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⁷ The result Thomson published in the first edition of his Conduction of Electricity through Gases (London, 1903)Google Scholar was out by a factor of 2, which he corrected in time for the second edition (London, 1906), 321–325.

⁸ “Polarized Röntgen Radiation”, Phil. Trans., cciv (1905), 467–479Google Scholar; Proc. R. Soc., lxxiv (1905), 474–475Google Scholar; preliminary announcement in Nature, lix (1904), 463.Google Scholar

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²⁷ “Secondary Radiation from a Plate exposed to Rays from Radium”, Phil. Mag., xiv (1907), 176–187, especially 187Google Scholar. Mackenzie also independently observed the forward-backward asymmetry in secondary β-rays excited by γ-rays.

²⁸ Bumstead, H. A., “The Heating Effects produced by Röntgen Rays in Different Metals, and their Relation to the Question of Charge in the Atom”, Phil. Mag., xi (1906), 292–317CrossRefGoogle Scholar; “On the Heating Effects Produced by Röntgen Rays in Lead and Zinc”, Phil. Mag., xv (1908), 432–437Google Scholar; Angerer, E., “Bolometrische Untersuchungen über die Energie der X-Strahlen”, Annalen der Physik, xxi (1906), 87–117CrossRefGoogle Scholar; “Ursprung der Wärmeentwickelung bei Absorption von Röntgenstrahlen”, Annalen der Physik, xxiv (1907), 370–380.Google Scholar

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³² “The Nature of γ and X-Rays”, Nature, lxxvii (1908), 509–510.Google Scholar Bragg did not mention that Cooksey disagreed with his interpretation, believing rather that the electromagnetic momentum of a pulse was responsible for ejecting the β-rays asymmetrically.

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⁴⁴ “On a Want of Symmetry shown by Secondary X-Rays”, Phil. Mag., xvii (1909), 855–864 (with J. L. Glasson).Google Scholar

⁴⁵ Ibid., 863.

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⁴⁸ “Secondary γ Radiation”, Phil. Mag., xvii (1909), 423–448.Google Scholar Madsen, thoroughly convinced of Bragg's corpuscular ideas, described the softening as due to billiard-ball type collisions of the γ-ray particles.

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⁵⁴ Bragg, , op. cit. (54), 386.Google Scholar

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⁵⁷ The three letters from W. H. Bragg to A. Sommerfeld are deposited in the Archive for History of Quantum Physics (AHQP) at the American Philosophical Society Library (Philadelphia), University of California Library (Berkeley), and the Universitets Institut for Teoretisk Fysik (Copenhagen); the letter from Sommerfeld to Bragg was found by Sir Lawrence Bragg in his father's papers, and a copy of it was kindly sent to me by Sir Lawrence. I should like to express my gratitude to Sir Lawrence and to Dr.-Ing. Ernst Sommerfeld for permission to reprint them all here. The translation of Sommerfeld's letter is my own. For W. Friedrich's Munich Dissertation see “Räumliche Intensitätsverteilung der X-Strahlen, die von einer Platinaantikathode ausgehen”, Annalen der Physik, xxxix (1912), 377–430Google Scholar; E. Bassler's 1909 work on the polarization of X-rays is discussed and referenced on p. 378.

^57a Walter and Pohl had cast serious doubt on the validity of Haga and Wind's earlier experiments.

⁵⁸ “Über die Struktur der γ-Strahlen”, Sbr. bayer. Akad. Wiss. Mathematisch-physikalische Klasse, xxxxi (1911), 1–60.Google Scholar For a modern discussion of the “forward peaking”, see for example Jackson, J. D., Classical Electrodynamics (New York, 1962), 473.Google Scholar

⁵⁹ For C. T. R. Wilson's original photographs and paper, see “On a Method of Making Visible the Paths of Ionizing Particles through a Gas”, Proc. R. Soc., lxxxv (1911), 285–288.Google Scholar

⁶⁰ “The Consequences of the Corpuscular Hypothesis of the γ and X Rays, and the Range of β Rays”, Phil. Mag., xx (1910), 415.Google Scholar

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⁶² “Energy Transformations of X-Rays”, Proc. R. Soc., lxxxv (1911), 349–365.Google Scholar See also Bragg, W. H., “The Mode of lonization by X-Rays”, Phil. Mag., xxii (1911), 222–223Google Scholar; “On the Direct or Indirect Nature of the lonization by X-rays”, Phil. Mag., xxiii (1912), 647–650.Google Scholar

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⁶⁵ Studies in Radioactivity (London, 1912), 191–192.Google Scholar This is a somewhat different explanation than he gave in “The Secondary Radiation produced by the Beta Rays of Radium”, Physical Review, xxx (1910), 638–640.Google Scholar

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⁶⁸ Ibid.

⁶⁹ “A Difference in the Photoelectric Effect caused by Incident and Divergent Light”, Nature, lxxxiii (1910), 311Google Scholar; Phil. Mag., xx (1910), 331–339.Google Scholar

⁷⁰ “A Difference in the Photoelectric Effect caused by Incident and Divergent Light”, Nature, lxxxiii (1910), 339Google Scholar; “On the Direction of Motion of an Electron ejected from an Atom by Ultra-Violet Light”, Proc. R. Soc., lxxxiv (1910), 92–99.Google Scholar

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⁷⁵ Nature, lxxxvii (1911), 501.Google Scholar

⁷⁶ Ibid. This is a curious statement, in view of the radiation pressure experiments of Lebedev and Nichols and Hull at the turn of the century.

⁷⁷ Ibid.

⁷⁸ Bragg, , op. cit. (65), vii.Google Scholar

⁷⁹ Ibid., 191.

⁸⁰ Ibid., vii.

⁸¹ Ibid., 192.

⁸² Ibid., 192–193.

⁸³ Ibid., 193.

⁸⁴ Ibid., 188.

⁸⁵ Ibid., 193.

⁸⁶ “Radiations Old and New”, Nature, xc (1913), 560Google Scholar; see also 529–532.

⁸⁷ Ibid., 558.

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⁸⁹ See reference (55).

⁹⁰ Ewald, P. P., “Max von Laue”, Obituary Notices of Fellows of the Royal Society, vi (1960), 139.Google Scholar

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⁹³ Quoted in Compton, Arthur H., X-Rays and Electrons (New York, 1926), 90.Google Scholar

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⁹⁷ On deposit in the AHQP, reference (69).

⁹⁸ See identical statement by Bragg in “X-rays and Crystals”, Nature, xc (1912), 360.Google Scholar

⁹⁹ Ibid.

¹⁰⁰ For Nobel Lecture see “The Diffraction of X-Rays by Crystals”, Nobel Lectures: Physics (Amsterdam, 1967), i, 370–382.Google Scholar

¹⁰¹ “The Reflection of X-rays by Crystals”, Proc. R. Soc., lxxxviii (1913), 436.Google Scholar

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¹⁰³ On deposit in the O. W. Richardson Collection in the Miriam Lutcher Stark Library at the University of Texas. I am indebted to Sir Lawrence Bragg and to the Stark Library for permission to quote from this letter.

¹⁰⁴ The exact relationships between Thomson and Compton scattering may be seen from the plots presented by Ann T. Nelms in “Graphs of the Compton Energy-Angle Relationship and the Klein-Nishina Formula”, National Bureau of Standards Circular Number 542 (1953).Google Scholar

¹⁰⁵ There is of course a longer wavelength Compton component in scattered X-rays as well as in scattered γ-rays. Since, however, the change in wavelength for X-rays is only a few per cent, while for γ-rays it is of the order of 100 per cent, the longer wavelength γ-ray component is much easier to observe than the longer wavelength X-ray component.

¹⁰⁶ For a discussion of Kossel's work see Heilbron, John L., “The Kossel-Sommerfeld Theory and the Ring Atom”, Isis, lviii (1967), 451–485, especially 462–466.Google Scholar

¹⁰⁷ Curiously, as I shall show in a future publication, Arthur Compton, while in no way building on Einstein's work, may have received this crucial insight (that a single quantum must interact with a single electron) from Bragg's work. I should also mention that my reason for terming Einstein's hypothesis “long-neglected” in spite of Millikan's 1915 photoelectric effect experiments is that Millikan (in common with virtually every other contemporary physicist except Einstein) did not accept these experiments as proof of Einstein's hypothesis. See my “Non-Einsteinian Interpretations of the Photoelectric Effect” in Stuewer, Roger H., ed., Historical and Philosophical Perspectives of Science (Minneapolis: University of Minnesota Press, 1970).Google Scholar

¹⁰⁸ Eddington, Arthur, The Nature of the Physical World; paperback reprint (Ann Arbor, 1958), 194.Google Scholar