Sir Joseph John "J. J." Thomson, OM, FRS[1] (18 December 1856 – 30 August 1940) was a British physicist. In 1897, Thomson showed that cathode rays were composed of a previously unknown negatively charged particle, and thus is credited with the discovery and identification of the electron. Thomson is also credited with finding the first evidence for isotopes of a stable (non-radioactive) element in 1913 as part of his exploration into the composition of canal rays (positive ions) and with the invention of the mass spectrometer. Thomson was awarded the 1906 Nobel Prize in Physics for the discovery of the electron and for his work on the conduction of electricity in gases.

J. J. Thomson, 1861.


Joseph John Thomson was born in 1856 in Cheetham Hill, Manchester, England. His mother, Emma Swindells, came from a local textile family. His father, Joseph James Thomson, ran an antiquarian bookshop founded by a great-grandfather. He had a brother two years younger than him, Frederick Vernon Thoms
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His early education was in small private schools where he demonstrated great talent and interest in science. In 1870 he was admitted to Owens College at the unusually young age of 14. His parents planned to enroll him as an apprentice engineer to Sharp-Stewart & Co, a locomotive manufacturer, but these plans were cut short when his father died in 1873

He moved on to Trinity College, Cambridge in 1876. In 1880, he obtained his BA in mathematics (Second Wrangler and 2nd Smith's Prize) and MA (with Adams Prize) in 1883.[3] In 1884 he became Cavendish Professor of Physics. One of his students was Ernest Rutherford, who later succeeded him in the post. In 1890 he married Rose Elisabeth Paget, daughter of Sir George Edward Paget, KCB, a physician and then Regius Professor of Physic at Cambridge. He had one son, George Paget Thomson, and one daughter, Joan Paget Thomson, with her. One of Thomson's greatest contributions to modern science was in his role as a highly gifted teacher: seven of his research assistants and his son won Nobel Prizes in physics. His son won the Nobel Prize in 1937 for proving the wavelike properties of electrons.
He was awarded a Nobel Prize in 1906, "in recognition of the great merits of his theoretical and experimental investigations on the conduction of electricity by gases." 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 on August 30, 1940 and was buried in Westminster Abbey, close to Sir Isaac Newton.
Thomson was elected a Fellow of the Royal Society[1] on 12 June 1884 and was President of the Royal Society from 1915 to 1920.

Several scientists, such as William Prout and Norman Lockyer, had suggested that atoms were built up from a more fundamental unit, but they envisioned this unit to be the size of the smallest atom, hydrogen. Thomson, in 1897, was the first to suggest that the fundamental unit was over 1000 times smaller than an atom, suggesting the subatomic particles now known as electrons. Thomson discovered this through his explorations on the properties of cathode rays. Thomson made his suggestion on 30 April 1897 following his discovery that Lenard rays could travel much further through air than expected for an atom-sized particle.[4] He estimated the mass of cathode rays by measuring the heat generated when the rays hit a thermal junction and comparing this with the magnetic deflection of the rays. His experiments suggested not only that cathode rays were over 1000 times lighter than the hydrogen atom, but also that their mass was the same whatever type of atom they came from. He concluded that the rays were composed of very light, negatively charged particles which were a universal building block of atoms. He called the particles "corpuscles", but later scientists preferred the name electron which had been suggested by George Johnstone Stoney in 1891, prior to Thomson's actual discovery.[5]
In April 1897 Thomson had only early indications that the cathode rays could be deflected electrically (previous investigators such as Heinrich Hertz had thought they could not be). A month after Thomson's announcement of the corpuscle he found that he could reliably deflect the rays by an electric field if he evacuated the discharge tube to a very low pressure. By comparing the deflection of a beam of cathode rays by electric and magnetic fields he obtained more robust measurements of the mass to charge ratio that confirmed his previous estimates.[6] This became the classic means of measuring the charge and mass of the electron.
Thomson believed that the corpuscles emerged from the atoms of the trace gas inside his cathode ray tubes. He thus concluded that atoms were divisible, and that the corpuscles were their building blocks. To explain the overall neutral charge of the atom, he proposed that the corpuscles were distributed in a uniform sea of positive charge; this was the "plum pudding" model—the electrons were embedded in the positive charge like plums in a plum pudding (although in Thomson's model they were not stationary, but orbiting rapidly