picture into another; but it has a greater power, which has not always been appreciated and taken advantage of by directors, the power of producing for the eye a pictorial rhythm of tonal intensities. This effect is somewhat like the "crescendo" and "diminuendo" in music.
When we consider that changing tonal value may be combined with changing direction, as well as with changing velocity, of moving spots, moving lines, moving patterns, and moving textures, we realize more keenly the problems of the cinema composer. His medium is at once extremely complex, extremely flexible, and extremely delicate.
But we have not yet revealed all of the strange qualities of the motion picture. A unique power of the screen, which can never be utilized by any other graphic art, is that which gives motion to things that are themselves absolutely at rest and immovable. Even the pyramids of Egypt can be invested with apparent motion, so that their sharp lines flow constantly into new patterns. It can be done by simply moving the camera itself while the film is being exposed. The appeal of apparent motion in natural setting is familiar to any one who has ever gazed dreamily from the window of a railroad car or from the deck of a yacht sailing among islands. Apparent motion on the screen makes a similar appeal, which can be enhanced by changing distance and point of view and by artistic combination with real motions in the picture.
Still other fresh means of pleasing the eye may be found in the altering of natural motions, as by the retarding action of the slow-motion camera, which
