Kirchhoff, Gustav Robert

s´täf rō´bĕrt kĭrkh´hôf), 1824–87, German physicist. He served as professor of physics at the universities of Breslau (1850–54), Heidelberg (1854–74), and Berlin (from 1875). He is known especially for his work with the spectroscope in association with R. W. Bunsen, with whom he discovered the elements cesium and rubidium, and for his explanation of the Fraunhofer lines in the solar spectrum. He also did important research in electricity (he formulated Kirchhoff's laws) and thermodynamics.