The Metric of Revolution

“A Global Scheme! Ah knew it!” Dixon beginning to scream, “what’d Ah tell thee?”

“Get a grip on yerrself, man,” mutters Mason, “what happen’d to ‘We’re men of Science?’ ”

“And Men of Science,” cries Dixon, “may be but the simple Tools of others, with no more idea of what they are about, than a Hammer knows of a House.”

—THOMAS PYNCHON, Mason & Dixon

I fear that the mathematicians, who have not yet troubled the world, will trouble it at last; their turn has come.


The French Revolution was not one thing but many things, although it was principally a contest to assert just what one thing the Revolution was. Paris was the arena where this contest was the fiercest. But across the nation, villagers, townspeople, and peasants also asserted just what the Revolution meant to them. For some, the Revolution was a noble struggle between a virtuous people and a parasitic aristocracy. For others, the Revolution was a civil war between godless usurpers and a loyal flock. Some proclaimed the Revolution a war of national defense; others, a movement of international liberation; still others, a war of foreign conquest. The Revolution, some said, was an attempt by Paris to bring the countryside to heel; others said it was an attempt by the provinces to establish their autonomy. Some saw the Revolution as a movement to liberate commerce; others, as a social struggle to guarantee a just price for bread. And always, everywhere, the Revolution was a chance to launch a career, make a fortune, join a parade, set out on an adventure, or bemoan the passing of the good old order. Electric promises of equality and panicked warnings of betrayal traveled in waves from Paris to the nation’s boundaries—and were returned: distorted, amplified, transformed. Like a body of water pelted with stones, the nation was roiled by waves that seemed occasionally to cancel each other out while, under the calm, pressure built for another surge.

The moment the authorities unsealed his carriages and supplied him with new passports, Delambre rushed to Saint-Martin-du-Tertre to sight the Collégiale at Dammartin before the church was demolished for scrap. Thanks to the National Assembly’s declaration that the meridian expedition was a mission of national importance, he could move freely through the Republic. It helped too that two weeks later the French armies stemmed the Prussian tide at Valmy. The countryside calmed down for the harvest.

Yet no sooner had human events broken his way than nature conspired against him. A northern gray autumn settled on the land. Every day that dismal September Delambre climbed the steeple of the church at Saint-Martin-du-Tertre to peer across the shrouded farmlands. But even though his angle calculations told him exactly where to look, he could pick out neither the Collégiale of Dammartin nor the Paris dome of the Invalides through the mist.

Conditions in the church steeple hardly approximated the laboratory ideal. Wind and icy rains chilled the bones and clogged the repeating circle. Every toll of the bell seemed likely to shake the narrow belfry to pieces. Even a slight shift in Delambre’s weight unsettled the floorboards and rattled the instrument. Eventually, he turned the observations over to his young aides, Lefrançais and Bellet, who took fixed spots in the high cramped tower so they could alternate scopes without having to shift positions. Lefrançais was smaller than Delambre, and fit into the confined space more easily. And Delambre’s weak eyesight obliged him to adjust the focus every time he swapped scopes, enough to disturb the instrument.

Delambre and his team would wait three weeks for a clear view of Paris from the narrow church tower at Saint-Martin-du-Tertre, only to discover, after a rainstorm finally cleansed the atmosphere, that a low hill had been blocking their view of the Invalides dome all along. This left the Panthéon as the only plausible Paris station, meaning they would have to redo all the measurements they had conducted since the beginning of their expedition in June. After four months of labor and danger, they had yet to travel more than forty miles from Paris, and were no further advanced than when they had begun. It was progress worthy of Don Quixote.

With the days growing shorter and the northern skies darkening Delambre pressed on, reversing his route of the previous summer to work his way clockwise around the capital. He completed the Collégiale at Dammartin just before ownership transferred to the demolition men. He returned to the Château de Belle-Assise, the scene of his earlier arrest, to retake his measurements there, this time without incident. (In the nineteenth century, years after these measurements were done, the château would come into the hands of Baron de Rothschild, before being destroyed, all but an ancient windmill that still stands watch over the valley of Euro Disney today.) Delambre observed from the church at Brie-Comte-Robert in early November. And by the end of the month he was back in Montlhéry, where he had begun his journey half a year earlier, in what was now another historical era. This time he decorated his signal pole as a Liberty tree to placate local suspicions. The winter was advancing. The team lit an open fire at the foot of the ancient tower to warm themselves as they worked.

Delambre had hoped to call a halt at that point and return to the capital for the winter, but the owners of the Malvoisine farm, who had kindly allowed him to elevate their chimney as a signal, feared the structure would collapse during the next winter storm and asked him to remove it. This meant he would first have to complete his observations from the Malvoisine roof and from all its adjacent stations. Among these Delambre had selected a site dear to his heart, one he knew with astronomical intimacy: the Château de Morionville, the country residence of his patroness, Madame d’Assy, located just outside the town of Bruyères-le-Châtel. On summer days before the Revolution he had often set his astronomical equipment on the terrace outside his rooms there, or conducted observations from his open window. Viewed from the rooftop of the farm at Malvoisine, Madame d’Assy’s garden door appeared in his scope like a black stain against a white background.



This drawing of the cupola on top of the dome of the Paris Panthéon was annotated by Delambre and shows the position of the illuminated globe he used as his sighting target during his triangulations of 1792–93, as well as the special observatory the architects rigged for him at (C). The illuminated globe was a temporary replacement for the cross that had once capped the dome. In February 1793, just before Delambre returned to the capital, it was in turn replaced by a half-dome pedestal for a statue of Renommée (Fame). Note that Delambre has penciled in the various dimensions in the old Paris measures. (From the Archives de l’Observatoire de Paris)



In this drawing of 1794 the artist De Machy imagines how the Panthéon would appear were it to be capped by the statue of Renommée (Fame). A full-scale model of the statue was made, but it was never installed on its pedestal. (From the Bibliothèque Nationale de France, Paris; Collection Destailleur)

These were the last observations he conducted that season. As he surveyed his way south toward the outskirts of the royal forests of Fontainebleau, snow began to fall on the woods. In these conditions, geodetic measurements became impracticable. No sooner had Delambre finally worked his way out of sight of Paris than it was time to return to the capital. He would spend February and March at the top of the dome of the Panthéon—the central geodetic station for the city of Paris—triangulating all the sites surrounding the city.

The Panthéon, commissioned by Louis XV as the Church of Sainte-Geneviève, had been on the verge of completion when the Revolution erupted. It had since been converted into a temporary warehouse for the thousands of old weights and measures sent in by provincial towns to await comparison with the new Republican measures. Now the nation’s leaders wanted to transform the warehouse into a mausoleum for the nation’s greatest heroes. The building’s monumental gray dome dominated the capital’s highest hilltop, and the Revolutionaries felt that its pure neoclassical form made it a suitable architectural rebuke to the Gothic obscurantism of the royal tombs at Saint-Denis.

But first the Panthéon had to be stripped of its churchly attributes. First to go was the cross on top of the cupola, replaced with an illuminated globe. It was this globe that Delambre had used as his sighting target while he circled the city. The architects had still grander plans, however, and in November—just as Delambre slipped out of sight of the capital—they had replaced the small illuminated globe with a much larger half-globe pedestal, slightly flattened, upon which they planned to set a colossal female statue dedicated to Renommée (Fame). Already a sculptor had prepared a full-scale model of the bare-breasted thirty-foot figure, with a fifty-foot wingspan and a trumpet at her lips that would sound (if only metaphorically) “to the frontiers of France, and be noted from the middle of the ocean.”

It was an ideal spot from which to measure the world. Delambre obtained permission to build a temporary four-windowed observatory high up in the cupola where he could work sheltered from the icy winds. The architect even talked of building a permanent astronomical observatory in the hollowed-out half-globe under Fame’s feet, thereby “uniting the beauty of art with usefulness to science.” This goal was consonant with the building’s greater dedication to the triumph of Truth over Falsehood. In the pediment over the mausoleum’s motto—“AUX GRANDS HOMMES, LAPATRIE RECONNAISSANTE” (“TO GREAT MEN, A GRATEFUL NATION”)—a frieze depicted the sort of heroes entitled to admittance. As the architect explained, it was by “the conquest of Error” that Genius, in the guise of a robust young man, might manfully seize the laurels of immortal remembrance.

Thus far, the men deemed worthy of being considered for this honor were Mirabeau, the nation’s greatest politician; Voltaire, its greatest literary lion; Rousseau, its greatest political thinker; and Descartes, its greatest savant. Mirabeau was the first actually to be buried there. Soon after, Voltaire’s remains were borne to the Panthéon in a stately procession witnessed by a hundred thousand spectators. And preparations were now underway to accord Rousseau the same honor. But one man’s hero is another man’s scoundrel, and just as Delambre returned to the capital, a young radical politician named Maximilien Robespierre demanded that Mirabeau be disinterred for not living up to Republican ideals. The decision on Descartes was postponed. In the meantime, the interior of the Panthéon remained stacked with provincial bushels, pints, and pound weights, sent in for comparison with the new metric measures.

In January and February 1793, during the month it took the architects to build Delambre his neat little crow’s-nest observatory 227 feet above the pavement, the king of France was tried, judged, and executed, war was declared on Great Britain, and food riots ravaged Paris. Then from February to March, while Delambre climbed the cupola daily to triangulate all the stations surrounding the capital, war was declared against Spain, the west of France rose up in a counterrevolution, and preparations began in the National Assembly to create a Committee of Public Safety to organize the nation’s defense. His was an admirable perch above a city in turmoil. Delambre sighted the new semaphore telegraph station on Montmartre; it could relay battle news from the northern front in thirty minutes. He sighted his own personal observatory at 1, rue de Paradis. He sighted the stations at Saint-Martin-du-Tertre, Dammartin, Belle-Assise, and Montlhéry. When he came down from the Panthéon for the last time on March 9, 1793, he had finally completed the stretch of the meridian that traversed the area around Paris. This represented less than one-tenth of his assigned sector, whereas Méchain in that time had completed nearly half his sector, and was wrapping up his latitude measurements at Mont-Jouy.

Delambre wrote immediately to Méchain to tell him where things stood in the north. Try as they might, his experience of the past year gave him little reason to hope that they would be able to link their triangles this year. “Too many obstacles will get in our way,” he predicted. Already the new administrators of radical Paris were ignoring his request for a passport, despite the proclamation of the National Assembly approving their mission. (He apologized for the fact that the proclamation listed his name first, but “I was not there to tell them that your entry into the Academy predates mine.”) “Farewell, my dear colleague. I wish you health, fortitude, and patience. Be assured of my sincere friendship.” By the time the letter arrived, Méchain’s progress had also come to a halt; he was confined to bed, immobilized, out of funds, and detained by Spanish law.


The French government was running out of patience. Several years had passed since the Academy had first promised that the survey of the meridian would be done within a year. The actual expedition had been underway for a year now, yet both Delambre and Méchain had stalled far short of their rendezvous point. Various proposals for the reform of measures had been in circulation since the earliest days of the Revolution, and the radical legislature was impatient to bring France into the metric age. Officials had begun to ask if the meridian expedition was really worth the wait. It was a question that some people had been asking from the start.

Paradoxically, one of these people was Jérôme Lalande, the savant who had given both Delambre and Méchain their start in astronomy. Lalande had been the first person to take advantage of the French Revolution to place before the nation’s representatives a proposal to reform its weights and measures. In April 1789—before the taking of the Bastille, even before the representatives summoned by the king had constituted themselves as the National Assembly—Lalande had denounced the “unconscionable and multiple abuses of the diversity of measures,” and urged the representatives to create a uniform system of measures by simply declaring the Paris measures to be the national standard. In this speech he also demanded a moratorium on the slave trade, the substitution of free public education for the Ancien Régime’s religious schools, and the “liberation” of all monks and nuns.

Lalande had always been a man ahead of his time, yet curiously Ancien Régime in his obsessions. He was not only France’s foremost astronomer, he was its foremost popularizer of science—in an age when the popularization of science was the principal weapon against intolerance, superstition, and injustice. Lalande had also trained with the Jesuits and had nearly taken orders, only to become France’s most notorious atheist. His father, a Burgundian postmaster and tobacco merchant, sent him to Paris to study law, but every night he slipped out of his student chambers in the Hôtel de Cluny to join the astronomers on their rooftop observatory. In 1751, when Lalande was nineteen, his mentor sent him on an astronomical mission to Berlin to help determine, by parallax, the distance from the earth to the moon. In Berlin, Lalande dined with Frederick the Great (Europe’s greatest benign despot), lodged with Leonhard Euler (its greatest mathematician), and conversed with Voltaire (its greatest wit). On his return to Paris in 1753, he was unanimously elected to the French Academy of Sciences. He was twenty-one years old.

Immediately he was plunged into controversy. Lalande did not agree with his mentor about how to correct his results for the shape of the earth. Lalande was vindicated by the Academy, and his mentor refused to speak to him again. Polemics and controversy pursued him for the next fifty years.

In 1773 a rumor circulated through Paris: Lalande had calculated that a comet might swing close enough to the earth in 1789 to drive the seas from their beds and devastate the earth. The Archbishop of Paris recommended forty hours of prayer and the kingdom’s police chief asked the Academy of Sciences to repudiate Lalande’s findings. The Academy replied that it could not repudiate the laws of astronomy. Then, when Lalande finally published the paper, he gave such a low estimate of the odds of disaster (about one chance in 64,000) that many readers assumed the government had suppressed the truth. In the countryside, word of the impending apocalypse caused public repentances and (supposedly) stillbirths. (If only Lalande had predicted the end of the kingdom instead of the end of the world, one wag later remarked, he would have been the greatest prognosticator of the century.) Some good at least had come of the panic, according to Condorcet. Court ladies and market women had confessed their sins, and the bakeries had experienced a run on unleavened bread, boosting the local economy. Where the laity had once heeded necromancers, they now hearkened to scientific prognosticators. “The time of prophets has passed; that of dupes will never end.”

Lalande had an insatiable thirst for fame. He cultivated friendships with the great minds of the age and published incessantly. He wrote about paper and platinum, canals and calendars, music and morals. He wrote eulogies for the dead, tributes to the living (including his own estranged mentor), and predictions of astronomical events to come. He was a prodigious travel writer. In Italy he catalogued antiquities, met the Pope, and lobbied him to remove the writings of Copernicus and Galileo from the Index of prohibited books. In England he visited the Greenwich Observatory, exchanged pleasantries with King George III, and helped smuggle out the first description of Harrison’s famous chronometer, designed to determine longitude at sea. He dismissed balloon flight as impossible; then, when the Montgolfiers proved him wrong, claimed he had predicted success and demanded to be taken on the next flight. Later, he set out on a three-hundred-mile balloon voyage to attend a scientific conference in Germany, got as far as the Bois de Boulogne, and declared victory in the form of bad verse. He even wrote the first history of the secretive International Brotherhood of Masons and cofounded its infamous Lodge of the Nine Sisters, which claimed as brothers such luminaries as Condorcet, Danton, Diderot, d’Alembert, Voltaire, and Benjamin Franklin.

Such boundless enthusiasm always attracts naysayers—or at least it does in France. One wit diagnosed Lalande as suffering from “dropsy of celebrity.” Lalande confessed the fault, but excused himself on the basis of his “innate truthfulness and love of virtue.” Eventually, his mania for fame itself became a theme in the commentaries on his doings, generating still more publicity. Voltaire praised him “for having found the secret of making the truth as interesting as a novel,” and the poet even knocked off a couplet in the astronomer’s honor.

Your glory is known throughout the universe,

And only when it ends, will your name disperse.

As for his notorious taste for insects and bugs, he reported that spiders had the flavor of fine hazelnuts, whereas caterpillars tasted more like peaches. He dined on the latter regularly at a friend’s house, directly after Saturday meetings of the Academy. The friend noted, “As my home opened directly onto a fine garden, Lalande could easily find enough caterpillars there to appease the first pangs of his hunger; but as my wife liked to do things properly, she would gather a goodly number in the afternoon so she might serve them to him as soon as he arrived. Because I always offered him my portion of this ragout, I cannot tell you except by hearsay how they tasted.”

He was a supremely ugly man, and proud of it. His eggplant-shaped skull and shock of straggly hair trailing behind like a comet’s tail made him a favorite of portraitists and caricaturists. He claimed to stand five feet tall but, precise as he was at calculating the heights of stars, he seems to have exaggerated his own altitude on earth. He loved women, especially brilliant women, and promoted them in both word and deed. His longtime mistress, Louise-Elisabeth-Félicité du Piery, was the first woman to teach astronomy in Paris. He sang the praises of women astronomers such as Caroline Herschel and Madame Lepaute. When he was appointed director of the Collège de France during the Revolution, his first official act was to open classes to female students. He dedicated hisLadies’ Astronomy to his mistress, and this serious primer, with its examples of active women researchers, was still being published sixty years later.

Yet he loved women in ways they did not always find agreeable. He never married, though he bragged of refusing advantageous offers. When at the age of forty-four he finally did propose, the fourteen-year-old girl refused him. He had a salacious turn of mind. He noted in his diary that“Monsieur de V———loved his pretty wife so much that he invited the most agreeable young men to his home and let them have sex with her in front of him; Helvetius was among them.” He made an unwelcome pass at the gifted young mathematician Sophie Germain and wrote an abject apology the next morning—including an apology for slighting her scientific knowledge. As he liked to tell pretty women: “You have the power to make me happy, but not the power to make me unhappy.” He loved women, he said, but not so much as to distract him from his greatest love: the stars.



This pastel portrait of Lalande was drawn by Joseph Ducreux in 1802, when the astronomer was seventy years old. It shows him in the uniform of the new post-Revolutionary Academy of Sciences. (From the Musée de Versailles, Réunion des Musées Nationaux; photograph by Art Resource, New York)

In short, he was a shameless self-promoter, a trait which made him especially effective at the calling he prized above all others: teaching. Lalande was a gifted pedagogue, a missionary for his science. His Astronomy became the field’s standard textbook. His lectures at the Collège de France attracted two hundred students, with auditors from across Europe, who then joined his worldwide network of correspondents. By the 1780s, he had trained France’s next generation of astronomers, among them Delambre and Méchain, putting them all to work in his scientific workshop, the Lalande family enterprise.

For Lalande, astronomy was the family business. He had brought his young cousin Lefrançais in from the country, adopted him as his nephew, trained him in astronomy, and then married him to his illegitimate fifteen-year-old daughter, Marie-Jeanne-Amélie Harlay, whom he had trained in mathematics to calculate his celestial data. He was very attached to his “niece” and “nephew”—as he called them—and easily moved to tears where they were concerned. Amélie performed the bulk of the calculations for the massive navigation tables he published in 1793, “tiresome calculations, but here acquiring a more noble character by the aid they offer navigators, connecting remote parts of the universe.” He could be a hard taskmaster. He complained to his mistress, “When I’m not around, my shop goes on holiday.” “Wash out my nephew’s head if he’s not working.” At the start of the Revolution, he announced a new goal for his astronomical family: a monumental catalogue of thirty thousand stars that would surpass the old celestial survey. His students were likewise expected to contribute to this enterprise.

Méchain had already done the lion’s share of the work for the second edition of Lalande’s Astronomy, which appeared in 1781. The prize competition of the Academy that year was to chart the trajectory of the comet Lalande had predicted might devastate the earth in 1789. Méchain wrote a paper that showed that his mentor had erred by confusing the appearances of two different comets. When the Academy of Sciences awarded its 1781 prize to Méchain, Lalande had the good grace to be pleased. In 1782 he got Méchain elected to the Academy, then looked around for a new recruit.

In 1783 Delambre began supplying Lalande with data for his third edition of Astronomy, and Lalande soon ran out of words of praise for his abilities. “Monsieur Delambre . . . is currently the most able astronomer of any country in the world. . . . We must encourage so valuable a recruit, and bind him to a science in which he performs prodigious feats without hope of any position or advantage.” Delambre’s first astronomical coup likewise came at his mentor’s expense. In 1786, he was one of only two astronomers in Paris to record the last flicker of Mercury during the planet’s transit across the sun. This was not merely an observational coup, it was a theoretical triumph. As was his custom, Lalande had publicized the time of the planet’s transit in advance. However, the overnight clouds persisted beyond the appointed hour, and the country’s leading astronomers all quit their posts. When the clouds broke at eight in the morning, Delambre, still at his telescope, saw Mercury exit the sun forty minutes after Lalande had predicted it would. The only other observer to capture the transit had been looking for sunspots. Delambre had stayed at his post because he doubted Lalande’s calculations.

For all his boundless vanity, Lalande never took offense when his students contradicted him. “I am waterproof to insults, and a sponge for praise,” he said. Perhaps he remembered the repudiation he had suffered at the hands of his own maître. In any case, there was work enough in heaven for all. Science was a collective triumph, even if the race was run by men hungry for personal fame. He presented Delambre’s Mercury results at the next meeting of the Academy of Sciences—with Delambre in attendance—then promptly used the data to update his own tables.

The Mercury coup exhibited the scientific virtues that would sustain Delambre on his seven-year pursuit of the meridian: his patience and perseverance, his precision and skepticism, his ability to marry observation and theory, and his confident willingness to show up his elders. Méchain, despite tremendous preparation, had missed the observation of Mercury. As he noted ruefully, he had believed Lalande’s prediction.

Delambre also knew how to parlay success into greater opportunities. At that same Academy meeting, Pierre-Simon Laplace presented another installment of his System of the World, his life’s work synthesizing Newton’s cosmology. Laplace was the same age as Delambre, but he was already his era’s leading physicist, a theoretician who claimed that were the position and motion of all the world’s particles known, the entire future of the universe could be predicted by a being of infinite intelligence. This particular paper refined a technique for tracking the perturbations which one planet caused in the orbit of another. Delambre was dazzled by the ability to calculate orbits so precisely. Several years before, Méchain had supplied Laplace with some preliminary data for the newly discovered planet of Uranus. Delambre now proposed to confirm Laplace’s theory using Uranus. This involved tremendous labor: for nearly two years Delambre observed at night for eight hours at a stretch, then spent equal time on daytime calculations. His achievement did not go unrewarded. At the prompting of Laplace and Lalande, the Academy of Sciences announced that the topic for its 1789 prize competition would focus on the precise calculation of the orbit of Uranus. As Delambre remarked to a friend, he could be sure his memoir would be the best, since it was the only one submitted. The prize committee consisted of Cassini, Lalande, and Méchain. As Delambre privately admitted, it would have been hard to find judges more “favorably disposed.” In the report which awarded his student the prize, Lalande praised Delambre as “an astronomer of wisdom and fortitude, able to review 130 years of astronomical observations, assess their inadequacies, and extract their value.”

How did Méchain feel about this rising new talent? Did he resent Delambre’s Mercury coup, his one-upmanship on the Uranus data? Was he jealous of his maître’s newfound favorite? Méchain’s feelings mattered to Delambre. Méchain not only sat on the prize committees; as a member of the Academy, he could have blocked his rival’s election. The two astronomers had occasionally observed the stars together. Lalande asked them to collaborate on yet another edition of his Astronomy. And Méchain published Delambre’s work in his astronomical journal. Yet relations between the two remained formal and Delambre still thought it wise to ask his friends to put in a good word about him with Méchain. For his part, Méchain always addressed the up-and-coming astronomer with elaborate courtesy as the “abbé de Lambre.”

Delambre would later acknowledge that “one can trace certain similarities between the early years of Delambre and Méchain.” Both were men of modest background, sons of provincial Picardy, educated by the Jesuits, rejected by the Ancien Régime’s institutions of higher learning, and later employed as tutors. And from there, their lives converged ever more closely: the same scientific discipline, the same maître, the same expedition. But a career trajectory does not decide one’s fate.


Lalande’s proposal that the nation adopt the Paris measurement standards received little attention until the juridical revolution of August 1789, when the nobility renounced all its legal privileges, including its authority over weights and measures. From that point onward, a flood of proposals poured in from the members of provincial learned societies, underemployed state engineers, and enthusiastic citizens of all stripes. Each of these pamphleteers had his own pet notions about the form the nation’s new system of measures should take.

Yet in the end the metric system that emerged was essentially the creation of a core of savants from the Paris Academy of Sciences. The French kings had traditionally referred questions of measurement to their Academy. In the run-up to the Revolution, Lavoisier and other academicians had been invited onto royal commissions to consider the advantages of uniform measures. Now savants such as Condorcet, Lavoisier, Laplace, Borda, and Legendre quickly formed a Commission of Weights and Measures to hammer out the specifics of the metric reform. Some of these men, like Condorcet, themselves sat in the legislative assembly. Other members of the legislature, such as a young engineer named Claude-Antoine Prieur-Duvernois, known as Prieur de la Côte-d’Or, helped promote the reform from within the ranks of officialdom. Over the next four years, these men transformed the citizenry’s simple plea for a uniform system of weights and measures into a hyperrational system, combining features which had long been sought by savants and from them assembling a system of perfect metrical communication. Yet each of these features was proposed independently, and each proved controversial.

The single demand which united all the savants, legislators, and pamphleteers was the expectation that the new weights and measures would be applied uniformly throughout France. It was true that in 1788 some of the complainants in the Cahiers de doléanceshad thought it sufficient to demand regional measures based on the standards of provincial market towns. But merely regional measures quickly came to seem inadequate to the leaders of the new national government, and in February 1790 the first proposal for metric reform to reach the National Assembly reiterated Lalande’s plea that the legislators adopt the Paris standards throughout the nation. It was a proposal bound to appeal to a nation newly conscious of its unity. It was also the logical culmination of a thousand years of French centralization. In any other nation at any other time, this proposal would undoubtedly have become the law of the land—in which case the metric system would almost certainly never have existed in anything like its current form.

But it was not just any nation and it was not just any time. It was a nation conscious of its place at the vanguard of history at a time when history called for actions of universal significance. Even the men who proposed the Paris standard recognized the thrum in the air. They knew that some of their comrades had grander ambitions, and they feared that those ambitions would scuttle any chance for a more limited success. “Do not,” they pleaded, “take us beyond our desires and our hopes.” The savants, however, were determined not to let slip this chance to design a truly rational system of weights and measures.

One month later, in March 1790, Charles-Maurice de Talleyrand offered the legislature a far grander proposal. While the adoption of the Paris measures might seem expedient, it failed to rise, he said, to “the importance of the matter, nor the aspirations of enlightened and exacting men.” In its place, the former bishop, sometime revolutionary, and perennial master of French foreign policy advanced the proposal favored by the savants, especially by Condorcet. In place of a measure derived from history or the fiat of kings, he asked that the legislature derive its fundamental measure from nature, the common heritage of all mankind. Only a measure derived from nature, he declared, could be eternal because only such a standard could be reconstructed should its man-made physical embodiment suffer the ravages of time. For instance, the Paris toise—which equaled, by definition, six times the length of the royal pied (foot)—was actually a bar of iron mortised into the wall at the foot of the staircase of the great Châtelet courthouse. Yet, as everyone knew, the original bar had become badly bent as the building settled and had been replaced in 1666. By 1758 even the new bar, equal to half the width of the entrance to the royal Palais du Louvre, had begun to show its age. Surely so ephemeral a standard would not suffice for a new régime founded on the rights of man. Only a measure taken from nature could be said to transcend the interests of any single nation, thereby commanding global assent and hastening the day when all the world’s peoples would engage in peaceable commerce and the exchange of information without encumbrance.

Talleyrand—again, at Condorcet’s prompting—also proposed an additional feature for the new system of measures: that its various units (length, area, capacity, weight, et cetera) be rigorously linked by an interconnected system. The idea was that once the unit of length had been derived from nature, all the other units might be defined in relation to it. This would ease all kinds of calculations and comparisons, especially for those professionals—engineers, doctors, savants, artisans—who transformed nature into useful things. This provision was reiterated in all subsequent proposals, although the savants would themselves disagree about how to define these relationships, especially for the unit of weight. Lavoisier and the crystallographer René-Just Haüy set to work early in 1793 to define the grave (as the gram was then called) as a cubic centimeter of rainwater weighed in a vacuum at the melting point of ice. But without a definitive determination of the meter, their findings were necessarily provisional. Ultimately, in 1799, the chemist Lefèvre-Guineau would define the gram as one cubic centimeter of rainwater weighed in a vacuum at the temperature of maximum density.

Not longer after Talleyrand’s proposal had been voted into law, the legislature authorized the addition of a third feature, one long desired by savants. They declared that all the metric units would be divided by a decimal scale. The idea for universal decimal measures went all the way back to the proposals of Simon Stevin, the Flemish engineer who had invented the decimal point in the Renaissance. In the seventeenth century the advantages of decimal measures had been echoed by the English philosopher John Locke and the French military engineer Sébastien Le Prestre de Vauban. More recently, in his textbook for the new chemistry, Lavoisier had urged that decimal measurement be adopted by all the world’s savants. Given the near universality of the decimal scale in arithmetic, the savants pointed out, a complementary system of measures would ease calculation, not only for learned folk, but for everyone engaged in trade, commerce, or construction. The decimal system could even be considered a kind of natural scale because human beings have ten fingers. To cap this reform, the National Assembly was also considering a proposal to decimalize the new national currency, as the American republic had done a few years before.

Yet even this proposal proved controversial. Several pamphleteers suggested that the metric system be designed around a duodecimal scale. Because of its many divisors, a base-12 system would allow buyers and sellers to divide and subdivide goods easily, enabling butchers to chop sausages into halves, thirds, or quarters. The admitted drawback of the duodecimal system, its incompatibility with the usual arithmetic scale, could be solved by switching our arithmetic to a duodecimal system and adding two new single digits for “10” and “11.” The Revolution was a chance to rethink all old assumptions. Then again, other pamphleteers preferred a scale derived from base 8 because it would enable commodities to be divided in half again and again and again, like a pie. Yet another pamphleteer proposed instead division by base 2. And one great mathematician even toyed with the idea of a scale built around a prime number, like base 11, since from a mathematician’s point of view a fundamental unit ought not itself to be divisible.

The fourth and final addition made by the savants—and certainly the one that most baffled their countrymen—was their proposal for a nomenclature of prefixes. Only gradually did the Academy come around to the view that the new measures needed new names. In May 1790, the citizen Auguste-Savinien Leblond was the first to propose the neologism “the meter” for the fundamental unit of length, “a name so expressive that I would almost say it was French.” And for the next few years, the reformers continued to assume that the multiples and subdivisions of the meter would go by their own simple names like the perche (10 meters) and stade (100 meters), or the palme (0.1 meters) and doigt (0.01 meters). The idea that one might use Greek and Latin prefixes—kilo-to mean 1000, and milli-to mean 0.001—first surfaced in a report by the Commission on Weights and Measures in May 1793. In spite of a counterproposal that the prefixes would be more authentically French if taken instead from Low Breton, this system of classical prefixes was the final element to be added to the metric system as we currently know it today.


Each of these features was controversial, added in succession, and debated in turn during the early years of the Revolution. Yet no single feature caused more consternation, frustration, and second-guessing than the proposal to base the fundamental unit of length on the measure of the earth. “Was it really necessary,” one critic asked, “to go so far to find what lay so near?”

Indeed, Talleyrand had initially proposed that the fundamental unit of length be derived from the length of a pendulum beating one second. This was an idea with a long pedigree, going back to the early seventeenth century when Galileo had first demonstrated that the period of a pendulum’s beat was determined entirely by its length, so long as its swing was not too wide. In the 1620s, the Dutch savant Isaac Beeckman and Father Marin Mersenne of Paris had discussed a natural standard for length calibrated against the length of a pendulum beating at one-second intervals. In 1775, the reform-minded Chief Minister Turgot had asked Condorcet, the rising star of the Academy of Sciences, to draw up a plan for a scientific system of weights and measures based on the one-second pendulum.

Talleyrand, on Condorcet’s advice, had initially proposed that the French government invite two savants from each of the world’s nations to participate in a joint experiment to determine the length of a pendulum beating one second. Talleyrand further announced that he was in contact with Sir John Riggs Miller, a member of the British Parliament who had introduced similar legislation in the House of Commons. Talleyrand considered this a hopeful sign, and wondered if it were “permissible to see in the concourse of two nations interrogating Nature together the principle of a political union by the mediation of science.” If successful, such a measurement system might extend beyond Europe and around the globe. A savant from France’s young sister republic across the Atlantic had sent word that he too was interested in this project. Thomas Jefferson, in his capacity as the nation’s first Secretary of State, had been asked by President Washington to report on the reform of American weights and measures, and he had likewise agreed to coordinate his proposals with the French. Condorcet privately predicted that the French, the British, and the Americans—“the world’s three most enlightened and active nations”—would all be employing the same measures in short order.

There was only one catch. In the two centuries since Galileo’s day, the savants had learned that the length of the one-second pendulum was also sensitive to the latitude at which it was measured, because gravity varied slightly with latitude. Hence, Talleyrand reminded the legislators that this pendulum experiment would have to be conducted at some specific location. The equator might have seemed the most natural choice, positioned as it was, equidistant from the poles. But the equator was unfortunately remote from the scientific nations. So the second most natural location, Talleyrand argued (on Condorcet’s advice), would be the midpoint between the pole and the equator—at 45 degrees of north latitude—where the pendulum possessed its average length. And since the experiment ought to be carried out at sea level and far from any disturbing mountains, the most plausible site on earth was on the outskirts of Bordeaux in southwest France.

Needless to say, this aspect of Talleyrand’s proposal did not meet with international approval. Miller of Britain plumped for a measurement in London. Jefferson of Virginia argued for a measurement on the 38th parallel, both the median latitude of the United States and conveniently downhill from his estate at Monticello. And some Parisians dared to suggest that the experiment might most easily be carried out in Paris. The achievement of universality, it seemed, would require some delicate diplomacy. But Talleyrand was a master diplomat. He saw to it that the law passed by the National Assembly on May 8, 1790, gently suggested the pendulum measurement be taken at 45 degrees, “or whatever other latitude might be preferred,” and invited the Academy of Sciences to form a Commission of Weights and Measures to carry out this plan. In England Miller praised this concession before the House of Commons, and Jefferson redrafted his final report to the U.S. House of Representatives to tout the advantages of cooperating on the measurements at the 45th parallel “with the hope that it will become a line of union with the rest of the world.”

Yet after all these delicate negotiations were concluded, when the Commission reported back one year later, on March 19, 1791, they urged that the pendulum standard be dropped altogether in place of a meter based on one ten-millionth of the distance from the North Pole to the equator as established by a survey of the meridian that ran from Dunkerque to Barcelona.

It was Borda, as chairman of the Commission, who justified this change on scientific grounds. The problem with the pendulum, he noted, was that it would make one fundamental unit (the length of the meter) depend upon another unit (a second of time). What would then happen if the units of time were themselves to change? Even as he spoke, the Academy was considering whether the arbitrary division—inherited from the Babylonians—of a day divided into 24 hours of 60 minutes of 60 seconds each should likewise be converted to the decimal scale, so that the day might be more rationally divided into 10 hours of 100 minutes of 100 seconds. By contrast, there could be nothing simpler or more natural than basing the fundamental unit of length (the meter) upon another unit of length (the size of the earth).

Besides, it was only fitting that a measure for all the world’s people be based on a measure of the world. It was consonant with the universal aspirations of the Revolution. As Laplace would later point out, a meter based on the size of the earth would entitle even the most humble landowner to say, “The field that nourishes my children is a known portion of the globe; and so, in proportion, am I a co-owner of the World.”

Obviously, the circumference of the entire earth would make an awkward unit of length for ordinary purposes. But a measure of length based on the quarter meridian divided by ten million would come out to very near the length of the aune of Paris, a three-foot length comfortably on the human scale and familiar to many French citizens. To determine that length with the necessary precision, the National Assembly need only to authorize a new expedition to measure a meridian—or at least a portion of one.

Borda explained how the French academicians had selected just such a meridian on the basis of rational criteria that would “exclude all that was arbitrary.” First, the selected arc would have to traverse at least 10 degrees of latitude to allow for a valid extrapolation to the full arc of the earth. Second, the selected arc would have to straddle the 45th parallel, which, as the intermediate distance between the pole and the equator, would minimize any uncertainty caused by the eccentricity of the earth’s shape. Third, its two end points would have to be located at sea level, the natural level of the earth’s figure. And fourth, the meridian would have to traverse a region already well surveyed so that it could be quickly measured. There was only one meridian in the entire world which met all these requirements: the meridian which ran from Dunkerque through Paris to Barcelona. He assured the legislators that “there was nothing in this proposal that would give any nation the least pretext for reproach.” He also assured them that the task could be completed in a year.

As Borda noted, the idea of basing a natural unit of measurement on the circumference of the earth had long been a cherished dream of savants. Centuries before Columbus set sail west from Spain, learned folk had known that the earth was round. Eratosthenes, director of the fabulous Library of Alexandria in the third century B.C.E., was also the father of geodesy and had measured the earth’s circumference to within 10 percent. Eratosthenes knew that in the Egyptian town of Syène (Aswan), located 5,000 stades due south of Alexandria, the sun stood directly overhead at noon on the spring equinox because its light then reached the bottom of a deep well. So one spring equinox around 240 B.C.E., he simultaneously measured the solar height at noon in Alexandria by means of the shadow cast by an upright stick, and found it to be 7.2 degrees from vertical, or approximately one fiftieth of the total circle of 360 degrees. From this, he deduced that the earth’s circumference was fifty times greater than the 5,000-stade distance between the two towns, or 250,000 stades. Not a bad estimate, given what we know about the length of the stade.

Two millennia would pass before anyone came up with a better one. Jean Fresnel, doctor to Henry II of France, took a comparatively crude approach in the sixteenth century. He measured the distance from Paris to Amiens by counting the number of times his carriage wheel turned along the route (a mechanical ticker inside his carriage helped him keep track of the rotations). Because he knew Amiens was located one degree of latitude due north of the capital, and the road between the two ran straight, he simply multiplied the number of rotations by the circumference of his wheel and again by the full 360 degrees of the globe. Considering his methods, he was not far wrong either. The modern technique for using triangles to measure earthly distances, however, was introduced in 1617 by Willebrord Snell, “the Dutch Eratosthenes,” on the frozen fields outside Leyden, and his method persisted for the next 340 years.

One of the earliest official acts of the French Academy of Sciences had been to remeasure Fresnel’s itinerary from Paris to Amiens by triangulation, and this measure of the globe’s regularity had inspired Gabriel Mouton, a chaplain-astronomer in Lyon, to propose that the earth serve as the basis for all human measurements. In 1670 he suggested that the fundamental unit of length, which he dubbed the mille, be set at the length of one degree of the earth’s arc, with all subunits determined by decimal division, such that the virgula (about the length of the king’s pied or foot) would equal one ten-thousandth of the mille. The marvel of nature’s regularity suggested that human activities be aligned according to the same metric.

But all these learned folk, from Greek astronomers through European scholars, had assumed that the earth was a perfect sphere until Isaac Newton—without ever setting sail from Cambridge—announced that our round planet was slightly flattened at the poles. His hypothesis of an oblate earth began as a theoretical prediction. Calculating the effect of rotation upon a homogenous liquid sphere (our earth) in which all particles attract one another all the time, Newton estimated that centripetal forces would produce an earthly eccentricity of 1/230. In other words he suggested that the earth’s radius at the pole was 1/230 shorter than its radius at the equator. Newton then corroborated this prediction by several choice pieces of evidence. He reanalyzed the French Academy’s meridian survey to show that the earth had flattened slightly as the triangulation proceeded north. He noted that the pendulum clock carried by another French savant to the Caribbean in 1672 had beat more slowly as it approached the equator, suggesting that gravity weakened slightly as the earth bulged, because the point was farther from the earth’s center. Finally, he pointed out, astronomers had noticed that Jupiter was flattened at the poles. On earth, then, as it is in heaven. And to cap it all off, Newton made one final startling deduction. The bulge around the earth’s middle, he surmised, explained a phenomenon that had baffled astronomers for two thousand years. The pull of the sun and moon on the earth’s bulgy middle was responsible for the precession of the equinoxes, the slow but steady 26,000-year swivel of the earth’s axis of rotation. Newton had banished the earth’s spherical perfection along with the planets’ circular orbits. We do not live on a perfectly round orange, but on a flattened tomato. Nature’s perfection lay not in childish geometry, but in nature’s forces deeply hidden—and by Newton revealed.

The century-long debate that followed proved to be the golden age of geodesy; that is to say, an age of bitter controversy and world-shaking reversals. A survey of the meridian of France, undertaken by Cassini I in 1700, seemed to confirm Newton’s hypothesis, until his son, Cassini II, reviewed the data and dared to suggest the opposite, that Newton had in fact erred and the globe, if anything, was elongated at the poles: prolate rather than oblate, a long lemon rather than a flat tomato. The question was not just academic; it affected mapping projects on land and sea. The difficulty was that a 1 percent error in the determination of the latitudes was enough to flip the earth from oblate to prolate, from tomato to lemon—or the other way round.

To resolve the question, the Academy of Sciences launched an expedition to Peru to determine whether the earth bulged at the equator. It also dispatched rival savants to Lapland to measure the earth’s curvature as it approached the pole. These stirring voyages cast science in a heroic light, bringing Newtonian physics to public attention and entertaining the salons of Paris with the splenetic quarrels of the academicians. In 1740 the French Crown also sponsored Cassini III’s survey of the meridian from Dunkerque to Perpignan to help settle the controversy—and recast the map of France. On his return, Cassini abjured his father’s prolate earth and acknowledged that we live on Newton’s flattened globe—although no two savants could quite agree on just how flattened it was.

As one chieftain of eighteenth-century science confessed, this controversy had seemed to dash the “flattering dream” of a universal measure based on the perfection of nature. But natural philosophers do not give up so easily on nature’s perfection. Several savants—Laplace in particular—remained convinced that the earth, flattened though it was, might still serve as the basis for a perfect meter. As Condorcet explained to the National Assembly, these arguments had convinced him to switch his allegiance from a simple pendulum standard to a geodetic mission. And he pleaded with the Assembly likewise to embrace this revised plan. The meridian project was based on the soundest science, he noted, of such universal principles that in future years no one would even be able to say which nation had performed the task. And he went on to urge them, in somewhat contradictory terms, not to wait for “the concourse of other nations” before settling on a standard. As the representatives of a great and enlightened nation, one whose vision reached out to all people and all times, it was incumbent on the French to reject the easy path, and instead “approach perfection.” On March 26, 1791, despite some grumbling about the likely cost and delays, the National Assembly adopted this meridian standard.

This decision had lasting repercussions. In the short run, it ended any chance of international cooperation. To savants outside France the meridian project smacked of self-interest. Those savants who favored the pendulum standard refused to concede its inferiority. Geodesers, they pointed out, also relied on many other units like time and angles to measure the globe, so no unit could ever be truly fundamental. The leaders of London’s Royal Society accused their French colleagues of seeking to “divert the attention of the European public from the true amount of their proposal, which in fact is that their measurement of 9 or 10 degrees of a meridian in France shall be adopted as the Universal standard.” Jefferson likewise withdrew his support from the metric system when he learned that the French would survey their own meridian. As he pointed out: “If other nations adopt this unit, they must take the word of the French mathematicians for it’s [sic] length. . . . So there is an end to it.”

For the French savants themselves, however, the expedition paid handsome dividends. Thanks to the extravagance of the meridian project, the budget for the creation of the metric system was revised upwards to 300,000 livres, roughly three times the annual operating costs of the entire Academy under the Ancien Régime. Government funds also flowed into the coffers of instrument-makers like Lenoir, who had been hit hard by the disruption of the luxury trade at the advent of the Revolution. Almost every one of the Academy’s savants who worked in the physical sciences found employment on the metric system project. All, that is, except for Lalande, who refused to participate in a project he considered pointless—though he wished his former students well.

Even within France, some criticism was heard. The literary critic Louis-Sébastien Mercier thought the meridian expedition smelled of charlatanism. The savants, he said, had “preserved their pensions and salaries . . . under the pretext of measuring the arc of the meridian.” Other commentators were more scathing. Jean-Paul Marat, bilious enemy of the Academy (“those cowardly lackeys of despotism”) deemed the 300,000-livre budget “a little gâteau they will share out among confederates.” There were even some savants who (privately) ascribed the change in plans to ulterior motives. Delambre himself later speculated that Borda had pushed the meridian project to enhance the reputation of his repeating circles. Others wondered whether Laplace and the other physicists had primarily promoted the project as a way to pin down the exact shape of the earth, rather than as an attempt to ascertain the length of the meter.

Of course, as many commentators have pointed out then and since, the decision to base the meter on one ten-millionth of a quarter of the earth’s meridian was itself arbitrary. To begin with, it was not even a real distance, but a calculated distance along a portion of the surface of an imaginary sea-level geoid that would have to be extrapolated from one small segment of the arc to the whole. And metric kibitzers suggested many alternative ways of slicing up the globe. Some preferred a meter based on the circumference of the equator. Not only was the equator unique, it was apparently circular and unchanging. A meridian, by contrast, was arbitrary, elliptical, and possibly subject to change over time. Still others agreed with the choice of a meridian, but wondered why the savants had not chosen their standard to equal one hundred-millionth of the total meridian (rather than one ten-millionth of the quarter meridian) to make the meter more nearly come out to the length of the foot, a more manageable size for daily use. Occasionally—as the meridian project suffered one delay after another—politicians and ordinary citizens even had the temerity to ask whether a natural standard was necessary at all. Nature was changeable and irregular, some said. “Everything in nature is unequal,” another complained. Even the shape of the earth might change over time, as Laplace himself admitted—though surely the measure of the meridian would not take that long to complete.

All along, Lalande, the old iconoclast, stuck to his preference for a physical standard, like the copper toise of Paris which the Academy had in its keeping. Such a standard could be defined with much greater ease and accuracy, whereas any attempt to find a standard in nature would prove ephemeral because too many factors influenced the investigation of natural phenomena. For instance, there were many factors that might influence the length of a pendulum besides the latitude at which it was measured; from the arc of its swing and the ambient temperature to the air resistance. Moreover, he noted, savants could not even be sure that the pendulum’s periodicity was the same at every spot along the same latitude, since the tug of nearby mountains or other deformities of the earth might affect its oscillation. The same factors would affect any measure based on geodesy. Given these uncertainties, Lalande predicted that the progress of science (in which he most fervently believed) would produce more accurate results twenty years hence. And what would happen then? Would the natural standards have to be periodically revised to take account of the improved results? Under the circumstances, what was the point of striving for precision now?


Eager as he was to resume his campaign as soon as the spring weather allowed—delay might give the bureaucrats an excuse to cancel the mission, and the cost of transportation was rising—Delambre still needed official permission before he set out. The barricades of the previous year had taught him the value of a valid passport. In March, he petitioned the Paris municipal council for permission to move freely throughout the Republic. The council—now in the hands of the radical sans-culottes party and hostile to the Academy as an elitist institution—voted unanimously against his petition. “Is it possible,” he wrote back, “that in Paris, at the center of enlightenment and the arts, the executors of a law applauded across Europe find themselves stymied in their tracks?” He resubmitted his petition, countersigned this time by prominent administrators. The council voted unanimously to issue him a passport. As an extra precaution, he wrote in advance to all the towns along his route to assure them that his mission was benign.

The Republican government had proclaimed France a nation of “one law, one weight, and one measure.” It had promised to end the shameful inequalities of Ancien Régime justice and taxation. It had promised to open careers to talent and to liberate commerce. But the Revolution had also shattered the royal authority that governed France from the center. Placing sovereignty in the hands of the people had made every town its own master. Markets were in disarray, and food prices were rising. The towns were suspicious of the countryside; the peasants mistrustful of the towns. At every step Delambre had to present his papers. When he passed through his hometown of Amiens, an old friend had to prepare a dossier of official documents for him, all signed, stamped, and dressed with fancy seals.

At least Delambre had a strategy for this campaign season. Rather than circle Paris in futility, he and his two collaborators, Lefrançais and Bellet, would begin at the beginning. They would start at Dunkerque, the northernmost station, and work their way south. The strategy was logical, but circumstances have their own logic. The optimal season for geodetic campaigning coincided with the optimal season for military campaigning. All that spring, while Delambre had been waiting for a passport in Paris, the Prussian-Austrian army had been massing on the frontier for another drive to restore the monarchy. By the time he arrived in the north country, the plains of Flanders had become a battlefield, with the invaders again advancing toward Paris.

In mid-May of 1793 Delambre hurried to Dunkerque before the French defenses collapsed. There he was assisted in the bell tower by Monsieur Garcia, whose family had been tower masters for three hundred years. Sometime during that long interval, the 162-foot tower had been separated from the main body of the church by a road that still serves as the main thoroughfare through the city center. From the top of the red-brick belfry—a climb of 264 steps, “and we counted”—the team had a view of several nations: France, the Low Countries, and across the Channel, England. Cassini and Méchain had used the belfry in their 1788 survey to link Paris and Greenwich. Nearer to view, Delambre could see the dunes along the beach, the port made idle by war with Britain, and the long low coast that swept into the gray mists. Inland, he could see the French armies maneuvering along the border.

From Dunkerque, Delambre made steady progress south through Picardy, his home region. It was an ideal landscape for triangulation, and summer was the ideal season for geodesy. The corrugated countryside was laced with low ridges, and each town boasted an elegant church steeple. Excellent stations were abundant, though each presented its particular challenge. In Watten, a small town a dozen miles inland on the Aa River, the church tower was not high enough to be seen from afar, so he capped it with a crown of white planks. At Cassel, to the immediate east, the summer heat in the steeple was suffocating. At Mesnil, he had to wait four days to erect his signal until the local carpenters had finished celebrating their village festival in the cabarets. At Fiefs, he had to wait for permission to punch holes in the church steeple so that he might have a clear view in all directions. At Bayonvilles, he had to chop down several trees to open up a line of sight. By mid-July he had closed ten triangles, accomplishing more in one month than in all the previous year. By his own account, this was his happiest portion of the meridian, and the most well favored. Behind him, the battle was turning against the French. The British had laid siege to Dunkerque and the Hanoverians were closing in on Lille. But by then Delambre was approaching his hometown of Amiens.

Lefrançais never made it there. In mid-July he had to rush back to Paris. His wife (Lalande’s daughter) was approaching her due date. On July 27, she gave birth to a girl, Uranie, though the baptism was postponed until Delambre could stand in as her godfather. Delambre wrote to congratulate the young mother. “I admire you for having resumed your astronomical labors so soon; in giving us a Uranie you have accomplished enough and could have rested yourself a bit longer.” He had six more stations to complete before he could return to Paris for the baptism of “our new muse.” As for Lefrançais, grandfather Lalande wrote that he would return to the mission as soon as he was elected to the Academy in his own right, probably at the meeting set for August 7.

Lefrançais would never return to the mission. On August 8 the Academy was abolished, and Lalande put his nephew back to work on his all-important celestial chart.

Delambre was setting up a signal in the cathedral spire of Amiens when he learned of the Academy’s demise. “I don’t know if I still have the right to call you my colleague,” Lavoisier wrote, “though I send you this letter as a fellow believer in the progress of science.” The good news was that the savants had managed to preserve the metric reform, and the meridian survey along with it. “The suppression of the Academy ought not in any way disrupt your labor, nor diminish your indefatigable activity.” The bad news was that there was no money to pay Lefrançais, and the continuation of the survey had been ransomed with a dangerous concession: the establishment of a “provisional meter.”



This iron meter stick was made to match the specifications of the 1793 provisional meter. It reads: “Meter stick equal to one ten-millionth part of a quarter of the earth’s meridian, Borda, 1793.” (From the Musée des Arts et Métiers-CNAM, Paris; photograph by CNAM)

The suppression of the Academy did not come as a complete shock to Delambre. For years the academicians had been attacked as self-appointed elitists who disparaged popular inventors and thinkers. In the past months, radical politicians had called for the dissolution of all royal institutions. Some legislators had tried to exempt the Academy of Sciences because of the transcendent truthfulness of science and the useful services it provided the nation—especially with regard to the reform of weights and measures—but to no avail. In the end, some academicians even came to agree that the Academy was undemocratic and applauded its fall. When Cassini IV tried a procedural motion to delay the final closing, some of the Republican savants echoed the phrase that the drunken militiaman of Lagny had hurled at Delambre, shouting: “There is no moreAcademy!”

This time they were right. Everything was now reversed. Instead of the Academy of Sciences sponsoring a meridian expedition to define the metric system, the creation of a metric system had become the main justification for the state-funding of science. On August 1, 1793, one week before the dissolution of the Academy of Sciences, a new law codified the metric system as we know it today and gave the French people one year to prepare themselves for its obligatory use. Of course, the meridian expedition would not be completed by then, as everyone recognized. Hence, the law established a “provisional” meter which state administrators and commercial enterprises might use while they waited for the meridian survey’s “definitive” results. The value for this provisional meter had been coaxed out of the Academy under some duress.

Even before Delambre and Méchain had set out, Borda had privately estimated that the meter would come out to about 443.5 lignes in the old Paris units. (A ligne was one-twelfth of a pouce (inch), so that a pied (foot) contained 144 lignes.) It was a quick back-of-the-envelope calculation based on what everyone already knew about the size and shape of the earth. In public, however, Borda said nothing. To announce this estimate might have undercut the efforts to measure the meridian properly.

Several state agencies were impatient to know this value, however. The plan for a new national map, which would enable the government to accurately tax every piece of landed property in France, had been stalled because the surveyors were expecting to use the new standard of length. Nor could the Treasury decimalize the currency without some sense of the weight of the new silver coins. In January 1793 the Finance Committee begged the Commission of Weights of Measures to make a serious estimate of the likely length of the meter. To oblige them, Borda, Lagrange, and Laplace, three of the most illustrious mathematical physicists of all time, did so in three easy steps. They assumed that the length of a 1 degree of arc at 45 degrees of north latitude was average for the entire quarter meridian; they took the value for this distance from Cassini III’s survey of 1740; then they multiplied this number by 90 (for the 90 degrees of the quarter meridian) and divided by 10 million. Their guesstimate came to 443.44 lignes. Nothing could be simpler.

Yet only when the Academy was threatened with dissolution later that year did the Commission cough up this value. By then, control of the nation’s legislature had been seized by the Jacobin party, who had vested executive power in the hands of a Committee of Public Safety. This Committee included not only political radicals like Robespierre and Saint-Just, but also military engineers like Lazare Carnot and Prieur de la Côte-d’Or, whose task it was to direct the war effort and organize the production of war matériel. The law of August 1, 1793, was intended to implement the metric system as soon as possible, using this provisional meter as the standard. Not long thereafter, Lalande wrote to Delambre to tell him there was little point now in pressing on with the mission. “The new measures are being adopted for commerce independent of the new measure of the earth; so there’s little need for you to push yourself too hard to bring your results in now.”

Delambre spent that week in his hometown of Amiens, conducting his observations from the second story of the cathedral’s spire, the loftiest in France. The interior of the spire was encumbered with heavy carpentry and massive bells. The steeple also inclined slightly to the west, which slightly skewed his observations. Below, the red-brick town appeared calm, and no one was without bread—although food riots had disturbed the city the previous month, and bakers were again running low on provisions. On September 9, shortly after Delambre left town, officials arrested sixty-four priests who refused to swear allegiance to the state.

Though he rarely went home or commented on politics, Delambre had joined an Amiens political society in 1791, one cofounded by his brother-in-law. The Société des Amis de la Constitution preached moderation, despite its motto: Vivre libre ou mourir (“Live free or die”). Delambre shared the Society’s principled moderation. Amid the passion, he dared suggest to his hometown newspaper that both democrats and aristocrats repudiate their extremist factions and discuss their differences at a nightly educative assembly. “To be reasonable,” he urged, “one must be without passion.” This modest proposal was blasted by another local citizen, Gracchus Babeuf, the radical politician who would one day be called the world’s first Communist. Delambre, he sneered, had failed to understand that “a man without passion is incapable of noble enterprises; great deeds are beyond his reach; he is without energy and hence contemptible.” Delambre’s response was to emphasize the modesty of his proposal, and to express the hope that his opponent, by venting his bilious tirade, had at least improved his health. This was as close to political commentary as Delambre would get in thirty years of service to a half-dozen régimes: the Ancien Régime monarchy, the constitutional monarchy, the Republic, the Directory, Napoleon’s Empire, and finally the Restoration monarchy. Throughout his decades of public service he maintained a careful ambiguity about his political views.

His duty lay to his mission and on that basis he was determined to proceed. He could manage without Lefrançais, so long as Bellet remained with him. The young instrument-maker had proved himself an excellent observer and a cheerful companion. He accompanied Delambre at every step of the mission, and would do so until its final triangle. Delambre paid him a 500-livre bonus out of the savings from Lefrançais’ salary. And now that the Academy was abolished, he himself could collect a daily wage as a Commissioner for Weights and Measures. It came to the princely sum of 10 francs a day, roughly the salary of a competent artisan.

In early October Delambre at last connected the new season’s chain of triangles with the Paris chain of the previous year. This meant that he had now formed a continual lattice of triangles from Dunkerque through the Ile-de-France, about one-third of the distance to his rendezvous in Rodez. In late October he passed to the south of the capital to pick up where he had left off the previous winter.

Working in the Orléans forest just north of the Loire River, Delambre was caught up in the political tensions he had so far evaded that year. The church tower at Cour-Dieu which had served as Cassini III’s signal in 1740 was completely hemmed in by trees, and no plausible substitute could be found amid the rolling terrain of tall oaks in the old royal forests, a favorite hunting spot of the Bourbon kings. Delambre’s only option was to construct an observation tower on a low hill called Châtillon. Where nature offered no elevated view, and belfries were unavailable, the geodeser had to build from scratch.

The construction of this sixty-four-foot wooden tower took over a month and attracted unwanted attention. The citizens of the surrounding hamlets wondered about the strange doings in the former royal forest. “They reported seeing three or four hundred brigands building scaffolds and piercing holes in church towers . . . , undoubtedly in preparation for a counterrevolutionary uprising.” This would have been amusing but for the fact that the local citizens had called for six hundred soldiers to attack the site. Fortunately, when the time came they vented their anger elsewhere. On December 27, just as the tower was nearing completion, the local popular society unanimously voted instead to destroy a nearby stone obelisk erected in honor of the 1740 survey by Cassini as an “odious sign of extinct despotism in the guise of a stone pyramid called the meridian and built by the one-time lords as a sign of their greatness.” The obelisk was torn down to be used for paving stones at the same time that the eminent jurist Malesherbes, on whose land the obelisk stood, was executed for acting as the king’s lead counsel in his final (futile) defense.

On New Year’s Eve, Delambre and Bellet climbed their high tower platform at Châtillon for the first time and began to hoist their precious circle into position with ropes and pulleys. The observation deck had been boxed in to provide shelter from storms and snow. Unfortunately, this protection also gave the wind a broader surface area to push against. The circle had just arrived safely when a tremendous gust shook the tower, forcing the observers to scramble back to earth, a fifteen-minute ordeal because the circle had to be lowered with care. The next day, the wind was calmer and they remounted the tower. But the cold was painful, the day short, and their observations of poor quality.

Yet when the devastating blow came two days later, it emanated from neither the local citizenry, nor the weather, but from the supreme power in the land. On January 4, 1794, Delambre received a letter from the Commission of Weights and Measures notifying him that by order of the Committee of Public Safety he had been purged from the meridian survey along with several of his colleagues. The letter informed him that he was to hand over all his field notes, calculations, and instruments so that a successor might take his place “should the meridian survey continue.”

Whatever this meant for the future of the mission, to quit there would have negated the months of labor that had gone into building the Châtillon tower. If a winter storm toppled the tower, all the surrounding triangles would have to be redone. At a minimum, the survey ought to terminate at fixed stations—such as the church towers along the Loire at Châteauneuf and Orléans—so that his successor, should one ever be appointed, might start his labors from a secure foundation. Moreover, Delambre estimated that he would need at least three months to put his notebooks in order and complete his calculations. He wrote to the Commission, begging for a chance to implement this plan, while setting furiously to work to carry it out before they refused.

Their sealed response arrived a few days later in the hands of the engineer Gaspard Prony, Delambre’s former colleague in the former Academy and, as it turned out, his replacement on the Commission. Yet Prony always found an excuse not to hand over their answer. Instead, he assisted Delambre with his observations at Châtillon, and even accompanied him to Orléans to finish the triangles on the banks of the Loire. The crucifix that had once stood at the top of the Orléans cathedral spire—and that would have made an ideal signal, like the crosshairs on a telescopic sight—had recently been replaced with a misshapen cast-iron Liberty bonnet. The cathedral, now known as the Temple of Reason, had just that week witnessed an even greater sacrilege. La belle Rosalie, a young prostitute who worked the rue Soufflet, had been costumed as a goddess, with a pike in one hand and a Revolutionary red cap on her head, so that she might be paraded through town on a tremendous chariot bedecked with tricolor flags and pulled by twelve white horses led by six young men in togas. All the town’s citizenry had followed, wearing Roman attire. At one point, the float had to squeeze under a low portal and the goddess was heard to shout, “Hey, you bastards! Hey, buggers! Stop, you fuckers, I’m falling off!” before she hopped down into the crowd so as to clamber back up on the other side.

In a year and a half of labor, Delambre had covered nearly half his assigned itinerary from Dunkerque to Rodez, surveying a two-hundred-mile arc from the North Sea coast to the banks of the Loire. In doing so he had zigzagged more than twelve times that distance, or some twenty-four hundred miles on the hard roads of France. On January 22, 1794, he made a final note in his expedition logbook: “It began to rain and there was no time to redo the angles.” Later that day, Prony handed over the Commission’s response, now three weeks overdue. The cover letter read:


The Commission of Weights and Measures has sent one of its members to bring you the decree of the Committee of Public Safety regarding your request, and to invite you to conclude your operations in such a way as to ensure that your temporary signals become unnecessary. It further enjoins you to complete the transcription of your calculations and observations as you suggest.

Lagrange, President of the Commission of Weights and Measures

In ambiguous language, his friends on the Commission had honored Delambre’s request, allowing him to keep his expedition logbooks for the time being. The enclosed order in the hand of Prieur de la Côte-d’Or was written on the imposing stationery of the Committee of Public Safety. It was dated December 23, 1793, now a full month past:

The Committee of Public Safety, considering how important it is for the improvement of public morale that government officials delegate their powers and functions solely to men known to be trustworthy for their Republican virtues and their abhorrence of kings . . . decrees that from this day forth Borda, Lavoisier, Laplace, Coulomb, Brisson, and Delambre cease to be members of the Commission of Weights and Measures, and that they immediately hand over to the remaining commissioners all their instruments, calculations, notebooks, with a full inventory of the same. And furthermore, that the remaining members of the Commission . . . apply Revolutionary enthusiasm to bring the new weights and measures into use among all citizens.

C.-A. Prieur, B. Barère, Carnot, R. Lindet, Billaud-Varenne

The next day Delambre packed his equipment to return to Paris. “Even though, for the life of me, I cannot understand why I have been recalled, I will return without complaint to those occupations from which I was regrettably torn away.” On his way he had one personal matter to attend to. His patron, Geoffroy d’Assy, was being sought by the Revolutionary police. Delambre needed to stop at the d’Assy country residence in Bruyères-le-Châtel, where d’Assy was living in retreat.

The Revolution had entered the phase known as the Terror, when the Jacobin state declared an emergency military draft, imposed wage and price controls, and enforced its decrees with imprisonment and execution. The world’s first war of mass mobilization was being fought. On the frontiers of France, a coalition of Prussians, Austrians, English, and Spaniards was ranged against the Republic. From within, the Republic was being undermined by defiant aristocrats, reactionary peasants, grain-hoarding merchants, and recalcitrant priests. Lavoisier had been arrested earlier that month along with the rest of the financiers of the “tax farm” that had once collected so many odious and unfair levies on the king’s behalf. And just as Delambre arrived at the d’Assy residence, his patron was likewise hauled off to the Luxembourg prison.

Later that winter, a storm felled the Châtillon tower.

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