John Harrison - Britain's Greatest Horologist?

John 'Longitude' Harrison is world famous for finding a way to accurately measure longitude, one of the thorniest challenges ever set to man. Uniquely, he transcends the normally arcane world of horology. There is a best-selling book and a TV series about him, where he is portrayed as a determined genius who spent his life fighting ignorant bureaucrats. He came 39th in the 2002 BBC poll of the Greatest Britons, with no other clockmaker or watchmaker even getting onto the list.

Here we investigate whether the accolades are deserved, then go on a tour to see the places he lived and the devices he made.

Harrison's reputation

In 1707, four Royal Navy ships, 2000 men and fleet commander Admiral Shovell were all lost in the 'Scilly naval disaster'. It was caused by the miscalculation of their location. Various tools, such as astrolabes and sextants, had been used to accurately measure latitude since Phoenician times, but there was still no way to measure longitude. Instead, navigators used a method known as 'dead reckoning', in which they calculated their position using their speed and heading from their last known location. It didn't work well during a storm, which is how Shovell's fleet came to be so far off course.

In 1714, the government offered enormously generous prizes to anyone that could come up with an accurate way to calculate longitude. The Board of Longitude administered the prize fund and assessed the submissions. The top prize of £20,000 prize (worth over £3m at today's rates) was for the most precise measure of longitude, accurate to within 30 nautical miles. There were smaller prizes for less accurate measures. They also gave ad-hoc discretionary grants to fund any research they thought might help.

Until 1720 Harrison was an ordinary clockmaker making fairly ordinary longcase clocks. Then he developed the 'grasshopper' escapement, the world's first low-friction escapement. Presumably he already had an eye on the Longitude prize, because he thought that a low-friction escapement was a fundamental requirement to win the Longitude prize (he turned out to be wrong). He also thought that temperature compensation was a requirement to win the Longitude prize, because the trial would pass through tropical regions. In the mid-1720s, he invented the 'gridiron' temperature compensating pendulum. He tested the gridiron pendulum and the grasshopper escapement in at least three precision longcase clocks. They were the most accurate clocks in the world at the time they were made.

Harrison's precision longcase clocks must have given him encouragement that he could win the main Longitude prize. Henceforth, he dedicated his professional life to marine chronometers. He presented his first chronometer design to Sir Edmund Halley in 1730. Halley introduced him to George Graham, Britain's most eminent watchmaker at the time. Graham provided technical help and funding to build Harrison's device. It came to be known as H1. It was washing machine sized and made with some wooden components to minimise the effect of temperature changes. H1 went on a sea trial to Portugal and back in 1736. It performed reasonably well, but not well enough to win any prizes. Back to the drawing board.

Over the next 19 years Harrison designed and made two more chronometers, now known as H2 and H3. H2 was a compact (though still huge) and rugged version of H1. H3 incorporated some new features to improve accuracy. Most noticeably, it used balance wheels in place of balance bars. None of them had pendulums, so they could not use the gridiron. H1 and H2 had no temperature compensation. H3 used a bimetallic strip to compensate for temperature change by automatically adjusting the length of its balance spring. It also had a (snappily named) 'maintaining-power' system, to keep the clock running while it was being wound. And it had caged roller bearings, to help neutralise the roll of the ship. All three of these innovations were invented by Harrison.

One problem: H3 was not terribly accurate. Harrison discovered that Thomas Mudge's everyday watches were at least as accurate as his chronometers. And this was before Mudge had invented the lever escapement. He was still using his mentor George Graham's relatively high friction 'cylinder' escapement.

Hitherto, Harrison had thought that it would be impossible to achieve the required tolerances on devices as small as a watch. Mudge's watches persuaded him otherwise. And watch sized chronometers would be more convenient on a ship; portable and easier to mount in gimbles. Better still, although it is doubtful that Harrison understood why at the time, the small fast spring balances on watches had far higher stored energy, which isolated the movement from the ship's motion.

Harrison dropped almost everything he had designed for H1, H2 and H3, resolving instead to make a watch-sized chronometer that was based on Mudge's design, but more rugged. The grasshopper escapement would not work in a watch. Harrison therefore devised a hybrid verge-anchor escapement that had pallets like a verge and a freely spinning spring balance like an anchor. He prototyped this, as well as miniature versions of his H3 temperature compensator and maintaining-power, in a personal watch he commissioned from watchmaker John Jeffreys in 1752.

Remarkably, the new escapement was not particuarly low-friction; it was lower friction than a verge or cylinder escapement but far higher than the grasshopper. Presumably, Harrison reasoned that if Mudge's watches could be as accurate as they were using a cylinder escapement, it was more important to go for reliability than absolute accuracy.

Harrison then embarked upon H4, a double-size (13cm wide) watch made almost entirely with brass and steel components. According to horologists, its most important improvement over H3 was a small fast spring balance running at 300 beats a minute, to maximise stored energy. It had a fusée and a remontoire to stay isochronous as its mainspring unwound. Both springs used Harrison's tempered steel to prevent long term loss of accuracy through work hardening. It had the hybrid verge-anchor escapement, improved with tiny frictionless diamond pallets, plus the miniature temperature compensation system and the maintaining-power from the Jeffreys watch.

The rest of the story is well known from the TV series and book. In brief, H4 was successfully trialled on a sea voyage to Jamaica and back in 1761. It was accurate enough to win the prize. The Board of Longitude, fearing that H4 might have serious inaccuracies that happened to cancel each other out on the sea trial, demanded a rerun. It was equally successful. Unfortunately, in the meantime Harrison's rival Nevil Maskelyne had been promoted to Astronomer Royal and did everything in his power to prevent Harrison receiving his reward. During the second sea trial Harrison made a copy of H4, now known as H5, which he presented to the King. The King tested it himself, finding it to be as accurate as claimed. The King instructed parliament to pay Harrison's reward.

Does Harrison deserve his reputation?

Unusually for a Momentous Britain investigation, there is no doubt that Harrison did fulfil the achievement upon which his reputation is based. H4 performed comfortably within the Longitude prize's accuracy criteria. The Board of Longitude were unhappy. H4 was not as practical, reproducible or affordable as the Board had hoped (it had cost almost as much as a warship to build). This was not Harrison's fault. These were not criteria for winning the prize.

Harrison deserved to win the Longitude prize. Only he didn't. The Board refused to acknowledge that Harrison had won the prize and refused to pay out. The King instructed parliament to pay, but the Board still only paid out less than half and never acknowledged that Harrison had won.

Harrison's reputation also derives from his selfless dedication and innovative genius. We think Dava Sobel invented most of it to boost book sales. Harrison might have been dedicated, but he was hardly selfless. He worked on commission until he was 30, then he was sponsored by George Graham, then he received £14,300 - worth some £2,000,000 at today's rates - from the Board of Longitude for R&D. Admittedly some of this would have been defrayed to suppliers, but not much. After all, H1, H2 and H3 were made by Harrison from cheap materials, while H4 was mostly made from scaled up standard watch components. As far as we can see, Harrison lived a comfortable family life while spending most of his professional time experimenting and lobbying the government for funding. It would be a familiar lifestyle to any successful academic researcher today. Then in 1776 he received £8,750 as part payment of the Longitude prize, so he died the equivalent of a millionaire.

Nor was he an innovative genius. He did overcome a lot of technical challenges, but most of them were caused by his early decision to build huge machines with wooden components. He did invent the bimetallic strip and the caged roller bearing, which are still used in thermostats and other devices. He invented the grasshopper escapement and the hybrid verge-anchor escapement, but they were almost never used elsewhere. His only inventions that found widespread use in timepieces were the bimetallic strip, which had to be completely redesigned, tempered steel springs and his maintaining-power. Is this a good haul for 60 years of dedicated R&D where all the costs were indemnified? In our opinion, it is good but not great.

Most of Harrison's innovations are applications of existing engineering solutions to watchmaking problems. He was a better engineer than he was a chronometer maker. And he was extraordinarily lucky, not least for getting Graham's sponsorship and for getting Mudge's advice when he was on completely the wrong track.

Our main interest here is momentousness. One big problem in this respect, as the Board of Longitude complained, is that the technologies used in H4 were mostly abandoned. Just one H4 was cloned and deployed to the Navy. It was made by Larcum Kendall, a star protege of Thomas Mudge. In the way of early chronometers, it takes its modern name from its maker, so it is now known as K1. It went with Captain James Cook on his second and third voyages around the southern oceans. Cook was delighted with it, until he got eaten. Kendall persuaded the Board of Longitude to change the design for two subsequent devices, now known as K2 and K3, to make them more practical and cost effective. Even though they retain some features fromn H4, they are not really Harrison chronometers.

In the meantime, Pierre Le Roy had invented the almost frictionless 'detent' escapement. He moved Harrison's bimetallic temperature compensator from the length of the balance spring to the outside of the balance wheel, which made it more isochronous. These features became standard on all marine chronometers. John Arnold then patented an improvement to the detent escapement. Arnold's marine chronometers were more accurate than H4 and more practical for less than half the cost. When Arnold's patents expired, Robert Earnshaw, with sponsorship from the Board of Longitude, improved Arnold's design to make chronometers even more accurate, even more practical, and less expensive still. His was the model adopted by marine chronometers for the next 150 years. The only Harrison features that survived into Earnshaw's chronometers, and into other clocks or watches for that matter, were his tempered steel springs and his maintaining-power.

We do not think Harrison's achievements warrant his position as the 39th Greatest Briton ... or even the 139th. He was nowhere near Britain's greatest or most momentous horologist. After all, he only produced a handful of devices in his whole life and virtually nothing he invented was widely used in timepieces. His bimetallic strip and caged roller bearings make him a more momentous engineer than he was clockmaker or watchmaker. He barely deserves three momentousness medals. We think his timepiece achievements rank below Hooke, Huygens. Tompion, Le Roy, Graham, Mudge, Arnold, Earnshaw and Breguet. In our opinion, Tompion is marginally Britain's greatest horologist and by far the most momentous. We discuss this in another blog.

We will end with a famous story about H5. Harrison was frustrated by vested interests that prevented him collecting his Longitude prize in full. He had an audience with King George III. The King decided to verify H5's accuracy for himself. It is said that he took daily recordings in the palace, concluding after 10 weeks that H5 lost less than 0.3 seconds per day. We were always a bit sceptical that the King could calculate noon to within 20 seconds. We tried an experiment in our garden. It consisted of a plumb-bobbed vertical 2m stick and a line of wool pegged in the direction of Polaris one night. Happily our experiment was in 2018 when every day of summer was sunny and warm. The tip of the shadow moved roughly 2mm per minute. So we were wrong. If the King had used a 10m flagpole instead of a 2m stick, he probably could have measured noon to within 6 seconds (i.e. 1mm of shadow).

Longitude tour

Despite our reservations, John Harrison is far and away Britain's most famous timepiece maker. We wanted to visit the places he worked and to see the devices he made. Some of our tours encompass dozens of places and take months. Our Harrison tour took two days to visit just eight places: Wakefield, Leeds, Barrow-upon-Humber, Holborn, the Science Museum, the Royal Observatory, Summit House and Hampstead Parish Church.


Harrison was born in Foulby near Wakefield in what is now West Yorkshire. A house in Doncaster Road bears a blue plaque (above) saying that it is on the location of the former Harrison family home.

In 1700, when John was 7, the Harrisons moved to Barrow-upon-Humber in Lincolnshire. His house was accidentally demolished in 1968. There is a DIY blue plaque (left) on the house at the western end of Barton Lane that replaced it. John's father was a carpenter. He sometimes repaired clocks. This is presumably how John got to understand how clocks work and why he made his first clocks with wood components.

Harrison had a workshop at his house. He made clocks while his brothers made bells and bell-frames. John's first two clocks were longcases made in 1713 and 1715. The movement and faces of both clocks - below left and below middle - now belong to the Worshipful Company of Clockmakers. Their collection moved to the Science Museum in 2015. These two objects are in the Harrison display case.

The face and movement from Harrison's third clock, made in 1717, have been put into a more modern casing (above right) which is on display at Nostell Priory near Wakefield, where John Harrison's father was the resident carpenter. This is now a National Trust property, open to the public almost every day of the year.

In the early 1720s, Harrison turned his attention to technologies he might use to win the Longitude prize. His first important advance was the grasshopper escapement. This was first used in the turret clock belonging to Brocklebury Estates. It is not far from Harrison's home in Barrow, but it is privately owned and we were not allowed in to see the clock. There seem to be many events in the grounds. Perhaps some of them allow viewings of the famous turret clock.

In the mid-1720s, Harrison experimented with his new technologies in three, or perhaps more, precision longcase pendulum clocks. They are referred to as Precision Clock 1, 2 and 3. No. 1 is in private hands. No. 2 is on display at Leeds Museums and Galleries. No.3 belongs to the Worshipful Company of Clockmakers. It is on display in the Science Museum.

Harrison designed and made his first chronometer, H1, while still living in Barrow. He moved to London in 1727 or 1728. He lived the rest of his life in Red Lion Square, Holborn, at the site now occupied by Summit House. It is a modernist building. We considered visiting it for our Bauhaus blog, but decided it was not the right style. Weirdly, many years ago we used to visit Summit House professionally, when it belonged to Cable & Wireless.

There is a blue plaque (above) on Summit House explaining that it is the site where Harrison lived and died. Note that the plaque is actually on the Dane Street side of the building. It claims that Harrison invented the Marine Chronometer. Wikipedia agrees. We don't. If it was invented by anyone, it was by Henry Sully in France. His device was not terribly acccurate in rolling seas, but neither were any of Harrison's chronometers. H4 was accurate enough to win the Longitude prize, but that only required an arbitrary accuracy to within 30 nautical miles. It still left a lot of room for error. We think that Pierre Le Roy invented the first truly accurate marine chronometer. The plaque should say something like "John Harrison 1693-1776 inventor of the first practical marine chronometer".

Harrison finished H1 in 1735. It went on a sea trial in 1736. Meanwhile Harrison had started building H2 as a compact version of H1. He finished H2 in 1741. It was never tested at sea because Britain was at war. Harrison started H3, with the innovative new features listed above. He worked on H3 for sixteen years before abandoning the table clock form factor, wooden components and the grasshopper escapement. In case we have not done justice to the size of these suckers, the photo above shows H3 is more than half the height of a person.

H1, H2, H3 (all above), H4 and K1 (both below) all belong to the Royal Maritime Group. They are on display at the Royal Observatory at Greenwich. We urge you to go. Regardless their timekeeping merits, these devices are serene, peaceful and beautiful. It is incredible to think that they are nearly 300 years old. They gleem as if they were made yesterday. Yet they look like they could be incredibly ancient. We imagine them having been made by Hephaestus for Zeus; designed to run forever.

Martin Burgess's Clock B which implemented Harrison's design for the most accurate clock in the world is also on display at the Royal Observatory. His Clock A, which is almost identical used to be on display in a Norwich shopping mall, but was not there when we last visited. Kendall's K1 is an impressively accurate clone of H4. H4 is the one on the left below.

H5, which has an almost identical movement to H4, belongs to the Worshipful Company of Clockmakers. Along with the rest of their collection it is now on display in the Science Museum (below).

Harrison is buried in a rather grand tomb in the churchyard of Hampstead Parish Church. There is also a floor plaque remembering him in Westminster Abbey. We didn't go because we are still boycotting Westminster Abbey in response to its exorbitant entrance charge.