Here's a clever way of projecting the same movie onto several screens throughout a building using tubes, mirrors and multiple apertures:

It must be assumed that the average reader understands how a picture film passes through the projection machine. The "frames" –that is, each individual picture on the strip of film–are exposed momentarily before the aperture in the gate of the projection machine. A powerful light is focused upon the aperture, and projects the image on the film through a lens to the screen. Seemingly, pictures in motion result.

Now, if a second aperture is cut in the gate, two frames can be exposed simultaneously. A special condenser lens floods both apertures with light. The light beam from the second aperture, carrying the picture image, is conveyed through a black-lined tube fitted with special mirrors and lenses, to a remote point where it is projected on the back of a ground glass plate. The visible result is similar to looking into the finder of a camera.