Kuhn Losses Regained: Van Vleck from Spectra to Susceptibilities

“The chemist is apt to conceive of the physicist as some one who is so entranced in spectral lines that he closes his eyes to other phenomena” (Van Vleck, 1928a, p. 493). This observation was made by the American theoretical physicist John H. Van Vleck (1899– 1980) in an article on the new quantum mechanics in Chemical Reviews. Only a few years earlier, Van Vleck himself would have fit this characterization of a physicist to a tee. Between 1923 and 1926, as a young assistant professor in Minneapolis, he spent much of his time writing a book-length Bulletin for the National Research Council (NRC) on the old quantum theory (Van Vleck, 1926b). As its title, Quantum Principles and Line Spectra, suggests, this book deals almost exclusively with spectroscopy. Only after a seemingly jarring change of focus in his research, a switch to the theory of electric and magnetic susceptibilities in gases, did he come to consider his previous focus myopic. In 1927–28, now a full professor in Minnesota, he published a three-part paper on susceptibilities in Physical Review (Van Vleck, 1927a,b, 1928b). This became the basis for a second book, The Theory of Electric and Magnetic Susceptibilities (Van Vleck, 1932b), which he started to write shortly after he moved to Madison, Wisconsin, in the fall of 1928.