It is well known, that in certain diseases of the brain, such as delirium and insanity, spectral delusions take place, even during the space of many days. But it has not been generally observed, that a partial affection of the brain may exist, which renders the patient liable to such imaginary impressions, either of sight or sound, without disordering his judgment or memory. From this peculiar condition of the sensorium, I conceive that the best supported stories of apparitions may be completely accounted for. To render this inquiry more perspicuous, I shall consider, I. The general law of the system, to which the origin of the spectral impressions may be referred: II. The proof of the existence of morbid impressions of this nature, without any sensible external agency: III. The application of these principles to the best-authenticated examples of apparitions. § I. It is a well-known law of the human œconomy, that the impressions produced on some of the external senses, especially on the eye, are more durable than the application of the impressing cause. The effect of looking at the sun, in producing the impression of a luminous globe, for some time after the eye has been withdrawn from the object, is familiar to every one. This subject has been so thoroughly investigated by the late Dr. Darwin, that I need only to refer the reader to his treatise on ocular spectra.[1] In young persons, the effects resulting from this permanence of impression are extremely curious. I remember, that about the age of fourteen, it was a source of great amusement to myself. If I had been viewing any interesting object in the course of the day, such as a romantic ruin, a fine seat, or a review of a body of troops, as soon as evening came on, if I had occasion to go into a dark room, the whole scene was brought before my eyes, with a brilliancy equal to what it had possessed in day-light, and remained visible for several minutes. I have no doubt, that dismal and frightful images have been presented, in the same manner, to young persons, after scenes of domestic affliction, or public horror. From this renewal of external impressions, also, many of the phænomena of dreams admit an easy explanation. When an object is presented to the mind, during sleep, while the operations of judgment are suspended, the imagination is busily employed in forming a story, to account for the appearance, whether agreeable or distressing. Then the author enjoys the delight of perusing works of infinite wit and elegance, which never had any real existence, and of which, to his utter mortification, he cannot recollect a single line, next morning; and then the Bibliomane purchases illuminated manuscripts, and early editions on vellum, for sums so trifling, that he cannot conceal his joy from the imaginary vender.