whole stage. Now we see the stage through the glass; and if we look at
it with one eye only it is evident that every single spot on the stage
must throw its light to our eye by light rays which cross the glass
plate at a particular point. For our seeing it would make no difference
whether the stage is actually behind that glass plate or whether all the
light rays which pass through the plate come from the plate itself. If
those rays with all their different shades of light and dark started
from the surface of the glass plate, the effect on the one eye would
necessarily be the same as if they originated at different distances
behind the glass. This is exactly the case of the screen. If the
pictures are well taken and the projection is sharp and we sit at the
right distance from the picture, we must have the same impression as if
we looked through a glass plate into a real space.

The photoplay is therefore poorly characterized if the flatness of the
pictorial view is presented as an essential feature. That flatness is an
objective part of the technical physical arrangements, but not a feature
of that which we really see in the performance of the photoplay. We are
there in the midst of a three-dimensional world, and the movements of
the persons or of the animals or even of the lifeless things, like the
streaming of the water in the brook or the movements of the leaves in
the wind, strongly maintain our immediate impression of depth. Many
secondary features characteristic of the motion picture may help. For
instance, by a well-known optical illusion the feeling of depth is
strengthened if the foreground is at rest and the background moving.
Thus the ship passing in front of the motionless background of the
harbor by no means suggests depth to the same degree as the picture
taken on the gliding ship itself so that the ship appears to be at rest
and the harbor itself passing by.