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CHAP.

IV.

Of Hearing.

danger sufficient to impress fear for so far is terror from being a source of the sublime, that the smallest degree of fear instantly annihilates it, as far as relates to the person frightened; and to that person only is the object terrible. To all others it is merely powerful, or capable of inspiring terror to those who are more susceptible of it. But of this more shall be said in the proper place.

CHAPTER V.

OF SIGHT.

1. SIGHT, as well as hearing, is produced by immediate contact of the exciting cause with the organ; which exciting cause is the light reflected, from the objects seen, upon the retina of the eye; the pictures upon which, by some impressions or irritations upon the optic nerves, the modes of which muft be for ever unknown to us, are conveyed to the mind, and produce the sense of vision, the most valuable of all our senses.

2. The sensation, therefore, felt upon opening the eyes for the first time, must necessarily be that of the objects seen touching them; as it proved to be in the case of the boy, who, at the age of fourteen or thereabouts, obtained his sight, after having been blind from his birth, by an operation performed upon his eyes by Cheselden. For a considerable time, and till the sense of seeing had been aided and corrected by that of touch, all the objects seen appeared only as variations of light acting upon the eye for the colours of objects are only different rays of light variously reflected from their surfaces*; and their visible pro

See Newton's Theory of Light and Colours,

CHAP

V.

Of Sight.

CHAP.

V.

Of Sight.

jection is merely gradation and opposition of
light and shadow; which, in round and undu-
lating bodies, are intermixed gradually; and,
in those of angular forms, abruptly.
It is,

therefore, only by habit and experience that we
form analogies between the perceptions of vi-
sion and those of touch, and thus learn to dis-
cover projection by the eye: for, naturally, the
eye sees only superficial dimension; as clearly
appears in painting and all other optical decep-
tions, which produce the appearance of projec-
tion or thickness upon a flat surface. The
faculty, however, when acquired, as it is in all
adult persons who have seen from their birth, is
exercised as readily and instantaneously as any
natural faculty whatsoever *.

3. The perception of visible projection being thus artificial, that of visible distance must necessarily be so likewise: for distance is only projection extended. Accordingly we find that our improved perception of visible distance extends no further than that experience, by which it has been formed and improved : for of the immense distances of the heavenly bodies from each other, and from the earth, we discover nothing by looking at them; they all appearing to occupy the surface of one

* See Dr. Reid's Essay on the Mind, where a very clear and full explanation of the theory of vision is given.

blue vault, whose diameter is that of the visible horizon; which the sun, moon, and stars seem equally to touch at their rising and setting. Hence the notion of these luminaries setting in, and rising from the ocean has universally prevailed through all nations: and it has not been by the evidence of improved sense; but by the calculations and discoveries of improved intellect, that the error has been removed.

4. The visible magnitude of bodies depending entirely upon their distance from the eye, we have, of course, as imperfect and inadequate perceptions of it from the unaided sense of vision, as we have of distance. The pen, which I hold between my fingers, occupies a greater space in the retina, when only a foot from the eye, than the spire of Salisbury does, when seen at the distance of a mile; and, consequently, as far as concerns the mere organ of sense, is bigger: for though the real magnitude of an object, which is perceived by a computation of its distance, rendered instantaneous by habit, may affect the imagination, the visible dimensions of it alone are impressed upon the eye; and, consequently, can alone affect the sensation excited.

5. Hence we may learn how to estimate the theory of an eminent writer, who supposes that objects of large dimensions are sublime,

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СИАР..

V.

because the great number of rays, which they emit, crowd into the eye together, or in quick Of Sight. succession, and produce a degree of tension in the membrane of the retina, which, approaching nearly to the nature of what causes pains must (in his own words) produce an idea of the sublime *. But, to say nothing of this assumed connection between the causes of pain and the ideas of the sublime, the slightest knowledge of optics would have informed him that the sheet of paper, upon which he was writing, being seen thus close to the eye, reflected a greater, and more forcible mass of light; and, consequently, produced more irritation and tension, than the Peak of Teneriffe or Mount St. Elias would, if seen at the distance of a few miles:-yet, surely he would not say that the sheet of paper excited more grand and perfect ideas of the sublime.

6. That the irritation, produced in the membranes of the eye by vision, is proportioned to the quantity of light poured into it, we may perceive by the dilation and contraction of that membrane called the iris; which always expands its circle, as the quantity of light, to which it is exposed, is diminished, and contracts it, as it is increased. In the eyes of animals formed to see with a very small quan

* Sublime and Beautiful, Part IV. f. ix.

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