Joseph John Thomson

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Joseph John Thomson

J.J. Thomson

Sir Joseph John Thomson, OM, FRS (18 December 1856 - 30 August 1940) often known as J. J. Thomson, was an English physicist, the discoverer of the electron.

Joseph John Thomson was born in 1856 near Manchester in England, of Scottish parentage. He studied engineering at Owens College, Manchester, and moved on to Trinity College, Cambridge. In 1884 he became Cavendish Professor of Physics. In 1890 he married Rose Paget, and he had two children with her. One of his students was Ernest Rutherford, who would later succeed him in the post.

Influenced by the work of James Clerk Maxwell as well as the discovery of the X-ray, he deduced that cathode rays (produced by Crookes tube) exhibited a single charge-to-mass ratio e/m and must be composed of a single type of negatively charged particle. He called these particles "corpuscles." The term electron had been proposed earlier, by G. Johnstone Stoney, as a fixed quantum of electric charge in electrochemistry, but Thomson realized that it was also a subatomic particle, the first one to be discovered. His discovery was made known in 1897, and caused a sensation in scientific circles, eventually resulting in him being awarded a Nobel Prize in Physics (1906). His son George Paget Thomson later received the prize for proving that the electron also had properties of a wave (See wave-particle duality). Much of this work was done at the Cavendish Laboratory.

Thomson's investigations into the action of electrostatic and magnetic fields on the nature of so called "anode rays" or "canal rays" with an instrument he called a parabola spectrograph [1]) are considered as the invention of the mass spectrometer, a tool which was later improved by Francis Aston and allows the determination of the mass-to-charge ratio of ions and which has since become an ubiquitous research tool in Chemistry. Prior to the outbreak of World War I, he made another ground-breaking discovery: the isotope. In addition, Thomson proposed the Plum pudding model of the atom in 1904, though it was disproven in 1909.

He was knighted in 1908 and appointed to the Order of Merit in 1912. In 1914 he gave the Romanes Lecture in Oxford on "The atomic theory". In 1918 he became Master of Trinity College, Cambridge, where he remained until his death. He died in 1940 and was buried in Westminster Abbey, close to Sir Isaac Newton.

Thomson, a recipient of the Order of Merit, was knighted in 1908. He was elected Fellow of the Royal Society in 1884 and was President during 1916-1920; he received the Royal and Hughes Medals in 1894 and 1902, and the Copley Medal in 1914. He was awarded the Hodgkins Medal (Smithsonian Institute, Washington) in 1902; the Franklin Medal and Scott Medal (Philadelphia), 1923; the Mascart Medal (Paris), 1927; the Dalton Medal (Manchester), 1931; and the Faraday Medal (Institute of Civil Engineers) in 1938. He was President of the British Association in 1909 (and of Section A in 1896 and 1931) and he held honorary doctorate degrees from the Universities of Oxford, Dublin, London, Victoria, Columbia, Cambridge, Durham, Birmingham, Göttingen, Leeds, Oslo, Sorbonne, Edinburgh, Reading, Princeton, Glasgow, Johns Hopkins, Aberdeen, Athens, Cracow and Philadelphia.

Encyclopedia of World Biography on Joseph John Thomson, Sir

The English physicist Sir Joseph John Thomson (1856-1940) is credited with the discovery of the electron.

On Dec. 18, 1856, J. J. Thomson was born at Cheetham Hill near Manchester. His father, a bookseller and publisher, planned a career in engineering for Joseph, but since no apprenticeship could be found for him in any engineering firm, he was sent "temporarily" to college in Manchester at the age of 14. As a result of his ability and determination, he won a scholarship in 1876 and entered Trinity College, Cambridge; he remained there for the rest of his life.

After graduation Thomson began working in the Cavendish Laboratory, which was under the direction of Lord Rayleigh. Thomson's brilliance brought him membership in the Royal Society at 27 and his appointment as Rayleigh's successor at 28. He proved to be inspiring and effective both as a teacher and as a research director, and as time passed, students came to him from all over the world. He sometimes had as many as 40 to advise at once, and for the first quarter of the 20th century the Cavendish Laboratory, where Thomson insisted that theory should be considered "a policy, not a creed," was the world center for particle research.

Thomson began his studies of the properties of "cathode rays" in 1894 and proved in 1895 that they carried a negative charge. In 1897 he passed the rays through a vacuum and showed that they are deflected in both magnetic and electric fields. He was thus able to determine the ratio of the charge to the mass of the supposed particles and showed that its mass was about 2,000 times larger than the mass of the hydrogen atom. The identification of the electron necessitated a revision of the atomic concept: Thomson visualized it as a mass of positively charged matter in which electrons were distributed like raisins in a cake.

About 1906 Thomson turned his attention to "positive rays"--positively charged ions. By 1912, using his deflection techniques and measuring the charge to mass ratio, he had shown that neon was a mixture of at least two kinds of atoms, with differing deflectibilities. Thomson had thus opened the door to the world of isotopes and had provided a beginning for the method of analysis now known as mass spectrography.

During his career Thomson published 13 books and over 200 papers. He was awarded the Nobel Prize in physics in 1906 and was knighted in 1908. In 1918 he abandoned research to become master of Trinity College, where he died on Aug. 30, 1940.

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