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 Effect

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.

Cosmic-ray Work

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.

Further Reading on Arthur Holly Compton

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).

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