by Ken Alder
Eighteenth-century warfare was suffused with its own contradictions. Courtesy coexisted with brutality, even between the defenders of the Catholic monarchy and the apostles of Revolutionary liberation. The Spanish generals allowed the captured French officers to spend a night in Perpignan before marching them off to prison. The Revolutionaries tried to persuade the Catalonians to adopt their cause. Like eighteenth-century scientific rivals, enemy officers often had more in common with one another than with the leaders who sent them into battle. With the advent of this new kind of mass war, however, the tug of nationalism began to pull even science apart.
Two months after the fact, Lavoisier at last wrote to Méchain to inform him that the Academy had been abolished, but that as a member of the Commission on Weights and Measures, he was entitled to a salary of 10 francs a day, which his wife might collect on his behalf. At least his family was now getting paid for his labor. Yet Méchain never received this letter. A few months later, at a time when Delambre was being purged from the meridian project and his former colleagues were being imprisoned and threatened with execution, Méchain was still writing to Paris to say that he would defer to the Academy’s wishes. He did hear rumors of the demise of the Academy, however, and believed (with some reason) that the Paris administrators were seeking to replace him. Indeed, he seems to have been spared from the general purge only because the Committee of Public Safety worried that any such threat would cause him to seek permanent asylum in Spain, along with his precious repeating circles and his detailed geodetic data.
So when he was offered a prestigious scientific appointment by the Spanish Crown, Méchain was understandably tempted. Tens of thousands of French men and women had fled their country. Thousands had taken up arms against their own nation. The dead king’s younger brothers were leading armies against their own people. Compared to this, what harm was there in measuring a few geodetic triangles for Spain? How could scientific work be traitorous? Lavoisier had said it best: “The sciences are not at war.” Moreover, Méchain was penniless. The Barcelona bankers had frozen his account, his French paper money was worthless, and a French law prevented his colleagues from sending him hard currency.
Most of all, Méchain despised the radical turn his country had taken since 1792. Even the comparatively mild upheavals of 1789 had distressed him painfully, while recent events had horrified him. But if the Revolution had frayed the knots of his patriotism, it had not loosened his sense of duty to his colleagues and to his mission. Méchain’s virtue was exactitude—a prosaic virtue perhaps, and one rarely associated with genius—but with it came a fierce determination to complete what he had begun. The frontier stations he had once hoped to approach from the French side of the border were now deep in Spanish-occupied territory. Delambre had offered to hurry down from the north of France to help measure them if that were necessary. If, on the other hand, Méchain wanted to measure them himself, this might be his only chance.
Fortunately, his arm had begun to heal, and he had the capable Tranchot to help him. So early in that autumn of 1793 he secured permission from General Ricardos to complete his triangles along the peaks of the Pyrénées. The general would now allow him—the emissary of an enemy power—to conduct sensitive geodetic measurements in a war zone. Already the Frenchmen had calculated the pinpoint locations of Catalonia’s major fortresses. In return, Méchain gave his solemn word that no member of his team would leave the country without official blessing, nor provide their data to the French until the war was over.
That September the two Frenchmen, accompanied by Captain Bueno, ventured back into the Pyrénées in a bold attempt to complete the high mountain stations. At the massive fort of Figuères—which Méchain wove into his triangles—they split into two parties, each taking one of the repeating circles. Méchain and Bueno angled toward Puig Camellas, the hilltop from which the Spanish cannon had pounded the Bellegarde fortress into rubble, while Tranchot struck out on his own for the high inland mountains.
Tranchot’s goal was Puig de l’Estella, a 5,800-foot peak on top of an old iron mine. The summit lay in the shadow of the Massif de Canigou, the glaciated blue behemoth which dominated the eastern Pyrénées. All this had once been French territory. Indeed, just as Tranchot arrived at Puig de l’Estella the French army, beefed up with reinforcements, broke free of their encirclement at Perpignan. Striking inland from the fort at Salses, just north of Perpignan, they began to drive up the Tech valley, forcing the Spaniards to regroup at Boulou, the strategic town where the Grande Route crossed the Tech River. Outnumbered, 9,000 to 29,000, the French were nonetheless supported by several thousand miquelets, who traveled along the flanks of the army, assailing the Spanish and terrorizing peasants. In response, the peasants organized into protective bands. The countryside was in turmoil.
Above the cool pine forests, the high dry air offered superb views of the neighboring geodetic stations, as well as the two armies jostling for position in the valley below. Each side was trying to maneuver their cannon onto the dominant hill. Over the course of twenty-four days the French probed the Spanish positions with eleven skirmishes and three general attacks. On September 22 alone they lost 3,000 men. On October 1, French reinforcements arrived in the face of a Spanish barrage and took a hilltop outpost. On October 5, the French let loose a cannonade of their own to protect a cavalry charge. On October 6, they established a new battery on the heights, which opened fire the next day on the main Spanish camp. Standing on the bare mountain peak beside his bizarre conical signal, sighting with his double-scoped instrument, Tranchot made a visible target.
He had been taking intermittent measurements for a week—the weather was changeable and strong winds threatened to topple his circle—when on the morning of October 7, just as the French battery at Banyuls opened fire on the Spanish positions below, a band of six villagers from the nearby hamlet of Vallmagne ambushed him in the name of the Revolution. Tranchot protested that he too was a French loyalist, an ardent Revolutionary, and on a mission from the National Assembly. He showed them his papers, his passports, and a copy of his commission, along with the newly certified documents sent by Delambre. But the villagers would not allow an unknown engineer to “conduct surveillance” along the front. Puig de l’Estella looked straight down on the valley where the French army was advancing. They bound Tranchot, gagged him, fastened a rope around his neck, and led him by garrote to their town, where the local mayor advised them to conduct him to the district capital, whence he was escorted to Perpignan.
This near disaster turned out to be a stroke of good fortune. Francesc-Xavier Llucía, the chief administrator of Perpignan, was familiar with the meridian mission; he secured Tranchot’s immediate release and more. A few weeks earlier, Méchain had begged Llucía to plant signals on the peaks of Mount Bugarach and Mount Forceral, well behind French lines, so that he might sight them from the frontier. With Tranchot suddenly on the French side of the front, Llucía now authorized him to carry out this task. Two weeks after his arrest the signals had been planted, and Tranchot was climbing back up the Puig de l’Estella to continue where he had left off, just as the battle of the “Battery of Blood” threatened to engulf his mountain aerie. For several days, 6,000 French troops assaulted Puig Singli, where the Spanish cannon commanded the heights over Boulou. The first seven attacks were repulsed, the next three gained the position temporarily, and the eleventh effort, with the Spanish out of ammunition, won the day—until a Spanish counterattack massacred the lot of them the next morning. Calm above the chaos, Tranchot performed his exacting labor.
This would be the only station Méchain ever allowed Tranchot to observe with the circle on his own, and one may well wonder why. It was not due to any lack of experience. Tranchot had toiled for two decades on the triangulation of Corsica, a country as rough as Catalonia. Born in Koeur-le-Petit, a hamlet of Lorraine where French mingles with German, he had survived a difficult birth to grow into a vigorous man. He may have lacked a formal education or
an academic title, but he was among the nation’s most capable cartographers, a man of proven integrity. Toward the end of the Corsican project, accusations of scientific fraud had been bandied about. Tranchot’s final measures had resolved the controversy. Méchain had himself signed the Academy report which singled out Tranchot’s contribution as “infinitely precious for the precision of geography.” From Méchain, there could be no higher praise. By this date, moreover, Tranchot had mastered the repeating circle. Méchain himself admitted, “I could rely on him as I relied on myself.” Yet he always supplied Tranchot with prepared data sheets, and never let him perform his own calculations or look into the expedition notebooks. By way of contrast, Delambre allowed Bellet, a mere instrument-maker, to take observations, record data, and doublecheck calculations.
It is hard to imagine that Méchain’s scruples were justified on technical grounds. In 1790, the two men had collaborated on the navy’s charts of the Mediterranean coast. He knew Tranchot was a geodetic surveyor of consummate skill. Yet collaboration never came easily to Méchain. Despite his time in Lalande’s astronomical workshop, despite the assistance he accepted from his wife and the aides he employed on his journal, Méchain remained an astronomer who worked best alone. His virtue lay in his ability to know the earth, the planets, and the stars. He had less knowledge of his fellow man.
Or perhaps he knew his fellow man all too well. Perhaps Méchain learned what Tranchot had really been up to during his excursion across the border—and that at some time during his foray into France Tranchot had met with his military superiors and supplied them with the plans and geodetic locations of all the fortresses the team had triangulated in Catalonia: Figuères, Girona, Roses, Barcelona, and Mont-Jouy—all the major military installations of northeastern Spain. As a captain of military cartography, Tranchot was obliged to supply his commanders with this information. Failure to do so would have been treason, at a time when treason meant immediate execution. Besides, Tranchot was a patriot and committed to the Revolution, and these plans would help the Republican cause.
For Méchain, though, this would have been a betrayal. Scientific knowledge gathered for the benefit of the world’s people ought never to be used for harmful purposes. Méchain valued allegiance to science over allegiance to nation. At a minimum, Tranchot’s foray into France broke the promise Méchain had made to the Spanish general. His honor demanded that he keep his word. A savant’s reputation was the outward sign that he remained true to his science. To betray one’s own honor was worse than treason.
And this suggests the real reason Méchain did not trust Tranchot. Having betrayed the mission, what was to prevent Tranchot from betraying Méchain and usurping his command of the southern expedition? Tranchot deserved credit for many of the mission’s successes to date. And he was the most likely replacement for Méchain should the astronomer be declared incapacitated. It was this haunting thought which drove Méchain, despite his wounded right arm, back into the Pyrénées.
Méchain and Commander Bueno had their own view of the battle of the Tech from their station at the summit of Puig Camellas. From there, they could see across the battle lines into the besieged town of Perpignan, where the French generals were directing their breakout. They could see south into Spanish Catalonia and the district outside Figuères, where a crumbling sea-blackened turret, the Tour de Mala-Vehina (the “Tower of the Bad Neighbor”) stood on a crest of land belonging to Captain Bueno himself. They could see north toward Bugarach and Forceral, deep in French territory, where Tranchot had placed his signals. And on the bright, clear morning of October 25, as they turned their scopes across the Tech valley, they could see a figure on the summit of Puig de l’Estella, standing beside the double-cone signal—a dark figure against the blue sky hunched over a brilliant brass circle: Tranchot adjusting and readjusting the scopes of his circle while the battle boomed in the valley between them.
When Méchain completed his measurements ten days later, Tranchot was still triangulating. And when another week passed, and another, and Tranchot still had not returned, Méchain grew anxious. He was less concerned about Tranchot’s safety than about the possibility that his aide would remain in France. With these angle measurements done, their mission in Catalonia had ended. Lalande, for one, expected Tranchot to remain in France, and even urged Méchain to slip across the border to join him.
This was to underestimate Méchain’s scrupulousness. He sent a message to Tranchot demanding that he return to Spain immediately. “It is for the sake of my duty and my honor to enjoin you not to leave for France without my permission, neither by any route nor by any means. It is for this reason, and not for the continuation of our mission, that I insist so strongly. It would disgrace us greatly, and deservedly, for you to conduct yourself in any other fashion.” At stake was something greater than the success of a scientific project—“the most important any man has ever been charged with.” At stake was Méchain’s reputation as a man of his word.
The Spanish army chose just that moment to counterattack. They took advantage of their superior numbers and once again drove the French back down the Tech valley, conquering the coastal towns of Collioure and Bagnols and renewing their siege of Perpignan. In the process, they sealed off Tranchot. He was trapped in France, he said, by “force of arms.” Perpignan now became the scene of an all-out political struggle between moderates and radicals. Another failed French general was guillotined. Individuals suspected of counterrevolutionary activities—especially those with ties to the aristocracy, the Church, or the party out of favor—faced summary execution. Among these was Llucía, the French Catalan Revolutionary who had once declared that “It is time to electrify all souls.” He had saved Tranchot, but he could not save himself. Some fifty heads fell that month in Perpignan alone. Only the weather stopped the Spanish advance this time. The November rains ended both the military and the geodetic campaigns. In the Tech valley the soldiers slept in mud. Méchain returned to Barcelona. And some time that winter, Tranchot slipped back across the frontier to rejoin him.
This proof of the Frenchmen’s integrity did not persuade General Ricardos. Despite petitions and personal pleas, he insisted that Méchain and Tranchot remain in Barcelona until a peace was concluded. Nor would Méchain be allowed to send home any more communiqués with numerical data; these would be confiscated at the border as encoded letters. No military leader could knowingly allow this information to fall into enemy hands, although Ricardos was raising the drawbridge after the moat had been breached.
That spring, the fortunes of war shifted once again. In March, while visiting Madrid, the victorious General Ricardos died. His replacement, General La Unión, was the youngest general in the Spanish army, a devout Catholic of high moral sentiment, repelled by the populist atheism of the French Revolution. Soon after, a new French general, Jacques-Coquille Dugommier, fresh from his victory at Toulon (where he had commanded the young Napoleon Bonaparte), took charge of the Revolutionary army in the region. Dugommier quickly set in motion the republic’s plan to liberate—or rather, subjugate—Catalonia. Catalonia, he proclaimed, was ripe for revolution. The province was rich in mines and industry. The people loved liberty and hated their Castilian overlords. If they embraced equality and became an autonomous republic, the province might serve as France’s boulevard to the rest of the Iberian peninsula.
Dugommier attacked as soon as the season allowed. By mid-June, the French had recaptured the high mountain passes and had begun to push their way down the southern slopes of the Pyrénées. The Spanish retreated to their massive fortress at Figuères on the Grande Route, positioning 9,000 soldiers and thirty-two artillery pieces to hold their right flank at the Tour de Mala-Vehina on the lands of Méchain’s cartographic collaborator, the good Captain Bueno. Should Figuères fall, as seemed likely, the road was open to Gerona, and beyond that, Barcelona.
For the past nine months Méchain had heard no news from his colleagues in France, only rumors. He wrote them a long lett
er anyway. He had failed to secure passage on a vessel out of Barcelona, and the Spanish were holding him in “unjust detention.” With the Academy abolished, as reported in the public papers, the meridian project had no doubt been canceled as well, and the meter would be determined with a pendulum, as originally planned. If his mission had indeed been canceled he begged to be informed of this at once. If not, he could see a way to complete the meridian survey by the end of the year. He had the scenario all worked out. As soon as the Spanish general released him, he would return to France and triangulate his way north toward Delambre. Because the French terrain had already been surveyed and mapped by Cassini, he would simply revisit those old angle measurements with the repeating circle. If he began next month, he could triangulate as far as Evaux by July. Evaux was the halfway point of the meridian arc, well north of Rodez, where he had been scheduled to meet Delambre. With luck, he might even triangulate as far as Bourges, which would mean that he would have surveyed two thirds of the total arc, instead of the one third he had been assigned. Then the two astronomers would together measure the two baselines in August, one in Delambre’s northern sector and one in his own southern sector, and have the mission wrapped up by the end of the summer.
