DORGELO, HENDRIK BEREND

(b. Dedemsvaart. Netherlands, 9 February 1894; d. Eindhoven, Netherlands, 6 March 1961)

physics.

Dorgelo contributed greatly to the scientific and technical development of the Netherlands, partly as a research physicist and partly as a teacher and organizer of technical physics. His primary field of research was experimental spectroscopy; his name is associated mainly with the spectroscopical investigations of multiplet spectra. These investigations proved important in the transition from the old quantum theory to the new quantum mechanics.

Having completed secondary school Dorgelo worked in the academic year 1912–1913 as a primary school teacher in his hometown. During World War I he served as a reserve army officer. After the demobilization in 1918, Dorgelo went to Utrecht to study physics at the university. He was supervised by Leonard S. Ornstein, director of the Physical Institute, which Dorgelo joined in 1922 as an assistant. Under Ornstein’s guidance he specialized in the study of the multiplet lines recently discovered by the Spanish physicist Miguel A. Catalàn. His dissertation, submitted in 1924, dealt with the intensities of the components of multiple spectral lines.

In order to measure the intensity of the multiplet lines with sufficient accuracy, in 1923 Dorgelo developed a new photographic technique that made possible precise determination of the intensity ratios of neighboring spectral lines as well as of lines widely separated in wavelength. He used the improved technique on his own in collaboration with Ornstein and Herman C. Burger, then chief assistant in physics at the University of Utrecht. In 1924 Dorgelo found that the intensity ratios of doublets and triplets can be represented by the ratios of small integers (2:1 for the alkali doublet, 5:3:1 for the triplet of alkaline earths). He also was able to confirm experimentally a suggestion of Arnold Sommerfeld that the scheme might also hold for higher multiplets.

The intensity rules discovered by the Utrecht spectroscopists were relevant to the atomic models of the old quantum theory, especially the vector core model of Sommerfeld and Alfred Landé, and to the correspondence principle of Niels Bohr. Inspired by Sommerfeld, Dorgelo and Burger succeeded, in 1924. in relating the observed intensity ratios to the inner quantum number (j), introduced formally by Sommerfeld in 1920 and used by Lande (as J = j +1/2) in his atomic model They also showed that the intensity ratios o( multiplet components arising from atoms in the same initial state do not depend on how the atoms are excited. Dorgelo and Burger arrived at several “sum rules”, one of which states that the sum of the intensities of the components of a multiplet associated with the same initial state is proportional to the value of the inner quantum number (J) of the state.

An experimentalist at heart, Dorgelo did not try to justify the sum rules theoretically; Werner Heisenberg did so in 1924. This was a triumph for the old quantum theory and for the correspondence principle. However, it forced Heisenberg to sharpen the arguments based on the correspondence principle and thus contributed to the process that led him to quantum mechanics less than a year later.

After having obtained his doctorate, Dorgelo spent three years at the Philips Incandescent Lamp Company at Eindhoven. He thus had to stop his work on multiplet intensities at a time when it looked most promising. At Eindhoven, Dorgelo investigated the metastable states of inert gases, carrying further the work of Friedrich Paschen and Karl Meissner. He was the first to determine the lifetime of metastable neon, a result obtained in 1925.

In 1927 Dorgelo was appointed professor of physics at the Technical University of Delft, a position he held for twenty-nine years. During this period he worked on spectroscopy gas discharges, electron optics, and X-ray analysis. Much of the work was done in collaboration with Dutch industrial firms such as Philips and Shell. Though technically valuable, Dorgelo’s research at Delft did not reach the level of scientific quality of that done at Utrecht, Much of his time was spent on administration and teaching. He was a popular teacher and wrote several textbooks for students of technical physics. An efficient organizer, Dorgelo was instrumental in the construction of the electron microscope at Delft in the late 1930’s, one of the first effective instruments of its kind.

Dorgelo ended his career as rector of the Technical University at Eindhoven, a post he held from 1956 until his death.

BIBLIOGRAPHY

I. Original Works. “Die Intensitat der Mehrfachlinien” in Zeitschrift für Physik13 (1923), 206–210; “Die Intensität Mehrfacher Spektrallinien,” ibid., 22 “(1924), 170–177; “Beziehungen zwischen inneren Quantenzahlen und Intensitäen von Mehrfachlinien.” ibid., 23 (1924). 258–266. written with Herman C. Burger;’ Die pholographische Spektralpholometrie, ’ in Physikalische Zeitschrift, 26 (1925), 756–794: “Die Lebensdauer der metastabilen s₃ und s₅ Zustände des Neons,” in Zeitschrift für Physik, 34 (1925), 766–774.

II. Secondary Works. M. J. Druyvesteyn, ’ In memoriam Prof. Dr. H. B. Dorgelo, ’ in Nederlands tijdschrift voor natuurkunde, 27 (1961), 181–184; A. C. S. van Heel.’ H. B. Dorgelo vijfentwintig jaar hoogleraar, ’ ibid., 18 (1952), 26–30: and Jagdish Mehra and Helmut Rechenherg. The Historical Development of Quantum Theory, 1 pt. 2 (New York, 1982).

Helge Kragh