John Harrison: The Carpenter Who Solved the Longitude Problem
The Remarkable Story of a Genius Who Revolutionised Navigation
In the early 18th century, the problem of accurately determining a ship’s longitude at sea was one of the greatest challenges facing sailors. Without a reliable way to measure longitude, ships often found themselves lost at sea, leading to countless tragedies and significant loss of life and property. It was in this context that John Harrison, a self-taught carpenter, and clockmaker from England, would emerge as the unlikely hero who would solve the longitude problem and revolutionise navigation forever.
Quick shout out to Wouter van Wijk who put me onto this awesome miniseries which was the inspiration for this post. The bad news: you can’t rent or buy this old film on the usual platforms. The good news: you can watch it for free on YouTube (~3hrs).
ScrewDownCrown is a reader-supported guide to the world of watch collecting, behavioural psychology, & other first world problems.
The Longitude Problem
You’ve probably already heard how the longitude problem had plagued mariners for centuries. Determining latitude was fairly easy, using the position of the sun or stars - but longitude seemed to have baffled everyone for a while. Longitude is a measure of east-west position on the Earth’s surface, and without an accurate way to determine it, sailors had no way of knowing how far east or west they had travelled.
The problem became so dire that the British government eventully passed the Longitude Act, offering a prize of up to £20,000 (~ £3.58 million today) to anyone who could devise a practical method for determining longitude at sea1. The act established the Board of Longitude, a group of experts who would evaluate proposed solutions and award the prize.
What was so difficult, exactly?
Measuring longitude accurately was a major challenge because it required precise timekeeping. Latitude can be determined using the altitude of the sun or stars – these are measured fairly easily (apparently) using instruments like the sextant.
Longitude, however, is a measure of east-west position on the Earth’s surface, and there is no easy way to determine it based on celestial observations alone.
To understand why this is the case, consider the images above with lines of latitude and longitude as shown. As you can see, the lines of latitude run parallel to the equator, while the lines of longitude run from pole to pole, intersecting at the poles.
As the Earth rotates on its axis, the position of the sun in the sky changes at a steady rate. At noon, the sun reaches its highest point in the sky - this is known as solar noon - and it occurs at different times which are correlated with your longitude. We all know how, as the Earth rotates, the sun appears to move across the sky from east to west…
Some may view this as a contradiction. Why are we concerned with the solar noon and longitude which runs from north to south, when the sun moves across the sky from east to west? The simplest approach I have found to make sense of it, is to think of lines of longitude like lines on a ruler. The lines on the ruler actually run perpendicular to the thing you are measuring. As you measure along a dimension (like a piece of paper), you are counting how many of these perpendicular markings on the ruler you ‘cross.’ In the same way, measuring longitude, (which runs north to south) is measured perpendicularly (which is east to west)!
In other words, the big puzzle being solved was as follows: if you know the time difference between solar noon at your location out in the middle of the ocean, and solar noon at a reference point (such as the Prime Meridian in Greenwich, England), you can calculate your longitude, and therefore, will know exactly where you are. You see this in the film I mentioned at the start… The sailors would always take measurements at the location they were departing, just before they departed - this was their baseline which would be referenced later at sea.
If this is still gobbledygook, consider this mathematical example: If solar noon occurs one hour later at your location (say, in the middle of the sea) than at the Prime Meridian (where you started), you will know for sure you are 15 degrees east of the Prime Meridian (because the Earth rotates 360 degrees in 24 hours - which is 15 degrees per hour).
The challenge, of course, is knowing the precise time difference between your location and the reference point. This requires a clock or watch that can keep accurate time over long distances and under the harsh conditions of a sea voyage.
To quote Dava Sobel in her book Longitude:
“To learn one’s longitude at sea, one needs to know what time it is aboard ship and also the time at the home port or another place of known longitude-at that very same moment. The two clock times enable the navigator to convert the hour difference into geographical separation. Since the earth takes 24 hours to complete one full revolution of 360 degrees, one hour marks 1/24 of a revolution or 15 degrees. And so each hour’s time difference between the ship and starting point marks a progress of fifteen degrees of longitude to the east or west.”2
In other words, if you have a watch that both 1) keeps precise3 time and 2) is synchronised with a clock at a known longitude, you can calculate longitude by comparing the time on your watch to the time of solar noon at your location. Every four minutes of time difference corresponds to one degree of longitude.
This is why the development of the marine chronometer was so important. Prior to Harrison’s invention, there was no reliable way to keep accurate time at sea, and thus no way to determine longitude with any precision. Ships often found themselves lost or off course, leading to delays, wasted resources, and even disasters like the Scilly naval disaster of 1707, in which four ships ran aground due to navigational errors, killing between 1400 and 2,000 sailors.
With a reliable marine chronometer, however, navigators could finally determine their longitude with confidence. As Captain James Cook wrote in his log during his second voyage of discovery:
“I must here take notice that our Longitude can never be erroneous while we have so good a guide as Mr. Kendall’s watch.”4
Cook was referring to the K1; a copy of Harrison’s H4 chronometer made by Larcum Kendall, which Cook used to navigate during his historic voyages of exploration in the Pacific Ocean. The accuracy and reliability of the chronometer gave Cook the confidence to venture into uncharted waters and to be honest, it seems he was a well-loved man:
Cook’s contributions to knowledge gained international recognition during his lifetime. In 1779, while the American colonies were fighting Britain for their independence, Benjamin Franklin wrote to captains of colonial warships at sea, recommending that if they came into contact with Cook’s vessel, they were to “not consider her an enemy, nor suffer any plunder to be made of the effects contained in her, nor obstruct her immediate return to England by detaining her or sending her into any other part of Europe or to America; but that you treat the said Captain Cook and his people with all civility and kindness ... as common friends to mankind.”
Anyway, I digress…
John Harrison’s Early Life and Work
John Harrison was born in 1693 in Foulby, Yorkshire, England. He was the first of five children born to a carpenter and a housewife. From a young age, Harrison showed a natural aptitude for mechanics and as you can imagine, a fascination with clocks.
As a young man, Harrison worked as a carpenter and a clockmaker, honing his skills and developing a reputation for his precise and innovative designs. In 1713, at the age of 20, he built his first pendulum clock entirely out of wood, a remarkable feat of engineering at the time5.
Harrison’s work caught the attention of some of the most prominent scientists and clockmakers of the day, including George Graham, a renowned watchmaker who would become one of Harrison’s most important mentors and supporters.
The Road to H4
In 1728, Harrison travelled to London to present his ideas for a marine chronometer to the Board of Longitude. His first design, known as H1, was a large, cumbersome machine that used a pair of counter-oscillating weighted beams connected by springs to keep time. While the design showed promise, it was too large and impractical for use at sea.
Over the next several years, Harrison would continue to refine his designs, building three more marine chronometers, each smaller and more precise than the last. His second design, H2, was completed in 1741 and was smaller than H1 but still too large for practical use.
H3, completed in 1759, included several important innovations such as bi-metallic strips for temperature compensation and caged roller bearings, but its circular balances still proved too inaccurate.
It wasn’t until 1761, more than 30 years after he first presented his ideas to the Board of Longitude, that Harrison would finally achieve his breakthrough with his fourth marine chronometer: the H4. His H4 was a masterpiece of engineering, a pocket-sized watch that was just 5 inches in diameter and accurate to within a fraction of a second per day.
As an aside, Larcum Kendall (who made the K1 above) eventually took over John Jefferys workshop after he died.
If you’d like to read more about the H4 movement, and get into some ultra geeky levels of detail,
wrote an exceptional deep-dive here. I see no reason to regurgitate it in this post.The Board of Longitude Trials
In 1761, Harrison submitted H4 for a sea trial to the West Indies, as required by the Longitude Act. The chronometer performed admirably, losing just 5 seconds over the course of the 81-day voyage. This was well within the margin of error required by the act, which stipulated that the method must be accurate to within half a degree of longitude (about 30 miles at the equator).
Despite the success of the trial, the Board of Longitude was reluctant to award Harrison the full prize money. There were several reasons for this, including scepticism about the practicality of Harrison’s design and concerns about the cost and difficulty of reproducing it.
In the film, it seemed the main issue was in fact the conflicts of interest within the Board itself. Nevil Maskelyne, the Astronomer Royal and a key member of the Board, was a proponent of the lunar distance method for determining longitude, which relied on astronomical observations rather than time keeping. Maskelyne was indeed, a bit of a cvnt. He basically saw Harrison’s work as a threat to his own preferred solution, which didn’t even work reliably at the time. Still, he had the power to block Harrison, so he did.
Ultimately, Harrison would not receive the full prize money until 1773, after intervention by King George III and a parliamentary act that specifically awarded him £8,750 (around £1.7 million today) in addition to the £14,315 he had already received along the way for the continued development (H1→H2→H3). In total, Harrison received £23,065 (around £4.4 million today) for his work on the longitude problem, spanning more than three decades.
Marine Chronometers
While Harrison’s H4 was a groundbreaking achievement, it was not the only attempt to solve the longitude problem using a timekeeper. In fact, the concept of a marine chronometer - a precision device that could keep accurate time at sea - had been around since at least the 16th century.
One of the earliest proposals for a marine chronometer came from the Dutch scientist Gemma Frisius, who suggested using a clock to determine longitude in 1530. Still, it would be nearly two centuries before the first practical marine chronometers were developed.
In 1714, around the same time that the Longitude Act was passed, the English clockmaker Henry Sully created a marine timekeeper that used a vacuum chamber to protect the mechanism from the effects of temperature and pressure changes. Sully’s design was ultimately unsuccessful, but it represented an important step forward in the development of marine chronometers.
Other important figures in the early history of marine chronometers include the English clockmakers Jeremy Thacker and John Arnold, as well as the French clockmaker Pierre Le Roy. Le Roy’s work in particular, was influential in the development of the modern chronometer, as he introduced several key innovations such as the detent escapement, the temperature-compensated balance and the isochronous balance spring.
Having said all that, it was the carpenter Harrison’s H4 which ultimately proved to be the most successful and influential design. The compact size, accuracy, and reliability made it practical for use at sea, and it would serve as the basis for marine chronometers for generations to come.
Legacy and Impact
Harrison’s work on the marine chronometer clearly revolutionised marine navigation. In the years following Harrison’s death, marine chronometers based on his designs became standard equipment on ships around the world. They allowed sailors to accurately determine their longitude and navigate with greater precision than ever before, dramatically reducing the risk of shipwrecks and undoubtedly saving countless lives.
Harrison’s legacy lives on at The Royal Observatory in Greenwich, where his original chronometers are on display. This is also a UNESCO World Heritage Site and a popular tourist attraction - it also London’s only Planetarium! If you ever decide to visit London, hit me up, and perhaps I’ll join you! This is the place;
Two more things
One
If you’re hungry for more on the subject, you will enjoy this post from
:Two
Check out this old insight post about the F.P. Journe Chronomètre Optimum - this one is for extreme watchmaking nerds, but this quote from the article will explain why I am including this link here :
“In fact, the Chronomètre Optimum would fit comfortably in on an exhibition of precision instruments alongside marine chronometers, rather than in an exhibition of high horology wristwatches.”
Happy reading, and thanks for making it to the end!
Believe it or not, that “❤️ Like” button matters – it serves as a proxy to new visitors of this publication’s value. If you enjoyed this post, please let others know. Thanks for reading!
Andrewes, W. J. H. (1996). The Quest for Longitude: The Proceedings of the Longitude Symposium Harvard University, Cambridge, Massachusetts November 4-6, 1993. Harvard University Collection of Historical Scientific Instruments.
Sobel, D. (1995). Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time. Walker.
By the way - precision and accuracy aren’t the same thing. The film also had scenes where they mention a watch losing 4 seconds a day - they would then account for this variation, because they trusted it would be 4 seconds a day, every day. After 10 days, it would be 40 seconds, an so on.
Beaglehole, J. C. (Ed.). (1961). The Journals of Captain James Cook on His Voyages of Discovery: The Voyage of the Resolution and Adventure, 1772-1775. Cambridge University Press.
Gould, R. T. (1923). The Marine Chronometer: Its History and Development. J.D. Potter.
They say you truly understand something if you can explain it on a simple way. So you nailed it, fantastic work! Thanks ❤️
Still want to watch the movie though….
Actually thinking back over the pictures in this piece and considering the technology and tools they had available to them at the time it’s absolutely mind-boggling to me how Harrison and other early watch and clockmakers, especially Breguet , could possibly have hand fashioned and put together all the pieces much less have imagined them in the first place!
Of course it’s being done now, but that’s after having the general patterns and concepts evolve and be passed on over centuries