John Harrison: inventor of the precision timekeeper Jonathan Betts

With the start of the great voyages of discovery in the fifteenth 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 1000 crowns, the Netherlands 10,000 florins, and the British Board of Longitude (17 14) E20,000, very large sums by the standards of the day. In the event success came finally to John Harrison, the tercentenary of whose birth falls this year. In 1773, after nearly 50 years’ work, he finally received in full the coveted British prize.

By the end of the seventeenth century, London was universally recognised as the world’s most important centre for the manufacture of clocks and watches. Virtually all the important design improve- ments which shaped the modem 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.

From the end of the fifteenth century, adventurers and merchants took to the open seas in unprecendented 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 coordinates: 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 by the pole star at night, but longitude had always been a problem.

Because 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

Jonathan Betts, F.B.H.1, F.R.S.A.

Has been a professional horologist since 1975. In 1990 he was appointed Senior Horology Conser- vator 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.

Endeavour, New Series, Volume 17, No. 4,1993. 01&I-9327/93 $6.00 + 0.00. Pergamon Press Ltd. PrInted In Great Brltaln.

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violent movements of the ship and tempera- ture changes. In 1700, almost no one believed such a clock could be made. Even Isaac Newton considered it most unlikely VI.

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 in 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 [2].

The great longitude prize Increased pressure from influential mer- chants and seamen persuaded the Govern- ment to offer, by Act of Parliament in 1714, large prizes for a solution to the longitude problem.

The greatest prize was f20,OOO (equiva- lent to about El million today) and the successful method had to provide a measure of longitude to within half-a-degree. Such a huge sum of money attracted the attention of all manner of cranks and charlatans. The Board of Longitude, the official body set up to judge and administer the rewards, was flooded with weird and wonderful sugges- tions. Many simply believed the problem could not be solved.

It was over half a century before a solution was found and the story of how this was done is a great tale of man’s success over adversity. It was one of the major techno- logical achievements of the eighteenth century. The solution, after all, was the invention of a precision timekeeper - not just the first practical marine chronometer but the basis of all subsequent precision watches.

John Harrison: clockmaker and scientist John Harrison was a working-class joiner from Lincolnshire with little formal edu-

cation. Born on 24 March 1693 at Foulby, near Wakefield in Yorkshire, Harrison was brought up in the remote village of Barrow in Lincolnshire, just south of the great port of Hull.

Little is known of his early education. It seems to have been little more than what his family could pass on to him, along with the woodworking skills taught him by his father. Harrison was, nevertheless, a precocious youth, sufficiently bright to catch the attention of a visiting clergyman, who, in about 1712 lent him a copy of some lectures on mechanics by Nicholas Saunderson (1682- 1739). The young Harrison copied out the whole book [3].

Where Harrison’s interest in clockmaking came from, we simply do not know. We do know that in 1713, at the age of 20, he had completed a longcase clock, which although relatively ordinary in external appearance, had a mechanism made almost entirely of wood. This choice of material was perhaps not so peculiar for one trained as a joiner. Three of Harrison’s early wooden clocks have survived-of1713, 1715,and 1717 - now at The Clockmakers’ Company Museum, the Science Museum, and Nostell Priory respectively. Simply constructed in oak, they all have the conventional ‘anchor’ escapement (the part of the clock which counts the beats of the pendulum and keeps it swinging) and the standard countwheel system of hour-striking. The wheels and pinions are also made of wood. Even in these early clocks, however, Harrison’s ingenuity is seen. He used the mill worker’s technique of morticing segments of three or four teeth into the rim. This meant cutting the segments along the grain of the wood and laying them radially into the wheel, thereby making the teeth considerably stronger.

During the latter part of his early career as a clockmaker, John had his younger brother, James, to help him and it seems the pair soon developed an interest in the technical aspects of clocks and watches. Their first major clockmaking project - and an important early commission for them - was a revolutionary turret clock made in the

early 1720s for the stables at Brocklesby Park. It was revolutionary because it needed no lubrication. Even modern clock oil tends to deteriorate with age: eighteenth century oils were particularly poor and tended to be one of the major causes of clocks failing to work. With no formal education, John Harrison was always a radical thinker. Instead of trying to improve the oil, he designed a clock that did not need it. He discovered that the dense greasy tropical hardwood lignum vitae (Guaiacum oJicinale), in combination with brass, provided an excellent oil-free bearing surface. The clock originally had an anchor escapement but Harrison improved this with a new invention, the grasshopper escapement, which contained no sliding actions and, therefore, no longer required oiling. The turret clock is still at Brocklesby Park, running and keeping time - still without need for lubrication! [4]

John Harrison tells us that he heard of the great longitude prize in the mid-l 720s and, under his direction, James set 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. He also eliminated another sig- nificant error. Clocks go slower when they get warmer because the pendulum expands, getting longer. Harrison solved this problem by inventing a pendulum with a gridiron rod made up of alternate wires of brass and steel (figure 2). This ensured that the effective length of the pendulum (the distance between the point of suspension and the centre of gravity) remained the same what- ever the temperature. As a result, these early regulators achieved the astonishing accuracy of one second in a month, a performance far exceeding the best London clocks of the day.

The marine timekeepers To qualify for tbe main longitude prize, a timekeeper would have to keep time with a variation no greater than 2.8 s a day; but, before 1750, portable timepieces (i.e. watches) were hopelessly poor timekeepers. Even the very best watches of the day lost or gained at least a minute a day. The only timepieces capable of the required accuracy were large regulators, fixed to the wall like a longcase clock. To Harrison and most

Figure 1 Portrait of John Harrison by Thomas King. The portrait can be dated quite closely to the early months of 1766. (Courtesy of the Science Museum.)

Figure 2 Harrison’s gridiron compensation pendulum as fitted to his regulator clocks made during the middle 1720s. The part with a row of holes is known as the ‘tin whistle’ adjuster and was used to make fine adjustments to the compensation. Illustration by David Penney (Copyright).

clockmakers of the day, only one logical course of action seemed clear: to win the longitude prize, he would have to make a portable clock on the scale of his precision regulator. As we shall see, however, this progressive, and apparently logical, approach was not the correct one.

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By 1730, following at least four years of careful thought and study, Harrison had formulated a plan for his first marine timekeeper. He decided that now was the time to take his ideas to London. Taking an illustrated manuscript of his design with him, Harrison set off to Greenwich to seek the advice of the Astronomer Royal. At the time, this was Edmond Halley who received Harrison very kindly, but felt unable to judge the soundness of his plans. He suggested that Harrison go directly to London with his manuscript and plans to see George Graham (1673- 175 l), the greatest clockmaker of his day.

Harrison, having arrived at 10 am, was still discussing timekeeper-design with Graham at dinner in the latter’s house when, late into the evening, Graham extended the offer of a loan. This stranger from Lincoln- shire must have made quite an impression.

On returning to Barrow, Harrison spent the next five years, with his brother, constructing the timekeeper now known as ‘Hl’. After preliminary but rigorous tests on a barge on the River Humber, Harrison felt ready to have the machine tested more formally. Hl 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. Harrison was besieged with requests to see Hl by both scientists and socialites. It is also possible that some came to see Harrison the man: the curiosity from the country, the ingenious clockmaker. It was arranged by the First Lord of the Admiralty himself that Harrison and his timekeeper should be sent on board the warship Centurion to Lisbon in May 1736. Before departing, the ship’s Captain, George Proctor, wrote that he found Harrison ‘a very sober, very industrious and withal, a very modest man. . . ’ but he feared that at sea ‘. . . the dijj?culty of measuring time truly . . . gives me concern for the honest man and makes me fear he has attempted impossibilities . . . ’ [S].

After a week-long voyage in tempestuous weather, Proctor wrote from Lisbon that Harrison ‘was sea sick withall, but . . . seems satisfied that the motion of the ship was not in the least detrimental to its keeping truetime . ..‘[a].

In Lisbon, Hl was transferred to the Olford. On the long homeward voyage, Harrison used Hl to correct a misreading of the ship’s longitude. On 30 June 1737, the Board of Longitude was convened, for the first time, to hear how Hl’s trial had gone and to inspect this model of ‘high technology’. The news the Board received was evidence that, after all, a marine time- keeper* might just prove to be a practical solution to the longitude problem [7].

* Today, ‘timekeepers’ are referred to as marine chronometers, but the term chronometer was not widely used until at?er Harrison’s death. The word timekeeper, however, had very special sig- nificance in the eighteenth century. It was only used to describe a portable machine capable of high accuracy.

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Hl was essentially a portable version of Harrison’s precision wooden clocks, except that it ran for only one day; the wooden clocks run for eight. Only the wheel work was made of wood (oak). The main frame and ancillaries of the timekeeper are all made in brass or other alloys. It was spring driven (with a fusee to ensure uniform driving force) and all the moving parts were counterbalanced and controlled by springs so that the machine was entirely independent of gravity. The movement of Hl was also considerably larger than the wooden move- ments, weighing 34 kg and standing 63 ems high. For the timekeeping element, Harrison replaced the pendulum (which would obviously be useless in a rocking ship) with two interlinked bat-balances, connected across their centres with crossed ribbons - a type of frictionless gearing - between them (figure 3). This ensured that any motion affecting one balance was counter- acted by that same effect on the other. The balances were also linked with helical steel springs at top and bottom. When swung apart, they oscillated together, each swing taking one second.

With an adapted version of the grass- hopper escapement and the elaborate anti- friction devices kept in the design, the clock requited no lubrication (figure 4). Harrison

Figure 3 Hl’s interlinked balances. Their motion is almost completely unaffected by any movement of the timekeeper, because they are connected at their centres with steel cross-over ribbons. Illustration by David Penney (Copyright).

Figure 4 Hl’s balances roll on small segments of circular wheels (a continuation of these ‘wheels’ shown to emphasize the point) and do not require oiling. The wheels in the clock also have antifriction rolls like this, and the centres of those antifriction rolls are of Lignum Vitae, running on brass pins, so they need no oil either. Illustration by David Penney (Copyright).

also adapted the gridiron principle from his (a) pendulum in order to compensate the timekeeper for changes in temperature. (In the balance-controlled timekeepers, a rise in temperature not only causes the balances to get larger, but also the balance springs to become weaker, making the errors to be corrected even greater) [8].

In spite of its good performance on Centurion and Orford, Harrison was evidently not entirely satisfied with its timekeeping. He did not ask for a second official trial of Hl i but requested financial assistance from the Board to make an improved version. They allocated him f250 there and then, with the promise of another X250 on completion. In agreeing to this support, the Commissioners were, in effect, instigating the very first Govemment- sponsored research and development project undertaken by a private contractor. Harrison moved to London in 1736 on his return from Lisbon.

The second marine timekeeper: ‘H2’ Harrison began the second timekeeper immediately and by January 1741 he was before the Board again. By this time he had already real&d a deficiency in the design of H2 and had begun work on a third timekeeper, H3 (figure 5). Notwithstanding this, H2 was as remarkable a timekeeper as Hl and had a more professional feel to its construction.

Larger and heavier than Hl , I-I2 was made almost entirely of brass. The concept was fundamentally the same as H 1 ‘s, except that Harrison had fitted a remontoir to H2. In an ordinary clock, which has a long series of wheels to supply the power to the escape- ment, small errors in manufacture cause variations in the driving force. This, in turn, causes variations in timekeeping. The remontoir is intended to remove these variations. Harrison’s backers petitioned the Board on his behalf for more money to continue with H3. Still highly impressed with his ingenuity, the Commissioners duly awarded Harrison another f500 and work continued on the nascent third timekeeper.

Harrison’s third timekeeper: H3 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 Hl, 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 E3000 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

Figure 5 Harrison’s first three timekeepers: (a) Hl - the world’s first practical marine timekeeper; (b) H3 with its case - this was intended as his masterpiece, but failed to perform as well as expected. It can also just be seen in Harrison’s portrait, behind him, on the left of the picture; (c) H2 - with the help of London craftsmen it took just two years to make. Courtesy of National Maritime Museum.

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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 dumbbells 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. H3 was mounted like H2 and is depicted behind Harrison in the portrait by Thomas King (figure 1).

In order to compensate for temperature changes, a new and revolutionary device was invented, the bimetallic strip (figure 6). 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

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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 enlarging 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 (figure 7), the ultimate version of his anti- friction devices. It was the predecessor of the caged ball-bearing, a device used in virtually every machine made today.

The breakthrough 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 whiie 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 [9].

Harrison’s fourth timekeeper: H4 In most respects, the large silver cased watch that Harrison made next - just 13 cm in diameter and weighing 1.45 kg - is com- pletely different from the earlier machines. Both externally and to some extent inter- nally, it looks like a very large, contem- porary pocket watch, even to the extent of having pair cases (with an inner case for the movement and a protective outer case around it, see figure 8). 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 that the balance had a great deal more energy stored in it when running, which rendered it much less vulnerable to physical disturb- ance. 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 miniaturize the anti-friction 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 Facie (1664- 1753) and the Debaufre brothers Peter (1646-1722) and Jacob, in London in 17041 but such extensive use was quite revolu- tionary [lo].

In common with the other three time- keepers, the watch also has maintaining power, a device to ensure that the mech- anism 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 (figure 9).

Trials and rewards 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

Figure 6 The world’s first bimetallic strip in the temperature compensation of H3. With a rise in temperature, shortening the effective length of the spring with the bimetallic strip compensates for its lower modulus of elasticity and the spring’s force remains the same. Illustration by David Penney (Copyright).

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 18 July 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 expec- tations. 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 18 November 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 on 19 January 1762 (the official end of the trial). After ascertaining exact local time at Port Royal by equal altitudes, the error of the watch was calculated to be just 5.1 s slow!

It was a remarkable achievement but was spoilt by one crucial oversight. There had been failure to discuss and agree the rare of the watch. Even very accurate, reliable timekeepers do not usually keep exucr time. It is extremely difficult to adjust a clock or watch so it does not gain or lose anything. As long as the amount is regular and predictable this really does not matter. If, for example, it gains 5 s each day (its ‘rate’) then one simply makes that much allowance everydayandcorrecttimecanbededuced. However, for testing timekeepers this concept was then 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 pe$onnance of mine (though nearly to truth itselj,I must be altogether a deception ’ 1111.

Considerations of character should also 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 per- haps 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 4 August 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 1 s a day) to the Admiralty on 24 March 1764 and he and Thomas Wyatt, a companion, departed with H4 in the Tartur from Spithead on the 28th.

In the event, the trial was an astonishing success story for H4. The average com- putation put the watch’s error at just 39.2 s 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 that 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, ElO,OOO, once Harrison had made a proper expose of H4’s mechanism, on oath, to a specially appointed 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 E10,OOO 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.

Figure 7 The caged roller race as invented by Harrison and fitted to H3. This was the ultimate development of his antifriction devices. The rollers and tracks are all in a high tin bronze with a very high compressive strength. Illustration by David Penney (Copyright).

The panel of six experts consisted of three well-respected practical watchmakers: Thomas Mudge (1717-1794), William Matthews, and Larcum Kendall (1721- 1790); the Reverends William Ludlam (1717-1788) and John Michell (1724- 1793) (both of Cambridge Univer- sity), and the London instrument-maker John Bird (1709- 1776). 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 arden supporter of the Lunar Distance method, to oversee the presentation.

The Board of Longitude met again on 28 October 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 watch- maker. 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.

The second ElO,OOO 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 23 May 1766, without any advance warning, Nevil Maskelyne - of all people - turned up at Red Lion Square to collect Hl , 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 (Hl) was dropped.

In the meantime, H4 had begun a

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Figure 8 H4. Arguably the most important timekeeper ever constructed and the ‘foundation stone’ of all precision watches which came after. Its relatively light, high frequency balance, which stored a lot of energy when running, was the key to the watch’s good performance. Courtesy of National Maritime Museum.

lo-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 well. In the end, both parties must share 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 of Harrison’s difficulties to date had been merely procrastinations. Kendall’s watch (now known as Kl) 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. (Kl was, in due course, to prove its worth with Captain Cook on his second (1772- 1775) and third (1776-1780) voyages of discovery). By 1772, further finishing and adjusting of H5 provided only one further timekeeper.

The idea that Harrison himself, now 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 now 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 31 January 1772 by letter, via the King’s private astronomer at Richmond, Dr Stephen Demainbray (1710-1782). 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 interview the King is said to have remarked ‘ . . . these people have been cruelly wronged . . . By God, Harrison, Z will see you righted! ’ [ 121.

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 10 weeks averaged out at less than a third of a second per day. Both the King and Demainbray were very

Figure 9 The movement of H4 with its beautifully engraved upper plate. It is probable Harrison was afraid that if the watch had looked too plain it may not have been taken seriously enough by those judging whether it merited reward. Courtesy of National Maritime Museum.

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 fg750 which, in addition to all the sums he had from the Board before, including expenses, actually came to a bit more than the total f20,ooO. 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 24 March 1776, Harrison died at Red Lion Square. It was his 83rd birthday.

Conclusion The story of the marine chronometer does not end here. Following Harrison’s proof that such a timekeeper was possible, a number of successive inventions by later London watchmakers, most notably John Arnold and Thomas Earnshaw (along with the French maker Pierre LeRoy), provided means by which a practical marine chrono- meter could be made cheaply and in large numbers. Thus, England remained at the forefront of chronometer and precision- watch production up to the end of the nineteenth century.

References [l] Newton, I. Letter to Secretary to the

Admiralty 26 August 1725. [2] Howse, D. ‘Greenwich Time and the

Discovery of the Longitude’, Oxford University Press, 1980.

r31

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Quill, H. ‘John Harrison, the Man Who Found Longitude’, Baker, London, 1966. Quill, H. Horological J., 46, 155, 234, 1954. Anon. ‘An Account of the Proceedings in order to the Discovery of the Longitude at Sea ’ London, 1763. Baugh, D. The Mariner’s Mirror, 64, 235, 1978. Gould, R.T. ‘The Marine Chronometer. Its History and Development’, Potter, London, 1923. Randall, A. Antiquarian Horology, 18, 145, 261, 1989. Betts, J. ‘Harrison’, National Maritime Museum, London, 1993. Betts, J. ‘Timekeepers’, British Horological Institute, Notts, 1983. Harrison, J. Manuscript in Clockmakers’ Company Library, London (Ref No: MS 3972/l), 1763. Horrins, J. ‘Memoires of a trait in the Character of George III’, London 1835.

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