It would not be proper to claim for this budget of psychological studies a pre-arranged unity of design or a serial unfoldment of argument. They represent the unity of interest of a worker in a special field, who has his favorite excursions and vistas, who at times ventures away from the beaten paths and as frequently returns along those already traversed, but with varying purposes, and reaches the outlook from a different approach. There seems enough of singleness of purpose in the several presentations to warrant their inclusion in a single volume with a common name. There is enough also to make it pertinent to explain that the occasional repetitions of the same line of thought seemed less objectionable than frequent reference from one essay to another. All of the essays have been previously printed in the pages of various scientific and popular magazines; and I have accordingly to acknowledge the courtesy of the several publishers, which makes possible their appearance in their present form. The essays have, however, been subjected to a critical revision, in the hope of increasing their acceptability in regard to form and material, and of giving them a setting appropriate to the interests of the present-day readers of psychological literature. Both in the selection of the essays from a larger group of published studies, and in their arrangement and elaboration, I have attempted to bear in mind the several current interests in questions of this type, and to direct these interests formatively along lines which seem to me fertile in promise and sterling in value. In the recasting thus made necessary it has come about (markedly in two cases, The Problems of Psychical Research and The Logic of Mental Telegraphy) that some of the essays have been entirely rewritten and bear only a generic resemblance to their former appearance.