"Version: 20201101"--Title page verso.Includes bibliographical references.1. Preliminaries -- 1.1. On the sizes of atoms -- 1.2. Spectroscopy, the quantum concept, and the Balmer formula -- 1.3. Circular orbit forces and energetics -- 1.4. The radiative collapse problem2. The Bohr model I : hydrogenic atoms -- 2.1. Niels Bohr : early life and paper I of the trilogy -- 2.2. The Bohr model : orbiā¦