With the start of great voyages of discovery in the 15th century, and the establishment of a worldwide trade network, a means of accurately determining longitude at sea became increasingly urgent. This led the great maritime nations to offer substantial prizes for a practical solution to the problem. Spain offered 1,000 crowns, the Netherlands 10,000 florins and the British Board of Longitude, in 1714, £20,000 - very large sums by the standards of the day.
From the end of the 15th century, adventurers and merchants took to the sea in unprecedented numbers. These journeys were hazardous not only because of the inherent dangers but also because, once out of sight of land, sailors had no accurate means of knowing their exact position.
One's position on the earth is defined by two co-ordinates: latitude - the distance north or south of the equator, and longitude - the distance east or west from an agreed place. Latitude was easy to find by observation of the sun at midday, or the pole star at night; but longitude had always been a problem. Since the earth revolves on its axis, longitude is a function of time. To find longitude at sea, one needs to know what time it is at some other known location on earth - usually the home port. Then, by noting local time (which is relatively easy to do using the sun or the stars), the difference between the two times measures the longitude.
The real problem was how to discover the time at the home port. The obvious answer would be to take a portable clock, set to "home" time. Such a clock would have to be both very accurate and unaffected by the violent movements of the ship and temperature changes. In 1700, almost no one believed such a clock could be made; even Isaac Newton considered it most unlikely. London was universally recognised as the world's most
Inventor of the Precision Timekeeper - by Jonathan Betts,
Senior Curator of Horology, Royal Observatory Greenwich
Related further reading...
important centre for the manufacture of clocks and watches. Virtually all the important design improvements which shaped the modern mechanical clock were incorporated in English clocks by 1700. Only one real challenge remained to be met with an advance in clock design and it is no wonder the world looked to England for a solution.
One alternative was to use the movement of the moon as a kind of clock. Unfortunately though, this method - called the Lunar Distance method - was very time-consuming. It could take four hours to find longitude this way. Nevertheless, most people believed that the lunar distance method was the answer to the longitude problem, and the Royal Observatory was founded at Greenwich in 1675 for the express navigational purpose of making charts of the skies and-to record the position of the moon throughout the year.
Following increased pressure from influential merchants and seamen for a solution to the longitude problem, the Government Act of 1714 offered a top prize of £20,000 (equivalent to around £1 m today) for a successful measure of longitude to within half-a-degree. The Board of Longitude, who administered the award, was flooded with weird and wonderful suggestions. It was over half a century before a solution was found.
John Harrison was a working-class joiner from Lincolnshire with little formal education. Born 1693 at Foulby, near Wakefield, Harrison was brought up in the remote village of Barrow in Lincolnshire. Around 1712, a visiting clergyman lent him a copy of some lectures on Mechanics by Nicholas Saunderson (1682-1739) and Harrison copied out the whole book, and by 1713 he had completed a longcase clock with a mechanism made almost entirely of wood.
In the early 1720s, working with his younger brother, James, he completed a revolutionary turret clock for the stables of Brocklesby Park. Innovative use of a dense greasy tropical hardwood (guaiacum officinale) and brass, to provide an excellent oil-free bearing surface, meant this clock needed no lubrication, and hence resolved the problem of the deterioration of clock oil with age. The turret clock is still running, and keeping time, without need for lubrication!
In the mid-1720s Harrison heard of the great longitude prize and set James to work on a series of remarkable precision longcase clocks (regulators), smaller versions of the turret clock, to see just how far they could push the capabilities of this fixed-clock design. Harrison also eliminated the significant error caused by expansion of the pendulum with heat with his gridiron rod pendulum which ensured a constant pendulum length. The early regulators achieved astonishing accuracy of one second per month, far exceeding the performance of the best London clocks of the day.
To qualify for the main longitude prize, a timekeeper would have to keep time with a variation no greater than 2.8 seconds a day, but before 1750 even the best portable timepieces (i.e. watches) lost or gained at least a minute a day. The only timepieces capable of the required accuracy were large regulators, and so Harrison concluded he would have to make a portable clock on the scale of his precision regulator.
By 1730 Harrison had formulated a plan for his first marine timekeeper, and he set off with an illustrated manuscript of the design to Greenwich. Edmond Halley, the Astronomer Royal, felt unable to judge the soundness of the plans and sent him to London to George Graham (1673-1751), the greatest clockmaker of his day. After a day of discussion, Graham offered him a loan. Harrison returned to Barrow and spent the next five years, with his brother, constructing the timepiece now known as "H1." Essentially a portable version of Harrison's precision wooden clocks, H1 ran for one day, not eight. Only the wheel work was made of wood (oak), the main frame and ancillaries being made of brass or other alloys. It was spring-driven, with all moving parts counterbalanced and controlled by springs so that the machine was completely independent of gravity.
H1's movement weighed 34kg and stood 63cm high. The pendulum would be useless in a rocking ship, so Harrison replaced it with two interlinked bar-balances, connected with crossed ribbons - a type of frictionless gearing. Other refinements meant the clock required no lubrication, and was compensated for temperature changes.
After preliminary testing on a barge in the Humber, H1 was brought to London, to Graham, and publicly displayed to the scientific community. It was widely regarded as one of the wonders of its age. The First Lord of the Admiralty arranged for Harrison and his timekeeper to be sent on board the warship Centurion to Lisbon in May 1736. In Lisbon, H1 was transferred to Orford, and on the long homeward journey Harrison used H1 to correct a misreading of the ship's longitude.
On June 30, 1737 the Board of Longitude was convened, for the first time, to hear how H1's trial had gone and to inspect this model of high technology. The news the board received was evidence that, after all, a marine timekeeper (known nowadays as a "marine chronometer") might just prove to be a practical solution to the longitude problem.
Harrison was not entirely satisfied with H1's timekeeping, but requested financial assistance from the board to make an improved version. They allocated him £250 there and then, with the promise of another £250 on completion. In agreeing to this support, the Commissioners were, in effect, instigating the very first Government-sponsored research and development project undertaken by a private contractor.
Harrison moved to London on his return from Lisbon in 1736, and began the second timekeeper immediately. By January 1741 he was before the board again. H2 was made almost entirely of brass, and conceptually the same as H1 except for the addition of a remontoir which reduced variations in the driving force caused by small errors in the manufacture.
Harrison, however, had already realised a deficiency in H2, and had begun work on a third timekeeper, H3. His backers petitioned the Board on his behalf for more money to continue with H3, and, still highly impressed with his ingenuity, the Commissioners duly awarded him another £500.
Even after 19 years of painstaking labour, H3 was stubbornly refusing to reach the necessary accuracy. Although Harrison learned a great deal from this Herculean endeavour and incorporated a number of brilliant inventions into H3, its ultimate role was solely to convince him that the solution lay in another design altogether. Work on H3 seemed to be leading nowhere.
After his initial success with H1, the late 1740s and early 1750s must have been something of a mid-life crisis for Harrison. The Board of Longitude, however, continued to support him with grants until 1760, awarding him over £3,000 during the period. Other members of the scientific community, not having an official role to play, were aware of the much wider implications for science in what Harrison was attempting. In 1749, even though H3 had still not provided the breakthrough, the Royal Society awarded Harrison its highest honour, the gold Copley Medal.
H3's balances were wheels instead of dumb-bells and were arranged one above the other. They were still linked together, beat seconds, and were driven by the grasshopper escapement. The helical springs had been replaced with one short spiral spring, which controlled the upper balance only. A remontoir of 30 seconds period was fitted to provide uniform power supply.
In order to compensate for temperature changes, a new and revolutionary device, was invented - the bimetallic strip. This consisted of two flat strips, one of brass, one of steel, riveted together. Because brass expands more than steel with a rise in temperature, this bimetal bends into a curved shape with the brass on the convex side.
With one end fixed, the movement of the other end can then be used to shorten the balance spring. A shorter spring is normally stiffer, so the strip can be adjusted to compensate exactly for the spring's weakening and the enlarged balance. The bimetallic strip was a tremendously versatile invention, and most households today have conveniences utilising it as a thermostatic control.
Another important invention that Harrison created for H3 was the caged roller race, the ultimate version of his anti-friction device. It was the predecessor of the caged ball-bearing, a device used in virtually every machine made today.
In 1753 Harrison had commissioned John Jefferys, a London watchmaker, to make him a watch following Harrison's own designs. The watch, which Harrison would have finished and adjusted himself, was intended for his personal use - he needed as accurate a watch as possible to help with his astronomical observing and clock testing. It would also be used while making observations on deck, when navigating.
As already mentioned, no one in the 1750s thought of the pocket watch as a serious timekeeper. Harrison discovered with his new watch, however, that if made with certain vital improvements, it had the potential to be an excellent timekeeper. He found that timepieces with small, high-frequency oscillators (such as the watch balance), if made to the correct proportions, are much more stable timekeepers when they are carried about than the earlier portable clocks. This apparently simple discovery is one of Harrison's great achievements.
In most respects, the large silver cased watch (H4) that Harrison made next - just 13cm in diameter and weighing 1.45kg - is completely different from the earlier machines. Both externally, and to some extent internally, H4 looks like a very large, contemporary pocket watch, even to the extent of having pair cases (with an inner case for the movement and a protective outer case around it).
Technically, however, it was different from an ordinary watch in a number of significant ways. Apart from being very finely constructed, its balance was much larger, although still relatively light, and of higher frequency: it oscillated five times a second. This means the balance had a great deal more energy stored in it when running, which rendered it much less vulnerable to physical disturbance.
Temperature change was compensated for by using the bimetallic strip, a smaller version of H3's device. It also contained a miniature remontoir, rewinding eight times a minute to ensure constant power. A type of verge escapement (the sort used in common watches) was fitted, of a modified form, which ensured that the balance was isochronous.
Although Harrison was unable to miniaturise the antifriction devices and H4 required oil on all its bearing surfaces, jewelled bearings were fitted in many places to reduce friction to a minimum. The use of jewelled bearings was not Harrison's invention (their use had been known since their introduction by Nicholas Facio (1664-1753) and the Debaufre brothers Peter (1646-1722) and Jacob, in London in 1704), but such extensive use was quite revolutionary. In common with the other three timekeepers, the watch also has maintaining power, a device to ensure that the mechanism keeps going while it is being wound up. In Harrison's version, this is automatic and does not need to be brought into action manually. Of the highest quality throughout, the upper plates of the movement are beautifully engraved.
Harrison had made great progress with H4, but he was now not the only one coming closer to winning the longitude prize. In 1756, the Astronomer Royal himself, James Bradley (1693-1762), recommended that the Board of Longitude reconsider the potential of the lunar distance method for solving the longitude problem. At the Board's meeting on July 18, 1760, Harrison asked for a trial of H3 hoping that it would be possible to send the watch (H4) as well, as it had far exceeded his expectations. In March 1761, the board agreed and told John's son William (now in partnership with his father) to prepare for a trial voyage to Jamaica in charge of the timekeepers.
After innumerable delays, on November 18, 1761 the Deptford sailed for the West Indies with William and H4 (in the event H3 was not sent with them). They arrived at Jamaica, the official end of the trial, on January 19, 1762. After ascertaining exact local time at Port Royal by equal altitudes, the error of the watch was calculated to be just 5.1 seconds slow! It was a remarkable achievement but was spoilt by one crucial oversight.
There had been failure to discuss and agree the rate of the watch. Even very accurate, reliable, timekeepers do not usually keep exact time. It is extremely difficult to adjust a clock or watch so it does not gain or lose. As long as the amount is regular and predictable this does not really matter. If, for example, it gains five seconds per day (its "rate") one simply makes that much allowance every day and correct time can be deduced. However, for testing timekeepers this concept was entirely new and the trial was therefore next to useless.
At their meeting in June 1762, the Board announced that they were dissatisfied with the trial on a number of counts, and not surprisingly, top of the agenda was the question of applying a rate. From this point on, the attitude of the board to the Harrisons began to harden. In 1763, Harrison himself complained bitterly: "But they still say a watch...can but be a watch...and that the performance of mine (though nearly to truth itself) must be altogether a deception".
Considerations of character should not be underestimated. We know, from his writings, that Harrison had considerable difficulty expressing himself clearly. Many of the concepts he was trying to describe had no name, and he was constantly having to invent a new technological language. Add to this the emergence of the increasingly perfected lunar tables - a mathematical solution which undoubtedly appealed more to the board as theoreticians - and perhaps the diminishing favour accorded the Harrisons is not so difficult to understand.
At the August meeting of the board, Harrison reluctantly agreed to a second trial of H4 to the West Indies. When the board met on August 4, 1763 to make the necessary arrangements, the first item on the agenda was the dreaded question of deciding H4's rate. It was finally agreed that Harrison should be allowed to provide his own statement of what the rate should be. William Harrison made his declaration of H4's rate (gaining one second a day) to the Admiralty on March 24, 1764, and he and Thomas Wyatt, a companion, departed with H4 in the Tartar from Spithead on the 28th.
In the event, the trial was an astonishing success story for H4. The average computation put the watch's error at just 39.2 seconds after the voyage of 47 days. This was three times better than the performance needed to win the full £20,000 longitude prize. Whatever may have been said and done before, the board should now have recognised the prize had been won.
Sadly, the board saw matters differently; they were not yet ready to pay anything. First, they stated that they would pay half the total once Harrison had made a proper exposé of H4's mechanism, on oath, to a special committee. The details would then be published for the benefit of the world at large. Second, the board implied that the watch was a fluke and that others of the same kind should be made and tested.
Third, the board then had these requirements sanctioned in an Act of Parliament which also included the demand that all four timekeepers should be handed over once the £10,000 had been paid to Harrison. At this stage the Harrisons' relations with the board were at an all-time low, but realising that they would get nowhere if they did not compromise, the Harrisons finally agreed to sign the oath and disclose the inner workings of the watch.
The panel of six experts consisted of three well-respected practical watchmakers: Thomas Mudge (1717-94), William Matthews, and Larcum Kendall (1721-90); the Reverends William Ludlam (1717-88) and John Michell (1724-93) - both of Cambridge University; and the London instrument maker John Bird (1709-76). The meeting could scarcely have been a relaxed affair under these circumstances, but - to add to the tension - the board appointed Nevil Maskelyne, the Astronomer Royal and an ardent supporter of the Lunar Distance method, to oversee the presentation.
The Board of Longitude met again on October 28, 1765 and granted Harrison enough money to make up the first half of the full reward. In return, they insisted on taking H4 (which had become their property). They also asked Harrison to recommend someone suitable for copying the watch; he suggested Larcum Kendall, a leading London watchmaker. At last, Harrison had half the prize; but, for him, it was only the whole reward, and the recognition that went with it, that mattered.
Harrison knew that, in order to qualify for the second part of the longitude prize, he had to make at least two other watches similar to H4 and have them tested. Knowing that he would not give up the challenge of winning the whole longitude prize, the Board decided to test all four of Harrison's timekeepers at Greenwich. To add insult to injury, on May 23, 1766, without any advance warning, Nevil Maskelyne - of all people - turned up at Red Lion Square to collect H1, H2 and H3 from Harrison. He arrived with an unsprung cart - the sort of transport that could do more damage to Harrison's timekeepers than years at sea! Harrison was extremely reluctant to advise how they should best be moved, lest he be implicated if they were damaged in transit.
Predictably, one of the timekeepers (H1) was dropped. In the meantime, H4 had begun a 10-month trial at Greenwich, a trial which, it seems, was destined to go badly from the very outset. Owing to the fact that H4 had not been cleaned, and because it did not have entirely fair treatment while under Maskelyne's care at the Observatory, it did not perform very well. In the end, both parties must share the blame for the poor results of this trial. Greatly embittered, but still determined to see the project to its end, Harrison and his son began to make the first "copy timekeeper" to qualify for the remaining prize money.
Kendall's good progress on his copy of H4 had the adverse effect of persuading the board that all Harrison's difficulties to date had been merely procrastinations. Kendall's watch (now known as K1) was completed in 1769 and inspected in early 1770 by the same panel that had seen H4. William Harrison was also present at the demonstration and admitted the copy was exceptional. (K1 was, in due course, to prove its worth with Captain Cook on his second (1772-75) and third (1776-80) voyages of discovery). By 1772, further finishing and adjusting of H5 provided only one further timekeeper.
The idea that Harrison, aged 79, might sit down to make a second watch was clearly absurd. Father and son had reached the end of the road, and desperate measures were needed if further progress was to be made. As a last resort, John decided to appeal to the highest authority in the land, the King himself. An approach was made to George III on January 31, 1772, by letter, via the King's private astronomer at Richmond, Dr Stephen Demainbray (1710-82). William Harrison requested an opportunity for H5 to be put on trial by the King himself at his private observatory. He was summoned for interview at Windsor, and asked to expand on some of the details.
At this point the King is said to have remarked: "... these people have been cruelly wronged... by God, Harrison, I will see you righted!" H5 went on trial at Richmond from May to July of that year. After a false start caused by leaving the watch too close to some magnets, H5 performed superbly. Its daily rate over the whole ten weeks averaged out at less than a third of a second per day. Both the King and Demainbray were very impressed and the Harrisons believed their own personal trial was nearing its end.
Probably at the suggestion of the King himself, Harrison now formally approached the Prime Minister, Lord North, with the full story. The Harrisons' petition to Parliament eventually bore fruit and the Act of 13 George III, chapter 77, duly received Royal Assent. This awarded Harrison £8,750 which, in addition to all the sums he had received from the board before, including expenses, actually came to a bit more than the total £20,000. Harrison had, at last, won the great longitude prize. Perhaps more important to John, however, was that the award was seen to be his. Even though not all of it came from the Board of Longitude, here was public recognition that John Harrison had solved the longitude problem.
Within three years, on March 24, 1776, Harrison died at Red Lion Square. It was his 83rd birthday.
Jonathan Betts, F.B.H.I, F.R.S.A, has been a professional
horologist since 1975.
In 1980 he was appointed Senior Horology Conservator at the National Maritime Museum, Greenwich, and since 1992 has been Curator of Horology.
The Museum awarded him its Callender Award in 1989 for achievements in horology.
Original Inventors World magazine Photographs courtesy of the National Maritime Museum.
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H4 Commemorative Stamps