I remember seeing parts of the TV movie and liking it, so when the book came up in a Kindle sale, I picked it up. I can see why it was so popular as Sobel has a clear, concise style that is informative, yet not bogged down in minutiae. It is interesting to note not only the knowledge gained in the attempt, but also the way that knowledge is judged and disseminated. Two competing paradigms for computing longitude arose, one (favored by the astronomers), depended on the distance between the moon and sun and moon and stars, the other relied on an accurate seagoing clock (chronometer). To me, the most interesting part of the story was in how far each was willing to go to prove their method was the best, with the politics of science being more important than the science itself. A quick and enjoyable read - I may have to track down the TV movie now to watch it in full.

This is a non-fiction book, which describes why knowing longitude is so important for sea voyages, multiple ways its correct and precise estimation was suggested and finally a life and struggle of John Harrison, the inventor of chronometer. I read it as a part of monthly reading for October 2022 at Non Fiction Book Club group.

The book starts with a calamity: in 1707, the Scillies became unmarked tombstones for two thousand of British troops because in the fog they went significantly off course and ran onto the ground. There are a few more examples of how ships lost their way and wrecked or lost crew to scurvy because they were unable to get their own coordinates. Moreover, it turns out that despite the oceans are vast, it was easy to ambush ships because most followed narrow routes to avoid confusion. So, in 1714 Parliamentary committee assembled to respond to its challenge, with such prominent experts as Sir Isaac Newton, by then a grand old man of seventy-two, and his friend Edmond Halley (one of the famous comet). It was assumed that the solution is in the stellar clocks – e.g. following moons of Jupiter or the movement of the Moon over the star sky to find out the precise time. Mechanical clocks were disregarded because back then a clock running fast/late by 15 minutes daily was assumed quite accurate. Moreover, the movement of a ship, and differences in temperature and humidity led even precise clocks to significant errors.

One of the interesting solutions was presented by William Whiston and Humphrey Ditton, mathematicians and friends. The idea was that sounds might serve as a signal to seamen. Cannon reports or other very loud noises, intentionally sounded at certain times from known reference points, could fill the oceans with audible landmarks. If enough signal boats, therefore, were stationed at strategic points from sea to sea, sailors could gauge their distance from these stationary gun ships by comparing the known time of the expected signal to the actual shipboard time when the signal was heard. Then Whiston hit on the idea of combining sound and light. If the proposed signal guns were loaded with cannon shells that shot more than a mile high into the air, and exploded there, sailors could time the delay between seeing the fireball and hearing its big bang. A well-timed bomb, exploding 6,440 feet in the air (the limit of available technology), could be seen from a distance of 100 miles. Therefore, a new breed of fleet must be dispatched and anchored at 600-mile intervals in the oceans shooting cannons in the air.

This scheme was untenable on a lot of points, but it was one of the more reasonable ones. However, there was no need for it for a self-taught English clockmaker John Harrison, a mechanical genius who devoted his life to the quest for portable precision timekeeping. He accomplished what Newton had feared was impossible: He invented a clock that would carry the true time from the home port, like an eternal flame, to any remote corner of the world. However, due to his own desire to create a perfect chronometer and to machinations of opponents, who favored a stellar clock approach, his first contraption sailed in 1736 on a trial voyage to Lisbon aboard H.M.S. Centurion but he received his prize for solving the problem only in 1773.

A great book with a lot of interesting facts and awesome storytelling.

"What are you reading?" "A book about marine navigation between the 16th and 18th century!" The girlfriend was not impressed.. But in all honesty, this is a page-turner. How did sea vessels navigate the great oceans before the modern-day where we simply look at a magical map with a dot showing our current location? Measuring latitude (north-south co-ordinate) is easy and has been well-known since at least the Age of Discovery: measure the angle from the horizon to the North Star, Polaris. The angle is equal to your north-south (latitude) position.

Great, now how do we know how far east-west (longitude) we are? You didn't.. until the mid 1700s. The best you could do to figure out roughly where you were was to periodically throw a log in the water to figure out how fast you were going. Then, look at your compass and log both in your logbook. Imagine doing that accurately when waves are 10 meters high and the weather is terrible. If you do something slightly wrong or don't have the ability to do it for a while, you're good old fashioned lost at sea. This primitive navigation meant that the same trade routes were plied, making piracy easy in the Atlantic, and whalers stumbling upon each other. The biggest sea-going nations at the time: the Spanish, Portuguese, British, and the Dutch were all losing ships left and right: shipwrecks, pirating, and others that just never returned.

The root cause: the inability to figure out where you were. The inability to determine your longitude. Prizes by the nations mentioned earlier went out at the equivalent of a million dollars today to find a reliable way on ships to measure longitude within half a degree of accuracy. This was one of the greatest scientific problems at the time with Newton, Galileo, and others giving it a shot. The first method that worked was Galileo's method of using Jupiter's moons (this was impossible at sea though, because even your heartbeat would throw the telescope off enough to miss the moons -- meant it was OK at land, but not at sea). When Ole Rømer looked into this method to determine longitude, he discovered discrepancies. He finally explained this by realizing that light did not instantly get from A to B, but that light like sound has a speed. Nifty by-product of solving one of the most important problems of his time.

Finally, in the mid 1700s a method was published that relied on moon's movement. You'd measure the angle from the moon to some known celestial body and consult a table published annually to convert the angle into a longitude. This could take up to four hours (!). However, there was another way that no-one thought possible: using time. If you knew the time in, say, Greenwich, England and you knew your time where you are currently -- you could figure out your longitude. Each hour difference is equal to 360/24 = 15 degrees longitude. So, say you're in tumultuous waters off the Azores and would be delighted to know where you are. At high noon you're measuring your latitude, as per usual. Now, imagine you also had a clock synced to Greenwich and you noted the time of the clock at high noon too. The clock shows 14:13:00 when the sun is at the highest altitude where you are. Your longitude then comes out to ((13.00/60) + 2) * 15 = 33.25. To find the latitude, you take out your good ol' sextant and measure the angle to the sun at 37.0 degrees, so your coordinates are (37.0, 33.25). Ta-da! You're now ready to be sent on an Age of Discovery era ship with just a compass, sextant, and pocket watch.

Problem was... no-one could create a sea-faring clock that was accurate enough. To measure within a half degree accuracy (~40km), which was required by the prize, you couldn't drift more than 3 seconds a day. Most clocks of the 1700s drifted by 5-15 minutes a day! Factor in the humidity, temperature, and vibrations at sea -- you wouldn't get even close. However, John Harrison persevered for something like 50 years finally creating a clock (through much drama with the longitude prize board) that was accurate enough. For example, one of the big problems was that some metals would shrink and others enlarge based on temperature. He'd find materials that complemented each other to keep time syncing, if one shrank, another would enlarge in harmony. The clock worked, but was only available to few as it was expensive and took years to create each one. James Cook had one, and found it invaluable to chart out the Pacific. Over the next 60 years other clock-makers made it cheaper and cheaper by decade. By the 1850s, almost everyone was using a chronometer derived from Harrison's and lunar tables went into the pages of history.

I really enjoyed this book. Great science tale of solving a massive problem, being biased toward a particular type of solution (astronomy), discovering useful other things along the way (speed of light), and perseverance.

The book, unfortunately, can't get the 5th star. The reason comes down to how there's not a single picture in the book, which makes the concepts hard to understand. I had to read up on them independently of the book to understand them properly. Dana seems to skate over the significance of the lunar distance tables that predated Harrison's clocks, which is a shame, because they were a revolution themselves despite their complexity.

4 ☆

Before Britannia could rule the waves, its captains needed to figure out where their ships were going and, just as importantly, how to return home.

Sure, the concept of sectioning off the world by concentric lines of latitude (running east-west) and longitude (aligned by the poles) had existed as early as 300 B.C. The astronomer and cartographer Ptolemy had plotted in 150 C.E. his first world atlas with the Equator as 0° Latitude. Many dedicated astronomers had already witnessed that the sun, moon, and planets passed almost directly overhead at the earth's equator so Ptolemy's decision had been based on scientific observation. But for centuries, where to set 0° longitude was a political selection, so it had bounced around from the Canary Islands (Ptolemy's choice) to Rome to Jerusalem and to many more locations. Finally in 1884, representatives from 26 countries agreed at the International Meridian Conference to make the Greenwich meridian the world's prime meridian.

In Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time, Dava Sobel focused on the 18th century when the British and many others (except perhaps the Polynesians - see Sea People: The Puzzle of Polynesia) were beset by maritime misadventures and tragedies. In the early 1700s, determining a ship's position was a highly imprecise and challenging process as the main method of navigation was by dead reckoning, guided only by compass and the direction of the sun's path. Sailors could reasonably determine which latitude the ship occupied but they were literally and figuratively "at sea" when it came to the question of their longitudinal location. [Sextants weren't invented until the 1730s. Even then celestial navigation would require hours of observation, nautical charts, and an accurate timekeeper.]

The continued loss of ships, lives, and cargoes finally motivated London's various shipping interests to unite in their petition to Parliament to solve the "longitude problem" (which was really a navigation problem). The Longitude Act of 1714 established the Board of Longitude as judges to determine the recipient of prize money which ranged from £10,000 to £20,000, depending on the solution's level of accuracy. According to the Bank of England's inflation calculator, the 1714 prizes would be equivalent to £1.5 to £3 million today.

Dava Sobel wrote an interesting narrative about an unlikely hero, John Harrison, who became enmeshed in a David and Goliath battle that lasted decades. Although John Harrison worked as a carpenter, his mind had mechanical inclinations. He taught himself how to make a clock before he turned twenty. Upon learning of the prize from the Longitude Act, he sought to create the perfect timekeeper, despite the ways a moving vessel with its humid atmosphere eventually rendered all contemporaneous clocks erroneous. When navigators simultaneously knew the local time aboard the ship and the time at another location which had a known longitude, then they could could calculate their ship's longitude.

The Board of Longitude consisted of government officials, naval officers, and scientists from both astronomy and mathematics. By the mid-18th century, one Board member -- the astronomer royal Reverend Nevil Maskelyne -- keenly wanted a solution that reflected his scientific discipline. In particular, Maskelyne favored the lunar distancing method. He/the Board adopted unscrupulous methods to thwart Harrison: sabotage, backstabbing, and theft of intellectual property. Maritime navigation is a technical issue, but this tale reeked of jealousy, competitiveness, and political intrigue. Nothing like money and professional glory to elicit all the ugly sides of human nature.

Be still my geeky heart because this little book (4 hours for the audiobook) touched upon maritime history, astronomy, timekeeping, and even cartography. For an esoteric topic, this story was engaging, concise, and clear. The book only lacked images.

This link shows John Harrison's first submission for consideration. Completed in 1735, the H1 weighed 75 pounds and was housed in a 4' x 4' x 4' case.
https://www.rmg.co.uk/collections/obj...

This link is for Harrison's prize-winning H4, finished in 1759. This elegant chronometer with its pretty detailing had been miniaturized down to a diameter of 5 inches.
https://www.rmg.co.uk/collections/obj...

Harrison was an inventor with a perfectionist's streak. He continued to improve his masterpiece. This link is for John Harrison and Son's H5, made in 1770:
https://collection.sciencemuseumgroup...

This book is just about perfection. Why and who decided to venture out and sail the "flat" world and risk dropping off the edge? How did charts and early navigational equipment come to be? There is latitude but what is longitude and who are the pioneers of this science? Answers all contained but in an easy to read and understand book. Well recommended.

De esas historias que nos hubiera encantado que nos la contaran en la escuela.
Sin duda, Zweig debió incluir a John Harrison en sus Momentos estelares de la humanidad, por todo lo que representó el problema de la longitud por tantos siglos. No me explico como Zweig no lo metió, quizá por falta de tiempo, en fin...
Un libro de divulgación ameno, que nos lleva de la mano a comprender este acertijo que dio tantos dolores a los navegantes, hasta que un humilde relojero-carpintero trajo la solución con un artefacto que parecía venir de otro mundo. Halley, Newton y otros personajes menos amables que fungen como los típicos villanos-antihéroes gravitan alrededor de este maravilloso momento estelar de la mente del ser humano.

As far as popular science writing, or popular history of science writing (take your pick) goes, I've read better books. This is a book about a self-taught village clock-maker who created a whole new breed of amazingly precise chronometers, which enable the accurate measurement of longitude, and the fight he had with astronomers to get his solution recognised (and rewarded). High stakes (both in terms of the potential benefits to be had from being able to use longitude, and in terms of the reward value placed on finding a solution), but while the author keeps on reminding us that it's very important, and telling us that his struggles with the politics of the board who were supposed to award the reward were very severe, I generally felt underwhelmed by the story, or maybe the way it was being told and structured.

After starting off very dramatically, (at one point even blaming the problems of scurvy on the inability to find longitude), the early part of the story of John Harrison (the clock-maker) seemed pretty bland and lacking in tension. When tension did arrive later on (basically after he'd already solved the problem), everything got kind of rushed through - it is a very short book, and it might have been better with a little more time devoted to rounding out some of the ideas, so that diversions into a brief recap of Captain Cook's death, or the voyage of the Beagle actually felt like they belonged, rather than being shoehorned in for some broader appeal. All in all, I ended up feeling like Sobel had manufactured a bunch of tension and drama, but not actually delivered on filling in the colour and texture of it all.

It's not a bad book, but it itches for a rewrite for hacking and resorting and building into a better flow.

On October 22, 1707 four English warships crashed into the rocks of the Scilly Isles southwest of England. They quickly sank killing 2,000 men. The cause of this catastrophe was the inability to determine longitude, a problem that beset mariners everywhere. In 1714 the British Parliament set a £20,000 reward for whoever could solve the problem. The Board of Longitude, which would be primarily comprised of astronomers, was set up to award the money. To win the full prize, the method or device had to be accurate to within one-half degree on a trip from England to the West Indies.

There had been many ideas about how to determine longitude, but none worked reliably. They fell into two basic camps: the astronomical and the clock. The idea behind astronomy was to find a pattern of stars, the track of the moon or even the eclipses of the four known moons of Jupiter that would yield longitude. The clock idea was based on time difference. 15 degrees of longitude equals an hour. So a clock that could keep accurate time set to London time could be compared with a clock set to local time. The local time could be determined by sighting the sun at noon. The time difference would give the degrees of longitude from London. But prior to the eighteenth century clocks didn’t work reliably in the rough environment of ships at sea, so the London clock would be off.

In 1727, a self-educated village carpenter and clock maker, John Harrison, heard about the prize. In 1730 he had plans for a chronometer as mariner’s clocks of sufficient accuracy would later be called. He showed his plans to Edmund Halley of comet fame, a board member, who sent him to a prominent clockmaker and fellow Royal Society member who encouraged Harrison to build his clock. Five years later Harrison presented the clock to the board. He had been able to take it on a voyage to Lisbon where it proved its worth. Harrison’s clock was original, intricate and exquisitely crafted. The board was impressed but Harrison himself was not. He felt he could do better and took another five years to build a second chronometer. The Royal Society tested the second clock and gave it accolades but Harrison again decided he could do even better and took twenty years to build a third.

In the thirty years Harrison was building his three clocks astronomers were busily cataloging stars and navigational instruments were vastly improving. By 1760 the board was considering a complicated but effective method of calculating a ship’s longitude from the positions of the moon and stars. And since the board was mostly made up of astronomers, they instinctively preferred an astronomical solution to a simply mechanical one.

Harrison was awarded the prestigious Copley Gold Medal in 1749 at the recommendation of the Royal Society for the many innovations he had made in his clocks that made them so accurate and reliable. But as usual Harrison himself was the hardest to satisfy. Immediately after completing clock three he built a fourth, a pocket watch that ultimately would win the coveted prize. On a West Indies trip the pocket chronometer worked perfectly, but the astronomers on the board dawdled about awarding the prize since they were now enamored with an astronomical solution.

Since presenting his first chronometer, Harrison had been receiving stipends so that his work could continue, but the prize was elusive. Harrison felt his chief nemesis was Astronomer Royal, Nevil Maskelyne, a strong advocate of the astronomical method. Maskelyne took it upon himself to conduct further tests on Harrison’s watch. Finally in 1765 the board awarded Harrison £10,000, half the prize, and ordered him to make two more of the watches to show it could be duplicated. The board also commissioned another clockmaker to build an identical twin of Harrison’s watch. The twin was selected to accompany Captain Cook on his second voyage around the world. The chronometer won high praise from Cook who used it to make accurate maps. Finally through the intervention of King George III, Harrison received a final £8,750 in 1773.

One of the biggest problems with Harrison’s chronometer was the cost, at least £400 to duplicate when a sextant and tables cost £20. But fifteen years later the price would drop to £80 and would keep declining. By 1815 over 5,000 chronometers were in service. The problem of longitude had been solved.

Sobel’s short history reads quickly. The book contains nice photographs of Harrison’s clocks showing their complex inner workings. The chronometers have been restored and now reside in British museums. Sobel explains some of the principles of clock mechanisms and details some of Harrison’s innovations. She also covers failed as well as successful astronomical approaches to finding longitude. But this is also a human interest story of an odd difficult man, a homespun insular genius, who faces the complex scientific society of eighteenth century England. Recommended for the science buff and general reader alike.

3.5 stars

For a very short book—175 pages of text, and they’re small pages—this little work of history packs in a decent amount of information. It’s about the centuries-long quest to discover an accurate way of measuring longitude at sea, and particularly the 18th century British solutions.

With the right instruments and calculations, latitude is fairly easy to determine from the position of the sun and stars; people have been doing that for millennia. Longitude is much harder, because everyone at the same latitude sees the same sun and stars, just at different times of day. Essentially, the earth is a giant clock—so, without satellites, how to figure where on it you are, especially at sea without landmarks? For centuries, thinkers have understood that the answer was measuring time, and eventually two possible solutions emerged. One was observing a celestial event (Galileo chose the eclipses of the moons of Jupiter) and comparing the local time at which it occurs to the time calculated in an almanac at which it will occur at some known location. The other was comparing your local time, determined through the angle of the sun, to the time at some known location, from which you can calculate the degree of difference between the two places. Unfortunately, up through the 18th century, there were no sufficiently accurate instruments to use either of these methods at sea, resulting in great loss of life when navigators didn’t know where they were. (Not helped, in the British fleet, by an apparent rule prohibiting common seamen from keeping tabs on the navigation themselves. One brave soul came forward with his calculations in an attempt to avert a disaster and was promptly hanged for mutiny, his warning ignored; the fleet then foundered and most of the crew died.)

The book summarizes the situation and the journey of 18th century clockmaker John Harrison to building timepieces that could keep sufficiently accurate time (despite the jostling, temperature and humidity changes, etc., that had doomed prior sea clocks) to allow ships to find their way. It’s readable and interesting, and I certainly learned a lot about early clocks and watches and the mathematics of navigation, as well as some fun tidbits on a variety of other topics. There’s also a lot about the jostling for position among the various men who wanted to claim credit (and a large financial reward) for solving the longitude problem.

On the other hand, the book is quite brief, and the author seems overly enamored of Harrison, though she doesn’t actually refer to him as a “lone genius” as stated in the subtitle (he seems to have collaborated as much as anyone else at the time, when there was less apparent need for lab assistants than today). It seems odd that she never addresses what appears to me the reason most people won’t have heard of Harrison: in the sciences we tend to lionize those who came up with big ideas, rather than the hands-on technicians who made them work. And Harrison was an instrument maker, very much a hands-on technician; his wasn’t a conceptual breakthrough but a technical one.

Overall, a perfectly adequate book, though not to my mind a remarkable one. But if you’re interested, it’s worth taking a look as it certainly won’t take long to read.

I had gotten glowing recommendations for this book, but it left me disappointed. For a book about the history of technology, there's precious little technology in the book: Harrison's marine chronometers are repeatedly praised, but there's little in the way of description of how they work, or why they represented such an advance in clockmaking. Sobel will frequently describe a piece of clockwork, then say that Harrison didn't or couldn't use it in his marine timepieces, but without ever saying what Harrison did instead. H4 and H5, the miniaturized sea watches, are given particularly short shrift, with almost zero description of how they work. Sobel describes what they look like, their external appearance, but opts not to go deeper, beyond the surface, and explain their workings.

My other disappointment is that there are no pictures or illustration of any of the clocks or even clock mechanisms to support the text. Early in the book, Sobel tries in vain to describe what a grasshopper escapement looks like, but it seems like she gives up on this by the end of the book, and simply references clock pieces without attempting any description at all.

"Longitude" is a narrative, not, as Sobel admits/claims in the acknowledgements, "a scholarly study." The story is certainly engaging, and well told, but Sobel sometimes lets the narrative arc of the Harrisons' shabby treatment by the Longitude Board overwhelm common sense. Quoting from Chapter 13,

"""
Seeking proof positive of H-4's true reproducibility, the board also hired the watchmaker Larcum Kendall to attempt an exact copy. These efforts evince the board's ferocious pursuit of the spirit of the law as they interpreted it, for the original Longitude Act never stipulated that the "Practicable and Useful" method must be copied by its inventor or anyone else.
"""

A marine chronometer that cannot be reproduced at scale is not "Practicable and Useful". Citing this as evidence of John Harrison's misuse by the Board is letting the story get ahead of the facts.

Overall, I found "Longitude" a good popular overview of this piece history, but it left me wanting more detail about the technology being chronicled. Have Google handy when reading it so you can look up terms like "backstaff", "reflecting quadrant", "winding rods", "grasshopper escapement", etc, as you go.

A fun and informative little non fiction book about something I knew nothing about. It's a dramatic tale, filled with neat historical tidbits. It's worth a read, especially if you have no idea about the quest to find longitude at sea!

If you are expecting 200 pages of mechanical drawings and equations, or even a detailed explanation of how Harrison's clock worked, you're out of luck. Likewise, if you're expecting a a blow-by-blow account of his inventions and dealings with the Board of Longitude, you are also going to be disappointed.

However, if you are looking for an interesting, fast read about the problems of calculating the longitude of a point on earth and how these were eventually solved, you have come to the right place.

This is popular science-history - a tale of people and personalities as well as inventions and discoveries. Sobel's writing is accessible and her verve carries the reader along in the same way as reading a good novel. In just over 200 pages, there isn't much in the way of detail - but the reader does come away with a broad-brush overview of what the problem was, the reasons why it was so intractable, the various methods for solving it, and why the problem was solved in the way it was.

I do find it interesting, though, that Sobel didn't comment that one of the early, wacky 'solutions' proposed - that of anchoring ships at strategic points in the oceans and having them fire off flares that passing ships could then use for position fixes - has come full circle. Only now we have satellites and radio signals instead of ships and flares, and Harrison's clocks (and the chronometers that followed) may themselves become obsolete eventually.