Duane, William (17.02.1872–7.03.1935) was an American physicist and a member of the National Academy of Sciences (1920). Born in Philadelphia. Graduated from the University of Pennsylvania (1892) and Harvard University (1893), and in 1897 received the degree of doctor of philosophy at the University of Berlin. In 1893–95 he was an assistant at Harvard University, and in 1898–1907 professor at the University of Colorado. In 1907–12 he worked at the University of Paris, and from 1913 at Harvard (professor in 1917–34).
His work concerned the study of radioactivity and of X-rays, quantum theory, electromagnetism, physical chemistry and biophysics. He measured the charge of the particles of alpha and beta rays. In 1915 he established the law determining the short-wavelength limit of the continuous spectrum of X-rays (the Duane–Hunt law). He used X-rays in the treatment of cancer. He constructed a quantum theory of the diffraction grating. He found (1923) a connection between the momentum of matter and a kind of wave number (the Duane equation). He developed a method for determining Planck's constant.