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World Patent Information 28 (2006) 330–335

J.J. Thomson, the electron and the birth of electronics

Brian Spear

36 Starling Close, Buckhurst Hill, Essex IG95TN, United Kingdom

Abstract

J.J. Thomson won the 1906 Physics Nobel Prize for his work on gaseous conductivity and the discovery of the electron that led tomodern atomic physics. At the same time the electronics industry started with its consequent patent activity. On the 100th anniversary ofThomson’s Nobel Prize, the history of the electron/electronics, and the relationship between them, is explored.� 2006 Elsevier Ltd. All rights reserved.

Keywords: Cathode rays; Thomson; Electron; Nobel Prize; Fleming; Diode; De Forest; Triode; Patents

1. One hundred years ago

In 1906 the British physicist Joseph John Thomson(1856–1940) was awarded the prestigious Nobel Prize forPhysics ‘‘in recognition of the great merits of his theoreticaland experimental investigations on the conduction of elec-tricity by gases’’. The most famous result of these investiga-tions is that he is considered to have ‘‘discovered’’ theelectron which had profound implications in the field oftheoretical physics and eventually nuclear technology.Around this time was the birth of the electronics industrywith the consequent economic and societal changes we livewith today. On the 100th anniversary of his prize it is worthreconsidering the history of this fundamental discovery andwhat effect, if any, it had on the early development ofelectronics.

2. Atomic theory

The idea that matter can be subdivided till it is reducedto small indivisible particles called atoms goes back to theGreek philosopher Democritus around 400BC. This wasrejected by Aristotle and nearly everyone else for over2000 years till Dalton produced his atomic theory in

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1803. In the late 19th century it was still the received scien-tific wisdom that atoms were indivisible particles interact-ing with each other according to the laws of Newtonianmechanics though there were a few niggling queries to becleared up. By the 1930s the received wisdom was the atomcomprised neutrons, protons and electrons while today weare accustomed to the idea of at least 200 sub-atomicparticles of increasing degrees of complexity and strange-ness. How did this paradigm shift come about and whatwas Thomson’s role?

3. Cathode rays

Interest in the often spectacular electrical discharges ingases goes back to at least the 18th century, e.g. BenjaminFranklin’s famous ‘‘sentry box’’ experiment to harnesslightning discharges which he wisely did not attempt. Oth-ers did and at least one, G.W. Richmann in St. Petersburg,died as a result of his attempt to draw atmospheric electric-ity down to earth using a wet kite string. By the mid 19thcentury there were not only reliable electric power sourcesbut Heinrich Geissler’s invention of the mercury vapourpump allowed glass tubes to be evacuated to a hithertounknown degree of vacuum. Cathode rays are invisiblebut, at this degree of rarifaction, the green fluorescencethey produce stands out and they were first identified byJulius Plucker in 1859. It was observed that thesedischarges could be deflected by magnetic fields and C.F.

Fig. 1. J.J. Thomson. Source: IET Archives.

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Varley concluded in the 1860s that discharges were ‘‘atten-uated particles of matter projected from the negative poleby electricity in all directions, but that the magnet controlstheir course’’. As the negative electrode is the cathode thedischarges became known as ‘‘cathode rays’’. One prolificexperimentalist was William Crookes (1832–1919) whoshowed that cathode rays move in a straight line with hisfamous ‘‘Maltese Cross’’ experiment. In 1879 he postulatedthe existence of a fourth state of matter where ‘‘the corpus-cular theory of light may be true and where light does notalways move in straight lines, but where we can never enter,and with which we must be content to observe and exper-iment from the outside’’. Like many Victorian scientists hewas very interested in spiritualism which may explain hisesoteric choice of language! Numerous physicists subse-quently investigated cathode rays and, by 1895, there werebroadly two schools of thought. One, mainly English withsome French support, felt the rays were a stream of mate-rial, electrically charged particles, while the other, mainlyGerman, held they were electromagnetic wave propagationin an all pervasive aether. To complicate matters in 1895Wilhelm Conrad Roentgen in Germany discovered X-rays,which were themselves triggered by high energy cathoderays, for which he gained the 1901 Nobel Prize. Thus inthe 1895–1897 period the nature of cathode rays becamea very hot topic.

4. Thomson’s background

Thomson—see Fig. 1—originally trained in Manchesteras an engineer but subsequently came second in the rigo-rous Cambridge mathematics Tripos in 1880 and stayedthere investigating energy transformation using modifiedLagrangian theory, a highly theoretical subject, laterteaching mathematics. He won the prestigious AdamsPrize in 1882 for work on actions of two closed vorticesin a perfectly incompressible fluid, another highly mathe-matical area, and even did some practical work in theCavendish laboratory. It must be noted that, before the1870s, British professors and their students were notnormally expected to do experimental work and the open-ing of the Cavendish laboratory in 1874 at very traditionalCambridge was something of an innovation, only madepossible by the generosity of William Cavendish, Dukeof Devonshire and descendent of the 18th century scientistHenry Cavendish. Even then it was in something of alimbo as student practical work was not compulsory till1881 since it was felt to be ungentlemanly by many univer-sity staff. The first Cavendish Professor (i.e. laboratoryhead) was James Clerk Maxwell till his death in 1879and when his successor, Lord Rayleigh, resigned in 1884there was much competition for the post. It surprisedmany when 28 year old Thomson was appointed, espe-cially given his very limited practical experience. In thewords of one senior university member: ‘‘matters havecome to a pretty pass when they elect mere boys profes-sors’’! It appears the Cambridge mathematical elite did

not really approve of industrial laboratories so his lackof hands on experience, together with his strong mathe-matical bent, was very much in his favour.

5. Thomson’s research

Once safely installed in a permanent job he was largelyfree to pursue his own interests (academics being lessconstrained in that era) and he spent the rest of his lifeinvestigating electric discharge through gases, a subjecthis original mentor, Arthur Schuster, described as fit onlyfor ‘‘cranks and visionaries’’. Being convinced that Croo-kes’ experiments would give evidence of the structure ofmatter and the nature of electricity, he decided to pursuethe matter himself with his colleague Richard Threlfall(1861–1932) who was very skilled with his hands, despitehaving blown several fingers off in a boyhood experimentwith explosives. Threlfall became Professor of Physics atSydney University from 1886 to 1899 and later researchdirector at the UK chemical company Albright andWilson. It must be noted that Thomson was decidedlynot good with his hands but he did show a keen interestin his students’ work. He also married one of the firstfemale students in 1889.

Fig. 2. US patent 307031 of 1884.

332 B. Spear / World Patent Information 28 (2006) 330–335

In early 1897 Emil Wiechert in Germany had calculatedthe ratio of (m), the mass of the putative cathode ray parti-cle, to (e), its electric charge. Thomson firstly tried to sepa-rate the charge from the particle by magnetic deflection andfailed, thus proving they were indivisible. Then by furtherexhausting the tube he managed to bend the rays with anelectric field (which Hertz and others had failed to do)and finally calculated his own value for m/e which wascomparable to Wiechert’s. Since m/e was about 1000 timessmaller than that of a charged hydrogen atom, either cath-ode rays carried an enormous charge (compared with acharged atom) or they were very light in relation to theircharge. He first publicly argued that cathode rays were cor-puscles, small negatively charged particles from whichatoms are made up, at the Royal Institution in Londonon 30 April 1897 and this was formally published in threepapers in the Philosophical Magazine from 1897 to 1879.This idea quickly displaced the luminiferous aether alterna-tive (though the idea did not die, as late as 1909 the distin-guished British physicist Oliver Lodge wrote a book on thesubject) but Thomson held that the positive charge in theatom was distributed (the plum pudding model) rather thanconcentrated in the nucleus. Although, as for most discov-eries, it can be argued that many researchers had an influ-ence on the final result the consensus of historians is thatThomson assembled the conclusive evidence through rigor-ous experimental work (rather surprisingly considering hisbackground) and deservedly won the Nobel Prize.

6. The electron and atomic physics

The term ‘‘electron’’ was first coined by George John-stone Stoney (1826–1911) around 1891 and was widelyused but Thomson continued to use the term ‘‘corpuscle’’in his Nobel lecture of 11 December 1906, possibly becausehe wished to distinguish the real ponderable negative elec-tron (i.e. his corpuscle) from the positive electron which (inhis view) remained theoretical around 1900. He continuedat the Cavendish which produced a succession of distin-guished researchers under his leadership, seven of whomwon Nobel Prizes. Rutherford repudiated the plum pud-ding model with his scattering experiments which showedthat the positive charge, and most of the mass, lay in a tinynucleus of the atom. He named the hydrogen nucleus theproton in 1911 and postulated the existence of the neutronin 1920, discovered by James Chadwick in 1932. Betweenthem they had a crucial impact on modern atomic physics.Thomson made way for Rutherford at the Cavendish in1919 to become Master of Trinity College but continuedresearching till the 1930s, publishing over 50 papers after1918. He was on the Government Board for Inventionand Research during WW1, acting as an interface betweeninventors and producers of new equipment. However, hisson George Paget Thomson, a Professor at ImperialCollege and winner of the 1937 Noble Prize for Physics,claimed his father never filed any patents; George certainlydid though.

7. Electrical engineering and the Edison effect

The electrical engineering industry started with telegra-phy in the 1840s and developed through power genera-tion/distribution and lighting to become one of the majorsuccess stories of the second industrial revolution. By1900 electricity was an integral part of modern economiesand yet this had been achieved without any profound graspof what electricity actually was. Engineers are practicalpeople and lack of theory never hindered the search forprofitable innovation; it was enough that electricity couldbe generated and harnessed though some understandingof the theory was a definite bonus in many cases. Forexample during the growth of electric lighting around1880 it had been noted that, in carbon filament lamps,carbon particles sputtered off the filament and blackenedthe inside of the glass. When the filament was a single loopand supplied with direct current (DC) a line on the glassremained clear. Thomas Edison, the prolific inventor andpatentee, investigated this phenomenon which becameknown as the Edison effect. He fixed an additional metalplate (insulated from the filament) in the lamp. When thelamp was hot a small current flowed to the plate if it wasconnected to the positive side of the filament so the platewas collecting negative electricity. Edison covered this witha US patent in 1884 [1] but it remained a curiosity as therewas no demand for a relatively high current in the filamentto yield a very small rectified current—see Fig. 2.

8. Fleming and the diode valve

John Ambrose Fleming (1849–1945) trained as a chem-ist, transferred to physics under the influence of ProfessorFrederick Guthrie in London and, after spells of schoolteaching, studied at the Cavendish laboratory underMaxwell. He thus had a strong theoretical backgroundbut, unlike Thomson, was a natural experimentalisttoo—see Fig. 3. Apart from academic posts he became sci-entific adviser to the Edison Telephone company and to the

Fig. 3. J.A. Fleming. Source: IET Archives.

Fig. 4. GB patent 24850 of 1904.

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Edison Electric Light Company whose London powerstation started in 1882. In 1885 he became Professor of elec-trical engineering at University College London where hestayed for the rest of his career but successfully combinedthis with technical consultancy, unusual for academics atthat time. He was among many who had studied the Edisoneffect and in 1890 read a paper on the phenomenon to theRoyal Society and explained it in terms of ‘‘molecules’’transmitted between the electrodes, a view he repeated ina Royal Institution lecture that year. In 1896 he read apaper to the Physical Society in which he said ‘‘we may jus-tifiably make the hypothesis that these carbon molecules oratoms so projected from the conductor when intenselyheated by the current flowing through it are all negatively

charged’’. He was also a regular patentee in this period.

9. Wireless

Herz had proved the existence of radio waves in 1887and Marconi formed a company for wireless transmission,initially using a coherer for detecting radio waves and latera magnetic receiver. In 1899 Fleming became a scientificadvisor to Marconi, initially working on the power plantfor production of Trans-Atlantic signals which succeededin 1901. In 1904 there was a problem in that the magneticdetector was more certain in its action than the coherer, buthad the disadvantage that the sound could only be heard astelephone sounds, not recorded on a tape. In Fleming’swords:

‘‘The problem before me then was to discover how tochange this feeble electric oscillation into a feeble directcurrent which could work the ordinary cable recordinginstruments. . . Thinking over the subject intensely, Ihad in October 1904, a sudden very happy thought. Irecalled to mind my experiments on the ‘‘Edison effect’’,and in particular my observation that the space betweenan incandescent carbon filament and a cold metal platein a bulb exhausted of its air had a one way conductivityfor electricity. Then I said to myself, ‘‘If that is the casewe have here the exact implement required to rectifyhigh-frequency oscillations’’.

A few experiments proved this to be so and he patentedthis in the UK in 1904 [2], which had overseas equivalentsincluding US 803684, and assigned the rights to Marconi—see Fig. 4. As the bulb acted liked a valve in a pipe, lettingwater only go one way, he called it a valve and the namestuck. The small particles of electricity sent from the hotsurface were called thermions hence it became known asthermionic valve, or diode as it had two electrodes.Although he was no doubt fully aware of Thomson’s cor-pusles/electrons it seems unlikely that they had any effecton the invention of the valve which was clearly stimulatedby a practical problem.

10. De Forest and the triode

Lee De Forest (1873–1961) had received his PhD onradio waves from Yale, started various companies, andeventually held over 300 patents. In 1907 he modified theEdison/Fleming device by inserting a third electrodebetween the anode and cathode thus converting a simplerectifier to an amplifier which let weak signals be heardmore clearly. This he called the Audion, more commonlyknown as the triode, and was covered by US patent

Fig. 5. US patent 841387 of 1907.

334 B. Spear / World Patent Information 28 (2006) 330–335

841387 in 1907 [3]—see Fig. 5. The development of wirelessled to a flood of patent applications for valve based devices(which would nowadays be labelled ‘‘electronic’’) many ofwhich may well have been influenced by the widespreadknowledge of the nature of the electron by the 1920s. Valvetechnology remained predominant until the large scale useof the transistor in the 1950s.

11. Patents

The EPO’s esp@cenet� database lists over 20 patents forJohn Ambrose Fleming from 1894 to 1922. Patents fromDe Forest and Armstrong (see below) are very numerousbut nothing was found for J.J. Thomson in the GB NameIndexes to Patent Applications 1890–1920. His son, G.P.Thomson published three patents relating to nucleartechnology in the 1959–1961 period.

12. The patent disputes

Given the commercial importance of radio and itsrelated equipment it was not surprising that Marconi(who held the rights to Fleming’s patents) and RCA suedDe Forest and his licencees for US patent infringement.The situation was effectively that Edison had patented adevice, Fleming had patented the use of the device for anew application while De Forest had produced a modifieddevice for that application. Were Edison or De Forest enti-tled to valid patents and, if so, who was being infringed?Litigation went on for nearly twenty years through variouscourts (mainly in the US) which sometimes upheld Flem-ing’s claims and sometimes reversed the decisions. Subse-quently Marconi sued the US government for patentinfringement and that, with other cases, was finally decidedin a US Supreme Court Decision in 1943. In this Fleming’svalve patent was declared invalid because of a 1915disclaimer which limited the use of the diode to highfrequency oscillations. It was felt the way the disclaimerwas made rendered the patent invalid which was not a verysatisfactory conclusion. Thus Fleming’s patent cases hadall the durability of the famous Jarndyce v Jarndyce casein the novel Bleak House by Charles Dickens!

However, this was not unusual in that era. In 1912 DeForest sold the triode patent to the American Telephoneand Telegraph Company (AT&T) for use in telephonesystems. Edwin Howard Armstrong (1890–1954) workedout what was really going on in the Audion, somethingDe Forest never quite managed, and cycled the outputback to the input many times over (US patent 1113149granted 1914). He called this regeneration and thus usedthe Audion as a compact energy-efficient transmitter. Arm-strong added the superhet which amplified radio transmis-sion sound ever further and thus made radio commercial.De Forest patented a very similar regenerative process in1916 and sold that patent to AT&T. The consequent legalbattle between Armstrong and De Forest lasted from 1922to 1934 which De Forest finally won in a controversial USSupreme Court decision, though the scientific communityfelt otherwise and Armstrong was a awarded the GoldMedal from the Institute of Radio Engineers.

13. What happened to them?

Fleming had a long successful academic and consultingcareer despite severe deafness and did not formally retiretill 1927, the year he was nominated for (but did notreceive) the Nobel Prize for Physics. Many other honourscame his way including a knighthood in 1929. Apart fromhis technical work he had a strong Christian faith andwrote several books reconciling science and religion. Heremained active till an advanced age (he read his last paperto the Physical Society aged 90) and, his first wife havingdied childless in 1917, he married a lady of 34 in 1933 whenhe was 84. De Forest was more successful as an inventorthan a businessman and, like Fleming, also failed to getthe Nobel Prize for Physics. Essentially an individualist,like many inventors, he had a rather controversial reputa-tion and became increasingly paranoid as he aged. Hehad four wives before his death aged 88. He was at leastluckier than his antagonist Armstrong who patented FM(Frequency Modulation) in 1933 and was involved in 21actions against large companies infringing his patents afterWW2. Worn down by constant litigation he committedsuicide in 1954, though his widow eventually won all 21by 1967.

14. Finally

Did the ‘‘discovery’’ of the electron trigger off the elec-tronics revolution? It is clear that Fleming was well awareof Thomson’s views on the corpuscle/electron but there isno evidence that this influenced the development of thevalve which was clearly a product of the demands of theexpanding wireless industry. It seems likely that this wastrue for many of the other early pioneers like De Forestso, as far as one can determine, theory and technology werenot in synchronism, in the early days at least. However, itseems likely that Thomson’s work formed a good basis forelectronic developments later in the 20th century.

B. Spear / World Patent Information 28 (2006) 330–335 335

Acknowledgements

The images in Figs. 1 and 3 are reproduced with the kindpermission of The Institution of Engineering and Tech-nology (IET) and the assistance of Anne Locker, IETArchivist.

References

[1] Edison TA. Electrical Indicator, US307031, granted 21 October 1884.[2] Fleming JA. Improvements in instruments for detecting and measuring

alternating electric current, GB 24850 dated 16 November 1904.[3] De Forrest L. Device for amplifying feeble electrical currents. US

patent 841387, granted 15 January 1907.

Select Bibliography

[4] Davis EA, Falconer IJ. J.J. Thomson and the Discovery of theElectron (London: Taylor and Francis, 1997), p. 139–52 have thecomplete report of the meeting of 30 April 1897.

[5] Thomson GP. J.J Thomson and the Cavendish laboratory. Lon-don: Thomas Nelson & Sons; 1964.

[6] Buchwald JZ, Warwick A. Histories of the electron the birth ofmicrophysics. Cambridge MA: MIT Press; 2001. especially p. 21–76,403–24.

[7] Dahl Per F. Flash of the cathode rays. Bristol and Philadelphia: IOPPublishing; 1997.

[8] MacGregor-Morris JT. The inventor of the valve a biography of SirAmbrose Fleming (London, The Television Society, 1954), e.g. p. 65–83.

[9] Fleming Valve Centenary Conference 1–2 July 2004 (London:Communications Engineering Doctorate Centre, University College2004).

[10] Lodge Sir OJ. The ether of space. New York: Harper; 1909.[11] Dyella HF, Corneliussen ST. John Ambrose Fleming and the

beginning of electronics. J Vac Sci Technol A:Vacuum, Surf Films2005;23(4):1244–51.

[12] Griffiths IW. J.J. Thomson—the centenary of his discovery of theelectron and of his invention of mass spectrometry. Rapid CommunMass Spectrom 1997;11(1):2–16.

[13] There are numerous references to the patent disputes on the internet.Available from: http://www.mercurians.org/nov98/misreading.html.http://world.std.com/~jlr/doom/armstrng.htm.

Brian Spear is a Chartered Engineer and Fellowof the Institution of Electrical Engineers whosecareer was spent in the UK Patent Office. Thisincluded 22 years examining patents relating tocomputers, control systems and telecommunica-tions. He has also spent 10 years on developingcomputer databases/searching, working in theircommercial search arm—the Search and Advi-sory Service, and on IPR lecturing to a wide rangeof organisations. Since retiring he has completedan M.Sc. in the History of Science, Medicine and

Technology at Imperial College London.