A Calculating People

There are certain ideas of uniformity which sometimes seize great minds (as they did Charlemagne’s), but which invariably strike the petty. They find in them a kind of perfection which they recognize because it is impossible not to discover it; the same weights and measures in commerce, the same laws in the state, the same religion in all parts. But is uniformity always appropriate without exception?


[This] chapter has earned Montesquieu the indulgence of all people of prejudice. . . . Ideas of uniformity, of regularity, please all minds, and especially just minds. . . . Uniformity of measures can only displease those lawyers who fear to see the number of lawsuits diminished, and those traders who fear a loss of profit from anything which renders commercial transactions easy and simple. . . . A good law ought to be good for all men, as a true proposition [in geometry] is true for all men.

—M.-J.-A.-N. DE CONDORCET, Observations on “The Spirit of Laws,” 1793

Delambre had been stopped in his tracks. Méchain had been trapped behind enemy lines. Like a suspension bridge abandoned after its end supports had been raised, the meridian survey had been called off in mid-execution, leaving a span half the length of France unbuilt between them. Not that the leaders of the Revolutionary government cared. They considered the meridian arc a monument to futility. Now that they had the provisional meter in hand, they could leave the ruins of the meridian survey unfinished, a folly of scientific presumption. For them, the challenge was not to push precision to an ever narrower closure, but to bring the advantages of the metric system to the common people. This meant putting meter sticks in the hands of 25 million French men and women.

Yet when the date for the obligatory use of the metric system arrived on July 1, 1794, the Revolutionary government had produced fewer than one thousand meter sticks and not a single French citizen was using the new system. Even the petty officials who answered to the dictatorial Committee of Public Safety were still filling out their reports in the old measures, making it impossible for the central government to monitor grain supplies. Prieur de la Côte-d’Or and the other members of the Committee pleaded with their subordinates to conduct the nation’s business in the new metric system. They denounced the feudal diversity of measures as a barbarous remnant of the Ancien Régime. They expressed their frustration: Why had the people who had pleaded so passionately for metric reform in the Cahiers de doléances become suddenly so reluctant to accept the metric system?

This paradox would not have been so surprising had the politicians and savants put aside their willful disregard for the meaning of measurement in the Ancien Régime—and considered the enormity of the change they were demanding. Understanding that change will clarify the meaning of measurement, both for them—and for us. A modern system of measurement allows objects to be described in abstracted, commensurable units that relate to an absolute standard. This is true of the new metric system the French were seeking to establish, as it is of the nonmetric measures still in use in America today. In either system a measurement stays fixed, no matter where the object is measured, or which measurement instrument is used. A meter is a meter; as a foot is a foot, a pound is a pound, and a kilogram is a kilogram. The dimensions of any other object can be described by reference to these units. The ultimate guarantor of these standards is a national or international agency with precise standards and a staff of inspectors. These inspectors are rarely seen any more because they have built their supervisory role into the measuring instruments we use every day: rulers, scales, graduated cylinders, clocks, or gauges. Only in cases of extreme controversy are the inspectors obliged actually to check the calibration. Until that time, we trust the instruments. This form of measurement is adapted to our modern economy, in which buyers and sellers remote from one another in time and space conduct impersonal exchanges, quite certain that their measures are commensurable.

Under the Ancien Régime, by contrast, measurement was inseparable from the object being measured and the customs of the community which performed the measurement. These measurements were not enforced by a remote bureaucracy, but by local people answerable to their neighbors for their fairness. Far from being irrational or unnatural, this hodgepodge of measures made real sense to the peasants, artisans, shopkeepers, and consumers who used them every day.

To begin with, each act of measurement in the Ancien Régime referred to a particular physical standard, held in local hands and safeguarded by local officials. A town’s measure for the length of building materials, for instance, might derive from an iron fathom mortised into the wall of the town’s market hall. The local measure for the weight of bread might derive from a master pound preserved in the guildhall of the area’s bakers. The district’s volume for grain might derive from a master bushel secured in the lord’s château. And the local volume of wine might derive from a master barrel stored in the cellar of the monastery that owned the vineyard. It was the obligation of local officials—these aldermen, guild-masters, lords, and abbots—to enforce these standards, ensuring that exchanges made in the marketplace were fair. In return, they were entitled to extract a small fee for their services.

Not only did the physical standards differ from community to community, but the technique of measurement depended on local custom. One district measured grain heaped high in its bushel; another measured grain after it had been leveled off; still another, after the bushel had been struck to settle its contents. Even the height from which grain was poured into the receptacle was dictated by custom, since contents may settle upon handling. A slight nudge might alter the amount of grain in the bushel, a difference of great concern to those who paid taxes in kind or who bought or sold foodstuffs in bulk—that is to say, the vast majority of French men and women. Similarly, the aune (the ell), a measure of cloth, generally equaled the width of local looms, so that a square aune of fabric could be appraised by folding a quick triangle. Alternatively, the shopkeeper might measure an aune by extending the cloth from his nose to his outstretched arm, with a complimentary thumb’s worth thrown in “for good measure.” Quantity in the Ancien Régime was bound up in ritual and custom.



These pre-Revolutionary measurement standards from the town of Laon, Méchain’s birthplace, are still mortised into the wall under the archway of the town hall. They are among the last Ancien Régime measures still in situ. From left to right: the “T” measured the size of barrels; the rectangles are matrices to gauge bricks (above) and roof tiles(below); and the “I” is an aune (an ell, about three feet in length) to measure cloth. (From the Musée de Laôn)

This meant that measurement standards were potentially open to dispute, negotiation, and change—albeit with the consent of the local community. Indeed, in many places the quantity that local people called “a bushel” had actually altered over the years, as lords and tenants disputed its “true” amount (and hence the proper level of taxation and a fair price for basic foodstuffs). As such, local measures served as a living record of the shifting balance of power within the community. Outsiders, of course, did not understand these measures, but local buyers and sellers did—which suggests one of the main advantages of local diversity. They kept outsiders out. Distinctive measures protected small-town traders from big-city merchants, or at least forced the latter to pay the equivalent of a fee before they could enter the local market. Artisanal guilds took charge of their own measures so that they might define their goods in a unique way, identify interlopers, and drive them out of business with ruinous lawsuits. This was as true of gunsmiths and milliners then as it is true of the computer industry today. Control over standards is control over the rules of economic life, and Ancien Régime standards were everywhere local. Yet beneath this local diversity lay the deeper meaning of measurement in the Ancien Régime.

Many Ancien Régime measures—especially those that related to the world of production—had at their origin an anthropometric meaning derived from human needs and human interests. This does not mean that they directly reflected the size of the human body, the pied (foot) as the size of the king’s foot, or as the length of the average human foot. Rather, many Ancien Régime measures reflected the quantity of labor a person could do in a given period of time. Thus, coal in one region of France was measured in acharge (“load”) equal to one-twelfth of a miner’s daily output. Arable land was often measured by the homme (“man”) or journée (“day”) so as to designate the amount of land a peasant might plow or harvest in one day. Other units expressed the local people’s evaluation of worth or quality. Thus, the size of a plot of arable land might also be measured in bushels; that is to say, a plot of land was equal to the number of bushels of grain it took to sow that field. Even in districts where land area was ostensibly measured in a unit like the arpent, which referred to a number of square pieds (feet), the dimensions of the surface area would actually vary depending on the type of field and the quality of its soil. For instance, pastureland measured in arpents was often divided into five distinct degrés, based on the best use for the field. In some cases, properties described in arpents in the official records were in practice divided intojournées—which could not be compared with one another on the basis of their abstract surface area.

As the economic historian Witold Kula has pointed out, these anthropometric measures expressed features of primary concern to those who worked the soil or produced the goods. After all, a peasant whose plot of land was physically smaller than his neighbor’s “five-bushel” plot, but which took six bushels to sow because it was on a gentle slope and had fertile soil, might well have found that “six bushels” expressed his stake in the land far more vividly than an abstract surface area. Moreover, these measures did not simply express the value of the land, they guided work rules and set customary limits on the labor a landlord might extract. Thus, when a foreman hired four peasants to pick a vineyard of eight journées, the laborers knew not to settle for less than two days’ wages each; nor would they do the work with only three peasants on their gang. In this sense, the anthropometric measures of the Ancien Régime acted as a control on productivity, and indeed, masked the very idea that productivity was a value that could be measured.

For just this reason, some eighteenth-century landlords had begun to map their property in geometric units rather than in units of labor. They hired surveyors who could “put all these defective [measures] in good order, so that in each district their content is regulated in either perches, pas,or pieds (rods, yards, or feet).” Armed with the new square units, these landlords hoped to monitor productivity and pocket any gains. This new breed of efficiency-minded landlord-farmer was the great hope of the “physiocrats,” a group of reformers who had acquired much influence with the French royal administration and were also known as “the economists,” being the first to practice that dismal science. The physiocrats touted agricultural reform and free trade as the key to improving standards of living, and they—like economic historians ever since—have expended great effort to determine whether productivity was rising in France. Unfortunately, the question is virtually unanswerable for much of France because the process of translating anthropometric measures into modern measures erases the very information that defined productivity in the Ancien Régime. When England’s leading agronomist set out to assess French agriculture in the 1780s, he discovered that he could not rely on the official measures listed in the public records.

The denomination of French measures, as the reader will see, are almost infinite and without any common standard to which they can be referred. . . . The only clue tolerably general that can be in the least relied upon is drawn from the quantity of seed sown. . . . [And] inquiries of this kind are not to be made in the bureaus of great cities; books and papers will not afford the information; a man must travel through the country or must always remain ignorant though surrounded by ten thousand volumes.



This meter stick is the official provisional meter of 1793, which measured 443.44 lignes in the old Paris units. It was made by Lenoir out of copper. The cadil was the name for the liter until it was changed in 1795. The kilogram weight pictured here was based on the original definition of a gram (then called a grave), which equaled the weight of one cubic centimeter of water at the freezing temperature. For the definitive kilogram of 1799, the gram was based on a cubic centimeter of water at its temperature of maximum density (about 4°C). (From the Musée des Arts et Métiers-CNAM, Paris; photograph by CNAM)

Even the surveyors hired by “improving” landlords were daunted by the challenge of transforming land into a factor of production expressible in square units. They warned their employers that for the actual partitioning of fields “it is best to stick to the report of those who sow the land.” That is because these anthropometric measures of land and other commodities were the outcome of centuries of protracted negotiations among artisans, peasants, traders, and lords. Their value had been ritualized and fixed in ways that reflected the relative bargaining power of different members of the local community. As such, Ancien Régime measures had come to express that community’s sense of the proper social equilibrium. And any attempt to substitute a new kind of measurement was read as a threat to that social balance.

No wonder peasants hated surveyors—and why Delambre and Méchain met with such mistrust on their route. They too were surveyors of a sort, come to supplant the anthropometric measures that were the lifeblood of the peasant economy. They too were measuring the earth for the purposes of a new partition.

The savants said the new measures would be “natural” because they were based on the size of the earth. For these savants, a metric unit was natural when it could be defined without reference to human interests. The meter, they said, would be independent of all social negotiation or temporal change, transcending the interests of any particular community or nation. These men invoked nature as the guarantor that all people would benefit equally because no person benefited in particular. This spoke to the ideal of justice as blind. Indeed, this Enlightenment project has often been read as an attempt to displace personal relations as the foundation of the social order, and in their stead substitute a universal metric, imported from the natural sciences, by which the social world might be subject to dispassionate analysis—and schemes for improvement. But the people of the Ancien Régime also considered their measures “natural,” in that they had been built into the dimensions of the lived world and expressed their needs, their values, and the history of their shared life. Their anthropometric measures sanctified man as the measure of all things, and expressed a different notion of justice, one which governed not only the domain of productive labor, but also the realm of economic exchange.

The Ancien Régime was governed by a “just price” economy, in which basic foodstuffs were sold at a customary price set by the local community at a level which most of the people in that community could afford. The just price was enforced by moral sanction and ultimately by the threat of violence. The theory of this “just price” economy had been legitimized, moreover, by medieval scholastic doctrine, although this does not mean that prices were thought to be divinely sanctioned. The people of the Ancien Régime understood that production and consumption would halt if buyers and sellers were unwilling to trade. To induce production and exchange, then, the just price needed to reflect the costs of doing business, with these important caveats: that the authorities intervene in times of dearth, that locals not extort exorbitant fees from wayfarers or people in desperate need, and that sellers not conspire to rig prices.

In such an economy, the diversity of weights and measures greased the wheels of commerce. In an age where bakers dared not charge more than the “just price” for a loaf of bread for fear of precipitating a riot, bakers who wanted to preserve their livelihood when the cost of flour rose simply baked a smaller loaf. The same ruse allowed monasteries to circumvent Christian restrictions against profits by buying wine in large barrels and then selling it (for the same price) in smaller barrels. Sometimes this could lead to accusations of fraud, as when the petitioners of Notre-Damme-de-Lisque complained in 1788 that their abbot’s tax collector had increased the measure of grain. More probably, he was simply trying to maintain his own revenue during a time of rapidly increasing prices.

The workings of this economy were familiar to Ancien Régime officials. One government agent noted that local grain merchants profited by buying grain at one measure and selling it (for the same price) at a lesser measure. But rather than condemn this practice, he noted that it encouraged commerce in the region, since attempts to raise prices risked the wrath of the local populace. A provincial assembly warned in 1788 that “the establishment of a uniform measure would ruin this genre of commerce, destroying at the same time an infinity of little markets which subsist only on these differences and, though of no great importance, supply the needs of nearby consumers.”

In many towns, Ancien Régime officials themselves served as the “fair mediators” who interposed themselves between buyers and sellers, setting the just price for essential foodstuffs like bread, meat, wine, and beer. Indeed, superintending the economy in this way was one of the obligations of a benevolent monarch, and among the principal justifications for his rule. In setting the just price, local officials generally took market conditions into account. The price of bread, for instance, was governed by tarifs, numerical tables that translated the current market price of wheat into the just price for a four-pound loaf of bread of a specified quality (white bread, brown bread, second-class bread, and so on). In major towns, these tarifs were drawn up collaboratively by aldermen and bakers, who jointly estimated the cost of milling and baking bread, andoutfitting a shop, while guaranteeing a modest return for the baker. These regulated prices, however, were “sticky” in the sense that bakers could not fine-tune their prices to meet daily fluctuations in the cost of wheat. Also, bakers tended to set their prices in round numbers because of a persistent shortage of small coins. Instead of adjusting prices, bakers then altered the weight of their loaves or diluted their ingredients. Such practices were illegal, but even consumers who were aware of them generally tolerated them so long as everyone could still afford a “pound” of bread. Equity mattered more than efficiency. Yet in times of dearth any attempt to raise prices or to “short” bread too egregiously could spark violence. Price was not the paramount variable in the Ancien Régime economy, but merely one variable among many, including quantity, quality, the cost of production, and local custom.

In short, the old diversity of weights and measures, far from being irrational and unnatural, formed the backbone of the Ancien Régime economy. These measures did not simply define a distinct kind of economy, they defined a kind of human being. Today, we assume “the market” consists of the aggregate of innumerable one-on-one private exchanges, the sum total of which sets prices. We might call this the market principle. The Ancien Régime operated according to the idea of the market as a place, which one might imagine as a kind of bazaar or village fair in which buyers and sellers met in public to conduct exchanges under the watchful eye of a third party. That third party—typically an emissary of the king, a town alderman, the local lord, or the nearby abbot—justified the taxation of these transactions by ensuring that the needy did not go hungry and the producer got a fair return for his troubles. Thus, in addition to providing peasants and artisans with a ready guide to the value of their land and labor, the weights and measures of the Ancien Régime also provided shopkeepers and consumers with some guarantee that their marketplace transactions would be fair.

In this context, the French savants’ scheme to reform weights and measures was a revolutionary rupture, far more radical than the sort of translation involved in the switch from, say, Anglo-American units to the metric system. Indeed, the revolutionariesintended the metric system to eradicate the assumptions underlying the old just-price economy. Their goal was to make productivity the visible measure of economic progress, and to make price the paramount variable in commercial exchange. They saw the metric reform as a crucial stage in the education of modern Homo economicus.

To this end, the Academy of Sciences proposed in 1793 a decimal division for its currency, so that its value too would be based upon the new metric units of weight. The Academy proposed that one franc should equal 0.01 grams of gold. “Thus will all measures, weights, and money refer to a unique and foundational base: a quarter of the earth’s meridian.” By defining the scale of worth as well as that of quantity, science would provide a secure foundation for a rational economy. On December 7, 1794, the new franc was declared equal to the old livre, now divisible into 100 centimes. This rationalization was the brainchild of the same savants and politicians who had pushed for metric reform: Lavoisier, Condorcet, and Prieur de la Côte-d’Or.

Lavoisier was not only the world’s premier chemist, he was also one of the Ancien Régime’s “tax farmers,” the financiers who collected the king’s taxes—and took a healthy cut for their pains. This position had earned him one of France’s great fortunes, as well as the hatred of millions of ordinary French men and women. Despite the source of his income, however, Lavoisier was committed to the physiocrats’ policies of laissez-faire and the elimination of the Ancien Régime’s many taxes, both visible and invisible. He had thought long and hard about the optimal way to manage a national economy, and his thinking on this point was closely connected to his understanding of chemistry. His lofty principle that “matter is neither created nor destroyed, all it knows is transformation” committed his young science to precision measurement. How else could the chemist know whether matter had been conserved or not? If the chemical equation was to be the new mode of thought about the material world, then the finely tuned balance scale would be the proof that such thinking paid off. Novelty, productivity, and profit all relied on careful bookkeeping. Economic exchange, like chemical transformation, should be measured in universal units so that transactions would be transparent, with buyers and sellers equally informed about the deal they were cutting. Such transactions would also be easier for the centralized state to monitor for fairness and, of course, to tax. Without the decimalization of money, he noted, “the metric system will have been adopted in vain.”

Condorcet, in addition to his role as Permanent Secretary of the Academy of Sciences, had served as Master of the Royal Mint. Along with his contributions to mathematical social science, he was one of the nation’s premier political economists. For Condorcet, economic progress went hand in hand with political progress. He was history’s greatest optimist. His goal was to reconcile freedom, equality, and material well-being through a program of universal education and a new social science that would match human laws with social needs. That nature’s laws were everywhere the same meant, for Condorcet, that the hodgepodge of human laws must be aligned with universal principles. Reduce the legal code to its essentials and the law would be comprehensible to all literate men and women. This would diminish the unfair advantage that those in authority held over the powerless. Give all citizens equal access to knowledge and they would all have the power to control their own fate. Condorcet had imagined a scheme to classify all knowledge in a decimal system, a forerunner of the Dewey Decimal System. More grandly still, he imagined a language of universal signs to replace all forms of logical thought, much the way algebra expresses mathematics. Such a language would apply to social relations as well as to logical ones. It would “bring to all objects embraced by human intelligence a rigor and precision that would render knowledge of the truth easy, and error almost impossible.”

Condorcet considered the metric system a first step toward achieving this new universal language for the objects of the material world. In combination with the reform of the French currency, the metric system would bring efficiency to economic relations—and this, in turn, would foster political equality and freedom. “[It] will ensure that in the future all citizens will be self-reliant in all those calculations which bear upon their own interests; because without this independence citizens can neither be equal in rights . . . , nor truly free. . . .”

As for Prieur de la Côte-d’Or, he had an engineer’s appreciation of optimization, plus an administrator’s preference for clear protocols—which is another way of saying that he embraced the clichés of the day. Prieur was younger than Lavoisier or Condorcet, and nowhere near their intellectual equal. Under the Ancien Régime he had been a run-of-the-mill military engineer: underemployed, a bit shy, lame in one leg, uncomfortable with public speaking, formerly his mother’s darling, in love with a married woman, well trained in mathematics, primed with the ambition to rationalize the world, and not much of an original thinker. But from his new position on the Committee of Public Safety, he had the clout to make things happen.

Prieur believed that uniform measures would make France a great nation, smoothly administered from the center and united through trade. The metric system would transform France into “a vast market, each part exchanging its surplus.” It would make exchanges “direct, healthy, and rapid,” diminishing the “frictions” which impeded the wheels of commerce. These frictions included anything that masked the true price of an item, such as the variable measures of the Ancien Régime. The price of an item, Prieur argued, necessarily depended on many factors: its scarcity, the work necessary to produce it, the quality of the product. But in the final analysis, price was whatever people agreed it should be. This meant that when people agreed on a price they needed to know what they were getting, not be baffled by secret shifts in the quantity being exchanged. Those who claimed that differences in measures aided commerce were just talking about their personal profits. “The French Republic,” he wrote, “can no longer tolerate men who earn their living by mystery.” Worse, those who profited from the diversity of measures, said Prieur, corrupted those who tried to conduct honest and transparent exchanges by “complicating commerce, spoiling good faith, and sowing error and fraud among the nations.” Until commerce was carried out with complete probity, the common people would doubt the advantages of free trade. Only if price were the sole variable in exchange would these exchanges be based on clear understanding between parties.


Instruction in this new form of “right thinking” about economic matters would come from the metric weights and measures themselves. The people’s new rulers would be the rulers they used every day. Rational measures would engender a rational citizenry.

If we want the people to put some order in their acts and subsequently in their ideas, it is necessary that the custom of that order be traced for them by all that surrounds them. . . . We can therefore look upon the metric system as an excellent means of education to be introduced into those social institutions which conjure up the most disorder and confusion. Even the least practiced minds will acquire a taste for this order once they come to know it. It will be reflected by the objects which all citizens have constantly before their eyes and in their hands.

Today, many of these ideas are taken for granted and hence unexpressed. But like many things that appear ordinary on the surface, they mask a long history of bitter controversy. Making measurement banal proved to be hard work and would take more than a century of struggle and conflict.

For instance, these reformers all presumed something we are apt to forget: that free trade would have to be fostered by state action. It may be that people everywhere have an innate desire to “truck and barter,” as Adam Smith taught, but the leaders of the new French republic understood that a “free market” was something quite different and required a new set of social institutions. The proponents of the metric system wanted both a powerful state apparatus and a free citizenry empowered to participate in the political and economic life of the nation. To resolve this apparent contradiction, they wished to transform their fellow citizens into a calculating people. The savants, engineers, and administrators of eighteenth-century France were already superb calculators who had earned their posts thanks, in large part, to their mathematical merits. They simply wanted the French people to become more like them.


The advocates of the metric system, like today’s advocates of globalization, saw their goal as creating at one stroke a new kind of economy and a radical new kind of politics. This is not to say that the savants were innate revolutionaries. The French savants of the eighteenth century had been as fond of their comfortable Ancien Régime lives as the lawyers, financiers, and military men who likewise stepped warily into the new age. They had little cause for complaint. Foreign savants who visited Paris before the Revolution often remarked wistfully on the respect their French colleagues received at the hands of the kingdom’s great nobles and ministers. The savants were appreciated, and they enjoyed their daily routines. Yet their very routines masked a radical premise. Give scientists a chance to remake the world, and who knows what will be left standing when they are done? What human habit can survive the blade of logic? What social institution can justify its ways to mathematics? What ancient custom can be assayed with precision? The metric system belonged to that radical strain of the French Revolution which sought to destroy all local distinctions to make way for a future in which everything was the same everywhere, much as today’s critics of globalization suggest that the Information Age will level all cultural differences around the world. The metric system was to be the new language of the material world. And just as the Revolutionaries sought, in the name of linguistic unity and rational communication, to eliminate the diversity of France’s various patois—its many regional languages and dialects—substituting French as the sole language of rational communication, so did the savants dream of extending their metric language to all domains of scientific and public life.



This calendar of 1797 enabled users to convert between Revolutionary and Gregorian dates. The Revolutionary calendar came into existence in October 1793 and began with the year II. It was abolished early in the year XIV in time to start 1806 on January 1. (From the Photothèque des Musées de la Ville de Paris)

Time was first. The Revolution had marked a new beginning in human history. Where the Gregorian calendar had wed the year’s rhythm to Christian holy days, a secular republic needed a calendar based on nature and reason—although pinpointing the exact moment of rupture proved contentious. Was it January 1, 1789—the beginning of the year which had proved so liberating? Or was it July 14, 1789—the date the Bastille fell? Both moments of origin, and many others, were proposed. Not until 1793 did the mathematician-turned-politician Gilbert Romme—on the advice of his friend, Jérôme Lalande—settle upon a solution. Year I of the new era would be backdated to the founding of the French Republic on September 22, 1792, which happily coincided with the autumn equinox, a most auspicious conjunction of nature and reason. “Thus, the sun illuminated both poles simultaneously, and in succession the entire globe, on the same day that, for the first time, in all its purity, the flame of liberty, which must one day illuminate all humankind, shone on the French nation.” The calendar would contain twelve months of thirty days, each poetically named after its season as experienced in France.


month of the wine harvest



month of fog



month of frost



month of snow



month of rain



month of wind



month of germination



month of flowering



month of meadows



month of the harvest



month of heat



month of fruits


Each month was then divided into three ten-day weeks known as décades; no more Sundays, no more saints’ days. National festivals would commemorate the anniversaries of Revolutionary uprisings, with a climactic festive sans-culottide of five days (six in leap years) to ensure that each year began anew on the autumnal equinox. No creation of the Republic, wrote Lalande, would do more to break the hold of the priests over their superstitious dupes. He did admit, however, that ordinary people might find the ten-day work-week a tad on the longish side, and proposed a midweek holiday, the quintidi, to ensure that the Revolutionary calendar and the Revolution itself would become popular.



In 1794 and 1795 the French government briefly mandated the use of a decimal clock with a day divided into 10 hours of 100 minutes of 100 seconds each. Of all the unpopular changes associated with the metric system, this was the most unpopular. Some forward-thinking individuals, like Laplace, had their Ancien Régime pocket watches modified accordingly. A clock in the Palais des Tuileries still kept decimal time as late as 1801. But decimal time was otherwise ignored. (From the Musée des Arts et Métiers-CNAM, Paris; photograph by Pascal Faligot, Seventh Square)

And while they were at it, the rationalizers reasoned, why not divide each day into ten hours, and each hour into one hundred minutes? A law of 11 brumaire of the year II (November 1, 1793) so decreed. Master watchmakers designed prototype clocks that pointed to “V o’clock” at midday, and “X o’clock” at midnight. Laplace had the dial of his pocket watch adapted to show decimal time.

And why stop at time? Why divide circles into 360 degrees just because the ancient Babylonians had done so? A 400-degree circle (with a 100-degree right angle) would not only ease calculation, it would synchronize astronomy and navigation. In a world where the quarter meridian was 10 million meters long, each degree of latitude would then measure 100 kilometers. This would simplify maps and assist sailors. Already, as a pledge of the metric system’s coherence, Etienne Lenoir had ruled his repeating circles for Delambre and Méchain in 400 rather than 360 degrees.The new angular division would require new trigonometric and logarithmic tables. But their production too could be rationalized. By breaking down the complex formulas into a series of simple arithmetical tasks, the savants could portion out the work to semiskilled “calculators,” creating a factory of mathematical results. Condorcet proposed employing the graduates of the deaf-mute schools because they would be less easily distracted from their labors than other people. In the event, the savants employed out-of-work wig-makers, laid off by the Revolutionary assault on aristocratic hairstyles. This collective human computer—inspired by Adam Smith, and the inspiration for Charles Babbage—prefigured our information economy: universal measures, transparent numbers, and the division of mental labor.


Condorcet and Lavoisier were well placed to press for metric reform, at least at first. As the Permanent Secretary of the Academy of Sciences, Condorcet spoke for that body. He was also an elected representative to the National Assembly, where he became a chief advocate of equality for women, Jews, and blacks. He urged public education for all French children. He believed that virtue and reason were forever conjoined. These views would also garner him enemies, especially when the Jacobin party came to power. Not that the Jacobins disputed those goals exactly, but they despised Condorcet’s voluntarist methods of achieving them. When the Committee of Public Safety condemned Condorcet along with the rest of his political allies, he went into hiding. There he composed his great utopian tract, Sketch for a Historical Picture of the Progress of the Human Mind, which he left unfinished when he killed himself rather than face execution in May 1794.

Though he lacked a formal political role in the new Republic, Lavoisier had considerable power to promote the metric system. As Treasurer of the Academy of Sciences, he controlled the purse strings of the meridian expedition. As the patron of one of Paris’ finest salons, he hosted dinner parties on the boulevard de la Madeleine where the scientific elite could hash out policy and win political allies. Lavoisier was a man who knew everyone and was everywhere respected. He secured an exemption from the military draft for the savants and instrument-makers working on the metric system, including Delambre, Méchain, and their assistants. He determined the standard for mass, which he defined as the weight of a cubic centimeter of distilled water at the temperature of melting ice. He was just completing these experiments when the Committee of Public Safety incarcerated him, along with the rest of the tax farmers, in the Porte-Libre prison (the “Free-Entry” prison).

Lavoisier, who had fretted over the fate of the injured Méchain, now found himself in need of a protector of his own. Borda wrote to the Revolutionary authorities, bravely demanding that Lavoisier be released so that he might resume his labors for the metric system. Where once Lavoisier had cited the ongoing metric reform project as the chief rationale for preserving the Academy of Sciences (to no avail), his colleagues now cited his labor for the metric reform as the chief rationale for preserving his life. The Committee of Public Safety responded by purging Borda—along with Delambre, Laplace, and several others—from the Commission of Weights and Measures. The signature on the order was that of Prieur de la Côte-d’Or.

For the past few years, Prieur had been a regular guest at Lavoisier’s home, where the nation’s greatest scientific minds had gathered over dinner to thrash out the details of the new metric system. The conversation often turned to politics. Prieur, the youngest person present and no scientific luminary, often found himself alone in defending the Revolutionary government, of which he was a rising member. Conversation became animated; these were men who spoke their minds. At times, Prieur’s views were mocked. It was this personal pique, according to Delambre, that explained Prieur’s vendetta against the senior savants. “As a result he nourished a resentment against Lavoisier and those of his colleagues, such as Borda . . . , who showed themselves to be most ardent, lively, or witty in their disputes.” In his own mind, of course, Prieur had only acted to “regenerate” the Commission of Weights and Measures. He had cancelled the superfluous meridian expedition so that the government might focus on the far more important task of implementing the metric system. The scientific portion of the mission, he wrote, had been “carried to that point of maturation at which the need for reflective thought separates itself from the need for action.” The time for action had come.

That winter, while Lavoisier languished in prison, the same forces closed in on Delambre’s patron, Geoffroy d’Assy, also a wealthy financier associated with the detested taxation system of the Ancien Régime. The neighborhood council in the Marais—renamed the Section de l’Homme Armé (the Armed Man)—sent two officials to search the d’Assy residence in Paris for evidence of disloyalty. When the house servants explained that the d’Assy family had relocated to the countryside, the officials sealed shut the residence at 1, rue de Paradis. Then on January 25, 1794—just as Delambre arrived at the d’Assy country château on his way north from Orléans—d’Assy was arrested there. No explanation was given, but in light of d’Assy’s position in the Ancien Régime, none was needed. A second search of the d’Assy residence in Paris a week later turned up a table lamp engraved with the fleurs-delys and made by an artisan who worked “by appointment to His Majesty.”

It was up to Delambre to remove any further incriminating evidence from the house. After a week spent comforting the family in Bruyères, he drove his custom-built carriage back to Paris, paid a last month of wages to Bellet and his manservant Michel, returned his repeating circle to Lenoir’s workshop, and presented himself to the neighborhood council. He showed them his passport, signed by the Minister of the Interior, declaring his residence to be 1, rue de Paradis. He showed them the certificate attesting to his status as the Republic’s Commissioner for the Measure of the Meridian. And he explained to the council that he needed to gain access to the d’Assy residence to recover important astronomical equipment essential to his mission. Needless to say, he did not mention that he had been purged earlier that month from the meridian expedition for “lacking revolutionary zeal.”

Delambre’s ostensible goal was to retrieve his own papers from his apartment on the third floor. He was accompanied by two officials. On entering his room, he discovered that his secretary-cabinet was locked and that he had forgotten the key. This enabled him to make a second trip inside the sealed building a month later. On the second occasion, the officials examined every scrap of paper he removed from the cabinet, including a piece of parchment covered with a Latin scrawl and signed by King George III of England. This document attested to Delambre’s membership as a foreign correspondent in the Royal Society of London. The officials seemed uneasy about this document, as well as several other sheets covered with scribbled calculations and drawings; these might be ciphers or secret plans. In the end, however, they let Delambre remove these papers, having found “nothing suspect.” He later recalled that “this was a supreme indulgence on their part for a man they thought in correspondence with kings.”

Lavoisier was not so fortunate. He was executed on May 8, 1794, along with the twenty-seven other tax farmers. As one mathematician confided to Delambre: “It only took them an instant to cut off that head, and it is unlikely that a hundred years will suffice to produce a comparable one.”

By that time Geoffroy d’Assy had spent five months in the Luxembourg prison. Initially, conditions were tolerable; prisoners had the use of a café in the prison’s central courtyard. But as war fever intensified, the Committee of Public Safety suppressed dissent by populists and moderates alike. That summer, the Revolutionary Tribunal sentenced d’Assy to death, along with fifty other coconspirators who had plotted a prison revolt to “reestablish the monarchy and tyrannical power.” A more motley set of conspirators could hardly be imagined: aristocrats, bakers, and an entire family. Only an elderly wine merchant and a fourteen-year-old boy escaped the death sentence—although the boy’s sixteen-year-old brother was executed. Two weeks later, Robespierre himself was guillotined during the counterrevolution of thermidor.

The incarceration and death of Delambre’s patron made him now the chief protector of the d’Assy family. In June, he returned to the d’Assy home in Paris, armed with a power of attorney from Madame d’Assy, to retrieve various legal documents belonging to the family. In January 1795 he petitioned to recover all his own possessions from the house, including his astronomical equipment, his furniture, and a small portrait of himself on the dressing table of Madame d’Assy. He spent the rest of this period far from Paris in the d’Assy country château near Bruyères-le-Châtel, then renamed Bruyères-Libre. When Madame d’Assy’s brother died of a fever later that year, Delambre promised to shed tears for him as soon as he had a spare moment. At the time the tragedies were coming too fast.

The Revolution had provided the French savants with a unique chance to rewrite the world’s measures. Yet the opportunity carried corresponding risks. Persist in the old ways of treating your subordinates and they might take you down a peg. Place your talents in the service of the state, and the state might call you to account for your findings. Commit an astronomical error, and you might wind up in prison.

Most of the purged members of the Commission had sequestered themselves in the countryside during the long hot summer that became known as the Terror. Borda retired to his family estate. Laplace retreated with his wife and two young children to Melun, thirty miles southeast of Paris. But Cassini IV’s residence was the Paris Observatory, and he now paid the price of having refused to serve the Republic. In the decade before the Revolution, Cassini had hired three men as astronomical aides and housed them on the Observatory grounds, where they might be instructed by Méchain and the rest of the staff. These apprentice astronomers now demanded equality with their boss, as well as the other rights of free men. The eldest, a mild fifty-year-old monk named Nicolas-Antoine Nouet, who also served as Observatory chaplain, informed Cassini that he wished to marry his personal serving woman. Cassini was horrified and the two men, once cordial, never spoke again. The second student, a young man of astronomical talent named Jean Perny, returned drunk to the Observatory late one night after a meeting of his Revolutionary club, and banged on his patron’s door with the butt of his sword, shouting “Cassini the aristocrat must be killed!” He had to be subdued and taken to bed. A few days later he penned an abject letter of apology. The third student, Alexandre Ruelle, a youthful deserter from a dragoon regiment, whom Cassini had harbored and trained until his amnesty came through, became his benefactor’s most bitter enemy.

The apprentices’ complaint was the perennial complaint of junior scientists in the laboratories of their seniors: they accused Cassini of having appropriated their work to publish it under his own name. They wanted equal credit and equal pay. The “horrific despotism,” of the Observatory director, they claimed, had “stolen the fruits of their nighttime labor.” In truth, Cassini had generally acknowledged his students’ contribution in his reports to the Academy, albeit in a patronizing manner.

In this topsy-turvy time, however, the assistants made their accusations stick. With the aid of a sympathetic politician, they reorganized the Observatory along egalitarian lines. Science, after all, was a democratic enterprise, open to all aspirants. No savant should inherit his position like an aristocratic title. The government created four new posts of “Observatory Professor.” Cassini retained one of these. But rather than give the other three to the country’s leading astronomers—Lalande, Delambre, and Méchain—the apprentices convinced the authorities that these savants harbored “aristocratic” sympathies, and had themselves appointed instead. Cassini’s salary was halved, and Perny was elected the first director in rotation. Faced with this humiliation, Cassini resigned, ending 120 years of family rule. His resignation only worsened his situation. His students were able to evict him from his apartments in the Observatory. Then the government seized his map of France, the family’s great commercial and scientific enterprise and, when Cassini dared to protest this theft, threw him in prison. Immediately, his student Ruelle, a member of the neighborhood’s Revolutionary council, suggested that his former protector be sent before the Revolutionary Tribunal, a certain death sentence. Mercifully, the council rejected his suggestion.

But topsy-turvy times will flip and flip again. Once Robespierre himself had fallen from power, the student-professors fell out among themselves. Suddenly Ruelle found himself under attack by his fellow students. Apparently he had committed an error of ten seconds in a solar observation. More damaging still, his results were fraudulent, based on theoretical guesswork, rather than on direct observation as he had claimed. For this crime against science—and also, of course, for his affiliation with the radical party now out of favor—Ruelle was himself imprisoned on August 22. Such were the risks of scientific error in perilous times. To replace him, the other two former students invited Delambre to join them as Observatory Professor.

Thus the winds of revolution shifted in science as they did in politics. Robespierre’s Republican successors, self-conscious moderates, made a great show of reviving the nation’s scientific institutions. In June 1795 they established a new institution, the Bureau of Longitudes, in imitation of Britain’s Board of Longitudes, to help France rival that nation’s commercial and naval dominance. The Bureau supervised the Observatory of Paris, and was staffed by the nation’s finest savants, including Lalande, Laplace, Legendre, and Borda, plus Delambre and Méchain. Then they restored the Academy of Sciences as part of the new National Institute, where almost all the (surviving) academicians—Delambre and Méchain included—resumed their old chairs.

Now it was Cassini who was free, while Ruelle languished in prison—though neither found scientific redemption. When Ruelle was finally released, only Lalande would vouch for him, and he finished his career at the national lottery, where one hopes he did not indulge the sort of fabrications that had cost him his career in astronomy. As for Cassini, he spurned the entreaties of Delambre and Lalande that he rejoin the scientific fold. He said he had witnessed too many bitter divisions in the Academy to contemplate a return. He retreated to his country château in Thury with his mother, his five children, and nine nuns evicted from a nearby convent. “My swallows,” he called them. “I have named it the Republic of Thury,” he wrote, “where I assure you we lack only Republicans.” The savant who had once claimed the meridian expedition as his birthright no longer believed in the metric reform—nor even in science.

“But what of your astronomy?” you ask. I confess, it is nothing to me now. . . . “But,” you ask, “does not your glory, your reputation, your duty as a savant all speak against this retreat?” My friend, the duty of a father surpasses that of an academician. . . . And as for my reputation, my glory, I have sacrificed them, and it has cost me little. . . . Obliged to flee the Observatory, I saw the Academy of Sciences delivered to the government of the sans-culottes. And what grieved me most, I saw the savants themselves up in arms, divided against one another, partaking of the delirium and the rage of the Revolutionary horde, adopting their morals, their manners, and even their language. . . . How can I recognize myself in the changes they have wrought in our old ways of calculating, our old measures, when we had not ten hours in a day, but twenty-four, and no circles of four hundred degrees . . . ? Everything has changed, and I am too old to abandon my old habits and ideas. The year, the months, the almanac, the astronomical tables, all are changed. If Galileo, Newton, or Kepler were to descend from heaven and appear at the Academy, they would not comprehend a word in the presentation of Citizen Lalande when he told them that on 20 brumaire, the moon, in a 200 degree opposition to the sun, passed the meridian at 5 hours. . . .”

Peasants, shopkeepers, and villagers were not the only ones attached to the old numbers of the Ancien Régime. To the numerate, numbers matter. Some old-time savants, like Cassini, considered the metric system an affront to the harmonious values that had once described their universe.

But where Cassini retreated, Citizen Lalande advanced. On May 17, 1795, he became the new Director of the Observatory. Throughout the advances and reversals of the Revolution, the great iconoclast remained unbowed. When he was elected to the head of the Collège de France in 1791, his first official act was to admit women to all classes. He ended the announcement of prizes in Latin. He even tried to get professors to teach their own courses. Every evening, rain or shine, he took his long constitutional through the streets of Paris—sometimes walking for five or six miles—handing out alms. With his purple waistcoat and his umbrella (a newfangled invention), he cut a singular figure on the city streets: under five feet tall, unkempt, unwashed, his thick gray hair matted to the back of his eggplant-shaped skull. Yet shameless men can demonstrate great courage. “I am so constituted,” he reflected, “as to fear no thing nor person, neither danger nor death.” It may have been his philosophe’s vanity, yet he always insisted on speaking the truth. “I am frank to the point of rudeness; I have never dissimulated, even when the truth might displease.” He had spoken his mind during the Ancien Régime, and he refused to quit now.

He later admitted that it was probably his notorious reputation as an atheist that saved his life during the Terror. If so, it was the only time his irreligion found favor with the powers that be. “I don’t feel sorry for the nuns who lose their pensions because they refuse to swear allegiance to the state,” he wrote to his daughter. “It ought to be a joy for them to starve to death for God.” Yet he proved to be an ecumenical savior. He hid the monarchist Du Pont de Nemours in the dome of his observatory in the Collège des Quatre-Nations, and brought him food and drink there for several weeks at the risk of his own life. Years later, at Lalande’s funeral, the founder of the Du Pont Corporation asked God to bless the notorious atheist. Lalande also disguised several condemned priests as astronomers for their protection, telling them not to worry about this deception. “But of course you are astronomers; who can better claim that title than men who live for heaven?” At a time when it was risky to do so, Lalande also published laudatory eulogies of guillotined savants such as Lavoisier—and then quibbled with their scientific views.

His finest moment was the inaugural Festival of the Supreme Being, where he helped celebrate the deity of the ersatz religion Robespierre had hoped to substitute for Christianity. The ceremony took place on June 8, 1794, inside the Panthéon, a year after Delambre had observed the Paris triangles from its cupola. Offered at last a pulpit to preach his atheism and denounce the priestly cabal, Lalande instead seized the occasion to warn against the ferocious patriotism of the times.

The time has come to declare these important and incontestable truths, known to all people, at all times, and in every corner of the globe: love of country, love of virtue, and the reign of reason. . . . Love of country is not a patriot’s only duty; charity is also a duty. We cannot all serve our nation in the army, in the state, in the arts and sciences, but we can all come to the aid of our brothers. . . . It is in this way that charity, added to love of country, will make us truly worthy of our Revolution, our victories, and the admiration of the entire Universe.

But however great his love for his nation or his fellow man—and woman!—Lalande’s highest priority was always his stars. A few days after his Festival address, he announced he had added 1,200 new stars to his catalogue in the past ten days, bringing his total to 21,000. Six months later—during which time Robespierre was deposed and the moderates took power—he added another thousand. He refused to serve on a criminal jury lest it distract him from astronomy. “There is no sanction,” he informed the authorities, “which would make me leave my stars; I would do anything rather than defer to your summons.” Sometime in 1796, the family workshop surpassed their initial goal of 30,000 stars and decided to shoot for 50,000. His daughter continued to calculate “with a courage rare for her age and sex.” Her young son Isaac was placed in childcare because he so distracted his mother and grandfather. When Lalande hit 41,000 stars in 1797, he boasted that “this inventory of the heavens has been my constant project for the past twenty years, and occupies me to the point that I could die without regret, knowing that I have left behind a monument of my passage here on earth.”


All this time, Delambre had quietly been plying his astronomical trade at the d’Assy country château at Bruyères. To be on the safe side, he secured a certificate from the local municipal council attesting to the fact that he was not an émigré, and had never been imprisoned. Mostly he stayed out of the public eye. On only one occasion did the Jacobin government call upon his expert advice: Delambre had detected a flaw in the new Republican calendar.

In their efforts to keep the autumnal equinox aligned with the birthday of the Republic, the calendar’s designers had instituted the franciade, a leap-year day. But they had failed to see that it would not fall every four years as intended, but occasionally in the fifth year instead. A perfect alignment of Republic and nature was not a simple matter. Looking 150 years into the future, for instance, Delambre discovered a year in which it would be impossible to predict whether the equinox would occur before or after midnight on September 22. He brought these prognostications to Lalande, who informed the calendar’s principal author, Romme, who in turn asked Delambre to help resolve the problem. Delambre suggested some possible solutions, although he warned that certain inconsistencies would resurface 36,000 years hence. When Romme presented these modifications to the relevant government committee, they pronounced themselves unconcerned. “Do you want us to legislate eternity?” one member wanted to know. No, Romme responded, he would be satisfied if the committee agreed to revisit the issue in 36,000 years. And so, to general amusement, it was decreed. Romme himself would not live to see another year, however. He was arrested and executed for his Jacobin sympathies two months later.

By then France’s military conquests—thanks to its Jacobin-led armies—had inspired a new sponsor of geodesy. In 1794, General Etienne-Nicolas Calon was appointed Director of the Dépôt de la Guerre et de la Marine, thereby uniting the army and navy cartographers under a single command. Calon dreamed of a detailed geographic survey to extend the Cassini map to France’s newly conquered territories in the Low Countries, Germany, and Italy. He was a perpetual enthusiast, a self-promoting military cartographer, now a brigadier general and a member of the national legislature. More to the point, he had the budget to make things happen. He envisaged a “museum of geography” assembling forty-five of the nation’s leading savants in an effort “to raise to the highest possible degree the development and glory of the astronomical and geographical sciences.” The spine of this geographical knowledge would be a precise geodetic survey of the meridian.

In pursuit of this goal, Calon decided to consult the learned savant Jean-Baptiste-Joseph Delambre, initiator of the meridian survey. Unfortunately, he did not know in which prison to seek the savant. He asked Lenoir to locate the right facility, and was pleased to learn that Delambre was residing comfortably in a country manor. He invited the savant to Paris to plan a resumption of the expedition, and petitioned the Committee of Public Safety to re-engage both Delambre and Méchain to that end.

Soon afterwards, under the impetus of Representative Prieur de la Côte-d’Or, the National Convention passed the law of 18 germinal III (April 7, 1795). This law represented the final evolution of the metric system as we know it today. It provided the final set of prefixes and names that comprise the metric nomenclature. The new law also signaled some retreats from the principle of rationalization. Although the Revolutionary calendar was preserved, the decimalization of the hours was abandoned, ostensibly because of the cost of replacing all the nation’s clocks, and because the decimalization of time would help only astronomers, not ordinary citizens. Prieur also recognized that the transition to the new measures would have to proceed more “gently.” To oversee the process he created a Temporary Agency of Weights and Measures under the leadership of the gifted mathematician Legendre. He also decided that the meter would be introduced in Paris first, and set a target date three months in the future so that merchants and customers could prepare themselves. The rest of the country would follow later.

The new law also formally relaunched the meridian expedition. Prieur set aside his preference for a quick, cheap standard, and praised the “rightly celebrated” savants he had purged from the project eighteen months before. For the meter to become a truly international standard, he now noted, it had to be based on something grander than the fifty-year-old Cassini survey used to define the provisional meter. He urged Delambre and Méchain to recommence their survey “as soon as possible.” Any further delay was inimical to the public good. He even authorized the savants to approach him directly should they encounter the least obstacle. “I will endeavor with assiduousness,” he wrote to Delambre, “to prove to you my zeal for the success of your mission.” Prieur had good reason to demonstrate his good will; he was himself under suspicion for having allied himself too closely with the Jacobins during the Terror. Delambre smiled inwardly at this switch. As he noted to Méchain, “I would have accomplished a lot more last winter had I not been in the bad graces of Robespierre and one of his colleagues—whose name I’ll tell you later—and who has since treated me more favorably.”

Delambre had learned a thing or two about state-sponsored research in the intervening years. This time, before setting out on his expedition, he made a few requests. Even a savant could learn to calculate as other men did. “It is true that until now the astronomers charged with this mission have been unstinting in their efforts and parsimonious in their expenditures, such as one might expect from impecunious savants who spare the Republic every expense as if the costs were their own. They have neither requested nor received any payment for their labor.” Now, however, the expedition leaders deserved a salary like any other citizens employed by the state, plus back pay for the twenty-one months of geodetic work done before the Academy had been shut. In May 1795, after he and Calon agreed on terms, Delambre rejoined the Commission of Weights and Measures.


On June 28, 1795, Delambre left Paris in his custom-built carriage after an eighteen-month hiatus, accompanied as before by his manservant Michel and the instrument-maker Bellet, plus a new assistant to keep the logbook. The team provisioned their carriage for an extended journey, including thirty pounds of axle grease, a set of ropes and pulleys to hoist the repeating circle into church towers, two crates of astronomical texts, plus tools for repairs: borax, copper, mercury, oil, nails, and steel for screws and springs.

Their first night south of the city, the team put up in the d’Assy country château, where Delambre was always welcome. Two days later, they arrived in Orléans on the banks of the Loire, where Delambre had been forced to halt his operations eighteen months before. Three days later, they pulled into the cathedral town of Bourges, which was to serve as their base of operations while they worked their way back north toward Orléans. The team took lodgings at an inn known as the Coeur de Boeuf, located just off the square where a Liberty tree stood. By sighting from the inn to the nearby cathedral Delambre verified that the expedition team of 1740 had lodged in the same inn. Thus trigonometry informed history. The meridian expedition was back in business.

Bourges cathedral is a jewel of Gothic architecture. Above the front portal, the archangel Gabriel weighs the souls of the dead on Judgment Day. Inside, the stained-glass scenes of redemption rise in blue panels like an interior heaven. The town had served as an entrepôt for Renaissance finance, the central town of France’s Centre. But the sixteenth-century wars of religion had ravaged the region, and Huguenot zealots had decapitated the statues of the apostles in the cathedral. More recently, local revolutionaries had beheaded the copper effigies of the Duc and Duchesse de Berry, and turned the building over to the worship of the Supreme Being “who likewise rules from on high.”

The cathedral tower dominated the countryside for thirty miles around and more. It was 396 steps up the hexagonal stairwell to the platform two hundred feet above the pavement, itself at the summit of the hilltop town. In one corner of the platform, a filigree iron bell tower rose twenty feet further still; at its peak turned a weathervane in the form of a pelican. The selfless metallic bird, a symbol of Christ’s devotion, pierced its own breast for blood to feed its young. It would serve as Delambre’s signal, the point he would observe from afar. Beyond the low balustrade the rolling plain of patchwork farmland, dotted with small towns, stretched into the vaporous distance. Out there was his destination, if he could ever leave Bourges.



This view from the top of the tower of Bourges Cathedral shows its pelican weathervane, unique in France, which Delambre used as his sighting target. In medieval legend, the pelican fed its young with blood plucked from its breast, and hence served as a symbol of Christ’s sacrifice. (Photograph from Valoire-Blois, France)

Delambre had left behind the noise and violence of Paris; yet even in this pastoral center, the retreating tide of Revolution threatened to suck him under. No sooner had he arrived in Bourges than the expedition stalled. The cost of travel had risen beyond his means. Inflation had gathered a frightening momentum since the fall of Robespierre. In the earliest days of the Revolution, the legislature had created a paper money called assignats to pay off the national debt (itself one of the principal causes of the Revolution), backing its value with the sale of confiscated church lands and the property of émigrés. This paper currency had always been treated with skepticism in the countryside, and the war had set off a first round of price increases. The Committee of Public Safety had tried to contain the escalation with wage and price controls. But the moderates had decided to lift the controls and print more money. The value of the assignats began to plummet with alarming speed. Delambre’s expense book documents the accelerating price of food, lodgings, and transportation as he traveled away from Paris. At each successive post, the cost of rented horses doubled and doubled again. The first stage out of Paris cost 92 francs; the last stage to arrive in Bourges a week later cost 804 francs. A few months later, the cost of a stage had doubled again to 1,400 francs. As the price of ink, paper, and basic foodstuffs soared, so did the cost of repairing church towers, erecting scaffolding, and building observation stations. Even the gratuity for the stableboys had risen by a factor of ten. Within a few weeks Delambre had spent his entire budget for the campaign season. He pleaded with General Calon for more funds. Without hard currency, he would be stuck in Bourges for the entire summer.

Nearly a month passed before Calon came through with the money. The Treasury would only release assignats, even though provincials would accept nothing but hard currency. To compensate, Calon raised the men’s salary (reduced to a pittance by inflation), and awarded them military rank: Delambre, Méchain, and Tranchot became captains. This entitled them to food rations. The challenge was to get the peasants and innkeepers to accept the army’s coupons.

Money was not the only obstacle. Geography also presented a challenge. The mournful region between Orléans and Bourges—triste (dreary) Sologne—was one of France’s most level. Where the expedition had once battled suspicious peasants and northern fogs, they now confronted a marshy terrain almost impossible to survey. The green ponds, tall grasses, and patchy forests offered few views into the distance. The rare church steeples were hard to make out through the mists: the steeple at Salbris, used by the surveyors of 1740, had been incinerated by a lightning strike; elsewhere, the Revolution had taken its toll. Delambre expressed his disappointment. “The sans-culottes have destroyed half the steeples in the Bourges region for ‘daring insolently to rise above the height of their humble cottages.’ ” It took Delambre three trips up and down the region to select a chain of workable triangles.

The villages of the Sologne are as isolated today as they were before the region’s swamps were drained. Ponds collect seepage, ditches surround farms, and ruler-straight roads run between twin rows of plane trees. The whine of an occasional motorbike only emphasizes the quiet. The churches are locked year round and are badly in need of repair. The area is depopulated, the number of priests dwindling. In the eighteenth century, the region was already known as the nation’s Siberia. Sandy soil, barren heaths, and thick swamps made even subsistence agriculture burdensome. “There is no soil more unyielding and painful to labor in all the world,” said the locals. Peasants rarely owned their own land. The cattle were sickly, the sheep weak. The ponds bred “Sologne fever” (probably malaria), which afflicted the villages each autumn. And on top of this, the people were beset by a plethora of taxes.

Such a climate bred suspicion. Certain families were said to have the power to bring storms upon their enemies. Sorcerers gathered before dawn at ponds like Boisgibault to beat the waters with great sticks and shout horrible cries. “It was enough for them to seek to change the weather and the blue sky would cloud over and the thunder rumble.” To clear away the fogs and evil vapors required holy incantation and the continual ringing of church bells, called the dindon. The curés had to stuff cotton in their ears to withstand the continual pealing.

The church in Vouzon dates from the sixteenth century and the bell in the square tower used by Delambre still tolls the hours, although the rest of the edifice burned down in the 1880s. At Souesme the church tower has been rebuilt since Delambre’s day, and is covered with scaffolding in anticipation of further repairs. The octagonal Sainte-Montaine belfry still stands, dwarfed by a venerable chestnut tree. Luckily for Delambre, when he visited the site in November the tree was bare of foliage and he could make out the surrounding signals between the branches.

Where no steeple was available Delambre paid locals to build him an observation tower. At Oizon, he had a twenty-two-foot signal built in the form of a pyramid, which he covered with planks of wood painted white. At Ennorde, he had a twenty-four-foot pyramid built, which he then had transported to the middle of a hummocky wheat field. At Morogues, northeast of Bourges, he had a twenty-five-foot signal erected beside a road as it crested a small hillock. Delambre and Bellet climbed the scaffolding and perched themselves on bales of hay to sight the surrounding stations. At Méri-es-bois, just north of Bourges, an elderly villager led them to the ruins of the signal post used in the survey of 1740, and assured Delambre that he remembered Cassini’s passage through town fifty-five years earlier, but that some local lads had torn down the signal last year as a sign of “feudalism.” All this activity attracted unwanted attention.

Even those with the best notion of who we were, took us to be prisoners of war being transported from place to place. Others, on seeing the crates for our circles, took us for charlatan salesmen and refused to give us lodging. That’s what happened in Vouzon. At Souesme, we were also refused a place at the inn; but that was because they knew who we were, and knew we only had assignats to pay them. Without the help of the municipal council, who promised to compensate with grain anyone who sold us bread, we would not have been able to procure any food. Even so we passed several days with nothing to eat but bread. . . . Not only that, but an epidemic was then sweeping through Vouzon, and one of my collaborators fell sufficiently ill that we had to leave him behind when we left the town for Chaumont.

Triste Sologne took Delambre several months to measure, and proved the least accurate sector of the entire survey because the triangles could not be evenly spaced. By working well past the optimal season for geodetic measurement, however, he managed to complete the chain of triangles between Bourges and Orléans by late November. He planned to use the winter—otherwise impractical for geodesy—to conduct his astronomical measurements at Dunkerque and determine the latitude of the northern extremity of the meridian arc, the counterpoint to the measurements Méchain had already conducted at Mont-Jouy.

So before leaving Orléans for Dunkerque Delambre composed a letter to his distant colleague. This letter renewed their correspondence after a two-year silence. Delambre was pleased to be back in touch with his colleague: he was eager to trade information about data, funding, and personal matters too. There was one thing in particular he wished to know. As Méchain had already performed the latitude measurements at the southern end of the arc in Mont-Jouy—and with such precision—might he advise Delambre as to which stars he had observed, what methods he had used to measure their height, and what precautions he had taken against the possibility of error? This information would ensure that his own results could be most fruitfully compared with the superb results Méchain had already achieved.

No innocent request could have touched so sensitive a nerve in so sensitive a man as Pierre-François-André Méchain.

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