Zernike, Frits

7/16/1888–3/10/1966
DUTCH
PHYSICIST

Frits Zernike was a pioneer in forensic science ; his invention of the phase-contrast microscope enabled scientists to study living tissue samples under magnification for the first time. Zernike won the 1953 Nobel Prize in physics for his invention.

Zernike's background in statistical mathematics and thermodynamics was responsible for his groundbreaking discovery. A conventional microscope utilizes ordinary light, and under these instruments living tissues, particularly transparent ones, are not visible unless stained. Yet staining usually kills the specimen or produces artifacts that are impossible to differentiate from the specimen. The phase-contrast technique can reveal variations in opacity as well as variations in the thickness of transparent objects.

Born on July 16, 1888, in Amsterdam, Zernike was the son of two mathematicians, Carl Frederick August Zernike and Antje Dieperink Zernike. Early in life he was recognized for his mathematical abilities. He received both his B.S. and his Ph.D. in physics from the University of Amsterdam, and he worked at an astronomy laboratory while pursuing his graduate studies. His doctoral thesis, "Critical Opalescence, Theoretical and Experimental," quickly established him as a leader in his field. In 1915 he was appointed lecturer in theoretical physics at the University of Groningen. In 1920, he was promoted to professor, where he remained for the rest of his career.

It was while working in the field of astronomy that Zernike first discovered the advantages of phase-contrast techniques. Irregularities on the surfaces of the curved mirrors of telescopes were a common problem at that time; these mirrors sometimes produced "ghost" images and Zernike hypothesized that they were caused by out-of-phase wavelengths. If he could somehow bring direct and diffracted images back into phase, perhaps these aberrations would disappear. He developed a glass plate with tiny grooves etched in it to be placed in the focal plane of the telescope; he called this a phase plate. His experiment worked: when looking through the phase plate, the out-of-phase areas became clearly visible. Zernike published these findings in 1934, and by 1935 he was applying these same principles to microscopes , which he knew had optical problems that were similar to telescopes.

Although the practical applications of Zernike's findings seem obvious now, it was some years before he could find a manufacturer for a phase-contrast microscope. He first approached the German company, Carl Zeiss, in 1932. Finally, in 1941, Carl Zeiss agreed to produce the instrument. But it was not untilAmerican troops arrived in Germany in 1945 and discovered photomicrographs taken by a phase-contrast microscope that Zernike's instrument received worldwide attention. When he won the Nobel Prize in 1953, the phase-contrast microscope was cited as being a key to insights into cancer research.

Though the phase-contrast microscope is considered his crowning achievement, Zernike is also known for other work. Early in his career he invented the Zernike galvanometer, an instrument used to detect and measure small electrical currents. The Zernike polynomials are a method he developed regarding the wave theory of light, and are widely used by mathematicians. He also made many improvements in infrared and ultraviolet spectroscopy , as well as in the construction of the electromagnet.

Although Zernike stayed at his alma mater for his entire career, he was a visiting professor of physics at the Johns Hopkins University in Baltimore in 1948. In 1950 he was elected to the Royal Microscopical Society of London, and he was presented with the Rumford Medal of the British Royal Society in 1952.

Zernike married Dora van Bommel van Vloten in 1929. The couple had two children; his wife died in 1944. In 1954, Zernike married L. Koperberg-Baanders. He retired in 1958 and died in Groningen on March 10, 1966.

see also Microscopes; Spectroscopy.

ZERNIKE, FRITS

(b. Amsterdam, Netherlands, 16 July 1888; d. Naarden, near Amsterdam, 10 March 1966)

theoretical physics, technical physics.

Zernike’s father, headmaster of an elementary school, was well-known for his textbooks on arithmetic. While a chemistry student at Amsterdam University, Zernike won two gold medals for prize questions in mathematics and physics. In 1913 he became assistant to the astronomer J. C. Kapteyn at the University of Groningen, where he held various academic positions until his retirement at the age of seventy.

Zernike’s dissertation, "L’opalescence critique, theorie et experiments" (Amsterdam, 1915), is still worth reading. In 1915 he succeeded L. S. Ornstein as lecturer in theoretical physics at Groningen: in 1920 he became full professor: and in 1941 his chair was extended to include mathematical and technical physics and theoretical mechanics. He became a member of the Royal Netherlands Academy of Sciences at Amsterdam in 1946, and seven years later he won the Nobel Prize in physics.

Widely read and wide-ranging in his work, Zernike paid especial interest to three main areas: statistical physics and fluctuation phenomena, the construction of instruments, and interference of light waves. He was an able speaker and possessed an extraordinary combination of mathematical and instrument-making skill, always using these abilities to bring out, in the simplest way, the essential physical principles of a problem or the characteristics of an instrument. Later his methods often found wider application.

For instance, in the wave theory of light he introduced the set of polynomials orthogonal on a circle that is widely used by mathematicians under the name of Zernike polynomials. In molecular statistics he introduced the concept of a radial distribution function g(r) giving the mean number density of molecular centers around an arbitrary molecular center. Through Fourier inversion it leads to exact expressions for the scattering of light or the diffraction of X rays in liquids, and its use has been extended to other fields.

In constructing instruments Zernike always started from first principles and worked out the significant mathematical consequences. This procedure often led to unexpected results-for instance, the discovery that for a sensitive moving-coil galvanometer, the moment of inertia of the mirror has to be roughly three times that of the moving coil. The usual technique of instrument makers had been just the opposite: making the mirror quite small compared with the moving coil. He also worked on the ultracentrifuge and thermoelectrical devices.

Experimental and mathematical skill also formed the base of Zernike’s best-known contribution, the method of phase contrast in wave theory. It is now generally used in microscopy but has a much wider application: it was used, for instance, in his study of errors in telescope mirrors and in the Groningen Rowland grating (in the winter of 1930-193 1, the first application of phase contrast). It led Zernike to study the "degree of coherence" in light and to approach what is now called holography. The essential point is that in the "primary" diffraction pattern, already studied by Abbe, a phase difference between the central part and the wings of the pattern exists-and can be manipulated to increase the contrast in the image or to reconstruct the object in three dimensions.

It has rightly been said that the spirit of Zernike’s work is reminiscent of Lord Rayleigh’s, to whom Zernike often referred in his lectures.

BIBLIOGRAPHY

Lists of Zernike’s writings are included in the obituaries by Tolansky and by Prins and Nijboer (see below). An autobiographical article is “How I Discovered Phase Contrast,” in Les prix Nobel en1953 (Stockholm, 1953), 107-114.

See H. Brinkman, in Nederlands tijdschrift voor natuurkunde, 24 (1958), 139; J. A. Prins, in Jaarboek der Koninklijke Nederlandsche akademie van wetenschappen (1965-1966), 370-377: J. A. Prins and B. R. A. Nijboer, in Nederlands tijdschrift voor natuurkunde, 19 (1953), 314-328; S. Tolansky, in Biographical Memoirs of Fellow’s of the Royal Society (London), 13 (1967), 393-402, with portrait; and N. G. van Kampen, in Nature, 211 (1966), 465-also see 172 (1953), 938.

J. A. Prins

Zernike, Frits (1888–1966) Dutch physicist. In 1935, Zernike developed the phase contrast microscope, in which objects being viewed (often living-cell biological specimens) take on a different colour from their surroundings. For this work, he received the 1953 Nobel Prize in physics.