The basic aesthetics of film as of any other art must be descriptive and analytic, giving an account of the relevant variables and their means of variation. And any such account must be rooted in some notion, however imprecise, of what a work of the art in question is. What, then, is a film? It seems to be characteristic of the art that acceptable definitions need to specify not only the nature of the work itself but also the means essential to its production and its characteristic effects. A sample definition might go like this: "A film is a series of motionless images projected onto a screen so fast as to create in the mind of anyone watching the screen an impression of continuous motion, such images being projected by a light shining through a corresponding series of images arranged on a continuous band of flexible material."1 Much variation in detail and in emphasis is possible, but no definition can dispense with two important features: a succinct description of at least the basic features of the mechanism employed, and an allusion to the creation of an illusion of motion. Let us consider these necessary features in turn.