Ritz, Walter, 1878–1909, Swiss physicist. He taught at the universities of Zürich and Göttingen. Ritz's combination principle, confirmed by later research, stated that the frequencies of spectral lines could be expressed as differences between a relatively small number of "terms," later identified by Niels Bohr, a Danish physicist, as the permissible energy levels of the radiating atoms. Ritz also developed important theories of radiation, magnetism, and electrodynamics.
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