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1 progressively
adverb progresivamentetr[prə'gresɪvlɪ]1 progresivamentee, cada vez másprogressively [prə'grɛsɪvli] adv: progresivamente, poco a pocoprə'gresɪvli[prǝ'ɡresɪvlɪ]ADV progresivamente, poco a pocoit diminishes progressively — disminuye progresivamente or poco a poco
* * *[prə'gresɪvli] -
2 Huygens, Christiaan
SUBJECT AREA: Horology[br]b. 14 April 1629 The Hague, the Netherlandsd. 8 June 1695 The Hague, the Netherlands[br]Dutch scientist who was responsible for two of the greatest advances in horology: the successful application of both the pendulum to the clock and the balance spring to the watch.[br]Huygens was born into a cultured and privileged class. His father, Constantijn, was a poet and statesman who had wide interests. Constantijn exerted a strong influence on his son, who was educated at home until he reached the age of 16. Christiaan studied law and mathematics at Ley den University from 1645 to 1647, and continued his studies at the Collegium Arausiacum in Breda until 1649. He then lived at The Hague, where he had the means to devote his time entirely to study. In 1666 he became a Member of the Académie des Sciences in Paris and settled there until his return to The Hague in 1681. He also had a close relationship with the Royal Society and visited London on three occasions, meeting Newton on his last visit in 1689. Huygens had a wide range of interests and made significant contributions in mathematics, astronomy, optics and mechanics. He also made technical advances in optical instruments and horology.Despite the efforts of Burgi there had been no significant improvement in the performance of ordinary clocks and watches from their inception to Huygens's time, as they were controlled by foliots or balances which had no natural period of oscillation. The pendulum appeared to offer a means of improvement as it had a natural period of oscillation that was almost independent of amplitude. Galileo Galilei had already pioneered the use of a freely suspended pendulum for timing events, but it was by no means obvious how it could be kept swinging and used to control a clock. Towards the end of his life Galileo described such a. mechanism to his son Vincenzio, who constructed a model after his father's death, although it was not completed when he himself died in 1642. This model appears to have been copied in Italy, but it had little influence on horology, partly because of the circumstances in which it was produced and possibly also because it differed radically from clocks of that period. The crucial event occurred on Christmas Day 1656 when Huygens, quite independently, succeeded in adapting an existing spring-driven table clock so that it was not only controlled by a pendulum but also kept it swinging. In the following year he was granted a privilege or patent for this clock, and several were made by the clockmaker Salomon Coster of The Hague. The use of the pendulum produced a dramatic improvement in timekeeping, reducing the daily error from minutes to seconds, but Huygens was aware that the pendulum was not truly isochronous. This error was magnified by the use of the existing verge escapement, which made the pendulum swing through a large arc. He overcame this defect very elegantly by fitting cheeks at the pendulum suspension point, progressively reducing the effective length of the pendulum as the amplitude increased. Initially the cheeks were shaped empirically, but he was later able to show that they should have a cycloidal shape. The cheeks were not adopted universally because they introduced other defects, and the problem was eventually solved more prosaically by way of new escapements which reduced the swing of the pendulum. Huygens's clocks had another innovatory feature: maintaining power, which kept the clock going while it was being wound.Pendulums could not be used for portable timepieces, which continued to use balances despite their deficiencies. Robert Hooke was probably the first to apply a spring to the balance, but his efforts were not successful. From his work on the pendulum Huygens was well aware of the conditions necessary for isochronism in a vibrating system, and in January 1675, with a flash of inspiration, he realized that this could be achieved by controlling the oscillations of the balance with a spiral spring, an arrangement that is still used in mechanical watches. The first model was made for Huygens in Paris by the clockmaker Isaac Thuret, who attempted to appropriate the invention and patent it himself. Huygens had for many years been trying unsuccessfully to adapt the pendulum clock for use at sea (in order to determine longitude), and he hoped that a balance-spring timekeeper might be better suited for this purpose. However, he was disillusioned as its timekeeping proved to be much more susceptible to changes in temperature than that of the pendulum clock.[br]Principal Honours and DistinctionsFRS 1663. Member of the Académie Royale des Sciences 1666.BibliographyFor his complete works, see Oeuvres complètes de Christian Huygens, 1888–1950, 22 vols, The Hague.1658, Horologium, The Hague; repub., 1970, trans. E.L.Edwardes, AntiquarianHorology 7:35–55 (describes the pendulum clock).1673, Horologium Oscillatorium, Paris; repub., 1986, The Pendulum Clock or Demonstrations Concerning the Motion ofPendula as Applied to Clocks, trans.R.J.Blackwell, Ames.The balance spring watch was first described in Journal des Sçavans 25 February 1675, and translated in Philosophical Transactions of the Royal Society (1675) 4:272–3.Further ReadingH.J.M.Bos, 1972, Dictionary of Scientific Biography, ed. C.C.Gillispie, Vol. 6, New York, pp. 597–613 (for a fuller account of his life and scientific work, but note the incorrect date of his death).R.Plomp, 1979, Spring-Driven Dutch Pendulum Clocks, 1657–1710, Schiedam (describes Huygens's application of the pendulum to the clock).S.A.Bedini, 1991, The Pulse of Time, Florence (describes Galileo's contribution of the pendulum to the clock).J.H.Leopold, 1982, "L"Invention par Christiaan Huygens du ressort spiral réglant pour les montres', Huygens et la France, Paris, pp. 154–7 (describes the application of the balance spring to the watch).A.R.Hall, 1978, "Horology and criticism", Studia Copernica 16:261–81 (discusses Hooke's contribution).DV
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