ACHRONICAL

, or Achronycal. See Acronychal.

ACOUSTICS. This term, in physico-mathematical meaning, signifies the doctrine of hearing, and the art of assisting that sense by means of speaking trumpets, hearing trumpets, whispering galleries, and such like. See Stentrophonic Tube.

Sturmius, in his Elements of Universal Mechanics, treating of Acoustics, after examining into the nature of sounds, describes the several parts of the external and internal ear, and their several uses and connexions with each other; and from thence deduces the mechanism of hearing: and lastly, he treats of the means of adding an intensity of force to the voice and other sounds; and explains the nature of echoes, otacoustic tubes, and speaking trumpets. See Sound, Ear, Voice, and Echo.

Dr. Hook, in the preface to his Micrography, asserts that the lowest whisper, by certain means, may be heard at the distance of a furlong; and that he knew a way by which it is easy to hear any one speak through a wall of three feet thick; also that by means of an extended wire, sound may be conveyed to a very great distance, almost in an instant.