ROOD, Ogden Nicholas, physicist, born in Danbury, Connecticut, 3 February, 1831. He was graduated at Princeton in 1852, and then studied at the Sheffield scientific school of Yale, and at the universities of Munich and Berlin, making a specialty of science. In 1858, soon after his return, he was chosen professor of chemistry and physics at Troy university, where he remained for nearly five years. He was called in 1863 to the chair of physics in Columbia, and has since delivered lectures there and in the School of mines of that institution. His original investigations have been numerous, and include special studies of questions in mechanics, optics, acoustics, and electricity. Professor Rood was one of the first to apply photography to the microscope, and to take binocular pictures with that instrument. His studies of the nature of the electric spark and of the duration of the flashes are particularly interesting, involving the determination of much more minute intervals of time than any that were ever measured before. In 1880 lie devised a mercurial air-pump giving an exhaustion of 1/388 millionth of an atmosphere, a degree that has not been attained by other pumps up to the present time (1888). The methods of photometry that he has originated, and his investigations of phenomena that depend on the physiology of vision, are very ingenious, and he was the first to make quantitative experiments on color-contrast. AI-though not an artist by profession, he paints in water-colors, is frequently represented at, the annual exhibitions, and has been a member of the American water-color society since its foundation in 1866. He was elected to the National academy of sciences in 1865, and in 1867 was vice-president of the American association for the advancement of science. The results of his various researches are included in about sixty memoirs that have appeared in scientific journals, both in the United States and abroad, but chiefly in the "American Journal of Science." Sixteen of his most important memoirs were originally read before the National academy of sciences. Professor Rood has published " Modern Chromatics," a work that, besides presenting the fundamental facts as to perception of color, contains the results of numerous original investigations on the subject (New York, 1881).