Summary: Publisher Summary 1 Reprint of a classic 1950 text presenting underlying principles and theory in a manner understandable to engineers and physicists whose primary interest is in applying the ideas and methods to concrete physical problems. Annotation copyright Book News, Inc. Portland, Or.   Publisher Summary 2 Presents underlying principles and theories using an easily understood approach. Focuses specifically on those features of the problems in which nonlinearity results in a variety of distinctive new phenomena that can be treated by techniques both interesting and instructive in themselves and which do not require the use of sophisticated mathematics. Recent work discussed includes the endeavors of Levinson and Smith on the existence and uniqueness of the periodic solution in a general case of the self-excited type, Haag and Dorodnitsyn on asymptotic developments and quantities associated with relaxation oscillations. Along with 5 appendices containing rigorous existence and uniqueness proofs, readers are both implicitly and explicitly supplied with hints regarding new problems to be tackled plus numerous ideas and techniques that can be used to solve them.