In 1906, Thomson was awarded theNobel Prize in Physics "in recognition of the great merits of his theoretical and experimental investigations on the conduction of electricity by gases".[5]
Thomson is credited with finding the first evidence forisotopes of a stable (non-radioactive) element in 1912, as part of his exploration into the composition ofcanal rays (positiveions). His experiments to determine the nature of positively charged particles, withFrancis William Aston, were the first use ofmass spectrometry and led to the development of the mass spectrograph.[4][6]
Joseph John Thomson was born on 18 December 1856 inCheetham Hill,Manchester. His mother, Emma Swindells, came from a local textile family. His father, Joseph James Thomson, ran anantiquarian bookshop founded by Thomson's great-grandfather. Joseph John had a brother, Frederick Vernon Thomson, who was two years younger than he was.[8] Thomson was a reserved yet devoutAnglican.[9][10][11]
Thomson's early education was in small private schools where he demonstrated outstanding talent and interest in science. In 1870, he was admitted toOwens College in Manchester (now theUniversity of Manchester) at the unusually young age of 14, and came under the influence ofBalfour Stewart, Professor of Physics, who initiated him into physical research.[12] He began experimenting with contact electrification and soon published his first scientific paper.[13] His parents planned to enroll him as an apprentice engineer toSharp, Stewart & Co, a locomotive manufacturer, but these plans were cut short when his father died in 1873.[8]
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 ofLord Kelvin'svortex theory of the atom.[17]
Thomson published a number of papers addressing both mathematical and experimental issues ofelectromagnetism. He examined the electromagnetic theory of light ofJames Clerk Maxwell, introduced the concept ofelectromagnetic mass of a charged particle, and demonstrated that a moving charged body would apparently increase in mass.[17]
Much of his work in mathematical modelling of chemical processes can be thought of as earlycomputational chemistry.[4] In further work, published in book form asApplications 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.[17] His next book,Notes on recent researches in electricity and magnetism (1893), built upon Maxwell'sTreatise 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.[17] His third book,Elements of the mathematical theory of electricity and magnetism (1895)[28] was a readable introduction to a wide variety of subjects, and achieved considerable popularity as a textbook.[17]
First page toNotes on Recent Researches in Electricity and Magnetism (1893)
A series of four lectures, given by Thomson on a visit toPrinceton University in 1896, were subsequently published asDischarge of electricity through gases (1897). He also presented a series of six lectures atYale University in 1904.[3]
Several scientists, such asWilliam Prout andNorman 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 of the atom 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 ofcathode rays. Thomson made his suggestion on 30 April 1897 following his discovery that cathode rays (at the time known asLenard rays) could travel much further through air than expected for an atom-sized particle.[29] 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 nameelectron, which had been suggested byGeorge Johnstone Stoney in 1891, prior to Thomson's discovery.[30]
In April 1897, Thomson had only early indications that the cathode rays could be deflected electrically (previous investigators such asHeinrich 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.[31] This became the classic means of measuring the charge-to-mass ratio of the electron. Later in 1899 he measured the charge of the electron to be of6.8×10−10 esu.[32]
Thomson believed that the corpuscles emerged from the atoms of the trace gas inside hiscathode-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.[4] 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 raisins in a plum pudding (although in Thomson's model they were not stationary, but orbiting rapidly).[33][34]
Thomson made the discovery around the same time thatWalter Kaufmann andEmil Wiechert discovered the correct mass to charge ratio of these cathode rays (electrons).[35]
The nameelectron was adopted for these particles by the scientific community, mainly due to the advocation byGeorge Francis FitzGerald,Joseph Larmor, andHendrik Lorentz.[36]: 273 The term was originally coined byGeorge Johnstone Stoney in 1891 as a tentative name for the basic unit of electrical charge (which had then yet to be discovered).[37][38] For some years Thomson resisted using the word "electron" because he didn't like how some physicists talked of a "positive electron" that was supposed to be the elementary unit of positive charge just as the "negative electron" is the elementary unit of negative charge. Thomson preferred to stick with the word "corpuscle" which he strictly defined as negatively charged.[39] He relented by 1914, using the word "electron" in his bookThe Atomic Theory.[40] In 1920, Rutherford and his fellows agreed to call the nucleus of the hydrogen ion "proton", establishing a distinct name for the smallest known positively-charged particle of matter (that can exist independently anyway).[41]
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 ascanal 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.[8] 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 twoisotopes.[42][43] 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 certainradioactive elements.
Thomson's separation of neon isotopes by their mass was the first example ofmass spectrometry, which was subsequently improved and developed into a general method byF. W. Aston and byA. J. Dempster.[4][6]
Earlier, physicists debated whether cathode rays were immaterial like light ("some process in theaether") or were "in fact wholly material, and ... mark the paths of particles of matter charged with negative electricity", quoting Thomson.[31] The aetherial hypothesis was vague,[31] but the particle hypothesis was definite enough for Thomson to test.
Thomson first investigated themagnetic 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 mainbell jar, where they were deflected by a magnet. Thomson detected their path by thefluorescence 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.[44]
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 inCrookes tubes,[citation needed] they believed that they are a mere by-product and that the cathode rays themselves are immaterial.[citation needed] Thomson set out to investigate whether or not he could actually separate the charge from the rays.
Thomson constructed a Crookes tube with anelectrometer 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.[29]
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.
The cathode ray (blue line) was deflected by the electric field (yellow).
Cathode-ray tube with electrical deflection
In May–June 1897, Thomson investigated whether or not the rays could be deflected by an electric field.[8] Previous experimenters had failed to observe this, but Thomson believed their experiments were flawed because their tubes contained too much gas.
Thomson constructed aCrookes 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. 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.
In his classic experiment, Thomson measured themass-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 timeslower than that of a hydrogen ion (H+), suggesting either that the particles were very light and/or very highly charged.[31] Significantly, the rays from every cathode yielded the same mass-to-charge ratio. This is in contrast toanode 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 (in his original notation, using F instead of E for the electric field and H instead of B for the magnetic field):
The electric deflection is given by, 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, 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. This can be simplified to give. 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.
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.
Thomson imagined the atom as being made up of these corpuscles orbiting in a sea of positive charge; this was hisplum pudding model. This model was later proved incorrect when his studentErnest Rutherford showed that the positive charge is concentrated in the nucleus of the atom.
In 1906, Thomson demonstrated thathydrogen had only a singleelectron per atom. Previous theories allowed various numbers of electrons.[47][48]
From 1916 to 1918, Thomson chaired the "Committee appointed by the Prime Minister to enquire into the Position of Natural Science in the Educational System of Great Britain". The Report of the Committee, published in 1918, was known as the Thomson Report.[49]
In 1890, Thomson married Rose Elisabeth Paget at the church ofSt. Mary the Less. Rose, who was the daughter ofSir George Edward Paget, a physician and thenRegius Professor of Physic at Cambridge, was interested in physics. Beginning in 1882, women could attend demonstrations and lectures at the University of Cambridge. Rose attended demonstrations and lectures, among them Thomson's, leading to their relationship.[50]
They had two children:George Paget Thomson, who was also awarded a Nobel Prize for his work on the wave properties of the electron, and Joan Paget Thomson (later Charnock),[51] who became an author, writing children's books, non-fiction and biographies.[52]
Plaque commemorating J. J. Thomson's discovery of the electron outside the old Cavendish Laboratory in CambridgeAutochrome portrait by Georges Chevalier, 1923Thomsonc. 1920–1925
^Sengupta, Sudipto (6 April 2015)."Extraordinary Professor: JJ Thomson and his Nobel Prize Factory".Probashi. Durga Puja & Cultural Association (India). Retrieved7 August 2022.His Nobel Laureate students include Rutherford, Aston, Wilson, Bragg, Barkla, Richardson, and Appleton
^abcdDavis & Falconer,J.J. Thomson and the Discovery of the Electron
^Peter J. Bowler,Reconciling Science and Religion: The Debate in Early-Twentieth-Century Britain (2014). University of Chicago Press. p. 35.ISBN9780226068596. "Both Lord Rayleigh and J. J. Thomson were Anglicans."
^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).
^Richardson, Owen. 1970. "Joseph J. Thomson", inDictionary of National Biography, 1931–1940. L. G. Wickham Legg, editor.Oxford University Press.
^"Charles Glover Barkla – Biographical".The Nobel Prize. Nobel Lectures, Physics 1901–1921, Elsevier Publishing Company. 1967. Retrieved11 October 2022.he worked under J. J. Thomson at the Cavendish Laboratory in Cambridge.
^"Niels Bohr – Biographical".The Nobel Prize. Nobel Lectures, Physics 1922–1941, Elsevier Publishing Company, Amsterdam. 1965. Retrieved18 October 2022.he made a stay at Cambridge, where he profited by following the experimental work going on in the Cavendish Laboratory under Sir J.J. Thomson's guidance
^"Max Born- Biographical".The Nobel Prize. Nobel Lectures, Physics 1942–1962, Elsevier Publishing Company. 1964. Retrieved11 October 2022.Born next went to Cambridge for a short time, to study under Larmor and J. J. Thomson.
^"Sir Owen Willans Richardson, British physicist".Encyclopædia Britannica. Retrieved18 October 2022.Richardson, a graduate (1900) of Trinity College, Cambridge, and a student of J. J. Thomson at the Cavendish Laboratory
^"Francis W. Aston – Biographical".The Nobel Prize. Nobel Lectures, Physics 1922–1941, Elsevier Publishing Company. 1966. Retrieved13 October 2022.At the end of 1909 he accepted the invitation of Sir J. J. Thomson to work as his assistant at the Cavendish Laboratory
^"Ernest Rutherford – Biography". NobelPrize.org. Retrieved6 August 2013.as a research student at the Cavendish Laboratory under J.J. Thomson.
^"George Paget Thomson Biographical".The Nobel Prize. Retrieved8 June 2022.he carried out experiments on the behaviour of electrons ... which showed that electrons behave as waves ...
^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.
^Chown, Marcus (29 March 1997)."Forum: Just who did discover the electron?".New Scientist (2075). Retrieved17 October 2020.Marcus Chown says the truth is not quite as the history books suggest.
^O'Hara, J. G. (March 1975). "George Johnstone Stoney, F.R.S., and the Concept of the Electron".Notes and Records of the Royal Society of London.29 (2). Royal Society:265–276.doi:10.1098/rsnr.1975.0018.JSTOR531468.S2CID145353314.
^J. J. Thomson (1907)."The Modern Theory of Electrical Conductivity of Metals".Journal of the Institution of Electrical Engineers.38 (183):455–468.doi:10.1049/jiee-1.1907.0026.: "Perhaps I can best show my appreciation by trying to answer the questions which Professor Silvanus Thompson addressed to me. I think his first question was a question rather of notation, as to the difference between the electron and the corpuscle. I prefer the corpuscle for two reasons: first of all, it is my own child, and I have a kind of parental affection for it; and, secondly, I think it has one merit which the term electron has not. We talk about positive and negative electrons, and I think when you use the same term for the two the suggestion is that there is an equality, so to speak, in the properties. From my point of view the difference between the negative and the positive is essential, and much greater than I think would be suggested by the term positive electron and negative electron. Therefore I prefer to use a special term for the negative units and call it a corpuscle. A corpuscle is just a negative electron."
^Orme Masson (1921)."The Constitution of Atoms".The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science.41 (242):281–285.doi:10.1080/14786442108636219.[permanent dead link] Footnote by Ernest Rutherford: 'At the time of writing this paper in Australia, Professor Orme Masson was not aware that the name "proton" had already been suggested as a suitable name for the unit of mass nearly 1, in terms of oxygen 16, that appears to enter into the nuclear structure of atoms. The question of a suitable name for this unit was discussed at an informal meeting of a number of members of Section A of the British Association [for the Advancement of Science] at Cardiff this year. The name "baron" suggested by Professor Masson was mentioned, but was considered unsuitable on account of the existing variety of meanings. Finally the name " proton" met with general approval, particularly as it suggests the original term "protyle " given by Prout in his well-known hypothesis that all atoms are built up of hydrogen. The need of a special name for the nuclear unit of mass 1 was drawn attention to by Sir Oliver Lodge at the Sectional meeting, and the writer then suggested the name "proton."'
^J.J. Thomson (1912) "Further experiments on positive rays,"Philosophical Magazine, series 6,24 (140): 209–253.
^J. J. Thomson (1913) "Rays of positive electricity",Proceedings of the Royal Society A,89: 1–20.
^Thomson, J. J. (8 February 1897). "On the cathode rays".Proceedings of the Cambridge Philosophical Society.9: 243.
^Thomson, J. J. (1897)."Cathode rays".Philosophical Magazine.44: 293.
^Memoirs And Proceedings Of The Manchester Literary And Philosophical Society Volume 152 2013-14
^ Complete List of the Members & Officers of the Manchester Literary & Philosophical Society.From its institution on February 28th 1781 to April, 1896.
^"Joseph John Thomson".American Academy of Arts & Sciences. 10 February 2023. Retrieved2 February 2024.
^"Awards Page – Thomson Medal Award".International Mass Spectrometry Foundation. Archived fromthe original on 13 May 2019. Retrieved7 March 2023.The Thomson Medal Award is named after Sir J. J. Thomson, who was responsible for the first mass spectrograph
Title page toNotes on Recent Researches in Electricity and Magnetism (1893)Title page toElectricity and Matter (1904)
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:ISBN0-543-95696-2.
1888.Applications of Dynamics to Physics and Chemistry. London: Macmillan and Co., pp. 326. Recent reprint:ISBN1-4021-8397-6.
J.J. Thomson (1897) "Cathode Rays",The Electrician 39, 104, also published inProceedings 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 (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 theThomson Problem is posed.
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 (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 asdigital 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.ISBN978-0-7484-0696-8
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.
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