Numberless other illuftrations of the fame general fact occur to me; but the following is, I think, one of the moft ftriking. I mention it, in preference to the reft, as it appears to me to connect the doctrine in question with fome principles which are now univerfally admitted among philofophers.

The diftinction between the original and the acquired perceptions of fight, is familiarly known to every one who has the flighteft acquaintance with the elements of optics. That this fenfe, prior to experience, conveys to us the notion of extenfion in two dimenfions only, and that it gives us no information concerning the distances at which objects are placed from the eye, are propofitions which nobody, I prefume, in the prefent ftate of science, will be dif pofed to controvert. In what manner we are enabled, by a comparison between the perceptions of fight and thofe of touch, to extend the province of the former sense to a variety of qualities originally perceived by the latter fenfe only, optical writers have explained at great length; but it is not neceffary for my prefent purpose to enter into any particular details with refpect to their reafonings on the fubject. It is fufficient for me to remark, that, according to the received doctrine, the original perceptions of fight become, in confequence 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 diftances, feems, from early and conftant habits, to be an inftantaneous perception; yet, in many cafes, it implies an exercife of the judgment, being founded on a comparifon of a variety of different circumstances.

From these principles, it is an obvious confequence, 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 difcourse, indeed, we afcribe this knowledge, on account of the inftantaneousness with which it is obtained, to the power of perception; but if the common doctrine on the fubject be juft, it is the refult of a complex operation of the mind; comprehending, first, the perception of thofe qualities, which are the proper and original objects of fight; and, fecondly, the conception of those tangible qualities of which the original perceptions of fight are found from experience to be the figns. The notions, therefore, we form, by means of the eye, of the tangible qualities of bodies, and of the distances of thefe objects from the organ, are mere conceptions; ftrongly, and indeed indiffolubly, affociated, by early and constant habit, with the original perceptions of fight.

When we open our eyes on a magnificent profpect, the various distances at which all its different parts are placed from the eye, and the immenfe extent of the whole scene before us, feems to be perceived as immediately, and as inftantaneoufly, by the mind, as the coloured furface which is painted on the retina. The truth, however, unquestionably is, that this variety of diftance, and this immensity of extent, are not objects of fenfe but of conception; and the notions we form of them when our eyes are open, differ from thofe we fhould form of them with our eyes fhut, only in this, that they are kept steadily in the view of the mind, by being strongly affociated with the fenfations of colour, and with the original perceptions of fight. This obfervation will be the more readily admitted, if it be confidered, that, by a skilful imitation of a natural landscape, in a common fhew-box, the mind may be led to form the fame notions of variety of distance, and even of immenfe extent, as if the original scene were prefented to our fenfes and that, although, in this cafe, we have a speculative conviction that the sphere of our

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vifion only extends to a few inches; yet fo ftrong is the affociation between the original perceptions of fight, and the conceptions which they habitually produce, that it is not poffible for us, by any effort of our will, to prevent thefe conceptions from taking place.

From these observations it appears, that when the conceptions of the mind are rendered fteady and permanent, by being ftrongly affociated with any fenfible impreffion, they command our belief no lefs than our actual perceptions; and, therefore, if it were poffible for us, with our eyes fhut, 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 fenfes.

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 miftaken for realities, than when their momentary effects on the belief are continually checked and corrected by the objects which the light of day prefents to our perceptions; yet, even total darkness is not fo alarming to a perfon impreffed with the vulgar ftories 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 fomething which is obfcurely 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 fuch an occafion, of the human figure, is much more diftinct and much more steady, than it would be poffible for us to form, if we had no fenfible object before us; infomuch that when on a more attentive obfervation, the crow shrinks to its own dimenfions, we find it impoffible, by any effort, to conjure up the phantom which a moment before we feemed to perceive.

If these observations are admitted, the effects which

exhibitions of fictitious diftrefs produce on the mind, will appear less wonderful, than they are fuppofed 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 moft cafes, from a momentary belief, that the dif treffes are real. I say, in moft cafes; because I acknowledge, that independently of any fuch belief, there is fomething contagious in a faithful expreffion of any of the paffions.

The emotions produced by tragedy are, upon this fuppofition, fomewhat analogous to the dread we feel when we look down from the battlement of a tower.* In both cafes, 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 precautions for their own safety, but remain completely masters of themselves 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 appeared inaccessible after their violent passions had subsided.

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CHAPTER FOURTH.

Of Abstraction.

SECTION I.

General obfervations on this Faculty of the Mind.

by

THE origin of appellative, or, in other words, the origin of those claffes of objects which, in the schools, are called genera, and fpecies, has been confid fome philofophers as one of the most difficult lems in metaphyfics. The account of it which is given by Mr. Smith, in his Differtation on the Origin of Languages, appears to me to be equally fimple and fatisfactory.

"The affignation" (fays he) " of particular names, "to denote particular objects; that is, the inftitution " of nouns fubftantive; would probably be one of "the first steps towards the formation of Language. "The particular cave, whose covering fheltered the "favage from the weather; the particular tree, "whofe fruit relieved his hunger; the particular "fountain, whose water allayed his thirft; would "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

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perience of this favage had led him to observe, "and his neceffary occafions obliged him to make ❝mention of, other caves, and other trees, and other "fountains; he would naturally bestow upon each "of those new objects, the fame name by which he "had been accustomed to exprefs the fimilar object

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