up and continued from the point where
it ended (on the screen) when the bust picture was flashed.

_11. Masks_

After Tom has openly accused his brother of forgery, as shown by the
cut-in leader, the scene changes to the hallway outside the library
door. We see Wilkins, the butler, who is implicated in the plot
against Ralph, kneeling and peering into the room through the
key-hole. This is a very short scene, but it is necessary to show two
things: not only that the brothers are being spied upon, for we are
not interested in merely watching the butler kneeling there, but it is
important for us to see _what_ he is watching so intently--the action
in the library. So, after we have shown the spy kneeling outside the
door, the scene is shifted back to the continuation of the interview
between Tom and Ralph. This time, however, we see it on the screen in
a way that merely _suggests_ the butler kneeling outside the closed
door. On the screen appears a large key-hole, and within its limits
the scene between the brothers is acted.

The effect thus produced is termed a "mask." Ordinarily the lens of a
moving picture camera is masked by a metal plate, rectangular in
shape, one inch wide by three-quarters of an inch high. The use of
this mask prevents the light from spreading up or down the film as it
is being exposed. As explained in Chapter III, each of the sixteen
tiny pictures that make up a foot of film is termed a "frame," and,
the camera being masked as described, the light is permitted to act
upon only one frame at a time. But within this limit of one inch by
three-quarters of an inch another mask may be used, cut in any form
that the producer may desire. It may be a key-hole mask, as in the
foregoing example; it may be simply circular, to suggest that the
scene is viewed through a telescope; or a mask with hair-line bars,
which will suggest that you are looking through a window. We examined
a script a short while ago in which a travelling salesman for an
optical goods house amused himself in the interval before train time
by watching through a pair of binoculars the street below and the
buildings opposite his hotel window. The scene enacted in an office of
a building not far away led him to believe that a murder was being
committed, and the action which followed was extremely funny. The
scene in the office, watched by the "drummer" through the binoculars,
appeared on the screen as though viewed through a large and ve