point out, that, in well-authenticated ghost-stories of a supposed supernatural character, the ideas which had been rendered so unduly intense as to induce spectral illusions, might be traced to such fantastical objects of prior belief as are incorporated in the various systems of superstition, which for ages have possessed the minds of the vulgar.

In the present and far most considerable part of this treatise, the research is of a novel kind. Since apparitions are ideas' equalling or exceeding in vividness actual impressions, there ought to be some important and definite laws of the mind which have given rise to this undue degree of vividness. It was chiefly, therefore, for the purpose of explaining such laws that this dissertation was written.

An investigation of this kind the late Dr Ferriar had evidently in view, when he wrote the first pages of his work, entitled, A Theory of Apparitions. But it must be confessed, that this entertaining author has been far more successful in affording abundant evidence of the existence of morbid impressions of this nature, without any sensible external agency, than in establishing, as he proposed, a general law of the system, to which the origin of spectral impressions could be referred. "It is a well-known law," he remarks, "that the impressions produced on some of the external senses, especially on the eye, are more durable than the application of the impressing cause." This statement comprises the whole of the writer's theory of apparitions; and the brevity with which it is given is in exact conformity with the abruptness of its dismissal; for, after being applied to explain one or two

cases only of mental illusions, numerous other instances of the kind are related, but the theory is not honoured with any farther notice. This neglect, which probably arose from the reasonable doubts subsequently entertained by the author himself, of the sufficiency of his hypothesis, or, rather, of the generality of its application, will render it the less necessary for me to bestow upon it any attention. The truth is, that a proper theory of apparitions embraces the consideration, not of one law only, but of many laws of the human mind; on which account, it will be absolutely impossible to proceed in this inquiry, until certain principles of thought are at the same time perspicuously stated. This object, therefore, I shall attempt, although, from the restricted nature of the present dissertation, it will be impossible for me to enter into any explanation and defence of the metaphysical views which may be advanced, in contradiction to opinions that deserve the highest respect, in deference to the names with which they are associated. Any one, also, conversant in the smallest degree with researches of this kind, will be but too well aware of the difficulties which they involve. For this reason, I must request every indulgence, whenever I shall have occasion to state, as briefly as the subject will allow me, certain primary laws of the mind, which, from the maturest consideration, I have been induced to advocate.

CHAPTER II.

INDICATIONS AFFORDED BY MENTAL EXCITEMENTS, THAT ORGANS OF SENSATION ARE THE MEDIUM THROUGH WHICH PAST FEELINGS ARE RENOVATED.

"Phantasma enim est sentiendi actus; neque differt a sensione, aliter quam fieri differt a factum esse." HOBBES.

My first object is to give validity to the conjecture which I threw out on a former occasion, that past feelings are renovated through the medium of organs of sense. It will, indeed, be impossible to proceed much farther in our researches, until this curious subject has met with due consideration.

In the commencement of these researches, I set out with stating the view of the late Dr Brown respecting the mind, namely, that it was simple and indivisible, and that every mental feeling was only the mind itself existing in a certain state.

Sensations were, at the same time, considered as states of the mind induced by objects actually present, and acting upon the organs of sense. I need scarcely add, that such mental states admit of various degrees of intensity, vividness, or faintness; first, from the greater or less susceptibility of any sensitive structure to actual impressions; and, secondly, from

the greater or less force with which material causes act upon our organs of sense.

It has also been pointed out, that pleasurable feelings, from whatever source they may be derived, depend upon a freedom being given to the expansive power of the circulating mass, while pain is induced by any cause which tends to deprive it of this vital property. But regarding the instrumentality by which such changes are induced, I have already adverted to the conclusions of Dr Wilson Philip, deduced from his experiments, namely, that "the nervous system consists of parts endowed with the vital principle, yet capable of acting in concert with inanimate matter; and that in man, as well as in certain well-known animals, electricity is the agent thus capable of being collected by nervous organs, and of being universally diffused for purposes intimately connected with the animal economy throughout every part of the human system." But without founding any system on this particular view, I considered the nerves as not only the natural dispensers of that influence upon which the opposite qualities of pleasure and pain depend, but, likewise, as the natural source, whence all the degrees of vividness imparted through the medium of the circulating fluid to our various sensations, had their origin. At the same time it was shewn, that under certain morbid circumstances, substances affecting the blood, without the intervention of the nerves, had the same effect of exciting or even depressing the feelings of the mind. I shall therefore now add, that from the different circumstances of the circulating fluid, as it supplies different structures

of the human frame, arise our various susceptibilities of sensation.

In what, then, consists a susceptibility to ideas? This question has been already in part answered. Since an idea is nothing more than a past feeling renovated with a diminution of vividness proportional to the intensity of the original impression, we are justified in entertaining the suspicion, that the susceptibility of the mind to sensations and ideas ought to refer to similar circumstances of corporeal structure. Accordingly, there can be little or no doubt, as I have before hinted, that organs of sense are the actual medium through which past feelings are renovated; or, that when, from strong mental excitements, ideas have become more vivid than actual impressions, this intensity is induced by an absolute affection of those particular parts of the organic tissue on which sensations depend. Thus, the mere idea of some favourite food is well known to occasionally excite the salivary glands no less than if the sapid body itself were actually present, and stimulating the papillæ of the fauces.

After this explanation, there can be little difficulty in understanding why strong mental excitements should occasionally, though rarely, restore impressions of touch, which are indeed seldom so proportionally vivid as renovated feelings of vision or of hearing. Such appears to have been the case when Sir Humphry Davy subjected himself to the vivifying influence of the nitrous oxide. He confesses to an increased sensibility of touch, and occasionally notices what he names a tangible extension. In Dr