Originally published in 1951 and the first English book on the subject, this textbook is aimed at both the specialist and non-specialist alike and provides a thorough and detailed introduction on the principles that underlie the action of automatic controls, servo-mechanisms and regulators. The early chapters provide a solid foundation to the theory of control and are in the most part descriptive, introducing fundamental terminology and explaining the principles, which underlie the operation of all control systems, whilst in the last three chapters more advanced techniques are used to give an account of the methods employed by control engineers. Modern contributions to the theory at the time are included and questions are set at the end of each chapter. Giving a 'historical summary of the main landmarks in the development of control theory', this book will be of value to anyone with an interest in the history of engineering.