Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time

“The zero-degree parallel of latitude is fixed by the laws of nature, while the zero-degree meridian of longitude shifts like the sands of time. This difference makes finding latitude child’s play, and turns the determination of longitude, especially at sea, into an adult dilemma—one that stumped the wisest minds of the world for the better part of human history.” 

Latitude is simple: The Earth spins on its axis, and the widest point of that spin, effectively the waist of the planet, is the Equator, which mapmakers set at zero degrees. All parallel lines on maps of the Earth are lines of latitude, measured in degrees north or south of the Equator. Lines of longitude run north and south through the poles, and knowing which line a ship is on will tell sailors how far from home they are. They must, however, possess two clocks: one set to the local time at their home port and one set by the location of the sun or moon in the sky. The difference between those two times tells them how far away they are from home.

“In literally hundreds of instances, a vessel’s ignorance of her longitude led swiftly to her destruction.” 

Without accurate timepieces, location at sea was always hard to know. Ships regularly struck reefs or crashed into landforms. Each time, sailors died. Dead men, lost ships, and sunk trade goods made sea voyages costly. A way to reckon position would be worth its weight in gold.

“The sky turns day to night with a sunset, measures the passing months by the phases of the moon, and marks each season’s change with a solstice or an equinox. The rotating, revolving Earth is a cog in a clockwork universe, and people have told time by its motion since time began.” 

By keeping track of the moon, sun, and stars, people can keep track of the time of day and of the weeks, months, and seasons. They also can reckon their distance north or south of the equator. Finding location east or west, though, puzzled mariners for thousands of years.

“In his warrant establishing the Observatory at Greenwich, the king charged Flamsteed to apply ‘the most exact Care and Diligence to rectifying the Tables of the Motions of the Heavens, and the Places of the fixed Stars, so as to find out the so-much desired Longitude at Sea, for perfecting the art of Navigation.’” 

King Charles II of England so admired astronomer John Flamsteed’s plan to calculate precise time data for the moon’s motion past various stars that he paid for the Greenwich Observatory, where Flamsteed could carry out the necessary observations. The purpose was to solve the longitude problem, vital to trading ships and the English Navy. Flamsteed and his successor Observatory directors would collect data over the next several decades and assemble it into books called ephemerides that sailors could use, in a complicated procedure involving star sightings and calculations, to find their longitude within acceptable limits.

“Even when the bulbs of the hourglass shatter, when darkness withholds the shadow from the sundial, when the mainspring winds down so far that the clock hands hold still as death, time itself keeps on. The most we can hope a watch to do is mark that progress. And since time sets its own tempo, like a heartbeat or an ebb tide, timepieces don’t really keep time. They just keep up with it, if they’re able.” 

Time-keeping devices make us more aware of the passage of time. Its fleeting nature intrigues and troubles us. We try to control time by measuring it, yet the more we do so, the more time controls us. Greater precision gives us more ability to do time-limited things, but it also ties us to our timepieces.

“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.” 

The sheer number of prominent political, military, and scientific figures attached to the Board that would award the longitude prize speaks to the desperation of seafaring interests. At that time, mariners had no reliable way to avoid getting lost or sunk for lack of knowing precisely where they were on the oceans. Trade with other nations, along with naval defense, relied on ships that could find their way quickly and efficiently. The substantial prize also pointed to the value of a workable solution.

“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.” 

Over time, the technical problems that dog civilization tend to get solved, and new problems take their place. The longitude problem required centuries of effort to solve; John Harrison developed his invention over the last 30 years of that struggle. Today’s important puzzles—sequestering CO2 or developing clean energy, for example—probably will require large teams of people to solve, but they can take inspiration from Harrison’s relentless pursuit of the perfect sea clock.

“So indifferent and mediocre were the proposals submitted to the board, that individual commissioners had simply sent out letters of rejection to the hopeful inventors. Not a single suggested solution had held enough promise to inspire any five commissioners—the minimum required by the Longitude Act for a quorum—to bother gathering together for a serious discussion of the method’s merits.” 

For the first 15 years of its existence, the Board of Longitude never met. Not until John Harrison presented his sea clock did the Board find an invention good enough to merit its attention. The solution to the longitude problem, it turned out, would require unusual levels of innovation and extreme technical precision—qualities that just happened to reside together within the mind of clockmaker Harrison.

“Built of brightly shining brass, with rods and balances sticking out at odd angles, its broad bottom and tall projections recall some ancient vessel that never existed. It looks like a cross between a galley and a galleon, with a high, ornate stern facing forward, two towering masts that carry no sails, and knobbed brass oars to be manned by tiers of unseen rowers. It is a model ship, escaped from its bottle, afloat on the sea of time.” 

Harrison’s first version of a sea clock, today known informally as H-1, is complex and ungainly: 75 pounds of brass arranged in an intricate assembly whose only resemblance to a clock is its face, with four sweep hands that track hours, minutes, seconds, and days. The clock performed well and seemed to meet the Longitude Act’s minimum standards for success. One problem, according to its creator, was that the H-1 was too big, and he spent years making it smaller.

“When the ship neared land at last, Wills assumed it to be the Start, a well-known point on the south coast around Dartmouth. That was where his reckoning placed the ship. Harrison, however, going by his sea clock, countered that the land sighted must be the Lizard on the Penzance peninsula, more than sixty miles west of the Start. And so it was. This correction greatly impressed Master Wills. Later, he swore out an affidavit admitting his own mistake and praising the accuracy of the timekeeper.” 

The success of this short trial run from London to Lisbon and back was a great public victory for Harrison’s sea clock. The test proved that a mechanical device could keep track of time accurately enough for a ship to compute its own longitude. This would have been the prelude to a much longer test voyage across the Atlantic to the Caribbean, but Harrison withdrew the clock to make improvements.

“The same vicelike conviction that led him to his finest innovations—along his own lines of thinking, without regard for the opinions of others—rendered him deaf to praise. What did it matter what the Royal Society thought of H-2, if its mechanism did not pass muster with him?” 

Harrison’s perfectionism would persist for decades, postponing the final introduction of accurate sea clocks until the 1760s. This very perfectionism, however, in combination with Harrison’s unique ways of thinking and innovating, would solve the longitude problem so perfectly that it would be centuries before even more accurate positioning systems replaced the sea clock.

“The moving moon, full, gibbous, or crescent-shaped, shone at last for the navigators of the eighteenth century like a luminous hand on the clock of heaven. The broad expanse of sky served as dial for this celestial clock, while the sun, the planets, and the stars painted the numbers on its face.” 

It became possible during the 18th century to calculate longitude to acceptable accuracy by studying the sky. This celestial, or lunar, method relied on hand-held quadrants and later sextants to sight objects in the sky, note their distances from one another, consult books filled with tables, make calculations, and finally arrive at a location east or west of a chosen home city (usually London or Paris). This entire process at first took four hours; later, it improved to just 30 minutes, but an accurate clock might reduce the time to just a few minutes.

“In addition to the need for measuring the altitudes of the various heavenly bodies and the angular distances between them, a navigator had to factor in the objects’ nearness to the horizon, where the steep refraction of light would put their apparent positions considerably above their actual positions. The navigator also battled the problem of lunar parallax, since the tables were formulated for an observer at the center of the Earth, while a ship rides the waves at about sea level, and the sailor on the quarterdeck might stand a good twenty feet higher than that. Such factors required rectifying by the appropriate calculations.”

The sheer complexity of calculating longitude at sea—careful observations, consulting tomes filled with data, and making mathematical corrections—might seem daunting, but instead it was viewed as heroic. Astronomers and naval officers believed in the process, and it did work despite the hours daily required in doing the calculations. By comparison, Harrison’s clock, with all its difficulties hidden away inside it, might require mere moments to make the same calculation. Its very simplicity, though, gave it the aura of a vulgar magic trick.

“Rome wasn’t built in a day, they say. Even a small part of Rome, the Sistine Chapel, took eight years to construct, plus another eleven years to decorate, with Michelangelo sprawled atop his scaffolding from 1508 to 1512, frescoing scenes from the Old Testament on the ceiling. Fourteen years passed from the conception to the completion of the Statue of Liberty. The carving of the Mount Rushmore Monument likewise spanned a period of fourteen years. The Suez and Panama Canals each took about ten years to excavate, and it was arguably ten years from the decision to put a man on the moon to the successful landing of the Apollo lunar module. It took John Harrison nineteen years to build H-3.” 

Great projects are great, in part, because they take so long to complete. Many of the great books were years in the making, some movies require more than a decade, and to this day, major construction work can demand a generation. Sometimes the project simply needs a great deal of painstaking work by a great many people; in John Harrison’s case, the task was important, intricate, required exacting standards, and had to be carried out by the inventor himself with little in the way of assistance. On top of that, Harrison was famously perfectionistic. The results changed the world.

“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 spent 20 years trying to perfect a large sea clock, but something stymied him about its design. Meanwhile, he commissioned watchmaker John Jeffreys to build a pocket watch to his specifications, and the result was so accurate that Harrison began to see the possibilities of a miniaturized clock. The much smaller H-4 emerged from that combination of circumstances.

“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.’”

Small enough to keep in a coat pocket, the Watch was beautifully crafted, its face elegantly painted, and its gearbox ornately carved from brass. These artistic flourishes, unnecessary in terms of pure utility, speak to Harrison’s devotion to his craft.

“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.” 

The Reverend Nevil Maskelyne, a proper and meticulous scientist, worked with Astronomer Royal James Bradley on the quadrant-and-ephemerides method that competed with John Harrison’s sea clocks for the lucrative longitude prize. As Harrison’s devices neared perfection and endured oceanic tests, Maskelyne tried to impede his opponent’s venture. It was natural that they should find fault with each other and become bitter enemies. The intense animosity between the men likely flowed in part from how personal their pursuits were; without teams of assistants, researchers, data-collectors, etc., each man was working almost entirely alone and consequently pouring years of his life into his efforts.

“Sauerkraut. That was the watchword on Captain James Cook’s triumphant second voyage, which set sail in 1772. By adding generous portions of the German staple to the diet of his English crew (some of whom foolishly turned up their noses at it), the great circumnavigator kicked scurvy overboard. Not only is sauerkraut’s chief ingredient, cabbage, loaded with vitamin C but the fine-cut cabbage must be salted and allowed to ferment until sour to be worthy of the name. Practically pickled in brine, sauerkraut keeps forever aboard ship—or at least as long as the duration of a voyage around the world. Cook made it his oceangoing vegetable, and sauerkraut went on saving sailors’ lives until lemon juice and, later, limes replaced it in the provisions of the Royal Navy.” 

Longitude is replete with asides about scientific and technical discoveries that took place alongside Harrison’s development of the chronometer. Captain Cook’s innovation was the first step in solving another (though sometimes resultant) problem: the disease of scurvy that struck sailors long at sea. Scurvy is a nutritional deficiency caused by lack of vitamin C, which sauerkraut had plenty of. Cook’s innovation is important not only to the history of sailing ships but to Harrison’s story as well, because it permitted the sailors charged with using and monitoring the K-1 sea clock to remain healthy enough to complete their tasks.

“‘Mr Kendall’s Watch (which cost £450),’ the captain reported, ‘exceeded the expectations of its most zealous advocate and by being now and then corrected by lunar observations has been our faithful guide through all vicissitudes of climates.’” 

Captain Cook’s comment reflects not only his satisfaction with Larcum Kendall’s copy of John Harrison’s H-4 sea clock but the immense success of the timepiece as a means of computing location at sea. The captain notes the clock’s cost—tens of thousands of US dollars in today’s money—which would be worth the expense to any sea captain. The search for a solution to the longitude problem was thus decisively settled, though the quest for full recognition of Harrison’s brilliant invention would extend beyond his time on Earth.

“In comparison tests, chronometers proved themselves an order of magnitude more precise than lunars, primarily because they were simpler to use. The unwieldy lunar method, which demanded a series of astronomical observations, ephemerides consultations, and corrective computations, opened many doors through which error could enter.” 

Affordable chronometers grew in number and accuracy until the cheap-but-time-consuming lunar method fell from popularity in favor of the more expensive, but faster and more accurate, chronometer method of finding longitude. The British Navy began to stockpile the devices. Fifteen years into the 19th century, several thousand chronometers were in use around the world, their prices low enough for most ships to afford.

“In 1860, when the Royal Navy counted fewer than two hundred ships on all seven seas, it owned close to eight hundred chronometers. Clearly, this was an idea whose time had come. The infinite practicality of John Harrison’s approach had been demonstrated so thoroughly that its once formidable competition simply disappeared.” 

Despite their opposition to chronometers, astronomers lost the battle for supremacy in the realm of longitude-finding. Inexpensive watches of great accuracy were easy to use, highly portable, and more accurate. The laborious process of sighting the moon against a changing night sky and consulting books filled with numbers stood no chance against the much simpler method that simply kept the time at home port on a chronometer’s face.

“‘The worst job was the last,’ [Gould] confessed, ‘adjusting the little steel check-pieces on the balance-springs; a process which I can only describe as like trying to thread a needle stuck into the tailboard of a motor-lorry which you are chasing on a bicycle. I finished this, with a gale lashing the rain on to the windows of my garret, about 4 P.M. on February 1st, 1933—and five minutes later No. 1 had begun to go again for the first time since June 17th, 1767: an interval of 165 years.’” 

Rupert Gould spent 12 years cleaning and repairing the neglected Harrison clocks and got them all to run again. The most difficult was H-1, and his description of it makes clear how painstaking the process was. This reflects the amount of patience, fortitude, and perfectionism needed to build the clocks to begin with.

“The Maritime Museum curator who now cares for the sea clocks refers to them reverently as ‘the Harrisons,’ as though they were a family of people instead of things. He dons white gloves to unlock their exhibit boxes and wind them, early every morning, before the visitors arrive.” 

The Harrison clocks, which suffered from decades of neglect, finally found the care and honor they deserve. They’re exhibited at the Maritime Museum of the Greenwich Observatory, where visitors can see the first mechanisms accurate enough to determine location on the high seas. As precious treasures of England and the world, they’re today treated with the respect they deserve.