Wenzel, Kramers, Brillouin

The Bohr theory was extended in various ways, particularly by Arnold Sonunofeld. This old quantum theory is still used as a tool to understand quantum mechanics and to obtain LQ)proximate solutions. The old quantum theory deals with, for example, the Bohr-Sonunerfeld quantum condition (quantization of action along a path) EBK theory of A. Einstein, L. Brillouin, and J. B. KeUer and JWKB theory of H. Jeffreys, G. Wenzel, H. A. Kramers, and L. Brillouin. Unfortunately, there is no possibiUty of giving justice to the various aspects of old quantum theory in this book. 

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