[f. TOPO- + Gr. -φωνος sounding, φωνή voice, sound.] (See quots.)
1880. Patent Specif., No. 495. A topophone, or instrument for locating sounds, applicable more especially to the navigation of a vessel in a fog.
1881. Standard, 1 Jan. The topophone of Professor Mayer … is intended to determine the direction and approximately the distance of a fog-horn.
1902. Harper’s Mag., Feb., 498. Another wireless telephone for maritime use is known as the topophone. Ibid., 499. By the use of the topophone,… sounds can be heard which are inaudible to the unassisted ear.
