total reflexion of the light by the surface struck by it. Again, when
the eye registers 'black' in both cases it registers an identical
process, namely, total absorption of the light.1

Seen thus, the phenomenon informs us of the significant fact that our
eye is not at all concerned with the colour of the light that enters
its own cavity, but rather with what happens between the light and the
surface on which the light falls. In other words, the phenomenon shows
that our process of seeing is not confined to the bodily organ of the
eye, but extends into outer space to the point where we experience the
visible object to be.2

This picture of the visual process, to which we have been led here by
simple optical observation, was reached by Thomas Reid through his own
experience of how, in the act of perceiving the world, man is linked
intuitively with it. We remember that he intended in his philosophy to
carry ad absurdum the hypothesis that 'the images of the external
objects are conveyed by the organs of sense to the brain and are there
perceived by the mind'. Common Sense makes Reid speak as follows: 'If
any man will shew how the mind may perceive images of the brain, I will
undertake to shew how it may perceive the most distant objects; for if
we give eyes to the mind, to perceive what is transacted at home in its
dark chamber, why may we not make the eyes a little longer-sighted? And
then we shall have no occasion for that unphilosophical fiction of
images in the brain.' (Inq., VI, 12.) Reid proceeds to show this by
pointing out, first, that we must only use the idea of 'image' for
truly visual perceptions; secondly, that the sole place of this image
is the background of the eye, and not any part of the nervous system
lying beyond; thirdly, that even this retina-image, as such, does not
come to our consciousness, but serves only to direct the consciousness