The Fundamental Constants of Atomic Physics.- I. Introduction.- a) General plan.- b) The atomic constants.- c) The need for the method of least squares.- II. History of our knowledge of the atomic constants.- a) Description of important experiments.- b) Progress on the atomic constants in the period 1929 to 1949.- c) High precision measurements since 1950.- III. Least squares adjustment of the atomic constants.- a) Theory and application of the method of least squares.- b) Least squares adjustment for 1955.- Addendum.- References.- Quantum Mechanics of One- and Two-Electron Systems.- I. The hydrogen atom without external fields.- a) Nonrelativistic theory.- b) Dirac theory.- c) Radiative and other corrections.- II. The helium atom without external fields.- a) Nonrelativistic theory.- b) Relativistic theory.- III. Atoms in external fields.- a) Zeeman effect.- b) Stark effect in hydrogen.- c) Stark effect in helium.- IV. Interaction with radiation.- a) Discrete spectrum.- b) The photoeffect.- c) Bremsstrahlung.- Sachregister (Deutsch-Englisch).- Subject Index (English-German).