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Thomson, J(oseph) J(ohn) (1856-1940) was a British physicist who is famous for discovering the electron and for his research into the conduction of electricity through gases, for which he was awarded the 1906 Nobel Prize in Physics. He also received several other honours, including a knighthood in 1908 and the Order of Merit in 1912. Thomson was born at Cheetham Hill, near Manchester, on 18 December 1856, the son of an antiquarian bookseller. At the age of 14 he went to Owens College, Manchester (later Manchester University), to study engineering. When his father died two years later, however, his family could not afford the premium for engineering training and so, with the help of a scholarship, Thomson studied physics, chemistry and mathematics. In 1876 he won a scholarship to Trinity College, Cambridge, where he remained - except for visiting lectureships to Princeton University in 1896 and to Yale University in 1904 - for the rest of his life. After graduating in mathematics in 1880, he worked at the Cavendish Laboratory under Lord Rayleigh, succeeding him as Cavendish Professor of Experimental Physics in 1884. In 1919 he resigned the Cavendish professorship (being succeeded in turn by his student Ernest Rutherford), having been elected Master of Trinity College the previous year. He held this post until his death (in Cambridge) on 30 August 1940. Thomson's first important research concerned vortex rings, which won him the Adam's Prize in 1883. It was then thought that atoms may be in the form of vortex rings in the 'ether', an idea which although untrue, led Thomson to begin his investigations into cathode rays and these, in turn, led to his famous discovery of the electron in 1897. At the end of the 19th century there was considerable debate as to whether cathode rays were charged particles or whether they were some undefined process in the ether. Hertz had apparently shown that cathode rays were not deflected by an electric field (a finding which indicated that they were not particulate) but Thomson proved this to be incorrect in 1897, and demonstrated that Hertz's failure to obtain a deflection was caused by his use of an insufficiently evacuated cathode-ray tube. Having proved the particulate nature of cathode rays, Thomson went on to determine their charge-to-mass ratio, finding it to be constant - irrespective of the gas in the cathode ray tube - and with a value nearly 1,000 times smaller than that obtained for hydrogen ions in liquid electrolysis. He also measured the charge of the cathode-ray particles and found it to be the same in the gaseous discharge as in electrolysis. Thus he demonstrated that cathode rays are fundamental, negatively charged particles with a mass much less than the lightest atom known. He announced these findings during a lecture at the Royal Institution on 30 April 1897, calling the cathode- ray particles 'corpuscles'. The Dutch physicist Hendrik Lorentz later named them 'electrons' (a term first used - with a slightly different meaning - by the Irish physicist George Stoney), which became generally accepted. Thomson then spent several years investigating the nature and properties of electrons, after which he began researching into 'canal rays', streams of positively charged ions, which Thomson named positive rays. Using magnetic and electric fields to deflect these rays, he found (in 1912) that ions of neon gas are deflected by different amounts, indicating that they consist of a mixture of ions with different charge-to-mass ratios. The British chemist Frederick Soddy had earlier proposed the existence of isotopes and Thomson proved this idea correct when he identified - also in 1912 - the isotope neon-22. This work was later continued by Francis Aston (one of Thomson's students and, later, the developer of the mass spectrograph), A.J. Dempster and other scientists, and led to the discovery of many other isotopes. In addition to his pioneering research, Thomson wrote several notable works that were widely used in British universities, including Notes on Recent Researches in Electricity and Magnetism (1893), Elements of the Mathematical Theory of Electricity and Magnetism (1895) and, with John Poynting, the four-volume Textbook of Physics. Equally important, Thomson developed the Cavendish Laboratory into the world' s leading centre for subatomic physics in the early 20th century. Furthermore, he trained a generation of scientists who subsequently made fundamental contributions to physics: seven of his research assistants - including his only son, George Thomson - later won Nobel Prizes. Author not available, Thomson, J(oseph) J(ohn) (1856-1940). , The Hutchinson Dictionary of Scientific Biography, 01-01-1998. |