rom
the light; it is reasonable to think that the contraction of the radial
fibres of the iris is proportionally greater; and that this part may by
great darkness come to be so contracted, as to 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; this 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
apprised 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 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.

SECTION XVII.

THE EFFECTS OF BLACKNESS.

Blackness is but a _partial darkness_; and therefore it derive