J. J. Thomson

Sir Joseph John Thomson OM PRS[1] (18 December 1856 – 30 August 1940) was an English physicist and Nobel Laureate in Physics, credited with the discovery and identification of the electron, the first subatomic particle to be discovered.

In 1897, Thomson showed that cathode rays were composed of previously unknown negatively charged particles (now called electrons), which he calculated must have bodies much smaller than atoms and a very large charge-to-mass ratio.[2] 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). His experiments to determine the nature of positively charged particles, with Francis William Aston, were the first use of mass spectrometry and led to the development of the mass spectrograph.[2]

Thomson was awarded the 1906 Nobel Prize in Physics for his work on the conduction of electricity in gases.[3]

Sir J. J. Thomson

J.J Thomson
Joseph John Thomson

18 December 1856
Died30 August 1940 (aged 83)
Cambridge, England
Alma materOwens College (now the University of Manchester)
Trinity College, Cambridge (BA)
Known forPlum pudding model
Discovery of electron
Discovery of isotopes
Mass spectrometer invention
First m/e measurement
Proposed first waveguide
Thomson scattering
Thomson problem
Coining term 'delta ray'
Coining term 'epsilon radiation'
Thomson (unit)
ChildrenGeorge Paget Thomson, Joan Paget Thomson
AwardsSmith's Prize (1880)
Royal Medal (1894)
Hughes Medal (1902)
Nobel Prize in Physics (1906)
Elliott Cresson Medal (1910)
Copley Medal (1914)
Albert Medal (1915)
Franklin Medal (1922)
Faraday Medal (1925)
Scientific career
InstitutionsTrinity College, Cambridge
Academic advisorsJohn Strutt (Rayleigh)
Edward John Routh
Notable studentsCharles Glover Barkla
Charles T. R. Wilson
Ernest Rutherford
Francis William Aston
John Townsend
J. Robert Oppenheimer
Owen Richardson
William Henry Bragg
H. Stanley Allen
John Zeleny
Daniel Frost Comstock
Max Born
T. H. Laby
Paul Langevin
Balthasar van der Pol
Geoffrey Ingram Taylor
Niels Bohr
George Paget Thomson
Jjthomson sig
External video
Title page On the Chemical Combination of Gases by Joseph John Thomson 1856-1940
The Early Life of J.J. Thomson: Computational Chemistry and Gas Discharge Experiments

Education and personal life

Joseph John Thomson was born 18 December 1856 in Cheetham Hill, Manchester, Lancashire, 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, Frederick Vernon Thomson, who was two years younger than he was.[4] J. J. Thomson was a reserved yet devout Anglican.[5][6][7]

His early education was in small private schools where he demonstrated outstanding talent and interest in science. In 1870, he was admitted to Owens College in Manchester (now University of Manchester) 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.[4]

He moved on to Trinity College, Cambridge, in 1876. In 1880, he obtained his Bachelor of Arts degree in mathematics (Second Wrangler in the Tripos[8] and 2nd Smith's Prize).[9] He applied for and became a Fellow of Trinity College in 1881.[10] Thomson received his Master of Arts degree (with Adams Prize) in 1883.[9]


In 1890, Thomson married Rose Elisabeth Paget, one of his former students,[11] daughter of Sir George Edward Paget, KCB, a physician and then Regius Professor of Physic at Cambridge at the church of St. Mary the Less. They had one son, George Paget Thomson, and one daughter, Joan Paget Thomson.

Career and research


On 22 December 1884, Thomson was appointed Cavendish Professor of Physics at the University of Cambridge.[2] The appointment caused considerable surprise, given that candidates such as Osborne Reynolds or Richard Glazebrook were older and more experienced in laboratory work. Thomson was known for his work as a mathematician, where he was recognized as an exceptional talent.[12]

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. Joseph John Thomson died on 30 August 1940; his ashes rest in Westminster Abbey, near the graves of Sir Isaac Newton and his former student, Ernest Rutherford.[13]

One of Thomson's greatest contributions to modern science was in his role as a highly gifted teacher. One of his students was Ernest Rutherford, who later succeeded him as Cavendish Professor of Physics. In addition to Thomson himself, six of his research assistants (Charles Glover Barkla, Niels Bohr, Max Born, William Henry Bragg, Owen Willans Richardson and Charles Thomson Rees Wilson) won Nobel Prizes in physics, and two (Francis William Aston and Ernest Rutherford) won Nobel prizes in chemistry. In addition, Thomson's son (George Paget Thomson) won the 1937 Nobel Prize in physics for proving the wave-like properties of electrons.

Early work

Thomson's prize-winning master's work, Treatise on the motion of vortex rings, shows his early interest in atomic structure.[3] In it, Thomson mathematically described the motions of William Thomson's vortex theory of atoms.[12]

Thomson published a number of papers addressing both mathematical and experimental issues of electromagnetism. He examined the electromagnetic theory of light of James Clerk Maxwell, introduced the concept of electromagnetic mass of a charged particle, and demonstrated that a moving charged body would apparently increase in mass.[12]

Much of his work in mathematical modelling of chemical processes can be thought of as early computational chemistry.[2] In further work, published in book form as Applications of dynamics to physics and chemistry (1888), Thomson addressed the transformation of energy in mathematical and theoretical terms, suggesting that all energy might be kinetic.[12] His next book, Notes on recent researches in electricity and magnetism (1893), built upon Maxwell's Treatise upon electricity and magnetism, and was sometimes referred to as "the third volume of Maxwell".[3] In it, Thomson emphasized physical methods and experimentation and included extensive figures and diagrams of apparatus, including a number for the passage of electricity through gases.[12] His third book, Elements of the mathematical theory of electricity and magnetism (1895)[14] was a readable introduction to a wide variety of subjects, and achieved considerable popularity as a textbook.[12]

A series of four lectures, given by Thomson on a visit to Princeton University in 1896, were subsequently published as Discharge of electricity through gases (1897). Thomson also presented a series of six lectures at Yale University in 1904.[3]

Discovery of the electron

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 one of the fundamental units was more than 1,000 times smaller than an atom, suggesting the subatomic particle now known as the electron. Thomson discovered this through his explorations on the properties of cathode rays. Thomson made his suggestion on 30 April 1897 following his discovery that cathode rays (at the time known as Lenard rays) could travel much further through air than expected for an atom-sized particle.[15] 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 1,000 times lighter than the hydrogen atom, but also that their mass was the same in whichever 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.[16]

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.[17] This became the classic means of measuring the charge-to-mass ratio of the electron. (The charge itself was not measured until Robert A. Millikan's oil drop experiment in 1909.)

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. In 1904, Thomson suggested a model of the atom, hypothesizing that it was a sphere of positive matter within which electrostatic forces determined the positioning of the corpuscles.[2] To explain the overall neutral charge of the atom, he proposed that the corpuscles were distributed in a uniform sea of positive charge. In this "plum pudding" model, the electrons were seen as embedded in the positive charge like plums in a plum pudding (although in Thomson's model they were not stationary, but orbiting rapidly).[18][19]

Isotopes and mass spectrometry

Discovery of neon isotopes
In the bottom right corner of this photographic plate are markings for the two isotopes of neon: neon-20 and neon-22.

In 1912, as part of his exploration into the composition of the streams of positively charged particles then known as canal rays, Thomson and his research assistant F. W. Aston channelled a stream of neon ions through a magnetic and an electric field and measured its deflection by placing a photographic plate in its path.[4] They observed two patches of light on the photographic plate (see image on right), which suggested two different parabolas of deflection, and concluded that neon is composed of atoms of two different atomic masses (neon-20 and neon-22), that is to say of two isotopes.[20][21] This was the first evidence for isotopes of a stable element; Frederick Soddy had previously proposed the existence of isotopes to explain the decay of certain radioactive elements.

J.J. Thomson's separation of neon isotopes by their mass was the first example of mass spectrometry, which was subsequently improved and developed into a general method by F. W. Aston and by A. J. Dempster.[2]

Experiments with cathode rays

Earlier, physicists debated whether cathode rays were immaterial like light ("some process in the aether") or were "in fact wholly material, and ... mark the paths of particles of matter charged with negative electricity", quoting Thomson.[17] The aetherial hypothesis was vague,[17] but the particle hypothesis was definite enough for Thomson to test.

Magnetic deflection

Thomson first investigated the magnetic deflection of cathode rays. Cathode rays were produced in the side tube on the left of the apparatus and passed through the anode into the main bell jar, where they were deflected by a magnet. Thomson detected their path by the fluorescence on a squared screen in the jar. He found that whatever the material of the anode and the gas in the jar, the deflection of the rays was the same, suggesting that the rays were of the same form whatever their origin.[22]

Electrical charge

JJ Thomson Cathode Ray Tube 1
The cathode ray tube by which J.J. Thomson demonstrated that cathode rays could be deflected by a magnetic field, and that their negative charge was not a separate phenomenon.

While supporters of the aetherial theory accepted the possibility that negatively charged particles are produced in Crookes tubes, they believed that they are a mere by-product and that the cathode rays themselves are immaterial. Thomson set out to investigate whether or not he could actually separate the charge from the rays.

Thomson constructed a Crookes tube with an electrometer set to one side, out of the direct path of the cathode rays. Thomson could trace the path of the ray by observing the phosphorescent patch it created where it hit the surface of the tube. Thomson observed that the electrometer registered a charge only when he deflected the cathode ray to it with a magnet. He concluded that the negative charge and the rays were one and the same.[15]

Electrical deflection

JJ Thomson Cathode Ray 2
Thomson's illustration of the Crookes tube by which he observed the deflection of cathode rays by an electric field (and later measured their mass-to-charge ratio). Cathode rays were emitted from the cathode C, passed through slits A (the anode) and B (grounded), then through the electric field generated between plates D and E, finally impacting the surface at the far end.
Thomson cathode ray exp
The cathode ray (blue line) was deflected by the electric field (yellow).

In May–June 1897, Thomson investigated whether or not the rays could be deflected by an electric field.[4] Previous experimenters had failed to observe this, but Thomson believed their experiments were flawed because their tubes contained too much gas.

Thomson constructed a Crookes tube with a better vacuum. At the start of the tube was the cathode from which the rays projected. The rays were sharpened to a beam by two metal slits – the first of these slits doubled as the anode, the second was connected to the earth. The beam then passed between two parallel aluminium plates, which produced an electric field between them when they were connected to a battery. The end of the tube was a large sphere where the beam would impact on the glass, created a glowing patch. Thomson pasted a scale to the surface of this sphere to measure the deflection of the beam. Note that any electron beam would collide with some residual gas atoms within the Crookes tube, thereby ionizing them and producing electrons and ions in the tube (space charge); in previous experiments this space charge electrically screened the externally applied electric field. However, in Thomson's Crookes tube the density of residual atoms was so low that the space charge from the electrons and ions was insufficient to electrically screen the externally applied electric field, which permitted Thomson to successfully observe electrical deflection.

When the upper plate was connected to the negative pole of the battery and the lower plate to the positive pole, the glowing patch moved downwards, and when the polarity was reversed, the patch moved upwards.

Measurement of mass-to-charge ratio

JJ Thomson exp3

In his classic experiment, Thomson measured the mass-to-charge ratio of the cathode rays by measuring how much they were deflected by a magnetic field and comparing this with the electric deflection. He used the same apparatus as in his previous experiment, but placed the discharge tube between the poles of a large electromagnet. He found that the mass-to-charge ratio was over a thousand times lower than that of a hydrogen ion (H+), suggesting either that the particles were very light and/or very highly charged.[17] Significantly, the rays from every cathode yielded the same mass-to-charge ratio. This is in contrast to anode rays (now known to arise from positive ions emitted by the anode), where the mass-to-charge ratio varies from anode-to-anode. Thomson himself remained critical of what his work established, in his Nobel Prize acceptance speech referring to "corpuscles" rather than "electrons".

Thomson's calculations can be summarised as follows (notice that we reproduce here Thomson's original notations, using F instead of E for the electric field and H instead of B for the magnetic field):

The electric deflection is given by Θ = Fel/mv2 where Θ is the angular electric deflection, F is applied electric intensity, e is the charge of the cathode ray particles, l is the length of the electric plates, m is the mass of the cathode ray particles and v is the velocity of the cathode ray particles.

The magnetic deflection is given by φ = Hel/mv where φ is the angular magnetic deflection and H is the applied magnetic field intensity.

The magnetic field was varied until the magnetic and electric deflections were the same, when Θ = φ and Fel/mv2= Hel/mv. This can be simplified to give m/e = H2l/FΘ. The electric deflection was measured separately to give Θ and H, F and l were known, so m/e could be calculated.


As the cathode rays carry a charge of negative electricity, are deflected by an electrostatic force as if they were negatively electrified, and are acted on by a magnetic force in just the way in which this force would act on a negatively electrified body moving along the path of these rays, I can see no escape from the conclusion that they are charges of negative electricity carried by particles of matter.

— J. J. Thomson[17]

As to the source of these particles, Thomson believed they emerged from the molecules of gas in the vicinity of the cathode.

If, in the very intense electric field in the neighbourhood of the cathode, the molecules of the gas are dissociated and are split up, not into the ordinary chemical atoms, but into these primordial atoms, which we shall for brevity call corpuscles; and if these corpuscles are charged with electricity and projected from the cathode by the electric field, they would behave exactly like the cathode rays.

— J. J. Thomson[23]

Thomson imagined the atom as being made up of these corpuscles orbiting in a sea of positive charge; this was his plum pudding model. This model was later proved incorrect when his student Ernest Rutherford showed that the positive charge is concentrated in the nucleus of the atom.

Other work

In 1905, Thomson discovered the natural radioactivity of potassium.[24]

In 1906, Thomson demonstrated that hydrogen had only a single electron per atom. Previous theories allowed various numbers of electrons.[25][26]

Awards and honours

J.J. Thomson Plaque outside the Old Cavendish Laboratory
Plaque commemorating J. J. Thomson's discovery of the electron outside the old Cavendish Laboratory in Cambridge

Thomson was elected a Fellow of the Royal Society (FRS)[1][27] and appointed to the Cavendish Professorship of Experimental Physics at the Cavendish Laboratory, University of Cambridge in 1884.[2] Thomson won numerous awards and honours during his career including:

Thomson was elected a Fellow of the Royal Society[1] on 12 June 1884 and served as President of the Royal Society from 1915 to 1920.

Posthumous honours

In 1991, the thomson (symbol: Th) was proposed as a unit to measure mass-to-charge ratio in mass spectrometry in his honour.[28]

J J Thomson Avenue, on the University of Cambridge's West Cambridge site, is named after Thomson.[29]

In November 1927, J.J. Thomson opened the Thomson building, named in his honour, in the Leys School, Cambridge.[30]


  1. ^ a b c Rayleigh (1941). "Joseph John Thomson. 1856-1940". Obituary Notices of Fellows of the Royal Society. 3 (10): 586–609. doi:10.1098/rsbm.1941.0024.
  2. ^ a b c d e f g "Joseph John "J. J." Thomson". Science History Institute. June 2016. Retrieved 20 March 2018.
  3. ^ a b c d "J.J. Thomson - Biographical". The Nobel Prize in Physics 1906. The Nobel Foundation. Retrieved 11 February 2015.
  4. ^ a b c d Davis & Falconer, J.J. Thomson and the Discovery of the Electron
  5. ^ Peter J. Bowler, Reconciling Science and Religion: The Debate in Early-Twentieth-Century Britain (2014). University of Chicago Press. p. 35. ISBN 9780226068596. "Both Lord Rayleigh and J. J. Thomson were Anglicans."
  6. ^ Seeger, Raymond. 1986. "J. J. Thomson, Anglican," in Perspectives on Science and Christian Faith, 38 (June 1986): 131-132. The Journal of the American Scientific Affiliation. ""As a Professor, J.J. Thomson did attend the Sunday evening college chapel service, and as Master, the morning service. He was a regular communicant in the Anglican Church. In addition, he showed an active interest in the Trinity Mission at Camberwell. With respect to his private devotional life, J.J. Thomson would invariably practice kneeling for daily prayer, and read his Bible before retiring each night. He truly was a practicing Christian!" (Raymond Seeger 1986, 132)."
  7. ^ Richardson, Owen. 1970. "Joseph J. Thomson," in The Dictionary of National Biography, 1931-1940. L. G. Wickham Legg - editor. Oxford University Press.
  8. ^ Grayson, Mike (May 22, 2013). "The Early Life of J.J. Thomson: Computational Chemistry and Gas Discharge Experiments". Profiles in Chemistry. Chemical Heritage Foundation. Retrieved 11 February 2015.
  9. ^ a b "Thomson, Joseph John (THN876JJ)". A Cambridge Alumni Database. University of Cambridge.
  10. ^ The Victoria University Calendar for the Session 1881-2. 1882. p. 184. Retrieved 11 February 2015.
  11. ^ The Biographical Dictionary of Women in Science: L-Z by By Marilyn Bailey Ogilvie and Joy Dorothy Harvey, Taylor & Francis, p.972
  12. ^ a b c d e f Kim, Dong-Won (2002). Leadership and creativity : a history of the Cavendish Laboratory, 1871 - 1919. Dordrecht: Kluwer Acad. Publ. ISBN 9781402004759. Retrieved 11 February 2015.
  13. ^ Westminster Abbey. "Sir Joseph John Thomson".
  14. ^ Mackenzie, A. Stanley (1896). "Review: Elements of the Mathematical Theory of Electricity and Magnetism by J. J. Thomson" (PDF). Bull. Amer. Math. Soc. 2 (10): 329–333. doi:10.1090/s0002-9904-1896-00357-8.
  15. ^ a b Thomson, J.J. (1897). "Cathode Rays". The Electrician. 39: 104.
  16. ^ Falconer, Isobel (2001). "Corpuscles to electrons" (PDF). In Buchwald, J. Z.; Warwick, A. Histories of the Electron. MIT Press. p. 77–100. ISBN 9780262024945.
  17. ^ a b c d e Thomson, J. J. (7 August 1897). "Cathode Rays". Philosophical Magazine. 5. 44 (269): 293. doi:10.1080/14786449708621070. Retrieved 4 August 2014.
  18. ^ Mellor, Joseph William (1917), Modern Inorganic Chemistry, Longmans, Green and Company, p. 868, According to J. J. Thomson's hypothesis, atoms are built of systems of rotating rings of electrons.
  19. ^ Dahl (1997), p. 324: "Thomson's model, then, consisted of a uniformly charged sphere of positive electricity (the pudding), with discrete corpuscles (the plums) rotating about the center in circular orbits, whose total charge was equal and opposite to the positive charge."
  20. ^ J.J. Thomson (1912) "Further experiments on positive rays," Philosophical Magazine, series 6, 24 (140): 209–253.
  21. ^ J.J. Thomson (1913) "Rays of positive electricity," Proceedings of the Royal Society A, 89: 1–20.
  22. ^ Thomson, J. J. (8 February 1897). "On the cathode rays". Proceedings of the Cambridge Philosophical Society. 9: 243.
  23. ^ Thomson, J. J. (1897). "Cathode rays". Philosophical Magazine. 44: 293.
  24. ^ Thomson, J. J. (1905). "On the emission of negative corpuscles by the alkali metals". Philosophical Magazine. Series 6. 10 (59): 584–590. doi:10.1080/14786440509463405.
  25. ^ Hellemans, Alexander; Bunch, Bryan (1988). The Timetables of Science. Simon & Schuster. p. 411. ISBN 0671621300.
  26. ^ Thomson, J. J. (June 1906). "On the Number of Corpuscles in an Atom". Philosophical Magazine. 11 (66): 769–781. doi:10.1080/14786440609463496. Archived from the original on 19 December 2007. Retrieved 4 October 2008.
  27. ^ Thomson, Sir George Paget. "Sir J.J. Thomson, British Physicist". Encyclopædia Brittanica. Retrieved 11 February 2015.
  28. ^ Cooks, R. G.; A. L. Rockwood (1991). "The 'Thomson'. A suggested unit for mass spectroscopists". Rapid Communications in Mass Spectrometry. 5 (2): 93.
  29. ^ "Cambridge Physicist is streets ahead". 2002-07-18. Retrieved 2014-07-31.
  30. ^ "Opening of the New Science Building: Thomson". 2005-12-01. Archived from the original on 2015-01-11. Retrieved 2015-01-10.


  • 1883. A Treatise on the Motion of Vortex Rings: An essay to which the Adams Prize was adjudged in 1882, in the University of Cambridge. London: Macmillan and Co., pp. 146. Recent reprint: ISBN 0-543-95696-2.
  • 1888. Applications of Dynamics to Physics and Chemistry. London: Macmillan and Co., pp. 326. Recent reprint: ISBN 1-4021-8397-6.
  • 1893. Notes on recent researches in electricity and magnetism: intended as a sequel to Professor Clerk-Maxwell's 'Treatise on Electricity and Magnetism'. Oxford University Press, pp.xvi and 578. 1991, Cornell University Monograph: ISBN 1-4297-4053-1.
  • 1921 (1895). Elements Of The Mathematical Theory Of Electricity And Magnetism. London: Macmillan and Co. Scan of 1895 edition.
  • A Text book of Physics in Five Volumes, co-authored with J.H. Poynting: (1) Properties of Matter, (2) Sound, (3) Heat, (4) Light, and (5) Electricity and Magnetism. Dated 1901 and later, and with revised later editions.
  • Dahl, Per F., "Flash of the Cathode Rays: A History of J.J. Thomson's Electron". Institute of Physics Publishing. June 1997. ISBN 0-7503-0453-7
  • J.J. Thomson (1897) "Cathode Rays", The Electrician 39, 104, also published in Proceedings of the Royal Institution 30 April 1897, 1–14—first announcement of the "corpuscle" (before the classic mass and charge experiment)
  • J.J. Thomson (1897), Cathode rays, Philosophical Magazine, 44, 293—The classic measurement of the electron mass and charge
  • J.J. Thomson (1912), "Further experiments on positive rays" Philosophical Magazine, 24, 209–253—first announcement of the two neon parabolae
  • J.J. Thomson (1913), Rays of positive electricity, Proceedings of the Royal Society, A 89, 1–20—Discovery of neon isotopes
  • J.J. Thomson (1904), "On the Structure of the Atom: an Investigation of the Stability and Periods of Oscillation of a number of Corpuscles arranged at equal intervals around the Circumference of a Circle; with Application of the Results to the Theory of Atomic Structure," Philosophical Magazine Series 6, Volume 7, Number 39, pp. 237–265. This paper presents the classical "plum pudding model" from which the Thomson Problem is posed.
  • J.J. Thomson (1923), The Electron in Chemistry: Being Five Lectures Delivered at the Franklin Institute, Philadelphia.
  • Thomson, Sir J. J. (1936), Recollections and Reflections, London: G. Bell & Sons, Ltd. Republished as digital edition, Cambridge: University Press, 2011 (Cambridge Library Collection series).
  • Thomson, George Paget. (1964) J.J. Thomson: Discoverer of the Electron. Great Britain: Thomas Nelson & Sons, Ltd.
  • Davis, Eward Arthur & Falconer, Isobel (1997), J.J. Thomson and the Discovery of the Electron. ISBN 978-0-7484-0696-8
  • Falconer, Isobel (1988) "J.J. Thomson's Work on Positive Rays, 1906–1914" Historical Studies in the Physical and Biological Sciences 18(2) 265–310
  • Falconer, Isobel (2001) "Corpuscles to Electrons" in J Buchwald and A Warwick (eds) Histories of the Electron, Cambridge, Mass: MIT Press, pp. 77–100.
  • Navarro, Jaume (2005). "J. J. Thomson on the Nature of Matter: Corpuscles and the Continuum". Centaurus. 47 (4): 259–282. doi:10.1111/j.1600-0498.2005.00028.x.
  • Downard, Kevin M. (2009). "J. J. Thomson goes to America". Journal of the American Society for Mass Spectrometry. 20 (11): 1964–1973. doi:10.1016/j.jasms.2009.07.008. PMID 19734055.

External links

Academic offices
Preceded by
Henry Montagu Butler
Master of Trinity College, Cambridge
Succeeded by
George Macaulay Trevelyan
A Treatise on Electricity and Magnetism

A Treatise on Electricity and Magnetism is a two-volume treatise on electromagnetism written by James Clerk Maxwell in 1873. Maxwell was revising the Treatise for a second edition when he died in 1879. The revision was completed by William Davidson Niven for publication in 1881. A third edition was prepared by J. J. Thomson for publication in 1892.

According to one historian,

The Treatise was notoriously hard to read; it teemed with ideas but lacked the clear focus and orderly presentation that might have enabled it to win converts more readily. Rather than simply expounding his own system, Maxwell had set out to write a comprehensive treatise on electrical science, and so he had allowed his own new distinctive ideas, notably that of the displacement current, to be almost buried under long accounts of miscellaneous phenomena discussed from several points of view. Except for a fuller treatment of the Faraday effect (in which he again invoked the molecular vortices), Maxwell added little to his earlier work on the electromagnetic theory of light; he said nothing, for example, about how electromagnetic waves might be generated, nor did he attempt to derive laws governing reflection and refraction.Maxwell introduced the use of vector fields, and his labels have been perpetuated:

A (vector potential), B (magnetic induction), C (electric current), D (displacement), E (electric field – Maxwell's electromotive intensity), F (mechanical force), H (magnetic field – Maxwell's magnetic force).Maxwell's work is considered an exemplar of rhetoric of science:

Lagrange's equations appear in the Treatise as the culmination of a long series of rhetorical moves, including (among others) Green's theorem, Gauss's potential theory and Faraday's lines of force – all of which have prepared the reader for the Lagrangian vision of a natural world that is whole and connected: a veritable sea change from Newton's vision.

Anode ray

An anode ray (also positive ray or canal ray) is a beam of positive ions that is created by certain types of gas-discharge tubes. They were first observed in Crookes tubes during experiments by the German scientist Eugen Goldstein, in 1886. Later work on anode rays by Wilhelm Wien and J. J. Thomson led to the development of mass spectrometry.

Atomic physics

Atomic physics is the field of physics that studies atoms as an isolated system of electrons and an atomic nucleus. It is primarily concerned with the arrangement of electrons around the nucleus and

the processes by which these arrangements change. This comprises ions, neutral atoms and, unless otherwise stated, it can be assumed that the term atom includes ions.The term atomic physics can be associated with nuclear power and nuclear weapons, due to the synonymous use of atomic and nuclear in standard English. Physicists distinguish between atomic physics — which deals with the atom as a system consisting of a nucleus and electrons — and nuclear physics, which considers atomic nuclei alone.

As with many scientific fields, strict delineation can be highly contrived and atomic physics is often considered in the wider context of atomic, molecular, and optical physics. Physics research groups are usually so classified.

Cathode ray

Cathode rays (electron beam or e-beam) are streams of electrons observed in vacuum tubes. If an evacuated glass tube is equipped with two electrodes and a voltage is applied, glass behind the positive electrode is observed to glow, due to electrons emitted from the cathode (the electrode connected to the negative terminal of the voltage supply). They were first observed in 1869 by German physicist Johann Wilhelm Hittorf, and were named in 1876 by Eugen Goldstein Kathodenstrahlen, or cathode rays. In 1897, British physicist J. J. Thomson showed that cathode rays were composed of a previously unknown negatively charged particle, which was later named the electron. Cathode ray tubes (CRTs) use a focused beam of electrons deflected by electric or magnetic fields to render an image on a screen.

Cavendish Professor of Physics

The Cavendish Professorship is one of the senior faculty positions in physics at the University of Cambridge. It was founded on 9 February 1871 alongside the famous Cavendish Laboratory, which was completed three years later. William Cavendish, 7th Duke of Devonshire endowed both the professorship and laboratory in honor of his relative, chemist and physicist Henry Cavendish.

Delta ray

A delta ray is a secondary electron with enough energy to escape a significant distance away from the primary radiation beam and produce further ionization", and is sometimes used to describe any recoil particle caused by secondary ionization. The term was coined by J. J. Thomson.

Elizabeth Laird (physicist)

Elizabeth Rebecca Laird (December 6, 1874 – March 3, 1969) was a Canadian physicist who chaired the physics department at Mount Holyoke College for nearly four decades. She was the first woman accepted by Sir J. J. Thomson to conduct research at Cambridge University's Cavendish Laboratory. Laird graduated from the London Collegiate Institute in 1893, and attended University College of the University of Toronto after, due to her gender, she was denied an exhibition scholarship where she could have studied abroad. She earned her Ph.D. in physics and mathematics from Bryn Mawr College in 1901.

Asteroid (16192) Laird is named in her honour.

Epsilon radiation

Epsilon radiation is tertiary radiation caused by secondary radiation (e.g., delta radiation). Epsilon rays are a form of particle radiation and are composed of electrons. The term was coined by J. J. Thomson, but is very rarely used today.

Institute of Physics Joseph Thomson Medal and Prize

The Thomson Medal and Prize is an award which has been made biennially in even-numbered years since 2008 by the British Institute of Physics for "distinguished research in atomic (including quantum optics) or molecular physics". It is named after Sir J. J. Thomson and comprises a medal and a prize of £1000.

Joseph Thomson

Joseph or Joe Thomson is the name of:

J. J. Thomson (1856–1940), physicist

Joseph Thomson (explorer) (1858–1895), African explorer

Joseph Angus Thomson (1856–1943), Australian politician

Joe Thomson (1948–2018), academic

Joe Thomson (footballer) (born 1997), Scottish footballer with Celtic

Karoro Pond

Karoro Pond (77°40′29″S 162°16′03″E) is pond 0.8 nautical miles (1.5 km) north-northeast of Mount J. J. Thomson on the rock divide separating Matterhorn Glacier and Rhone Glacier in Victoria Land. It was named by the New Zealand Geographic Board in 1998 after the New Zealand gull of that name.


In particle physics, a lepton is an elementary particle of half-integer spin (spin ​1⁄2) that does not undergo strong interactions. Two main classes of leptons exist: charged leptons (also known as the electron-like leptons), and neutral leptons (better known as neutrinos). Charged leptons can combine with other particles to form various composite particles such as atoms and positronium, while neutrinos rarely interact with anything, and are consequently rarely observed. The best known of all leptons is the electron.

There are six types of leptons, known as flavours, grouped in three generations. The first-generation leptons, also called electronic leptons, comprise the electron (e−) and the electron neutrino (νe); the second are the muonic leptons, comprising the muon (μ−) and the muon neutrino (νμ); and the third are the tauonic leptons, comprising the tau (τ−) and the tau neutrino (ντ). Electrons have the least mass of all the charged leptons. The heavier muons and taus will rapidly change into electrons and neutrinos through a process of particle decay: the transformation from a higher mass state to a lower mass state. Thus electrons are stable and the most common charged lepton in the universe, whereas muons and taus can only be produced in high energy collisions (such as those involving cosmic rays and those carried out in particle accelerators).

Leptons have various intrinsic properties, including electric charge, spin, and mass. Unlike quarks however, leptons are not subject to the strong interaction, but they are subject to the other three fundamental interactions: gravitation, the weak interaction, and to electromagnetism, of which the latter is proportional to charge, and is thus zero for the electrically neutral neutrinos.

For every lepton flavor there is a corresponding type of antiparticle, known as an antilepton, that differs from the lepton only in that some of its properties have equal magnitude but opposite sign. According to certain theories, neutrinos may be their own antiparticle. It is not currently known whether this is the case.

The first charged lepton, the electron, was theorized in the mid-19th century by several scientists and was discovered in 1897 by J. J. Thomson. The next lepton to be observed was the muon, discovered by Carl D. Anderson in 1936, which was classified as a meson at the time. After investigation, it was realized that the muon did not have the expected properties of a meson, but rather behaved like an electron, only with higher mass. It took until 1947 for the concept of "leptons" as a family of particle to be proposed. The first neutrino, the electron neutrino, was proposed by Wolfgang Pauli in 1930 to explain certain characteristics of beta decay. It was first observed in the Cowan–Reines neutrino experiment conducted by Clyde Cowan and Frederick Reines in 1956. The muon neutrino was discovered in 1962 by Leon M. Lederman, Melvin Schwartz, and Jack Steinberger, and the tau discovered between 1974 and 1977 by Martin Lewis Perl and his colleagues from the Stanford Linear Accelerator Center and Lawrence Berkeley National Laboratory. The tau neutrino remained elusive until July 2000, when the DONUT collaboration from Fermilab announced its discovery.Leptons are an important part of the Standard Model. Electrons are one of the components of atoms, alongside protons and neutrons. Exotic atoms with muons and taus instead of electrons can also be synthesized, as well as lepton–antilepton particles such as positronium.

Line of force

A line of force in Faraday's extended sense is synonymous with Maxwell's line of induction. According to J.J. Thomson, Faraday usually discusses lines of force as chains of polarized particles in a dielectric, yet sometimes Faraday discusses them as having an existence all their own as in stretching across a vacuum. In addition to lines of force, J.J. Thomson—similar to Maxwell—also calls them tubes of electrostatic inductance, or simply Faraday tubes. From the 20th century perspective, lines of force are energy linkages embedded in a 19th-century unified field theory that led to more mathematically and experimentally sophisticated concepts and theories, including Maxwell's equations, electromagnetic waves, and Einstein's relativity.

Lines of force originated with Michael Faraday, whose theory holds that all of reality is made up of force itself. His theory predicts that electricity, light, and gravity have finite propagation delays. The theories and experimental data of later scientific figures such as Maxwell, Hertz, Einstein, and others are in agreement with the ramifications of Faraday's theory. Nevertheless, Faraday's theory remains distinct. Unlike Faraday, Maxwell and others (e.g., J.J. Thomson) thought that light and electricity must propagate through an ether. In Einstein's relativity, there is no ether, yet the physical reality of force is much weaker than in the theories of Faraday.Historian Nancy J. Nersessian in her paper "Faraday's Field Concept" distinguishes between the ideas of Maxwell and Faraday:

The specific features of Faraday's field concept, in its 'favourite' and most complete form, are that force is a substance, that it is the only substance and that all forces are interconvertible through various motions of the lines of force. These features of Faraday's 'favourite notion' were not carried on. Maxwell, in his approach to the problem of finding a mathematical representation for the continuous transmission of electric and magnetic forces, considered these to be states of stress and strain in a mechanical aether. This was part of the quite different network of beliefs and problems with which Maxwell was working.

Mount J. J. Thomson

Mount J. J. Thomson (77°41′19″S 162°15′40″E) is a prominent hump-shaped peak along the north wall of Taylor Valley, standing above Lake Bonney, between Rhone Glacier and Matterhorn Glacier, in Victoria Land, Antarctica. It was so named by the Western Journey Party, led by Thomas Griffith Taylor, of the British Antarctic Expedition, 1910–13. The initials have been retained to distinguish the name from Mount Allan Thomson (also named by the 1910–13 British expedition) near Mackay Glacier, Victoria Land.

New Museums Site

The New Museums Site is a major site of the University of Cambridge, located on Pembroke Street and Free School Lane, sandwiched between Corpus Christi College, Pembroke College and Lion Yard. Its postcode is CB2 3QH. The smaller and older of two university city-centre science sites (the other is the Downing Site), the New Museums Site houses many of the university's science departments, lecture halls and examination rooms, as well as two museums.

Formerly the site of the university Botanic Garden (which is now between Hills Road and Trumpington Road in the south of the city), the New Museums Site is an eclectic mixture of grand Victorian buildings erected between 1870 and 1909, such as the Old Cavendish Laboratory; yellow-brick buildings from the 1930–40s, largely utilitarian with the exception of the Mond Building; and modernist glass-and-concrete buildings dating from the 1970s, such as the Materials Science and Metallurgy tower.

Several important scientific developments of the 19th and 20th centuries were made here, mainly at the Old Cavendish Laboratory, including the discoveries of the electron by J.J. Thomson (1897) and the neutron by Chadwick (1932), splitting the atom by Cockcroft and Walton (1932), mechanism of nervous conduction by Hodgkin and Huxley (1930s–40s), and DNA structure by Watson and Crick (1953).

Plum pudding model

The plum pudding model is one of several scientific models of the atom. First proposed by J. J. Thomson in 1904 soon after the discovery of the electron, but before the discovery of the atomic nucleus, the model represented an attempt to consolidate the known properties of atoms at the time: 1) electrons are negatively-charged particles and 2) atoms are neutrally-charged.

Science and engineering in Manchester

Manchester is one of the principal cities of the United Kingdom, gaining city status in 1853, thus becoming the first new city in over 300 years since Bristol in 1542. Often regarded as the first industrialised city, Manchester was a city built by the Industrial Revolution and had little pre-medieval history to speak of. Manchester had a population of 10,000 in 1717, but by 1911 it had burgeoned to 2.3 million.As its population and influence burgeoned, Manchester became a centre for new discoveries, scientific breakthroughs and technological developments in engineering. A famous but unattributed quote linked to Manchester is: "What Manchester does today, the rest of the world does tomorrow". Pioneering breakthroughs such as the first 'true' canal which spawned 'Canal Mania', the first intercity railway station which led to 'railway mania' and the first stored-program computer. The city has achieved great success in the field of physics, with the electron (J. J. Thomson, 1897), proton (Rutherford, 1917), neutron (James Chadwick, 1934) all being discovered by scientists educated (Chadwick and Rutherford) or born (Thomson) in Manchester.

Famous scientists to have studied in Manchester include John Dalton, James Prescott Joule, J. J. Thomson, Ernest Rutherford, James Chadwick and Alan Turing. A creative and often seen as a bohemian city, Manchester also had the highest number of patent applications per head of population in the United Kingdom in 2003. The city is served by the University of Manchester, previously UMIST and the Victoria University of Manchester pre-2004. The university has a total of 25 Nobel Laureates; only the Oxbridge universities have more Nobel laureates. The city is also served by the Museum of Science and Industry celebrating Mancunian, as well as national achievements in both fields.

Thomson (unit)

The thomson (symbol: Th) is a unit that has appeared infrequently in scientific literature relating to the field of mass spectrometry as a unit of mass-to-charge ratio. The unit was proposed by Cooks and Rockwood naming it in honour of J. J. Thomson who measured the mass-to-charge ratio of electrons and ions.

Yuen-Ron Shen

Yuen-Ron Shen (Chinese: 沈元壤; pinyin: Shěn Yuánrǎng) is a professor emeritus of physics at the University of California, Berkeley, known for his work on non-linear optics. He was born in Shanghai and graduated from National Taiwan University. He received his Ph.D. in Applied Physics from Harvard under physicist and Nobel Laureate Nicolaas Bloembergen in 1963, and joined the department of physics at Berkeley in 1964. In the early years, Dr. Shen was probably best known for his work on self-focusing and filament propagation of laser beams in materials. These fundamental studies enabled the creation of ultrafast supercontinuum light sources. In the 1970s and 1980s, he collaborated with Yuan T. Lee on the study of multiphoton dissociation of molecular clusters. The molecular-beam photofragmentation translational spectroscopy that they developed has clarified much of the initial confusion concerning the dynamics of infrared multiphoton dissociation processes. In the 1980s and 1990s, Professor Shen developed various nonlinear optics methods for the study of material surfaces and interfaces. Among these techniques, second-harmonic generation and sum frequency generation spectroscopy are best known and now widely used by scientists from various fields. He has collaborated with Gabor Somorjai on the use of the technique of Sum Frequency Generation Spectroscopy to study catalyst surfaces. He is the author of the book The Principles of Nonlinear Optics. Professor Shen belongs to the prolific J. J. Thomson academic lineage tree. Currently, Professor Shen works in U. C. Berkeley and Fudan University in Shanghai.

Recipients of the Copley Medal (1901–1950)
17th century
18th century
19th century
20th century
21st century
SI base units
SI derived units
Non SI units
Physical constants

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