3479960 Arrangement of microphones on either side of the prompt box on the stage of the Theatre Francais, 1881; (add.info.: Arrangement of microphones on either side of the prompt box on the stage of the Theatre Francais, used to transmit the performances to special rooms in the Palais de l\'Industrie during the Paris Exhibition of 1881. By sending a separate signal to each ear, Ader managed to achieve a stereophonic effect.); Universal History Archive/UIG; out of copyright.