The Day the World Discovered the Sun (30 page)

As Pauly observed, “It will be a matter of admiration to look over the account of this observation.” The moon entered the earth's penumbra (half shadow), Chappe, recorded, at 10:45
PM
. At 11:08, Chappe recorded, “the eclipse started, I think, within the minute. The shadow is so clear and the moon is so brilliant, I think I estimated that start time too late.”
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So Chappe picked up the pace. Starting at 11:11
PM
and 41 seconds, he began to record the entry of the earth's complete shadow across every lunar crater he could find. He recorded a stunning thirty-two observations, revealing not only expert offhand knowledge of lunar geography but also a phenomenal stamina in the face of a severe malady.
As the eclipse passed its halfway point, and the end of the earth's shadow was sweeping its way past the same lunar craters, starting at 12:40
AM
, Chappe recorded another thirty-four time-stamped observations as the “lighted segment” of the eclipse swept past the Harpalus, Aristarchus, Galileus, Menelaus, and Tycho craters. No doubt shivering and gripped by extraordinary pain, Chappe recorded his final entry for the night at 2:48
AM
. “The edge of the moon is perfectly [out of eclipse],” Chappe wrote. “But it still seems smeared.”
¹⁰

Ultimately Chappe's lunar eclipse data was not deemed as useful as his other longitude-determining observations, including both observations of Jupiter's moons and observations during the Venus transit. But Chappe's data in aggregate yielded a longitude determination for Misión Estero of 112 degrees, 2 arc minutes, and 30 arc seconds west of the royal Paris observatory—or 109 degrees, 42 arc minutes, and 19 arc seconds west of the Greenwich prime meridian.
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By any measure, this was an impressive result.

Misión Estero was shuttered the following century, and during its 110 years it had multiple locations within and near San José, so the exact placement of Chappe's observatory is unknown. But the latitude and longitude that Chappe's data produced places the crosshairs squarely on the small city itself—as close to spot-on as present evidence can determine.

After the lunar eclipse, however, Chappe's condition worsened. In desperation he tried to ride out of the mission on horseback but had to return. “He lay in a most deplorable condition, suffering the sharpest pains, and destitute of all assistance,” wrote Pauly, who was fighting his own case of the fever. “The village . . . was by this time a mere desert. Three-fourths of the inhabitants were dead, and the rest had fled to seek a less infectious air. But the contagion had already spread far and wide.”

Still, Chappe managed to record nine more days of solar observations to continue refining the accuracy of his timekeeper. In his logbook for
June 29, Chappe recorded the brief but revealing confession, “I observed, fatigued by lack of sleep and illness.”
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He stayed up another nine June and July nights, dutifully recording culmination measurements of the stars Arcturus and Kornephoros and immersion and emersion of Jupiter's moons.

The smell of death would have been inescapable, as well as the groans of sick and dying explorers and natives. Food remained available during this plentiful season, but picking and preparing, with no healthy servants to call on, was another matter. Chappe didn't have to venture far to get to his telescope, clock, and quadrant. But finding date palms near the mission whose fruit bunches hadn't already been completely picked apart was no small challenge for the rare healthy person in this pitiful realm of the dying. Climbing the trees—braving the knife-sharp basal leaves that guard the dates—was difficult enough. Now an unsteady hand, a weak body, and sometimes delirious mind made simple subsistence its own cruel daily punishment.

The jail fever chronicler described the last phase of the sickness. “Often either from neglect or an improper treatment in the beginning . . . [typhus] puts on a more fatal and alarming form. The pain of the head continues . . . the tongue as well as base of the teeth are covered with a thick black crust and the patient is unable to thrust it out of his mouth and loses the power of speech and of swallowing. . . . The pulse becomes weaker and quicker. . . . The patient is now altogether insensible. . . . He knows not the by-standers. . . . His muscles become flaccid. . . . He is affected with . . . convulsive startings and twitchings of the muscles. . . . His extremities become cold. A final quantity of blood sometimes distills from his nostrils. His face has a livid and cadaverous appearance, and death which soon follows these symptoms puts a period to his sufferings.”
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On August 1, 1769, the forty-two-year-old Jean-Baptiste Chappe d'Auteroche drew his final breath. On his deathbed Chappe had said,
“I feel I have little time to live. But I have fulfilled my purpose, and I die happy.”
¹⁴

When he died, Chappe was surrounded by Pauly and Noël, whose own severe illnesses no doubt made them wonder how many days hence they might accompany their superior to the grave. “Doz and Medina did their best to pay last respects to Chappe for the priest was long since dead,” Pauly said. “The Spanish, French and every one of the survivors then collected what little strength they had left and performed the most melancholy of all offices.”

Chappe had asked Pauly to bury him in a Franciscan habit, a request that the morbidly bedraggled expedition honored. Crucially, Chappe had also charged Pauly with collecting his papers and ensuring their safe passage back to Paris. Fighting his own pain, delirium, and fever, Pauly gathered what journals and logbooks he could find and packed them in a casket, addressing it to the viceroy of New Spain. Pauly instructed one of the local chiefs to ensure the casket make it onto the ship that would be sailing for the mainland in September—should Pauly himself not survive the ensuing month and a half.

When word of Chappe's death reached Mexico City, Alzate—the polymath who had so delighted in the visiting Frenchman's presence five months before—was “greatly affected,” Alzate wrote to the president of the French Royal Academy of Sciences. “New Spain has lost in him a man whose talents would have been of great service, to make known a thousand natural curiosities which here lie buried in oblivion.”
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Chappe's colleagues at the Academy of Sciences in Paris could only concur. In the words of Chappe's eulogist, the academy's permanent secretary, the deceased “had an open and candid, unpretentious soul, and a noble, straightforward and honest heart; he was naturally lively, gregarious and amiable. He was known in the highest circles; the King himself deigned to converse with him and honored his death with expressions of regret. Never was there one more unselfish than he. He liked fame; he
wished to earn its favors, not to steal them. . . . One could only have wished that the last proof he gave, so worthy of praise, had not been fatal to him.”
¹⁶

Pauly and expedition artist Noël survived the cursed voyage, making them two of just nine (out of 28) who returned home. They made their way back to Paris via Mexico City—where the magnanimous viceroy had given them three expense-paid months to fully recover—and on to Vera Cruz and Cadiz. The voyage's scientific instruments, still property of the Royal Academy of Sciences, were returned to their rightful owners. Chappe's bereaved brother returned Ferdinand Berthoud's marine watch to the clockmaker. And Pauly put the contents of that casket full of papers and logbooks into the hands of France's Astronomer Royal, César-François Cassini de Thury.

Cassini, as he was known, edited Chappe's papers and published them three years later in
Voyage en Californie pour l'observation du passage de Vénus sur le disque du soleil
, a comprehensive volume commemorating the abbot's journey, reproducing his diaries and logbooks, and publishing the whole of Chappe's transit-related data. In the same 1772 volume, Cassini also wrote up his own history of the Venus transit and his summary of the data gathered worldwide on June 3, 1769, and its subsequent analysis.

The Venus transit expeditions of 1761, Cassini said, left a frustratingly vague answer to the ultimate question of the sun's distance. (Astronomers used a different number, the solar parallax, as a proxy for distance to the sun. See this book's Technical Appendix for more details.) “The result of the 1761 transit . . . enlarged the range of [possible parallaxes] from 8 1/2 arc seconds up to 10 1/2 arc seconds,” Cassini
wrote. “Thus the speculations of theory are found only too often belied by practice. One finds it very far indeed from the precision forecasted by Mr. Halley.”
¹⁷

Fortunately, Cassini noted, 1769 provided the world with a second chance. In fact, he calculated, the magnitude of the 1769 parallax—the difference in transit time at the North Pole compared to the equator—and the favorable locations available to observe it would not be duplicated again for a long time. The next three Venus transits—in 1874, 1882, and 2004—wouldn't offer nearly as propitious an opportunity to those distant future generations as did the most recent alignment of sun and planets. “It won't be until 2012 that the transit of Venus will be nearly as advantageous as it was in 1769,” he said.

However, Cassini said, the many observers sent across the planet to witness the transit left behind an ocean of data. Some of it was good; some was not so good. Cassini argued, though, for concentrating on the most successful expeditions. “Three major voyages which, by their importance and usefulness, should be distinguished here: That of Father Hell to Vardø island, that of M. Chappe to California, and that of the English to the South Seas.”

Because of his arrival at Vardø seven months before the transit, Cassini noted, Father Hell “had ample time to prepare and make a bountiful harvest of observations of different kinds that we hope to see in interesting detail in the considerable book this scholar promises us.” Still smarting from the war of words between Hell and Lalande, Cassini laced his description of Hell's expedition with sarcasm—but conceded that Hell had at least provided all the detailed Venus transit data that the academy might require.

The data from Captain Cook's expedition, Cassini noted, constitutes “an observation whose success was so important to us and to serve as the standard of comparison of all the others. . . . [And] it cost the lives of those to whom we are indebted.”
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As for the voyage to California, “I will only say that M. Chappe's original destination was not California. It is infinitely desired that he went to the South Seas, the most favorable observing station. . . . The fruits that astronomy has derived from this observation have made it that much more precious and perpetuates forever the memory of the death of M. Chappe and of Don Salvador de Medina, one of the Spanish astronomers.”

Sifting through the data and competing parallax calculations, then, Cassini points out that the final number ultimately hinges on whether or not to reject Hell's transit observations.
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Provisionally accepting Hell, Cassini says, enables five scientists to independently derive parallax figures that are remarkably close to one another: 8.7 arc seconds (Jérôme de Lalande), 8.7 arc seconds (Father Hell), 8.68 arc seconds (the Swiss mathematician Leonhard Euler), 8.76 arc seconds (French astronomy professor Jean Guillaume Wallot), and 8.88 arc seconds (astronomer Alexandre Guy Pingré).

These numbers are remarkably close to the correct value known today: 8.794 arc seconds. Technically, the ranking would be Wallot (99.6 percent of the exact result) followed by Pingré (99.0 percent), Lalande (98.9 percent), and Hell (98.9 percent). Euler—though undeniably the greatest genius of anyone remotely connected with the 1760s Venus transit voyages—nevertheless places last with a still laudable 98.7 percent. In all cases, the blinding view of hindsight suggests the story should end here.

However, because the imperfect results of the 1769 transit left open-ended questions, Cassini rejected every one of these calculations and instead settled on 8.5 arc seconds—adopting an arbitrarily rounded-off result that his colleague Lalande had arrived at. “Time, by which everything achieves its perfection, will clear up [the matters of] this article better than we can do,” Cassini writes. “Until then, the average parallax of eight-and-a-half arc seconds, which had already been settled
upon by the transit of 1761 [!], can be adopted, I think, without worrying too much about the truth.”
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Cassini's arrogance in sweeping away such hard-won data—representing the greatest scientific cooperative endeavor in the history of mankind to date—is breathtaking. Fortunately, his pronouncement on the matter would not be the last.

Across the English Channel, Oxford University astronomy professor Thomas Hornsby—who had initially projected the best places in the world to observe the 1769 transit—also concentrated on data from Chappe, Hell, and Cook/Green in tabulating the solar parallax. Hornsby finessed the data too, recognizing that Cook made a more accurate observation of the transit's beginning (ingress) and that Cook and Green together satisfactorily observed the transit's end (egress). So Hornsby averaged Cook's and Green's egress result.

“The mean parallax will be found to be 8.78 (arc seconds), and if the semidiameter of the earth be supposed equal to 3,985 English miles, the mean distance of the earth to the sun will be 93,726,900 English miles,” Hornsby stated. This is a number that Hornsby, unlike the pusillanimous Cassini, stuck with. And it was 99.8 percent accurate—exactly, as it happens, Halley's hoped-for result.
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