ABSTRACT
This chapter describes experiments using external electric and magnetic fields, which enable further investigation of atomic structure. The vast majority of the primary experimental investigations of atomic structure were carried out using gas discharge tubes. The development of the original Stern-Gerlach apparatus can give precise values for atomic parameters by studying the frequencies associated with transitions between levels. The atomic beam magnetic resonance apparatus first conceived by Rabi enables transitions between levels in the hyperfine structure of the atomic system which could never be resolved by optical spectroscopy. Quite early in the history of experimental spectroscopy it was noted by Zeeman and others that a constant magnetic field imposed on an atomic discharge tube produced a splitting of spectral lines. The 'anomalous' Zeeman effect occurs much more commonly, when other types of transition are observed.
