Early Experiments in Quantum Physics

Despite his success with it, quantum theory needed a more solid foundation than Bohr s intuition. Arnold Sommerfeld in Munich was an early contributor to that work after the war the brightest young men, searching out the growing point of physics, signed on to help. Bohr remembered the period as a unique cooperation of a whole generation of theoretical physicists from many countries, an unforgettable experience. He was lonesome no more. 

X-ray absorption and emission spectroscopy is a field with a distinguished history. At the beginning, i.e., from 1913 to the early thirties, these spectroscopies were dedicated to a systematic exploration of the atomic structure in the context of the periodic system of the elements. The intense work of numerous spectroscopists, which contributed prominently to the foundations of modern atomic physics and to the development of quantum theory, was reviewed in the classical books Spektroskopie der Rontgenstrahlen by M. Siegbahn (1913) and X-Rays in Theory and Experiment by Compton and Allison (1935). 

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