Cato Maximilian Guldberg (left) and Peter Waage
Photogravure by H. Riffart, Berlin. Scanned, image processed and uploaded by <a href="//commons.wikimedia.org/wiki/User:Kuebi" title="User:Kuebi">Kuebi</a> = Armin Kübelbeck
prior or equal 1891
Zeitschrift für Physikalische Chemie, Band 8, von 1891