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1 professorship
1 ( chair) chaire f ; to apply for/obtain a professorship postuler pour/obtenir une chaire ; the professorship of Physics la chaire de physique ; -
2 Weber, Wilhelm Eduard
SUBJECT AREA: Electricity[br]b. 24 October 1804 Wittenberg, Germanyd. 23 June 1891 Göttingen, Germany[br]German physicist, the founder of precise measurement of electrical quantities.[br]Weber began scientific experiments at an early age and entered the University of Halle, where he came under the influence of J.S.C.Schweigger, inventor of the galvanometer. Completing his education with a dissertation on the theory of organ pipes and making important contributions to the science of acoustics, he was awarded a lectureship and later an assistant professorship at Halle. Weber was offered the Chair of Physics at Göttingen in 1831 and jointly with Gauss began investigations into the precision measurement of magnetic quantities. In 1841 he invented the electrodynamometer type of electrical measuring instrument. This was a development of the galvanometer in which, instead of a needle, a small coil was suspended within an outer coil. A current flowing through both coils tended to turn the inner coil, the sine of the angle through which the suspending wires were twisted being proportional to the square of the strength of the current. A variation of the electrodynamometer was capable of measuring directly the power in electrical circuits.The introduction by Weber of a system of absolute units for the measurement of electrical quantities was a most important step in electrical science. He had a considerable influence on the British Association committees on electrical standards organized in 1861 to promote a coherent system of electrical units. Weber's ideas also led him to define elementary electric particles, ascribing mass and charge to them. His name was used for a time before 1883 as the unit of electric current, until the name "ampere" was proposed by Helmholtz. Since 1948 the term "weber" has been used for the SI unit of magnetic flux.[br]Principal Honours and DistinctionsFRS 1850. Royal Society Copley Medal 1859.Bibliography1892–4, William Weber's Werke, 6 vols, Berlin.Further ReadingP.Lenard, 1954, Great Men of Science, London, pp. 263–70 (a reliable, short biography). C.C.Gillispie (ed.), 1976, Dictionary of Scientific Biography, Vol. XIV, New York, pp.203–9 (discusses his theoretical contributions).S.P.Bordeau, 1982, Volts to Herz, Minneapolis, pp. 172 and 181 (discusses Weber's influence on contemporary scientists).GW -
3 Fermi, Enrico
[br]b. 29 September 1901 Rome, Italyd. 28 November 1954 Chicago, USA[br]Italian nuclear physicist.[br]Fermi was one of the most versatile of twentieth-century physicists, one of the few to excel in both theory and experiment. His greatest theoretical achievements lay in the field of statistics and his theory of beta decay. His statistics, parallel to but independent of Dirac, were the key to the modern theory of metals and the statistical modds of the atomic nucleus. On the experimental side, his most notable discoveries were artificial radioactivity produced by neutron bombardment and the realization of a controlled nuclear chain reaction, in the world's first nuclear reactor.Fermi received a conventional education with a chemical bias, but reached proficiency in mathematics and physics largely through his own reading. He studied at Pisa University, where he taught himself modern physics and then travelled to extend his knowledge, spending time with Max Born at Göttingen. On his return to Italy, he secured posts in Florence and, in 1927, in Rome, where he obtained the first Italian Chair in Theoretical Physics, a subject in which Italy had so far lagged behind. He helped to bring about a rebirth of physics in Italy and devoted himself to the application of statistics to his model of the atom. For this work, Fermi was awarded the Nobel Prize in Physics in 1938, but in December of that year, finding the Fascist regime uncongenial, he transferred to the USA and Columbia University. The news that nuclear fission had been achieved broke shortly before the Second World War erupted and it stimulated Fermi to consider this a way of generating secondary nuclear emission and the initiation of chain reactions. His experiments in this direction led first to the discovery of slow neutrons.Fermi's work assumed a more practical aspect when he was invited to join the Manhattan Project for the construction of the first atomic bomb. His small-scale work at Columbia became large-scale at Chicago University. This culminated on 2 December 1942 when the first controlled nuclear reaction took place at Stagg Field, Chicago, an historic event indeed. Later, Fermi spent most of the period from September 1944 to early 1945 at Los Alamos, New Mexico, taking part in the preparations for the first test explosion of the atomic bomb on 16 July 1945. President Truman invited Fermi to serve on his Committee to advise him on the use of the bomb. Then Chicago University established an Institute for Nuclear Studies and offered Fermi a professorship, which he took up early in 1946, spending the rest of his relatively short life there.[br]Principal Honours and DistinctionsNobel Prize for Physics 1938.Bibliography1962–5, Collected Papers, ed. E.Segrè et al., 2 vols, Chicago (includes a biographical introduction and bibliography).Further ReadingL.Fermi, 1954, Atoms in the Family, Chicago (a personal account by his wife).E.Segrè, 1970, Enrico Fermi, Physicist, Chicago (deals with the more scientific aspects of his life).LRD -
4 Cady, Walter Guyton
[br]b. 10 December 1874 Providence, Rhode Island, USAd. 9 December 1974 Providence, Rhode Island, USA[br]American physicist renowned for his pioneering work on piezo-electricity.[br]After obtaining BSc and MSc degrees in physics at Brown University in 1896 and 1897, respectively, Cady went to Berlin, obtaining his PhD in 1900. Returning to the USA he initially worked for the US Coast and Geodetic Survey, but in 1902 he took up a post at the Wesleyan University, Connecticut, remaining as Professor of Physics from 1907 until his retirement in 1946. During the First World War he became interested in piezo-electricity as a result of attending a meeting on techniques for detecting submarines, and after the war he continued to work on the use of piezo-electricity as a transducer for generating sonar beams. In the process he discovered that piezo-electric materials, such as quartz, exhibited high-stability electrical resonance, and in 1921 he produced the first working piezo-electric resonator. This idea was subsequently taken up by George Washington Pierce and others, resulting in very stable oscillators and narrow-band filters that are widely used in the 1990s in radio communications, electronic clocks and watches.Internationally known for his work, Cady retired from his professorship in 1946, but he continued to work for the US Navy. From 1951 to 1955 he was a consultant and research associate at the California Institute of Technology, after which he returned to Providence to continue research at Brown, filing his last patent (one of over fifty) at the age of 93 years.[br]Principal Honours and DistinctionsPresident, Institute of Radio Engineers 1932. London Physical Society Duddell Medal. Institute of Electrical and Electronics Engineers Morris N.Liebmann Memorial Prize 1928.Bibliography28 January 1920, US patent no. 1,450,246 (piezo-electric resonator).1921, "The piezo-electric resonator", Physical Review 17:531. 1946, Piezoelectricity, New York: McGraw Hill (his classic work).Further ReadingB.Jaffe, W.R.Cooke \& H.Jaffe, 1971, Piezoelectric Ceramics.KF -
5 Poulsen, Valdemar
[br]b. 23 November 1869 Copenhagen, Denmarkd. 23 July 1942 Gentofte, Denmark[br]Danish engineer who developed practical magnetic recording and the arc generator for continuous radio waves.[br]From an early age he was absorbed by phenomena of physics to the exclusion of all other subjects, including mathematics. When choosing his subjects for the final three years in Borgedydskolen in Christianshavn (Copenhagen) before university, he opted for languages and history. At the University of Copenhagen he embarked on the study of medicine in 1889, but broke it off and was apprenticed to the machine firm of A/S Frichs Eftf. in Aarhus. He was employed between 1893 and 1899 as a mechanic and assistant in the laboratory of the Copenhagen Telephone Company KTAS. Eventually he advanced to be Head of the line fault department. This suited his desire for experiment and measurement perfectly. After the invention of the telegraphone in 1898, he left the laboratory and with responsible business people he created Aktieselskabet Telegrafonen, Patent Poulsen in order to develop it further, together with Peder Oluf Pedersen (1874– 1941). Pedersen brought with him the mathematical background which eventually led to his professorship in electronic engineering in 1922.The telegraphone was the basis for multinational industrial endeavours after it was demonstrated at the 1900 World's Exhibition in Paris. It must be said that its strength was also its weakness, because the telegraphone was unique in bringing sound recording and reproduction to the telephone field, but the lack of electronic amplifiers delayed its use outside this and the dictation fields (where headphones could be used) until the 1920s. However, commercial interest was great enough to provoke a number of court cases concerning patent infringement, in which Poulsen frequently figured as a witness.In 1903–4 Poulsen and Pedersen developed the arc generator for continuous radio waves which was used worldwide for radio transmitters in competition with Marconi's spark-generating system. The inspiration for this work came from the research by William Duddell on the musical arc. Whereas Duddell had proposed the use of the oscillations generated in his electric arc for telegraphy in his 1901 UK patent, Poulsen contributed a chamber of hydrogen and a transverse magnetic field which increased the efficiency remarkably. He filed patent applications on these constructions from 1902 and the first publication in a scientific forum took place at the International Electrical Congress in St Louis, Missouri, in 1904.In order to use continuous waves efficiently (the high frequency constituted a carrier), Poulsen developed both a modulator for telegraphy and a detector for the carrier wave. The modulator was such that even the more primitive spark-communication receivers could be used. Later Poulsen and Pedersen developed frequency-shift keying.The Amalgamated Radio-Telegraph Company Ltd was launched in London in 1906, combining the developments of Poulsen and those of De Forest Wireless Telegraph Syndicate. Poulsen contributed his English and American patents. When this company was liquidated in 1908, its assets were taken over by Det Kontinentale Syndikat for Poulsen Radio Telegrafi, A/S in Copenhagen (liquidated 1930–1). Some of the patents had been sold to C.Lorenz AG in Berlin, which was very active.The arc transmitting system was in use worldwide from about 1910 to 1925, and the power increased from 12 kW to 1,000 kW. In 1921 an exceptional transmitter rated at 1,800 kW was erected on Java for communications with the Netherlands. More than one thousand installations had been in use worldwide. The competing systems were initially spark transmitters (Marconi) and later rotary converters ( Westinghouse). Similar power was available from valve transmitters only much later.From c. 1912 Poulsen did not contribute actively to further development. He led a life as a well-respected engineer and scientist and served on several committees. He had his private laboratory and made experiments in the composition of matter and certain resonance phenomena; however, nothing was published. It has recently been suggested that Poulsen could not have been unaware of Oberlin Smith's work and publication in 1888, but his extreme honesty in technical matters indicates that his development was indeed independent. In the case of the arc generator, Poulsen was always extremely frank about the inspiration he gained from earlier developers' work.[br]Bibliography1899, British patent no. 8,961 (the first British telegraphone patent). 1903, British patent no. 15,599 (the first British arc-genera tor patent).His scientific publications are few, but fundamental accounts of his contribution are: 1900, "Das Telegraphon", Ann. d. Physik 3:754–60; 1904, "System for producing continuous oscillations", Trans. Int. El. Congr. St. Louis, Vol. II, pp. 963–71.Further ReadingA.Larsen, 1950, Telegrafonen og den Traadløse, Ingeniørvidenskabelige Skrifter no. 2, Copenhagen (provides a very complete, although somewhat confusing, account of Poulsen's contributions; a list of his patents is given on pp. 285–93).F.K.Engel, 1990, Documents on the Invention of Magnetic Re cor ding in 1878, New York: Audio Engineering Society, reprint no. 2,914 (G2) (it is here that doubt is expressed about whether Poulsen's ideas were developed independently).GB-N
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