Bjerknes, Vilhelm Frimann Koren, 1862-1951, Norwegian physicist and pioneer in modern meteorology. He worked on applying hydrodynamic and thermodynamic theories to atmospheric and hydrospheric conditions in order to predict future weather conditions. Bjerknes was professor at the universities of Oslo (1907-12, 1926-32); Leipzig (1912-17); and Bergen (1917-26), where he set up a geophysical institute. His work in meteorology and on electric waves was important in the early development of wireless telegraphy. His publications include Fields of Force (1906) and the classic book On the Dynamics of the Circular Vortex with Applications to the Atmosphere and to Atmospheric Vortex and Wave Motion (1921); he is also coauthor with J. W. Sandström (on Vol. I) and with T. Hesselberg and O. Devik (on Vol. II) of Dynamic Meteorology and Hydrography (Vol. I and II, 1910-11; Vol. III, 1951). He evolved a theory of cyclones known as the polar front theory with his son Jakob Aall Bonnevie Bjerknes, 1897-1975, who became a U.S. citizen in 1946. Jakob Bjerknes served as professor of meteorology at the Univ. of Bergen (1931-40) and at the Univ. of California (from 1940).