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

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, and the discovery of the X-ray, he deduced that cathode rays (see cathode ray tube), because they exhibited a single charge-to-mass ratio e/m, 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 realised 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 his being awarded a Nobel prize (1906). In one of the greatest ironies of modern physics his son George Paget Thomson later received the prize for proving that the electron was in fact 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" would eventually result in the invention of the mass spectrometer (then called a parabola spectrograph) by Francis Aston, a tool which 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 1918, he became Master of Trinity College, Cambridge, where he remained till his death. He died in 1940 and is buried in Westminster Abbey, close to Isaac Newton.

Further reading

• Dahl, Per F., "Flash of the Cathode Rays: A History of J.J. Thomson's Electron". Institute of Physics Publishing. June, 1997. ISBN 0750304537

External links

• About Joseph John Thomson
• The Discovery of the Electron