J. J. Thomson

Joseph John Thomson was born on December 18, 1856, at Cheetham Hill near Manchester, the elder son of his family.⁠[1][2][3][4][5]

His father, Joseph James Thomson (died 1873), was an antiquarian bookseller and publisher with a shop in a suburb of Manchester. His mother, Emma Swindells (died 1901), came from a branch of the local Vernon family, who owned a Manchester cotton-spinning firm; Westminster Abbey’s page prints her maiden name as Swindell.⁠[6][4][7][5][8][3][9]

His younger brother, Frederick Vernon Thomson, was born in 1859, worked for the calico merchants Claflin & Co. and died in 1917. He grew up in a middle-class household with his parents and younger brother.⁠[4][6][9][5]

As a child he was chiefly interested in botany, an interest he kept all his life, and he had little exposure to physics or mathematics.⁠[9][5]

His parents expected him to become a locomotive engineer, but the apprenticeship he planned at Sharp, Stewart & Co. had too long a waiting list. At 14 his father entered him at Owens College, Manchester, now the University of ManchesterUniversity of ManchesterThe University of Manchester is a research university in Manchester, England, formed in 2004 by combining the Victoria University of Manchester and the University of Manchester Institute of Science and Technology (UMIST). It traces its origins to 1824 and is a member of the Russell Group.Open the full entry, to begin training as an engineer, and he expected to become an engineering apprentice. The Nobel Prize biography gives the year of enrolment as 1870; the catalogue of his supplementary papers compiled by the National Cataloguing Unit for the Archives of Contemporary Scientists (NCUACS) gives 1871. He later regarded entering Owens College as the first key turning point of his life.⁠[5][9][7][8][2][4]

At Owens College he studied with Osborne Reynolds and took some of the first courses in experimental physics; he studied engineering, mathematics, physics and chemistry there, and by the time he left in 1876 he had given up engineering and wanted to do original research.⁠[8][4]

Two years after he entered the college, in 1873, his father died, when Thomson was sixteen, and the family’s finances worsened, putting an engineering apprenticeship out of reach. Thomas Barker, the professor of mathematics, persuaded him to finish his engineering course, after which he spent an extra year at Owens studying mathematics and physics and won scholarships in mathematics, taught by Barker, and physics, taught by Balfour Stewart. It was his mathematics professor who encouraged him to apply for a scholarship to Trinity College, University of Cambridge.⁠[5][9][6][10][11]

In 1876 he won an entrance scholarship to Trinity College and entered as a minor scholar to read mathematics. He failed the entrance examination at the first attempt and passed at the second, entering in October 1876 at the age of 19. He later regarded applying for the Trinity scholarship as the second key turning point of his life, having never planned to pursue an advanced education. The Royal Society of Edinburgh’s obituary, however, states that he had been a member of Trinity College uninterruptedly since 1875.⁠[2][4][5][12][13]

Cambridge mathematics at the time relied on physical analogies and a mechanical world-view built on analytical dynamics such as Lagrange’s equations and Hamilton’s principle; his coach, Edward Routh, gave him a thorough grounding in these methods. His advisers at Cambridge included Edward John Routh, William Davidson Niven and Lord RayleighLord RayleighLord Rayleigh (John William Strutt, 3rd Baron Rayleigh, 1842–1919) was a British physicist whose work ranged over acoustics, optics and electricity; he explained the blue of the sky by scattering, wrote The Theory of Sound and, with Sir William Ramsay, discovered argon, receiving the whole of the 1904 Nobel Prize in Physics for his investigations of gas densities and the discovery of argon.Open the full entry.⁠[9][11]

In 1880 he came second in the Mathematical Tripos as Second Wrangler, behind Joseph Larmor, and was Second Smith’s Prizeman; that year he took his BA in mathematics.⁠[2][10][13][11][4]

In 1880 he became a Fellow of Trinity College; he stayed in Cambridge, chose to concentrate on physics and began experimental work at the Cavendish Laboratory under Lord Rayleigh. His Fellowship dissertation extended a known result of dynamics about two mutually influencing bodies to physical and chemical phenomena whose mechanism may be unknown: for example, if the magnetization of iron changes with temperature, a magnet moved between fields must be heated. It won a Fellowship at the first attempt, and the Royal Society of Edinburgh’s obituary considers that its central idea strongly influenced physical chemistry.⁠[2][4][12]

In 1881 he published a major paper in the Philosophical Magazine showing that the mass of a charged particle increases when it moves: a moving electrified sphere, acting as a current, gains extra mass from its charge. This was an early hint of a link between mass and energy, and he was the first to suggest electromagnetic mass.⁠[4][9]

His Treatise on the Motion of Vortex Rings won the Adams Prize, which the Nobel Prize biography dates to 1884; Isobel Falconer’s article in a supplement to the Macmillan Encyclopedia of Physics states that he won the prize in 1882 for A Treatise on Vortex Motion. The treatise examined the stability of interlocked vortex rings and developed the idea that atoms were vortices in the ether, linked to the periodic table, showing his early interest in atomic structure.⁠[2][9][13]

Building on Kelvin’s vortex-ring atoms, he modelled electrical discharge in gases as the dissociation of paired vortex rings, a model that predicted that the field needed for discharge falls as the gas is rarefied.⁠[12]

In 1883 he became a Lecturer of Trinity College, and that year he took his MA in mathematics. His early work in the 1880s on the chemical combination of gases informed his later research on the electron.⁠[2][4][11][5]

On June 12, 1884, he was elected a Fellow of the Royal Society.⁠[6][2][4]

That year he succeeded Lord Rayleigh as Cavendish Professor of Experimental Physics at the University of Cambridge, at the age of 28; the Cavendish Laboratory had been founded in 1871 with James Clerk Maxwell as the first Cavendish Professor, and Thomson was the third, after Maxwell and Lord Rayleigh. Isobel Falconer writes that at college he had identified himself with Cambridge values and social mores, and that the appointment came once his conventional standing and scientific record were established. The Cavendish Laboratory’s historical timeline says that his appointment marked the start of an exciting era of exploring the inner workings of molecules and atoms.⁠[2][4][3][9][10][14][8]

He was inexperienced at experiments but learned quickly and led a flourishing period of experimental physics at the Cavendish. His former assistant H. F. Newall recalled: “J.J. was very awkward with his fingers, and I found it very necessary not to encourage him to handle the instruments!” and added: “But he was very helpful in talking over the ways in which he thought things ought to go.”⁠[10]

The NCUACS catalogue states that under him the Cavendish became the leading experimental physics laboratory in the world, and that his reputation drew talented young researchers such as E. Rutherford, J. S. E. Townsend and J. A. McClelland.⁠[4]

The Nobel Prize biography gives his tenure of the chair as 1884–1918, and the NCUACS catalogue and the Trinity College memorial inscription speak of thirty-four years; the American Institute of Physics’ exhibit and Isobel Falconer’s article state that he resigned the Cavendish professorship in 1919.⁠[2][4][13][10][9]

On January 22, 1890, he married Rose Elisabeth Paget. Her father, Sir George Edward Paget, KCB (born 1809), was a physician, elected a Fellow of the Royal Society in 1873 and knighted in 1885; the NCUACS catalogue calls him Regius Professor of Physic at Cambridge from 1872 to 1892, Isobel Falconer’s article Cambridge’s Professor of Physic (medicine), and Trinity College’s memorial page prints Regius Professor of Physics.⁠[10][2][13][4][9][6]

Rose Paget, born in 1860, belonged to the first generation of women admitted to advanced university study and had been his student at the Cavendish Laboratory, attending his lectures; in 1889 she carried out experiments on soap films there. Her name is printed Rose Elisabeth in the Nobel Prize biography and on Trinity College’s memorial page, and Rose Elizabeth in the NCUACS catalogue.⁠[3][10][5][2][13][4]

In 1893 he discovered electromagnetic momentum, which the Royal Society of Edinburgh’s obituary calls perhaps his greatest achievement in pure theory, noting that the principle is necessary for the construction of the energy tensor and so for relativity and quantum electrodynamics. In 1894 he received the Royal Medal of the Royal Society and was President of the Cambridge Philosophical Society.⁠[12][2][11][4]

In 1895 Cambridge introduced the status of “advanced student,” which brought many graduates of other universities to his laboratory; the first generation of physics graduate students included Ernest Rutherford (who graduated in 1899) and Charles Wilson, who, like Thomson, went on to win Nobel Prizes. X-rays were discovered that year and proved crucial, because they ionized a gas in a controllable way, allowing the effects of ionization to be separated from those of secondary radiation; within a year he and his student Rutherford had convincing evidence for his theory that discharge occurs through the ionization of molecules.⁠[12][14][9]

In 1896 he visited the United StatesUnited StatesThe United States is a federal country in North America made up of 50 states, the District of Columbia as the seat of government, and territories such as Puerto Rico and Guam; its capital is Washington, D.C. The Continental Congress adopted the Declaration of Independence on July 4, 1776. The 2020 census (April 1, 2020) counted a resident population of 331,449,281, and the 435 seats of the House of Representatives are apportioned among the states on the basis of the census.Open the full entry to give a course of four lectures summarizing his current research at Princeton UniversityPrinceton UniversityPrinceton University is a private university and Ivy League member in Princeton, New Jersey. Chartered on October 22, 1746 as the College of New Jersey, it moved to Princeton in 1756 and adopted its present name in 1896. Undergraduate education leads to A.B. and B.S.E. degrees and emphasizes small-group discussion, independent research and residential college life. Graduate education spans the humanities, social sciences, natural sciences and engineering. As of October 2026, Christopher L. Eisgruber was president. Its 2026–27 operating budget was $3.407 billion, including $342 million for undergraduate aid.Open the full entry, published in 1898 as The Discharge of Electricity through Gases. That year he was president of Section A of the British Association.⁠[2][2][4]

In 1893 he wrote: “There is no other branch of physics which affords us so promising an opportunity of penetrating the secret of electricity.” At the time it was undecided what the cathode rays in vacuum tubes were: Hittorf had shown in 1869 that they travel in straight lines; some thought them waves in the ether, others material particles, and Thomson and many other physicists thought that material particles might themselves be structures made of ether. German physicists such as Hertz and Lenard favoured the ether-wave explanation, British physicists including Thomson the particle view.⁠[15][12]

Magnets could deflect the rays, but Heinrich Hertz found that they were not deflected by an electric field as charged particles should be; Hertz and his student Philipp Lenard also found that the glass still glowed with a thin metal foil placed in the rays’ path, as if the rays were waves. In 1894 Thomson measured the velocity of the rays with a rotating mirror and found it far below that of light. In 1895 Jean Perrin in France showed that cathode rays carried a negative charge, and in January 1897 Emil Wiechert in Germany measured a mass-to-charge ratio more than a thousand times smaller than that of the smallest charged atom.⁠[15][12][16]

He carried out three experiments. The first adapted Jean Perrin’s experiment of 1895: when the rays entered a slit in a pair of metal cylinders, the connected electrometer registered a large negative charge, and when a magnet bent the rays away from the slit the charge almost vanished, showing that the charge and the rays could not be separated. In the second he removed nearly all the gas from the tube, and the rays were then bent by an electric field; earlier failures had been due to residual gas made conductive by the rays. In the third he measured how much a magnetic field bent the rays and how much energy they carried, and from these calculated the particles’ mass-to-charge ratio; with various tubes and gases it came out more than a thousand times smaller than that of a charged hydrogen atom.⁠[16]

He balanced the electric and magnetic deflections to find the particles’ speed and then used the magnetic deflection to obtain the mass-to-charge ratio, which was independent of the gas and of the cathode and less than a thousandth of that of the hydrogen ion. C. T. R. Wilson’s method indicated a charge equal to that of the hydrogen ion, so the particle was far smaller than the smallest atom.⁠[12]

Such a ratio meant that the particles either carried a very large charge or were extremely light for their charge. Philipp Lenard passed cathode rays through a metal foil and measured how far they travelled through various gases, concluding that if they were particles they must be far lighter than any atom; the result was not conclusive, but measurements of the charge by other researchers within the next two years supported it.⁠[16][15]

He concluded that cathode rays are “charges of negative electricity carried by particles of matter,” and asked whether these particles were atoms, molecules or matter in a still finer state of subdivision. The particles were smaller than any atom and a building block of all atoms; he called them corpuscles, now called electrons. He also proposed that in the cathode rays matter was in a new state, subdivided much further than in an ordinary gas, in which all matter is of one and the same kind, the substance from which all the chemical elements are built up. BritannicaEncyclopædia BritannicaEncyclopædia Britannica is a general English-language encyclopedia first published in Edinburgh, Scotland, in 1768; the name also refers to its publisher, Chicago-based Encyclopædia Britannica, Inc. (which presents itself as The Britannica Group). The print edition ended in 2012, and the company’s main businesses since then have been the online encyclopedia Britannica.com, digital education products for schools and libraries, and Merriam-Webster dictionaries.Open the full entry’s summary states that by measuring how electric and magnetic fields deflected the particles he found them to be nearly 2,000 times less massive than the lightest known atomic particle.⁠[16][15][9][17][5][1]

He made the first public announcement of the discovery in his evening lecture at the Royal Institution on Friday, April 30, 1897, describing the particles as a state of matter “more finely subdivided” than the atom of an element and relating this to the old idea that the elements are compounds of one primordial substance; he suggested that the corpuscles, present in all atoms, rather than hydrogen as in Prout’s hypothesis, were that fundamental substance. The NCUACS catalogue states that he argued that the cathode-ray particles were more than a thousand times lighter than the lightest atom and a universal constituent of matter, opening subatomic physics to experiment.⁠[2][4][12][5]

From his 1897 experiments he put forward three hypotheses: cathode rays are charged particles; these corpuscles are parts of atoms; and they are the only parts of atoms. At first few believed in bodies smaller than atoms; he later recalled that a distinguished physicist who had attended his Royal Institution lecture said to him long afterwards that he had thought Thomson had been pulling their legs. The second and third hypotheses were especially controversial; the third proved false, while the first two were gradually accepted, though their meanings shifted somewhat.⁠[18]

The word electron had been coined by G. Johnstone Stoney in 1891 for the unit of charge found in experiments passing current through chemicals; Joseph Larmor, Thomson’s Cambridge classmate, used the word in that sense and described the electron as a structure in the ether, not as part of the atom. In 1897 the Irish physicist George Francis FitzGerald suggested that Thomson’s corpuscles were really free electrons, but he meant electrons of Larmor’s kind and was in fact disagreeing with Thomson.⁠[18]

In an 1899 paper he described the atom as an uncharged unit containing negatively charged corpuscles within a space of positive charge; in 1903 he revised this, with corpuscles revolving within a positively charged sphere, and he often called his work on the structure of the atom a “rough analogy.” The model is often called the plum pudding or raisin cake model. Isobel Falconer describes thousands of corpuscles orbiting in a sphere of positive electrification and judges the model quite sophisticated, giving a qualitative account of the periodic table and of ionic bonding; the American Institute of Physics’ exhibit describes thousands of tiny negatively charged corpuscles floating in a cloud of massless positive charge.⁠[5][18][9]

The model inspired many physicists, notably his own student Ernest Rutherford, to develop more detailed models of the atom. Rutherford refuted it with a different kind of particle beam, finding evidence for a small central core, the nucleus, and suggested that the atom might resemble a tiny solar system, with a few electrons orbiting a massive positive centre. Rutherford wrote in 1911 that Thomson’s model did not stand up to the weight of experimental evidence but had been useful in pointing out new lines of research.⁠[5][18]

In 1902 he received the Hughes Medal of the Royal Society and the Hodgkins Medal of the Smithsonian InstitutionSmithsonian InstitutionThe Smithsonian Institution is a museum, education and research institution created by the U.S. Congress in 1846 with the bequest of the English scientist James Smithson. Based in Washington, D.C., it runs museums such as the National Air and Space Museum and the National Museum of Natural History, as well as the National Zoo.Open the full entry. In 1903 he published Conduction of Electricity through Gases, which Lord Rayleigh described as a review of “Thomson's great days at the Cavendish Laboratory.” That year he proposed a discontinuous theory of light that anticipated Albert EinsteinAlbert EinsteinAlbert Einstein (1879–1955) was a German-born physicist who formulated the special theory of relativity in 1905 and the general theory in 1915 and received the 1921 Nobel Prize in Physics for his discovery of the law of the photoelectric effect. From 1933 until his death he was a professor at the Institute for Advanced Study in Princeton, New Jersey, United States.Open the full entry’s later photon theory; Isobel Falconer considers that his work on the structure of light expedited the acceptance of the quantum theory of radiation in Britain.⁠[2][11][2][17][9]

In 1904 he returned to the United States to deliver six lectures on electricity and matter at Yale UniversityYale UniversityYale University is a research university in New Haven, Connecticut. Its predecessor, the Collegiate School, received a charter in 1701. Trustees chose New Haven in 1716; the institution became Yale College in 1718 and Yale University in 1887. Yale provides undergraduate, graduate and professional education and has 14 undergraduate residential colleges. As of October 2026, its president was Maurie McInnis, who took office in July 2024. In 2026, Yale expanded aid for incoming undergraduates and celebrated its 325th anniversary.Open the full entry, which contained some important suggestions as to the structure of the atom.⁠[2]

From 1905 he turned his attention away from cathode rays towards positive rays, beginning experiments with positive ions to investigate the mass of the atom.⁠[4][9]

He received the whole of the 1906 Nobel Prize in Physics “in recognition of the great merits of his theoretical and experimental investigations on the conduction of electricity by gases.” At the time of the award his affiliation was the University of Cambridge.⁠[1]

At the award ceremony on December 10, 1906, the presentation speech was given by J. P. Klason, President of the Royal Swedish Academy of Sciences. It described how he and C. T. R. Wilson had used Röntgen rays to produce small charged particles in air and exploited the property, found by Richard von Helmholtz in 1887, that small charged particles condense steam around them: he measured the total charge in a sample of air, expanded the steam-saturated air so that droplets formed on the charged particles, calculated the droplets’ size from the speed of their fall and divided the total charge among them, finding a charge of 3.4 × 10⁻¹⁰ electrostatic units on each particle, close to the estimates of the kinetic theory of gases; from this the number of molecules in a cubic centimetre of gas at zero degrees and one atmosphere was calculated as not less than 40 × 10¹⁸.⁠[19]

The speech said that he and many students had studied the charged particles produced in gases by Röntgen rays, Becquerel rays, ultraviolet light, discharge from points and glowing metals, the most notable being the cathode-ray particles in highly rarefied gases, called electrons, whose foremost investigators were Philipp Lenard, the previous year’s laureate in physics, and Thomson; if an electron carries one negative unit charge, it has about a thousandth of the mass of the lightest atom, hydrogen. Since all substances studied can emit negative electrons, he held that negative charge is the real form of electricity and positive charge the result of atoms losing electrons, giving physical meaning to Benjamin FranklinBenjamin FranklinBenjamin Franklin (January 17, 1706 – April 17, 1790) was a printer, publisher, scientist, diplomat, and statesman of colonial North America and the founding era of the United States, and one of the Founding Fathers of the United States. In Philadelphia he ran the Pennsylvania Gazette and published Poor Richard’s Almanack, founded the first lending library in North America, and proposed the school that later became the University of Pennsylvania; known for his electrical experiments and inventions such as the lightning rod, he served as the first Postmaster General of the United States, took part in drafting the Declaration of Independence, signed the treaty between the United States and France while in France, and signed the Treaty of Paris that ended the Revolutionary War.Open the full entry’s view of 1747 that there is only one kind of electricity.⁠[19]

The speech also noted that in 1892 he had shown that a charged body in motion possesses electromagnetic energy, which increases its apparent mass; from Kaufmann’s measurements of the velocities of beta rays from radium he concluded that negative electrons have no real mass, only an apparent mass due to their charge, while his investigations of 1906 seemed to show that only about a thousandth of the mass of matter is apparent and due to electric forces. Klason closed by praising him for treading in the footsteps of his great compatriots Faraday and Maxwell.⁠[19]

On December 11 he delivered his Nobel Lecture, “Carriers of Negative Electricity.”⁠[20]

Also in 1906 he pioneered the use of scattering calculations in atomic theory, showing that the number of corpuscles in an atom was comparable to its atomic weight.⁠[9]

In 1908 he was knighted by Edward VII. In 1909 he was President of the British Association for the Advancement of Science, presiding over its annual meeting in Winnipeg, Canada. In 1910 he was President of the Junior Institution of Electrical Engineers.⁠[2][7][9][4][5][3][11]

In 1912 he was appointed to the Order of Merit.⁠[9][4][13]

Using positive rays to separate different kinds of atoms and molecules, he found, besides the parabola of atomic weight 20, another corresponding to atomic weight 22, and with his research assistant F. W. Aston discovered the isotopes of neon, the first non-radioactive isotopes to be found; the work also led to the recognition of the H3+ ion. The NCUACS catalogue dates the discovery of the neon isotopes to 1912, Isobel Falconer’s article to 1913.⁠[2][12][4][9][5]

The method was later developed by Aston, Dempster and others, leading to the discovery of many isotopes. Isobel Falconer’s article states that the discovery of the neon isotopes prompted Aston’s invention of the mass spectrograph in 1919; the Science History Institute’s profile states that Thomson’s work led to the development of the mass spectrograph, which Aston used to discover isotopes in a large number of elements; Britannica’s summary states that Thomson invented mass spectrometry.⁠[2][9][5][17]

In 1914 he received the Copley Medal of the Royal Society and gave the Romanes Lecture at Oxford, on “The atomic theory.”⁠[2][11][13]

Isobel Falconer’s article, the American Institute of Physics’ record, the NCUACS catalogue and Trinity College’s memorial page give his presidency of the Royal Society as 1915–1920; the Nobel Prize biography gives 1916–1920.⁠[9][11][4][13][2]

During the First World War he advised various government departments and served on the Board of Invention and Research, set up in July 1915 by Arthur Balfour, then First Lord of the Admiralty, to mobilise the country’s science for the war.⁠[9][4]

In 1918 he was appointed Master of Trinity College, a Crown appointment, and held the post until his death. When he gave up the Cavendish professorship, the University made him Honorary Professor of Physics so that he could continue his research there. The American Institute of Physics’ exhibit describes him as guiding the College with his characteristic good sense and kindness.⁠[2][9][4][13][17][10]

His former student Ernest Rutherford succeeded him as Cavendish Professor in 1919.⁠[13][5][14]

He became a leading public voice for science. From 1919 to 1923 he was a member of the University Grants Committee, and he served on the Committee on Science in the Educational System of Great Britain; he helped to form the Department of Scientific and Industrial Research, set up in 1919, and sat on its advisory council until 1927.⁠[4][9]

He continued to work on the discharge of electricity through gases for the rest of his life, though this work was overshadowed by his discovery of the electron. After leaving the Cavendish chair he remained active in the laboratory, publishing fifty more papers before his death in 1940, and he continued experimenting until a few years before his death; Isobel Falconer considers that this work laid, among other things, the foundations of plasma physics.⁠[4][5][9]

On November 30, 1921, he unveiled the memorial to his predecessor in the Cavendish chair, Lord Rayleigh, in Westminster Abbey, a tablet with a portrait relief by Francis Derwent Wood.⁠[21][2]

With his son George he wrote a new edition of Conduction of Electricity through Gases, published in two volumes in 1928 and 1933. In 1931 he was again president of Section A of the British Association. In 1936 he published his autobiography, Recollections and Reflections.⁠[2][2][4][2]

He died at the Trinity Lodge, Trinity College, Cambridge, on August 30, 1940, at the age of 83.⁠[12][1][2][13]

On September 4, 1940, his ashes were interred in the nave of Westminster Abbey during his funeral service, near the graves of Sir Isaac Newton and Ernest Rutherford. The original stone was inscribed “Joseph John Thomson, OM, Physicist 1856-1940. Master of Trinity College Cambridge.”⁠[3][12][13]

His wife Rose died in 1951; her funeral service was held at Great St. Mary’s, Cambridge, on May 28, and she was buried with him on June 8, 1951. In 1991 the stone was replaced at the family’s request, with the inscription “1856-1940 JOSEPH JOHN THOMSON. ORDER OF MERIT. PHYSICIST. MASTER OF TRINITY COLLEGE CAMBRIDGE AND ROSE HIS WIFE 1860-1951.”⁠[3][4]

He and Rose had a son and a daughter. Their son, George Paget Thomson (1892–1975), also became a physicist and was advised by his father; he was appointed Professor of Natural Philosophy at Aberdeen University in 1922, married Kathleen Buchanan Adam Smith in 1924, was elected a Fellow of the Royal Society in 1930, shared the 1937 Nobel Prize in Physics with C. J. Davisson for showing that electrons have wave-like properties, was knighted in 1943 and later became Master of Corpus Christi College, Cambridge. On his professorship, the Nobel Prize biography describes him as Emeritus Professor of Physics at the University of London, and the Science History Institute’s profile states that he was later appointed Professor of Physics at Cambridge.⁠[2][4][11][6][13][5][10][3]

Their daughter, Joan Paget Thomson, was born in 1903 and married Harry Charnock in 1946; they had one daughter, Rosemary. Joan often travelled with her father in his later years. He sent both children to private schools.⁠[4][10][6][9]

Rose Thomson was Chairman of the Divinity Reading Union, and her papers include religious notes, Mothers’ Union material and cookery notebooks. The supplementary papers catalogued by the NCUACS were received from his grandson, David Paget Thomson, in August 1997 and December 1999.⁠[4][4]

The Royal Society of Edinburgh’s obituary describes him as the active head and inspirer of a great research school throughout his tenure and states that by 1940 nearly all the important chairs of physics in the Empire were filled by his disciples. At times as many as 40 students were doing research under him; he took an active interest in young researchers, checked their progress daily and often suggested improvements. After the discovery of X-rays and radioactivity his imaginative work inspired many young researchers, including Ernest Rutherford, W. L. Bragg and C. T. R. Wilson.⁠[12][5][10][8]

On the number of his students who won Nobel Prizes, Britannica’s summary states that seven of his assistants became Nobel laureates; the American Institute of Physics’ exhibit that the laboratory under him trained seven Nobel Prize winners and 27 Fellows of the Royal Society; Trinity College’s memorial page that seven of his research assistants and his son won Nobel Prizes in physics; and the Science History Institute’s profile that seven of his students won Nobel Prizes; Isobel Falconer’s article states that eight of his students won Nobel Prizes and that many held influential posts throughout the English-speaking world.⁠[17][10][13][5][9]

Those advised by him at Cambridge included Edward Victor Appleton, Francis William Aston (also his assistant), C. G. Barkla, Max Born, Devendramohan Bose, William Lawrence Bragg, E. F. Burton, Hugh Longbourne Callender, Bergen Davis, Clinton Joseph Davisson, R. W. Ditchburn, Arthur Llewelyn Hughes, R. W. James, D. A. Keys, T. H. Laby, Paul Langevin, Theodore Lyman, John Cunningham McLennan, Wladyslaw Natanson, J. Robert OppenheimerJ. Robert OppenheimerJ. Robert Oppenheimer (1904–1967) was an American theoretical physicist and science administrator who directed the Los Alamos laboratory that developed the atomic bomb during World War II.Open the full entry, Balthasar van der Pol, Peter Pringsheim, O. W. Richardson, Ernest Rutherford, Geoffrey Ingram Taylor, John Townsend, Herbert Edmeston Watson, Richard Whiddington, Charles Thomson Rees Wilson, Harold A. Wilson, John Zeleny and Lord Rayleigh’s son Robert John Strutt.⁠[11][22]

Trinity College’s memorial inscription describes him as a kindly, modest and simple man who, as Scholar, Fellow and Master, cherished the College with unusual devotion for sixty-four years. Late in life he wrote: “I have had good parents, good teachers, good colleagues, good pupils, good friends, great opportunities, good luck, and good health.” He never lost his curiosity or his love of learning.⁠[13][12][5]

He was a member of the Athenaeum and Saville clubs and of the Family Cycle, a dining club, and he was a supporter of university education for women.⁠[9][4]

His other books include Application of Dynamics to Physics and Chemistry (1886); Notes on Recent Researches in Electricity and Magnetism (1892), often referred to as “the third volume of Maxwell”; the four-volume textbook Properties of Matter, written with J. H. Poynting; Elements of the Mathematical Theory of Electricity and Magnetism (1895; 5th edition 1921); The Structure of Light (1907); The Corpuscular Theory of Matter (1907); Rays of Positive Electricity (1913); and The Electron in Chemistry (1923).⁠[2][2]

The Royal Society’s archive holds papers he submitted, including one on the vortex-ring theory of gases and the law of the distribution of energy among molecules; two written with Hugh Frank Newall, on the formation of vortex rings by drops falling into liquids and allied phenomena, and on the rate at which electricity leaks through liquids that are bad conductors; two written with Richard Threlfall, on an effect produced by the passage of an electric discharge through pure nitrogen and on experiments on the production of ozone; and one on the effect of conductors near a wire on the rate of propagation of electrical disturbances along it, with a determination of that rate. The archive also holds his referee reports on papers by Alfred Einhorn, John Henry Poynting, Herbert Tomlinson, Chichester A Bell, S A Hill and Horace Lamb.⁠[6]

Later medals included the Albert Medal (1915), the Franklin Medal and the Scott Medal of the Franklin Institute, Philadelphia (1923), the Mascart Medal, Paris (1927), the Dalton Medal of the Manchester Literary and Philosophical Society (1931) and the Faraday Medal of the Institution of Civil Engineers (1938). He was also an honorary member of the Royal Society of Medicine (1919), the Franklin Institute (1922) and the Institution of Civil Engineers (1925).⁠[2][11][4]

He held honorary doctorates from the University of OxfordUniversity of OxfordThe University of Oxford is a university in Oxford, England, where teaching existed in some form by 1096; it describes itself as the oldest university in the English-speaking world and is organised as a federal system of the university and dozens of self-governing colleges.Open the full entry, Dublin, London, Victoria, Columbia UniversityColumbia UniversityColumbia University, formally Columbia University in the City of New York, is a private research university in New York City and a member of the Ivy League. Founded in 1754 by royal charter from King George II as King's College, it is the oldest institution of higher education in New York State and the fifth oldest in the United States. It was renamed Columbia College in 1784 and adopted the university name and moved to Manhattan's Morningside Heights in 1896. It has 17 schools and four affiliated colleges, with 35,978 students enrolled in fall 2025. Legal scholar Jennifer L. Mnookin became president on July 1, 2026.Open the full entry, the University of Cambridge, Durham, Birmingham, Göttingen, Leeds, Oslo, the Sorbonne, the University of EdinburghUniversity of EdinburghThe University of Edinburgh is a research university in Edinburgh, Scotland. Founded by the Town Council in 1583, it is one of Scotland’s four ancient universities and a member of the Russell Group.Open the full entry, Reading, Princeton University, the University of GlasgowUniversity of GlasgowThe University of Glasgow is a research university in Glasgow, Scotland. Founded in 1451, it describes itself as the fourth oldest university in the UK, and it is a member of the Russell Group.Open the full entry, Johns Hopkins, Aberdeen, Athens, Cracow and Philadelphia. The NCUACS catalogue also lists St Andrews and Baltimore among the universities that gave him honorary degrees. He was also Honorary Professor of Physics at the Royal Institution, London.⁠[2][2][4]

In 1905 he was elected an Honorary Fellow of the Royal Society of Edinburgh.⁠[12]

A brass in his memory on the north wall of the Ante-Chapel of Trinity College carries a Latin inscription by Donald Struan Robertson, which records that as Cavendish Professor of Physics for thirty-four years he broke open the bolts of the portals of nature with the vital power of his mind and opened up new roads of knowledge for his pupils, who came to him from all over the world.⁠[13]

A supplementary collection of his papers and correspondence, dating from 1836 to 1956 and filling 59 boxes, was catalogued by the National Cataloguing Unit for the Archives of Contemporary Scientists, whose catalogue was published in Bath in 2000; the papers are held in the Library of Trinity College.⁠[4]

George Paget Thomson’s Britannica article states that by his discovery of the electron in 1897 he “helped revolutionize the knowledge of atomic structure.” Britannica’s summary credits him with building the Cavendish Laboratory into a world-renowned institution between 1884 and 1918. The summary also calls him an outstanding teacher.⁠[7][17]

The Science History Institute’s profile calls him an “accidental physicist” and “a formidable teacher and role model.”⁠[5]

Westminster Abbey states that his discovery of the electron, announced in 1897, marked the beginning of modern atomic physics; the American Institute of Physics’ exhibit counts him among the most accomplished physicists of his era; Trinity College’s memorial page regards his teaching as one of his greatest contributions to science; and Isobel Falconer calls him a renowned teacher.⁠[3][10][13][9]

University of Cambridge: Official website: https://www.cam.ac.uk/ (opens in a new window).⁠[23]

University of Manchester: Official website: https://www.manchester.ac.uk/ (opens in a new window).⁠[24]

Royal Institution: Official website: https://www.rigb.org/ (opens in a new window).⁠[25]