idea, disagreeable only by association, has the cause of its ill effect on the passions evident enough at the first impression; in ordinary cases, it is indeed frequently lost; but this is, because the original association was made very early, and the consequent impression repeated often. In our instance, there was no time for such 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 pleasing ones. They had both probably their effects from their natural operation.

SECT. XVI.

oby WHY DARKNESS IS TERRIBLE.

IT may be worth while to examine how darkness can operate in such a manner as to cause pain. It is observable, that still as we recede from the light, nature has so contrived it, that the pupil is enlarged by the retiring of the iris, in proportion to our recess. Now, instead of declining from it but a little, suppose 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 so contracted, as to strain

T 4

strain the nerves that compose it beyond their natural tone; and by this means to produce a painful sensation. Such a tension it seems there certainly is, whilst we are involved in darkness; for in such a state whilst the eye remains open, there is a continual nisus to receive light; is manifest from the flashes and luminous appearances which often seem in these circumstances to play before it; and which can be nothing but the effect of spasms, produced by its own efforts in pursuit of its object; several other strong impulses will produce the idea of light in the eye, besides the substance of light itself, as we experience on many occasions. Some who allow darkness to be a cause of the sublime, would infer, from the dilatation of the pupil, that a relaxation may be productive of the sublime, as well as a convulsion: but they do not I believe consider that although the circular ring of the iris be in some sense a sphincter, which may possibly be dilated by a simple relaxation, yet in one respect it differs from most of the other sphincters of the body, that it is furnished with antagonist muscles, which are the radial fibres of the iris: no sooner does the circular muscle begin to relax, than these fibres, wanting their counterpoise, are forcibly drawn back, and open the pupil to a considerable wideness. But though we were not apprized of this, I believe any one will find, if he opens his eyes and makes an effort to see in a dark place, that a very perceivable pain ensues. And I have heard some ladies remark, that after having worked a long time upon u a ground of black, their eyes were so pained and weakened, they could hardly see. It may perhaps be objected to this theory of the mechanical effect of darkness, that the ill effects of darkness or blackness seem rather mental than corporeal: and I own it is true, that they do so; and so do all those that depend on the affections of the finer parts of our system. The ill effects of bad weather appear often no otherwise, than in a melancholy and dejection of spirits; though without doubt, in this case, the bodily organs suffer first, and the mind through these organs.

In

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

into a relaxation; out of which it as suddenly recovers by a convulsive spring. To illustrate this; let us consider, that when we intend to sit on a chair, and find it much lower than was expected, the shock is very violent; much more violent than could be thought from so slight a fall as the difference between one chair and another can possibly make. If, after descending a flight of stairs, we attempt inadvertently to take another step in the manner of the former ones, the shock is extremely rude and disagreeable; and by no art can we cause such a shock by the same means when we expect and prepare for it. When I say that this is owing to having the change made contrary to expectation; I do not mean solely, when the mind expects. I mean likewise, that when any organ of sense is for some time affected in some one manner, if it be suddenly affected otherwise, there ensues a convulsive motion; such a convulsion as is caused when any thing happens against the expectance of the mind. And though it may appear strange that such a change as produces a relaxation, should immediately produce a sudden convulsion; it is yet mos most certainly so, and so in all the senses. Every one knows that sleep is a relaxation; and that silence, where nothing keeps the organs of hearing in action, is in general fittest to bring on this relaxation; yet when a sort of murmuring sounds dispose a man to sleep, let these sounds cease suddenly, suddenly, and the person immediately awakes; that is, the parts are braced up suddenly, and he awakes. This I have often experienced myself, and I have heard the same from observing persons. In like manner, if a person in broad day-light were falling asleep, to introduce a sudden darkness would prevent his sleep for that time, though silence and darkness in themselves, and not suddenly introduced, are very favourable to it. This I knew only by conjecture on the analogy of the senses when I first digested these observations; but I have since experienced it. And I have often experienced, and so have a thousand others, that on the first inclining towards sleep, we have been suddenly awakened with a most violent start; and that this start was generally preceded by a sort of dream of our falling down a precipice: whence does this strange motion arise, but from the too sudden relaxation of the body, which by some mechanism in nature restores itself 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 cause. The parts relax too suddenly, 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 less sudden, and less on the extreme, we can seldom complain of this disagreeable sensation.