“We do not purchase an automobile, for example, merely to own some machinery. Indeed, it is not machinery we are buying at all, but what we can have by way of it: a means of rapidly carrying us from one location to another, an object of envy for others, protection from the weather. Similarly, a radio must cease to exist as equipment and become sound. A perfect radio will draw attention to itself, will make it seem we are in the very presence of the source of its sound. Neither do we watch a movie screen, nor look at television. We look at what is on television, or in the movie, and become annoyed when the equipment intrudes-when the film is unfocused or the picture tube malfunctions.”