The art of sound pictures (1930)

2 20 THE ART OF SOUND PICTURES penetrates all particles of air and all grosser material substances with which we are familiar. The tiny ether particles are, by their very minuteness, freed from the control of grosser substances such as the air. Light rays are really waves set up among these tremendously fine particles of ether. Thus, you can understand immediately how light waves can actually pass through certain substances which we call transparent or translucent, whereas sound waves cannot pass through these substances at all. You can also understand how light waves travel at very much higher rates of speed than do sound waves. This fact has an important bearing upon the new sound photography, which we shall have occasion to refer to later. For the moment, however, we are concerned with the device which catches or registers the comparatively gross and material sound waves and translates these waves of the air into minute light waves of the ether. This translation of the coarse air waves into fine ether waves cannot be made all in one process. We are compelled first of all to translate sound waves into electrical waves or currents. Then we amplify or increase the force of these electric currents and finally translate the electric current into a fine ether wave of light. The translation of sound waves into electric currents is a comparatively simple affair which is familiar to everyone who has used a telephone. When you speak into the transmitter of a telephone, the air waves of sound, caused by your voice, make a small metal diaphragm in the telephone transmitter vibrate back and forth in resonance to the sound. As the diaphragm vibrates back and forth, it changes the quantity of electric current which is passing over the circuit, connecting the transmitter into which you