Kirchhoff, Gustav Robert

(born March 12, 1824, Königsberg, Prussia—died Oct. 17, 1887, Berlin, Ger.) German physicist. Kirchhoff's laws (1845) allow calculation of the currents, voltages, and resistances of electrical networks (he was the first to show that current flows through a conductor at the speed of light) and generalized the equations describing current flow to three dimensions. With Robert Bunsen, he demonstrated that every element emits coloured light when heated at wavelengths specific to it, a fact that is the basis of spectrum analysis. They used this new research tool to discover cesium (1860) and rubidium (1861), and began a new era in astronomy when they applied it to the spectrum of the sun.