Kirchhoff, Gustav Robert 1824-87
German physicist

He was born in K�nigsberg, Prussia (now Kaliningrad, Russia), and while still a student, he devised 'Kirchhoff's laws' for electrical circuits. Professor at Heidelberg University (1854-75) and Berlin University (1875-86), he distinguished himself in electricity, heat, optics and especially (with Robert Bunsen) spectrum analysis, which led to the discovery of caesium and rubidium (1859). More importantly it resulted in his explanation of the Fraunhofer lines in the solar spectrum as the absorption of the corresponding spectral wavelengths in the Sun's atmosphere. He formulated Kirchoff's law of radiation, the key to the whole thermodynamics of radiation which, in the hands of his successor Max Planck, would later be developed into the concept of quanta. His electromagnetic theory of diffraction is still the most commonly used in optics.