The art of sound pictures (1930)

224 THE ART OF SOUND PICTURES the variable area method, on the other hand, there is little likelihood of this type of error creeping in. The variable area method is, on the whole, the more reliable of the two. Let us forget, for the moment, all the technical details of the processes just described, and think of them in the simplest possible terms, as follows; a player on the movie set speaks the line, “I love you.” As the words leave his lips, sound waves travel from his mouth to the microphone. As the microphone vibrates to these air waves, electric currents travel from the microphone to an electric light shining through a slit on a moving film in the camera. As the microphone currents strike the electric light, it flickers, changing its brightness in sensitive response to the microphone current. Or perhaps, instead of a light flickering, the slit through which the light shines upon the film changes its size automatically. The different quantities, or the different intensities, of light set up minute ether waves, which travel rapidly to the sensitized film. When these strike the film, they cause the chemicals on the film to change or develop in various degrees of light and shade. These chemical changes on the film are then fixed, and furnish permanent records, corresponding precisely to the original sound waves caused by the words, “I love you,” which the actor spoke. “I love you” then becomes, in photographic form, a series of black and white lines on the edge of a strip of celluloid. But these black and white marks on the sound track occupy only a very narrow section of the film. Alongside them is recorded a series of photographs. The photographs show the face and lips of the actor, who says, “I love you,” in various stages of the movement necessary to speak these words. In short, while the sounds of the words