composition contains a moving spot, the changing pattern of the wake, and the changing texture of the water. If we add to this picture a long train on the bank, trailing a ribbon of smoke, an airplane in the sky, and a sailing yacht on the lake, we have a subject which is difficult indeed to analyze, and infinitely more difficult to compose into pictorial beauty. Yet those are the very kinds of motion which a motion picture director must compose in every scene that he "shoots."
But we have not yet completed our analysis of the nature of pictorial motion. It has still another property, which we shall call "changing tonal value." Changing tonal value depends upon changes in the amount and kind of light which falls upon the subject, and upon changes in the surface of the subject itself. For example, the shadow of a cloud passing over a landscape gives a slightly different hue to every grove or meadow, to every rock or road. To watch these values come and go is one of the delights of the nature lover.
Nature's supreme example of the beauty of changing values may be seen in a sunset playing with delicate splendor on sea and sky. And if this beauty defies the skill of painters it is because they have no means of representing the subtle changes which run through any particular hue as the moments pass by.
The beauty of a sunset may long, perhaps forever, elude the cinematograph, but this machine can produce tonal changes in black and white at the will of the operator by the familiar trick of "fading in" and "fading out." This camera trick is of great service for dramatic effects, such as the dissolving of one
