MICHELSON, ALBERT ABRAHAM American physicist, was born in Strelno, Germany, Dec. 19, 1852. His parents moved to San Francisco, Calif., where he studied in the public schools. He graduated from the U.S. Naval Academy in 1873, and was instructor in physics and chemistry there (1875 79). He was then for a short time in the Nautical Almanac office. From 188o to 1882 he studied in Berlin, Heidelberg and Paris. He resigned from the Navy in 1881. In 1883 he was appointed professor of physics at the Case school of applied science, Cleve land, 0., and six years later accepted a similar position at Clark University. In 1892 he was appointed professor and head of the department of physics at the University of Chicago. He early directed his researches to the velocity of light, and while in Cleveland invented his interferometer for measuring distances by means of the length of light-waves. His researches enabled him to revise and improve upon the achievements of Fizeau in respect of the velocity of light. He perfected the methods for experi menting, and determined with great precision the speed at which light travels.
Michelson measured a metre in terms of the wave-length of cadmium light for the Paris Bureau International des Poids et Mesures. The consequence is that the metre bar, hitherto care fully safeguarded in Paris, can easily be replaced, since its length is known in terms of an absolute unit. In 1892 he was a member
of the Bureau International des Poids et Mesures and in 1897 of the International Committee of Weights and Measures. He was president of the American Physical Society in 1901, of the Ameri can Society for the Advancement of Science in 1910, and of the National Academy of Science (1923-27). He received medals and prizes from many learned societies, and in 1907 was awarded the Nobel Prize for physics. During the World War he rejoined the naval service and devoted his entire time to new devices for naval use. His range-finder was adopted as part of the U.S. Navy equipment. In 1920 he was able to demonstrate by means of light interference that the diameter of Betelgeuse was 260,000, 00o miles. This was the first approximately accurate determina tion of the size of a star. He published Velocity of Light (1902) ; Light Waves and Their Uses (r903); Studies in Optics (1927) ; and numerous papers in scientific journals. He was the first to be appointed "distinguished service professor" at the University of Chicago (1926). (For the "Michelson-Morley experiment" in interference of light, with its bearing on the Einstein theory, see RELATIVITY.) Michelson died May 9, 193r.