays and who had nothing to sell might be a tax collector, a spy or a bell thief employed by a rival village. The spidery lines and runic symbols that he etched on his chart did not necessarily explain his purpose. Mountain people who had seen hills and plains spread out at their feet usually had some sense of topography, but to people who lived in lowlands or in closed valleys, the two-dimensional representation of the earth from an imaginary point in space was a complete mystery. The very act of drawing was often an amazing novelty. Well into the nineteenth century, travellers with a sketchbook and an easel attracted crowds from far and wide. Prosper Mérimée instantly became the most famous person in Vézelay when he began to draw the basilica with the aid of a camera lucida. On a tour of Brittany in 1818, the English artist Charles Stothard asked to draw a girl in local costume.

  Several Bretons seated themselves upon the ground, to watch the motion of Mr. S—’s hand, others pressed around him, and even attempted to touch the pencil he was using, to ascertain, I imagine, what such a magical little implement could be.

  In some places, the arrival of a stranger with fantastic tools and an inexplicable plan was a major historical event. In gazetteers and guidebooks published decades later, the only thing worth mentioning in some places was the ‘ruins of a pyramid erected by Cassini’. The novelty was too much for some small villages. In 1773, in the heart of the Tarn, a young surveyor from Issoudun was pulled down from the tower of the ruined church of Saint-Martin-de-Carnac near the village of Cuq. Epidemics had passed through the region and left the local people fearful and resentful. His attackers set about him with clubs and knives. Somehow, he escaped. Later that day, a man with bleeding hands and a broken skull was seen staggering along the road from Castres to Lavaur, a mile south of Cuq. No one dared help the fleeing sorcerer. At last, he reached a roadside inn run by ‘the Widow Jullia’, who sent for a doctor and a surgeon. The surveyor survived but was forced to retire with a pension.

  Even before it was finished, it was clear that the map of France, with its standardized spellings and consistent symbols, would be considerably more coherent than the country itself.

  *

  THE EXPENSIVE DISASTER of the Seven Years War (1756–63) ended Treasury funding for the map of France. With the support of the King’s mistress, Mme de Pompadour, Cassini set up a company of fifty shareholders. The first sheet, published in 1750, served as an enticing prospectus. It showed Paris in the centre – just large enough to be divided into quartiers – and stretched from Dammartin in the top right to
Rambouillet in the bottom left. Like the subsequent hundred and eighty sheets, it measured 3' 5" by 2' 5" and used a scale of 1 ligne for every 100 toises, which is equivalent to 1:86,400.26 The Paris sheet was more detailed than the others, with forest paths beautifully picked out, partly to attract subscribers and partly because it included the properties of many of the noble sponsors. The epigraph, from the Natural History of an earlier explorer of Gaul, Pliny the Elder, sounded a cautiously pessimistic note: ‘It is sufficiently honourable and glorious to have been willing to make the attempt, though it should prove unsuccessful.’

  No one who sees a well-filled diagram of France in a confident history of the country would guess that it took almost seventy years to publish the Cassini map and that the last sheets (Brittany and the coastal Landes) did not appear until after the fall of Napoleon in 1815. Very few histories even mention the Cassini map, let alone the men who made it. Only about a dozen of the ninety-five surveyors whose names appear on the charts have left any trace. This entry on one of the surveyors, in Michaud’s Biographie universelle in 1855, is typical:

  Dupain-Montesson [Christian name unknown]: modest and tireless scholar, forgotten until now in all biographies; only fragmentary information could be obtained.