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idea, disagreeable only by affociation, has the cause of its ill effect on the paffions evident enough at the first impreffion; in ordinary cafes, it is indeed frequently loft; but this is, because the original affociation was made very early, and the confequent impreflion repeated often. In our inftance, there was no time for fuch an habit; and there is no reason to think that the ill effects of black on his imagination were more owing to its connexion. with any disagreeable ideas, than that the good effects of more cheerful colours were derived from their connexion with pleafing ones. They had both probably their effects from their natural operation.

SECT. XVI.

WHY DARKNESS IS TERRIBLE.

IT may be worth while to examine how darknefs can operate in fuch a manner as to cause pain. It is obfervable, that ftill as we recede from the light, nature has fo contrived it, that the pupil is enlarged by the retiring of the iris, in proportion to our recefs. Now, inftead of declining from it but a little, fuppofe that we withdraw entirely from the light; it is reasonable to think, that the contraction of the radial fibres of the iris is proportionably greater; and that this part may by great darkness come to be fo contracted, as to ftrain

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strain the nerves that compose it beyond their natural tone; and by this means to produce a painful fenfation. Such a tenfion it feems there certainly is, whilst we are involved in darkness; for in fuch a state whilft the eye remains open, there is a continual nifus to receive light; this is manifeft from the flashes and luminous appearances which often seem in these circumftances to play before it; and which can be nothing but the effect of fpafms, produced by its own efforts in purfuit of its object; feveral other ftrong impulfes will produce the idea of light in the eye, befides the fubftance of light itself, as we experience on many occafions. Some who allow darkness to be a cause of the fublime, would infer, from the dilation of the pupil, that a relaxation may be productive of the fublime, as well as convulfion: but they do not I believe confider that although the circular ring of the iris be in some sense a sphincter, which may poffibly be dilated by a fimple relaxation, yet in one respect it differs from moft of the other fphincters of the body, that it is furnished with antagonist muscles, which are the radial fibres of the iris: no fooner does the circular muscle begin to relax, than these fibres, wanting their counterpoife, are forcibly drawn back, and open the pupil to a confiderable widenefs. But though we were not apprized of this, I believe any one will find, if he opens his eyes and makes an effort to fee in a dark

a dark place, that a very perceivable pain enfues. And I have heard fome ladies remark, that after having worked a long time upon a ground of black, their eyes were fo pained and weakened, they could hardly fee. It may perhaps be objected to this theory of the mechanical effect of darkness, that the ill effects of darkness or blacknefs feem rather mental than corporeal: and I own it is true, that they do fo; and fo do all those that depend on the affections of the finer parts of our fyftem. The ill effects of bad weather appear often no otherwise, than in a melancholy and dejection of fpirits; though without doubt, in this cafe, the bodily organs fuffer first, and the mind through these organs.

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THE EFFECTS OF BLACKNESS.

BLACKNESS is but a partial darkness; and therefore it derives fome of its powers from being mixed and furrounded with coloured bodies. In its own nature, it cannot be confidered as a colour. Black bodies, reflecting none, or but a few rays, with regard to fight, are but as so many vacant spaces difperfed among the objects we view. When the eye lights on one of these vacuities, after having been kept in fome degree of tenfion by the play of the adjacent colours upon it, it fuddenly falls

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into a relaxation; out of which it as fuddenly recovers by a convulfive fpring. To illuftrate this; let us confider, that when we intend to fit on a chair, and find it much lower than we expected, the fhock is very violent; much more violent than could be thought from so flight a fall as the difference between one chair and another can poffibly make. If, after defcending a flight of stairs, we attempt inadvertently to take another ftep in the manner of the former ones, the shock is extremely rude and disagreeable; and by no art can we caufe fuch a fhock by the fame means when we expect and prepare for it. When I fay that this is owing to having the change made contrary to expecta tion; I do not mean folely, when the mind expects. I mean likewife, that when an organ of fenfe is for fome time affected in fome one manner, if it be fuddenly affected otherwife, there enfues a convulfive motion; fuch a convulfion as is caufed when any thing happens against the expectance of the mind. And though it may appear strange that fuch a change as produces a relaxation, should immediately produce a fudden convulfion; it is yet most certainly fo, and fo in all the fenfes, Every one knows that fleep is a relaxation; and that filence, where nothing keeps the organs of hearing in action, is in general fitteft to bring on this relaxation; yet when a fort of murmuring founds difpofe a man to fleep, let these founds cease

fuddenly,

fuddenly, and the perfon immediately awakes; that is, the parts are braced up suddenly, and he awakes. This I have often experienced myfelf, and I have heard the fame from obferving perfons. In like manner, if a perfon in broad day-light were falling afleep, to introduce a fudden darknefs would prevent his fleep for that time, though filence and darkness in themselves, and not fuddenly introduced, are very favourable to it. This I knew only by conjecture on the analogy of the fenses when I first digefted these observations; but I have fince experienced it. And I have often experienced, and fo have a thousand others, that on the first inclining toward fleep,we have been fuddenly awakened with a moft violent ftart; and that this ftart was generally preceded by a fort of dream of our falling down a precipice: whence does this ftrange motion arife, but from the too fudden relaxation of the body, which by some mechanism in nature reftores itfelf by as quick and vigorous an exertion of the contracting power of the muscles! The dream itself is caused by this relaxation; and it is of too uniform a nature to be attributed to any other caufe. The parts relax too fuddenly, which is in the nature of falling; and this accident of the body induces this image in the mind. When we are in a confirmed state of health and vigour, as all changes are then lefs fudden, and lefs on the extreme, we can feldom complain of this difagreeable fenfation.

SECT.

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