WHY FACES [SEEN] AT A DISTANCE LOOK DARK.

We see quite plainly that all the images of visible objects that lie
before us, whether large or small, reach our sense by the minute
aperture of the eye; and if, through so small a passage the image
can pass of the vast extent of sky and earth, the face of a
man--being by comparison with such large images almost nothing by
reason of the distance which diminishes it,--fills up so little of
the eye that it is indistinguishable. Having, also, to be
transmitted from the surface to the sense through a dark medium,
that is to say the crystalline lens which looks dark, this image,
not being strong in colour becomes affected by this darkness on its
passage, and on reaching the sense it appears dark; no other reason
can in any way be assigned. If the point in the eye is black, it is
because it is full of a transparent humour as clear as air and acts
like a perforation in a board; on looking into it it appears dark
and the objects seen through the bright air and a dark one become
confused in this darkness.

WHY A MAN SEEN AT A CERTAIN DISTANCE IS NOT RECOGNISABLE.

The perspective of diminution shows us that the farther away an
object is the smaller it looks. If you look at a man at a distance
from you of an arrow's flight, and hold the eye of a small needle
close to your own eye, you can see through it several men whose
images are transmitted to the eye and will all be comprised within
the size of the needle's eye; hence, if the man who is at the
distance of an arrow's flight can send his whole image to your eye,
occupying only a small space in the needle's eye how can you
[expect] in so small a figure to distinguish or see the nose or
mouth or any detail of his person? and, not seeing these you cannot
recognise the man, since these features, which he does not show, are
what give men different aspects.