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complementarity principle

(Encyclopedia)complementarity principle, physical principle enunciated by Niels Bohr in 1928 stating that certain physical concepts are complementary. If two concepts are complementary, an experiment that clearly i...

Dewar, Sir James

(Encyclopedia)Dewar, Sir James dyo͞oˈər [key], 1842–1923, British chemist and physicist, b. Scotland. He was professor of chemistry (from 1877) at the Royal Institution, London, and later was director of the D...

Ehrenfest, Paul

(Encyclopedia)Ehrenfest, Paul poul āˈrənfĕst [key], 1880–1933, Austrian physicist. In 1904, Ehrenfest received his doctorate in theoretical physics in Vienna and married the Russian mathematician Tatyana Alex...

U-2 incident

(Encyclopedia)U-2 incident, in U.S. and Soviet history, the events following the Soviet downing of an American U-2 high altitude reconnaissance aircraft over Soviet territory on May 1, 1960. The incident led to the...

Landau, Lev Davidovich

(Encyclopedia)Landau, Lev Davidovich lyĕf dəvēˈdəvĭch ləndouˈ [key], 1908–68, Soviet physicist, b. Baku, Azerbaijan. A child prodigy in mathematics, he entered Baku Univ. at 14; at 21 he received a doctor...

Sommerfeld, Arnold Johannes Wilhelm

(Encyclopedia)Sommerfeld, Arnold Johannes Wilhelm ärˈnōlt yōhänˈəs vĭlˈhĕlm zômˈərfĕlt [key], 1868–1951, German physicist and teacher. He received a Ph.D. at Königsburg Univ. in 1891 and was a prof...

Steno, Nicolaus

(Encyclopedia)Steno, Nicolaus nēls stānˈsən [key], 1638–86, Danish anatomist, geologist, and Roman Catholic prelate. He lived principally in Copenhagen, Paris, and Florence. He investigated the heart, brain, ...

Niépce, Joseph Nicéphore

(Encyclopedia)Niépce, Joseph Nicéphore zhôzĕfˈ nēsāfôrˈ nyĕps [key], 1765–1833, French chemist who originated a process of photography (see photography, still). In 1826 he produced the first known photo...

correspondence principle

(Encyclopedia)correspondence principle, physical principle, enunciated by Niels Bohr in 1923, according to which the predictions of the quantum theory must correspond to the predictions of the classical theories of...

Nielsen, Carl

(Encyclopedia)Nielsen, Carl nēlˈsən, Dan. nĭlˈsən [key], 1865–1931, Danish composer. Nielsen was a pupil of Niels Gade at the Royal Conservatory in Copenhagen. Considered Denmark's foremost composer, he is ...