The projected analysis has been crowned with success. The fumes of superstition have been driven off, and the ghosts have been reduced to rational elements. All trace of supernatural agency has vanished; and in its place are found three principles—one physical, two psychical—by the help of which every conceivable ghost may in future be alternately decomposed and recompounded by the merest tyro. The first of which I shall describe the nature and operation is a psychical truth, already known to most persons of education. It is of very general use in ghost-building; it forms the immediate _personnel_ of every ghost; and is of so active a nature that alone, or assisted by a little credulity, it is enough to constitute the simplest kind—a common fetch. Mixed with a dose of mental anxiety, or as much remorse as will lie on the point of a dagger, it will form a troublesome retrospective ghost. The second principle—a physical one, less generally known—is the basis of that sturdy apparition the churchyard ghost, which it will turn out in very fair style aided by fancy alone; but, to perfect the illusive result, the co-operation of the first principle is necessary. The third, an entirely new one, is the foundation of real ghosts—that is, of ghosts which announce unexpected events, distant in space or time; the same principle is concerned in true dreams, and in second-sight. The first of the three principles adverted to is the physiological fact that, when the blood is heated, the nervous system overstrained, or digestion out of sorts, the thereby directly or sympathetically disordered brain is liable to project before us illusory forms, which are coloured and move like life, and are so far undistinguishable from reality. Sometimes a second sense is drawn into the phantasmagoria, and the fictitious beings speak as you do. Almost always the illusion stops there. But in one or two marvellous cases, the touch has been involved in the hallucination, and the ghost has been tangible. These phenomena are termed sensorial illusions. The visual part of them, the first and commonest, has been the most attended to. The cause immediately producing it appears to be an affection, not of the organ of vision, but of that part of the brain in which the nerves of seeing take their origin. This organ it is which in health realizes our sensations of colour, and converts them into visual perceptions. Like other parts of the brain, it is stored with memories of its past impressions, ready to be evoked—either pure and true by conception, or any how combined by fancy. In perfect health, a chance moment of warm recollection will call up from this source the once familiar face transiently, but how distinctly! In its morbid state, the beings it projects before us are for the most part strangers, just as the personages we meet in our dreams are exceptionally only our living and present acquaintance.