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MANAGERS AND PROJECTIONISTS 977
storage battery, operates the Aeo lamp affixed to the camera after being amplified approximately 100,000 times at the amplifying panel. It therefore follows that since the power of the current which operates the lamp fluctuates exactly with, and in exact proportion to every fluctuation of the sound wave frequency, the brilliancy of the Aeo lamp, and therefore the brilliancy or illuminating power of the light it projects to the film through the slit varies in exact synchronism with and in exact proportion to the sound wave frequencies or intensity, with result that the sound band of the negative film is illuminated in exact proportion to the modulations of sound.
THE AEO LAMP. — The Aeo lamp used in recording sound is not a filament lamp. It consists of a glass bulb in which are fixed a small metal plate and a loop of platinum wire coated with alkaline earth oxides, located with reference to each other somewhat as shown in Fig. 382.
The Aeo lamp bulb is filled with Helium gas. The plate is positive and the loop negative. When in action, they are energized by a battery of about 350 volts, which causes the gas surrounding the plate to glow with a faint pink color, and the gas surrounding the loop to become very brilliant, the color being an intense light blue. This is the light source utilized for illuminating the film through the slit. However, all this would be useless without going further, because the light would be of even, unvarying intensity.
Examining the diagram Fig. 382, you will observe that circuit F attaches to the Aeo lamp circuit. Circuit F is the circuit connected, through the amplifier panel, to the microphone. It carries an A. C. current representing,