- Category : Science-Physics
- Type : MGP
- Profile : 2/4 - Hermit / Opportunist
- Definition : Split - Small (14,15)
- Incarnation Cross : RAX Explanation 4
Leonard Salomon Ornstein (November 12, 1880, Nijmegen, the Netherlands — May 20, 1941, Utrecht, the Netherlands) was a Dutch physicist.
He studied theoretical physics with Hendrik Antoon Lorentz at University of Leiden. He subsequently carried out Ph.D. research under the supervision of Lorentz, concerning an application of the statistical mechanics of Gibbs to molecular problems.
In 1914 he was appointed professor of physics, as successor of Peter Debye, at University of Utrecht. Among his doctoral students was Jan Frederik Schouten. In 1922 he became director of Physical Laboratory (Fysisch Laboratorium) and extended his research interests to experimental subjects. His measurements concerning intensities of spectral lines brought Physical Laboratory in the international limelight.
He is also remembered for the Ornstein-Zernike theory (named after Ornstein and Frederik Zernike) concerning correlation functions and the Ornstein-Uhlenbeck process a stochastic process.
Together with Gilles Holst, director of Philips Research Laboratories (Philips Natuurkundig Laboratorium), he was the driving force behind establishing the Dutch Physical Society (Nederlands Natuurkundig Vereniging, NNV) in 1921. From 1939 until November 1940 he was Chairman of this Society. From 1918 until 1922 Ornstein was Chairman of the Dutch Zionist Society (Nederlandse Zionistische Vereniging).
Immediately after the involvement of the Netherlands in the World War II (see Battle of the Netherlands), a friend from the United States of America, the astronomer Peter van de Kamp, offered to bring Ornstein and his family to America. However, Ornstein did not accept this offer, since, as he put it, he would not leave his laboratory in Utrecht. Owing to his Jewish heritage, Ornstein was summarily dismissed from University in September 1940; he was even barred from entering his own laboratory. In November 1940, he was officially dismissed from University. On his own initiative, on November 29, 1940, Ornstein withdrew his membership of the Dutch Physical Society. During this period he increasingly distanced himself from public life, to the degree that he no longer wished to receive guests at home. Ornstein died on May 20, 1941, six months after being barred from University.
One of the five buildings of Department of Physics of University of Utrecht, the Ornstein Laboratorium, is named in his honor.