The early history of electronicsVI. Discovery of the electronThe invention of the first thermionic devices, which ledto the massive development of electronic telecommunications in the20th century, was predicated on a discovery madein a British university laboratory as the19th century drew to its closeCharles Susskind University of California

The preceding five articles in this series described how field, with the exception of the discovery made by Faradayadvances in electromagnetic theory, one of the two parent in 1838 that the luminosity caused by an electric dischargesciences of today's electronics technology, led to its first between two electrodes in rarefied air exhibited a gapsuccesses at the turn of the century: "wireless" communi- just in front of the negative electrode4; this gap is nowcations. I But radiotelegraphy may well have remained an designated as the Faraday dark space. The reason the sub-expensive and uncertain medium, restricted to emergency ject proceeded so slowly may well have been a technologi-use in situations in which costs did not matter, if discov- cal one: it was difficult to reduce pressure reliably anderies in the other parent science-particle physics-had effectively to the extent necessary in investigating electricnot most conveniently come along at about the same time discharges. The dependence of the progress of science onand opened up undreamed-of possibilities in the genera- technological innovation is a well-known phenomenontion of high-frequency waves and the amplification of that is nowhere better exemplified than in the influenceweak signals. that air-pump design (accelerated by the exigencies of

incandescent-lamp manufacture) exercised on electricalThe concept of the electron research.' Heinrich Geissler (1815-1879) provided an im-As with many major discoveries, some writers have portant new tool for the study of electric discharges when

speculated why the concept of an electron was not enun- he developed the mercury air pump in 1855.ciated at least half a century before it was, as a result of Julius Plucker (1801-1868) at the University of Bonnthe development of electrochemistry. In 1833, Faraday and his pupil, Johann Wilhelm Hittorf (1824-1914),discovered the laws of electrolysis, by which the rate of brilliantly exploited the new Geissler high-vacuum tubesdecomposition of an electrolytic solution is proportional in an extensive series of researches on electric-dischargeto the electric current and independent of the strength of phenomenons.6 Plucker remembered that Sir Humphrythe solution or the size of the electrodes. In a comparison Davy (1778-1829) had shown in 1821 that an arc betweenof different electrolytes, a given electric current liberates two electrodes could be deflected by a magnet.7 Pluckerone atom of any element in the time it would take to repeated the experiment with a gaseous discharge and ob-liberate n atoms of hydrogen, where n is the valency of the tained a similar deflection. Moreover, the luminosity fromelement in question. (A charge of 96 580 coulombs, known the negative electrode appeared to follow the magnetic-as a faraday, is required to liberate Z/n grams of each ion, field lines. Plucker made two other important observa-where Z is the atomic weight. To be sure, Faraday knew tions. He noticed that particles of the electrode materialnothing of "valency," a concept that was established (which in this instance was platinum) left the cathode andlater; he expressed his results in terms of "electrochemical were deposited on the walls of the enclosing glass bulb,equivalents.") The implication that a given quantity of and that the walls in the vicinity of this cathode exhibitedelectricity is associated with every atom was clear to a luminous glow that could be likewise moved about by aFaraday, but he was wary of basing a new theory of mat- magnet. The second observation was further investigatedter on it "for," as he wrote, "though it is very easy to talk by Hittorf, who discovered that when an object wasof atoms, it is very difficult to form a clear idea of their placed in front of a point cathode, a shadow was cast innature, especially when compound bodies are under con- the glow.8 From this observation, Hittorf deduced thatsideration."2 the emission from the cathode propagated rectilinearly inAs we shall see, the idea of the discreteness of charge, "glow rays" (Glimmstrahlen). Moreover, he noticed that

based on Faraday's laws, was to bereopened in thel1880s the rectilinear propagation changed to a helical pathby Helmholtz and others. At the same time the question under the influence of a magnetic field.was also agitated in a new context, the experimentalKin- In 1871 Cromwell Fleetwood Varley (1828-1883) per-vestigation of electric discharges in rarefied gases. This formed an important experiment in which he deflectedstudy went back to the beginning of the 18th century, to the rays by an electrostatic field.9 He concluded that theythe discoveries of Francis Hauksbee (d. 1713 ?), who had consisted of "attenuated particles of metal, projectedobserved a luminosity on glass carrying an electric charge, from their negative pole by electricity"; in other words,and of Pierre Poliniere (1671-1734). 3 During the next negatively charged corpuscles. This hypothesis also servedcentury and a half, very little progress was made in this to explain their helical path in a magnetic field.

76 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~IEEEspectruml SEPTEMBER 1970

Cathode rays were later shown to be open to serious objections: theThe next important discovery was made in 1876 by first result sought is too small to be detectable by the

Eugen Goldstein (1850-1930), who found that the means that were at Hertz' disposal, and the second wasshadows observed by Hittorf as a result of placing a solid later contravened by a more carefully designed experi-object in the path of the rays were cast regardless of ment performed by Jean Baptiste Perrin (1870-1942) andwhether the cathode was a single point or an extended described in what was the future Nobel prizewinner'ssurface, as long as the obstacle was placed near the (physics, 1926) first published work. 16cathode. 10 This experiment showed that the entire cathode These experiments only reinforced Hertz' convictionsurface emitted rays in a direction perpendicular to the that cathode rays could not consist of particles. His con-surface. Goldstein named them cathode rays. viction was not based entirely on negative results. InDuring the next two decades, scientists kept up a run- what proved to be the last electrical research of his life,

ning argument: Were cathode rays indeed particles, or Hertz had confirmed a finding that seemed to him over-were they disturbances in the ether? By and large, the whelming proof that particles could not be involved: theformer view was held by the British physicists and the fact that cathode rays could to some extent pass throughlatter by the German school. In England, Crookes in- thin metal foils, such as gold leaf."7 This result was quiteclined toward the view that cathode rays were a molecular incontrovertible and was later amply confirmed by historrent."I He thought that molecules of the residual gas pupil Philipp Eduard Anton Lenard (1862-1947), whoimpinged on the cathode, became negative as a result, and managed to pass cathode rays out of the vacuum envelopewere then repelled by the negative cathode. This hypoth- through a thin aluminum window and to investigate theiresis was reinforced by his observation that the width of absorption in air. 18 The penetrating power of the rays wasa dark space that appeared in front of the cathode grew as certainly a serious objection to the corpuscular theory.the pressure in the tube was decreased, until the entire The only reply that the British physicists could muster wasglow disappeared. (This space, whose discovery was like- that in impinging on the metal window, the cathode rayswise predicated on improvements in air pumps, is now might conceivably generate a new lot of particles, so thatknown by his name and should not be confounded with the window itself became an emitter. This suggestion wasthe Faraday space.) Crookes described the cathode rays made by Joseph John Thomson (1856-1940), who hadas an "ultragaseous" or "fourth state" of matter, by long occupied himself with these questions and who waswhich he apparently meant a condition in which electri- soon to provide the correct explanation.cally charged gaseous molecules moved under pressure solow (i.e., a mean free path so long) that collisions with The electronother particles could be disregarded. Although it is true The end of the 19th century was an incredibly fruitfulthat the theoretical explanation proposed by Crookes was period in the history of electrical research, encompassingrather naive (he was primarily a chemist), it cannot be as it did the aforementioned researches of Hertz ongainsaid that the corpuscular hypothesis was considerably electromagnetic-wave propagation, the development of astrengthened by his experiments, which were character- general theory of discharge and ionization in rarefiedized by meticulous care and not a little sense of showman- gases by Arthur Schuster (1851-1934) at the University ofship. (That was also true of the experiments that Crookes Manchester,"9 the discovery of the photoelectric effect byhad performed with his radiometer, in which experimental Hertz and Wilhelm Hallwachs (1859-1922) in 1887-1888,technique likewise outdistanced his theoretical capabili- and the discovery of X rays by Wilhelm Konrad Rontgenties.) (1845-1923) in 1895.The German physicists, notably Eilhard Ernst Gustav J. J. Thomson was deeply involved in these investiga-

Wiedemann" (1852-1928), Goldstein,'3 and Hertz,'4 tions. What impressed him more than anything was thatvigorously opposed the notion that the cathode rays were cathode rays, as distinct from light or X rays, could becorpuscles. Hertz thought that the deflection of the deflected by a magnetic field. He rightly surmised that thecathode rays by a magnetic field could be explained by the true nature of the cathode rays would be revealed byaction of the magnet on the medium in which the rays careful measurements of this deflection. He was amazedwere propagating, much as the optical plane of polariza- by the result. "I had for a long time been convinced thattion is rotated when the medium through which the light these rays were charged particles," he said afterwards,passes is magnetized. As for C. F. Varley's observation "but it was some time before I had any suspicion that theythat cathode rays could be deflected by an electrostatic were anything but charged atoms. My first doubts as tofield, Hertz was unable to reproduce that result-largely this being the case arose when I measured the deflectionbecause, as it proved later, his vessels were insufficiently of the rays by a magnet, for this was far greater than Ievacuated, so that the residual gas molecules were ion- could account for by any hypothesis which seemed at allized by the cathode rays and aggregated along the deflect- reasonable if the particles had a mass at all approachinging plates, effectively shielding the cathode rays from the that of the hydrogen atom, the smallest then known.""0deflection fields. (The correct explanation was subse- Moreover, the deflection was independent of the kind ofquently provided by FitzGerald."1) In the same investiga- gas remaining in the tube. If one made the gratuitous buttion, carried out five years before his celebrated series of convenient assumption that the charge associated with theexperiments on electromagnetic waves described in our particles was the same as that which entered into the ratiosecond installment,'1 Hertz also tried to deflect a magnetic of mass to charge of an ordinary ionized atom, the ines-needle by a cathode ray, and to determine whether the capable conclusion was that he was dealing with particlescathode rays carried electric charges by directing them whose mass was smaller, by three orders of magnitude,into a metal collector (a Faraday cage) to which an elec- than that of atoms.trometer was connected. Again both results were negative, It is hard for us to appreciate, across the decades, whatowing to the employment of experimental techniques that courage was required to put forward the startling hy-

Siisskindl-The early history of electronics 77

pothesis that the atom of an clement was not the smallest -subdivision of matter. Thomson plunged in fearlessly atonce. In a lecture at the Royal Institution on April 30, |1897, he astutely utilized Lenard's own results to establishthe particulate nature of cathode rays. "From Lenard'sexperiments on the absorption of the rays outside thetube," he said, "it follows on the hypothesis that thecathode rays are charged particles moving with highvelocities that the size of the carriers must be small com-pared with the dimensions of ordinary atoms or mole-cules." 21

It should not be thought that the discovery of the elec-tron was accompanied by immediate understanding of thestructure of the atom; that came much later through theefforts ofThomson, of his pupil Ernest Rutherford (1871 -1937), of Niels Bohr (1885-1962), and of others. Thomsonrealized that the atom was electrically neutral and that thenegative charge carried by electrons had to be balancedby a positive charge, which he at first represented by an Sir Joseph John Thomson (1856-1940) was born nearadmittedly artificial model of a cloud diffused throughout Manchester, the son of a publisher and bookseller.the space occupied by the atom rather than concentrated IHe showed early talent in school and at Owens Col-atthe nLacUS Moreover, itthcatom rathen knn foncentrten lege in Manchester, where he studied under Balfourat the nucleus. Moreover, it had been known for a1 dozen Stewart and won many prizes. At Cambridge, heyears that rays with properties corresponding to the came in second in the mathematics examinationopposite polarity existed. Goldstein had shown in 1886 (Joseph Larmor was Senior Wrangler that year) andthat, in a discharge tube containing a perforated cathode, continued postgraduate work at the new Cavendishrays would pass through the perforations in a direction Laboratory, whose directorship had passed to Lordopposite to that of cathode rays; he had named them Rayleigh in 1879 on the death of the first professor,Ka nal/sirahlen (canal rays).22 These rays were now investi- James Clerk Maxwell. Rayleigh resigned five yearsgated in greater detail by Wilhelm Carl Werner Otto later and Thomson, then 28, became the thirdFritz Franz (Willy) Wien (1864-1928), who showed thait Cavendish Professor, a position he held for 34 yearsthese posiliie ions also behaved like particles, that (unlike and only gave up (to Ernest Rutherford) to becomeIMaster of Trinity College at Cambridge, a valuablethe electrons) their behavior depended on the nature of and prestigious sinecure. During his long tenure,the gas from which they originated, and that the ratio of the Cavendish came to occupy an eminent positionmass to charge of the smallest was comparable with the in the world of experimental physics (similar to thatratio obtained in electrolysis-i.e., about 1000 times as held in later years by Franck's G6ttingen and Law-large as that obtained by Thomson for the electron.23 rence's Berkeley), owing in no small part to theThomson had carried out the measurement of the mass- important innovation of making graduates of other

to-charge ratio before the end of 1897. having first re- universities eligible to receive Cambridge researchmoved the uncertainty created by Hertz' failure to deflect degrees and Fellowships.cathode rays electrostatically. Thomson showed that the Besides his epoch-making identification of theneutralizing efTect of the gas ionized by the passage of the electron as a separate charged particle, Thomson's

greatest contribution was a result of his work oncathode rays, which acts as a conductor to shield the rays "positive rays" (ion beams): the development of afrom the deflecting plates (and which had ruined Hertz' cross-field method of identifying various atoms andexperiment), could be minimized by insuring that the molecules, including isotopes of the same elementexperiment was carried out in a better vacuum. 21 Hertz not distinguishable by chemical means. That washimself had understood that if cathode rays should prove the beginning of mass spectroscopy.to consist of corpuscles after all, it should be possible to Thomson was the first recipient of the Hughesmake measurements on them by observing their path Medal of the Royal Society in 1902 and also receivedLinder the combined action of electrostatic and maignetic its Copley Medal, as well as many other honors fromfields; however, since he had failed to obtain electrostatic scientific and engineering societies. In 1906 he gotdeflection, this avenue had been closed to him. Schuster, the Nobel Prize for "his theoretical and experimentalwho believed that cathode rays were Made upl of charged investigations into the transmission of electricityatoms, halid suggested evenode earlrweth te

up ofcagd |through gasses." He was knighted in 1908 and re-ceived the Order of Merit in 1912. Among his pupilschairge ratio could be obtained from a knowledge of the were Rutherford, C. T. R. Wilson, Aston, Barkla,

magnetic and electric fieldls. But it was not until Thomn- W. H. Bragg, and Richardson, all of whom later re-son's classic experiment that these considerations were ceived the Nobel Prize, as did his son G. P. Thomson.applied to the measurement of the ratio of mass to charge In 1936, J. J. Thomson published his autobiog-of an electron. raphy, Recollections and Reflections and, shortly

In his experiment, Thomson used an electric field E to after his death, The Life of Sir J. J. Thomson (1942)counteract the deflecting force exerted on a particle of was published by the fourth Lord Rayleigh (a physi-chairgc e by a£1 magnetic field B, as indicated b) zero deflec- cist like his more famous father, the third baron),tion of the beam, so that who had also worked under Thomson.

eE= Ber

Having thus deterimiinedi the velocity c = E B. he inferred

78 IIFF. spectrdUI1 SIl - IM13BI t 1970

the deflecting force produced by the magnetic field from This study was sponsored in part by Grant GS-2411 from themeasurements of the radius r of the circular path of the National Science Foundation.beam when the magnetic field acted alone: REFERENCES AND NOTES

mv2 1. Suisskind, C., IEEE Spectrum, vol. 5, pp. 90-98, Aug. 1968;- = Bev vol. 5, pp. 57-60, Dec. 1968; vol. 6, pp. 69-74, Apr. 1969; vol. 6,r pp. 66-70, Aug. 1969; vol, 7, pp. 78-83, Apr. 1970.

2. Faraday, M., Experimental Researches in Electricity, Vol. 1.Hence the ratio of charge to mass was given by London: R. and J. E. Taylor, 1839, p. 256.e v E 3. Hauksbee, F., Trans. Roy. Soc., vol. 24, pp. 2165-2175, 1705.e = = For a description of Poliniere's simultaneous discovery of elec-m Br B2r troluminescence, see Corson, D. W., Isis, vol. 59, pp. 402-413,

1968.In that connection, the Harvard historian of science, I. 4. Faraday, M., Trans. Roy. Soc., pt. 1, pp. 125-168, 1838.

Bernard Cohen, has noted25 that the description of 5. See, for instance, Lafferty, J. M., Proc. IRE, vol. 49, pp. 1136-Thomson's experiment found in many modern textbooks 1154, 1961.

6. Plucker, J., Ann. Phys., ser. 2, vol. 103, pp. 88-106, 151-157,and college laboratory manuals is not an historic one, 1858; vol. 104, pp. 113-128, 622-630, 1858; vol. 105, pp. 77-313,inasmuch as it leads the latter-day student to believe that 1859; Phil. Mag., ser. 4, vol. 16, pp. 119-135, 408-418, 1858; vol.Thomson obtained his results with a highly evacuated 18, pp. 1-20, 1859.tube containing a thermionic cathode. In fact, the work 7. Davy, H., Trans. Roy. Soc., pt. 1, pp. 425-439, 1821.

was done with apoy8. Hittorf, J. W., Ann. Phys., ser. 2, vol. 136, pp. 1-31, 197-234,was done with a poorly evacuated cold-cathode discharge 1869. For a discussion of the contributions of Plucker, Geissler,tube, in which the ionization of the residual gas served to and Hittorf, see also Espenschied, L., IEEE Spectrum, vol. 4, p.introduce appreciable errors, since the relationship be- 140, Dec. 1967.

tween velocity and potential differee i9. Varley, C. F., Proc. Roy. Soc., vol. 19, pp. 236-242, 1871. Thetween velocity and potential difference iS substantially same volume also contains (p. 243) an important paper by Varleymore complex under these circumstances than in a highly on the polarization of metallic surfaces in aqueous solutions.evacuated tube. In his autobiography, written nearly 40 "Cromwell Varley was a man of remarkable mental vision," says

years later, Thosonhb."t i Rollo Appleyard in The History of the Institution of Electricalyears later, Thomson himself emphasized that point. "It iS Engineers (1871-1931), IEE, London, 1939, p. 35. Although henot possible to estimate from the potential difference made important scientific contributions, he was not a professionalbetween the cathode and anode of the discharge tube the scientist but a prominent telegraph engineer, one of the 66 foundermembers of the IEE's predecessor, The Society of Telegraphenergy possessed by a charged particle at any point in its Engineers, in 1871.course without knowing more about the mechanism of 10. Hittorf, J. W., Monatsber. Akad. Wiss. Berlin, pp. 279-295,the discharge than we do even at the present time."26 To 1876.which today's plasma physicist, after yet another 40 years, 1 . Crookes, W., Trans. Roy. Soc., vol. 170, pp. 135-164, 641-662,1879; Phil. Mag., ser. 5, vol. 7, pp. 57-64, 1879. For Crookes andcan only respond with a hearty "amen." the radiometer, see also Suisskind, C., Proc. IRE, vol. 50, pp. 326-As we have pointed out elsewhere,27 the name electron 327, 1962; Woodruff, A. E., Isis, vol. 57, pp. 188-198, 1966; and

was not coined by the discoverer of the particle but by the Brush, S. G. and Everitt, C. W. F., in Historical Studies in thePhysical Sciences. Philadelphia: University of Pennsylvania Press,Irish physicist George Johnstone Stoney (1826-1911) in 1969, vol. 1. This volume also contains a discussion by Tetu1894.28 The view that electricity came in discrete amounts, Hirosige of the growth of the theory of the electron out of the' matrix of electromagnetic-field theory and electrodynamics on theor quantums (so that the processes of gaseous discharges Continent, with particular emphasis on the work of Hendrik An-could be considered to be analogous to those of electrol- toon Lorentz (1853-1928).ysis), had been advocated as early as 1881 by Stoney29 12. Wiedemann, G., Ann. Phys., ser. 3, vol. 10, pp. 202-257, 1880;and almost simultaneously by Helmholtz.30 By 1891 Phil. Mag., ser. 5, vol. 10, pp. 357-380, 407-427, 1880.

13. Goldstein, E., Ann. Phys., ser. 3, vol. 10, pp. 90-109, 249-279,Stoney had concluded that each atom in electrolysis car- 1881.ries a charge that is given up when free hydrogen is liber- 14. Hertz, H., Ann. Phys., ser. 3, vol. 19, pp. 782-816, 1883.ated. He estimated the magnitude of the charge on the 15. FitzGerald, G. F., Nature, vol. 55, pp. 6-9, 1896.basis of the number ofatoms per unit volume of hydrogen 16. Perrin, J. B., Compt. Rend., vol. 121, pp. 1130-1134, 1895.gas (calculated from kinetic theory), and he proposed the 17. Hertz, H., Ann. Phys., ser. 3, vol. 45, pp. 28-32, 1892.name electron for this "natural unit of electricity." 18. Lenard, P., Ann. Phys., ser. 3, vol. 51, pp. 225-267, 1894;The term "electron" for a quantum of charge achieved vol. 52, pp. 23-33, 1894.

19. Schuster, A., Proc. Roy. Soc., vol. 37, pp. 317-339, 1884;fairly wide acceptance and was quickly applied to the vol. 42, pp. 371-379, 1887.particle discovered by Thomson; FitzGerald was the first 20. Rayleigh, R. J. S., The Life of Sir J. J. Thomson. London:to do so when he suggested, following Thomson's Royal Cambridge, 1942, p. 80.Institution lecture, that "we are dealing with free electrons 21. Thomson, J. J., Proc. Roy. Inst., vol. 15, pp. 419-432, 1897;in these cathode rays."'II Although the new interpretation Electrician, vol. 39, pp. 104-109, 1897.22. Goldstein, E., Monatsber. Akad. Wiss. Berlin, pp. 691-699'of the term was universally accepted, it is a curious fact 1886.that Thomson himself apparently had misgivings regard- 23. Wien, W., Ann. Phys., ser. 3, vol. 65, pp. 440-452, 1898.ing the change in its meaning (from quantum to particle) 24. Thomson, J. J., Phil. Mag., ser. 5, vol. 44, pp. 293-316, 1897.and continued to use the word "corpuscles" for over 20 25. Cohen, I. B., Am. J. Phys., vol. 18, pp. 343-359, 1950.years. Perhaps he also did not want to prejudge the ques- 26. Thomson, J. J., Recollections and Reflections. London: 0.

tion of electromagnetic mass. ~~~27. Siisskind, C., Proc. IERE, vol. 4, pp. 95-99, 1966; IEEE Spec-As had been the case for electromagnetic waves, the trum, vol. 3, pp. 72-79, May 1966.

action of electrons had been observed by several inventors 28. Stoney, 0. J., Phil. Mag., ser. 5, vol. 38, pp. 418-420, 1894.and scientists before Thomson came to his conclusions. 29. Stoney, G. J., Trans. Roy. Dublin Soc. Sci., vol. 3, pp. 5 1-60,One observer figured in both fields: Edison. We shall see in 1881; Phil. Mag., ser. 5, vol. 11, pp. 381-390, 1881.ounex intlmn.o i eoto htcm ob 30. Helmholtz, H., J. Chem. Soc, vol. 39, pp. 277-303, 1881.

31. FitzGerald, 0. F., Electrician, vol. 39, pp. 103-104, 1897.known as the "Edison effect" (thermionic emission),which antedated Thomson's discovery, led indirectly to Charles Susskind's biography appeared on page 76 of thethe invention of the first vacuum tube, the diode. March 1970 issue.

Siisskind-The early history of electronics