Characterization of Goethe’s prisms by external ion beam


Characterization of Goethe’s prisms by external ion beam

Munnik, F.; Mäder, M.; Heller, R.; Schreiber, A.; Müller, O.

Johann Wolfgang von Goethe is known the world over as a renowned writer. However, he was also involved in scientific studies and has written several scientific books, of which he considered the “Theory of colours” (“Farbenlehre”, 1400 pages published in 1810) his most important work overall. In this work, he characterises colours as arising from the interplay between light and dark. This is in contrast to Newton’s analytical treatment of colour from one century earlier, which is based on the observation that white light can be separated into colours with a prism, that Goethe opposed. Over the centuries, Goethe’s theory was discredited and Newton’s theory prevailed. However, Goethe performed systematic and accurate optical measurements.
For these experiments, he and his partner J. Ritter, who discovered UV-light, used water prisms and glass prisms ordered from a glassmaker in Jena. The aim of current research is to reconstruct these optical experiments and the observed spectra [1]. For this, detailed knowledge of the composition of the glass prisms is important. This knowledge is, for example, also important to evaluate how innovative his prisms were.
Therefore, eleven prisms from Goethe’s estate or from contemporary sources belonging to the Klassik Stiftung Weimar have been analysed at the external beam setup of the Ion Beam Center at the HZDR. A 4 MeV proton beam has been used to acquire PIXE, PIGE and RBS spectra, sometimes on several areas. Care had to be taken to minimise damage by using short measurement times and measuring on inconspicuous areas because the glass quickly showed dark spots under irradiation. The PIXE and PIGE spectra have been used for quantitative analysis in an iterative procedure and the RBS spectra have only been evaluated quantitatively. The results of this analysis and the interpretation are presented in this work.

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