The Measure of All Things

by Ken Alder

  For his part, Delambre advised Méchain to leave the resolution of his problems to the superior theoretical skills of Borda and Laplace. He could take pride in the fact that the world’s preeminent physicists would be constructing their theory from his superb Catalan data, “the best and most certain that exist.” Méchain’s integrity and meticulousness were legendary. Yet Delambre reminded Méchain that he must not try to accomplish the impossible. “No matter how much effort we put in, it will always be difficult to surpass one second of precision. You and I have reached that goal, I think, by avoiding exaggerated claims and contenting ourselves with the art of the possible.” Minor errors were inevitable in any operation of this magnitude, and would hardly affect the overall results. “Anyone with the least notion of the difficulties we have faced will take them into account when they consider the exactitude we have achieved.”

  These words of solace do not seem to have given Méchain much comfort. Having let an entire geodetic season pass without closing a single triangle, Méchain shifted his operations to Carcassonne that winter, so that he would be ready to advance on Rodez come the spring. But at the same time, he admitted to Lalande, he was on the verge of collapse. “After having withstood so many tests, my courage has given out, just when there are no more major difficulties to conquer. . . .” Weighing upon his mind was an unflattering comparison with his distant partner. While he stalled in the south, he noted, “Delambre works his way towards us with the swiftness of an eagle, having already traversed almost the entire length of France.”

  In the summer and fall of 1796, Delambre measured seven stations south from Bourges toward Evaux, each station posing its own particular problem, and each requiring its own solution. For instance, at Morlac, the first station south of Bourges, the belfry, which had once risen forty feet above the twelfth-century church, had been dismantled by the “hammer of the Revolutionaries.” Delambre offered to split the cost of a replacement tower with the villagers (population 748), but they refused. So Delambre offered instead to cap the church with a cheaper eighteen-foot wooden pyramid, the cost of which he would split with them and which would also keep the congregation dry when the rains came. They spurned this offer too. So, somewhat peeved, he cut a deal with a timber merchant, who helped him build the tower at a reduced fee in exchange for the right to reclaim the wood once the readings were done. When the merchant arrived to remove the church roof a month later, however, the villagers balked. A trial ensued, and five years later, the church tower was still in need of repairs. Then at Arpheuille, the last station in this sector, Delambre’s measurements were skewed by a large oak tree that cast a distracting shadow against the church belfry; even so, he refrained from pruning it because it also shaded the peasants’ Sunday dances.

  Delambre arrived in Evaux—the halfway point of the arc—on November 24, 1796, and took lodgings at the Auberge du Cheval Blanc. The inn also rented him space in an attic granary by the main town gate. There he pierced a hole in the roof to fashion an observatory, much as he had at Dunkerque. After a run of clear skies and 210 observations of Polaris, the weather turned dreary. Snow fell overnight. During the next two months only two nights were suitable for astronomy.

  His initial results disagreed sharply with those obtained by Cassini in 1740. This discrepancy, which would have sent Méchain into paroxysms of anxiety, led Delambre to recheck Cassini’s work. He discovered an error in Cassini’s methods. He spent his days updating his calculations, refining his formulas, and triple-checking his results. All of these he supplied regularly to Méchain, at Méchain’s request. No doubt he sampled the thermal baths as well.

  Evaux lies at the northern edge of the Massif Central where a hot spring emerges from the hillside at 60 degrees Celsius, flush with minerals. The town’s Roman bathhouse was destroyed by fire in the third century C.E. During the Middle Ages, the baths served as a pilgrimage site, the waters being said to heal injured limbs and chronic diseases. By the eighteenth century there were three bathhouses, superintended by a consulting doctor. After months of hard travel, Delambre would have found Evaux a welcome respite.

  Evaux is a fine place to rest, but not to get stranded. Delambre was determined to finish the expedition in the coming season. “No sacrifice is too great for me to finish this summer.” He hinted at some “additional reasons” for returning to Paris, though he did not specify what they were. We may speculate, however, that he wished to resume his scientific career, interrupted so soon after it had begun. And he presumably wanted to spend more time with a charming Paris widow he had recently come to know.

  In December he began soliciting an advance from Calon for the next campaign season, yet another round in a scientist’s endless scramble for grant renewals. Calon promised to do what he could, but the government had shifted strategies on inflation. While assignats and mandats were being phased out, hard currency was still difficult to come by. Delambre might supplement his pay with army rations; as a cavalry captain, he was entitled to 9 livres a day, plus double rations for himself and his horse. The problem was that these rations could only be redeemed near the war front, and as the paymaster kept reminding him, there was no place in France further from the front than Evaux. Worse, Calon himself was beginning to lose influence. He no longer sat in the legislature, and he had been accused of mismanaging his budget. He requested detailed accounts from Méchain and Delambre so that he might in turn justify their expenditures to his superiors. “Some of the employees I’ve had to fire are vile worms who seek to blacken even the most honorable conduct.” By the middle of spring, Calon himself had lost his post. To make up for the loss of their military patron, the Paris savants called in their political chits. Lalande lobbied Lazare Carnot, a former engineer, now one of the nation’s executive directors. Lalande also offered to chat up Lavoisier’s widow, “who they say is very rich.”

  The truth, Delambre wrote Méchain, was that he had salted away a backup fund of 2,000 francs in hard currency, money he had saved out of his salary and his small annuity. He also hoped to divert his honorarium as an Academy member. It would only be enough to fund one signal, but that was one less signal that had to be covered out of the budget. This slush fund had to be kept secret, of course. “It is best if they think us more beggarly than we are.” But if the only way to start his expedition in the spring was to finance it out of his own pocket, he would do so. And in the end, that is what he had to do.

  On April 1, 1797, after four months in the bathhouse town, Delambre began his final push toward Rodez. He had thirteen more signals to plant across the high Auvergne plateau, eleven triangles left to close. As he advanced south, each station posed a greater challenge, like the Stations of the Cross. In his eagerness, he may have set out prematurely. The early spring weather was horrendous; almost every day it rained. Some days he sheltered in an inn. On other days he was caught in the downpour. To the east, through the gloom, he could see a row of brooding beehive volcanoes, their black humps flecked with snow. The greatest of these was the Puy de Dôme. Over a century earlier, the great Blaise Pascal had sent his brother-in-law to the summit with a crude barometer to prove that the atmosphere was finite. Over a thousand years ago, the Romans had worshiped Mercury in a magnificent temple by the crater. Over ten thousand years ago, this entire plateau had been born in a volcanic surge—although it had only been ten years since savants had first suggested as much, and their theory was still controversial.

  Years, decades, centuries, millennia . . . day by day men crawled like ants across the corrugated arc of the world, peering ahead to the next ridge, seeking to uncover the processes that had shaped the earth. Where they had once expected perfection, they were beginning to learn how eccentric our planet is, suspended as it is between accident and necessity. And in the interstices between geological time and their daily labor, human history unfurled, likewise poised between accident and necessity. The planting season had begun. The earth was damp, the rivers flush, the air heavy with rain. The rich black s
oil fed lush green pastures. Cattle, sheep, and horses grazed by the road. Everywhere, nature had been shaped for human ends, in turn shaping human choice. Even the Gothic churches had been constructed of the black lava stone.

  From a distance, through the gloom, Delambre had difficulty picking out the clock tower of Herment, a walled medieval town of 527 souls perched on top of the steep summit of a conical hill. Each of the triple towers of Herment’s church had been demolished and rebuilt: destroyed by Huguenots, rebuilt by the Catholics, destroyed by Revolutionaries, and now rebuilt by science. When Delambre arrived, the fifty-three-foot clock tower was a dark skeleton. He filled the interior of the tower with bales of hay to make the tower solid and so visible from afar. But when he tried to drape the tower’s frame with a white signal cloth, the locals balked. White was the color of the royalist flag—and the region’s administrators were battling a reactionary resurgence. The townspeople did not want to be mistaken for counterrevolutionaries. Only a few weeks before, a crowd of hooligans had absconded with a baptismal font that they considered sacrilegious and heckled the curé for having sworn allegiance to the Republic. To appease the patriots, Delambre sewed a red strip of cloth to one edge of the white sheet and a blue strip to the other, transforming his signal into a makeshift Revolutionary tricolor flag. This satisfied the townsfolk long enough for him to conduct his measurements and get out of town. The day after he left, a rowdy royalist crowd circled the church and forced the curé to take part in their procession. “The enemies of law, government, and order have not surrendered their foolish hope of sowing chaos here,” complained one local administrator.

  At his next station Delambre needed to call on administrative help. No sooner had he set his signal on the strange gray organ-pipe cliffs above the town of Bort-les-Orgues, than a torrential storm brought a mudslide down from the hills, filling the streets with a three-foot-deep sludge of earth and stones. Residents blamed the flood on the bizarre signal on the mountaintop and demanded that it be torn down. This self-important town along the Dordogne had long suffered from inundations, despite its annual sacrifice to the river. Early each spring, on the eve of Ash Wednesday, a procession of boys in white robes marched through town, bearing torches and singing a dirge-like chant as they carted an effigy of an old man on a tumbrel: “Farewell, old man, you must go, I remain! Farewell, farewell, farewell!” When they reached the river, the oldest living man present set the effigy on fire and tossed it, still burning, into the river. The rite dated back to the Celts, who sacrificed their eldest travelers at rivers too wide for them to cross. By the eighteenth century, the ceremony had been supplemented by official demands for flood mitigation. Municipal leaders dissuaded the towns-people from destroying Delambre’s signal; it helped, too, that the signal was well out of reach, beyond the high cliffs.

  His next station, the peak of Puy Violent, was the highest point along the entire meridian arc: six thousand feet above sea level. There Delambre had the choice of lodging either in the nearby Renaissance town of Salers—an onyx outpost of judicial palaces, slate-roofed inns, and black-stone battlements, but an arduous three-hour climb to the mountaintop—or in a cowshed an hour from the peak. As it was mid-August, Delambre thought it would be safe to save himself the daily hike, and he decided to lodge in the cowshed.

  For the ten days of my labor, I slept in my clothes on bales of hay, living on milk and cheese. I could almost never sight two stations simultaneously because a thick fog obscured the horizon. In the long intervals while I waited ten or twelve hours for a view from the summit, I was scorched by the sun, chilled by the wind, and drenched by the rain, all in succession. But nothing irritated me more than the inaction.

  Though Puy Violent was not named for its weather, it might as well have been. It rose beside its sister peak like the cusp of a molar. To the east—to Delambre’s back—a range of higher mountains, scarred by barren cirques, hemmed in the view. To the west, the panorama opened out over a green skirt of lava that plunged toward convergent river valleys draining into an invisible Atlantic two hundred miles away. Geologists had recently come to suspect that this entire region had once been the site of a single vast volcano. When the clouds cleared, Delambre could look out over its well-worn shards. Through the scope of his circle, he could see the black battlements of Salers on its basalt prominence across the valley, plus all his surrounding stations: his signal above the organ-pipe cliffs of Bort, the church tower at La Bastide, and his next destination, the signal upon the ruined castle wall at Montsalvy. It was a silent perch under a long low sky, without a human being in sight, only hawks angling on the wind and cattle grazing on the slopes. Today’s red-coated Salers cattle are the result of late-nineteenth-century breeding, but their eighteenth-century forebears were already famous for their cheese, the region’s chief export. On summer days they grazed on the high slopes; every evening, to protect them from wolves, the shepherds drove them down to the shed where Delambre joined them for the night.

  The up-country people were handsome, with blue eyes and dark brown hair. They mistook Delambre for a sorcerer. Who else would have paid a team of men to cart four twenty-two-foot timbers to the peak of Puy Violent and assemble them in a pyramid? When a cow refused to give milk, when a plow broke in the field, when a journey proved unlucky, the sorcerer’s evil eye was to blame.

  As part of his mission, the government had asked Delambre to assess the common people’s view of the metric system as he traveled through the countryside. Delambre found that the vast majority of the common people had never heard of the new measures. The workmen who built his signals were illiterate, innumerate, and did not speak French. This did not mean that they were inarticulate or unskilled; Delambre found them quite adept at constructing his bizarre pyramids. For a sympathetic hearing, however, he addressed himself to the region’s “enlightened citizens”: its magistrates, state officials, and educated men. These citizens looked forward to the new era. During the Ancien Régime, the province of Auvergne had been ruled by a jumble of legal codes; half a village might owe allegiance to Roman law and the other half to the common law. This legal tangle nourished the region’s multiplicity of measures, turning every marketplace into an arena of “frauds, deceptions, cons, and thefts.” Or so the region’s enlightened citizens believed.

  In the past two hundred years, customs have changed, people have changed, animals have changed, even the terrain and weather have changed—all, paradoxically, while seeming to have stayed essentially unchanged. The population of these central regions has been stable for two hundred years, although there has been a steady emigration toward the towns and no one under the age of sixty habitually speaks Occitan anymore. The Salers cattle have multiplied, bred to a glossy muscularity, but the wolves are gone. Cantal cheese is still the mainstay of the region’s economy (after tourism), and is now exported around the world—except to America because the U.S. health inspectors ban the cheese, prompting bitter complaints from the French that the market for cheese is not global enough. The winters are less bitter than they were in the eighteenth century, though the great storm of 1999 leveled 300 million trees. Even the modern highway still follows the route laid by the Ancien Régime engineers, though it is now paved in asphalt. On the road out of Salers on his way to Montsalvy—known today as the D920, then as the Route de l’Intendant—Delambre was caught in a powerful rainstorm. It felt, he said, like traveling inside a cloud accompanied by continual thunder and lightning.

  At Montsalvy on August 12 Delambre sighted Rodez through his repeating circle for the first time. The horizon was hazy, and he had trouble distinguishing the target. But the next day he saw it sharply outlined against the blue: the serene red-stone head of the Virgin Mary rising from her pedestal on top of the cathedral. The statue would link his chain of stations and Méchain’s. Delambre’s observations from the hilltop just north of Montsalvy are commemorated today by a finely wrought orientation table, which points out features as near as Rodez and as far as the Pic de
Nore, Méchain’s station north of Carcassonne.

  Delambre’s final goal lay just ahead. Rodez sat on a hillock in the warm basin of Rouergue, and as he descended, the temperature rose to meet him. The soil lightened to a crumbly orange, the yellow houses turned their open windows toward the sun. Suddenly, he could no longer sense the Atlantic behind him, but instead smell the Mediterranean ahead: the fruit trees, the corn husks, the olive trees, the dry dust of the south. Lizards, some a foot long, skittered behind rocks. Delambre had entered the Midi. Half the Massif Central was yet to come, with pine-blue ranges and deep gorges that carried cool air down from the mountains. But it was the south nonetheless. Delambre had only two stations left, two stations to link his triangles with those of Méchain.

  He expected to hear from his colleague any day now, either at Rodez or at neighboring Rieupeyroux. The two savants had been out of contact since spring, presumably because Méchain was also converging on Rodez, traveling from town to town and out of reach of the mails. On August 23, while observing at Rieupeyroux, Delambre sighted one of Méchain’s signals to the immediate south. It was a good sign. It meant that he and Méchain were closing in simultaneously on Rodez. What a glorious finish that would be, the perfect resolution to their six-year mission of competition and cooperation. Hurrying to complete his measurements, he and Bellet set out the next day to drive the last twenty-five miles to Rodez. On the road, they met a traveler journeying alone in the opposite direction. It was Tranchot, on his way to look for them. His mission was complete, he said. Méchain had given him meticulous instructions to build a chain of signals from Carcassonne to Rodez, so that Méchain might follow behind, taking the geodetic measures with his repeating circle. It was Tranchot’s signal at La Gaste that Delambre had sighted a few days earlier. Yet Méchain was nowhere in sight.