Gustav Robert Kirchhoff, German physicist, c 1870s.

Photogravure after a photograph of Gustav Robert Kirchhoff (1824-1887), who distinguished himself in many fields, notably in the study of electricity, heat, optics and especially for his contributions to spectrum-analysis. He formulated Kirchhoff's law of radiation, the key to the whole thermodynamics of radiation, and his electromagnetic theory of diffraction is today still the most commonly used in optics. From a collection of portraits of scientists published by Photographische Gesellschaft, Berlin, c 1910. Dimensions: 460mm x 340mm.