Sound motion pictures : from the laboratory to their presentation (1929)

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378 SOUND MOTION PICTURES (3) An electrode toward which electrons flow within a device. (4) A positively charged electrode. Arc: An electric discharge of high intensity depending for its continued passage upon the heat it produces at one or both electrodes. In lighting, an arc is the result of maintaining an electromotive force between carbons which are somewhat separated, but between which current flows across an arc stream composed of the gases generated in the process of volatilization of carbon. Armature: (i) An iron member located in the field of a magnet. (2) The rotating part of a stationary-field motor or generator. Audibility: The loudness of sound as reproduced in a telephone receiver; usually stated as some number of times louder than a signal that can barely be heard or distinguished. Audio-frequency: A frequency of vibration that is within the normal audible range; usually taken as between 16 and 16,000 cycles per second. Audion: A vacuum tube containing a heated filamentary cathode, a cold anode, and a screen or grid control electrode interposed between them. Auto-transformer: A transformer in which the same winding acts as part of both primary and secondary coils. B battery: A battery for the plate of the anode circuit of a vacuum tube; usually made up in blocks of several dry or wet cells connected in series producing electromotive force. Buzzer: An electromagnetic circuit interrupter having a vibrating armature. By-pass condenser: A condenser of sufficient capacitance to offer low impedance to audio-frequency current, but much higher impedance to audio-frequency current than does the instrument across which it is connected. It may similarly be used to discriminate between audio-frequencies or lower frequencies and direct current.