CHAPTER 11: Lighting the Dark Path to Atomism: Spectroscopy Shows the Way: Fraunhofer, Bunsen, and Kirchhoff (Germany I)

Joseph von Fraunhofer, the prism-maker, discovered the dark lines in the solar spectrum, (“Fraunhofer lines”) that are the fingerprints of atoms in our Sun. We explore his glassworks in Benediktbeuren and a variety of Fraunhofer sites in Munich including the Deutsches Museum. In Heidelberg, Robert Bunsen and Gustav Kirchhoff used a prism to break the light from elemental “flame tests” into unique sets of spectral lines. Using their spectroscope, they discovered two new elements (cesium and rubidium) in the spa waters of Bad Dürkheim and correlated Fraunhofer's lines with various earth-bound elements. We explore a variety of Bunsen and Kirchhoff sites including the Hörsaal of the Chemistry Department with its stunning collection of Bunsen equipment and compounds and Beatrix Potter's watercolor of mice using a Bunsen burner to make toasted cheese. We also find houses where various other famous scientists lived and worked in Heidelberg and walk the Philosophenweg. Anders Angstrom's and Pierre Janssen's discoveries of hydrogen and helium on the Sun and the discoveries of thallium by Crookes, indium by Reich and Richter, and gallium by Lecoq de Boisbaudran are described. Johann Balmer's empirical equation for hydrogen line spectra is given and discussed.