The art of sound pictures (1930)

SOUND TECHNIQUE 219 the confusing details of specific inventions and devices. How, in the first place, can sound waves be translated into light waves? The sound wave is a movement of the air itself. When an actor speaks or when a musical instrument is played, the vocal cords of the speaker or the vibrating of the musical instrument sets up a series of air waves in the air immediately adjoining the speaker’s mouth or the mouth of the musical instrument. These sound waves travel quickly in all directions until they strike the ears of people who are sufficiently near the speakers or musical instruments. Nature has designed our ears in such a way that when sound waves strike them, certain brain currents are caused which give us the consciousness of sound. Thus, we can hear the dialogue or music if we are near enough to their source so that the air waves will travel from speakers or musicians to our ears without interruption. But we cannot, naturally, see sound. How, then, can a sound wave be caught and changed into such a form that it can be photographed? Only light waves can be photographed. That is to say, rays or waves of light are of such a nature that they produce chemical changes on a sensitive film or plate. These chemical changes are then fixed permanently upon a recording material, so that a permanent record of the light rays which originally struck the photographic film is produced. If, then, we can translate sound waves into light waves, we can easily produce a permanent sound record on a photographic film. This is the way the trick is done. Light waves are not air waves at all. Light vibrations travel through what used to be called the ether. You can think of ether as an incredibly minute substance which is so fine and which moves so rapidly that it inter