Used with
permission of Maiken Naylor, University at Buffalo, Buffalo, NY, USA,
http://ublib.buffalo.edu/libraries/units/sel/exhibits/stamps
Gustav Robert Kirchhoff (1824-1887) was a German physicist who worked with Bunsen on the development of the spectroscope and the measurement of spectra of the elements. He discovered that sodium emits the bright yellow lines appearing in absorption in the solar spectrum as observed by Fraunhofer; this suggested the possibility of investigating the composition of stars by spectrographic methods. His work in electricity is noted on this stamp: the sum of potential drops around a closed circuit loop is zero.