Longitude

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1:27It's October the 22nd, 1707, near the Isles of Scilly. A heavy storm is pressing down over the Atlantic, wind stirring the sea into an angry frenzy under a seamless black sky. HMS Association, a 90-gun warship, is guiding a fleet of over 20 English ships towards the western end of the English Channel. By now scattered and spread out thanks to bad weather, the fleet is under the command of Sir Admiral Cloudsley Shovel, one of England's most experienced naval commanders. They're returning from the war of the Spanish succession, homeward bound after months in the Mediterranean. At least, they're meant to be.

2:17England lies somewhere ahead. But for days, the sky hasn't cleared once to give them a view of either sun or stars. So they've had nothing to take a bearing from. No way to fix their position upon the sea. The ship rises, pauses, and drops again, hard enough to jar the teeth. Below deck, a young sailor grips the edge of a gun carriage as the floor tilts beneath him. His hair is salt stiff, his hands roar, and his body moves by instinct, bracing before each roll. Like the others on the gun deck, he has been weeks without a proper night's sleep. They are all exhausted, hungry, and desperate to be home.

3:07Though the sailor can't hear the words of the orders bellowed to the men above, you can hear the tone, and the tension it carries travels through the timbers. Every man aboard shares the same feeling of dread. The sea is always threatening and uncertain, but with no means of knowing where they are, right now it's even more so. Though they've already avoided countless untold unseen dangers by little more than good fortune or divine intervention, what lies ahead is an unfathomable labyrinth of peril. And their luck, surely, can only hold out for so long. The sailor shifts his grip as the ship lurches again.

3:47Across the deck, a cannon slams against its restraints, and another man scrambles to secure it. They climb another swell, and for a moment they hang suspended in time and place. Then, an awful grinding crunch tears through the ship, rumbling up through the hull like a kraken awoke. The deck heaves violently as the vessel comes to an immediate halt. The sailor is launched sideways, crashing into timber and iron. Around him, men are thrown against cannons, bulkheads, and each other. Though the fleet isn't yet supposed to be anywhere near land, the ship has run aground, stopped dead in her tracks.

4:38The freezing sea surges in below, and the sailor drags himself upright, hands slipping on wet wood. Scrabbling onto the sloping top deck, he narrowly avoids being crushed as the mast cracks and plummets. Blinking through the driving rain and spray, he sees others in the fleet meeting the same fate as, one after another, they are driven blindly onto the rocks. HMS Eagle, Romney and Firebrand are all sinking.

5:17By morning, the sea will be strewn with wreckage and bodies. the greatest maritime disaster of the age, claiming nearly 2 ,000 lives. But they have been taken by a problem less tangible than war or even weather. Out here, in the dark, with no sun and no stars, the world has no fixed edges. No reliable measure of east or west. And without that, even the greatest fleet in the world is easily lost. Battles may have been won at sea, but longitude remains unconquered.

6:02It was once one of the great unsolved problems of the early modern world, the calculation of exactly how far east or west a given point was on the surface of the Earth. Longitude was a challenge that sat at the intersection of science, navigation, empire, and time itself. For centuries, sailors had been able to determine latitude, or their position north or south, with reasonable confidence. But its counterpart remained dangerously elusive, leaving those traversing the oceans vulnerable to error, shipwreck, and disaster. In the search for a solution, astronomers, inventors, statesmen, and seafarers all played their part.

6:47But why was longitude so hard to figure out reliably? Who really solved the problem? And what changed when sailors could finally measure their position at sea with precision? I'm John Hopkins. From the Noiser Podcast Network, this is a short history of longitude.

7:15For as long as sailors have ventured beyond sight of land, they have faced a simple but vital problem. How can you be sure where you are, out on the open ocean, where there are no landmarks or fixed points to guide you? The north-south question, or latitude, is relatively easily solved. By measuring the height of the sun at noon, or the position of known stars, a navigator can estimate how far they are from the fixed points of the equator or the poles. It's still a kind of estimation, but at least it's reasonably reliable. Dr Emily Ackermans is curator of time at Royal Museums Greenwich. What sailors used to do was rely on dead reckoning.

7:59So this is a method that they measure their speed of travel, their direction of travel, they take into account currents and wind directions, and they're constantly estimating and plotting where they are. Though this method gives some certainty of a latitude, the east-west question of longitude is another matter entirely. On land, being wrong about your position might mean a delayed journey or a missed turning. At sea, it can be fatal. The problem with longitude is you need a measurement of time because you're measuring the rotation of the Earth. So longitude was all about knowing a difference in time.

8:39So in theory, it's really simple. If you know a difference in time between two places, so for example Greenwich and wherever you are on the ocean, if you know the difference in time between these two places, you know your longitude. Because the Earth spins 360 degrees in 24 hours, you can break this down. So that means 180 degrees in 12 hours, 90 degrees in 6 hours, 45 degrees in 3 hours, etc. So if you know you are 3 hours exactly from Greenwich, you know you are 45 degrees east or west of Greenwich. The theory sounds straightforward. In practice, it is anything but. To calculate longitude, you need to know two times at once.

9:22the local time on your ship and the time at your reference point far away. Local time can be estimated from the position of the sun, though that is dependent on clear skies and careful calculations. But the second value, the time somewhere else, requires a clock that remains precise for weeks, even months, at sea. Before the 18th century, no such timekeeper exists. The best clocks of the age rely on pendulums and delicate mechanisms that simply cannot keep steady time aboard a rolling ship with their damp, salty environments and extremes of heat and cold. Without that second measurement of time, accurately calculating longitude is impossible.

10:10As trade expands and empires stretch across the globe, this problem of crossing vast distances safely and arriving where and when you intend takes on new urgency

10:28By the late 15th and early 16th centuries, European voyages are pushing farther than ever before across the Atlantic, around the southern tip of Africa, and deep into the Indian and Pacific Oceans. Ships sail out heavy with cloth, metalware, weapons, and other trade goods, and return heavier still with silver, spices, textiles, and increasingly human cargo. Merchant ventures like the British or Dutch East India companies establish global networks, with navies to protect them. But though entire economies depend on the safe movement of ships across open ocean, the crucial element of longitude remains uncertain.

11:11And that is a daily, practical danger. It was particular routes, in particular the East India companies, so the Dutch ones, the English ones, they are sailing down south and they are having to turn east and then they're going to have to head north at the right time. They don't want to go too soon, they don't want to go too late, this could get them into trouble. So for them, it's really important to know exactly when to set that new course for ships.

11:40A small error in east-west position can have enormous consequences. Turn too soon and a ship may miss its destination entirely, lost in open water. Turn too late and it risks running aground on an unfamiliar coast, or inadvertently straying into a rival nation's territory, sparking war. Longitude becomes one of those rare problems where science, war, commerce, and state power all converge. And with the stakes rising, the question is, who will solve it first?

12:21In the desperate search for a solution, thinkers across Europe propose all manner of ways to determine longitude. But broadly, two approaches emerge. One looks to the heavens, the other to machinery. The celestial approach comes first. In the early 17th century, Italian astronomer Galileo Galilei proposes using the moons of Jupiter as a kind of universal clock, since their orbits are regular and predictable. By observing them and comparing their position to tables calculated at your starting point, it's possible to determine how many hours from home you are, and from that, your longitude. It's an elegant idea, and on land it works, but at sea it quickly falls apart.

13:11A telescope is hard enough to use on a stable surface. On a rolling deck, in wind and spray, it becomes almost impossible. Even the most brilliant astronomical solution is useless if it cannot be applied in the real conditions of a voyage. Still, the idea of using the heavens as a clock gains traction. and soon becomes the focus of a major new effort. In the late 17th century, the search for longitude is already an international race. Spanish, Portuguese, French, and Dutch navigators have all grappled with the problem, and governments across Europe have begun offering rewards for a solution. In the 1670s, a French astronomer called Jean Picard arrives in London, claiming he has found an answer by using the moon and stars to determine longitude at sea.

14:05But when a panel of experts examines his proposal, one problem becomes immediately clear. The method depends on an enormous amount of precise astronomical data. And that data does not yet exist. Among those consulted is British astronomer John Flamsteed, who argues that though the system is solid in theory, without far more accurate observations of the heavens, it just can't work. And so, in 1675, under the orders of King Charles II, the Royal Observatory Greenwich is established, with a clear purpose of improving navigation by measuring the heavens. Under Flamsteed, the first astronomer royal, they begin the painstaking work of mapping the stars.

14:55Night after night, observations are recorded and tables compiled of the angles between the moon and a fixed star at any given time in Greenwich. In these tables, the astronomers create a reference system that sailors might one day use at sea. And from this effort springs one of the most promising solutions yet. so a very important method which comes into use in the second half of the 18th century is what's known as the lunar distance method which is basically at its simplest you're using the heavens as a giant clock so the stars form like the dial of the clock and the moon moves relatively quickly against this background so you're basically using the moon as like the hands of your clock and it's actually a really complex method but what you're doing is you're observing the angle the distance between the moon and the sun or the moon and a thick star star you know the position of this is where it gets complicated what the astronomers have done at greenwich is they have predicted at which time that angle will be visible at greenwich so you look up that same angle in a table and that gives you your time at Greenwich.

16:10So a very complex but very important method. The hope is that by measuring the angle between the moon and a known star and comparing it to the Greenwich tables, a navigator could determine the time back home. From that, longitude might be calculated.

16:33It is a remarkable solution, but it is mathematically complex. It requires careful observation of clear skies, meticulous measurements, and time-consuming calculations. And interpretation of the resulting data requires skill and training. It works, but it's not easy. Worse still, the work required to make it practical takes decades. John Flamsteed spends more than 40 years compiling the necessary observations with sufficient accuracy. Others will continue the work after him, refining and expanding the data. It takes 100 years before the nautical almanac is actually published, so before sailors can actually use this method at sea, because there's so much they needed to know.

17:22They needed all this accurate star data. They needed to understand the moon's motion is really complicated, so they needed to understand how the motion works, because everything they need to do is predicting future positions. But while the astronomers continue their painstaking work, another idea comes into focus. If longitude depends on knowing the time somewhere else, why not carry that time with you? A portable clock set to a fixed reference point could provide the answer directly. But even now, clocks are delicate and unsuited to conditions at sea. No timepiece can survive a long sea journey with its accuracy intact.

18:05The search continues, but the stakes are only getting higher, as more voyages are undertaken, meaning more ships, cargo, and lives lost at sea.

18:22In 1714, the British Parliament passes the Longitude Act, turning the hunt for a solution into a formal, state-backed challenge. Substantial rewards are offered, scaled to accuracy, with up to£20 ,000 on offer, around£3.5 million today, for a method that can reliably and repeatedly determine longitude at sea. To oversee the process, a group of leading politicians, naval officers and scientists is appointed, alongside the Astronomer Royal, to evaluate proposals and to fund and test potential solutions. This body will become known as the Board of Longitude They are the people who oversee the ideas, the schemes Whether they're plausible, whether their ideas deserve merit Whether they deserve a reward And how trials will take place So if someone comes up with an idea They might be able to get some money to work on their idea And if that works out well, then they can ask for a trial And if they find the perfect way of finding longitude at sea They will get the reward Now, alongside the learned astronomers and scientists, the field of endeavour widens to include those beyond the established academic world.

19:36And in the coming decades, one such maker will emerge from a small market town in Lincolnshire with an idea for a clock that can keep time at sea. John Harrison is a man who can turn a skilful hand to many things. We don't really know loads about him as a young lad, but he does grow up. He becomes an intelligent young man. He learns land surveying. He learns carpentry. He has an interest in music. He tunes the bells for the local churches. He plays the bass viol. He's the choir master. And he starts making clocks. He is not a university-educated astronomer, but he is a practical and talented maker.

20:23Working first alone and then alongside his brother James, he sets out to build timepieces of extraordinary precision. But he quickly runs into the limits of existing clockmaking. Even on land, keeping accurate time is a delicate business. The performance of a clock depends on the behavior of the materials inside it. Changes in temperature cause metal components to expand and contract, subtly altering their movement In a pendulum clock, even the slightest variation in length is enough to change the rate at which it keeps time Since a pendulum is made of metal, which swells and becomes longer as it warms, this is a significant problem There are other issues too Inside the mechanism, multiple moving parts are in constant contact, creating friction.

21:19Clockmakers try to reduce this with oils, but the lubricants available at the time are mostly animal fats, which thicken, dry out, or degrade, and which can introduce further inaccuracy or stop the clock altogether. These fundamental obstacles to accurate timekeeping, for most clockmakers, are simply accepted as part of the craft. but Harrison approaches them differently. So basically Harrison with his brother James, they start making precision clocks and Harrison has this ingenious way of working and combining materials such as lignum vitae, a tropical hardwood with self-oiling properties, combining this with brass and just making his clocks in such a way that there actually is no friction in them.

22:05And this is incredibly unusual and he doesn't require any oiling at all. So he's kind of eliminated one big problem that's causing inaccuracy in clocks. And the other thing he does is this temperature problem. He creates what's called the gridiron system. So to stop the pendulum's length from changing, he comes up with this system of brass and steel rods. And because steel reacts different to brass, to temperature changes, it's cancelling out each other's movements. so it's not affecting the length of the pendulum, which is determining the timekeeping. So these are two huge achievements, and he's doing this in the 1720s.

22:45So he could have gone into the local history books from here, but he hears about this act of longitude, the rewards on offer, and he thinks he can make a C-clock.

22:59Convinced that the longitude problem can be solved by harnessing time in a suitable machine, Harrison journeys to London to the Royal Observatory in Greenwich. He meets with the astronomer Royal, who by this point is Edmund Halley, after whom the comet will later be named. Halley is no clockmaker, but likes Harrison's idea. He suggests he meet with one of London's most prestigious clockmakers, George Graham, who already supplies astronomical instruments and clocks to the Royal Observatory. John goes to see George and stays all day at George's workshop chatting about clocks and clockwork and he stays for dinner and he leaves with an interest-free loan from George which is very kind of him and so he goes back up north, back to Barrow-pon-Humber where he's living and he and his brother James start working on what's known as H1 Harrison's first sea clock John and James Harrison begin to build H1 in 1731 and four years later, they are ready to demonstrate it.

24:04The brothers transport the timepiece down to London and show it in George Graham's workshop to much attention and praise. The real question, though, is whether it can remain accurate at sea. And so H1 is sent on a trial voyage to Lisbon in 1736. It performs well, keeping time accurately enough to correct the ship's longitude during the journey. So it did really well. The captain was impressed, but there were sort of like limits of accuracy to which these reward schemes were. So it had to be an accuracy of half a degree, I believe, of longitude to get the biggest reward on offer. And although it was really good and really promising, it was not good enough to go for one of these larger rewards.

24:48But it was so promising that the board comes together for the first time. I think they're not a board at this point. I think they just come together as commissioners, you know, are impressed as well by Harrison's clock. and he gets£500 to go away and work on an improved version. With that£500, around£100 ,000 today, the brothers move to London to start work on H2. James doesn't take well to the city though, and soon returns to Lincolnshire, leaving his brother alone to his work. In London, John Harrison has access to some of the country's finest scientific instrument makers to help his designs.

25:28And while H2 looks very different, internally it's a fairly similar machine to its predecessor. But as work progresses, Harrison begins to see a problem. At the heart of the clock are two large, weighted bars, which act as balancing mechanisms that swing back and forth to regulate the timekeeping. They work well in controlled conditions. But a ship at sea rolls and pitches, and Harrison realizes that these complex shifting motions will interfere with the movement of the balances in ways he cannot fully predict or control. It is a fundamental flaw, and it cannot be fixed with small adjustments.

26:11So Harrison makes the remarkable decision to abandon the H2 design and start again with H3.

26:21H3 is a fascinating machine. In it, he changes his bar weights, he changes them into two massive round balances. He also incorporates a bimetallic strip, so the temperature compensation is basically two metals fused together, steel and brass, and he puts this in such a way that that will compensate for any temperature changes within the object. A version of that device operates inside the thermostat of most modern kettles today. And it's not the only innovation we have to thank Harrison for. Another thing he does is the cage roller bearing, again another anti-friction device, which we now see everywhere in engineering as the ball bearing.

26:59So there's some pretty cool parts to H3. But it never works to his expectations. He finishes it in a couple of years, but he spends 19 years working on it, and he never gets it right.