The Day the World Discovered the Sun (9 page)

On Friday, April 15, d'Éon met in London for a private dinner (the noontime meal) with the visiting astronomer Jérôme Lalande. Lalande had been traveling around the greater London area for four weeks. When town criers announced the armistice on March 22, British patriots on the streets near Whitehall shouted down the visiting Frenchman. “You are stupid,” they taunted Lalande, “like the peace!”
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Other than this pugnacious encounter, Lalande enjoyed something close to VIP status in London. During his stay, Lalande had been meeting mostly with Englishmen—instrument makers, scientists, authors,
and businessmen—and was working toward his own ultimate goal: nomination to the British Royal Society.

Lalande and d'Éon had first met at a dinner party at the French ambassador's residence in town.
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In the interim, Lalande had learned that his personally funded voyage to England was about to take a turn toward the national interest.

King George III had recently given his royal assent to “An Act [of Parliament] for the Encouragement of John Harrison to Publish and Make Known His Invention of a Machine, or Watch, for the Discovery of Longitude at Sea.”
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According to the terms of the act, the watchmaker John Harrison was sometime soon going to disclose the secrets behind his revolutionary new nautical chronometer—a watch that was said to keep time so well that over a recent eighty-one-day sea trial to Jamaica, it allegedly lost only 51 seconds. By comparison, a good standard-issue naval clock might gain or lose four minutes per day.
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This slippage meant that any navigator who relied on it for longitude could be off in his estimate of a ship's position by fifty miles or more. Rocky shores could find safe harbor in such fuzzy numbers, damning the most powerful gunboats in the world to ignominious death. Here beat the heart of the beast that swallowed ships and legions of sailors whole.

But if Harrison was right, the game was about to change. If Harrison's astounding feat could be replicated—and if his watch could be affordably duplicated—the centuries-long longitude quest might well be over. One of these new chronometers could keep London or Paris time onboard any ship. And comparing it to the local time anywhere around the globe, the ship's longitude could be immediately and easily calculated. As a result, Lalande and his fellow astronomers might also lose royal patronage and attention, becoming as outmoded as a regiment of pikemen in an age of musketeers. And England and France, and not a few other colonial nations besides, would be racing to sea and across the globe armed with a technology that would surely reshape the planet.

Then, five days before his dinner with d'Éon, Lalande learned of a scientific mission to England to pry out the secrets of John Harrison's phenomenal machine. Moles in the British government had assured the French ambassador that Harrison would be making his disclosures in public—or at least in a forum where well-connected Frenchmen could gain access. The visiting French horologists would thus be on hand to uncover, as Lalande wrote in his diary, “the secrets of longitude from Harrison.”
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And Lalande—fluent in English as none of the other French experts were—would serve as their unofficial liaison.

D'Éon lunched with Lalande that Friday, and the two spent the afternoon west of town. Their initial stop, Hyde Park, was a popular locale for Londoners to “take the air.” The park's grounds gave a breath of Elysium to a choking city. More than a few locals knew this too. One London wit said Hyde Park was bathed in beauty by the fashionable women who strolled its grounds—just as it was drenched in dust kicked up by the horses who carted them around.
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Lalande recalled the park being “extremely pleasant for coach drives and riding on horseback.”
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Their ultimate destination was Kensington Palace, a longtime residence of the recently deceased King George II.
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The astronomer and the spy walked down Kensington's “beautiful lawn, which surrounds the lake on the London side,” Lalande recorded. Inside, they admired the portraits in the palace's gallery and the ornate, marble-pillared and gilt-statued “cube room.” Although Lalande was only an unwitting accomplice, d'Éon continued to carry out his orders to reconnoiter strategic London locations, with an eye toward a day when France might turn the tables on its perennial enemy across the English Channel.

While d'Éon never dropped his cover, Lalande had loose lips. Lalande's proximity to the daily developments in, as Lalande put it, “the discovery of Harrison's secrets” surely caught the spy's ear. D'Éon continued meeting with Lalande for another eight dinner dates and assorted other diplomatic engagements.

Two days before the Kensington Palace outing, Lalande noted in his diary how he'd learned that commissioners carrying out the Act of Parliament would reward Harrison for his work and open the door for the French watchmakers to learn Harrison's tricks. Harrison was unhappy with what the commissioners expected of him. He felt that British officials didn't appreciate the potentially grave consequences that a public disclosure of his clock's design could bring about.

Harrison would be swatting away the French flies buzzing around him for months to come. And for good reason too. Not all were as incapable at espionage as the petit, self-aggrandizing, and conspicuous French philosophe who never quite understood the excitement over marine chronometers in the first place.

Lalande had now been to Parliament, where he'd met King George III. (Another dinner with d'Éon promptly followed.) And the next Friday, Lalande called on his colleague Nevil Maskelyne, who lived in a fashionable neighborhood of London, near Hanover Square. Wedding bells in Maskelyne's Mayfair region of town often rang for, as one chronicler put it, “swell marriages . . . [for] many a belle of the London Season” conducted at St. George's church down the street.
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And scarce were there two less romantic people in the city—well disposed to curse those damned bells in two-part harmony—than these gentlemen of mathematical and celestial calling. Table talk, at such a propitious moment for the host, could hardly have avoided the obvious. Maskelyne had been hard at work for nearly a year on a new book that was now just appearing in bookseller's stalls throughout the city. Maskelyne's
British Mariner's Guide Containing Complete and Easy Instructions for the Discovery of the Longitude at Sea
worked exactly as advertised. It compiled tables, instructions, and lessons Maskelyne learned
in measuring lunar longitudes during his 1761 Venus transit expedition. Maskelyne began his tome with the promise, “I . . . can from such experience venture to answer that this method carried into practice will (without disparagement to the labor and inventions of others) bring the longitude to great nearness.”
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Maskelyne and Lalande were men of the same mind. “I do not see why the longitude might not be as universally found at sea by this method as the latitude is at present,” Maskelyne said. As Lalande wrote in his own French almanac,
Connoissance des mouvemens célestes pour l'année 1762
, the lunar longitudes method “every day becomes easier and more accurate. Oh that we can make it as widespread and familiar among navigators! The benefits they derive will be immense.”
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As far as these two astronomers were concerned, the solution to the greatest problem of the day was at hand. What remained for the solution to be handed over to the world was a streamlining of their method and an instructional curriculum that taught their art.

Maskelyne and Lalande had long communicated from afar about astronomy, lunar longitudes, and the Venus transits. Here at last, as the two men broke bread together, they could collaborate in person.

Of the two men, Maskelyne would be chief evangelist. Lalande had too many varied interests to devote the kind of singular focus his British counterpart possessed. Even during his British visit, for instance, Lalande was also reading over proofs of a forthcoming book he'd written on the art of tanning chamois leather.
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Maskelyne, on the other hand, had in one book practically defined his career. The guide lays out in twelve pages of exquisite detail the four measurements his method required to discover a ship's longitude at sea: The angle between the horizon and the sun (a.k.a. the “solar altitude”), the lunar altitude, the angle separating sun and moon, and the time of the measurement. (If done at night, a bright reference star is used in the place of the sun.) Another sixteen tables over thirty-four pages laid out every finicky detail a navigator needed to know to determine his
ship's longitude accurately, from the height of the ship's deck above the surface of the water to the exact predicted location of the moon in the sky.

Predicting the moon's precise position a year or more in advance had for generations kept longitude outside human grasp, a mathematical and geopolitical will-o'-the-wisp. In its twenty-eight-day orbit around the earth, the moon advances almost 13 degrees through the sky every twenty-four hours. Its motion against the background stars is almost like the steady advance of an hour hand on a clock as big as the celestial sphere. If it were that simple, of course, determining longitude would never have been any more difficult than latitude. But exact prediction of the moon's motion is in fact very complex, because the sun slightly distorts the moon's path—over an elliptical orbit that forever wobbles like a spinning top owing to its 5-degree inclination compared to the orbit of the earth around the sun.

It took a German mapmaker in 1755, Tobias Mayer, to formulate the complex framework of equations that forecast the hourly positions of the moon every day and night for months or years ahead of time, an act of hardscrabble genius that earned him £3,000 from the British Board of Longitude. (Mayer had died in 1762, however. So his widow came to England to collect the reward—and met with Lalande during her English visit.)

Maskelyne tested Mayer's lunar theory on Maskelyne's Venus transit voyage and found that a couple of minutes of measuring and four hours of calculating provided reliable longitudes “always within about a degree and generally within half a degree.”
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But Maskelyne also discovered that most of his numbers could be crunched ahead of time and printed up in tables no more complex than hackney coach schedules. Four hours of labor could be thus reduced to thirty minutes. Maskelyne's lunar longitude method, one contemporary reviewer noted, “may seem a little troublesome . . . but we are informed that a very little practice will render it easy and familiar.”
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At the time of his lunch with Lalande, Maskelyne had every cause to suspect the
Mariner's Guide
would be setting a new standard for navigation—enabling both commercial and military ships around the world to keep their course and taming some of the fiercest savageries of the open seas.

The
Mariner's Guide
also planted a flag. As a convenience to him and his colleagues at the Royal Observatory, Maskelyne centered the
Mariner's Guide's
longitude tables at Greenwich. A subsequent set of annually published tables that Maskelyne would supervise (The
Nautical Almanac
) would use the same convention. Partly because he couldn't top them, Lalande would reprint Maskelyne's longitude tables verbatim in French navigational almanacs from 1772 onward.
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For almost a century, three-quarters of the shipping tonnage around the world used charts based on Maskelyne's standard.
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And these two friends, brought together over a few lunches in the spring of 1763, would ultimately enshrine Greenwich, England, as the reference point for keeping “universal time” as well as anchoring the earth's zero-degree longitude prime meridian.

For all the enthusiasm Lalande and Maskelyne exuded over lunar longitudes, some London correspondents had already picked their darling. It was fancy, slick, and full of gadgetry. Its inventor, Christopher Irwin, had a knack for public relations. He'd garnered the endorsement of a naval war hero newly elevated to the peerage after his viscount brother had died in action at a celebrated battle in the American colonies. The story was sexy.

The
British Palladium
reported that Irwin's new device left “no doubt of the Longitude's being discovered and settled to a very useful nearness.” The
Monthly Chronologer
relayed how both Prince Edward and
the king's “mathematical teacher” had tried the gadget out. “This will do!” the latter reportedly cried. “This will do!”
The Annual Register
noted, “Navigators are, for the future, to consider [its] invention . . . as one of the greatest benefits that can possibly accrue to their science.”
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The invention was called the “marine chair”—a gimbaled and counterweighted seat designed to hold its sitter still on a rocking and swaying boat. A telescope was affixed to the chair. Using the device, a sitter could then view the steadiest-ticking celestial clock in the solar system, the moons of Jupiter. With the reliable Jovian satellites serving as chronometer, longitudes might now be available down to a record-breaking one-third of a degree.

The London instrument maker Jeremiah Sisson had already shown Lalande one prototype marine chair. But now, two French horologists—those same peering eyes hoping to pry out the secrets of John Harrison's watch—had arrived in town. Sisson was ready.