Authors: Dava Sobel
The Prize
Her cutty sark, o’ Paisley harn,
That while a lassie she had worn,
In longitude tho’ sorely scanty,
It was her best, and she was vauntine.
—ROBERT BURNS
, “Tam o’ Shanter”
T
he merchants’ and seamen’s petition pressing for action on the matter of longitude arrived at Westminster Palace in May of 1714. In June, a Parliamentary committee assembled to respond to its challenge.
Under orders to act quickly, the committee members sought expert advice from Sir Isaac Newton, by then a grand old man of seventy-two, and his friend Edmond Halley. Halley had gone to the island of St. Helena some years earlier to map the stars of the southern hemisphere—virtually virgin territory on the landscape of the night. Halley’s published catalog of more than three hundred southern stars had won him election to the Royal Society. He had also traveled far and wide to measure magnetic variation, so he was well versed in longitude lore—and personally immersed in the quest.
Newton prepared written remarks for the committee members, which he read aloud to them, and also answered their questions, despite his “mental fatigue” that day. He summarized the existing means for determining longitude, saying that all of them were true in theory but “difficult to execute.” This was of course a gross understatement. Here, for example, is Newton’s description of the timekeeper approach:
“One [method] is by a Watch to keep time exactly. But, by reason of the motion of the Ship, the Variation of Heat and Cold, Wet and Dry, and the Difference of Gravity in different Latitudes, such a watch hath not yet been made.” And not likely to be, either, he implied.
Perhaps Newton mentioned the watch first so as to set it up as a straw man, before proceeding to the somewhat more promising though still problematic field of astronomical solutions. He mentioned the eclipses of Jupiter’s satellites, which worked on land, at any rate, though they left mariners in the lurch. Other astronomical methods, he said, counted on the predicted disappearances of known stars behind our own moon, or on the timed observations of lunar and solar eclipses. He also cited the grandiose “lunar distance” plan for divining longitude by measuring the distance between the moon and sun by day, between the moon and stars at night. (Even as Newton spoke, Flamsteed was giving himself a migraine at the Royal Observatory, trying to ascertain stellar positions as the basis for this much-vaunted method.)
The longitude committee incorporated Newton’s testimony in its official report. The document did not favor one approach over another, or even British genius over foreign ingenuity. It simply urged Parliament to welcome potential solutions from any field of science or art, put forth by individuals or groups of any nationality, and to reward success handsomely.
The actual Longitude Act, issued in the reign of Queen Anne on July 8, 1714, did all these things. On the subject of prize money, it named first-, second-, and third-prize amounts, as follows:
£20,000 (the equivalent of millions of dollars today) for a method to determine longitude to an accuracy of half a degree of a great circle;
£15,000 for a method accurate to within two-thirds of a degree;
£10,000 for a method accurate to within one degree.
Since one degree of longitude spans sixty nautical miles (the equivalent of sixty-eight geographical miles) over the surface of the globe at the Equator, even a fraction of a degree translates into a large distance—and consequently a great margin of error when trying to determine the whereabouts of a ship vis-à-vis its destination. The fact that the government was willing to award such huge sums for “Practicable and Useful” methods that could miss the mark by many miles eloquently expresses the nation’s desperation over navigation’s sorry state.
The Longitude Act established a blue ribbon panel of judges that became known as the Board of Longitude. This board, which consisted of scientists, naval officers, and government officials, exercised discretion over the distribution of the prize money. The astronomer royal served as an ex-officio member, as did the president of the Royal Society, the first lord of the Admiralty, the speaker of the House of Commons, the first commissioner of the Navy, and the Savilian, Lucasian, and Plumian professors of mathematics at Oxford and Cambridge Universities. (Newton, a Cambridge man, had held the Lucasian professorship for thirty years; in 1714 he was president of the Royal Society.)
The board, according to the Longitude Act, could give incentive awards to help impoverished inventors bring promising ideas to fruition. This power over purse strings made the Board of Longitude perhaps the world’s first official research-and-development agency. (Though none could have foreseen it at the outset, the Board of Longitude was to remain in existence for more than one hundred years. By the time it finally disbanded in 1828, it had disbursed funds in excess of £100,000.)
In order for the commissioners of longitude to judge the actual accuracy of any proposal, the technique had to be tested on one of Her Majesty’s ships, as it sailed “over the ocean, from Great Britain to any such Port in the West Indies as those Commissioners Choose . . . without losing their Longitude beyond the limits before mentioned.”
So-called solutions to the longitude problem had been a dime a dozen even before the act went into effect. After 1714, with their potential value exponentially raised, such schemes proliferated. In time, the board was literally besieged by any number of conniving and well-meaning persons who had heard word of the prize and wanted to win it. Some of these hopeful contenders were so galvanized by greed that they never stopped to consider the conditions of the contest. Thus the board received ideas for improving ships’ rudders, for purifying drinking water at sea, and for perfecting special sails to be used in storms. Over the course of its long history, the board received all too many blueprints for perpetual motion machines and proposals that purported to square the circle or make sense of the value of pi.
In the wake of the Longitude Act, the concept of “discovering the longitude” became a synonym for attempting the impossible. Longitude came up so commonly as a topic of conversation—and the butt of jokes—that it rooted itself in the literature of the age. In
Gulliver’s Travels
, for example, the good Captain Lemuel Gulliver, when asked to imagine himself as an immortal Struldbrugg, anticipates the enjoyment of witnessing the return of various comets, the lessening of mighty rivers into shallow brooks, and “the discovery of the
longitude
, the
perpetual motion
, the
universal medicine
, and many other great inventions brought to the utmost perfection.”
Part of the sport of tackling the longitude problem entailed ridiculing others in the competition. A pamphleteer who signed himself “R.B.” said of Mr. Whiston, the fireball proponent, “[I]f he has any such Thing as Brains, they are really crackt.”
Surely one of the most astute, succinct dismissals of fellow hopefuls came from the pen of Jeremy Thacker of Beverly, England. Having heard the half-baked bids to find longitude in the sound of cannon blasts, in compass needles heated by fire, in the moon’s motion, in the sun’s elevation, and what-else-have-you, Thacker developed a new clock ensconced in a vacuum chamber and declared it the best method of all: “In a word, I am satisfied that my Reader begins to think that the
Phonometers, Pyrometers, Selenometers, Heliometers
, and all the
Meters
are not worthy to be compared with my
Chronometer
.”
Thacker’s witty neologism is apparently the first coinage of the word
chronometer
. What he said in 1714, perhaps in jest, later gained acceptance as the perfect moniker for the marine timekeeper. We still call such a device a chronometer today. Thacker’s chronometer, however, was not quite as good as its name. To its credit, the clock boasted two important new advances. One was its glass house—the vacuum chamber that shielded the chronometer from troubling changes of atmospheric pressure and humidity. The other was a set of cleverly paired winding rods, configured so as to keep the machine going while being wound up. Until Thacker’s introduction of this “maintaining power,” spring-driven watches had simply stopped and lost track of time during winding. Thacker had also taken the precaution of suspending the whole machine in gimbals, like a ship’s compass, to keep it from thumping about on a storm-tossed deck.
What Thacker’s watch could
not
do was adjust to changes in temperature. Although the vacuum chamber provided some insulation against the effects of heat and cold, it fell short of perfection, and Thacker knew it.
Room temperature exerted a powerful influence on the going rate of any timekeeper. Metal pendulum rods expanded with heat, contracted when cooled, and beat out seconds at different tempos, depending on the temperature. Similarly, balance springs grew soft and weak when heated, stiffer and stronger when cooled. Thacker had considered this problem at great length when testing his chronometer. In fact, the proposal he submitted to the longitude board contained his careful records of the chronometer’s rate at various temperature readings, along with a sliding scale showing the range of error that could be expected at different temperatures. A mariner using the chronometer would simply have to weigh the time shown on the clock’s dial against the height of the mercury in the thermometer tube, and make the necessary calculations. This is where the plan falls apart: Someone would have to keep constant watch over the chronometer, noting all changes in ambient temperature and figuring them into the longitude reading. Then, too, even under ideal circumstances, Thacker owned that his chronometer occasionally erred by as many as six seconds a day.
Six seconds sound like nothing compared to the fifteen minutes routinely lost by earlier clocks. Why split hairs?
Because of the consequences—and the money— involved.
To prove worthy of the £20,000 prize, a clock had to find longitude within half a degree. This meant that it could not lose or gain more than three seconds in twenty-four hours. Arithmetic makes the point: Half a degree of longitude equals two minutes of time—the maximum allowable mistake over the course of a six-week voyage from England to the Caribbean. An error of only three seconds a day, compounded every day at sea for forty days, adds up to two minutes by journey’s end.
Thacker’s pamphlet, the best of the lot reviewed by members of the Board of Longitude during their first year, didn’t raise anyone’s hopes very high. So much remained to be done. And so little had actually been accomplished.
Newton grew impatient. It was clear to him now that any hope of settling the longitude matter lay in the stars. The lunar distance method that had been proposed several times over preceding centuries gained credence and adherents as the science of astronomy improved. Thanks to Newton’s own efforts in formulating the Universal Law of Gravitation, the moon’s motion was better understood and to some extent predictable. Yet the world was still waiting on Flamsteed to finish surveying the stars.
Flamsteed, meticulous to a fault, had spent forty years mapping the heavens—and had still not released his data. He kept it all under seal at Greenwich. Newton and Halley managed to get hold of most of Flamsteed’s records from the Royal Observatory, and published their own pirated edition of his star catalog in 1712. Flamsteed retaliated by collecting three hundred of the four hundred printed copies, and burning them.
“I committed them to the fire about a fortnight ago,” Flamsteed wrote to his former observing assistant Abraham Sharp. “If Sir I. N. would be sensible of it, I have done both him and Dr. Halley a very great kindness.” In other words, the published positions, insufficiently verified as they were, could only discredit a respectable astronomer’s reputation.
Despite the flap over the premature star catalog, Newton continued to believe that the regular motions of the clockwork universe would prevail in guiding ships at sea. A man-made clock would certainly prove a useful accessory to astronomical reckoning but could never stand in its stead. After seven years of service on the Board of Longitude, in 1721, Newton wrote these impressions in a letter to Josiah Burchett, the secretary of the Admiralty:
“A good watch may serve to keep a recconing at Sea for some days and to know the time of a celestial Observ[at]ion: and for this end a good Jewel watch may suffice till a better sort of Watch can be found out. But when the Longitude at sea is once lost, it cannot be found again by any watch.”
Newton died in 1727, and therefore did not live to see the great longitude prize awarded at last, four decades later, to the self-educated maker of an oversized pocket watch.
Cogmaker’s Journal
Oh! She was perfect, past all parallel—
Of any modern female saint’s comparison;
So far above the cunning powers of hell,
Her guardian angel had given up his garrison;
Even her minutest motions went as well
As those of the best time-piece made by Harrison.
—LORD BYRON
, “Don Juan”
S
o little is known of the early life of John Harrison that his biographers have had to spin the few thin facts into whole cloth.
These highlights, however, recall such stirring elements in the lives of other legendary men that they give Harrison’s story a leg up. For instance, Harrison educated himself with the same hunger for knowledge that kept young Abraham Lincoln reading through the night by candlelight. He went from, if not rags, then assuredly humble beginnings to riches by virtue of his own inventiveness and diligence, in the manner of Thomas Edison or Benjamin Franklin. And, at the risk of overstretching the metaphor, Harrison started out as a carpenter, spending the first thirty years of his life in virtual anonymity before his ideas began to attract the world’s attention.
John “Longitude” Harrison was born March 24, 1693, in the county of Yorkshire, the eldest of five children. His family, in keeping with the custom of the time, dealt out names so parsimoniously that it is impossible to keep track of all the Henrys, Johns, and Elizabeths without pencil and paper. To wit, John Harrison served as the son, grandson, brother, and uncle of one Henry Harrison or another, while his mother, his sister, both his wives, his only daughter, and two of his three daughters-in-law all answered to the name Elizabeth.
His first home seems to have been on the estate, called Nostell Priory, of a rich landowner who employed the elder Harrison as a carpenter and custodian. Early in John’s life—perhaps around his fourth birthday, not later than his seventh—the family moved, for reasons unknown, forty-two miles away to the small Lincolnshire village of Barrow, also called Barrow upon Humber because it sat on the south bank of that river.
In Barrow, young John learned woodworking from his father. No one knows where he learned music, but he played the viol, rang and tuned the church bells, and eventually took over as choirmaster at the Barrow parish church. (Many years later, as an adjunct to the 1775 publication explaining his timekeepers,
A Description Concerning Such Mechanism . . .
, Harrison would expound his radical theory on the musical scale.)
Somehow, John as a teenager let it be known that he craved book learning. He may have said as much aloud, or perhaps his fascination for the way things work burned in his eyes so brightly that others could see it. In any case, in about 1712, a clergyman visiting the parish encouraged John’s curiosity by letting him borrow a treasured textbook—a manuscript copy of a lecture series on natural philosophy delivered by mathematician Nicholas Saunderson at Cambridge University.
By the time this book reached his hands, John Harrison had already mastered reading and writing. He applied both skills to Saunderson’s work, making his own annotated copy, which he headed “Mr. Saunderson’s Mechanicks.” He wrote out every word and drew and labeled every diagram, the better to understand the nature of the laws of motion. He pored over this copybook again and again, in the manner of a biblical scholar, continuing to add his own marginal notes and later insights over the next several years. The handwriting throughout appears neat and small and regular, as one might expect from a man of methodical mind.
Although John Harrison forswore Shakespeare, never allowing the Bard’s works in his house, Newton’s
Principia
and Saunderson’s lectures stood him in good stead for the rest of his life, strengthening his own firm grasp on the natural world.
Harrison completed his first pendulum clock in 1713, before he was twenty years old. Why he chose to take on this project and how he excelled at it with no experience as a watchmaker’s apprentice, remain mysteries. Yet the clock itself remains. Its movement and dial—signed, dated fossils from that formative period—now occupy an exhibit case at The Worshipful Company of Clockmakers’ one-room museum at Guildhall in London.
Aside from the fact that the great John Harrison built it, the clock claims uniqueness for another singular feature: It is constructed almost entirely of wood. This is a carpenter’s clock, with oak wheels and boxwood axles connected and impelled by small amounts of brass and steel. Harrison, ever practical and resourceful, took what materials came to hand, and handled them well. The wooden teeth of the wheels never snapped off with normal wear but defied destruction by their design, which let them draw strength from the grain pattern of the mighty oak.
Historians wonder which clocks, if any, Harrison might have dismantled and studied before fashioning his own. A tale, probably apocryphal, holds that he sustained himself through a childhood illness by listening to the ticking of a pocket watch laid upon his pillow. But no one can guess where the boy would have gotten such a thing. Clocks and watches carried high price tags in Harrison’s youth. Even if his family could have afforded to buy one, they could not have found a ready source. No known clockmaker, other than self-taught Harrison himself, lived or worked anywhere around north Lincolnshire in the early eighteenth century.
Harrison built two more, almost identical, wooden clocks in 1715 and 1717. In the centuries since their completion, the pendulums and tall cases of these time machines have vanished, so that only the hearts of the works come down to us. The exception is a single piece, roughly the size of a legal document, from the wooden door of the last of the trio. In fact, an actual document, pasted to the door’s inside surface, seems to have preserved the soft wood for posterity. This protective paper, Harrison’s “equation of time” table, can be seen today in the same Guildhall exhibit case as his first clock.
The table enabled the clock’s user to rectify the difference between solar, or “true” time (as shown on a sundial) with the artificial but more regular “mean” time (as measured by clocks that strike noon every twenty-four hours). The disparity between solar noon and mean noon widens and narrows as the seasons change, on a sliding scale. We take no note of solar time today, relying solely on Greenwich mean time as our standard, but in Harrison’s era sundials still enjoyed wide use. A good mechanical clock had to be reckoned with the clockwork universe, and this was done through the application of some mathematical legerdemain called the Equation of Time. Harrison not only understood these calculations in his youth but also made his own astronomical observations and worked out the equation data by himself.
Summarizing the essence of his conversion chart in a handwritten heading, Harrison called it “A Table of the Sun rising and Setting in the Latitude of Barrow 53 degrees 18 Minutes; also of difference that should & will be betwixt ye Longpendillom & ye Sun if ye Clock go true.” This description owes its quaint sound partly to its antiquity, and partly to ambiguity. Harrison, according to those who admired him most, never could express himself clearly in writing. He wrote with the scrivener’s equivalent of marbles in the mouth. No matter how brilliantly ideas formed in his mind, or crystallized in his clockworks, his verbal descriptions failed to shine with the same light. His last published work, which outlines the whole history of his unsavory dealings with the Board of Longitude, brings his style of endless circumlocution to its peak. The first sentence runs on, virtually unpunctuated, for twenty-five pages.
Forthright in his personal encounters, Harrison proposed marriage to Elizabeth Barrel, and she became his wife on August 30, 1718. Their son, John, was born the following summer. Then Elizabeth fell ill and died in the spring before the boy turned seven.
The dearth of detail regarding the widower’s private life at this juncture comes as no surprise, for he left no diaries or letters describing his activities or his angst. Nevertheless, the parish records show that he found a new bride, ten years younger, within six months of Elizabeth’s death. Harrison wed his second wife, Elizabeth Scott, on November 23, 1726. At the start of their fifty years together they had two children—William, born in 1728, who was to become his father’s champion and right-hand man, and Elizabeth, born in 1732, about whom nothing is known save the date of her baptism, December 21. John, the child of Harrison’s first marriage, died when he was only eighteen.
No one knows when or how Harrison first heard word of the longitude prize. Some say that the nearby port of Hull, just five miles north of Harrison’s home and the third largest port in England, would have been abuzz with the news. From there, any seaman or merchant could have carried the announcement downstream across the Humber on the ferry.
One would imagine that Harrison grew up well aware of the longitude problem—just as any alert schoolchild nowadays knows that cancer cries out for a cure and that there’s no good way to get rid of nuclear waste. Longitude posed the great technological challenge of Harrison’s age. He seems to have begun thinking of a way to tell time and longitude at sea even before Parliament promised any reward for doing so— or at least before he learned of the posted reward. In any case, whether or not his thoughts favored longitude, Harrison kept busy with tasks that prepared his mind to solve the problem.
Sometime around 1720, after Harrison had acquired something of a local reputation as a clockmaker, Sir Charles Pelham hired him to build a tower clock above his new stable at the manor house in Brocklesby Park.
Brocklesby tower beckoned Harrison, the church-steeple bell ringer, to a familiar high perch. Only this time, instead of swinging on a bell rope, he would mastermind a new instrument that would toil in its high turret, broadcasting the true time to all and sundry.
The tower clock that Harrison completed about 1722 still tells time in Brocklesby Park. It has been running continuously for more than 270 years— except for a brief period in 1884 when workers stopped it for refurbishing.
From its fine cabinet to its friction-free gearing, the clock reveals its maker as a master carpenter. For example, the works run without oil. The clock never needs lubrication, because the parts that would normally call for it were carved out of lignum vitae, a tropical hardwood that exudes its own grease. Harrison studiously avoided the use of iron or steel anywhere in the clockwork, for fear it would rust in the damp conditions. Wherever he needed metal, he installed parts made of brass.
When it came to fabricating toothed gears from oak, Harrison invented a new kind of wheel. Each of the wheels in the clock’s going train resembles a child’s drawing of the sun, with the lines of the wood grain radiating from the center of the wheel to the tips of the teeth as though drawn there with pencil and ruler. Harrison further guaranteed the wheel teeth their enduring structure by selecting the oak from fast-growing trees, whose growth rings formed widely spaced ripples in the trunks. Such trees yield lumber with a wide grain and great might, due to the high percentage of new wood. (Under microscopic examination, growth rings resemble a honeycomb with hollows, while the new wood between the rings seems solid.) Elsewhere, wherever Harrison was willing to sacrifice strength for a lighter-weight material, as in the central portions of the wheels, he turned to slow-growing oak: With growth rings clinging closer together, this wood looks grainier and weighs less.
Harrison’s intimate knowledge of wood is perhaps better appreciated in modern times, when hindsight and X-ray vision can validate the choices he made. Looking back, it’s also obvious that Harrison took his first important step toward building a sea clock up there in the tower of Brocklesby Park—by eliminating the need for oil in the gears. A clock without oil, which till then was absolutely unheard of, would stand a much better chance of keeping time at sea than any clock yet built. For lubricants got thicker or thinner as temperatures dipped or soared over the course of a voyage, making the clock run faster or slower as a result— or cease running altogether.
As he built additional clocks, Harrison teamed up with his brother James, eleven years his junior but, like him, a superb craftsman. From 1725 to 1727 the brothers built two long-case, or grandfather, clocks. James Harrison signed them both in bold script right on their painted wood faces. The name John Harrison does not appear anywhere, outside or inside, though there is not a horologist in the world who doubts that John was the designer and driving force in the construction of these clocks. Judging from recorded acts of John’s generosity later in life, it appears that he gave his kid brother a boost by letting him put his own stamp on their joint venture.
Two fancy new gadgets enabled these grandfather clocks to keep nearly perfect time. These precision inventions of Harrison’s came to be called the “gridiron” and the “grasshopper.” You can see how the gridiron got its name if you peer through the small glass porthole on the case of the Harrison brothers’ clock that stands against the back wall in Guildhall. The part of the pendulum that shows here consists of several alternating strips of two different metals, much like the parallel bars of the gridirons cooks used to broil meat. And this gridiron pendulum can truly stand the heat with no ill effects.
Most pendulums of Harrison’s day expanded with heat, so they grew longer and ticked out time more slowly in hot weather. When cold made them contract, they speeded up the seconds, and threw the clock’s rate off in the opposite direction. Every metal displayed this annoying tendency, though each metal stretched and shrank at its own characteristic rate. By combining long and short strips of two different metals—brass and steel—in one pendulum, Harrison eliminated the problem. The bound-together metals counteracted each other’s changes in length as temperatures varied, so the pendulum never went too fast or too slow.