William W. Coblentz (born Nov. 20, 1873, North Lima, Ohio, U.S.—died Sept. 15, 1962, Washington, D.C.) was an American physicist and astronomer whose work lay primarily in infrared spectroscopy. Coblentz developed more accurate infrared spectrometers and extended their measurements to longer wavelengths. In 1905 he published a lengthy study of the infrared emission and absorption spectra of numerous elements and compounds. In 1914–16 he published improved values for the Stefan-Boltzmann constant of blackbody radiation and helped to confirm Planck’s radiation law. He then turned to astrophysics and measured the infrared radiation from stars, planets, and nebulae. From 1905 until 1945 Coblentz was the chief of the Radiometry Section of the U.S. National Bureau of Standards and is considered responsible for the adoption of radiometric standards. In 1937 he was awarded the Rumford Gold Medal by the American Academy of Arts and Sciences.