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1 Marrison, Warren Alvin
[br]b. 21 May 1896 Inverary, Canadad. 27 March 1980 Palo Verdes Estates, California, USA[br]Canadian (naturalized American) electrical engineer, pioneer of the quartz clock.[br]Marrison received his high-school education at Kingston Collegiate Institute, Ontario, and in 1914 he entered Queen's University in Kingston. He graduated in Engineering Physics in 1920, his college career having been interrupted by war service in the Royal Flying Corps. During his service in the Flying Corps he worked on radio, and when he returned to Kingston he established his own transmitter. This interest in radio was later to influence his professional life.In 1921 he entered Harvard University, where he obtained an MA, and shortly afterwards he joined the Western Electric Company in New York to work on the recording of sound on film. In 1925 he transferred to Western Electric's Bell Laboratory, where he began what was to become his life's work: the development of frequency standards for radio transmission. In 1922 Cady had used the elastic vibration of a quartz crystal to control the frequency of a valve oscillator, but at that time there was no way of counting and displaying the number of vibrations as the frequency was too high. In 1927 Marrison succeeded in dividing the frequency electronically until it was low enough to drive a synchronous motor. Although his purpose was to determine the frequency accurately by counting the number of vibrations that occurred in a given time, he had incidentally produced the first quartz-crystal -ontrolled clock. The results were sufficiently encouraging for him to build an improved version the following year, specifically as a time and frequency standard.[br]Principal Honours and DistinctionsBritish Horological Institute Gold Medal 1947. Clockmakers' Company Tompion Medal 1955.Bibliography1928, with J.W.Horton, "Precision measurement of frequency", Proceedings of the Institute of Radio Engineers 16:137–54 (provides details of the original quartz clock, although it was not described as such).1930, "The crystal clock", Proceedings of the National Academy of Sciences 16:496–507 (describes the second clock).Further ReadingW.R.Topham, 1989, "Warren A.Marrison—pioneer of the quartz revolution", NAWCC Bulletin 31(2):126–34.J.D.Weaver, 1982, Electrical and Electronic Clocks and Watches, London (a technical assessment of his work on the quartz clock).DV -
2 Horology
See also: INDEX BY SUBJECT AREA[br]Ctesibius of AlexandriaGrimthorpe, Edmund Beckett, BaronSu SongYi-XingZhang Sixun -
3 Electronics and information technology
See also: INDEX BY SUBJECT AREA[br]Byron, Ada AugustaNapier, JohnRiche, Gaspard-Clair-François-MarieSchickhard, WilhelmBiographical history of technology > Electronics and information technology
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4 Essen, Louis
SUBJECT AREA: Horology[br]b. 6 September 1908 Nottingham, England[br]English physicist who produced the first practical caesium atomic clock, which was later used to define the second.[br]Louis Essen joined the National Physical Laboratory (NPL) at Teddington in 1927 after graduating from London University. He spent his whole working life at the NPL and retired in 1972; his research there was recognized by the award of a DSc in 1948. At NPL he joined a team working on the development of frequency standards using quartz crystals and he designed a very successful quartz oscillator, which became known as the "Essen ring". He was also involved with radio frequency oscillators. His expertise in these fields was to play a crucial role in the development of the caesium clock. The idea of an atomic clock had been proposed by I.I.Rabbi in 1945, and an instrument was constructed shortly afterwards at the National Bureau of Standards in the USA. However, this device never realized the full potential of the concept, and after seeing it on a visit to the USA Essen was convinced that a more successful instrument could be built at Teddington. Assisted by J.V.L.Parry, he commenced work in the spring of 1953 and by June 1955 the clock was working reliably, with an accuracy that was equivalent to one second in three hundred years. This was significantly more accurate than the astronomical observations that were used at that time to determine the second: in 1967 the second was redefined in terms of the value for the frequency of vibration of caesium atoms that had been obtained with this clock.[br]Principal Honours and DistinctionsFRS 1960. Clockmakers' Company Tompion Gold Medal 1957. Physical Society C.V.Boys Prize 1957. USSR Academy of Science Popov Gold Medal 1959.Bibliography1957, with J.V.L.Parry, "The caesium resonator as a standard of frequency and time", Philosophical Transactions of the Royal Society (Series A) 25:45–69 (the first comprehensive description of the caesium clock).Further ReadingP.Forman, 1985, "Atomichron: the atomic clock from concept to commercial product", Proceedings of the IEEE 75:1,181–204 (an authoritative critical review of the development of the atomic clock).N.Cessons (ed.), 1992, The Making of the Modern World, London: Science Museum, pp.190–1 (contains a short account).See also: Marrison, Warren AlvinDV -
5 Riefler, Sigmund
SUBJECT AREA: Horology[br]b. 9 August 1847 Maria Rain, Germanyd. 21 October 1912 Munich, Germany[br]German engineer who invented the precision clock that bears his name.[br]Riefler's father was a scientific-instrument maker and clockmaker who in 1841 had founded the firm of Clemens Riefler to make mathematical instruments. After graduating in engineering from the University of Munich Sigmund worked as a surveyor, but when his father died in 1876 he and his brothers ran the family firm. Sigmund was responsible for technical development and in this capacity he designed a new system of drawing-instruments which established the reputation of the firm. He also worked to improve the performance of the precision clock, and in 1889 he was granted a patent for a new form of escapement. This escapement succeeded in reducing the interference of the clock mechanism with the free swinging of the pendulum by impulsing the pendulum through its suspension strip. It proved to be the greatest advance in precision timekeeping since the introduction of the dead-beat escapement about two hundred years earlier. When the firm of Clemens Riefler began to produce clocks with this escapement in 1890, they replaced clocks with Graham's dead-beat escapement as the standard regulator for use in observatories and other applications where the highest precision was required. In 1901 a movement was fitted with electrical rewind and was encapsulated in an airtight case, at low pressure, so that the timekeeping was not affected by changes in barometric pressure. This became the standard practice for precision clocks. Although the accuracy of the Riefler clock was later surpassed by the Shortt free-pendulum clock and the quartz clock, it remained in production until 1965, by which time over six hundred instruments had been made.[br]Principal Honours and DistinctionsFranklin Institute John Scott Medal 1894. Honorary doctorate, University of Munich 1897. Vereins zur Förderung des Gewerbefleisses in Preussen Gold Medal 1900.Bibliography1907, Präzisionspendeluhren und Zeitdienstanlagen fürSternwarten, Munich (for a complete bibliography see D.Riefler below).Further ReadingD.Riefler, 1981, Riefler-Präzisionspendeluhren, Munich (the definitive work on Riefler and his clock).A.L.Rawlings, 1948, The Science of Clocks and Watches, 2nd edn; repub. 1974 (a technical assessment of the Riefler escapement in its historical context).See also: Marrison, Warren AlvinDV -
6 Shortt, William Hamilton
SUBJECT AREA: Horology[br]b. 28 September 1881d. 4 February 1971[br]British railway engineer and amateur horologist who designed the first successful free-pendulum clock.[br]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.[br]Principal Honours and DistinctionsMaster of the Clockmakers' Company 1950. British Horological Society Gold Medal 1931. Clockmakers' Company Tompion Medal 1954. Franklin Institute John Price Wetherill Silver Medal.Bibliography1929, "Some experimental mechanisms, mechanical and otherwise, for the maintenance of vibration of a pendulum", Horological Journal 71:224–5.Further ReadingObituary, 1971, Proceedings of the Institution of Civil Engineers 56:396–7.F.Hope-Jones, 1949, Electrical Timekeeping, 2nd edn, London (a detailed but not entirely impartial account of the development of the free-pendulum clock).See also: Marrison, Warren AlvinDVBiographical history of technology > Shortt, William Hamilton
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