Haas, Wander Johannes De

(b. Lisse, Netherlands, 2 March 1878; d. Bilthoven, Netherlands, 26 April 1960)

physics.

De Haas was first educated to be a notary, but then studied physics at Leiden University where he was assistant to H. Kamerlingh Onnes. In 1912 he wrote his doctoral thesis, “On the Compressibility of Hydrogen Gas at Low Temperatures.” After working in Berlin and at the Physikalische Reichsanstalt in Potsdam, de Haas was assistant to H. A. Lorentz, his father-in-law and at that time director of the physics division in the Teyler Institute at Haarlem. De Haas first became a professor of physics at the Technische Hogeschool, Delft, in 1917. He left for Groningen University in 1922, and from 1924 to 1948 was professor at Leiden University.

Together with W. H. Keesom, de Haas was director of the Kamerlingh Onnes Laboratory of Experimental Physics, initially one of the few laboratories in the world where low-temperature work was systematically carried out. In 1922 he became a member of the Royal Netherlands Academy of Science and Letters at Amsterdam. His health was never very good, but with the help of his wife (a theoretical physicist) he was able to maintain his international scientific contacts and to execute the duties of his laboratory directorate. Although he specialized in magnetism, de Haas found time to dabble in many different branches of physics.

The general trend of de Haas’s work is shown by his early work at Berlin. There, in 1915, he performed an experiment suggested by Einstein, known as the Einstein-de Haas effect: the sudden magnetization of a suspended iron cylinder in a vertical solenoid causes a momentary torque in the cylinder. The theoretical foundation for this effect is that the unidirectional aligning of the spinning electrons in the magnetic field also aligns their mechanical moments, resulting in a torque pulse.

The experimental results of later scientists indicated that the ratio of the magnetic to the mechanical moment differed by a factor of two from the original classic expectation. This is the fundamental “halfinteger quantization” for the spinning electron, as compared to the integer quantization for the orbital moment, a difference which runs through the whole development of modern atomic physics.

Pioneering with simple apparatus was de Haas’s favorite conception of experimental physics. But he was also aware of the need for organization and routine techniques that had been introduced in the Leiden laboratory by Kamerlingh Onnes. Together with E. C. Wiersma, de Haas was a leader in the production of extremely low temperatures by adiabatic demagnetization of precooled magnetized material. Other lines of research led to the so-called Van Alphen-de Haas effect on the anomalous behavior of the resistance of a metal crystal in a magnetic field, and to magneto-optic researches on crystals, mainly done and published by Jean Becquerel. During World War II de Haas succeeded in preventing a large amount of uranium ore from being taken to Germany. After the war this uranium was useful in starting the Netherlands-Norway joint establishment for nuclear energy at Kjeller (Norway).

BIBLIOGRAPHY

For information on the Einstein-de Haas effect see “Experimenteller Nachweis der Ampèreschen Molekularströme,” in Verhandlungen der Deutschen physikalischen Gessellschft, 17 (1915), 152–170, written with Einstein. Also see E. Beck, Annalen der Physik, 60 (1919), 109. Other of de Haas’s publications are in Proceedings. K. Nederlandse akademie van wetenschappen and in Physica (The Hague). A biography of de Haas may be found in Jaarboek van de K. Akademie van wetenschappen gevestigd te Amsterdam (1959–1960), 300; on the World War II period see also S. A. Goudsmit, ALSOS (Schuman, N.Y., 1947), where de Haas is called “Professor X.”

J. A. Prins