It is a remarkable fact that every object we see has its picture
formed upon the back wall of our eyes. The eye is a darkened chamber,
and the whole of the front part of it acts as a lens to bring the rays
of light coming from objects we wish to see to a focus on its back
wall, thus forming a picture there as distinct as the picture formed
in the camera obscura of the photographer. This has not only been
proved by the laws of optics, but has been actually demonstrated in
the eyes of rabbits and other animals. Experimenters have held an
object before the eye of a rabbit for a few moments, and have then
killed the animal and removed the eye as quickly as possible, and laid
its back wall bare, and have distinctly seen there the picture of the
object upon which the eye had been fixed. It is a truly wonderful fact
that these pictures upon the back wall of the eye can be changed so
rapidly that the picture of the object last looked at disappears in an
instant and makes way for the picture of the next. We know that the
picture formed on the back wall of the eye is carried back to the
brain by the optic nerve, but there our knowledge stops. Science
cannot tell us how the brain, and through it the mind, completes the
act of seeing. It is there that the finite and the infinite touch,
and, as our minds are finite, we cannot comprehend the infinite.
But there is enough that we can understand, and it shall be my
endeavor in this paper to make some plain statements that will help as
a guide in the preservation of those wonderful and useful organs.