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It would be an endless task to ransack the pages of antiquity, for instances of this kind. The apparition of the Genius

Brutus, and of the Fury to Dion, cannot be doubted. We may be allowed, however, to enquire, whether the improved state of physiology affords any glimpse of light on this subject, and whether such extraordinary and terrific impressions cannot be explained, from the known laws of the animal economy, independent of supernatural causes, in the examples furnished by profane history.

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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 pecu

. liar 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,

1. 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.

§ 1. It is a well-known law of the human ceconomy, 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has been withdrawn from the object, is fa-. miliar 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.* 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

# The experiments in this Essay appear to have been suggested, by those of Mariotte, Le Cat, and Bernouilli.

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 wliat 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 admić 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, hę 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.

Dr. R. Darwin seems to believe, that it is from habit only, and want of attention, that we do not see the remains of former impressions, or the muscæ volitantes, on all objects.* Probably, this is an instance, in which the error of external sensation is corrected by experience, like the deceptions of perspective, which are undoubtedly strong in our childhood, and are only detected by repeated observation.

“ After having looked,” says Dr. Dar“ win, “ long at the meridian sun, in

making some of the preceding experi“ ments, till the disk faded into a pale

blue, I frequently observed a bright “ blue spectrum of the sun in other

* Zoonomia, Sect. xi. 2.

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