Compton, Arthur Holly
Compton, Arthur Holly
(b. Wooster, Ohio, 10 September 1892; d. Berkeley, California, 15 March 1962),
Arthur Holly Compton, who shared the Nobel Prize in physics in 1927 for his discovery of the effect that bears his name, was a son of a professor of philosophy and dean of the College of Wooster. His oldest brother, Karl, who became the head of the physics department at Princeton and, later, president of the Massachusetts Institute of Technology, was his close friend and most trusted scientific adviser. His brother Wilson was a distinguished economist and businessman. His sister, Mary, and her husband, C. Herbert Rice, were educators in India. Their mother, Otelia Augspurger, came from a long line of Mennonites and guided the Compton children long after they left Wooster.
The College of Wooster, with its strong missionary tradition, had a decisive influence on Compton throughout his career. His attitudes toward life, science, and the world in general were almost completely determined as he grew to manhood and received his basic education there. The Compton family were interested in many things besides the college: their church, a summer camp in Michigan, Karl’s early scientific experiments, Arthur’s early interest in paleontology and astronomy and his experiments with gliders, and the boys’ athletic activities. All these interests made for an active youth and developed a constructive and buoyant attitude toward life that carried Compton through all the complex and highly demanding responsibilities that his later duties called upon him to assume.
After graduating from the College of Wooster in 1913, Compton entered the graduate school of Princeton, where he earned a master’s degree in 1914 and a Ph.D. in 1916. His older brothers had already received the Ph.D. from Princeton. He was an outstanding graduate student, being a “whiz” at problem solving, and conducted research on the quantum nature of specific heats. He also perfected a laboratory method (developed earlier at his home at Wooster) to measure latitude and the earth’s rotation (as a vector) independently of astronomical observations. His Ph.D. thesis, begun under O. W. Richardson and completed under H. L. Cooke, began his interest in X-ray diffraction and scattering.
Compton also was active in sports, especially tennis, and in the social life and professional activities of the graduate student community. He became a personal friend and admirer of Henry Norris Russell, whose advice and counsel, along with that of Richardson and William F. Magie, was of great importance in shaping his early scientific career.
Upon completing his graduate studies at Princeton, Compton married his Wooster College classmate Betty Charity McCloskey. She was an enthusiastic and active partner in all of his professional activities, whether these were in the research laboratory or on journeys to the most distant parts of the earth for field measurements. Their children were Arthur Alan, an officer in the U.S. State Department, and John Joseph, professor and head of the philosophy department at Vanderbilt University.
After receiving his Ph.D., Compton taught physics for one year (1916–1917) at the University of Minnesota in the enthusiastic young department that included John T. Tate and Paul D. Foote. He next spent two years as research engineer for the Westinghouse Electric and Manufacturing Company in East Pittsburgh, Pennsylvania. During this period Compton developed aircraft instruments for the Signal Corps, did original work, and was awarded patents on designs for a sodium vapor lamp.
This work led to his later close association, at Nela Park, in Cleveland, Ohio, with the birth of the fluorescent lamp industry in the United States. He worked closely with Zay Jeffries, technical director of the General Electric Company at Nela Park during the years of greatest activity in fluorescent lamp development. In 1934 Compton played a decisive role in providing their engineers with critical information on the work being done at General Electric Ltd., Wembley, England (which had technical exchange relations with the U.S. General Electric Company), which enabled the Nela Park engineers to construct the prototype commercially feasible fluorescent lamp and initiate an extensive research and development program.
During the years (1917–1919) at Westinghouse, Compton’s X-ray work continued; two studies are of special interest. In attempting to obtain quantitative agreement between X-ray absorption and scattering data and the classical theory of J. J. Thomson, Compton advanced the hypothesis of an electron of finite size (radius of 1.85 × 10-10 cm.) to account for the observed dependence of intensity on scattering angle. This was the simple beginning that finally led to the concept of a “Compton wavelength” for the electron and other elementary particles. Later his own quantum theory of X-ray scattering and its extension into quantum electrodynamics fully developed the concept.
The second study was initiated with Oswald Rognley in 1917 at the University of Minnesota to determine the effect of magnetization on the intensity of X-ray reflections from magnetic crystals. This work indicated that orbital electron motions were not responsible; and Compton proposed that ferromagnetism was due to an inherent property of the electron itself, which he considered to be an elementary magnet. In 1930, after he had developed the doublecrystal X-ray spectrometer, this hypothesis was proved more conclusively by experiments of J. C. Stearns, a graduate student of his at the University of Chicago. Their results on the intensity of X rays diffracted by magnetized and unmagnetized magnetite and silicon steel proved that electronic orbital motions in crystals are not involved in ferromagnetism. This confirmed Compton’s prediction, made in 1917, that the electron’s magnetic orientation, due to its spin, is the ultimate cause of ferromagnetism.
Following World War I, Compton was awarded one of the first National Research Council fellowships, which enabled him to spend the year 1919–1920 in the Cavendish Laboratory at Cambridge. This was a most hectic and exciting year at that laboratory, which was crowded to capacity with young men from Great Britain and all parts of the British Empire who had just returned from the war to study with Ernest Rutherford and J. J. Thomson. Compton found this a most inspiring year, not only for his relationship with Rutherford, who provided laboratory space and such support as the crowded conditions at the university afforded, but also for his meetings with Thomson, who formed the highest opinion of Compton’s research abilities. The close relationship between Compton and Thomson continued throughout the latter’s lifetime.
At Cambridge high-voltage X-ray equipment was not available, so Compton performed a scattering experiment with gamma rays that not only confirmed earlier results of J. A. Gray and others but also started his planning for the more definitive X-ray experiments that would lead him to his greatest discovery.
In attempting to find a classical explanation for these early gamma-ray scattering results, Compton further developed his ideas for an electron of finite size and with various distributions of electricity. However, neither his own efforts nor those of Gray or others could provide a consistent explanation for either the intensity of the scattering or the progressive change in wavelength with scattering angle.
The association with British physicists and their work certainly provided a stimulus for Compton’s later great discovery; but since all these early efforts tried to provide a classical explanation for the phenomena, they could hardly have led him to his final correct explanations of the Compton effect as a quantum process, which came later, in his work at St. Louis.
Following the year at Cambridge, Compton returned to the United States in 1920 to begin his tenure as the Wayman Crow professor and head of the physics department at Washington University, in St. Louis, Missouri, where he made his greatest single discovery. This was suggested by his experiments with gamma rays at Cambridge, which provided the first opportunity to test ideas that originated during the Westinghouse period. In St. Louis he used monochromatic X rays, which permitted him, with the help of a Bragg crystal spectrometer, to measure accurately the change in wavelength of the X rays scattered from a target at various angles, the phenomenon since universally known as the Compton effect. Although this discovery can be considered a logical development of his gamma-ray experiments at Cambridge, which showed a systematic reduction in the penetrating power of gamma rays with increasing scattering angle, nevertheless, the Washington University data, determined with great precision, were the principal ones considered in his final development of the Compton quantum theory of scattering.
The definite change in X-ray wavelength on scattering from light elements such as carbon, depending systematically on the scattering angle, could not be reconciled with classical electrodynamics, even when extended by Compton’s own suggestion of scattering by electrons of finite size. Neither could his attempts to explain the results as fluorescence be maintained once the changes in wavelength with scattering angle were fully established.
Compton arrived at his revolutionary quantum theory for the scattering process rather suddenly in late 1922, after all his previous attempts at an explanation had failed. He now treated the interaction as a simple collision between a free electron and an X-ray quantum having energy hv and momentum hv/c and obeying the usual conservation laws. He had previously considered X rays as having linear momentum, but only in the classical sense suggested by the Poynting vector. He was well acquainted with Planck’s quantum of energy hv, principally from his brother Karl’s pioneer work on testing Einstein’s theory of the photoelectric effect. However, he does not seem to have been aware of Einstein’s 1917 paper suggesting that the photon has linear momentum until much later, and then probably only indirectly, through a 1922 paper by Schrodinger on the Doppler effect in scattering in which reference is made to Einstein’s paper.
It appears that Compton had been at work on a quantum theory for the scattering process for some time before the Schrödinger paper appeared, but he did not give up the classical concept of the momentum of radiation until he had tried in many ways to bring it into accord with his experimental results.
However, once Compton had the concept of an X-ray photon carrying linear momentum as well as energy, he derived his equations for the Compton effect in the form in which we now know them and found that they agreed perfectly with his data and led to a quantum Compton wavelength h/mc for the electron. However, in 1923 the “old quantum theory” gave no basic significance (other than the numerical agreement) for the Compton wavelength; and it was only after the development of the new quantum mechanics in its relativistic form that the Compton wavelength was seen as having the fundamental significance now ascribed to it.
When Compton reported his discovery at meetings of the American Physical Society, it aroused great interest and strong opposition, especially from William Duane of Harvard, in whose laboratory Compton’s results could not be confirmed.
The chief reasons for the reluctance of physicists to accept Compton’s experimental results and his theory were that they conflicted with Thomson’s theory of X-ray scattering based on classical electrodynamics and that Compton had developed his theory to explain the change in wavelength by using one of the most elegant early applications of the special theory of relativity, which had not received general acceptance at that time.
Compton continued to develop both his theoretical interpretation and the precision of his experiments, however, and reported the results so convincingly in both oral and written presentations that the scientific world at last accepted his data and his theoretical interpretation of them. The last public “debate” on the validity of the Compton effect was held at the Toronto meeting of the British Association for the Advancement of Science in the summer of 1924. Here interest was so great that the president, Sir William H. Bragg, scheduled a special session to consider the Compton effect. Compton’s masterful presentation, question answering, and persuasive discussion at this session won over practically everyone to his quantum interpretation of the phenomenon. Duane, in the spirit of a true scientist, however, returned to his laboratory and personally repeated the X-ray experiments that had been in conflict. He discovered some spurious effects in his earlier work and obtained new results which showed clearly that Compton was entirely correct. Duane corrected his stand at the next meeting of the American Physical Society.
The Compton effect, aptly characterized by Karl K. Darrow as one of the most superbly lucid processes in nature, is now part of the fabric of physics; and it is of interest to recall its influence on the development of the quantum theory during the years 1923–1930.
In the first place, it provided conclusive proof that Einstein’s concept of a photon as having both energy and directed momentum was essentially correct. Einstein himself brought considerable attention to Compton’s discovery by his discussions at the Berlin seminars. Interest was also high at Gottingen, Munich, Zurich, Copenhagen, and other Continental centers where theoretical physics was rapidly developing.
However, the quantitative proof of the photon character of radiation had been established by Compton’s use of a Bragg crystal spectrometer, the function of which depended directly on the wave nature of X rays. Thus a more general synthesis was clearly required, in which both the corpuscular photon and the electromagnetic wave would be included and would continue to play the roles demanded by experiment. Later experiments on the Compton effect also proved conclusively that the basic interaction between quantum and electron obeys the conservation laws in individual events and not just statistically, as the theory of Bohr, Kramers, and Slater had proposed in an effort to avoid the use of photons. However, the Bothe-Geiger and Compton-Simon experiments soon demonstrated the validity of the conservation laws for individual scattering events and showed that the Bohr-Kramers-Slater statistical view of these laws was untenable.
The final great synthesis of quantum mechanics and quantum electrodynamics was forced upon physics by the crucial experiments of the Compton effect, electron diffraction, space quantization, and the existence of sharp spectral lines, which could not be brought into line with classical theory. It required the final relativistic form of quantum méchanics, developed by Paul Dirac, to give a completely quantitative explanation of Compton scattering in regard to both intensity and state of polarization by the formula derived by O. Klein and Nishina from the Dirac relativistic theory of the electron. Compton and Hagenow had shown that the X rays used to discover the Compton effect are completely polarized in the scattering process, thus ruling out fluorescence as an explanation. However, for very high energy the Dirac theory predicted an unpolarized component in the scattered rays; this was confirmed by Eric Rogers in 1936.
One of the most important developments in quantum theory was Heisenberg’s uncertainty principle, which is often described as a direct consequence of the recoil of a Compton electron, produced by the high-energy radiation needed to locate its position accurately. This principle of indeterminacy, however, leads to subtler properties for the photon and its interactions than the “old quantum theory” explanations of Einstein and Compton contained. However, the concept of a fundamental length for the electron, the role of the conservation laws in the interaction, and the relationship to experiment in all modern developments are essentially the same as those given by Compton.
The Compton type of interaction is also of basic importance in the inverse Compton effect, in which a high-speed electron imparts great energy to a photon. This process is of central importance both in astrophysics and in high-energy accelerator physics. In the latter one may cite the production of highenergy monochromatic photon beams by the Compton interaction of laser light with the electron beam of the large Stanford linear accelerator.
In 1923 Compton accepted a position as professor of physics at the University of Chicago, a post formerly held by Robert A. Millikan. There he became a colleague of Albert A. Michelson, who was still active in research and whose great work was an inspiration. Compton spent twenty-two years at Chicago, becoming Charles H. Swift distinguished service professor in 1929. His first researches there were to extend his experiments on the Compton effect. These helped clarify and extend the basic discoveries made at Washington University. For his great series of experiments on the Compton effect and their theoretical interpretation he shared the Nobel Prize in physics in 1927. That same year he was elected to the National Academy of Sciences. He was then thirty-five years old.
Other notable work in the physics of X rays that Compton conducted in the early years at Chicago included the extension of his discovery, made at Washington University, of the total reflection of X rays from noncrystalline materials, such as glass and metals, and the first successful application of a ruled diffraction grating to the production of X-ray spectra.
These first X-ray spectra were produced by Richard L. Doan, who carried out a suggestion of Compton’s that such spectra might be obtained from a ruled grating by working within the angle of total reflection. Doan designed for this purpose a special grating that was ruled to his specification on Michelson’s ruling engine, and with it he photographed the first X-ray grating spectra in 1925.
This X-ray grating work was later developed with great precision by Compton’s students J. A. Bearden and N. S. Gingrich. This work alone, extending X rays as a branch of optics, would have assured Compton’s reputation as a distinguished physicist.
One of the more important results of this work was that the X-ray grating wavelengths led to values for the Avogadro number and for the electronic charge; the latter was at variance with Millikan’s oil-drop determinations, which up to that time had been considered as standard. This work in Compton’s laboratory definitively clarified discrepancies that had long existed in the values of fundamental atomic constants.
Other work at the University of Chicago, especially that of E. O. Wollan, used X-ray scattering to determine the density of diffracting matter in crystals and gases. This work required a deep understanding of the X-ray scattering process in order to separate the coherent and incoherent radiations and apply the related theories to the structure determinations. It was reminiscent of Compton’s Ph.D. thesis, in which he had first worked out methods to employ X-ray diffraction from crystals to determine the electron distributions in the lattice. This pioneer work, where Fourier analysis of X-ray data was first employed, was developed to a high art by W. L. Bragg and his school at Manchester University.
Compton was an inspiring teacher and research leader. His contagious enthusiasm, friendliness, and great mental powers made his classes and laboratory meetings memorable experiences for all who were privileged to attend them. He always shared most generously all he learned from his many distinguished visitors and from his own travels with his students and younger colleagues.
In the early 1930’s Compton changed his main research interest from X rays to cosmic rays. He was led to this because the interaction of high-energy gamma rays and electrons in cosmic rays is an important example of the Compton effect (as today the inverse Compton effect between high-speed electrons and low-energy photons is of central importance for astrophysics). To obtain the essential data needed to determine the nature of the primary cosmic rays, Compton organized and led expeditions to all parts of the world to measure the cosmic ray intensity over a wide range of geomagnetic latitudes and longitudes and at many elevations above sea level. His reports on these measurements often appeared as “Letters to the Editor” of the Physical Review.
The first important result of this worldwide study of cosmic rays was to support and greatly extend Jacob Clay’s earlier observations showing that the intensity of cosmic rays depends systematically on geomagnetic latitude and on altitude. It proved that, contrary to the generally accepted view held at that time, at least a significant fraction of the primary cosmic rays are charged particles and thus are subject to the influence of the earth’s magnetic field.
More refined results that strongly supported this belief were those which demonstrated an east-west asymmetry of the primary cosmic rays, as had been predicted by the theoretical work of Georges Lemaître and M. S. Vallarta and had been discovered experimentally by Compton’s student Luis W. Alvarez and, simultaneously, by T. H. Johnson in observations at Mexico City—in the latitude where the theory had predicted the largest effect.
Precise measurements of cosmic rays on the Pacific Ocean, made over long periods of time by Compton and Turner, revealed an anomalous dependence of cosmic ray intensity on atmospheric temperature and barometric pressure. These gave the first indication, as interpreted by P. M. S. Blackett, of the radioactivity of mesons.
Compton’s worldwide cosmic ray studies were sponsored in part by the Carnegie Institution of Washington. One of the leading scientists of that organization, Scott E. Forbush, continued the work, making important discoveries, especially the sudden changes in cosmic ray intensity related to conditions on the sun and its magnetic field.
The development of Compton’s cosmic ray program was greatly assisted by the collaboration of several of his former students and of refugee physicists from Europe, for whom he found a haven in Chicago. Their experiments gave additional early evidence on the nature and lifetime of the mu-meson.
The final summary of Compton’s cosmic ray work was made at a conference at the University of Chicago in the summer of 1939 which was attended by the leading workers in cosmic rays throughout the world. Compton inspired and led the conference, which was his last peacetime research work.
In spite of his broad sympathies and worldwide interests, Compton had never felt the need to join the pilgrimages to Göttingen, Copenhagen, or Munich, as had so many physicists of his generation. His year (1934–1935) as Eastman professor at Oxford, however, brought him more closely in touch with European scientists and the problems of a troubled world. He became increasingly involved with human problems, which soon led him to his greatest challenge and leadership responsibility.
World War II brought about a complete change in physics research. This was especially true for Compton, who early became involved in the “uranium problem” that led ultimately to the development of nuclear reactors and the atomic bomb. On 6 November 1941, Compton, as chairman of the National Academy of Sciences Committee on Uranium, presented a report on the military potentialities of atomic energy. This report was a masterpiece in setting forth both the scientific and technological possibilities. It had been prepared in close consultation with Ernest O. Lawrence, who had informed Compton of the discovery of plutonium at the Radiation Laboratory at the University of California in Berkeley. This discovery completely changed the long-range prospects for atomic energy, and the initiation of the vast Manhattan Project in the United States was due primarily to the leadership of Compton and Lawrence.
Compton soon gave up all his other activities to organize and direct the work of the Metallurgical Laboratory of the Manhattan District of the Corps of Engineers at the University of Chicago, which was responsible for the production of plutonium. He centralized all the activities in buildings of the University of Chicago and recruited Enrico Fermi, Walter Zinn, Glenn Seaborg, Richard L. Doan, Eugene Wigner, and a large group of young physicists, chemists, and engineers. He was in charge when the first successful nuclear chain reaction with uranium was accomplished by Enrico Fermi and others on 2 December 1942. This first nuclear reactor was designed by Fermi, but its success was possible only through the great support and encouragement given by Compton, who arranged for Crawford H. Greenewalt, an officer and later president of the Du Pont Company, to be present when the reactor first went critical. Greenewalt’s witnessing of this historical event was a decisive factor in the Du Pont Company’s continued interest in the uranium project. Thereafter, it agreed to build the reactors at Hanford, Washington, without which the whole project could not have succeeded.
Compton had the major role in establishing the Palos Park Laboratory (which became the Argonne National Laboratory) and the Clinton Engineer Works, Oak Ridge, Tennessee, as well as the plutonium production reactor establishment at Hanford, Washington.
As the war reached its end, Compton decided that he should devote himself to university administration and not begin a wholly new physics research program—a very hard decision for him, as he had never lost his keen interests in the laboratory and all new discoveries in physics. Accordingly, he accepted the position of chancellor of Washington University in St. Louis. This challenging assignment to continue the development of a great university was also for Compton a return to the place where he had made his greatest discovery in physics, some twenty-five years before.
When Compton accepted the post of chancellor of Washington University, he had already been offered several university presidencies. Many of his physics colleagues were greatly surprised that he would now make this change, when he could have continued at the University of Chicago and been the leader of the new Institutes for Nuclear Studies, Metals and Microbiology, which he had helped to create. However, his ties with Washington University were very strong, and the tradition of service was equally strong.
Compton’s chancellorship at Washington University resulted in many great advances for that distinguished institution. He improved and greatly strengthened the science departments, including the medical school. His own deep interests in the humanities ensured that he would greatly support these activities. He and his wife were able to develop strong support for the university, both in St. Louis and elsewhere in the nation.
In 1954, when Compton had reached the age at which he felt he must retire from the active administrative leadership of the university, he continued to serve with great distinction through his writing, lecturing, teaching, and public service. Perhaps his most notable publication during this period is the book Atomic Quest, which gives a complete, clear, and generous account of the activities of all his colleagues in the Manhattan Project during the war. This book and the more technically detailed Smyth Report constitute the basic historical documents on this epochmaking activity.
Although his health was not especially good in the later years, Compton continued to lecture and travel to the very end and accepted the invitation of the University of California to give a series of lectures. He had presented only two when he died.
Arthur Holly Compton will always be remembered as one of the world’s great physicists. His discovery of the Compton effect, so vital in the development of quantum physics, has ensured him a secure place among the great scientists.
I. Original Works. Compton’s books include X-Rays and Electrons (Princeton, N. J., 1926); X-Rays in Theory and Experiment (Princeton, N. J., 1935), written with S. K. Allison; Atomic Quest (New York, 1956); and The Cosmos of Arthur Holly Compton, Marjorie Johnston, ed. (New York, 1967), his public papers.
His principal articles in professional journals are “Latitude and Length of the Day,” in Popular Astronomy, 23 (1915), 199–207; “The Intensity of X-ray Reflection and the Distribution of the Electrons in Atoms,” in Physical Review, 9 (1917), 29–57, his Ph.D. thesis; “The Softening of Secondary X-Rays,” in Nature, 108 (1921), 366–367; “Secondary Radiations Produced by X-Rays,” in Bulletin of the National Research Council, no. 20 (1922), 16–72; “A Quantum Theory of the Scattering of X-Rays by Light Elements,” in Physical Review, 21 (1923), 483–502; “The Spectrum of Scattered X-Rays,” ibid., 22 (1923), 409–413; “The Total Reflection of X-Rays,” in Philosophical Magazine, 45 (1923), 1121–1131; “Polarization of Secondary X-Rays,” in Journal of the Optical Society of America, 8 (1924), 487–491, written with C. F. Hagenow; “X-ray Spectra From a Ruled Reflection Grating,” in Proceedings of the National Academy of Sciences of the United States of America, 11 (1925), 598–601, written with R. L. Doan; “Determination of Electron Distributions From Measurements of Scattered X-Rays,” in Physical Review, 35 (1930), 925–938; “A Geographic Study of Cosmic Rays,” ibid., 43 (1933), 387–403; “A Positively Changed Component of Cosmic Rays,” ibid., 835–836, written with L. W. Alvarez; “Cosmic Rays on the Pacific Ocean,” ibid., 52 (1937), 799–814, written with R. N. Turner; “Chicago Cosmic Ray Symposium,” in Science Monthly, 49 (1939), 280–284; and “The Scattering of X-Rays as Particles,” in American Journal of Physics, 29 (1961), 817–820
II. Secondary Literature. Biographical articles are S. K. Allison, “Arthur Holly Compton, Research Physicist,” in Science, 138 (1962), 794–799; and “Arthur Holly Compton, 1892–1962,” in Biographical Memoirs. National Academy of Sciences, 38 (1965), 81–110; and Zay Jeffries, “Arthur Holly Compton,” in Yearbook of the American Philosophical Society (1962), pp. 122–126.
Robert S. Shankland
Arthur Holly Compton
Arthur Holly Compton
The American physicist Arthur Holly Compton (1892-1962) discovered the "Compton effect" and the proof of the latitude intensity variation. He also played a critical role in the development of the atomic bomb.
Arthur Compton was born in Wooster, Ohio, on Sept. 10, 1892, the youngest child of Elias and Otelia Compton. It was midway during Arthur's early formal education that he became interested in science and carried out his first amateur researches. Although he wrote an intelligent student essay on the mammoth, it was chiefly astronomy and aviation that stimulated him. He purchased a telescope and photographed constellations and (in 1910) Halley's comet. Later he constructed and flew a 27-foot-wingspan glider.
During his undergraduate years at the College of Wooster (1909-1913) Compton had to choose a profession. His father encouraged him to devote his life to science. On his graduation from Wooster, therefore, Arthur decided to pursue graduate study, obtaining his master's degree in physics from Princeton University in 1914; in 1916 he obtained his doctoral degree. Immediately after receiving his degree, Compton married Betty Charity McCloskey, a former Wooster classmate; the Comptons had two sons.
Compton's first position was as an instructor in physics at the University of Minnesota (1916-1917), where he continued his x-ray researches. Leaving Minnesota, he became a research engineer at the newly established Westinghouse laboratory in East Pittsburgh, where he remained from 1917 to 1919, doing original work on the sodium-vapor lamp and developing instrumentation for aircraft. He left Westinghouse because he came to recognize that fundamentally his interest was not in industrial research but in pure research. In particular, he had become intrigued by a recent observation of the English physicist C. G. Barkla, who had scattered hard x-rays from aluminum and found that the total amount of scattered radiation was less than that predicted by a wellknown formula of J. J. Thomson. Compton found that he could account for Barkla's observation by assuming that the electrons in the scatterer were very large and therefore diffracting the incident radiation.
Anxious to pursue these studies further, Compton applied for and received a National Research Council fellowship to work with perhaps the foremost experimentalist of the day, Ernest Rutherford, at the Cavendish Laboratory in England. Compton's year in the extremely stimulating intellectual atmosphere at the Cavendish, during which time he carried out gamma-ray scattering experiments and pondered his results, marked a turning point in his career, as he became convinced that he was on the track of a very fundamental physical phenomenon.
Desiring to pursue it further on his own, Compton returned to the United States in 1920 to accept the Wayman Crow professorship of physics at Washington University in St. Louis. There he scattered x-rays from various substances and, eventually, analyzed the scattered radiation by use of a Bragg spectrometer. By the fall of 1922 he had definite experimental proof that x-rays undergo a distinct change in wavelength when scattered, the exact amount depending only on the angle through which they are scattered. Compton published this conclusion in October 1922 and within 2 months correctly accounted for it theoretically. He assumed that an x-ray—a particle of radiation—collides with an electron in the scatterer, conserving both energy and momentum. This process has since become famous as the Compton effect, a discovery for which he was awarded the Nobel Prize of 1927. The historical significance of Compton's discovery was that it forced physicists for the first time to seriously cope with Einstein's long-neglected and revolutionary 1905 light-quantum hypothesis: in the Compton effect an x-ray behaves exactly like any other colliding particle.
While the discovery of the Compton effect was undoubtedly Compton's single most important contribution to physics, he made many others, both earlier and later. He proved in 1922 that x-rays can be totally internally reflected from glass and silver mirrors, experiments which eventually led to precise values for the index of refraction and electronic populations of substances, as well as to a new and more precise value for the charge of the electron. After Compton left Washington University for the University of Chicago in 1923 (where he later became Charles H. Swift distinguished service professor in 1929 and chairman of the department of physics and dean of the physical sciences in 1940), he reactivated a very early interest and developed a diffraction method for determining electronic distributions in atoms. Still later he and J. C. Stearns proved that ferro-magnetism cannot be due to the tilting of electronic orbital planes.
Perhaps the most important work Compton carried out after going to Chicago was his work on cosmic rays. Realizing the importance of these rays for cosmological theories, Compton developed a greatly improved detector and convinced the Carnegie Institution to fund a world survey between 1931 and 1934. The globe was divided into nine regions, and roughly 100 physicists divided into smaller groups sailed oceans, traversed continents, and scaled mountains, carrying identical detectors to measure cosmic-ray intensities.
The most significant conclusion drawn from Compton's world survey was that the intensity of cosmic rays at the surface of the earth steadily decreases as one goes from either pole to the Equator. This "latitude effect" had been noted earlier by the Dutch physicist J. Clay, but the evidence had not been conclusive. Compton's survey therefore proved that the earth's magnetic field deflects at least most of the incident cosmic rays, which is only possible if they are charged particles. Compton's world survey marked a turning point in knowledge of cosmic rays.
Atomic Bomb and Postwar Endeavors
When World War II broke out, Compton was called upon to assess the chances of producing an atomic bomb. If it were possible to develop an atomic bomb, Compton believed it should be the United States that had possession of it. Detailed calculations on nuclear fission processes proved that the possibility of developing this awesome weapon existed. Compton recommended production, and for 4 years thereafter, as director of the U.S. government's Plutonium Research Project, he devoted all of his administrative, scientific, and inspirational energies to make the bomb a reality.
Compton was under extraordinary pressure as he made arrangements for the purification of uranium and the production of plutonium and many other elements that went into the construction of the atomic bomb. Ultimately, Compton was asked for his personal opinion as to whether the bomb should be dropped on Hiroshima. He gave an affirmative response in the firm conviction that it was the only way to bring the war to a swift conclusion and thereby save many American and Japanese lives.
Between 1945 and 1953 Compton was chancellor of Washington University in St. Louis and strove unceasingly to make that institution a guiding light in higher education. Between 1954 and 1961, as distinguished service professor of natural philosophy, he taught, wrote, and delivered lectures to many groups and, as always, served on numerous boards and committees. In 1961 he became professor-at-large, intending to divide his time between Washington University, the University of California at Berkeley, and Wooster College. His plans were cut short by his sudden death on March 15, 1962, in Berkeley.
Compton was an extraordinarily gifted human being. At the age of 35 he won the Nobel Prize and was also elected to the National Academy of Sciences; later, he was elected to numerous other honorary societies, both foreign and domestic. He received a large number of honorary degrees, medals (including the U.S. government's Medal for Merit), and other honors. In spite of his many achievements and honors, however, he remained a modest and warm human being.
The Cosmos of Arthur Holly Compton, edited by Marjorie Johnston (1968), contains Compton's "Personal Reminiscences," a selection of his writings on scientific and nonscientific subjects, and a bibliography of his scientific writings. Compton discusses his role in the development of the atomic bomb in Atomic Quest (1956). The early life of the Compton family is the subject of James R. Blackwood, The House on College Avenue: The Comptons at Wooster, 1891-1913 (1968). General works on modern physics which discuss Compton include Gerald Holton and Duane H.D. Roller, Foundations of Modern Physical Science (1958); Henry A. Boorse and Lloyd Motz, eds., The World of the Atom (2 vols., 1966); and Ira M. Freeman, Physics: Principles and Insights (1968). □
Arthur Holly Compton
Arthur Holly Compton
American physicist who was awarded the 1927 Nobel Prize for Physics for discovering the Compton effect—shifts in x-ray wavelength due to scattering. His quantum theoretical explanation of this phenomenon and derivation of equations for predicting scattered wavelengths confirmed the particle-wave duality of electromagnetic radiation. Throughout the 1930s Compton conducted extensive research on cosmic radiation, which helped establish that at least some cosmic rays are charged particles. He was one of the leaders in developing the atomic bomb during World War II.