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  Before the hecklers made good on their threats, administrator Noël intervened. Feigning severity, he ordered the suspect carriages placed under seal and towed into the abbey’s courtyard for safekeeping. Then he forced Delambre back into the town hall on the pretense that he wanted a more convincing account of his mission. Once inside, he obliged Delambre to spend the rest of the night in the company of the aldermen—for his own safety—while they requested instructions from Paris. Delambre and Bellet slept that night in armchairs in the town hall of Saint-Denis. Only at dawn were they allowed to take lodgings in the nearby inn known as the Trois-Maillets.

  The National Convention voted later that evening, September 7, 1792, to make Delambre and Méchain official emissaries of the Republic and ordered local authorities to assist them on their route. An expedition licensed by the King had become the people’s mission. Lefrançais brought Delambre the decree as soon as it was released, and together they took it to the Sunday morning meeting of the municipal council so that they might get the seals removed from their carriages and continue on their mission. That night the Benedictine monks performed their last holy Mass after a thousand years of continual prayer in the kingdom’s greatest abbey.

  HENRY IV EXHUMED

  The corpse of Henry IV, the most popular of all French kings, was briefly exhibited in the Basilica of Saint-Denis after its exhumation in 1793. (Photograph by Roman Stansberry)

  In the interim, the volunteers of Saint-Denis had been marched to a barracks outside Paris for accelerated training, and thence to meet the Prussian invaders at Châlons-sur-Marne. The volunteers of Saint-Denis helped save the Revolution. But the Revolution was not finished with Saint-Denis. In December, a crowd invaded the basilica, not to slaughter the living but to disinter the dead. The militia protected the royal graves, but popular calls for a mass exhumation multiplied after Louis XVI was guillotined in January 1793. The king’s body was dumped in an anonymous grave. His ancestors did not deserve a better resting place.

  Again the National Convention scrambled to lead the populist charge. In honor of the first anniversary of the uprising of August 10, they ordered the tombs of Saint-Denis destroyed so that the royal dead might be reburied in a mass grave at Valois and the lead from their coffins—nine tons in all—refashioned into cannonballs and musket shot. Only the statues of François I and other high Renaissance works were saved because of the excellence of their art. Chief Administrator Noël turned the first spade of earth. The first royal corpse brought to the surface was that of Henry IV, the nation’s most popular king, perfectly preserved, his face black as pitch. A young soldier cut a lock from Henry’s beard before laughing onlookers, held it to his chin, and declared: “Well, I’m a soldier too! Now I’m sure to vanquish those English bastards.” When the Sun King was exhumed, a worker sliced open the corpse’s belly to the applause of the crowd. To mask the stink, officials burned a mixture of vinegar and gunpowder and closed the basilica.

  Not long after, the municipality was debating whether to permit local patriots to use cannonballs to shoot down the basilica’s belfry, when the Commission of Weights and Measures intervened. The tower, they said, was crucial to the survey of the meridian that ran from Dunkerque to Barcelona. In consideration of its “great utility” for determining the new Republican measures and triangulating the territory of the Republic, as well as for other cartographic and scientific purposes, the council ought merely to efface those remaining crucifixes and fleurs-de-lys that offended the good patriots of Saint-Denis, and leave the tower standing. So science saved the basilica, even as science itself came under attack.

  CHAPTER TWO

  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 Paris expecting 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 Ca
ssini’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.