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Numberless other illustrations of the same general fact occur to me; but the following is, I think, one of the most striking. I mention it, in preference to the rest, as it appears to me to connect the doctrine in question with fome principles which are now universally admitted among philosophers.

The distinction between the original and the acquired perceptions of fight, is familiarly known to every one who has the slightest acquaintance with the elements of optics. That this sense, prior to experience, conveys to us the notion of extension in two dimensions only, and that it gives us no infor. mation concerning the distances at which objects are placed from the eye, are propositions which nobody, I presume, in the present state of science, will be dif. posed to controvert. In what manner we are enabled, by a comparison between the perceptions of fight and those of touch, to extend the province of the former sense to a variety of qualities originally perceived by the latter sense only, optical writers have explained at great length ; but it is not neceffary for my present purpose to enter into any particular details with respect to their reasonings on the subject. It is sufficient for me to remark, that, according to the received doctrine, the original perceptions of sight become, in consequence of experience, figns of the tangible qualities of external objects, and of the distances, at which they are placed from the organ; and that, although the knowledge we obtain, in this manner, of thefe qualities and distances, seems, from early and constant habits, to be an instantaneous perception ; yet, in many cases, it implies an exercise of the judgment, being founded on a compara ison of a variety of different circumstances.

From these principles, it is an obvious consequence, that the knowledge we obtain, by the eye, of the tangible qualities of bodies, involves'the exercise of conception, according to the definition of that pow. which has already been given. In ordinary discourse, indeed, we ascribe this knowledge, on account of the instantaneousness with which it is obtained, to the power of perception ; but if the common doctrine on the subject be juft, it is the result of a complex operation of the mind ; comprehending, first, the perception of those qualities, which are the proper and original objects of sight; and, secondly, the conception of those tangible qualities of which the original perceptions of fight are found from experience to be the signs. The notions, therefore, we form, by means of the eye, of the tangible qualities of bodies, and of the distances of these objects from the organ, are mere conceptions; strongly, and indeed indiflolubly, associated, by early and constant habit, with the original percep:ions of sight.

When we open our eyes on a magnificent prospect, the various distances at which all its different parts are placed from the eye, and the immense extent of the whole scene before us, seems to be perceived as immediately, and as instantaneously, by the mind, as the coloured surface which is painted on the retina. The truth, however, unquestionally is, that this variety of distance, and this immensity of extent, are not objects of sense but of conception ; and the notions we form of them when our eyes are open, differ from those we should form of them with our eyes shut, only in this, that they are kept steadily in the view of the mind, by being strongly associated with the sensations of colour, and with the original perceptions of sight.-This observation will be the more readily admitted, if it be considered, that, by a skilful imitation of a natural landscape, in a common shew-box, the mind may be led to form the fame notions of variety of diftanice, and even of immense extent, as if the original scene were presented to our senses : and that, although, in this case, we have a speculative conviction that the sphere of our

vision only extends to a few inches ; yet so strong is the association between the original perceptions of fight, and the conceptions which they habitually produce, that it is not possible for us, by any effort of our will, to prevent these conceptions from taking place.

From these observations it appears, that when the conceptions of the mind are rendered steady and permanent, by being strongly associated with any sensible impression, they cominand our belief no less than our actual perceptions ; and, therefore, if it were possible for us, with our eyes shut, to keep up, for a length of time, the conception of any sensible object, we should, as long as this effort continued, believe that the object was prefent to our senses.

It appears to me to be no flight confirmation of these remarks, that although, in the dark, the illufions of imagination are much more liable to be mistaken for realities, than when their momentary effects on the belief are continually checked and cor. rected by the objects which the light of day presents to our perceptions; yet, even total darkness is not so alarming to a person impressed with the vulgar stories of apparitions, as a faint and doubtful twilight, which affords to the conceptions an opportunity of fixing and prolonging their existence, by attaching themselves to something which is obscurely exhibited to the eye.-In like manner, when we look through a fog, we are frequently apt to mistake a crow for a man ; and the conception we have, upon such an occasion, of the human figure, is much more distinct and much more steady, than it would be possible for us to form, if we had no fensible object before us; insomuch that when on a more attentive obierva. tion, the crow shrinks to its own dimensions, we find it i.npossible, by any effort, to conjure up the phantom which a moment before we seemed to perceive.

If these observations are admitted, the effects which

exhibitions of fictitious distress produce on the mind, will appear less wonderful, than they are supposed to. be. During the representation of a tragedy, I acknowledge, that we have a general conviction that the whole is a fiction ; but, I believe, it will be found, that the violent emotions which are fometimes produced by the diftreffes of the stage, take their rise, in most cases, from a momentary belief, that the dis. trefses are real. I say, in most cases ; because I acknowledge, that independently of any such belief, there is something contagious in a faithful expression of any of the passions.

The emotions produced by tragedy are, upon this fuppofition, somewhat analogous to the dread we feel when we look down from the battlement of a tower. * In both cases, we have a general conviction, that there is no ground for the feelings we experi. ence; but the momentary influences of imagination are fo powerful as to produce these feelings, before reflection has time to come to our relief.

* With respect to the dread which we feel in looking down from the battlement of a tower, it is curious to remark the effects of habit in gradually destroying it. The manner in which habit operates in this case, seems to be by giving us a command over our thoughts, so as to enable us to withdraw our attention from the precipice before us, and direct it to any other object at pleasure. It is thus that the mason and the sailor not only can take precall. tions for their own safety, but remain completely masters of them. selves in situations where other men, engrossed with their imaginary danger, would experience a total suspension of their faculties. Any'strong passion which occupies the mind produces, for the moment, the same effect with habit. A person alarmed with the apprehension of fire, has been known to escape from the top of a house, by a path which, at another time, he would have considered as impracticable; and soldiers, in mounting a breach, are said to have Sometimes found their way to the enemy, by a route which ap.. peared inaccessible after their violent passions had subsided.

CHAPTER FOURTH.

Of Abstraction.

SECTION I.

General observations on this Faculty of the Mind.

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THE origin of appellative, or, in other words, the origin of those classes of objects which, in the schools, are called genera, and species, has been consid some philosophers as one of the most difficult lems in metaphysics. The account of it which is given by Mr. Smith, in his Dissertation on the Ori. gin of Languages, appears to me to be equally simple and satisfactory

“ The assignation” (says he) “ of particular names, “ to denote particular objects ; that is, the institution

of nouns fubftantive ; would probably be one of “ the first steps towards the formation of Language. “ The particular cave, whose covering sheltered the 6 favage from the weather ; the particular tree, " whole fruit relieved his hunger ; the particular “ fountain, whose water allayed his thirst; would 's first be denominated by the words, cave, tree, foun“ tain ; or by whatever other appellations he might « think proper, in that primitive jargon, to mark “ them. Afterwards, when the more enlarged ex“perience of this favage had led him to observe, “ and his neceffary occasions obliged him to make 6 mention of, other caves, and other trees, and other “ fountains; he would naturally bestow upon each 6 of those new objects, the same name by which he “ had been accustomed to express the similar object

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