Richardson's handbook of projection (1930)

976 HANDBOOK OF PROJECTION FOR scene, but not the sound is there impressed upon it, just as it is with silent pictures. The film then passes down past the aperture and is threaded into and passes through another "gate," in which is a very much smaller aperture, and as the portion representing the sound track passes over this aperture it is exposed to light from an "Aeo" lamp, which, acting just as the sunlight does in an ordinary camera, impresses the sound upon the film, though that is by no manner of means all the story. The microphone which is to receive the sound vibrations it is desired to record may be placed at any desired point, close to or far distant from the camera. The wires from the microphone, commonly known as the "mike," connect directly with the main amplifying panel. The amplifying panel is in turn connected with an "Aeo" lamp, which, acting through a slit system exactly similar to that described further along (see page 1104), illuminates a space approximately one one-thousandth (.001) of an inch high by one-tenth (1/10) of an inch wide. Put in different form, the Aeo lamp projects to the sound band, through a special lens system and a "slit," a line of light of the dimensions before indicated. This illumination occurs just fourteen and one-half (14*^) inches from the center of the picture aperture, which means that the sound record accompanying any one picture frame is opposite the frame 14J4 inches, or 19ys frames from it and "beyond" it. In other words it is made opposite a frame of pictures located 19^3 frames or 14^ inches before the sound impression itself. As I have told you, the current set up by the microphone which, by the way, is energized by a 200-volt