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A debate on magnetic current: the troubled Einstein–Ehrenhaft correspondence

Published online by Cambridge University Press:  08 October 2010

GILDO MAGALHÃES SANTOS
Affiliation:
History of Science, Department of History, University of São Paulo, Av. Prof. Luciano Gualberto, 315 Room N3, 05508-010 São Paulo, Brazil. Email: gildomsantos@hotmail.com.

Abstract

The unconventional correspondence between physicists Albert Einstein and Felix Ehrenhaft, especially at the height of the alleged production by the latter of magnetic monopoles, is examined in the following paper. Almost unknown by the general public, it is sometimes witty, yet it can be pathetic, and certainly bewildering. At one point the arguments they exchanged became a poetic duel between Einstein and Ehrenhaft's wife. Ignored by conventional Einstein biographies, this episode took place during the initial years of the Second World War, but was rooted in disputes dating back to the early years of the twentieth century. The interesting intersection of a series of scientific controversies also highlights some aspects of the personal dramas involved, and after so many years the whole affair in itself is still intriguing.

Type
Research Article
Copyright
Copyright © British Society for the History of Science 2010

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References

1 Manuscript sources: MSS 2898: Albert Einstein and Felix Ehrenhaft, letters, notes, memoranda and queries exchanged between 1939 and 1941, with preliminary letters 1917–1932; Felix Ehrenhaft, typescript of unpublished ‘Meine Erlebnisse mit Einstein 1908–1940’; idem, a collection of his lectures, articles and reprints; Lilly (Rona) Ehrenhaft, personal and scientific papers; Agathe Magnus, papers concerning patents by Lilly Rona. MSS122A: Albert Einstein, letter to Felix Ehrenhaft from 3 September 1939, Dibner Library of History of Science and Technology, American History Museum, Smithsonian Institution, Washington, DC, forty-seven items of correspondence (mostly in German) involving Einstein, Ehrenhaft and Lilly Rona-Ehrenhaft, besides other persons. There are also exemplars of published works of Ehrenhaft, some bearing affectionate handwritten dedications to Lilly. These items were purchased in 1960 for $2,500 by collector and historian Bern Dibner, apparently part of the personal archives of Lilly, and donated together with a substantial part of Dibner's collection of rare books and manuscripts to the Smithsonian, where they have been available to scholars since 1976.

2 Of course, ‘losing’ (and ‘winning’) are themselves historical appreciations, but what is highlighted here is the context of accepted scientific belief and practice, even if this understanding is eventually altered in the course of time.

3 Ehrenhaft's dedication included contributing to the Nobel Prize attribution to Einstein. Abraham Pais, in ‘Subtle Is the Lord’: The Science and the Life of Albert Einstein, Oxford: Oxford University Press, 1982, mentions Ehrenhaft's Einstein indications in 1916, 1918 and 1922. A recent book on this subject is Elzinga's, AantEinstein's Nobel Prize: A Glimpse behind Closed Doors, Sagamore Beach: Science History Publications, 2006Google Scholar, which relies on the official Nobel archives to attribute the successful nomination mainly to physicist Carl Wilhelm Oseen. Ehrenhaft, in his Einstein recollections (MSS 2898, ‘Meine Erlebnisse mit Einstein’), tells a different story: the arrangements he conducted with Arrhenius behind the scene would have been responsible for the prize. It may well be that Ehrenhaft is exaggerating his importance in the affair, but the official story may not be wholly reliable either.

4 Braunbeck, Joseph, Der andere Physiker. Das Leben von Felix Ehrenhaft, Vienna: Technisches Museum & Leykam, 2003Google Scholar. This biography is quite helpful, in spite of its sometimes excessively laudatory tone – a more complete biographical appreciation of Ehrenhaft emerged only with the examined letters and material at the Smithsonian, Vienna University, and Center for the History of Physics. Einstein's biographies hardly mention Ehrenhaft at all, and only the older (1947) biography by Frank, Philipp, Einstein, His Life and Times, 2nd edn, Cambridge, MA: Da Capo (Perseus), 2002, pp. 7273Google Scholar, indicates that after the First World War Einstein stayed in Vienna at Ehrenhaft's – whereas from the letters we learn that it was Ehrenhaft himself who wrote to Frank in 1940 providing information, including a series of Einstein anecdotes that are in Frank's book without disclosing the source.

5 Ehrenhaft, , ‘Das optische Verhalten der Metallkolloide und deren Teilchengrösse’, Annalen der Physik (1903) 11, p. 489CrossRefGoogle Scholar; idem, ‘Über die der Brownschen Molekularbewegung in Flüssigkeiten gleichartige Molekularbewegung in den Gasen’, Wiener Berichte (1907) 116, p. 1175.

6 The years between 1897, when Thomson reported on the electrical particle, and 1911, when Rutherford proposed concentrating most of the atomic mass in a smaller volume of the atom (nucleus), witnessed much discussion about the atomic structure. Many uncertainties on this subject were reflected in various other areas, as in the interpretation of radioactivity, and the constitution of the periodic table – cf. Serres, Michel (ed.), Eléments pour une histoire des sciences (1989), Portuguese translation, Lisboa: Terramar, 1996, vol. 3, pp. 7780Google Scholar.

7 The assessment of Thomson's contribution, both conceptually and practically, to the history of the electron and the atomic model, is not an easy task. The reader will benefit from consulting Buchwald, Jed Z. and Warwick, Andrew (eds.), Histories of the Electron, Cambridge, MA: MIT Press, 2001Google Scholar. The first part is an excellent historical account of the issues related to electrons as ‘corpuscles’. There were several different concepts of elementary particles of electricity, and only gradually a consensus emerged. We will not dwell upon these contrasting visions, since they are not the focus of the present work.

8 Helge Kragh, ‘Particle science’, in Robert Olby et al. (eds.), Companion to the History of Modern Science, London: Routledge, 1996, pp. 655–654.

9 Ehrenhaft, ‘Die Photophorese’, Annalen der Physik (1918) 56, p. 81.

10 Cf. Hiebert, Erwin, ‘Common frontiers of the exact sciences and the humanities’, Physics in Perspective (2000) 2, pp. 629CrossRefGoogle Scholar. In the scientific field, Exner could be associated with Mach and the tradition of Vienna indeterminism. An extensive study of Exner as a physicist, and author of the cultural evolutionist From Chaos to the Present can be found in Stöltzner, Michael, ‘Franz Serafin Exner's indeterminist theory of culture’, Physics in Perspective (2002) 4, pp. 267319CrossRefGoogle Scholar. Ehrenhaft's agreement with Mach was probably for reasons different from Exner's; most important for Ehrenhaft was the faith that experimental facts alone formed the basis of knowledge.

11 See Einstein's letter to Vienna University of 25 June 1920, quoted in Braunbeck, op. cit. (4), pp. 36–37.

12 Reinhard Siegmund-Schultze, ‘The problem of anti-Fascist resistance of ‘apolitical’ German scholars’, in Monika Renneberg and Mark Walker (eds.), Science, Technology and National Socialism, Cambridge: Cambridge University Press, 1993, pp. 312–323.

13 Ehrenhaft, , ‘Diffusion, Brownian movement, Loschmidt's number and light’, Physical Review (1940) 57, pp. 562CrossRefGoogle Scholar and 659; idem, ‘Photophorèse, électrophorèse et magnetophotophorèse’, Annales de Physique (1940) 13, p. 151; idem, ‘Physical and astronomical information concerning particles of the order of magnitude of the wavelength of light’, Journal of the Franklin Institute (1940) 230(3), pp. 381–393; idem, ‘Photophoresis and its interpretation by electric and magnetic ions’, Journal of the Franklin Institute (1942) 233(3), pp. 235–256; idem, ‘Stationary electric and magnetic fields in beams of light’, Nature (1941) 147, p. 251; idem, ‘The magnetic current’, Science (1941) 94, p. 232.

14 Among other US works, Lilly was commissioned to sculpt busts of Arturo Toscanini, President Eisenhower and Eleanor Roosevelt, which won her public praise.

15 ‘Abschrift eines Briefes von Prof. Einstein an Prof. Ehrenhaft, August 1917’, Dibner Library of History of Science and Technology, American History Museum, Smithsonian Institution, Washington, DC, MSS 2898.

16 This is expressed in several letters kept at the Center for History of Physics (College Park, MD), as in the one written to Einstein by W.F.G. Swann from the Bertol Research Foundation on 16 November 1940: ‘I suppose that most of us would agree that Ehrenhaft's interpretations of his experiments are likely to be wrong, but I personally feel that there may be something in the experiments themselves which should be further investigated’. In his reply of November 19 to Swann (op. cit.), Einstein said, ‘Concerning his results about the elementary charge I do not believe in his numerical results but I believe that nobody has a clear idea about the causes producing the apparent sub-electronic charges he found in careful investigations’.

17 Paul A.M. Dirac, ‘Ehrenhaft, the subelectron and the quark’, in C. Weiner (ed.), History of Twentieth Century Physics: Proceedings of the International School of Physics Enrico Fermi. Course LVII (1972), New York: Academic Press, 1977, p. 290. Gerald Holton's study was later included in The Scientific Imagination: Case Studies, London: Cambridge University Press, 1978.

18 Allan Franklin, in The Neglect of Experiment, New York: Cambridge University Press, 1986, pp. 138–164 and 215–225, challenged Holton's conclusions, stating that Millikan's data exclusion did not change the final value of e, yet he agreed that Millikan touched up some of his numbers, which reduced the statistical error – the larger uncertainty might have stirred up disagreement. Franklin's arguments are centred on the defence of Millikan's interpretation and selection of experimental data, and contrary to Holton, he does not contemplate Ehrenhaft's arguments.

19 See, for example, Ernan McMullin, ‘The development of philosophy of science 1600–1900’, in Robert C. Olby et al., Companion to the History of Modern Science, London: Routledge, 1990, pp. 834–836.

20 Cited in Braunbeck, op. cit. (4), pp. 42–44.

21 Any theory conceiving of an inner structure for ‘elementary particles’ faces the problem of continuity versus discontinuity – an example dealing with the elementary charge is the proposed structure for the electron based on helical plasma-like filaments advanced by Bostick, Winston M. in ‘The morphology of the electron’, International Journal of Fusion Energy (1985) 3, pp. 952.Google Scholar

22 Barnes, Barry, Bloor, David and Henry, John, Scientific Objectivity: A Sociological Analysis, London: Athlone, 1996, pp. 1845Google Scholar, have addressed the question of interpretation of experimental results, choosing as a case study exactly the historiography construed by Holton on the Millikan–Ehrenhaft subelectron debate, and the response to Holton advanced by Alan Franklin. The task of interpreting data is a complex one, often aggravated by the sociological contents of local culture, and their conclusion was that the debate is not over.

23 Dibner Library of History of Science and Technology, American History Museum, Smithsonian Institution, Washington, DC (hereafter DL), MSS 2898, letter from Einstein to Ehrenhaft, 19 May 1939.

24 Brownian motion consists of the displacement of minute particles (dust, pollen etc.) floating on liquids or suspended in gases, subject to random forces due to the thermal agitation of the fluid molecules. Einstein, in his famous 1905 article on Brownian motion, established a numerical relationship that could be experimentally tested to determine the value of Avogadro's number (the number of molecules in a mole of gas).

25 DL MSS 2898, letter from Einstein (Nassau Point) to Ehrenhaft, 30 August 1939.

26 DL MSS 122A, letter from Einstein (Nassau Point) to Ehrenhaft, 3 September 1939.

27 DL MSS 122A, letter from Einstein (Nassau Point) to Ehrenhaft, 3 September 1939.

28 Around 1900, Louis Bachelier first proposed that financial markets followed a ‘random walk’ which could be modelled by probability calculus and Brownian motion theory; see Sun Kelvin Hoon, ‘Brownian motion and the economic world’, Surprise 95, online journal available via www.doc.ic.ac.uk (accessed 28 June 2008).

29 Specifically, that Gauss's law for magnetism admits div B≠0, and Faraday's induction law includes a term related to the magnetic displacement current jm.

30 Ehrenhaft, ‘The magnetic current’, Science (September 1941) 94(2436), p. 232.

31 DL MSS 2898, letter from Ehrenhaft to Einstein, 14 February 1940.

32 Helge Kragh briefly mentions Dirac's refusal to discuss monopoles with Ehrenhaft in Dirac: A Scientific Biography, Cambridge: Cambridge University Press, 1990, pp. 216–217.

33 Dirac, op. cit. (17), p. 290. On a later occasion, after the alleged monopole detection in 1975 in a cosmic ray experiment, Dirac addressed the matter, and did not mention Ehrenhaft at all – see Dirac, Paul, Directions in Physics, New York: Wiley-Interscience, 1978, pp. 3954Google Scholar.

34 DL, MSS 2898, letter from Einstein to Ehrenhaft, 20 February 1940.

35 DL, MSS 2898, letter from Ehrenhaft to Einstein, 21 February 1940.

36 Paul Feyerabend, in Killing Time (1995), Portuguese translation, São Paulo: UNESP, 1996, p. 74, remembers when attending physics classes in 1947 that Professor Ehrenhaft still approved of the theoretical conceptions of ‘German physics’, and Braunbeck, op. cit. (4), p. 68, confirms that Ehrenhaft preferred to ignore the book's preface (with its anti-Semitic attacks) in favour of its physical contents. Ehrenhaft repeatedly said he followed Faraday's advice, of scepticism towards the use of theory, and precedence given to experiment (cited in Ehrenhaft, Felix, ‘Festrede an Michael Faraday’, Physik und Chemie (1932) 32(5), p. 14Google Scholar).

37 Ehrenhaft, ‘Einzelne magnetische Nord-und-Südpole und deren Auswirkung in den Naturwissenschaften (10 Vorlesungen gehalten im Sommer-Semester 1947 v. Dr. Felix Eherenhaft – Gastprofessor an der Universität Wien’ (mimeo)). See also idem, ‘Photophoresis and its interpretation by electric and magnetic ions’, Journal of the Franklin Institute, op. cit. (13).

38 Ehrenhaft relied very much on his condenser arrangement, first developed for the electron charge measurement. More technical details are found in Andreas Makus, ‘Der Physiker Felix Ehrenhaft (1879–1952) und die Bestimmung der Elementarladung. Ein Versuchsnachbau’, Blätter für Technikgeschichte 64 (2002), pp. 25–45.

39 The acquaintance of Ehrenhaft with Einstein's medical doctor Plesch is documented in Braunbeck, op. cit. (4), p. 53. His relationship with Einstein is also in Bernstein, Jeremy, Secrets of the Old One: Einstein, 1905, New York: Copernicus, 2005Google Scholar.

40 For that purpose he had counted on the help of a former collaborator and physics student in Vienna, Baron Robert Heine-Geldern (a descendant of the poet Heinrich Heine).

41 DL MSS 2898, letter from Ehrenhaft to Einstein, 27 March 1940.

42 This conclusion was communicated by Ehrenhaft in a published letter, ‘Diffusion, Brownian movement, Loschmidt–Avogadro number and light’, Physical Review (1940) 57(1050), pp. 562 and 659.

43 DL, MSS 2898, letter from Ehrenhaft to Einstein, 3 April 1940.

44 DL, MSS 2898, letter from Ehrenhaft to Einstein, 10 April 1940.

45 DL, MSS 2898, letter from Richard Kobler to Einstein, 31 May 1940.

46 DL, MSS 2898, letter from Einstein to Ehrenhaft, 26 July 1940.

47 Adapted from Ehrenhaft, ‘Einzelne magnetische Nord-und-Südpole’, op. cit. (37). The references to physicists and years are Ehrenhaft's.

48 DL, MSS 2898, letter from Einstein to Ehrenhaft, 16 August 1940. The poem translations are my own, and I have endeavoured to keep at least some traces of the poetic flavour of the original German verses.

49 DL, MSS 2898, letter from Ehrenhaft to Einstein, 26 August 1940.

50 DL, MSS 2898, telegram from Lilly Rona to Einstein, 17 September 1940. According to Whittaker, Edmund, A History of the Theories of Aether and Electricity (1951), College Park: American Institute of Physics, 1987, vol. 1, p. 190Google Scholar n. 1, the work of Morichini in Rome was published in 1813.

51 DL, MSS 2898, letter from Ehrenhaft to Einstein, 26 September 1940.

52 DL, MSS 2898, telegram from Ehrenhaft to Einstein, 15 October 1940.

53 DL, MSS 2898, telegram from Einstein to Ehrenhaft, 17 October 1940.

54 DL, MSS 2898, letter from Einstein to Ehrenhaft, 26 October 1940.

55 DL, MSS 2898, letter from Ehrenhaft to Einstein, 27 October 1940.

56 DL, MSS 2898, letter from Lilly Rona to Einstein, 22 April 1941.

57 DL, MSS 2898, letter from Einstein to Lilly Rona, 10 May 1941.

58 DL, MSS 2898, letter from Lilly Rona to Einstein, 12 May 1941.

59 ‘Defaming’ could just be the couple's impression, since it was widely held that Ehrenhaft was an iconoclast.

60 DL, MSS 2898, letter from Lilly Rona to Einstein, 2 February 1942.

61 DL, MSS 2898, letter from Lilly Rona to Einstein, 2 February 1942.

62 DL, MSS 2898, letter from Lilly Rona to Einstein, 18 March 1942. The work did appear in the Journal of the Franklin Institute (March 1942) 233(3).

63 DL, MSS 2898, ‘Die Gravitation: ein magneto-photophoretisches Phänomen der kosmischen Strahlung’, Natur und Technik, Heft 10–12, December 1949.

64 This poem, with slight variations, is reproduced in Braunbeck, op. cit. (4), p. 97, without acknowledging its authorship, and stating it was written during Christmas 1942.

65 Braunbeck, op. cit. (4), p. 105.

66 Manuscript, Center for History of Science, College Park, MD.

67 Feyerabend, op. cit. (36), pp. 73–76.

68 Feyerabend developed this argument more fully in his Against Method, London: NLB, 1975. The expression ‘iron curtain’, and the comparison between Galileo and Ehrenhaft, are Feyerabend's, op. cit. (36), Chapter 6.

69 Ehrenhaft, ‘Einzelne magnetische Nord-und-Südpole’, op. cit. (37).

70 Their old ties appear in the letter from Ehrenhaft to Lilly, 3 May 1950 (Center for the History of Physics, College Park, MD).

71 The Central Library for Physics, Vienna University, lists about a hundred of his communications covering roughly half a century, starting in 1902. Most were published in the main physics magazines in German, though in the 1940s he also published in English (Nature, Science, Physical Review) and French (Comptes rendus). In view of that, one could hardly say that he was an unknown physicist.

72 Ehrenhaft, ‘Physical and astronomical information’, op. cit. (13) .

73 For downloadable articles covering this issue at arXiv.org (accessed 19 May 2007), see, for example, Kimball A. Milton, ‘Theoretical and experimental status of magnetic monopoles’ (22 February 2006); Kragh, Helge, in ‘The concept of the monopole: a historical and analytical study’, Studies in the History and Philosophy of Science (1981) 12, pp. 159163CrossRefGoogle Scholar, recalls the false 1975 detection in Iowa; and Braunbeck, op. cit. (4), p. 136, mentions an alleged 1982 observation in Stanford. As a side note, since 1995 Joseph Newman has called attention – in quite sensationalistic tones – to a machine he invented which supposedly produces a great amount of power with a minimum of electricity. What is interesting is that Newman's Internet homepage (www.josephnewman.com – accessed 5 May 2007) reproduces Ehrenhaft's articles on the magnetic current.

74 See, for example, the letter (Center for History of Science, College Park, MD) from Kimble (Harvard University) to Swann (Bartol Laboratory), dated 10 December 1940, commenting on electrophoresis and magnetophoresis: ‘in order to stimulate a type of investigation not yet undertaken in this country it is desirable that Professor Ehrenhaft be given an opportunity to continue his work and to demonstrate the effects he has discovered. The financing of his experiments would be a service to science’.

75 One exception was Andreas Makus, op. cit. (38).

76 Klaus and Ann Hentschel refer to this as a ‘protracted conflict’, in Physics and National Socialism, Berlin: Birkhäuser, 1996. See Introduction, especially pp. lxx–lxxviii.

77 van Dongen, Jeroen, ‘Emil Rupp, Albert Einstein, and the canal ray experiments on wave–particle duality: scientific fraud and theoretical bias’, Historical Studies in the Physical and Biological Sciences (2007) 37, supplement, pp. 73120CrossRefGoogle Scholar; idem, ‘The interpretation of the Einstein–Rupp experiments and their influence on the history of quantum mechanics’, Historical Studies in the Physical and Biological Sciences (2007) 37, supplement, pp. 121–131.

78 Ehrenhaft once praised theory without experiment – in cases like special relativity. Cf. Ehrenhaft, ‘Festrede in der Festsitzung der Wiener Chemisch-Physikalischen Gesellschaft anlässlich der Hundertjahrfeier der Entdeckung der elektromagnetischen Induktion durch Michael Faraday’, Physik und Chemie (1932) 32(5), p. 12.

79 DL, MSS 2898, ‘Meine Erlebnisse mit Einstein’.

80 DL, MSS 2898, letter from Ehrenhaft to Einstein, 10 March 1940.

81 DL, MSS 2898, ‘Meine Erlebnisse mit Einstein’.

82 See Franklin, op. cit. (18), Chapter 4.

83 Helge Kragh, op. cit. (73), pp. 141–172. His final comment is on Einstein's special relativity theory: if it is not assumed that all material velocity is subluminal, then Maxwell's equations for charges exhibiting superluminal speeds will be symmetric, and magnetic monopoles can be admitted. Should one keep this in mind to fully appreciate Einstein's reactions to Ehrenhaft's monopoles?

84 The story of this cosmological model is told by one of its authors, Alan Guth, in The Inflationary Universe: The Quest for a New Theory of Cosmic Origins, Reading, MA: Addison-Wesley, 1997, Chapter 9.

85 Ehrenhaft, op. cit. (78).

86 DL, MSS 2898, ‘Meine Erlebnisse mit Einstein’.

87 DL, MSS 2898, letter from Ehrenhaft to Einstein, 14 February 1940.

88 Oersted's debt to Naturphilosophie has been minimized by H.A.M. Snelders, ‘Oersted's discovery of electromagnetism’, in Andrew Cunningham and Nicholas Jardine (eds.), Romanticism and the Sciences, Cambridge: Cambridge University Press, 1990, pp. 228–240, p. 232; as well as by Caneva, Kenneth L., ‘Physics and Naturphilosophie: a reconnaissance’, History of Science (1997) 35, pp. 35106CrossRefGoogle Scholar; and also by Shanahan, Timothy, ‘Kant, Naturphilosophie and Oersted's discovery of electromagnetism: a reassessment’, Studies in History and Philosophy of Science, (1989) 20, pp. 287305CrossRefGoogle Scholar. The contrary argument, as in Stauffer, Robert C., ‘Speculation and experiment in the background of Oersted's discovery of electromagnetism’, Isis (1957) 48, pp. 3350CrossRefGoogle Scholar, is, however, still very solid and can be appreciated by reading Oersted's own works, especially his ‘New investigations into the question: What is chemistry?’, and ‘Reflections on the history of chemistry’, in Hans Christian Oersted, Selected Scientific Works, tr. and ed. K. Jelved, A. Jackson and O. Knudsen, Princeton: Princeton University Press, 1997. See also Brain, Robert, Cohen, Robert and Knudsen, Ole (eds.), Hans Christian Oersted and the Romantic Legacy in Science: Ideas, Disciplines, Practices, Dordrecht: Springer, 2007CrossRefGoogle Scholar. The influence of Naturphilosophie on Faraday has not been directly established, but in Agassi's, JosephFaraday as a Natural Philosopher, Chicago: University of Chicago Press, 1971, pp. 203232Google Scholar, his ideas match well enough the presuppositions of Schelling's system, leading directly to the unity of all forces in nature.

89 Schelling's dynamical conception of matter is contrasted with the mechanical atomistic conception in Gower, Barry, ‘Speculation in physics: the history and practice of Naturphilosophie’, Studies in History and Philosophy of Science (1973) 3, pp. 320321CrossRefGoogle Scholar. The more ancient early nineteenth-century rift between ‘dynamists’ and ‘atomists’ is described by Armin Herman, in ‘Unity and metamorphosis of forces (1800–1850): Schelling, Oersted and Faraday’, Symmetries in Physics (1600–1980), Belaterra (Barcelona): Universitat Autònoma de Barcelona, 1983, pp. 53–63.

90 This is a delicate point: science has witnessed historical moments when small differences became nodal points of a new theory, such as in Kepler's correction of circular to elliptic planetary paths.

91 Allais, Maurice, ‘The experiments of Dayton C. Miller (1925–1926) and the theory of relativity’, 21st Century Science & Technology (1998) 11(1), pp. 2631Google Scholar. Allais, a Nobel Prize-winner in economics, has remained a lifelong experimental physicist; his work in Paris on this subject is described by himself in ‘Should the laws of gravitation be reconsidered?’, 21st Century Science &Technology (1998) 11(3), pp. 21–33. The history of the ‘ether’ in physics is a question far from being settled, even though its properties did change with time – see, for instance, Lévy, Joseph, Invariance of Light Speed: Reality or Fiction?, Paris: Encre, 1991Google Scholar.

92 Selleri, Franco, Die Debatte um die Quantentheorie, 2nd edn, Braunschweig: Vieweg, 1984, pp. 1517Google Scholar, 57–62, 87–91 and 118–120.

93 DL, MSS 122A, loose paper, autographed and dated ‘12.XI.23’.

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