Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time - Dava Sobel (2005)
Chapter 7. 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”
So 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.
The grasshopper escapement—the part that counted the heartbeats of the clock’s pacemaker—took its name from the motion of its crisscrossed components. These kicked like the hind legs of a leaping insect, quietly and without the friction that bedeviled existing escapement designs.
The Harrison brothers tested the accuracy of their gridiron-grasshopper clocks against the regular motions of the stars. The crosshairs of their homemade astronomical tracking instrument, with which they pinpointed the stars’ positions, consisted of the border of a windowpane and the silhouette of the neighbor’s chimney stack. Night after night, they marked the clock hour when given stars exited their field of view behind the chimney. From one night to the next, because of the Earth’s rotation, a star should transit exactly 3 minutes, 56 seconds (of solar time) earlier than the previous night. Any clock that can track this sidereal schedule proves itself as perfect as God’s magnificent clockwork.
In these late-night tests, the Harrisons’ clocks never erred more than a single second in a whole month. In comparison, the very finest quality watches being produced anywhere in the world at that time drifted off by about one minute every day. The only thing more remarkable than the Harrison clocks’ extraordinary accuracy was the fact that such unprecedented precision had been achieved by a couple of country bumpkins working independently—and not by one of the masters such as Thomas Tompion or George Graham, who commanded expensive materials and experienced machinists in the clock centers of cosmopolitan London.
By the year 1727, Harrison recalled late in life, visions of the longitude prize had turned his mind to the special challenge of marine timekeeping. He realized he could make himself rich and famous by making his fine clocks seaworthy.
He’d already found a way around the problem of lubricants, hit a new high in precision with a friction-free mechanism, and developed a pendulum for all seasons. He was ready to take on the salt air and the stormy sea. Ironically, Harrison saw he’d have to jettison his gridiron pendulum in order to win the £20,000.
Though the gridiron had triumphed on land, a pendulum was still a pendulum, and no pendulum could survive a rolling ocean. In place of the striated, swinging stick with its hanging bob, Harrison began picturing a springing set of seesaws, self-contained and counterbalanced to withstand the wildest waves.
When he had thought out the novel contraption to his own satisfaction, which took him almost four years, he set off for London—a journey of two hundred miles—to lay his plan before the Board of Longitude.