One of the most interesting phases of comparative ghost-lore is the study of the intricate personality of specters. With respect to dual personality the late supernatural stories are curiously reminiscent of the animistic belief that a ghost is a double of the mortal, a vapory projection of his actual body, to be detached at will during life and permanently at death. I do not know of any instances of doubles in classical literature, nor is the idea used in Gothic romance. Likewise Shakespeare's ghosts are all spirits of persons safely dead. It remained for the modern writer with his expertness in psychology and psychiatry to evoke the ghosts of the living persons, the strange cases of dual personality and of separate personalities supernaturally merged into one, and those inexplicable ghosts of subliminal memories. All these forms appear in elusive analysis, in complex suggestiveness, in modern uncanny stories, and constitute one of the distinct marks of advance over the earlier types. The double, a frequent figure in English fiction, bears a resemblance to the Doppelgänger of German folk-tales. Numerous examples of dual personality, of one being appearing in two forms, are seen, with different twists to the idea, yet much alike. It has been suggested that these stories have their germinal origin in Calderon's play,[134] where a man is haunted by himself. Poe's _William Wilson_ is a tense and tragic story of a man pursued by his double, till in desperation he kills him, only to realize that he has slain his better self, his conscience. His duplicate cries out, "Henceforward thou art also dead, dead to the world, to Heaven and to hope! In me thou didst exist and in my death, see by this thine image, which is thine own, how utterly thou hast murdered thyself!" Stevenson's _Markheim_ shows in the person of the stranger the incarnate conscience, an embodiment of a man's nobler self that leads him through the labyrinth of self-examination to the knowledge of the soul's truth. The stranger tests the murderer by offering him a way of escape, by suggesting further crime to him, by showing him relentlessly what the consequence of each act will be, till in despair Markheim, realizing that his life is hopelessly weak and involved, decides to surrender it rather than to sin further. Step by step the nameless visitor leads him, Markheim shuddering back from the evil that is suggested, thinking the stranger is a demonic tempter, till at last the transfigured face shows him to be the nobler angel. Stevenson's _Dr. Jekyll and Mr. Hyde_ is, of course, the best-known instance of this sort of dual personality, this walking forth in physical form of the evil in one's own nature, with a separate existence of its own. No writer could hope to express this idea more powerfully than has been done in this chemical allegory, this biological dissection of the soul. The thrill of suspense, the seemingly inexplicable mystery, the dramatic tenseness of the closing