Hedwig Kohn

Kohn in her laboratory, 1912

Hedwig Kohn (April 5, 1887 – 1964), was a pioneer in physics and one of only three women who obtained Habilitation (the qualification for university teaching in Germany) in physics before World War II. She and the other two physicists, Lise Meitner and Hertha Sponer, were forced to leave Germany during the Nazi regime.

Early life

Born in Breslau, Province of Silesia, Kohn was the daughter of Georg Kohn (1850–1932), a wholesale merchant of fine cloth, and Helene Hancke (1859–1926), a member of a well-to-do Breslau family. Hedwig entered the university in Breslau in 1907. She obtained her doctorate in physics under Otto Lummer in 1913, and was soon appointed as Lummer's assistant. She stayed at the university's Physics Institute during World War I, and obtained her Habilitation in 1930.

Escape from Germany

Kohn was dismissed from her position in 1933, due to Nazi regulations which barred Jews from government service. She survived by fulfilling contracts for applied research in the illumination industry until 1938, when she found herself without work or financial resources and came very close to being a victim of the Holocaust. Finally, she was offered temporary positions at three women's colleges in the United States through the aid of Rudolf Ladenburg, Lise Meitner, Hertha Sponer, the American Association of University Women (AAUW), and many others. She obtained a visa and left Germany in July 1940.

Life in America

The journey to her first position, at the Women's College of the University of North Carolina in Greensboro, took Kohn through Berlin, Stockholm, Leningrad, Moscow, Vladivostok, Yokohama, San Francisco, and Chicago. She taught at the Women's College of the University of North Carolina for a year and a half. In 1942, she began teaching at Wellesley College in Massachusetts. She retired in 1952 as a professor. Upon her retirement, Hertha Sponer, then professor of physics at Duke University in Durham, North Carolina, offered her a position as a research associate. Kohn set up a laboratory at Duke and resumed research, guiding two graduate students to their doctorates and recruiting two post-doctoral fellows. She worked there until very shortly before her death, in 1964.

Contributions to science

Kohn was trained by Lummer in the quantitative determination of the intensity of light, both from broad-band sources, such as a "black body", and from the discrete emission lines of atoms and molecules. She further developed such methods and devised ways of extracting information from intensity measurements and from emission line shapes. She wrote 270 pages in the leading physics text of the 1930s and 1940s in Germany, received one patent, and wrote numerous articles in scientific journals, some of which were still being cited into the 1980s. Two of her students became professors in Germany.

Selected bibliography

Mueller-Pouillets Lehrbuch der Physik. (II. Auflage), unter Mitwirkung zahlreicher Gelehrter herausgegeben von A. Eucken, O. Lummer (+), E. Waetzmann. In fuenf Baenden: I. Mechanik und Akustik; II. Lehre von der strahlenden Energie (Optik); III. Waermelehre; IV. Elektizitaet und Magnetismus; V. Physik der Erde und des Kosmos (einschl. Relativitaetstheorie). Braunschweig: 1925–1929. Band II, Zweite Hälfte, Erster Teil (Volume II, 2. half, 1. part), volume editor Karl W. Meissner: 1929.
Kohn, Hedwig. In Band II, Chapter 22, Photometrie. 1104–1320; Chapter 25, Temperaturbestimmung auf Grund von Strahlungsmessungen. 1428–1469; Chapter 26, Ziele und Grenzen der Lichttechnik. 1470–1482.
Kohn, Hedwig, Umkehrmessungen an Spektrallinien zur Bestimmung der Gesamtabsorption und der Besetzungszahlen angeregte Atomzustände, Phys. Zeitschrift 1932: 33, 957-963.