4 I know not whether I may not on this occasion add, that Colour is so far
from being an Inherent quality of the object in the sense that is wont to
be declar'd by the Schools, or even in the sense of some Modern Atomists,
that, if we consider the matter more attentively, we shall see cause to
suspect, if not to conclude, that though Light do more immediately affect
the organ of sight, than do the bodies that send it thither, yet Light it
self produces the sensation of a Colour, but as it produces such a
determinate kind of local motion in some part of the brain; which, though
it happen most commonly from the motion whereinto the slender strings of
the _Retina_ are put, by the appulse of Light, yet if the like motion
happen to be produc'd by any other cause, wherein the Light concurrs not at
all, a man shall think he sees the same Colour. For proof of this, I might
put you in mind, that 'tis usual for dreaming men to think they see the
Images that appear to them in their sleep, adorn'd some with this, and some
with that lively Colour, whilst yet, both the curtains of their bed, and
those of their eyes are close drawn. And I might add the confidence with
which distracted persons do oftentimes, when they are awake, think, they
see black fiends in places, where there is no black object in sight without
them.
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