"The Absorption Of Radiation By Multiply Periodic Orbits, And Its Relation To The Correspondence Principle And The Rayleigh-Jeans Law. Part I. Some Extensions Of The Correspondence Principle. // II. Calculation Of Absorption By Multiply Periodic Orbits." Both papers in: the Physical Review.

VAN VLECK, J.H. "The Absorption Of Radiation By Multiply Periodic Orbits, And Its Relation To The Correspondence Principle And The Rayleigh-Jeans Law. Part I. Some Extensions Of The Correspondence Principle. // II. Calculation Of Absorption By Multiply Periodic Orbits." Both papers in: the Physical Review, 2nd series, vol 24, July-December 1924, the entire full volume for the half year offered, 704pp. The two Van Vleck papers run consecutively, pp 330-346 and 347-365 (pp 330-365). Bound in stout green cloth. Provenance: U.S. Geological Survey, and then to the Library of Congress—there is a USGS bookplate and a rubber stamp on the front free flyleaf. FINE copy. [++] "Van Vleck made his greatest contribution to the old quantum theory in 1924, when he conceived his correspondence principle for absorption. He demonstrated that in the limit of high quantum numbers there would be a correspondence between absorption by classical, multiply periodic systems, and by their quantum analogues. His proof depended on interpreting net absorption in the quantum theory as the difference between gross absorption and stimulated emission of radiation (an interpretation prompted by a remark of Breit’s). Van Vleck was particularly pleased that his classical theory reproduced the quantum result without the need for stimulated emission, which he referred to as "negative absorption.Van Vleck’s theory of absorption by multiply periodic systems was consistent with the newly derived Kramers theory of dispersion, and it convinced Bohr that his correspondence principle applied not only to emission but also to absorption. Further, Van Vleck’s 1924 calculation made use of several of the ideas that Werner Heisenberg used in his matrix mechanics a year later. Van Vleck’s work, however, did not lead in the direction of matrix mechanics. His intent was to explain quantum phenomena (especially “negative absorption”) in classical terms rather than to devise an internally consistent quantum theory. --Complete Dictionary of Scientific Biography online.…