The South-Going Astronomer

Welcome to [Barcelona], thou mirror, lanthorn, planet, and polar star of all chivalry in its utmost extent! welcome valorous Don Quixote de la Mancha, not the false, fictitious and apocryphal adventurer, lately in spurious history described; but, the real, legal, and loyal knight. . . .

—MIGUEL DE CERVANTES, The History and Adventures of the Renowned Don Quixote

According to the official account of the meridian expedition—Delambre’s magisterial Base du système métrique—Méchain left Paris for Barcelona on June 25, 1792, accompanied by three aides, riding in his custom-built carriage, and bearing the scientific instruments he had waited so long to receive. After years of delay, the expedition was finally underway. The Academy had originally hoped to launch the survey when it named its commissioners in the spring of 1791. Their departure had been postponed while Lenoir finished building the measuring instruments and Cassini dithered. By January 1792, Lenoir had delivered the instruments and Méchain was expecting to leave the next spring. In April the French Foreign Ministry secured the full cooperation of the Spanish government, and in May Méchain informed the Spaniards he would be leaving Paris on June 10. Yet Méchain appeared in no rush to begin. On June 9, he announced that he would actually be leaving the capital on June 21. On June 23, he said he expected to leave the next morning. Every day counted; the nation’s chief minister was threatening to cancel the expedition. The government was having second thoughts about the cost of measuring a meridian measured several times before.

Yet three days after June 25—the date on which, according to Delambre, Méchain left Paris—the southbound astronomer was still in the capital. On June 28 a public notary visited the Méchain residence on the grounds of the Paris Observatory so that Citizen Méchain—“then being on the point of leaving for Barcelona in Spain as one of the Commissioners of the Academy of Sciences to determine the length of the arc of the meridian”—could sign a power of attorney over to his wife. The document empowered his wife to collect his salary during his absence, carry out financial transactions in their name, and dispose of their property as she saw fit.

Barbe-Thérèse Méchain, née Marjou, was an educated, competent woman who assisted her husband in his astronomical work. They had been married for fifteen years and lived with their three children—two sons and a daughter—in a small house on the grounds of the Paris Observatory. It was a comfortable life. The family had the right to plant vegetables in the plot behind the house, and their front windows looked out onto the rue du Faubourg St.-Jacques. Lodgings in the neat little house was one of the privileges with which a lucky savant on the royal payroll might supplement his meager income.

The Marjou family had also made their careers in royal service. Thérèse’s father had been a valet to the king’s brother at Versailles. Her elder brother earned a generous pension as head cook for the Duchesse d’Aiguillon. Thérèse had brought a substantial dowry to her marriage as well as a cool head for business. The Revolution, however, had wiped out her family’s fortune. Her parents had died of old age in 1789, just as her brother’s blue-blooded employers had fled the country. Versailles was deserted. The Méchain family now depended on her husband’s meager earnings. The metric expedition would not pay him a salary—as a member of the Academy, Méchain was expected to serve on the meridian mission for honor’s sake—and he could not afford to abandon his Paris duties. So Madame Méchain agreed to continue her husband’s astronomical measurements during his absence, including a study of lunar eclipses. As she would fulfill her husband’s official duties at the Observatory, it is hardly surprising that he granted her a power of attorney as well—whatever the exact date.

Yet exact dates matter. For astronomers, time is sacrosanct. The precise moment of a celestial event is the foundation upon which all heavenly knowledge rests. Why then did Delambre lie about so trivial—and verifiable—a matter? After all, Méchain’s presence at the Observatory could hardly have gone unnoticed. Most of the nation’s leading astronomers also lived on the grounds. Oddly enough, the solution to this mystery may be found in another falsehood Delambre published in the same official account. There he implied that his own first day on the mission was June 26, one day after Méchain’s supposed departure. Yet his private notebook—which he consulted while preparing his magisterial Base—indicates that he had been scouting sites for stations as early as June 24.

Two lies do not make a truth, but they may solve a mystery. With these two fabrications, Delambre established Méchain’s seniority on the project. This one-day priority, slim as it was, dignified Méchain as the senior partner on the expedition. Méchain was forty-seven and Delambre was forty-two, but Méchain had ten years of seniority within the Academy of Sciences and had been nominated to the meridian survey two years before Delambre. Scientific life in Ancien Régime France operated upon such slender courtesies. Even today, scientific careers still depend on the roll call of authorship, and colleagues read those rosters with a subtlety worthy of Biblical exegesis.

But we lie about time at our peril. An expedition sent forth to measure nature with unsurpassed precision ought not to begin under a cloud of dissimulation, especially when its central purpose is to define the attributes of time and distance for all people, for all time. Méchain left Parisexpecting to return in seven months. Seven years would pass before he set foot again in the capital.

Of course, none of this explains why Méchain delayed his departure. Can it be that he had doubts about its wisdom, or about his ability to carry it out during a time of such unrest? Already in 1789 Méchain was having trouble remaining calm amid the “brusque alarms, continual worries, and serious risks” that convulsed his Paris neighborhood. Two days after the fall of the Bastille a mob of three hundred armed citizens had invaded the Observatory to search for gunpowder, weapons, and food. They had forcibly entered his home, terrorized his wife, and obliged Cassini to conduct them through the labyrinthine cellars, where they found nothing more deadly than a kitchen rotisserie. Yet these “Don Quixotes,” as Cassini called them, also stripped the Observatory’s roof of lead to make musket shot. Soon after, Méchain had been drafted into the bourgeois militia to maintain order in his section of the city. “You can imagine,” he wrote to a colleague, “that it is not easy to keep one’s mind free and clear for scientific work under such circumstances.” Yet for the next several pages of his densely written letter he did just that, analyzing the exact dimensions of Saturn’s rings.

This single-minded concentration made Méchain an ideal choice for the meridian expedition. Accuracy was his religion. He was born on August 16, 1744, the son of a small-town plasterer from Laon, a medieval city perched on a narrow crescent ridge above the dense soil of Picardy, a lush green landscape punctuated by fortified towns. He had been educated by the Jesuits, and had demonstrated enough mathematical talent to win entry to the Ecole des Ponts et Chaussées, France’s preeminent school for civil engineers. His father, however, was unable to maintain his son in school, and Méchain was obliged to quit his studies and accept a tutoring position. There he saved enough money to indulge his youthful passion for astronomy, buying some telescopic equipment. Then calamity struck. His father lost a crippling lawsuit, and the son (or so the story goes) loyally agreed to sell his instruments to pay off the family debt. This setback proved his first stroke of fortune. His instruments were purchased by Jérôme Lalande, France’s most illustrious astronomer, with connections at every level of French society.

Lalande secured the young man a part-time position at the navy’s cartography department at Versailles. In that capacity, Méchain participated in mapping expeditions along the Normandy coast and prepared detailed military maps of the Mediterranean, using observations gathered by others to chart a coastline he had never seen. For twenty years he spent his days inside the dark bureau working his way through reams of calculations and his nights scanning the bright northern skies. Lalande was also a generous taskmaster and set the young man to work on his celestial tables.

Méchain was harder on himself than any master could be, the sort of astronomer who favored the long mathematical route to a sure answer over a quick superior technique which struck him as unproven. Eventually, these qualities made him one of France’s leading astronomers, the discoverer of eleven comets, a member of the Academy of Sciences, and the editor of the Connaissance des temps. This was France’s premier journal of astronomy, a work whose principal merit was its exactitude. Méchain transformed it into a worthy rival of Britain’s exemplary Nautical Almanac.

To reward these achievements, he was appointed capitaine-concierge of the Observatory. His sponsors assured Cassini that he would show the director “due deference.” They also pointed out that Méchain was “very capable, very honest, as well as young, poor, and married.” In 1783 the family moved into the cozy residence on the Observatory grounds, with its kitchen, dining room, bedrooms, offices, and small courtyard and back garden where the previous tenant, a botanist, had planted exotic trees. His youngest son was born there in 1786.

Méchain was a short dark-haired man, with pale delicate features which would have been regular if they had not been tugged in opposite directions by emotions working just below the surface: thick eyebrows hitched high in entreaty, liquid eyes that searched out commiseration, and a gentle mouth that drooped toward self-doubt. He had never hoped for public fame, and luckily (his second stroke of fortune) he had had little need to fret about his career once he married Thérèse Marjou. Still, he had steadily climbed the rungs of his profession until, in the very last year of the Ancien Régime, he had been named to the Franco-British expedition to survey the difference in longitude between the Paris and Greenwich Observatories.

It was this expedition which had first demonstrated both the promise of the Borda repeating circle and Méchain’s capacities as a geodeser. The natural philosophers of the world’s two greatest powers thought a cross-Channel survey would allow navigators to translate readily between British and French sea charts. They also hoped that a dash of scientific rivalry would spur their two governments to support science more generously. Pitted against Jesse Ramsden’s great theodolite, a massive new surveying instrument financed by George III, the French team would deploy their repeating circle, funded by Louis XVI and designed by Borda to be the ideal instrument for geodesy. The Borda circle was easier to build and transport than the Ramsden monstrosity (it weighed twenty pounds, rather than two hundred pounds); it could be adapted to measure both terrestrial and celestial angles; and it promised to reduce errors nearly to zero. The quest for precision demands cooperation; it is also a form of competition.

The British were unwilling to concede the contest. As their leader put it: “I perceive, Sir, that your small circle measures angles very justly when a mean of many observations can be taken. Our instrument I consider with regard to its construction and divisions as perfectly free from error.”

Throughout 1787 and 1788 the British and French teams triangulated toward their respective coasts and double-checked one another’s results across the Channel. In the end, they both achieved such a high degree of precision that they could not agree on their findings. While the French acknowledged that the British instrument produced errors of less than two seconds of arc, they boasted that they had closed their triangles to within 1.5 seconds of arc, a tenfold improvement over the results of the previous decade. Cassini considered this proof that the Borda circle had pushed science toward a perfection that bordered on the sacrilegious.

Usually, in the arts and sciences, the closer one approaches perfection, the more the number of difficulties multiply and accumulate; so that one is sometimes tempted to think that there is a limit beyond which even the genius and hand of man cannot cross, were not that unhoped-for success did not come to reanimate our trust, and prove to us that nothing is impossible for men of inquiry and perseverance.

Yet where the results of the two nations overlapped—such as at Blancnez—their angle values differed by six times as much as their vaunted precision, or a disheartening 12.7 seconds. Who was to blame? Not the French, said the French, and underscored their supreme confidence in their own measurements by pointing out that they had been verified by Méchain.

This confidence in Méchain was not misplaced. Throughout the operation, he had served as Cassini’s workhorse, measuring at Dunkerque, Watten, and the other stations along the French coast. Thanks to his seniority, Cassini had initially monopolized the use of the Borda circle, relegating Méchain to the secondary role of checking the circle’s accuracy against an older instrument called the sector. However, Méchain did get a chance to practice on the instrument, and by the project’s end he was proficient in its manipulation. This experience and his renowned exactitude made him an obvious choice for the meridian survey, his third (and final) stroke of fortune—just as the Revolution wiped out his wife’s modest income.

It was typical of Méchain’s pessimism, however, to read even this opportunity in the worst possible light. He saw little likelihood that the expedition would improve his prospects or enhance his reputation. “So you see,” he wrote to an old mentor on hearing of his selection, “that as insignificant as I have been until now, I must still not expect to become anything greater in the future.”

Méchain’s exactitude was not cold. He was a man of sentiment: anxious, melancholic, and acutely aware of other people’s feelings—especially when their troubles mirrored his own. Though born to the lower orders, Méchain identified with the institutions of the Ancien Régime, which had, after all, treated him rather well. When some of his colleagues, inspired by the new democratic ethos, suggested updating the Academy along more egalitarian lines, he sided with the traditionalists. He was a cautious man, a safe man; anxious to do the right thing. He had been thrust into the senior role in the metric expedition, and he had accepted that responsibility. That was what his honor required.


Sometime soon after June 28, 1792, Méchain finally left the capital, accompanied by his aides and bearing the two repeating circles he had waited so long to receive. His primary adjutant was a military cartographic engineer named Jean-Joseph Tranchot. The mountainous terrain of Catalonia had never been surveyed, and Méchain needed a skilled and hardy assistant. Tranchot was thirty-seven and a native of northeastern France, but he had spent half his life triangulating the Mediterranean island of Corsica, France’s most recent territorial acquisition—a terrain as rough and barren as any in Europe. The two men had already worked together to determine the position of Corsica relative to the map of the Mediterranean coast, and Méchain had personally instructed Tranchot in the finer points of astronomical observation and calculation. Méchain’s other assistant was the instrument-maker Esteveny, trained in Lenoir’s workshop. He was also accompanied by a manservant named Lebrun.

The team met only one obstacle on their voyage south. On the first day’s ride out of Paris, they were halted at a barricade near the town of Essonne, the sort of roadblock Delambre encountered at every turn. The local militia mistook their astronomical instruments for high-tech weaponry, and detained them while they conferred with local officials. In those days, however, before the fall of the monarchy, their royal proclamation saw them through. Past this barrier, they made good speed through a quiet countryside.

All was still calm when Méchain arrived a week later in Perpignan, the southernmost major town in France. The purple-walled Moorish city lay on a coastal plain of scorched vineyards and salt lagoons, locked in the long crooked arm of the Mediterranean as it reached out from Spain to embrace Italy. At the town’s back a range of hulking blue mountains, dominated by the Massif de Canigou, rose out of the parched lowlands like a dark muscular shoulder. These were the Pyrénées, where Méchain would begin his operations. The border with Spain lay along the crests of the mountains.

After presenting himself to the municipal assembly of Perpignan, Méchain and his team took the Grande Route toward Barcelona, then the major highway between the two kingdoms and still the route of a modern six-lane expressway today. Slanting away from the coast, the road traversed rich farmland before it climbed up hills broken by intermittent seasons of sun, rain, and frost toward a low mountain saddle, where it passed under the guns of the massive French fortress of Bellegarde and entered Spain. Thereafter, the French king’s magnificent highway became a “natural and miserable road,” descending through a desolate terrain of loose sandy soil, with cork trees growing on the upper slopes and olive trees cultivated sparsely below. Only as it once again approached the coast did the signs of human industry multiply. The air became fragrant with flowering shrubs and aromatic herbs. The road was bordered by hedges of aloe, Christ-thorn, and wild pomegranate. Chain pumps irrigated fields of maize and orange groves. The number of towns increased. Soon they had passed through the gates of Barcelona, a metropolis seized by the expectation of change.


Eighteenth-century Barcelona had prospered under the watchful gaze of its Castilian overlords. The Catalan town boasted silk manufactures, an Italian opera, and a half-mile-long quay that docked a hundred ships simultaneously. Gold streamed in from the Americas, and textiles and manufactured goods went out to the colonies. With the commercial boom, Barcelona also became an intellectual capital, in part because of its relative openness to its neighbor to the north.

This influx of French ideas was not always appreciated. With prosperity, the town’s population had tripled to 120,000. Many of the new arrivals were French, comprising nearly one-eighth of the residents by the end of the eighteenth century. These immigrants irritated the town’s residents and its Castilian rulers. Artisans viewed the newcomers as competitors, and the Castilians worried about radical ideas. The Revolution only confirmed their suspicions. The French were blamed for the rising price of bread and the downward spiral of wages. For several decades the writings of Enlightenment authors such as Voltaire and Rousseau had been smuggled into Spain, along with political pamphlets, antireligious tracts, and pornography, sometimes all folded together in one scintillating read. Madrid tried to staunch this flow of subversive works, even banning the scientificJournal de physique in 1791 for its purported atheism. Now, on top of these disturbing tracts came aristocrats and priests fleeing the godless Revolution. Not that these émigrés found a warm welcome themselves. The governor-general feared that Revolutionaries disguised as priests were fomenting trouble. In July he ordered the army to stop fugitives at the border. Refugees had to swear that they would remain in Spain and observe the Catholic religion.

Yet the Spanish Crown also wished to profit from the latest innovations in geodesy. For the past few years, the two nations had begun to cooperate on a venture to define their common border. The Spaniards were especially eager to have a look at the Borda repeating circle, so ideally suited to this task.

Immediately upon his arrival in Barcelona on July 10, Méchain met with Spanish officials and their team of scientific collaborators. Their leader was Lieutenant José Gonzales, commander of the frigate Corzo (Roebuck) and an expert in celestial navigation. Méchain was familiar with his work. He was seconded by Ensign Alvarez, as well as ship’s lieutenant Francisco Planez. Like most scientific men of the day, the Spaniards spoke French. They agreed to spend the rest of the month equipping their expedition. All told, they needed supplies for sixty men for several months.

During his stay, Méchain met the elite of the Catalan Enlightenment, savants in close touch with French ideas and thinkers. He was a man with a remarkable gift for friendship. At times melancholy, even petulant, he also inspired admiration and affection: a man of honor in a calling of integrity. His self-deprecating manner had its own charm. He had astronomical correspondents around the world—from Pisa to London and from Copenhagen to Madrid—men with whom he traded celestial data and discoveries. So it was perfectly natural that he befriended such Catalan intellectuals as the polymath general Antoni Martí i Franquès, an astronomer, mathematician, and chemist who was the first to calculate the correct mix of gases in air (revising Lavoisier’s estimates), and that he struck up a friendship with the medical innovator Doctor Francesc Salvà i Campillo.

Méchain had Barcelona’s artisans construct conical tents that would shade the repeating circle while marking the exact position of the station so that it could be located from afar. The tents could also double as shelters for the expedition at night. Méchain had designed the tents in the shape of tepees. A vertical spine composed of a heavy wooden rod having the dimensions of a carriage axle would be driven several feet into the earth, supported by three or four strong pieces of wood, then draped in canvas. Where the rod rose above the tent, it was capped with a double-backed cone like a giant child’s top, painted white to serve as a target for sighting. The bizarre design inspired rumors in talkative Barcelona, already abuzz with news of the tension between Bourbon Spain and Revolutionary France. As usual, the gossips got the story half right. A local grandee heard rumors that the tent-signals were to be planted on mountaintops and fortresses from Barcelona to the frontier to relay nightly news of war preparations against the French.

Once the tents were ready in early August, the team could set out north toward the mountains. In this first pass up the meridian, Méchain’s goal was to reconnoiter a workable chain of stations through the uncharted region between Barcelona and the high-mountain border, so that he might then double back south and measure the stations accurately with his repeating circle. The distance was not far as the crow flies: not much more than eighty miles. The terrain, however, was tortuous, the roads medieval. No carriage could negotiate the tracks, and Méchain had abandoned his custom-built carriage in Perpignan. Not even horses could negotiate the high mountain trails. To complicate matters, a two-week search in the Spanish archives had failed to turn up a single accurate map of Catalonia. The team hired mules to carry their supplies and local guides to lead them through the up-valley pastures and the staggered crests of the pine forests.



This drawing, in Méchain’s hand, shows the signals he designed for his triangulation through Catalonia. The lower conical section could be draped in canvas to form a tepee. The upper double cone was painted white to serve as a target for sighting from afar. The overall height was about twenty feet. (From the Archives Départementales des Pyrénées-Orientales, Perpignan, Méchain to Llucía, October 6, 1793)

In those days, the mountainous region straddling France and Spain was a zone of ambiguity and danger. The high country of the Pyrénées was uncharted, the border porous and ill defined. The Pyrénées march from the Atlantic to the Mediterranean in a series of interlaced chains that encompass fertile valleys and a population accustomed to moving freely between temperate farms, up-country pastures, and neighboring villages. Spain had ruled both sides of the range until the French conquered Roussillon (the part of Catalonia which lies north of the Pyrénées), and a 1659 treaty formally designated the border between the two kingdoms as lying along “the crests of the mountains.” But the French only considered the mountains a natural border as long as it suited their interests. In the 1710s, the Sun King’s armies had marched south toward Barcelona in an attempt to bring all Catalonia under Versailles’ rule. The conclusion of this war had seen a Bourbon placed on the Spanish throne and reaffirmed the border as the crests of the Pyrénées, without specifying which crests. At the end of the eighteenth century, the inhabitants on both slopes still spoke Catalan, and they asserted a fierce independence from both Paris and Madrid, now closely allied under the Bourbons. Smugglers and bandits—miquelets, in the local dialect—plied a dangerous trade in tobacco, firearms, and illegal books, harassing travelers, traders, and border patrols. This was another reason the French and Spanish governments were eager to cooperate on a meridian survey to Barcelona: the triangulations would help surveyors define the border between the two nations in scientific terms, so that trade between them might be policed, regulated, and taxed.

To expedite their search for workable stations, Méchain divided the men into two parties: Méchain and Gonzales took half the men, and Tranchot and Planez the rest. Each party advanced in parallel, planting signals the other party might sight. They began at the top of the Valvidrera ridge, which defines the western rim of the modern metropolis of Barcelona. From there, they worked their way north through the dry pine forests to the isolated monastery of Montserrat.

This medieval pilgrimage site was slotted into a narrow aerie halfway up a tremendous rack of cylindrical rock formations which resembled organ pipes and gave the monastery its name: “the serrated mountain.” Or as a Catalan poet put it: “With a saw of gold, the angels hewed twisting hills to make a place for you.” It took Méchain and his party three hours by mule to mount the thousand-year-old switchback trail, and even then the view was not grand enough. Méchain eventually planted his signal on the portico of the solitary Notre Dame chapel on top of the greatest of these stone organ-pipes, which rose another twelve hundred feet above the monastery and four thousand feet above the valley floor. From this vertiginous peak, he saw a full 360-degree panorama: from the cool northern curtain wall of the Pyrénées to the shimmering southern island of Mallorca. Directly below, in the terraced valley, he could trace out a tumult of broken forms: walnut trees and olive groves segregated by sinuous stone, red-roofed villages clustered along the river bank, dark ridges receding into barren mountains and, of course, the monastery itself directly below. “The peaks so closely surround the monastery that they seem about to crash down and destroy it,” he wrote.

At Montserrat, Méchain and his party were housed in a clean room and served good food and wine. Elsewhere in the region, the inns were wretched—three boards laid on trestles sufficed for a bed, and the windows were without glass. The team spent the next month traversing the desolate northern ranges of Catalonia, zigzagging their way further inland toward the high Pyrénées crests. The fields here were fallow or given over to hemp. The mountains were a savage country. Bears from the high country frequently attacked cattle and sheep, mounting their backs and smashing their heads. In winter, wolves attacked the bears. The shepherds carried firearms, and everyone smuggled.

By the time they approached the border in September the season was far advanced. Méchain had originally hoped to establish stations on the frontier mountains of Costa Bona (elevation 7,500 feet) and Massanet (elevation 6,000 feet). But snow had already put their summits out of reach. In the valleys it was raining heavily. More damaging still, political tension was rising along the border. News of the overthrow of the French monarchy had unleashed a violent reaction across southern France, and its repercussions had crossed over into Spain. The French feared a Spanish invasion; the Spaniards feared that the French Revolution would contaminate their virtuous kingdom. On the frontier near Costa Bona, Revolutionary enthusiasts had planted a Liberty tree, a symbol of Revolutionary regeneration. Bands of miquelets operated with impunity, and neither side could count on their loyalty. Under the circumstances, were Méchain’s joint party of French and Spanish officers to have begun taking telescopic sightings along the frontier, it might well have been considered a provocation to war. It might also have gotten them killed.

Indeed, on the same day that Delambre was delivering his impromptu geodesy lecture in Saint-Denis, Méchain was hunkered down in the Spanish hillside town of Camperdon, on the back slope of the Pyrénées. The governor-general of Catalonia had just ordered the expedition’s Spanish officers to move away from the border. And because Méchain’s passport obliged him to travel with his Spanish hosts, he would have to retreat too. This precaution was sensible. Just that week, he and his men had narrowly avoided an ambush. Twelve French partisans from the cross-border town of Prats de Mollò had been lying in wait for them on a little slip of French territory which happened to reach across the road between two stations. Luckily the expedition had taken another route. The price had been a three-day detour through “the roads of hell.” It had probably saved their lives.

Méchain was thoroughly frustrated. Didn’t these people understand that he was engaged in a peaceful scientific expedition? He wrote to the administrators of Perpignan to ask that a copy of his commission be posted in all the mountain villages. His mission was a scientific study, sponsored by both nations and dedicated to mankind’s highest aspirations for universal knowledge and peaceable commerce. Méchain acknowledged that his official commission—the same one Delambre was at that very moment reading out loud to the volunteers of Saint-Denis—had been signed by a king who no longer ruled. But it was all he had.

In the meantime, Méchain had no choice but to turn his back on the frontier and work his way south, station by station, back toward Barcelona. This time, he would conduct the definitive angle measurements using the repeating circle. He had brought two of them for the purpose: one ruled in the traditional 360-degree scale and the other ruled in the new decimal 400-degree scale, an expression of the new spirit of rationalization. The repeating circle was the brainchild of the Chevalier Jean-Charles de Borda, one of Méchain’s senior colleagues in the Academy. Borda was France’s leading experimental physicist, as well as a seasoned naval commander who had helped coordinate the French fleet’s campaign to liberate the American colonies—France’s first and last victory against the British at sea—with Borda himself commanding the sixty-four-gun Solitaire,captured in an action against overwhelming odds. In the mid-1780s, back in France, he had transformed one of his navigation instruments into a new device for the measurement of the earth. Elderly now, but as rigorous as ever, the stern aristocratic commander had worked with the dwarfish Etienne Lenoir, France’s finest maker of scientific apparatus, to create an instrument precise “beyond any ever conceived.”

The ingenious principle behind the repeating circle allowed the geodeser to take multiple readings of the same angle without resetting the instrument. This repetition promised virtually to annihilate any errors due to the uncertain sense perceptions of the observer or deficiencies in the manufacture of the angular scale. The Borda repeating circle was composed of two scopes set one above the other on brass rings which rotated independently against a precision-ruled circular scale. To measure the angular distance between two points on the earth’s surface, the geodeser set the plane of the circle in the plane defined by the two points. He then zeroed the top scope by sighting the right-hand station, tightening the screws that held that ring in place. He then switched to the lower scope and used it to sight the left-hand station, clamping down that ring as well. At this point, the geodeser could have simply read off the angle between the two stations on the circular scale and called it quits. Instead, he did something counterintuitive. He returned directly to the lower scope and rotated it in the opposite direction, clockwise this time, moving both rings and both scopes together until he had sighted the right-hand station. In doing so, he had necessarily rotated the top scope that much further clockwise as well. Now he loosened the ring for the top scope and rotated it alone counterclockwise until it sighted the left-hand station. This meant that in total the top scope had traversed the double of the angle he wished to measure. Indeed, by repeating this procedure again, he could add another double angle, and so on. Ten such additional doublings could take as little as fifteen minutes if the stations were easy to observe, or all day if they were difficult to make out. Finally, he noted the final position against the graduated scale and divided it by the number of doublings. The repeating circle’s great advantage was that by multiplying readings it sliced error ever more finely. Uncertainties of ten seconds in the observer’s sightings or in the instrument’s manufacture, if spread over enough readings, would be diminished, in the words of its inventor, to the point where “an observer of sufficient patience should be able to eliminate nearly all error.”



The Borda circle is here shown in its horizontal configuration for geodetic triangulation. (From J.-B.-J. Delambre, Base du système métrique décimal, 2, plate VII; photograph by Roman Stansberry)



This diagram illustrates the method of reiteration, which made the repeating circle a precision instrument. In the example that begins with the top–down view in (1) the sighting targets G (for “gauche,” left) and D (for “droit,” right) are separated by 10 degrees, as indicated by the placement of scopes F and L. Both scopes are initially coupled to the graduated circle. In (2) the lower scope F has been rotated clockwise to fix on the target D, thereby moving the upper scope L clockwise the same distance. In (3) the upper scope L has been decoupled from the circle and independently rotated to focus on G, such that it must pass through twice 10 degrees relative to its point of origin. Then in (4) the scope L has been recoupled to the circle, so that when it is refocused on D it moves the lower scope F as well. Thus when the scope F is independently refocused on G (5), it adds yet another 10 degrees to the gauge, while bringing the observer back to the original situation—except that instead of having only measured the 10-degree separation once, twice the original angle has been added to the original reading. This process can then be reiterated as many times as the observer desires—see (6) and (7)—without any need to reset the gauge. The final cumulative angle is then divided by the number of iterations to give a precise reading of the angular separation. This method has the advantage of reducing the uncertainties inherent in any single angle observation and of minimizing the impact of irregularities in the manufacture of the calibrated gauge. The side view, shown in (9) and (10), demonstrates how the same process of iteration could be used to measure the vertical height of a star S with scope AB relative to the horizontal defined by the level scope MN. In this situation the process begins by rotating the entire circle 180 degrees horizontally on its axis, and then sighting the star again with the scope AB (not pictured). (From Jean-Dominique Cassini IV, Pierre-François-André Méchain, and Adrien-Marie Legendre, Exposé des opérations faites en France en 1787, pour la jonction des observatoires de Paris et de Greenwich [Paris: Institution des Sourds-Muets, 1790], plate 3; photograph from the Houghton Library, Harvard University, Cambridge, MA)

Méchain began his measurements at the hermitage of Notre-Dame-du-Mont. He measured on the summits of Puig-se-Calm, Matagall, and Roca-Corra, where Alvarez slept in a tent on the peak until the station was surveyed from all the surrounding sites. He measured at Puig Rodos, where he and Gonzales lodged in a cowshed, making over a dozen four-hour trips up the mountain in hope of finding clear weather for their observations. He measured at Mount Matas, at the chapel above Montserrat and, in late October, over the Valvidrera ridge down into the basin of metropolitan Barcelona. On the night of November 28, 1792, residents in the city reported lights burning on Mont-Jouy, above the General’s Palace, and in other high spots around the perimeter of the city. Méchain and his colleagues were lighting parabolic mirrors to take accurate nighttime readings across the basin.

With these angles in hand, Méchain had every reason to consider the 1793 season a success. He had closed seven stations in less than three months, traversing with meteoric speed nearly half the total distance to his final rendezvous at Rodez—and the most difficult sector of the meridian to boot. If anything, he felt he had been somewhat rushed in his labors. The Spaniards, he complained, did not like to linger at the more “arduous” stations. Had he been working at his own deliberate pace, he would surely have conducted many more observations, despite the adverse conditions. Méchain was striving for a degree of precision that had eluded all other investigators, a precision that would be the best guarantor of the meter’s universality. He was not about to let icy winds or steep mountain climbs diminish the accuracy of a measure meant for all people, for all time. But compromise was the price one paid for collaborative work.

It was true that he had been as yet unable to measure the high mountain stations along the crests of the Pyrénées. But these frontier stations could always be approached later from the French side of the border. And once he returned to France he would have Cassini’s maps and precedent to follow, and would be able to observe to his own satisfaction. This left him only one remaining task in Spain: the latitude measurements that would fix the southern terminus of his arc in Barcelona. For this, Méchain decided to conduct his measurements at Mont-Jouy, the hilltop fortress on the southern edge of the city.


The outcrop of Mont-Jouy, with its castle fortress perched at the sea-cliff’s edge, is visible from everywhere in downtown Barcelona. The six-hundred-foot ascent from the Mediterranean is unassailable. Even on the city side, the slope is a stiff climb. Today, if you prefer, you can ride up in one of the bright red gondolas that shuttled spectators to the 1992 Olympic Games. Or you can drive up the switchback road through the terraced parkland, a legacy of the World’s Fair of 1929 and still the route of one of Spain’s most famous bicycle races and Grand Prix competitions. On quieter days, however, when the amusement rides are abandoned and stray cats sleep amid the disheveled palms and pines, you can easily imagine the hillside two hundred years ago, when eighteenth-century tourists hunted for fossils in the limestone, or unearthed heavy fragments of Hebrew gravestones, remnants of the pre-exile necropolis that gives the site its Catalan name: Montjuïch, or “mountain of the Jews.” In French it is known as “Mont-Jouy,” evoking a hillside of play and pleasure. In Latin it is “Mons Jovis,” the miniature Olympus where a temple to Jove once stood. In sum, it is a place of layered histories.

For centuries the Mont-Jouy site had been occupied by a lighthouse. Then in the seventeenth century, as France and Spain fought for control of Catalonia and the city periodically rebelled against both kingdoms, the hill had been fortified. In 1714 the Spanish monarch began building a fortress along modern lines, which English visitors considered so “perfect in its kind” as to make Barcelona “untenable by an enemy.” Massive walls were arrayed in a pentagon so defenders could train maximum firepower on assailants. The fort could accommodate 3,000 men and 120 cannon at one time. It enclosed a large parade ground and a series of well-appointed barracks for officers and men. Between the Mont-Jouy castle to the south and the massive new Ciutadella fortress to the north, the town was protected from attack and dissuaded from rebellion. From the heights of impregnable Mont-Jouy, where Méchain and his team were lodged for the winter, the town’s rising clamor against the French was a distant din. It was a fortress poised between the city and the sky.



(From Alexandre Laborde, Voyage pittoresque et historique de l’Espagne [Paris: Didot, 1806–22], plate I, photograph courtesy of Special Collections, Golda Meir Library, University of Wisconsin-Milwaukee)



(From Alexandre Laborde, Voyage pittoresque et historique de l’Espagne [Paris: Didot, 1806–22], plate IV, photograph courtesy of Special Collections, Golda Meir Library, University of Wisconsin-Milwaukee)

The view from the Mont-Jouy battlements takes in a vast sweep of the Costa Dorada. Far to the south, where the oceanic blue fades to a pale horizon, you can see, if the day is clear and you have the right kind of equipment, a yellowish break in the hazy line between sea and sky. That is Mallorca, the largest of the Balearic Islands, and if you can see it, then you are looking around the curvature of the earth, relying on the refracted light that bends through the low damp air of the Mediterranean atmosphere.

That long view was itself a temptation. In the flush of ambition, Méchain dreamed of surpassing the Academy’s mission and extending the meridian as far south as Mallorca. The means, moreover, were to hand. Commander Gonzales had offered to sail hisCorzo across the one-hundred-mile straits to light flares on the island peaks. Méchain wrote to France and secured permission from his colleagues to try the extension. In December he put that plan into action. While Gonzales set off with his crew of sailors to plant the special reflecting mirrors atop Mallorca’s five-thousand-foot Sillas Torellas peak, and Tranchot and Planez scouted locations down the mainland coast, Méchain took up his position on the battlements of Mont-Jouy. On the evening of December 16 he spotted through his telescope a faint light trembling on the horizon. Unfortunately, as he informed his colleagues back in Paris, the resolution was insufficient, and this geodetic triangle, the largest ever attempted, would only be feasible if his repeating circle were refitted with more powerful scopes and he were given larger parabolic mirrors. In the meantime, he assured them, his first priority was to complete the mission he had been sent on.

The rest of December was spent in erecting an astronomical observatory alongside the fortress tower of Mont-Jouy, overlooking the sea. The observatory was a wooden cabin, fifteen by twelve feet, with a retractable roof that could be raised by pulleys, and windows that opened out onto an unimpeded view south to the sea and north to the mountains. In this cabin, Méchain positioned his repeating circle in such a way as to capture the transit of stars that crossed the celestial meridian. This was nighttime labor, the work of a few experts. The mountain team was disbanded. While Gonzales counted off seconds from a pendulum clock and Tranchot held a lantern to verify the level of the instrument, Méchain measured the stars.

The latitude measurements to anchor the end points of the survey were the most delicate operation of the entire mission; the slightest stumble here would distort the final result. Ordinarily, the determination of latitude posed no great challenge to eighteenth-century astronomers. Unlike the longitude problem, which had stumped the world’s navigators for centuries, mariners had long known how to calculate their distance north or south of the equator by measuring the height of the sun, Polaris (the pole star), or some other celestial object. Latitude was routine. But science thrives on transforming old routines into new problems. Méchain hoped to determine the latitude of Mont-Jouy with a degree of precision hitherto unmatched in the history of astronomy. His goal was to pinpoint its position on the globe to within one second of a degree, a distance of about one hundred feet, an accuracy comparable to today’s commercial global positioning systems. This degree of precision transformed a routine measurement into an awesome challenge.

In this quest for celestial precision, Méchain’s sole armament was the same Borda repeating circle. But Méchain felt he was up to the challenge. “As Monsieur de Borda says, it depends only upon the patience of the observer to ensure that errors are in the end totally eliminated.” So far, Méchain’s forbearance and patient industry had surpassed all expectations. He wrote to the inventor himself to explain that he had just completed some preliminary calculations of his geodetic results and the sum of angles in his survey triangles never deviated more than 3.5 seconds from 180 degrees, a stunningly small 0.0005 percent discrepancy. Now he was ready to put the instrument to its astronomical test.

For Méchain, the pursuit of precision was a moral quest as much as a scientific one. Its consummation proved that the investigator possessed the patience, skill, and rectitude to reveal nature’s predictability and lawfulness. But the pursuit of precision, like all moral quests, is a hazardous affair. Zooming in on nature’s fine structure can produce unexpected explosions. If the results do not converge, who will take the blame? Nature or the investigator?

For this celestial operation, the plane of the repeating circle was flipped into a vertical position so that it stood erect like a stop sign aligned in the direction of the meridian. One of the scopes, the one that came equipped with a calibrated air-bubble level, was then directed toward the horizon and its position carefully monitored, while the other scope was angled toward the expected height of the transiting star. As the star approached the line of the meridian, the savant tracked its movement across the wire grid in the lens, listening out for the beat of the pendulum clock to mark the exact time. Prowess at this eye-and-ear method was one of the most basic and demanding astronomical skills, but the repeating circle demanded something more. Although the angle between the two scopes, when read off the graduated ring, gave a preliminary assessment of the stellar height, accurate results from the repeating circle once again depended on reiteration. To accomplish this, the savant rotated the entire instrument 180 degrees on its vertical axis, so that the stop sign faced the opposite direction, aligned once again along the meridian. Then he loosened the screws and swung the working scope back around the graduated ring until he could sight the star in the wire grid once more. In doing so, he had doubled the angle traced out along the graduated ring. This action, repeated, gave a value of four times the stellar height, and so on. The whirl of dextrous activity, with the astronomer alternately spinning the plane of the instrument one way and the scope the other, can be likened to a master mathematician solving a Rubik’s cube in the hopes that the right sequence of high-speed moves will unlock the secret combination of the heavens.

When Méchain refused to let his Spanish hosts take a crack at solving this puzzle themselves, they were understandably irritated. Planez complained that Méchain had relegated him to a “mere spectator,” insinuating that the Spanish king would not appreciate having his officers treated so high-handedly. Yet Méchain refused to relinquish the eyepiece. The task of measurement, he insisted, was his alone. Only he had the requisite skill and experience. He alone was answerable to the Academy for the results. This was the savant’s responsibility and his prerogative. It was the way Cassini had treated him on their 1788 expedition from Paris to Greenwich. In the end, Méchain had Planez dismissed and replaced with a more conciliatory assistant, the military engineer Captain Agustín Bueno.

Over the course of the next three months, Méchain took 1,050 sightings of six different stars, each comprised of ten repeated observations. It was a Herculean effort. At night the deep celestial cold caused buckets of water to ice over. All through the Christmas holidays and into the new year, Méchain, Tranchot, and Gonzales worked under the black Mediterranean nights high above the city, pinpointing the latitude of the fortress.

Occasionally he made other sightings. At 6:15 on the evening of January 10, 1793, he reported the discovery of a new comet. Comet-hunting was Méchain’s favorite activity and the basis of his scientific reputation, as all his colleagues knew. So lest they think he had been diverted from his official duties, he also reported that the comet was a bit to the west of Mizar, one of the stars he was using for his latitude measurements. “It’s not my fault,” he wrote. “I wasn’t looking for it.” This innocent discovery was written up in the Diario, Barcelona’s daily newspaper, where the editors felt compelled to add that a comet was a natural celestial body and its appearance did not, as the common people believed, foretell the coming of “war, pestilence, or the death of kings.” That very week the National Convention began its deliberations in Paris on the fate of Louis XVI. Ten days later, on January 21, 1793, the French king would be executed. War soon followed.

On the evening of February 20, in plain sight of Mont-Jouy—but beyond the reach of its guns—a French privateer sacked a Spanish convoy on its way into Barcelona harbor with a treasure of American gold. Huge crowds gathered along the sea wall to watch helplessly as the French pirates absconded with 80,000 duros due to the town’s merchants. Mobs clamored for vengeance, and stoned to death a citizen of Genoa whom they mistook for a Frenchman. The French consul feared that the populace would seize French goods in retribution. “The Catalans,” he wrote, “are reckless, bold, and vindictive; money is their god.” Méchain was distressed to learn that the frigate Corzo, under the command of his friend and scientific collaborator, José Gonzales, had been ordered to give chase to the pirates. Three days later, Gonzales returned empty-handed. The citizens of Barcelona were enraged. Indeed, some historians have called this incident one of the provocations that led to war between the former allies.

The time had come to wrap up the Catalan mission. On the day of Gonzales’ return, Méchain wrote for the first time to his northern collaborator, offering Delambre words of encouragement and sympathy. “Monsieur and dear colleague,” he wrote, “I heard of your misadventures, and felt for you; I learned of your successes, and they gave me much joy.” He suggested that they swap notes and advice. For instance, how did Delambre set up his signals? How had he positioned his repeating circle? For his part, Méchain described his procedures and, with elaborate modesty, assured his collaborator that his own southern triangles would never match the precision of Delambre’s northern ones. His own ineptitude, he hastened to add, was only partially to blame. Measurements in the mountains presented all sorts of difficulties such as one did not encounter in the lowlands. Up there, heavy clouds obscured stations; trails were treacherous; the cold hampered the instrument. Still, he had been ably seconded, and once his latitude data were complete he intended to return to France “sometime next month.”

Delambre answered from Paris with best wishes for Méchain’s “health, courage, and patience.” On a more practical note he also enclosed updated passports—without the seal of the former king.

But before Méchain could leave Barcelona, the Spanish authorities insisted that he report to them on his geodetic triangles and the latitude of Mont-Jouy. As equal partners in the expedition, the Spaniards had every right to this information. The data would enable them to draw the first accurate map of Catalonia, as well as locate their fortresses with pinpoint accuracy. Cajoling these data out of Méchain tried Gonzales’ patience, but at his insistence Méchain spent the month of March preparing a summary report for his Spanish collaborators. He also mailed a précis of his results to Borda in Paris.

What Méchain did not know—because no resident of Barcelona yet knew it—was that a new era was on its way. France and Spain were already at war, though the city had so far seen only signs of rising tension. In early March, the Spanish authorities ordered French citizens to leave the country, and Méchain had to petition to stay long enough to complete his report. Then, in late March, Méchain’s Spanish collaborators, military officers all, were ordered to report to their regiments. Commander Gonzales set out to sea in the Corzo to escort a supply convoy to the fortress port of Roses. This ended any hope of extending the meridian measurement to Mallorca. Méchain successfully pleaded to keep Captain Bueno with him. Without an escort he would never be allowed to visit the two frontier stations linking Spain and France.

The two kingdoms had been close allies throughout the eighteenth century, each ruled by a branch of the Bourbon family, with common enemies in England and the German states. The stirrings of the Revolution had not altered this basic equation, at least not initially. Carlos IV, newly ascended to the Spanish throne, promised not to join the coalition against the Republic so long as his cousin Louis remained unharmed. The French Republicans decided to treat this promise as an ultimatum. Not long after they executed Louis XVI, the French preemptively declared war on Spain. Spain reciprocated two weeks later, then waited another two weeks before summoning Barcelona’s citizens with church bells to hear the Crown’s vow to root out the Revolution. That same day, April 4, the Spanish military command ordered Méchain to leave Mont-Jouy castle and dismantle his observatory. The army could not tolerate the presence of an enemy citizen in the most important fortress on Spain’s Mediterranean coast. Obliged to take up residence in the city proper, Méchain rented a room in an inn known as the Fontana de Oro (the Golden Fountain). The hotel was located just off the renovated Rambla promenade on the Carrer des Escudellers, a street known in the eighteenth century for its fine hotels and potters, and famous today for its prostitutes and pottery shops.

Initially, the war on France’s southern frontier attracted scant attention from Paris, which was understandably preoccupied by the Prussian and Austrian armies two days’ march from the capital. Still, the fighting on the southern front was fierce. Tens of thousands of soldiers fought, and thousands died: regular troops for the Spaniards, and a mix of raw recruits and militia for the French. For more than two years the seesaw campaign would range up and down both sides of the Pyrénées. In the summer of 1793, Spain would seem on the verge of reconquering its former province of Roussillon, along with its capital city of Perpignan. In 1794, France would appear to be on the verge of conquering all of Catalonia, even Barcelona. For two years, troops, militia, andmiquelets—some owing allegiance to France, some to Spain, and some to neither—would attack through high passes, lay siege to valley towns, and fight for coastal fortresses. These battles would remind both sides that the frontier was not a natural border, but a line drawn in blood, defended with arms, and as yet unmarked by science.

In April 1793, however, Méchain still had reason to be satisfied, despite the disastrous turn of international events. His work in Spain was complete, and to his own exacting standards. Under the circumstances, he saw no harm in agreeing to take a long-delayed excursion with his friend, Doctor Francesc Salvà i Campillo. Salvà was one of Barcelona’s enlightened savants: a physician who had campaigned for inoculation against smallpox and for healthy fruit consumption, an inventor who had designed proto-railroads and submarines, a natural philosopher who corresponded with the leading physicists of Europe. He had long urged Méchain to visit an innovative pumping station on the outskirts of Barcelona, admired by English visitors for its mechanical ingenuity.

When they arrived at the pumping station, however, they found it closed for the May Day festivities, with no horses in harness to drive the beam. Méchain pronounced himself content to examine the machinery inert, but Salvà insisted on putting the pump in motion. With the help of his manservant he set to work turning the eight-foot beam, while Méchain gauged the water level in the reservoir. Sudden sharp cries roused Méchain from his post. A rise in the water pressure had forced the beam to reverse course, and it was now dragging the doctor and his servant backwards across the floor. Méchain leapt to their aid just as they released the bar. Struck in the chest, he was hurled against the wall, where he slumped to the floor, apparently dead.

A horrified Salvà and his manservant carried Méchain’s unconscious body to a nearby house, where the doctor—the leading physician in Barcelona—succeeded in reviving the Frenchman’s pulse, though he remained unconscious. Fearing the worst, they lifted him into the carriage and drove back to town. They arrived at midnight and immediately summoned Doctor Sanpons, the town’s best surgeon. The profusion of blood pouring from Méchain’s right ear made it seem doubtful that he would survive the night. Nonetheless, they bled him still more to prevent any build-up of fluid in his brain, wrapped him in sheep’s fleece, and put off any treatment of his wounds until morning. The next morning, Méchain was still alive—though unconscious—so they proceeded with their examination. The entire right side of his chest had been caved in, his ribs crushed, his collarbone broken in several places. They wrapped him in bandages and placed him under close surveillance. Three days later his fever broke and he regained consciousness. Later he would recall with rueful gratitude that “without Doctor Salvà my misfortune would never have occurred, and without his presence, I would not have survived.”

Méchain was immobilized. And even if he had been able to rise from his bed, he had nowhere to go. Whereas a month before he had been obliged to petition to stay in Spain, he was now told he would not be allowed to leave until the war was concluded. The new governor-general, appointed to direct the war effort against France, feared that Méchain’s geodetic data might aid his Revolutionary adversaries. On top of this, the Spanish Treasury had impounded French assets for the duration of the war, and Barcelona’s bankers refused to supply Méchain with additional funds.

No wonder a note of self-pity crept into the letter he dictated to his French colleagues—even as he downplayed the extent of his injuries. “I am unable to write this letter myself and it may lack coherence because I was badly injured two weeks ago . . . , though I certainly expect to be back on the job two weeks from now.” He neglected to mention that he had been injured on a trip unconnected to his mission. And he refused to admit the full extent of his injuries, for fear his Paris colleagues would replace him. Not only did he fear to lose his chance at glory, he could have no guarantee that his replacement would continue the mission with the same exquisite care.

News of Méchain’s accident took a month to reach Paris, where it caused great concern. Thérèse Méchain was beside herself with worry. She had been anticipating her husband’s return by summer’s end. Now she wanted to travel immediately to join him in Barcelona. Lavoisier and the other academicians dissuaded her. It would be difficult, to say the least, for her to cross the border where battles were raging. She spoke no Spanish. Besides, the news from Barcelona was already a month out of date; perhaps her husband had already recovered and was on his way back to France. In any case, her place was with her three young children.

For his part, Lavoisier wrote to Méchain to assure him that fresh funds were on their way. Already he had deposited 34,000 francs with the Barcelona banks in 1793. As Treasurer of the Academy, he would insist that the Spanish bankers honor drafts for a project “which concerns the commerce of all nations.” Moreover, he would personally guarantee the sum—and everyone knew Lavoisier was one of the richest men in France. In the meantime, Méchain should spare no expense in taking care of himself. Indeed, Lavoisier gently scolded his colleague for skimping on comforts, as he was wont to do. Such frugality was not commensurate with the supreme importance of his mission.

In truth, we should reproach you for having practiced too great an economy—one might even say parsimony—with regard to your expenses. You must not forget that you are carrying out the most important mission that any man has ever been charged with, that you are working for all nations of the world, and that you are the representative of the Academy of Sciences and all the savants of the universe.

Above all, Méchain should preserve his health and treat himself as “a person precious to science, to France, to his colleagues, and to his friends.”

Lavoisier wrote these noble words of consolation, exhortation, and financial relief in mid-June. The difficulty was to convey them to Barcelona. No letter of credit could cross the border because seals were being broken to prevent the transmission of military information. The circuitous mail route through neutral Geneva and Genoa was uncertain. The best Lavoisier could do was ask that the letter be transmitted directly from the French general in charge of the army of the Pyrénées to his opposing general on the Spanish side. Adversaries at war always maintained a channel of communication, and surely both parties would wish to aid an injured savant engaged on a mission approved by both governments and dedicated to the pursuit of knowledge for the common good. After all, as Lavoisier noted while pleading Méchain’s cause, “The sciences are not at war.”

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