FINDING THE LONGITUDE
The Trials and Rewards of
JOHN HARRISON the Inventor of the Marine Chronometer By F. A. Mercer and Kevin Haydon In the earl y 18th century, when the Lords of the Admiralty formed a commi ss ion to solve the problem of calcul ating longitude at sea, suggesti ons of all kinds were put forward. The commi ss ion eventuall y offered a prize to anyone who could solve the problem and in 1714 an Ac t was passed offe rin g £ 10,000 , £ 15 ,000 and £20,000 for any method of di scovering longitude to within 60, 40 and 30 miles respective ly. Some of the schemes put forw ard employed such unlikely ideas as perpetual motion machines, rocket " time signals" and even ex trasensory perception. Sir Isaac Newton had offered: " . . . one way is by a watch to keep time exactly . But, by reason of the motion of the ship, the variation of heat and cold, wet and dry and the difference ofgravity in different latitudes, such a watch hath not been made." In order to qualify fo r the main long itude pri ze, a timekeeper wo uld have to keep time with a variati on of no greater than 2.8 seconds a day; but, before 1750, portable timepieces were hopeless ly poor timekeepers. Even the very best watches of the day lost or gained at least a minute a day. The onl y timepieces capable of the required accuracy were large regulators, fi xed to the wall like a longcase clock. John Harri son ( 1693- 1776), a cabinetmaker and cl ockmaker from Foulby in Yorkshire, took up the challenge. Harri son was the son of an estate carpenter and c ustodian. Despite having no forma l education , and perhaps because of it, he was a profoundly innovative thinker. Even before he turned hi s attention to the Longitude Pri ze and the construction of the " impossibl e cl ock," he had already built a revolutionary turret clock that needed no lubrication, an achi evement that has never been matched, and invented a gridiron pendulum that reduced errors due totemperature variation. His first attempt at a marine timekeeper, fini shed in 1736, was found
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to be acc urate enough to determine longitude within 1.5 degrees (90 miles atthe equator). Harri son 's No. I (or H 1), as it was called, was well received by the scientific community and Harri son him self was hail ed as a curi os ity from the country, the ingeni ous clockmaker. The Board of Longitude were encouraged by hi s progtess, and awarded him £500 to continue hi s work. He fini shed hi s second instrument (H2) in 1739, three years later, and hi s third (H3) in 1758, a lmost twenty years later. After 19 years of painstaking labor, however, H3 stubbornl y refu sed to reach the necessary acc uracy. Thi s third timepiece and its predecessors, large complex clocks weighing from seventy to over one hundred pounds, were each based on refin ements of Harri son' s earlier precision regul ators, an approach that Harri son would have to discard to produce the revolutio nary H4. While H3 incorporated a numbe r of brilli ant inventions, its ultimate role was to convince him that the so lution lay in another des ign altogether. The fourth timekeeper Harri son offered to the commi ssion was the breakthrough he had sought througho ut hi s lonely years strugg ling with H3. H4 in-
corporated features of the common watch with the innovations ofH 3. Harri son had di scovered that timepi eces with sma ll , high freque ncy oscill ators, if made to the correct pro portions, are much more stable timekeepers when they are carried about, than the earlier " portable clocks." H4 was the size of a very large pocket watch, just 5.2 inc hes in di ameter and weighing onl y 3.2 pounds. In 176 1 this timepiece was taken to Jamaica and back in the HM S Deptford, tended by Harrison' s son Willi am. On the outward journey the timekeeper was fo und to have varied by onl y 5. 1 seconds. On the return voyage in 1762 aboard the sloop-of-war Merlin , the weather was so tempestuou s that, at times, Willi am had to cradle H4 in bl ankets to protect it from bu ffeting and sea water. He insisted, however, on keeping it going lest it sho uld be tho ught too frag ile fo r use at sea. In the event, it varied by only one minute and 54.5 seconds. Thi s was sufficient to determine the longitude to within 18 miles, and Harrison la id claim tothe prizeof£20,000 (equi vale nt to about £ 1,000,000 today). The commiss ioners, however, were sceptical and suspected that the good performance of the timepiece may have been accidenta l! They announced that they were di ssati sfi ed with the tri a l. They did ag ree to a ward Harri son £2,500, £ 1,000 of which was to be paid onl y after another trial. From thi s po int on , re lations 0 ~ between the Board and the Harri sons z tlJ began to deteriorate. Many years later (§ one of the commi ss ioners c laimed ~ that the Board never ex pected a time ~ keeper to qualify for the pri ze. The ~ ~
seeds of doubt may well have been sown durin g th e 19 yea rs th a t
°' <(
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H1, the world's first praclical marine timekeeper.featured interlinked balances. Their motion is almost completely unaffected by any movem ent of the timekeeper.
SEA HISTORY 66, SUMMER 1993