Frits Zernike, born in Amsterdam, July 16, 1888 was a Dutch physicist. Educated at Amsterdam and Groningen, he joined the staff of Groningen University in 1913 as an assistant in astronomy, became professor of theoretical physics and mechanics in 1920, and remained with the university throughout his career. In the 1920's he developed the Zernike galvanometer, which registers very weak electric currents and is now standard equipment in major laboratories. His spectroscopic studies led to his announcement in 1934 of a "phase contrast" method of detecting and compensating for the irregularities in the curved reflectors of astronomical telescopes. He had already applied the basic principles of this technique to microscopy also, but its practical aspects were not at once perceived, and the Zernike phase contrast microscope came into general use only after World War II.
The phase contrast (or phase) microscope makes it possible to study minute transparent cells of living matter without first staining them chemically. Since such staining usually kills the specimens, the instrument has been of great value in biological and medical investigation, particularly in cancer research. It is equipped with an annular light-controlling diaphragm and a transparent "phase plate" with an annular coating or groove. The plate produces a phase difference of about one-quarter wavelength between the direct and the diffracted light waves that pass through it. This, together with diffraction index variations in the cellular matter under observation, effects an apparent "coloring" of the cells and makes their structures visible as lighter or darker details. The Nobel Prize for physics for 1953 was awarded to Zernike for his invention of phase contrast. He also developed a "color phase" microscopic process and did important work in chemistry, thermodynamics, and mathematical theory.
Frits Zernike died on March 10, 1966.