STUDENTS of The Power-Book Library have long called for the present volume in that series, and it is hoped that the book now presented may justify their impatience and maintain the high standard of their expressed opinions concerning the author's studies in personal development. The field of human psychology is so vast, so complex, and so constantly enlarging and enriching by reason of advancing civilization, that no work on the subject can pretend to be more than an introduction. The great central things in mental science, however, are slowly being worked clean of errors and brought into the light of clearness and distinctness. It is also more and more recognized that the science has very practical bearings upon every department of our life. The book before you claims only to be a contribution. But the author believes that a part of this contribution is essentially new. Like all the Power-Books, the work all along insists that the student apply its suggestions to his practical life. And he is assured that both knowledge and power will follow his efforts.