Longitude

by Dava Sobel

  An odd coincidence—if you believe in coincidences—changed his thinking on that score. What with all the brass work and specialty detailing he required for the longitude timekeepers, Harrison had come to know and contract with various artisans in London. One of these was John Jefferys, a freeman with The Worshipful Company of Clockmakers. In 1753, Jefferys made Harrison a pocket watch for his personal use. He obviously followed Harrison’s design specifications, for Jefferys fitted the watch with a tiny bi-metallic strip to keep it beating true, come heat or cold. Other watches of the time sped up or slowed down by a factor of ten seconds for every one-degree change in temperature. And, whereas all previous watches either stopped dead or ran backward when they were being wound, this one boasted “maintaining power” that enabled it to keep running even through winding.

  Some horologists consider the Jefferys timepiece the first true precision watch. Harrison’s name is all over it, metaphorically speaking, but only John Jefferys signed it on the cap. (That it still exists, in the Clockmaker’s Museum, is something of a miracle, since the watch lay inside a jeweler’s safe in a shop that took a direct bomb hit during the Battle of Britain, then baked for ten days under the building’s smoldering ruins.)

  This watch proved remarkably dependable. Harrison’s descendants recall that it was always in his pocket. It occupied his mind, too, shrinking his vision of the sea clock. He mentioned the Jefferys watch to the Board of Longitude in June of 1755, during one of his de rigueur explanations of the latest delay attending H-3. According to the minutes of that meeting, Harrison said he had “good reason to think,” on the basis of a watch “already executed according to his direction”—i.e., the Jefferys watch—“that such small machines may be . . . of great service with respect to the longitude.”

  In 1759, when Harrison finished H-4, the timekeeper that ultimately won the longitude prize, it bore a stronger resemblance to the Jefferys watch than to any of its legitimate predecessors, H-1, H-2, or H-3.

  Coming at the end of that big brass lineage, H-4 is as surprising as a rabbit pulled out of a hat. Though large for a pocket watch, at five inches in diameter, it is minuscule for a sea clock, and weighs only three pounds. Within its paired silver cases, a genteel white face shows off four fanciful repeats of a fruit-and-foliage motif drawn in black. These patterns ring the dial of Roman numeral hours and Arabic seconds, where three blued-steel hands point unerringly to the correct time. The Watch, as it soon came to be known, embodied the essence of elegance and exactitude.

  Harrison loved it, and said so more clearly than he ever expressed another thought: “I think I may make bold to say, that there is neither any other Mechanical or Mathematical thing in the World that is more beautiful or curious in texture than this my watch or Timekeeper for the Longitude . . . and I heartily thank Almighty God that I have lived so long, as in some measure to complete it.”

  Inside this marvel, the parts look even lovelier than the face. Just under the silver case, a pierced and engraved plate protects the works behind a forest of flutings and flourishes. The designs serve no functional purpose other than to dazzle the beholder. A bold signature near the plate’s perimeter reads “John Harrison & Son A.D. 1759.” And under the plate, among the spinning wheels, diamonds and rubies do battle against friction. These tiny jewels, exquisitely cut, take over the work that was relegated to antifriction wheels and mechanical grasshoppers in all of Harrison’s big clocks.

  How he came to master the jeweling of his Watch remains one of the most tantalizing secrets of H-4. Harrison’s description of the watch simply states that “The pallets are diamonds.” No explanation follows as to why he chose this material, or by what technique he shaped the gems into their crucial configuration. Even during the years when the Watch was dissected and inspected by committees of watchmakers and astronomers as it went through the mill of repeated trials, no recorded question or discussion came up regarding the diamond parts.

  Lying in state now in an exhibit case at London’s National Maritime Museum, H-4 draws millions of visitors a year. Most tourists approach the Watch after having passed the cases containing H-1, H-2, and H-3. Adults and youngsters alike stand mesmerized before the big sea clocks. They move their heads to follow the swinging balances, which rock like metronomes on H-1 and H-2. They breathe in time to the regular rhythm of the ticking, and they gasp when startled by the sudden, sporadic spinning of the single-blade fan that protrudes from the bottom of H-2.

  But H-4 stops them cold. It purports to be the end of some orderly progression of thought and effort, yet it constitutes a complete non sequitur. What’s more, it holds still, in stark contrast to the whirring of the going clocks. Not only are its mechanisms hidden by the silver case enclosure, but the hands are frozen in time. Even the second hand lies motionless. H-4 does not run.

  It could run, if curators would allow it to, but they demur, on the grounds that H-4 enjoys something of the status of a sacred relic or a priceless work of art that must be preserved for posterity. To run it would be to ruin it.

  When wound up, H-4 goes for thirty hours at a time. In other words, it requires daily winding, just as the big sea clocks do. But unlike its larger predecessors, H-4 will not tolerate daily human intervention. Nay, H-4, often hailed as the most important timekeeper ever built, offers mute but eloquent testimony on this point, having suffered mistreatment at the hands of its own great popularity. As recently as fifty years ago, it lay in its original box, with the cushion and winding key. They have since been lost in the course of using H-4—transferring it from one place to another, exhibiting it, winding it, running it, cleaning it, transferring it again. In 1963, despite the sobering lesson of the lost box, H-4 visited the United States as part of an exhibition at the Naval Observatory in Washington.

  Harrison’s big sea clocks, like his tower clock at Brocklesby Park, have more wherewithal to withstand regular use because of their friction-free design features. They embody Harrison’s pioneering work to eliminate friction through the careful selection and assembly of components. But even Harrison was unable to miniaturize the antifriction wheels and the caged roller bearings for the construction of H-4. As a result, he was forced to lubricate the watch.

  The messy oil used for horological lubrication mandates scheduled maintenance (and this is as true today as it was in Harrison’s time). As it seeps about the works, the oil changes viscosity and acidity, until it no longer lubricates but merely loiters in interior recesses, threatening to sabotage the machinery. To keep H-4 running, therefore, caretakers would have to clean it regularly, approximately once every three years, which would require the complete dismantling of all parts—and incur risk that some of the parts, no matter how carefully held with tweezers and awe, would be damaged.

  Then, too, moving parts subjected to constant friction eventually wear out, even if they are kept lubricated, and then have to be replaced. Estimating the pace of this natural process of attrition, curators suppose that within three or four centuries, H-4 would become a very different object from the one Harrison bequeathed to us three centuries ago. In its present state of suspended animation, however, H-4 may look forward to a well-preserved life of undetermined longevity. It is expected to endure for hundreds of years, if not thousands—a future befitting the timepiece described as the Mona Lisa or The Night Watch of horology.

  11.

  Trial by Fire and

  Water

  Two lunar months are past, and more,

  Since of these heroes half a score

  Set out to try their strength and skill,

  And fairly start for Flamsteed-Hill . . .

  But take care, Rev. M-sk-l-n,

  Thou scientific harlequin,

  Nor think, by jockeying, to win . . .

  For the great donor of the prize

  Is just, as Jove who rules the skies.

  —“C.P.” “Greenwich Hoy!” or “The Astronomical Racers”

  A story that hails a hero must also hiss at a v
illain—in this case, the Reverend Nevil Maskelyne, remembered by history as “the seaman’s astronomer.”

  In all fairness, Maskelyne is more an antihero than a villain, probably more hardheaded than hardhearted. But John Harrison hated him with a passion, and with good reason. The tension between these two men turned the last stretch of the quest for the longitude prize into a pitched battle.

  Maskelyne took up, then embraced, then came to personify the lunar distance method. The man and the method melded easily, for Maskelyne, who put off marrying until he was fifty-two, enslaved himself to accurate observation and careful calculation. He kept records of everything, from astronomical positions to events in his personal life (including each expenditure, large or small, over the course of four-score years), and noted them all with the same detached matter-of-factness. He even wrote his own autobiography in the third person: “Dr. M.,” this surviving handwritten volume begins, “is the last male heir of an ancient family long settled at Purton in the County of Wilts.” On subsequent pages, Maskelyne refers to himself alternately as “he” and “Our Astronomer”— even before his main character becomes astronomer royal in 1765.

  The fourth in a long line of Nevils, Maskelyne was born on October 5, 1732. This made him about forty years younger than John Harrison, although he seemed never to have been young. Described by a biographer early on as “rather a swot” and “a bit of a prig,” he threw himself into the study of astronomy and optics with every intention of becoming an important scientist. Family letters refer to his older brothers, William and Edmund, as “Billy” and “Mun,” and call his younger sister, Margaret, “Peggy,” but Nevil was always and only Nevil.

  Unlike John Harrison, who had no formal education, Nevil Maskelyne attended Westminster School and Cambridge University. He worked his way through college, performing menial tasks in exchange for reduced tuition. As a fellow of Trinity College, he also took holy orders, which earned him the title of Reverend, and he served for a while as curate of the church at Chipping Barnet, roughly ten miles north of London. Sometime in the 1750s, while Maskelyne was still a student, his lifelong devotion to astronomy and his Cambridge connections brought him into the company of James Bradley, the third astronomer royal. They made a natural pair, and mated their two true methodical minds for life, in joint pursuit of a longitude solution.

  Bradley, at this point in his career, was on the verge of codifying the lunar distance method with the help of the tables sent over from Germany by the astronomer-mathematician-mapmaker Tobias Mayer. Between 1755 and 1760, according to Maskelyne’s account of the story, Bradley undertook 1,200 observations at Greenwich, followed by “laborious calculations” comparing them to Mayer’s predictions, in an effort to verify the tables.

  Maskelyne naturally took an interest in these matters. In 1761, on the occasion of the much-heralded astronomical event called the transit of Venus, Maskelyne won from Bradley a plum position on an expedition to prove the validity of Mayer’s work—and to demonstrate the value of the tables for navigation.

  Maskelyne voyaged to the tiny island of St. Helena, south of the Atlantic Equator, where Edmond Halley had journeyed in the previous century to map the southern stars, and where Napoleon Bonaparte would be condemned, in the following century, to live out his last days. Sailing to and from St. Helena, Maskelyne used Hadley’s quadrant and Mayer’s tables to find his longitude at sea, many times over, much to his and Bradley’s delight. The lunar distance technique worked like a charm in Maskelyne’s able hands.

  Maskelyne also used lunar distances to establish the precise longitude of St. Helena, which had not been known before.

  During his sojourn on the island, Maskelyne carried out what was ostensibly his primary mission: He watched over a period of hours as the planet Venus moved, like a small, dark blemish, across the sun’s face. In order for Venus to transit, or trespass in this fashion, the planet must pass precisely between the Earth and the sun. Because of the relative positions and paths of the three bodies, transits of Venus come in pairs, one transit eight years after the other—but only a single pair per century.

  Halley had witnessed part of a more common transit of Mercury from St. Helena in 1677. Very excited about the possibilities of such occurrences, he urged the Royal Society to track the next transit of Venus, which, like the return of Halley’s comet, he could not possibly live long enough to see firsthand. Halley argued convincingly that lots of careful observations of the transit, taken from widely separated points on the globe, would reveal the actual distance between the Earth and the sun.

  Thus, Maskelyne set out for St. Helena in January 1761 as part of a small but global scientific armada, which included numerous French astronomical excursions to carefully selected observing sites in Siberia, India, and South Africa. The June 6, 1761, transit of Venus also paired (Charles) Mason with (Jeremiah) Dixon on a successful observing run at the Cape of Good Hope—several years before the two British astronomers drew their famous boundary line between Pennsylvania and Maryland. The second transit, predicted for June 3, 1769, launched the first voyage of Captain James Cook, who proposed to view the event from Polynesia.

  Maskelyne discovered that the weather at St. Helena, unfortunately, had not improved much since Halley’s visit, and he missed the end of the transit behind a cloud. Nevertheless, he stayed on for many months, comparing the force of gravity at St. Helena with that at Greenwich, trying to measure the distance to the nearby bright star Sirius, and using observations of the moon to gauge the size of the Earth. This work, coupled with his prowess on the longitude frontier, more than made up for his problems in viewing Venus.

  Meanwhile, another voyage of monumental importance to the longitude story, though altogether unrelated to the transit expeditions, also set sail in 1761, when William Harrison carried his father’s watch on a sea trial to Jamaica.

  Harrison’s first timekeeper, H-1, had ventured only as far as Lisbon, Portugal, and H-2 had never gone to sea at all. H-3, almost twenty years in the making, might have been tried on the ocean immediately upon its completion in 1759 but for the inconvenience of the Seven Years War. This worldwide war spanned three continents, including North America, as it brought England, France, Russia, and Prussia, among other countries, into its fray. During the turmoil, Astronomer Royal Bradley had tested written copies of the lunar distance tables aboard warships patrolling the enemy coast of France. No one in his right mind, however, would send a one-of-a-kind instrument like H-3 into such troubled waters, where it might be captured by hostile forces. At least that was the argument Bradley gave in the beginning. But the argument fell apart in 1761, when the official trial of H-3 finally came up—despite the fact that the great war still raged, having progressed through only five of its eponymous seven years. It’s irresistible to imagine that, by then, Bradley wanted something bad to happen to H-3. In any case, the international drive to pursue the transit of Venus must somehow have legitimized all voyages flying under the flag of science.

  Between the completion and the trial date of H-3, Harrison had proudly presented his pièce de résistance, H-4, to the Board of Longitude in the summer of 1760. The Board opted to test both H-3 and H-4 together on the same voyage. Accordingly, in May of 1761, William Harrison sailed with the heavy sea clock, H-3, from London to the port of Portsmouth, where he had orders to wait for a ship assignment. John Harrison, fussing and fine-tuning H-4 till the very last minute, planned to meet William at Portsmouth and deliver the portable timekeeper into his hands just before the ship weighed anchor.

  Five months later, William was still on the dock in Portsmouth, waiting for his sailing orders. It was now October, and William fretted with frustration over the delayed trial and fear for the health of his wife, Elizabeth, still ill after the birth of their son, John.

  William suspected that Dr. Bradley had deliberately delayed the trial for his personal gain. By holding up the Harrison trial, Bradley could buy time for Maskelyne to produce proof positive supporting
the lunar distance method. This may sound like a paranoid delusion on William’s part, but he had evidence of Bradley’s own interest in the longitude prize. In a diary, William had recorded how he and his father chanced to encounter Dr. Bradley at an instrument-maker’s shop, where they incurred his obvious antagonism: “The Doctor seemed very much out of temper,” noted William, “and in the greatest passion told Mr. Harrison that if it had not been for him and his plaguey watch, Mr. Mayer and he should have shared Ten Thousand Pounds before now.”

  As astronomer royal, Bradley served on the Board of Longitude, and was therefore a judge in the contest for the longitude prize. This description of William’s makes it sound as though Bradley himself was also a contender for the prize. Bradley’s personal investment in the lunar distance method could be called a “conflict of interest,” except that the term seems too weak to define what the Harrisons stood up against.

  Whatever the cause of the delay, the Board convened to take action shortly after William returned to London in October, and November saw him embarked at last on H.M.S. Deptford. With H-4 alone. During the long predeparture delay, his father had seen fit to remove H-3 from the running. The Harrisons were banking everything on the Watch.

  The board insisted, as a means of quality control over the trial, that the box containing H-4 be fitted with four locks, each opening to a different key. William got one of the keys, of course, for he had charge of the daily winding. The other three went to trusted men willing to witness William’s every move— William Lyttleton, then governor-designate of Jamaica and William’s fellow passenger aboard the Deptford, the ship’s captain, Dudley Digges, and Digges’s first lieutenant, J. Seward.

  Two astronomers, one in Portsmouth and another one sailing along to Jamaica, took charge of establishing the correct local time of departure and arrival. William was required to set the Watch by them.