The Pamphlet Collection of Sir Robert Stout: Volume 38
The Double Audiphone
The Double Audiphone.
This instrument consists of two similar and parallel discs, with the lower edges united, from which a handle extends. The upper edges are separated about a quarter of an inch by beads, and adjusted to the teeth by means of notches. The voice of the mute falls between the discs, and is carried back, thus enabling him to hear his own voice.