In article abstract, the phase-contrast microscopy is claimed to have been invented in 1942. This is incorrect. The origins of phase-contrast date back to 1934 (not a microscopy yet) and 1935 (microscopy):
Zernike F. (1934)
Diffraction theory of the knife-edge test and its improved form, the phase-contrast method.
Monthly Notices of the Royal Astronomical Society 94 (5), 377-3 84 (originally published in Dutch).
(http://esoads.eso.org/journals_service.html)
Zernike F. (1935)
Phase-contrast method in microscopical observation (in German).
Physikalische Zeitschrift 36 (22/23): 848-851
Zeitschrift f r Technische Physik 16 (11): 454-457
(two identical papers)
Furthermore, the following reports (published when Zernike was only 16 or 17 years old) utilize, in a way, the principle of phase-contrast microscopy, even though only for absorbing (i.e., not phase) objects:
Rheinberg J. (1904 and 1905)
On the influence on images of gratings of phase differences amongst their spectra.
J. Roy. Microsc. Soc.; volumes-not-numbered (Part 4), 388-390; and (Part 2), 152-155.
(
www.biodiversitylibrary.org/bibliography/7413)
Conrady A. (1905)
An experimental proof of phase reversal in diffraction spectra.
J. Roy. Microsc. Soc.; volume-not-numbered (Part 2), 150-152.
(
www.biodiversitylibrary.org/bibliography/7413)