Longitude from Dava Sobel is a fascinating account of how a virtually unknown watchmaker named John Harrison conquered one of the oldest and thorniest problems surrounding the ocean voyages - the problem of accurately measuring longitude -, which stumped even the best of scientific minds for centuries.

A fascinating problem

It was Ptolemy in ‘Geographia’, written in the 2nd century, who contributed the concept of a co-ordinate system based on the imaginary lines of latitude and longitude, for accurately plotting any spot on the surface of earth. With these imaginary lines he bought a new light in to the maritime explorations and map-making methods of his time. The sailors while at the ocean found it pretty straightforward to find their current latitude - which is drawn parallel to each other while girdling the globe – by measuring the height of the sun or any known celestial bodies.

But accurately measuring their current longitude was an entirely different case, as the longitudinal lines loop from the North Pole to the South Pole and back again in great circles, which converge at the ends of the earth. Since it is an angular measurement, which is based on time, the sailors had to have access to two different times - the current time on-board the vessel and the time at a known and pre-selected longitudinal location – at the same instance for calculating the hour differences to work out the geographical separation and the longitude. From a modern viewpoint with our easy-to-carry accurate time-telling devices and instant communication this problem, which a sailor faced in finding the exact time at two different locations, may feel far-fetched. But a sailor in the middle of an ocean pre-dating 18th century only had limited resources in the form of either a pendulum driven clock which was not at all reliable – as the factors like gravity, motion of the vessel, temperature and atmospheric pressure affected the pendulum and there by the time – or by comparing positions of moon or planets like Mars with their anticipatory positions in working out the longitudinal values; both these methods were crude with a high level of inaccuracy.

Since the days of Ptolemy, legendary scientific and exploratory minds like Amarigo Vespucci, Sir Issac Newton and Galileo Galilei did a lot of research into this matter but it took sixteen more centuries for mankind to finally invent a reliable solution for this problem.

A tragedy & the declaration of a prize money

In 1707, a British fleet of vessels under Admiral Sir Clowdesley Shovell met with a tragic disaster as the result of miscalculations in their whereabouts leading to the sinking of four warships with a death toll of more than 1600 mariners. This disaster and huge protest from the merchants and seamen resulted in the formation of a parliamentary committee for finding a practical solution for the longitude problem. This was followed by the 1714 ‘Longitude Act’ by the parliament, which promised a prize money of £ 20,000 for a suitable solution. Dava Sobel covers this formation of the committee and the announcement of the reward in detail.

Sir Issac Newton, who was consulted by the committee, at first suggested the idea of a ‘watch’ for tackling the longitude problem.

“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.”

But he believed that such a watch with too many technical challenges was not going to be a reality and was aligned more towards finding a solution for the longitude problem in the realms of astronomy.

“A good watch may serve to keep a reckoning at Sea for some days and to know the time of a celestial Observation; 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 predecessor of the modern day chronometers become a reality. At the same time another less known figure; a skilled watchmaker from Lincolnshire named John Harrison who was stimulated by the scientific and the monetary factors surrounding this riddle decided to find a solution of his own. Possessed with a brilliant mind he succeeded initially in creating a prototype and then further versions of perfect working models of the world’s first marine-chronometers thereby revolutionizing the ocean travels. His handmade sea-clocks - which are elaborate pieces of engineering marvels and still in display in working condition at the Royal Observatory, Greenwich, England - gave the world the first reliable method for measuring the longitude.

Dava Sobel records the background and each step of this pioneering invention in an easy to read form, by guiding the reader through a tumultuous story of the sheer determination and relentless pursuit for perfection from a self made man and the obstructions, unkempt promises and villainy he had to face from some of his jealous contemporaries. This concise and engaging chronicle of an innovative engineering deed covers a lot of details on the history, science and politics, which led to this invention and is a recommended read for anyone who is interested in maritime history and science.

Since I read an updated fully illustrated edition of ‘Longitude’, which was published later, the book was a treasure trove with a large selection of rare photographs - including Harrison's sea-clocks, documents of declarations, letters, scientific articles, maps and diagrams which added greatly to the value of the volume. The illustrated edition is highly recommended.

The book contains a lot of interesting information, and I am glad I read it. I enjoyed the first half. At some point, though, I got tired of reading about how unfairly Harrison was treated in his efforts to claim the longitude prize. The last part of the book seemed to drag, for me.

Se trata de una aventura científica, y de cómo John Harrison, un humilde relojero, peleó durante décadas para resolver el problema de hallar la longitud en el globo para los navegantes. Posteriormente, este desconocido autor se tuvo que enfrentar al establishment científico de la época y reivindicar su invento frente al de otros.

Es una historia brillante, muy ligera y muy bien contado. No hace falta más para recomendar este libro.

I'm not quite sure how to classify this book - history, biography, scientific treatise. But I found it intriguing and educational. It had never occurred to me how different latitude and longitude are. Since ancient times, seafarers had understood how to measure latitude (concentric circles parallel to the equator) based on the angle of the sun and the time of year. But longitude (circles which intersect at each pole - used to measure east/west distance) is much more of a challenge. Determining a position requires much more sophisticated astronomical measurement and calculation. Or, it requires very accurate measurement of time.

In 1707, the British Parliament offered a prize equal to several million of today's dollars for an accurate and useful way to determine longitude. A tremendous race began with scientists and inventors determined to claim fame and fortune. Most focused on refining the astronomic method, but some believed the problem would only be solved by developing an extremely accurate timekeeping device. Since clockmaking was in its infancy, this challenge resulted in great innovation, and that's the core of this book's fascinating story. The hero is John Harrison, an English clockmaker, who devoted his life to the quest and eventually won the bulk of the prize.

For someone who has read many books about the “Age of Sail,” I was rather ignorant about the intricacies of navigation. I knew that sailors would take noon sightings to determine their position, but little else. I have seen the word chronometer, but not understand its definition or its significance. As a result, my interest was piqued by Dava Sobel’s book Longitude, which tells the story about the historical quest to determine accurate estimations of longitude.

Due to the orientation and spin of the Earth, determining one’s latitude and longitude require quite different approaches, with the latter being much more difficult to find than the former. The impossibility of ascertaining one’s longitude made navigation across open water a risky venture, and of course led to the loss of many ships and lives. Ultimately, it was an 18th century British clockmaker named John Harrison who solved the problem of longitude by making sea clocks that would keep time better than any clock before. These sea clocks became known as chronometers and by the early 19th century became a standard and essential device at sea.

Harrison’s story takes center stage in this book, but he was not the only one looking for solutions. Naturally, this pressing matter interested many of the great scientific minds of the day, particularly the astronomers. Accordingly, the author recounts how at the same time as Harrison was working on his clocks, a series of astronomers worked to catalogue the stars and the movements of the moon against them in search of an astronomical solution.

It is a fascinating story, especially for someone from the 21st century, where issues of navigation and timekeeping have been trivialized by satellite GPS and digital and atomic clocks. The human side of the story is made more complicated by the tensions between the two parties: the Harrisons and the astronomers.

Longitude is a good primer for what I have summarized above, but I wanted a lot more out of it. The book is very short at only 175 small pages of narrative, merely an unhurried afternoon’s read. There is practically no technical details about the chronometers themselves. Instead, most of the book is dedicated to the human and historical elements in this story. Sobel eschews a strictly chronological timeline in favor of one that jumps around, in order to play up the race between Harrison and the astronomers.

The narrative’s structure suffered as a result. For example, the lack of tension over Harrison’s actual creation of the chronometer—which is told early on—undercuts the storytelling aspect of the narrative. In addition, because of the nonlinear aspect, certain facts were repeated a few times, which is very noticeable in such a short book. Another irritation was when the author attempts to build drama over the need to find a solution to the longitude problem. The issue of scurvy on long sea voyages is explained in detail with multiple examples. Implicit is the the suggestion that being unable to determine longitude caused scurvy because sea voyages could be lengthened by the resultant poor navigation, which is an illogical argument.

I have a few other minor complaints. There are a few occasions where the author indulges in some speculation and dramatization—though thankfully not often enough to become truly distracting. It is also a shame that there are no illustrations, especially of the chronometers. Lastly, I would have liked there to be footnotes, though the author does explain that she chose not to include them since this is a popular, not an academic history.

That is the crux of it. I have to credit Dava Sobel with writing a good, non-technical introduction to a little-known but important bit of history. It is not her fault that I want to know a lot more about everything in the book. Fortunately, she includes a bibliography, and there, I will hopefully be able to sate my newfound interest in the subject of navigation and horology.

n  Time is to clock as mind is to brain. The clock or watch somehow contains the time. And yet time refuses to be bottled up like a genie stuffed in a lamp. Whether it flows as sand or turns on wheels within wheels, time escapes irretrievably, while we watch.n

If you read Bryson's A Short History of Nearly Everything, and are eager for more, Longitude will be right up your alley. (I've read so many "history of science" type books, I'm thinking I should create a GR shelf just for them.) A lot of the stars of History make an appearance, including Galileo, Cassini, Newton, Huygens, Hooke, Halley, and Euler.

I read this as a biography of John Harrison, watch-maker and longitude measurer, but that doesn't start until chapter 7, a fulll 33% into the book.

The most accurate description is that this is a micro history of the development of time-keeping instruments that allowed seamen to measure longitude accurately. If that sounds kind of dry, well, it is. This is interesting, well-written, readable, and brief, but it's not exactly scintillating. This tale is a fine example of how beauraucratic red tape is no modern invention, if anything it was even worse back in the early 1700s!

I learned one shocking factoid: keeping track of your location on the ocean was a hanging offense!

n  ...on that foggy night of October 22, 1707, the Scillies became unmarked tombstones for almost two thousand of Sir Clowdisley’s troops.

The flagship, the Association, struck first. She sank within minutes, drowning all hands. Before the rest of the vessels could react to the obvious danger, two more ships, the Eagle and the Romney, pricked themselves on the rocks and went down like stones. In all, four of the five warships were lost.

Only two men washed ashore alive. One of them was Sir Clowdisley himself, who may have watched the fifty-seven years of his life flash before his eyes as the waves carried him home. Certainly he had time to reflect on the events of the previous twenty-four hours, when he made what must have been the worst mistake in judgment of his naval career. He had been approached by a sailor, a member of the Association’s crew, who claimed to have kept his own reckoning of the fleet’s location during the whole cloudy passage. Such subversive navigation by an inferior was forbidden in the Royal Navy, as the unnamed seaman well knew. However, the danger appeared so enormous, by his calculations, that he risked his neck to make his concerns known to the officers. Admiral Shovell had the man hanged for mutiny on the spot.n

The key to determining longitude is knowing what time it is compared to a standard time. Not knowing one's longitude was one of the biggest perils to ships for most of history. Astronomers felt that they would have the answer, measuring the orbit of the moon as it traverses the sky. This theory caused the building of observatories and mapping of the stars. However, what do you do when you can't observe the heavens and the seas are choppy.
Meausuring time was not considered to be a promising solution. Timepieces of the age were just not that accurate. Plus, metals in the salt air corroded, they needed lubrication, and both the metals and lubricants reacted differently in heat and humidity.

Enter one John Harrison, an unschooled woodmaker who invented a clock that used wooden gears and didn't require lubrication. Unfortunately, his ability to express himself was abysmal. That, and the fact that the scientific community of the time favored astronomers caused his theory to languish for decades before being recognized. Fascinating story for the science nerd in me!

This was the great technology challenge of the 17th and 18th Centuries. Given its importance to commerce, not to mention the lives and fortunes of mariners and the world economy, it was perhaps of greater day-to-day practical importance than the moon shot may have been in our time. The riddle was a precise measure of longitude with which mariners could navigate (and avoid shipwreck); latitude was easy enough to find given the North Star but longitude was the great mystery. Britain would, through the Royal Astronomical Society, declare a reward of £10,000, a princely sum, to the person(s) who could find a method.

This book is a concise and compelling story of the search, which would take a century and follow a number of different paths. Newer methods of celestial navigation -- plotting the locations of stars, the sun and moon -- had their champions. There was also the method of timekeeping, clockwork precise enough to be the basis of longitudinal measure, and durable enough to stand up to the rigors of climate, sea air and ship movement, and it was this method championed by John and William Harrison, Yorkshire carpenters and clock-makers. We see how each prototype would take years of careful crafting, and survive years of jealousy and intrigue among other contestants, under successive Astronomers Royal.

It's a fascinating story and not just those who have sailed or have visited the observatory at Greenwich and its prime meridian (one outcome of the contest), and this book is a worthy and intriguing account.

Really fun! Also, really short! I listened to a quarter of it or so on audio while running errands and walking around the hospital in a bit of a daze as my latest little boy was born, so I know I missed some details in the beginning. Still really great though! Sobel does a really good job of bringing her material to life and communicating information in a delightful way, and hearing Neil Armstrong's Intro was pretty cool, too.

A very interesting, and informative book that for the most part, effectively balances character with information. I did start to feel like the book needed some diagrams or pictures, because it got really difficult forming mental images of such obscure and complex devices.

This is probably my third time reading this book, and I find it deeply satisfying every time. It is not particularly entertaining - in the sense of story told, but it is very informational, and unfolds in an order that I can understand. And that's generally a big ask. I am easily confused.

Here is why we have watches, timepieces carried on our persons, and that tick-tick-tick that runs every day of our lives. Here is a tool that can determine to the inch where we are on the planet at any given moment. If that is not magic, what is????

If you are interested in the whys and hows in life, this is a basic one. You might enjoy this read.

This book was intended for the general reader. Consequently it did not deal much with the details either of the astronomical or mechanical approaches to solving the problem of finding longitude on the high seas. Instead it focused on description of John Harrison's quest to build an ocean chronometer. The author treats the difficulties Harrison encountered convincing the Board of Longitude of the efficacy of his devices as a matter of petty politics and egotism without offering the reader sufficient detail about the technical disputes to make any judgments about the scientific debate at the center of the controversy.

This book was a bit of a disappointment considering the glowing reviews it received.