THE TELEPHONE.

Globe, Volume XXI, Issue 1772, 24 October 1879, Page 2

THE TELEPHONE.

The heretofore received theory of hearing by the telephone was that the thin diaphragm of metal, like that of the phonograph, served as a sort of artificial ear drum, which was vibrated to and fro by the electrically produced magnetic attractions and repulsions of the iron core. The most recent experiments, by observers such as M. Du Moncel, M. Ader, and H. Wildbrand, show that this explanation is incorrect, because the magnetic intensity of the telephone is found to be altogether too feeble to move the inertia of the metallic diaphragm. The corrected theory now is, that sounds heard in the telephone are due to a movement of the molecules composing the iron core of the telephone, induced by the electrical current. Those molecular movements are conveniently transmitted to the ear by the iron diaphragm; but paper or glass may be substituted for the iron ; indeed, the diaphragm may be altogether removed, and the sounds will then bo transmitted to the ear through the wooden case or handle of the telephone. M. Dn Moncel has made a telephone receiver, consisting merely of a piece of board having a magnetised watch spring fastened thereto by one end, and a flue helix secured to the board under the free end of the spring. In this device only molecular vibrations can take place ; but when the board ia applied to the ear speech can be heard more clearly than with an ordinary telephone, or oven the speaking microphone. The results of theae new experiments and observations seem to indicate that molecular vibrations must here ß after be taken into account in things relating to acoustics, and that a broad field for new discoveries in connection therewith ia now opened to the student.