Duane, William

Duane, William

(b. Philadelphia, Pennsylvania, 17 February 1872; d. Devon, Pennsylvania, 7 March 1935)

physics, radiology.

William Duane was the younger son, by his second wife, of Charles William Duane, an Episcopalian minister. On his father’s side he was a direct descendant of Benjamin Franklin and of several Duanes who had played prominent political roles in the early republic; through his mother he held a good Bostonian pedigree and was distantly related to Charles W. Eliot, president of Harvard. From 1882 to 1890 his father was rector of St. Andrew’s Church in West Philadelphia; young William attended private schools in Philadelphia and then the University of Pennsylvania, where he studied mathematics (including quaternions), wrote papers on the Sophists and on the “silver question,” and was graduated A.B. in 1892 as valedictorian of his class. Moving on to Harvard—his father was rector of Christ Church (Old North Church), Boston, from 1893 to 1910—he received an A.B. in 1893; was then two years assistant in physics, aiding John Trowbridge in experiments on the velocity of Hertzian waves; and received an A.M. in 1895.

With a Tyndall fellowship in physics from Harvard, Duane spent the next two or three years in Germany. At the University of Berlin he continued experimental work on electromagnetism under Emil Warburg (discovering an unforeseen effect and then showing it to be a “dirt effect”); heard the philosopher Wilhelm Dilthey; and studied physical chemistry with Landolt, mineralogy with Klein, experimental physics with Neesen, and especially theoretical physics with Planck, who testified in June 1898 that Duane had attended his lectures and exercise sessions for several semesters, displaying genuine aptitude and conscientious application. At Göttingen he heard the organic chemist Wallach but worked especially with Nernst. Duane’s experimental and theoretical investigation, Über elektrolytische Thermoketten, suggested and guided by Nernst, was accepted by Planck in December 1897 as a University of Berlin doctoral dissertation.

In 1898 Duane was appointed professor of physics at the University of Colorado. He married in 1899 (and eventually had four children) and began to accumulate apparatus for experimental work in physical chemistry (1900–1901). By 1902, however, Duane had lost interest in physical chemistry and turned back to electromagnetism—perhaps because of his teaching in this field. His attention was increasingly to applications, with much effort devoted to a multiplex telegraph based upon synchronous motors at the two stations. It was the sabbatical year 1904–1905 which brought Duane back to fundamental problems; the winter was spent in the Curies’ laboratory, where he learned techniques of research in radioactivity, and the spring with J. J. Thomson. In Paris he had determined the total ionization produced by a radioactive source of given intensity; back at the University of Colorado in the winter of 1905–1906 Duane was determining the total charge carried by the α and β rays rather than the ionization they produced.

Duane liked Paris, and the Curies had been impressed by him. Late in 1905 Pierre Curie asked Andrew Carnegie for a fellowship for Duane to continue work in the Laboratoire Curie. At the end of 1906, after Pierre Curie’s death, Carnegie provided Mme. Curie with 12,500 francs per year for two or three fellowships. Duane was granted 7,500 francs from that sum for each of three years; in fact, he stayed six, and remained thereafter a member of the Société Française de Physique. His work in this period, 1907–1913, was very solid but not truly outstanding, either quantitatively or qualitatively. Perhaps the most difficult and most important of these researches was the measurement of the rate of evolution of heat from minute samples of radioactive substances.

In 1913 the physics department at Harvard University had a vacancy due to the retirement of John Trowbridge; and the newly founded Harvard Cancer Commission, at the newly constructed Huntington Hospital, wished the services of a physicist experienced in handling radioactive substances to initiate there the treatment of cancer by implantation of sources of intense radiation. Duane was appointed assistant professor at the Jefferson Physical Laboratory in Cambridge and research fellow in physics at Huntington Hospital in Boston; his time and his salary were thenceforth divided between these two institutions. The techniques of collecting the radium emanation (radon) continually evolving from a dissolved radium salt, purifying it, compressing it, and sealing it into a tube whose volume was a fraction of a cubic millimeter were all familiar to Duane from his Paris period; he now designed a far more efficient apparatus for manufacturing such “radioactivelamps” and himself applied the “lamps” to the patients. In 1917 Duane was promoted to professor of biophysics, a title created for him; he proudly asserted it to be the first such in America.

Besides radioactivity there was a second area of physical research with direct applications to cancer therapy: X rays. Duane had had no experience in this field, but his new position and responsibilities demanded that he make himself thoroughly familiar with it; and so arose his truly important contributions to physics. The time and place were opportune: Laue and the Braggs had just opened the field of X-ray spectroscopy; W. D. Coolidge’s high-vacuum, high-voltage, heated cathode X-ray tubes were just becoming available; and Duane had inherited Trowbridge’s unique 45,000-volt storage battery—the ideal power supply to exploit the Coolidge tube. Duane’s initial concern was with the therapeutically important “Relation Between the Wave-Length and Absorption of X-Rays,” the title of a paper read to the American Physical Society at the end of October 1914 but not printed.

Duane’s attention soon turned, however, to the relation between the energy of the cathode rays and the frequency of the X rays produced by them, and at the end of December 1914 he described to the American Physical Society experiments showing that the ratio of these two quantities was equal, within a factor of two, to Planck’s constant, h. The real advance, reported at the annual meeting of the society in April 1915, was made in collaboration with Franklin L. Hunt,¹ the first of the many graduate students and postdoctoral assistants with whose aid almost all of Duane’s subsequent physical researches were carried out. Now for the first time Duane drove his Coolidge tube with the high-tension battery—i.e., with a constant voltage—and was impressed by the fact that “a constant difference of potential... does not produce homogeneous X-rays,” i.e., X rays whose fractional absorption per unit of path length is independent of the thickness of the (homogeneous) absorber. From this naïve discovery Duane and Hunt jumped to a sophisticated question: “We therefore set ourselves the problem of determining the minimum wave length that can be produced by a given difference of potential.”

From David L. Webster, then a young instructor at Harvard, they borrowed his newly constructed X-ray spectrometer. Fixing it at a given angle (i.e., wavelength), they observed the intensity of the X rays as a function of the voltage applied to the tube—possible because, and only because, of the Coolidge-Trowbridge apparatus. With decreasing voltage the intensity plunged to zero, thus showing dramatically that there was indeed a maximum frequency in the radiation produced by electrons of a given energy, and for this frequency the equation E = hv held to within a few tenths of a percent. In the next two years Duane developed the “Duane-Hunt law” into a precision method for determining h, and it soon came to be regarded as the most accurate method available.

The war brought only a slight dip in Duane’s productivity, and with the aid of Chinese and Japanese students he turned to accurate measurements, on a variety of elements, of the critical potentials and wavelengths for excitation of their characteristic X rays and, again, accurate measurements of the wavelengths of these X-ray spectra. Theoretical atomic physicists, notably Sommerfeld and Bohr, craved data of this sort to fix the number of electron shells and subshells in the various atoms, their energies, their quantum numbers, and the number of electrons in each shell. In the period 1918–1921 Manne Siegbahn’s laboratory in Lund—using photographic recording in a closed, evacuated spectrometer—and Duane’s laboratory—where the measurement of the intensity of the diffracted X rays at each angle by means of an ionization chamber achieved its highest development—were the two principal reliable sources of this vital data. Moreover, during these and especially the following years Duane gave much effort to the introduction and promotion of the treatment of cancer with high-voltage X rays—designing apparatus, supervising its installation at Huntington Hospital² and then at other institutions, developing the technique of measuring X-ray dosage in terms of the ionization of air, and securing the official adoption of this standard in the United States and then internationally in 1928.

In the year 1922–1923 Duane’s career reached its zenith—and then fell precipitously. In April 1920 he had been elected to the National Academy of Sciences; in the fall of 1922 he was selected to receive the 1923 Comstock Prize—an award made by the academy at five-year intervals—for having established through his X-ray researches “relations which are of fundamental significance, particularly in their bearings upon modern theories of the structure of matter and of the mechanism of radiation.”³ In 1922–1923 Duane was chairman of the Division of Physical Sciences of the National Research Council and in 1923 president of the Society for Cancer Research. All must have supposed that many more laurels would in the following years be laid upon the brow of this late-blooming, quiet, outwardly modest, unexcitable Episcopalian; this competent pianist and organist; this Beacon Street Bostonian who sought recreation in bridge whist with his friends at the Somerset Club.

At the end of 1921 George L. Clark came into Duane’s Cambridge laboratory as a postdoctoral National Research fellow. Three and a half years later it became clear that the several wholly new discoveries to which their fourteen collaborative papers had been devoted were so many pseudo phenomena. Clark was a chemist, then interested in crystal structure. The original goal of their research was a new method of crystal analysis using the Duane-Hunt limit to determine directly the wavelength of the X ray reflected at a given angle, and thus the interatomic distances in the reflecting crystal. With potassium iodide they found, along with other anomalous phenomena, intense reflected X rays not merely with the wavelengths of the characteristic X rays of the anticathode of the X-ray tube but also with the wavelengths of the K series of iodine. They had thus “discovered” the diffraction of the characteristic X radiation emitted by the atoms of the crystal—the very phenomenon which in 1912 Laue, Walter Friedrich, and Paul Knipping had unwarrantably expected to find when they in fact discovered diffraction of the incident X rays.⁴ Bohr, among many others, was especially interested in this “discovery,” for he felt it had to be explicable from the general viewpoint on the interaction of radiation and matter for which he had been groping and which emerged at the end of 1923 as the Bohr-Kramers-Slater theory.

This “discovery” also led Duane himself to some theoretical considerations of astonishing simplicity—and novelty. Reasonably well grounded in classical mathematical physics (as most of the best American experimentalists were) but for want of personal contact with the contemporary European theoretical physicists typically unaware of the extent of his naïveté, Duane had published a number of theoretical papers in the preceding years: on magnetism as the nuclear force (1915); on a new derivation of Planck’s law (1916); and on modifications of the electron ring positions, quantum numbers, and populations in the Bohr model (1921). These, quite properly, had been ignored by the theorists.

Now, however, stimulated by the fact that the selective reflection of the characteristic X radiations of the atoms of the diffracting crystal “does not appear to be explicable in a simple manner by the theory of interference of waves,” Duane suggested in February 1923 an interpretation of diffraction by a grating or crystal “based on quantum ideas without reference to interference laws.”⁵ In much the same way that A. H. Compton was simultaneously explaining the increased wavelength of scattered X rays, Duane pictured diffraction as a collision of a light quantum with a grating. He pointed out that if one applies the familiar quantum conditions to the grating, the periodicity of its structure restricts the momentum it can take up from, or impart to, the light quantum, with the result that all the equations expressing the conditions for constructive interference of waves (e.g., the Bragg law, n λ=2 d sin θ) are retrieved if the energy transferred to the grating can be neglected.

This reinterpretation came as a revelation to many theorists puzzling over the wave versus quantum theory of light (Gregory Breit, Paul Ehrenfest, Paul Epstein, Adolf Smekal, Gregor Wentzel—but not Bohr), although they of course disregarded the ad hoc extensions of this mechanism by means of which Duane claimed to have explained the selective reflection. A curious consequence of the theorists’ efforts to achieve a more general statement of Duane’s reinterpretation of diffraction was to bring forward once again the representation of a grating (or crystal) by a Fourier series or integral. Duane himself then pointed out that since the distribution of intensity in the spectrum is essentially the Fourier transform of the grating producing it, in principle it should be possible to invert the transform and from intensity measurements determine the distribution of electrons in the diffracting crystal.⁶ Duane put a National Research fellow to work on this, but the idea, which is the basis of all the subsequent analyses of the structure of biologically important molecules, caught on only through its adoption and advocacy by W. L. Bragg in the following years.

Perhaps even more damaging to Duane’s reputation than the “discovery” of selective reflection was his opposition to the Compton effect. The most eminent American X-ray spectroscopist was the last to reproduce Compton’s observation and the most vociferous in denying and explaining away his younger compatriot’s discovery—even to the point of claiming as his own discovery the tertiary radiation that he had originally advanced as the probable source of Compton’s shifted wavelengths.⁷ It was not, of course, that Duane was opposed to the notion of light quanta; rather, there was an element of competition between his own and Compton’s light quantum theories, which probably disposed Duane, who had in those years so little time for laboratory work, to accept uncritically the various new effects and negative observations with which Clark was plying him.

These disastrous episodes were scarcely behind Duane when, late in 1925, his capacity for work was severely reduced by the onset of acute diabetes, and in 1926 he was obliged to take a year’s leave. By 1927 his sight had so deteriorated that he was compelled to do much of his reading and writing through his secretary. In 1931 Duane suffered a paralytic stroke, recovering only slowly and incompletely; in the fall of 1933 he took a leave of absence and retired in the fall of 1934. Six months later he died of a second stroke.

NOTES

1. Duane and Hunt, “On X-Ray Wave-Lengths,” in Physical Review, 6 (1915). 166–171.

2. “Improved X-Rays for Cancer Work,” in New York Times (14 Feb. 1921), 7 , col. 2.

3. Report of the National Academy of Sciences for 1923 (Washington, D.C., 1924), pp. 5, 20.

4. P. Forman, “The Discovery of the Diffraction of X-Rays by Crystals: A Critique of the Myths,” in Archive for History of Exact Sciences, 6 (1969), 38–71.

5. Duane, “The Transfer in Quanta of Radiation Momentum to Matter,” in Proceedings of the National Academy of Sciences, 9 (1923). 158–164.

6. Duane, “An Application of Certain Quantum Laws to the Analysis of Crystals,” in Physical Review, 25 (1925), 881; R. J. Havighurst, “The Application of Fourier’s Series to Crystal Analysis,” ibid., Duane, “The Calculation of the X-Ray Diffracting Power at Points in a Crystal,” in Proceedings of the National Academy of Sciences, 11 (1925). 489–493; R. J. Havighurst, “The Distribution of Diffracting Power in Sodium Chloride,” ibid., 502–507.

7. Clark and Duane, “On the Theory of the Tertiary Radiation Produced by Impacts of Photoelectrons,” in Proceedings of the National Academy of Sciences, 10 (1924), 191–196.

BIBLIOGRAPHY

I. Original Works. The best bibliography of Duane’s publications, although still woefully incomplete in both form and content, is in Bridgman (below). A few letters from Duane to Bohr and Sommerfeld in 1924 are in the Archive for History of Quantum Physics, for which see T. S. Kuhn, et al., Sources for History of Quantum Physics (Philadelphia, 1967). The Niels Bohr Library, American Institute of Physics, New York, holds some twelve letters to Duane, notably a testimonial by Planck (1898), two letters from J. J. Thomson (1905), and four letters from Marie Curie (1905–1907).

II. Secondary Literature. Biographical articles are P. W. Bridgman, “Biographical Memoir of William Duane, 1872–1935,” in Biographical Memoirs. National Academy of Sciences, 18 (1937), 23–41; and G. W. Pierce, P. W. Bridgman, and F. H. Crawford, “Minute on the Life and Services of William Duane, Professor of Bio-Physics, Emeritus,” in Harvard University Gazette (11 May 1935). There is also “Charles William Duane,” in National Cyclopaedia of American Biography, XVIII (New York, 1922), 403–404. Useful information is contained in the vita of Duane’s dissertation, Über elektrolytische Thermoketten (Berlin, 1897). Recollections of the controversy with Compton by one of Duane’s postdoctoral students—the one who finally found the effect—may be found in Samuel K. Allison, “Arthur Holly Compton, Research Physicist,” in Science, 138 (1962), 794–797.

Paul Forman