Not intended for the uninitiated lay mind, but keyed to the reader who knows something of developments in physical science and seeks clarification on specific points of basic interest. It starts with a brief outline of the methods of thought, specifically leading to determinism and statistics as basic methods. Then follows sections on Radiation, the two theories of light; Matter, the kinetic theory, etc., The Nuclei of Atoms, radioactivity, etc., Matter and Radiation, X-rays, Gamma rays, etc., Modern Quantum Mechanics.