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Paul Sophus Epstein Papers

Identifier: 10067-MS

Scope and Content of Collection

The Paul Epstein papers consist of general and family correspondence, personal and biographical material, manuscripts, articles, technical notes, notebooks, reprints of Epstein's work including books, audiotapes, and reels.


  • 1898-1966



The collection is open for research. Researchers must apply in writing for access.

Publication Rights

Copyright may not have been assigned to the California Institute of Technology Archives. All requests for permission to publish or quote from manuscripts must be submitted in writing to the Head of the Archives. Permission for publication is given on behalf of the California Institute of Technology Archives as the owner of the physical items and is not intended to include or imply permission of the copyright holder, which must also be obtained by the reader.


Epstein was the first European-trained physicist to come to Caltech on a permanent basis. Recruited by Robert A. Millikan in 1921, he was one of a generation of prominent mathematical physicists who laid the foundations for modern atomic physics. Having studied and worked in Moscow, Munich, Zurich and Leyden before settling permanently in the United States, Epstein had wide personal and scientific contacts.

Epstein was born in 1883 in Warsaw to a moderately well-to-do Jewish family. He grew up in Minsk and later attended the Imperial University of Moscow, where he received B.S. and M.S. degrees. Foreseeing the Russian Revolution, he left Moscow to continue his studies in theoretical physics in Munich under Arnold Sommerfeld. His early research was in the theory of electromagnetic waves, particularly the theory of their diffraction. He received his Ph.D. at the outbreak of World War I, with the thesis "Über die Beugung an einem ebenen Schirm unter Berücksichtigung des Materialeinflusses" ("Diffraction from a Plane Screen...," 1914).

Though held as a civil prisoner in Germany during the war, he nonetheless continued to do research in the problems of the quantum theory of atomic structure based on classical mechanics. An important paper from this period is "Zur Theorie des Starkeffektes" ("The Theory of the Stark Effect," Ann. der Physik 50, 1916). In 1919, with the end of the war, Epstein was able to take up an appointment as Privatdocent at the University of Zurich. Upon applying for this position he wrote a paper (Habilitationsschrift) applying the quantum theory to optics, which caused a stir ("Anwendungen der Quantenlehre in der Theorie der Serienspektren," Die Naturwissenschaften 17, 1918).

As early as 1910 or 1911, Epstein had become interested in pyschoanalysis as a remedy for depression and associated physical symptoms. This interest eventually led to a meeting with Freud in Switzerland, circa 1911-12. Later Epstein was instrumental in founding the Los Angeles Institute of Pyschoanalysis. His knowledge of and practical involvement in this field lasted throughout his life.

Having lost most of his inherited means during the war and in need of a paying position, Epstein went to Leyden in 1921 to become assistant to H. A. Lorentz. There he met Millikan, who invited him to come to the newly created California Institute of Technology. Epstein arrived in Pasadena on a blistering September day in 1921, knowing very little English. He was to remain at Caltech until his retirement in 1953 at the age of 70. During this time he taught substantially all of the advanced courses in mathematical and theoretical physics.

At Caltech Epstein's research continued on Bohr's form of the quantum theory, which culminated in 1922 with the publication of four papers, three in the Zeitschrift für Physik and one in The Physical Review. Later he participated in the development of quantum mechanics. An important paper in this connection appeared in the Physical Review in 1926: "The Stark Effect from the Point of View of Schrödinger's Quantum Theory." In 1930, Epstein was elected to the National Academy of Sciences.

Epstein's range of interests was wide. He devoted considerable attention to borderline problems involving physics and other sciences, for example, his papers "Zur Theorie des Radiometers" (1929), "Reflection of Waves in an Inhomogeneous Absorbing Medium" (1930), and "On the Air Resistance of Projectiles" (1931). He wrote two important articles on general subjects outside of physics, both published in the Los Angeles literary/philosophical journal Reflex: "The Frontiers of Science" (June, 1935) and "The Uses and Abuses of Nationalism" (November, 1935). He also maintained a number of literary and artistic contacts, including Upton Sinclair.

Although not a Zionist, Epstein was deeply interested in Jewish affairs. He was a friend and supporter of the mathematician Abraham Fraenkel, a longtime resident of Jerusalem, who played a major role in the organization of secondary and advanced education in Israel. Epstein was active for many years in the Friends of the Hebrew University of Jerusalem and was President of the Southern California Chapter.

After his retirement from Caltech, Epstein served as a consultant to several large industrial firms. Among the many reports written by him at this time, especially significant is his "Theory of Wave Propagation in a Gyromagnetic Medium" (Reviews of Modern Physics 28, 1956).

Paul Epstein died at his home in Pasadena on February 8, 1966, at the age of 83.


17.25 linear feet (40 boxes)

Language of Materials



Epstein was a physicist at California Institute of Technology from 1921-1953; he taught advanced courses in mathematical and theoretical physics. Collection includes general and family correspondence; personal and biographical material; notebooks; manuscripts; class notes by a Caltech student; books, mostly technical and in Russian; reprints of Epstein's writings.


The collection contains materials spanning the period from Epstein's high school days in Minsk, beginning around 1898, up to shortly before his death in 1966. Included is general and family correspondence; personal and biographical material; notebooks containing a variety of subject matter; a large number of manuscripts, including articles, lectures and miscellaneous writings on both technical and nontechnical matters; a set of class notes by a Caltech student; books, mostly in Russian and of a technical nature; and a large quantity of reprints of writings by Epstein himself. Epstein's extensive collection of reprints by others has been preserved separately from his papers.

Epstein's correspondence appears in Russian, German, and English. Important individual correspondents include A. Berliner, N. Bohr, M. Born, P. Ehrenfest, A. Einstein, Sigmund Freud, G. Jaffe, A. Lande, M. von Laue, H. Lorentz, R. Oppenheimer, M. Planck, E. Rutherford, E. Schrödinger, A. Sommerfeld, and H. Weyl.

Acquisition Information

The Paul Epstein collection was given to the Caltech Archives in 1977 by his widow, Mrs. Alice Epstein.

Guide to the Papers of Paul Sophus Epstein, 1898-1966
Processed by Charlotte Erwin.
Description rules
Describing Archives: A Content Standard
Language of description
Script of description

Repository Details

Part of the California Institute of Technology Archives and Special Collections Repository

1200 East California Blvd.
MC B215-74
Pasadena California 91125 United States of America
(626) 395-2704