In 1859, Gustav Robert Kirchhoff and Robert Bunsen demonstrated the reversibility of emission lines:
"within the spectrum, an element absorbs the light at the exact location of the lines which it can emit". They stated the basic law of elementary spectrometry which states: "each element has specific properties as regards the light it emits".

[Kirchhoff and Bunsen experiment]

They explained Fraunhofer's black lines as being caused by the absorption of solar light by metal vapours present in the colder layers surrounding the sun. They even identified the element responsible for some of these black lines.
     This work paved the way for atomic spectrochemistry and announced the advent of modern physics.

Authors: Jean Charles Lefebvre, Jobin-Yvon Emission, and Richard Payling, Surface Analytical

First published on the web: 15 December 1999.