The microscope : its construction and management : including technique, photo-micrography, and the past and future of the microscope (1893)
Heurck, Henri van, 1838-1909 · London : C. Lockwood ; New York : D. Van Nostrand Co. · leaf 82
te of the valve. Under certain conditions of illumination, and especially with thenew objective of r6o numerical aperture, instead of round points,hexagonals are seen (figs. 53 and 54). It was thought that this wassimply an optical illusion, but we demonstrated in December, 1889,that these… … Fig. 54-Pleurosigma angulatum photographed with electric light.
Microscopy
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