In the magic-lantern and its improved form, the stereopticon, separate views of different subjects are shown in succession. Each picture is allowed to remain on the screen long enough to be readily beheld and appreciated. But the picture is at rest and does not move. With the motion-picture projector a series of slightly varying pictures of the same subject are projected in quick succession. This succession is at such a rapid rate that the interval of time during which one picture moves out of place to make way for the next is so short that it is nearly imperceptible. In consequence, the slightly varying pictures blend on the screen and we have a phantasmagoria of movement.
The phenomenon of this movement—this semblance to life—takes place, not on the screen, but within the eye. Its consideration, a subject proper for the science of physiology (and in some aspects psychology), has weight for us more particularly as a matter of physics.
Memory has been said to be an attribute of all organic matter. An instance of this seems to be the property of the eye to retain on its retina an after-image of anything just seen. That is to say, when an object impresses its image upon the retina and then moves away, or disappears, there still remains, for a measurable period, an image of this object within the eye. This singularity of the visual sense is spoken of as the persistence of vision or the formation of positive after-images. And it is referred to as a positive after-image in contradistinction to another visional phenomenon called the negative after-image. This latter kind is instanced in the well-known experiment of fixing the eyes for a few moments upon some design in a brilliant color and quickly turning away to gaze at a blank space of white where instantly the same design will be seen, but of a color complementary to that of the particular hue first gazed at.
The art of the motion-picture began when physicists first noticed this peculiarity of the organ of sight in retaining after-images. The whole art is based on its verity. It is the special quality of the visual sense that makes possible the appreciation of living screen pictures.
An interesting matter to bear in mind is the circumstance that the first attempt at giving to a screen image the effect of life was by means of a progressive series of drawings. When photographs came later, drawings were forgotten and only when the cinematographic art had reached its great development and universality, were drawings again brought into use to be synthesized on the screen.
To describe how these drawings are made, their use and application to the making of animated cartoons, is the purpose of this book.
Before proceeding with a sketch of the development of the art of making these cartoons, it will make the matter more readily understood if we give, at first, in a few paragraphs, a brief description of the present-day method of throwing a living picture on the screen by the motion-picture projector.
MAGIC-LANTERN AND MOTION-PICTURE PROJECTOR COMPARED.
The projector for motion-pictures, like the magic-lantern, consists of an illuminant, reflector, condenser, and objective. This last part is the combination of lenses that gather and focus the light rays carrying the pencils of lights and shadows composing the picture and throwing them on the screen. There is, in the magic-lantern, immediately back of the objective, a narrow aperture through which the glass slide holding a picture is thrust. In the motion-picture apparatus, the transparent surface containing the picture also passes back of the objective, but instead of the simple process of pushing one slide through to make way for another, there is a complicated mechanism to move a long ribbon containing the sequence of pictures that produces the image on the screen. Now this ribbon consists of a strip of transparent celluloid[1] each with a separate photograph of some one general scene but each with slight changes in the moving details—objects or figures. These changes record the movements from the beginning to the end of the particular story, action, or pantomime.