It is probably unfortunate that physics and chemistry over were separated. Chemistry is the science of atoms and of the way they com bine. Physics deals with the interatomic forces and with the large-scale properties of matter resulting from those forces. So long as chemistry was largely empirical and nonmathematical, and physics had not learned how to treat small-scale atomic forces, the two sciences seemed widely separated. But with statistical mechanics and the kinetic theory on the one hand and physical chemistry on the other, the two sciences began to come together. Now that statistical mechanics has led to quantum theory and wave mechanics, with its explanations of atomic interactions, there is really nothing separating them any more. A few years ago, though their ideas were close together, their experimental methods were still quite different chemists dealt with things in test tubes, making solutions, pre cipitating and filtering and evaporating, while physicists measured every thing with galvanometers and spectroscopes. But even this distinction has disappeared, with more and more physical apparatus finding its way into chemical laboratories. A wide range of study is common to both subjects. The sooner we realize this the better. For want of abetter name, since Physical Chemistry is already preempted, we may call this common field Chemical Physics. It is an overlapping field in which both physicists and chemists should be trained. There 4 seems no valid reason why their training in it should differ. This book is an attempt to incorporate some of the material of this common field in a unified presentation. What should be included in a discussion of chemical physics Logi cally, we should start with fundamental principles. We should begin with mechanics, then present electromagnetic theory, and should work up to wave mechanics and quantum theory.