e the chairs
or the rear wall of the room as further away from us than the persons in
the foreground. This is not surprising if we stop to think how we
perceive the depth, for instance, of a real stage. Let us fancy that we
sit in the orchestra of a real theater and see before us the stage set
as a room with furniture and persons in it. We now see the different
objects on the stage at different distances, some near, some far. One of
the causes was just mentioned. We see everything with our right or our
left eye from different points of view. But if now we close one eye and
look at the stage with the right eye only, the plastic effect does not
disappear. The psychological causes for this perception of depth with
one eye are essentially the differences of apparent size, the
perspective relations, the shadows, and the actions performed in the
space. Now all these factors which help us to grasp the furniture on
the stage as solid and substantial play their role no less in the room
which is projected on the screen.

We are too readily inclined to imagine that our eye can directly grasp
the different distances in our surroundings. Yet we need only imagine
that a large glass plate is put in the place of the curtain covering the
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-dimensiona