For those unwilling to wade through the long job of sorting sunspots, there was one other way to speed discovery. Le Verrier had published a short form of his Mercury findings in the September 12, 1859 edition of the Académie’s proceedings, Comptes Rendus. In the same issue, the secretary to the Académie, Hervé Faye, wrote that the best chance of seeing Le Verrier’s hypothetical asteroids was during a solar eclipse. By good fortune, the next readily accessible eclipse was almost upon them, to come on July 16, 1860, visible over northern Africa and Spain. During totality, the region closest to the limbs of the sun would suddenly be freed from the brutal glare of the sun, until “at the decisive moment,” Faye wrote, the few minutes of totality “would suffice to explore much of the area designated by M. Le Verrier.”
Faye’s report sparked a wave of preparation. Locations were chosen—near Bilbao, perhaps, or a few miles west of Zaragoza, or maybe across the Mediterranean to a point on the coast around Algiers—wherever each observing team believed they would find the best chance of clear skies on the sixteenth of July. Given Le Verrier’s history, it seemed plausible that one or more little planets might appear, even on a first attempt. And maybe they’d already been seen! Recalling the tally of misidentified sightings of Uranus, Le Verrier’s announcement sent some back to old records, looking for anything that might qualify as an intra-Mercurian body since Galileo had first turned his telescope skyward back in 1609. No persuasive candidates materialized in this first pass—but then again, despite Herschel’s turn of luck, knowing what you’re looking for is a powerful aid to discovery. On to Spain!
—
Edmond Modeste Lescarbault was a humble, almost diffident man. He lived a small life, confined mostly to a modest compass between the Seine and the Loire rivers, about seventy miles west and a touch south of Paris. He had studied medicine, and in 1848 opened a practice in a little country town, Orgères-en-Beauce. He stayed put there for the next quarter of a century. He died in 1894, ninety years old, locally honored—the street where he kept his surgery is now named rue du Dr. Lescarbault—and generally forgotten.
The country doctor had one great passion. As a boy, he had fallen in love with the night sky. Children grow up, of course, and most put away childish things. Not Lescarbault. Like many before and since, he discovered in astronomy the same consolation that would later comfort Albert Einstein: the contemplation of “this huge world, which exists independently of us,” which, he wrote, serves as “a liberation.”
For Lescarbault, liberating himself from the daily medical round led him to build a genuinely impressive amateur’s observatory: a low stone barn with a modest dome at one end. There he mounted a perfectly competent telescope, a four-foot-long refractor with an objective lens almost four inches in diameter. He would steal time there between patients, just minutes sometimes, sneaking from his office to the dome to look, perhaps to dream, just a little. The discovery of the asteroids in the belt between Mars and Jupiter led him to wonder: where else might such treasures lurk? An answer came to him on the 8th of May 1845—the day Le Verrier missed the timing of Mercury’s encounter with the sun.
Lescarbault watched Mercury’s moving dot across the solar face, untroubled by any mathematical subtleties. Instead, he thought not about the planet in transit, but whether there might be other unobserved transits to seek. If a Ceres- or a Pallas-sized asteroid lurked close to our star, its transits would likely be the only opportunity to see it—and the search for such events would be a perfect target for an enthusiastic amateur astronomer, eager for the thrill of finding something in the cosmos that not one other human in all of time had perceived.
He was slow to act on that epiphany. Ordinary life intervened. His medical practice needed nurturing, for one thing, but more important, he was a true amateur. He lacked both the knowledge and tools to achieve the precision needed to capture a phenomenon as delicate as an asteroid breaching the limb of the sun. It took him more than a decade to prepare, but by 1858, he had fitted his telescope with homemade instruments good enough to fix the position of objects within its field of view. He was, at last, ready to go hunting.
—
Saturday, March 26, 1859. Orgères, on the edge of spring, enjoys a sun-warmed afternoon. The flux of patients eases. As is his habit, Dr. Lescarbault takes the opportunity to retreat to his observatory. He turns his telescope toward the sun. An object leaps into view: a small, regular dot, just inside the edge, or limb of our star. He makes an estimate of its size: about one quarter the apparent diameter of Mercury. He has just missed its first appearance at the edge of the sun. Working backward from its apparent rate of motion, he estimates the time it crossed the solar limb at almost exactly four o’clock or, to be precise, at 3h 59m 46s P.M., plus or minus five seconds. He writes that down, using a piece of charcoal to scratch on a board. Another patient arrives and, likely with unrecorded frustration, he pulls his eye from his telescope. A few minutes later, he returns. The spot is still there, moving across the face of the sun. He tracks it continuously now, noting its nearest approach to the center of the solar circle, and then the instant and place it disappears over the solar limb. He records the time again: 5h 16m 55s. Total transit duration: one hour, seventeen minutes and nine seconds. If an asteroid were ever to be discovered within the innermost wards of the solar system, this is how it would reveal itself. Lescarbault meticulously transcribes his notes, and then…
Does nothing…
For nine months…
Until, at last, he permits himself to write a letter to be delivered—by hand—to Paris.
He “broke his silence,” Le Verrier later wrote, “solely because he had seen an article in the journal Cosmos on [my] work on Mercury.” Lescarbault described the data he had collected that Saturday in March—and added one bold claim: “I am persuaded also that [the planet’s] distance from the Sun is less than that of Mercury, and that this body is the planet, or one of the planets, whose existence in the vicinity of the Sun M. Le Verrier had made known a few months ago, by that wonderful power of calculation which enabled him to recognize the conditions of the existence of Neptune….”
Lescarbault entrusted it to a M. Vallée, “Honorary Inspector General of Roads and Bridges,” for delivery to the obvious recipient, Le Verrier himself. Dated December 22, 1859, it reached Paris a few days later. Le Verrier’s first reaction—as he told it—was one of doubt. But he was prepared to hope. There was only one way to be sure if Lescarbault could possibly have made the observations he claimed to have achieved: meet the man; inspect his instruments; test him. No matter how unlikely it might be that some rural hobbyist could have plucked such a prize, even the possibility that he might made any delay intolerable. Le Verrier was promised to his father-in-law’s for a New Year’s Day celebration—but the train schedules showed that it was just possible that he could get to Orgères and back to Paris before midnight on the 31st. He commandeered Vallée to return with him as a witness, and the two men set out to see if Lescarbault’s “planet” might actually exist.
Le Verrier and Vallée arrived at Orgères-en-Beauce unannounced, covering the last twelve miles from the nearest railway station on foot. A few days later, he painted for the Académie a calm, almost placid picture of the encounter: “We found M. Lescarbault to be a man long devoted to the study of science….He permitted us to examine his instruments closely, and he gave us the most detailed explanations of his work, and in particular of all the circumstances of the passage of a planet across the sun.” The two men from Paris made Lescarbault walk them through each phase of his observation until they were convinced that their amateur had in fact seen what he said he had—and, crucially, that his interpretation of the event was correct. “M. Lescarbault’s explanations, the simplicity with which he offered them to us gave us total conviction that the detailed observation he had completed must be admitted to science.”
Dr. Lescarbault’s observatory-turned-tourist attraction in this postcard from 1863.
—<
br />
Le Verrier told the story very differently in private. Released from the conventions of scientific discourse, he seems to have composed a hero’s epic. Abbé Moingo, editor of the same journal, Cosmos, in which Lescarbault had first read of the problem of the precession of Mercury, was present at one of these performances. Le Verrier told of setting out for Orgères, Moingo wrote, assuming that no mere rural medico could have both discovered a new planet and kept quiet about it for nine months. Yet he had “a secret conviction that the story might be true.” At the doctor’s house, the astronomer confronted “the lamb” who trembled before the lion from Paris: “One should have seen M. Lescarbault…so small, so simple, so modest and so timid.” Le Verrier roars; Lescarbault stammers—and yet, according to the Abbé, still manages to defend himself at every turn. “You will then have determined…the time of first and last contact?” Le Verrier demanded, noting that measuring first contact is “of such extreme delicacy that professional astronomers often fail in observing it.” Lescarbault admitted that he had missed first contact, but had estimated the timing by checking how long it took for his spot to travel the same distance again it had already passed from the limb. Not good enough, said Le Verrier, and on learning that the doctor’s chronometer lacked a second hand, stormed “What! With that old watch, showing only minutes, dare you talk of estimating seconds? My suspicions are already too well founded.”
Lescarbault rallied from even that devastating assault, though, showing his visitors the pendulum he used to count seconds, and reminding the astronomer that as a doctor “my profession is to feel pulses and count their pulsations…I have no difficulty in counting several successive seconds.” By this point in the remembered (and, to modern ears at least, suspiciously dramatic) account, it’s becoming clear what Moingo (and/or Le Verrier) is doing. The ebb and flow of leonine attack, each swipe seemingly fatal, and yet disarmed by a counter from the charmingly naive lamb, enlarges Lescarbault. The famous astronomer plays the part of the skeptic (never mind how much he may have hungered for one outcome over another), while the country doctor becomes more and more a competent, even an excellent man of science. The interrogation lasted an hour, enough to exhaust Le Verrier’s reservoir of doubt. At the last, he surrendered: “with a grace and dignity full of kindness, he congratulated Lescarbault on the important discovery he had made.” He would lead Lescarbault to a more tangible reward as well, securing within the month the Légion d’Honneur for “the village astronomer” who had, it seemed, discovered the first intra-Mercurian planet.
The next step was all Le Verrier. Lescarbault had none of the mathematical skill needed to transform his observation into a planetary orbit. Le Verrier did so in less than a week. By making the assumption that its orbit was nearly circular, he calculated that the new planet would complete one revolution around the sun in just under twenty days, on a path that never exceeded eight degrees distance from the sun. Such an object would be difficult if not impossible to see directly. But if Le Verrier’s analysis were even close to correct, the proposed planet would repeat its transits two to four times each year.
With that, planet fever hit the popular press—The Times of London, Popular Astronomy in the United States, The Spectator (which had some very kind words for Dr. Lescarbault). Alternative orbits were proposed: one reexamined the data on the assumption that the new planet traced a highly eccentric ellipse around the sun. Others returned to old records to see if Lescarbault’s planet had been seen and ignored previously—and just as with Uranus and Neptune, candidate objects soon turned up, reaching double figures in a series of sightings stretching back to the mid-eighteenth century.
It was clear more work needed to be done, beginning with a repeat observation of the mystery object. Nonetheless, the celebrations continued heedless of any lingering uncertainty—and for good reason. The faith in the new planet stood in equal measure on Le Verrier’s own reputation and the rock-solid logic behind the discovery. Mercury’s perihelion precession was and is real. Newtonian gravitation provides an obvious solution to such a problem. The appearance of an object exactly where necessity suggested it ought to be made perfect sense. It fit. It had a moral right to be true.
Celestial facts need labels. This time, there was no nationalistic controversy to navigate, no tussle pitting “Oceanus” vs. “Le Verrier.” The common practice held: planets major and minor took their identities from the gods of antiquity. It’s an oddity of history that there is no record of who first fixed on the ultimate choice, but the decision was easy. A body that never escaped the intense fires of the sun had only one real counterpart on Olympus: Venus’s husband, the lord of the forge. By no later than February 1860, the solar system’s newest planet knew its name:
Vulcan.
“THE SEARCH WILL END SATISFACTORILY”
Vulcan’s career began happily. Weeks after Le Verrier’s announcement, no less an old rival than the Royal Astronomical Society bowed before the new planet: “The singular merit of M. Lescarbault’s observations will be recognized by all who examine the attendant circumstances; and astronomers of all countries will unite in applauding this second triumphant conclusion to the theoretical inquiries of M. Le Verrier.” More practically, the news evoked the sincerest form of flattery—claims of prior, never-recorded encounters with the newcomer. Benjamin Scott, Chamberlain of the City of London and an avid amateur astronomer, wrote to The Times to assert that he had long before found an intra-Mercurian planet: a candidate object the apparent size of Venus glimpsed at sunset “at or about Midsummer 1847.”
Scott’s “discovery,” reported only in a conversation with a fellow of the Royal Astronomical Society, could hardly be taken seriously, but working astronomers wondered if they too had missed the prize. Rupert Wolf, a Zurich-based astronomer long fascinated by sunspots, reviewed his own and other solar observations to find potential mistakes—Vulcan transits he may have mistaken as mere spots—and came up with twenty-one possibilities that he published, and sent directly to Le Verrier as well, highlighting four that seemed the closest match to Lescarbault’s object.
Wolf’s list caught the attention of another astronomer, J.C.R. Radau, who used the data from two of Wolf’s candidates to refine what could be extracted from just a single Vulcan sighting. Radau joined other professionals who sniped at “the procrastinated publication of Dr. Lescarbault’s remarkable observation.” But once past his pique, Radau performed his analysis meticulously, generating exactly what astronomers needed to attempt the next phase of Vulcan research: a prediction for an observable transit. With the assumption that Wolf’s two suspects were in fact that same object as the one Lescarbault had seen, Radau published the results in early March: transits of Vulcan could next be expected between March 29 and April 7.
Radau’s transit would be visible in the southern hemisphere, and astronomers there readied themselves for the moment of discovery. The director of the Victoria Observatory, a Mr. Ellery, monitored the sun at half-hour intervals. Major Tennant, head of the Madras station, went one better, reporting that “the sun’s disk was watched every few minutes from March 27 to April 10.” At the Sydney Observatory, Mr. Scott set up a parallel search. Ellery summed up the outcome for all three: the planet hunt performed by multiple observers reached the end of the predicted period for Vulcan transits “without success.”
That was a blow, but hardly a fatal one. It had been obvious from the start that Vulcan would be hard to observe. If it weren’t, any large body—Mercury-sized or thereabouts—would have been seen long since. That was why Le Verrier had thought that an intra-Mercurian asteroid belt was the more likely option until Lescarbault’s report had raised hopes for a singular Vulcan. Still, while Lescarbault’s object appeared to be bigger than most if not all asteroids, his notes suggested it would be as small as one twentieth the diameter of Mercury. At that scale it could not account for all of the perihelion advance Le Verrier had discovered. Lescarbault himself largely disappeared from view after his sudden bu
rst of fame. The Légion d’Honneur he received in 1860 did not change his habits; he remained a country doctor and amateur astronomer until his death. After Le Verrier’s visit, he made no further claims about any intra-Mercurian objects.
Working astronomers, though, still had to deal with the problem. Any calculation of Vulcan’s orbit based on one or a few sightings would be an approximation at best, and stood a good chance of being just wrong. For Le Verrier as for many of his peers, the missing transit expected on the basis of Radau’s calculation only demonstrated, once again, that doing astronomy at the limit of the math and empirical capacity is really, really hard. The necessity of the search hadn’t changed one bit: Mercury still precessed, and whatever was compelling it to do so remained to be found.
—
As it was, swiftly.
In the middle of the nineteenth century, Manchester, England, prided itself on being smart as well as rich. In 1861, the city showcased both its wealth and brains as it hosted Britain’s largest celebration of knowledge, the annual meeting of the British Association for the Advancement of Science. Charles Darwin had published The Origin of Species less than two years before, and that explosion continued to reverberate through every gathering of the learned. At the Manchester meeting Darwin’s defenders prepared to battle religious doubters. One speaker, the “blind economist” Henry Fawcett, made the ultimate claim: Darwin was a true scientific hero, one who solved his problem by the same methods, the same approach to experiment, observation, and generalization that the great Isaac Newton himself had used in his physics.
Much else was discussed, of course—advances in dredging engineering, a report on birds of New Zealand, news from the balloon committee. The astronomy section was relatively quiet, but all in all, the meeting reflected a basic truth about Victorian curiosity: it was ubiquitous, constant, the common passion of both professionals and amateurs. No wonder, then, that Manchester’s citizen-scientists would chase new planets.
The Hunt for Vulcan Page 7
