Part of the precursor of the light-sheet microscope developed by Siedentopf and Zsigmondy with an upright microscope containing a specimen holder that appears to be mounted to its objective lens and orthogonal illumination at 90° from what appears to be an illuminating objective. Reproduced from H. Siedentopf and R. Zsigmondy, Uber Sichtbarmachung und Größenbestimmung ultramikoskopischer Teilchen, mit besonderer Anwendung auf Goldrubingläser, Ann. Phys., 1902, 315(1), 1–39. Copyright 1903 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.