The following pages represent in the main a discussion of certain celebrated mysteries, as viewed in the light of the discoveries set forth in the writer's earlier work "The Riddle of Personality."That dealt, it may briefly be recalled, with the achievements of those scientists whose special endeavor it is to illumine the nature of human personality. On the one hand, it reviewed the work of the psychopathologists, or investigators of abnormal mental life; and, on the other hand, the labors of the psychical researchers, those enthusiastic and patient explorers of the seemingly supernormal in human experience. Emphasis was laid on the fact that the two lines of inquiry are more closely interrelated than is commonly supposed, and that the discoveries made in each aid in the solution of problems apparently belonging exclusively in the other.To this phase of the subject the writer now returns. The problems under examination are, all of them, problems in psychical research: yet, as will be found, the majority in no small measure depend for elucidation on facts brought to light by the psychopathologists. Of course, it is not claimed that the last word has here been said with respect to any one of these human enigmas. But it is believed that, thanks to the knowledge gained by the investigations of the past quarter of a century, approximately correct solutions have been reached; and that, in any event, it is by no means imperative to regard the phenomena in question as inexplicable, or as explicable only on a spiritistic basis.Before attempting to solve the problems, it manifestly was necessary to state them. In doing this the writer has sought to present them in a readable and attractive form, but without any distortion or omission of material facts.