horologist

horologist

horologist

m, Uhrmacherin f watchmaker, clockmaker, horologist altm. und geh.

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clockmaker; watchmaker

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m(f) watchmaker/clockmaker, horologist spec

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Uhrmacher m, Uhrmacherin f watchmaker, clockmaker, horologist obs und geh

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watchmaker n.

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Uhrmacher m, Uhrmacherin f watchmaker, clockmaker, horologist obs und geh

clock master (noun)

horologist (noun)

watchmaker (noun)

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1) General subject: clockmaker, horologer, horologist, watch repairer, watch-maker, watchmaker

2) Church: horologium

v. be leaned

v. to lean

watchmaker, horologist

horologer

horologist

Uhr·ma·cher(in) m(f)

watchmaker/clockmaker, horologist spec

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SUBJECT AREA: Horology

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Born Edmund Beckett Denison, he was educated at Eton and Trinity College, Cambridge, where he studied mathematics, graduating in 1838. He was called to the Bar in 1841 and became a Queen's Counsel in 1854. He built up a large and lucrative practice which gave him the independence to pursue his many interests outside law. His interest in horology may have been stimulated by a friend and fellow lawyer, J.M. Bloxham, who interestingly had invented a gravity escapement with an affinity to the escapement eventually used by Denison. Denison studied horology with his usual thoroughness and by 1850 he had published his Rudimentary Treatise on Clock and Watchmaking. It was natural, therefore, that he should have been invited to be a referee when a disagreement arose over the design of the clock for the new Houses of Parliament. Typically, he interpreted his brief very liberally and designed the clock himself. The most distinctive feature of the clock, in its final form, was the incorporation of a gravity escapement. A gravity escapement was particularly desirable in a public clock as it enabled the pendulum to receive a constant impulse (and thus swing with a constant amplitude), despite the variable forces that might be exerted by the wind on the exposed hands. The excellent performance of the prestigious clock at Westminster made Denison's form of gravity escapement de rigueur for large mechanical public clocks produced in Britain and in many other countries. In 1874 he inherited his father's baronetcy, dropping the Denison name, but later adopted the name Grimthorpe when he was created a Baron in 1886.

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SUBJECT AREA: Horology, Ports and shipping

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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.

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See also: Burgi, Jost; Huygens, Christiaan

SUBJECT AREA: Horology

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Le Roy was born into a distinguished horological family: his father, Julien, was Clockmaker to the King. Pierre became Master in 1737 and continued to work with his father, taking over the business when his father died in 1759. However, he seems to have left the commercial side of the business to others so that he could concentrate on developing the marine chronometer. Unlike John Harrison, he believed that the solution lay in detaching the escapement from the balance, and in 1748 he submitted a proposal for the first detached escapement to the Académie des Sciences in Paris. He also differed from Harrison in his method of temperature compensation, which acted directly on the balance by altering its radius of gyration. This was achieved either by mounting thermometers on the balance or by using bimetallic strips which effectively reduced the diameter of the balance as the temperature rose (with refinements, this later became the standard method of temperature compensation in watches and chronometers). Le Roy had already discovered that for every spiral balance spring there was a particular length at which it would be isochronous, and this method of temperature compensation did not destroy that isochronism by altering the length, as other methods did. These innovations were incorporated in a chronometer with an improved detached escapement which he presented to Louis XV in 1766 and described in a memoir to the Académie des Sciences. This instrument contained the three essential elements of all subsequent chronometers: an isochronous balance spring, a detached escapement and a balance with temperature compensation. Its performance was similar to that of Harrison's fourth timepiece, and Le Roy was awarded prizes by the Académie des Sciences for the chronometer and for his memoir. However, his work was never fully appreciated in France, where he was over-shadowed by his rival Ferdinand Berthoud. When Berthoud was awarded the coveted title of Horloger de la Marine, Le Roy became disillusioned and shortly afterwards gave up chronometry and retired to the country.

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SUBJECT AREA: Horology

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Shortt entered the Engineering Department of the London and South Western Railway as an engineering cadet in 1902, remaining with the company and its successors until he retired in 1946. He became interested in precision horology in 1908, when he designed an instrument for recording the speed of trains; this led to a long and fruitful collaboration with Frank HopeJones, the proprietor of the Synchronome Company. This association culminated in the installation of a free-pendulum clock, with an accuracy of the order of one second per year, at Edinburgh Observatory in 1921. The clock's performance was far better than that of existing clocks, such as the Riefler, and a slightly modified version was produced commercially by the Synchronome Company. These clocks provided the time standard at Greenwich and many other observatories and scientific institutions across the world until they were supplanted by the quartz clock.

The period of a pendulum is constant if it swings freely with a constant amplitude in a vacuum. However, this ideal state cannot be achieved in a clock because the pendulum must be impulsed to maintain its amplitude and the swings have to be counted to indicate time. The free-pendulum clock is an attempt to approach this ideal as closely as possible. In 1898 R.J. Rudd used a slave clock, synchronized with a free pendulum, to time the impulses delivered to the free pendulum. This clock was not successful, but it provided the inspiration for Shortt's clock, which operates on the same principle. The Shortt clock used a standard Synchronome electric clock as the slave, and its pendulum was kept in step with the free pendulum by means of the "hit and miss" synchronizer that Shortt had patented in 1921. This allowed the pendulum to swing freely (in a vacuum), apart from the fraction of a second in which it received an impulse each half-minute.

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See also: Marrison, Warren Alvin