Early interest in science; training in physics and graduate work at Johns Hopkins, courses, books ,seminars,informal atmosphere,1927-33; summer work in spectroscopy labortory at National Bureau of Standards,1929; interest in elementary particles, attraction of nuclear physics,1933;post-doctoral work with G.Breit on pair theory; New York University 1933-34; potential well model and its application to experimental results,1933-35; studies at Bohr Institute,Copenhagen 1934-35; discussions in Copenhagen on electrodynamics; role of experimental results in formulation of Bohr’s concept of compoun