The Day the World Discovered the Sun

by Mark Anderson

  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.

  LONDON

  April 22, 1763

  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.13

  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.”14

  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.”15

  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.16

  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.”17 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.”18

  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.19 For almost a century, three-quarters of the shipping tonnage around the world used charts based on Maskelyne’s standard.20 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.

  LONDON

  May 8–9, 1763

  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.”21

  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.

  Sisson, who was modifying some of Irwin’s marine chair des
igns, pulled out three models for close inspection. Sisson’s shop—on The Strand, amid the clang and din of central London—crackled with the electricity of opportunity.

  Though very talented at his craft, Sisson had a flighty attention span that left the dilettantish Lalande ill at ease. The craftsman had of late been pawning his handiwork for easy cash. His visitors were marked for the full-on pitch.

  Out came a chair “mounted on a suspension with four pivots and two boots.” Sisson showcased a second seat, held high on a “knee joint from which a 6 foot pendulum hung, with the weight at the bottom in water.” Finally the French horologists viewed an eight-by-four-foot monstrosity “made up of two circles each having two pivots, but whose directions cross.”

  Sisson, Lalande recorded, “is obliged to work in great haste, and so achieves nothing worthwhile. But nevertheless there is no one who has as much ability as he.”22

  Lalande’s two countrymen—the clockmaker Ferdinand Berthoud and the mathematician Charles Étienne Louis Camus—no doubt hoped for a similar welcoming the next day when they called on John Harrison at his nearby house in Red Lion Square.

  More serious and steadfast in his persistence, Harrison was a man of defiant will who, for starters, had once dared to doubt the greatest scientific genius in history. In 1725 Sir Isaac Newton had informed the British Admiralty that two, and only two, practicable methods for finding longitude at sea existed: lunar longitudes and longitudes via the moons of Jupiter.23

  Moreover, latitude at sea had always come courtesy of measurements of the sun and stars. Expecting manmade springs and gearwheels to solve longitude was almost an affront to the heavens. As the French mathematician Jean-Baptiste Morin put it, “It would be folly to undertake it. . . . I don’t know if the Devil himself could do it.”24

  To both Lalande and Maskelyne—commanding increasing authority in their respective countries—Newton and Morin had stated what to their generation of natural philosophers had become self-evident. Marine chronometers were a pointless dream, a wild and distracted sprite. Longitude’s future was with the moon.

  But Harrison simply would not go away. A generation before, in 1735, Harrison completed his first sea clock—a portmanteau-size, seventy-two-pound, gear-shafted dial box that flexed long arms of spring-propelled brass spheres. The next year the Royal Society sent Harrison and his temporal dynamo to Lisbon to test it out. Absurd though the chronometer looked, it yielded impressive results on the sea journey there and back. For starters, when Harrison’s ship first returned to the channel, Harrison accurately informed the captain which English islands were coming into view. The navigation officers had instead located the ship sixty-eight miles east of where it actually was.

  The English Board of Longitude awarded Harrison £500 to develop a better chronometer. So Harrison completed his second machine in 1739, making a timekeeper bigger and heavier than the first. It still wasn’t reliable or rugged enough, however. In the next twenty years, he tinkered and fussed and ultimately made two breakthrough designs that better compensated for jostling seas and temperature extremes.25 Harrison finished his third marine chronometer in 1759, another unwieldy box. Then, just one year later, he was ready to unveil his true masterpiece—a palm-size, three-pound pocket watch with all the ocean readiness of his previous chronometers.

  This fourth Harrison design, presented to the Board of Longitude in July 1760, was the stroke of genius that had set French spies to knocking.

  Miscommunications in Harrison’s 1761 transatlantic trial of his sea watch left commissioners from the Board of Longitude unsatisfied, concluding that another transatlantic trial was needed. And so, in the spring of 1763, the master craftsman awaited the final opportunity to vindicate himself.

  Harrison had in fact shown his masterpiece watch to Lalande three Fridays before, on April 22. But that was before Berthoud and Camus had arrived in England. Lalande knew nothing about watchmaking. Lalande was no more able to appreciate Harrison’s meticulous handiwork as Harrison was able to recognize the enduring brilliance of the recent breakthroughs in lunar longitudes.

  So Lalande, Berthoud, and Camus called on Harrison on Monday, May 9. Harrison obliged and opened his home to his nation’s former enemies, setting out for their analysis and perusal his first three sea clocks.

  Berthoud, Lalande noted, “found these pieces very beautiful, very clever, very well executed. And though the regularity of [Harrison’s] watch was quite difficult for him to believe, he was even more impatient to see it after seeing the three clocks.”26

  Lalande translated his countrymen’s requests to inspect Harrison’s pièce de résistance. This is where the tour stopped. Parliament and the Board of Longitude may have been hopelessly naive in mandating open inspections of Harrison’s handiwork. The craftsman himself, however, was a little more cagey.

  Berthoud was left to gather what intelligence he could from Harrison’s first three chronometers—and from Lalande’s inexpert recall of Harrison’s marine watch.

  Nevertheless, Berthoud had learned enough to return to Paris and reconfigure his whole clock-making enterprise. Four of Harrison’s innovations soon found their way into Berthoud’s Horloge Marine 2. And Berthoud further turned out two marine watches, building on the knowledge and inspiration Harrison had imparted.27

  BRIDGETOWN, BARBADOS

  October 1763–August 1764

  Charles Green had everything now before him. After Charles Mason departed for the 1761 Venus transit mission, Green assumed Mason’s role as second in command at the Royal Greenwich Observatory. After Green’s boss—James Bradley, Astronomer Royal—died in July 1762, the next Astronomer Royal was sickly and spent most of his time at home in Oxford. Twenty-nine-year-old Charles Green was left to handle most of the duties himself. The young man had, in effect, taken the reins of arguably the most prestigious astronomical job in the world.

  In September 1763, with rising star Nevil Maskelyne, Green set sail for Bridgetown, Barbados, on a new transatlantic test of the top contending longitude technologies. The original inventor of the marine chairs, Christopher Irwin, had installed two working prototypes onboard their ship, the HMS Princess Louisa. During the voyage, Green and Maskelyne tried out these “marine machines” in a real oceanic setting. The tests proved a disaster. The astronomers each attempted on more than one night to sight Jupiter and its moons through the chair’s telescope, only to find that the planet wobbled and zipped around the scope’s field of view. Close monitoring of the planet and its moons was impossible. The creaking contraption could not compensate for the unsteady sea—even on a calm night. The chair, Maskelyne wrote in a private letter to his brother Edmund, “proves a mere bauble, not in the least useful for the purpose intended.”28

  Green and Maskelyne also took multiple lunar longitudes using both Maskelyne’s mahogany quadrant and a brass sextant on loan from the Board of Longitude. Their final longitude, just before making landfall off the coast of Barbados (thus making it independently verifiable), was a half degree off the true value. Combined with the lunars Maskelyne took in his Venus transit voyages, he now thought he had all the proof he needed to secure the Longitude Prize.

  Still, the Board of Longitude had sent Green and Maskelyne to Barbados primarily to provide precise, independently derived times and longitudes that would enable testing of John Harrison’s marine chronometer, which would be arriving on a separate ship.

  To Maskelyne, Bridgetown’s luscious tropical setting simply meant more cloudless nights for practicing his science. “This country is much better adapted for celestial observations than England, the air being generally much purer & serener, insomuch that for this month past I have miss’d scarce any observations that occur’d,” Maskelyne wrote to his brother.29

  The welcoming, aquamarine waters of Barbados bathed the travelers’ afternoons and evenings in the sun’s reflected glow. The seaside Fort Willoughby provided an open-air observatory whose warm and gentle evening breezes gave English astronomers—accu
stomed to night shivers huddled over a telescope—a new, tropical standard of comfort. But those same ocean breezes carried so much moisture, in fact, that exposed steel parts or instruments could rust overnight. Copper spoons portioned out the fresh cane sugar for their tea.30

  December’s cooling retained the warmth of a pleasant Hampshire summer, and colors of the Yuletide season—snowy whites and deep scarlets—blossomed on wild potato vines and Christmas bushes. Maskelyne and Green set to moving inland and sited a new observatory at the foot of Constitution Hill, 750 yards from their beachside Fort Willoughby accommodations. The eight-by-twelve-foot wooden shed was even tinier than the island’s slave shanties but concealed an outsize purpose. Here the competing technologies vying to reshape the entire world would feel the cold hand of the scientific method.

  Cold cash was on the line too. A prize of up to £20,000 (more than $5 million today) awaited Harrison or Maskelyne if either the marine chronometer or the British Mariner’s Guide could definitively fulfill the terms of the 1714 Longitude Act. The two key criteria were reliable longitudes accurate down to one-half of a degree and a method that was “practicable and useful at sea.”

  At 1:39 AM on January 7, 1764, Maskelyne recorded the exact time of what would be sixteen immersions or emersions of Jupiter’s moons over the coming eight months at the new location.31 Although not even the finest of the pitiful marine chairs could make Jovian measurements possible onboard a ship, on land Jupiter was still the quickest and easiest route to precision longitudes.

  Celestially derived longitudes may have been widely considered the only serious methods around, but the rapidly advancing watchmaking technology knew no such human prejudices. A showdown was coming. And when the HMS Tartar first appeared in Bridgetown’s Carlisle Bay on May 13, the Caribbean winds fanned the smoldering flame.