the rear wall in the room were actually ten or twenty feet behind the
furniture in the front. The effect is so striking that no one can
overcome the feeling of depth under these conditions.

But while the regular motion pictures certainly do not offer us this
complete plastic impression, it would simply be the usual confusion
between knowledge about the picture and its real appearance if we were
to deny that we get a certain impression of depth. If several persons
move in a room, we gain distinctly the feeling that one moves behind
another in the film picture. They move toward us and from us just as
much as they move to the right and left. We actually perceive 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 rôle 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