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1 Harrison, John
[br]b. 24 March 1693 Foulby, Yorkshire, Englandd. 24 March 1776 London, England[br]English horologist who constructed the first timekeeper of sufficient accuracy to determine longitude at sea and invented the gridiron pendulum for temperature compensation.[br]John Harrison was the son of a carpenter and was brought up to that trade. He was largely self-taught and learned mechanics from a copy of Nicholas Saunderson's lectures that had been lent to him. With the assistance of his younger brother, James, he built a series of unconventional clocks, mainly of wood. He was always concerned to reduce friction, without using oil, and this influenced the design of his "grasshopper" escapement. He also invented the "gridiron" compensation pendulum, which depended on the differential expansion of brass and steel. The excellent performance of his regulator clocks, which incorporated these devices, convinced him that they could also be used in a sea dock to compete for the longitude prize. In 1714 the Government had offered a prize of £20,000 for a method of determining longitude at sea to within half a degree after a voyage to the West Indies. In theory the longitude could be found by carrying an accurate timepiece that would indicate the time at a known longitude, but the requirements of the Act were very exacting. The timepiece would have to have a cumulative error of no more than two minutes after a voyage lasting six weeks.In 1730 Harrison went to London with his proposal for a sea clock, supported by examples of his grasshopper escapement and his gridiron pendulum. His proposal received sufficient encouragement and financial support, from George Graham and others, to enable him to return to Barrow and construct his first sea clock, which he completed five years later. This was a large and complicated machine that was made out of brass but retained the wooden wheelwork and the grasshopper escapement of the regulator clocks. The two balances were interlinked to counteract the rolling of the vessel and were controlled by helical springs operating in tension. It was the first timepiece with a balance to have temperature compensation. The effect of temperature change on the timekeeping of a balance is more pronounced than it is for a pendulum, as two effects are involved: the change in the size of the balance; and the change in the elasticity of the balance spring. Harrison compensated for both effects by using a gridiron arrangement to alter the tension in the springs. This timekeeper performed creditably when it was tested on a voyage to Lisbon, and the Board of Longitude agreed to finance improved models. Harrison's second timekeeper dispensed with the use of wood and had the added refinement of a remontoire, but even before it was tested he had embarked on a third machine. The balance of this machine was controlled by a spiral spring whose effective length was altered by a bimetallic strip to compensate for changes in temperature. In 1753 Harrison commissioned a London watchmaker, John Jefferys, to make a watch for his own personal use, with a similar form of temperature compensation and a modified verge escapement that was intended to compensate for the lack of isochronism of the balance spring. The time-keeping of this watch was surprisingly good and Harrison proceeded to build a larger and more sophisticated version, with a remontoire. This timekeeper was completed in 1759 and its performance was so remarkable that Harrison decided to enter it for the longitude prize in place of his third machine. It was tested on two voyages to the West Indies and on both occasions it met the requirements of the Act, but the Board of Longitude withheld half the prize money until they had proof that the timekeeper could be duplicated. Copies were made by Harrison and by Larcum Kendall, but the Board still continued to prevaricate and Harrison received the full amount of the prize in 1773 only after George III had intervened on his behalf.Although Harrison had shown that it was possible to construct a timepiece of sufficient accuracy to determine longitude at sea, his solution was too complex and costly to be produced in quantity. It had, for example, taken Larcum Kendall two years to produce his copy of Harrison's fourth timekeeper, but Harrison had overcome the psychological barrier and opened the door for others to produce chronometers in quantity at an affordable price. This was achieved before the end of the century by Arnold and Earnshaw, but they used an entirely different design that owed more to Le Roy than it did to Harrison and which only retained Harrison's maintaining power.[br]Principal Honours and DistinctionsRoyal Society Copley Medal 1749.Bibliography1767, The Principles of Mr Harrison's Time-keeper, with Plates of the Same, London. 1767, Remarks on a Pamphlet Lately Published by the Rev. Mr Maskelyne Under theAuthority of the Board of Longitude, London.1775, A Description Concerning Such Mechanisms as Will Afford a Nice or True Mensuration of Time, London.Further ReadingR.T.Gould, 1923, The Marine Chronometer: Its History and Development, London; reprinted 1960, Holland Press.—1978, John Harrison and His Timekeepers, 4th edn, London: National Maritime Museum.H.Quill, 1966, John Harrison, the Man who Found Longitude, London. A.G.Randall, 1989, "The technology of John Harrison's portable timekeepers", Antiquarian Horology 18:145–60, 261–77.J.Betts, 1993, John Harrison London (a good short account of Harrison's work). S.Smiles, 1905, Men of Invention and Industry; London: John Murray, Chapter III. Dictionary of National Biography, Vol. IX, pp. 35–6.DV -
2 Arnold, John
SUBJECT AREA: Horology[br]b. 1735/6 Bodmin (?), Cornwall, Englandd. 25 August 1799 Eltham, London, England[br]English clock, watch, and chronometer maker who invented the isochronous helical balance spring and an improved form of detached detent escapement.[br]John Arnold was apprenticed to his father, a watchmaker, and then worked as an itinerant journeyman in the Low Countries and, later, in England. He settled in London in 1762 and rapidly established his reputation at Court by presenting George III with a miniature repeating watch mounted in a ring. He later abandoned the security of the Court for a more precarious living developing his chronometers, with some financial assistance from the Board of Longitude. Symbolically, in 1771 he moved from the vicinity of the Court at St James's to John Adam Street, which was close to the premises of the Royal Society for the Encouragement of Arts, Manufactures \& Commerce.By the time Arnold became interested in chronometry, Harrison had already demonstrated that longitude could be determined by means of a timekeeper, and the need was for a simpler instrument that could be sold at an affordable price for universal use at sea. Le Roy had shown that it was possible to dispense with a remontoire by using a detached escapement with an isochronous balance; Arnold was obviously thinking along the same lines, although he may not have been aware of Le Roy's work. By 1772 Arnold had developed his detached escapement, a pivoted detent which was quite different from that used on the European continent, and three years later he took out a patent for a compensation balance and a helical balance spring (Arnold used the spring in torsion and not in tension as Harrison had done). His compensation balance was similar in principle to that described by Le Roy and used riveted bimetallic strips to alter the radius of gyration of the balance by moving small weights radially. Although the helical balance spring was not completely isochronous it was a great improvement on the spiral spring, and in a later patent (1782) he showed how it could be made more truly isochronous by shaping the ends. In this form it was used universally in marine chronometers.Although Arnold's chronometers performed well, their long-term stability was less satisfactory because of the deterioration of the oil on the pivot of the detent. In his patent of 1782 he eliminated this defect by replacing the pivot with a spring, producing the spring detent escapement. This was also done independendy at about the same time by Berthoud and Earnshaw, although Earnshaw claimed vehemently that Arnold had plagiarized his work. Ironically it was Earnshaw's design that was finally adopted, although he had merely replaced Arnold's pivoted detent with a spring, while Arnold had completely redesigned the escapement. Earnshaw also improved the compensation balance by fusing the steel to the brass to form the bimetallic element, and it was in this form that it began to be used universally for chronometers and high-grade watches.As a result of the efforts of Arnold and Earnshaw, the marine chronometer emerged in what was essentially its final form by the end of the eighteenth century. The standardization of the design in England enabled it to be produced economically; whereas Larcum Kendall was paid £500 to copy Harrison's fourth timekeeper, Arnold was able to sell his chronometers for less than one-fifth of that amount. This combination of price and quality led to Britain's domination of the chronometer market during the nineteenth century.[br]Bibliography30 December 1775, "Timekeepers", British patent no. 1,113.2 May 1782, "A new escapement, and also a balance to compensate the effects arising from heat and cold in pocket chronometers, and for incurving the ends of the helical spring…", British patent no. 1,382.Further ReadingR.T.Gould, 1923, The Marine Chronometer: Its History and Development, London; reprinted 1960, Holland Press (provides an overview).V.Mercer, 1972, John Arnold \& Son Chronometer Makers 1726–1843, London.See also: Phillips, EdouardDV
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