The New Student's Reference Work/Phonograph
Pho′nograph, an instrument invented by Edison in 1877 for recording and reproducing words spoken by the human voice. Leon Scott had already shown that, by speaking in front of a diaphragm, on the rear side of which was fixed a stylus, he could obtain a graphical record of the human voice on a cylinder rotating behind the diaphragm. The step which Edison made was to introduce a wax cylinder and a needlepoint attached to the diaphragm. On rotating the wax cylinder, the needle-point cuts a groove. If, while this groove is being cut, one “talks to the diaphragm” the indentations of the needle-point in the wax will vary with each pulsation of the voice. The axis of the cylinder is so provided with a screw that the groove takes the form of a spiral as the cylinder is rotated and translated while the stylus is fixed in one position. A record having been impressed upon the wax, it is only necessary to allow the stylus again to trace the groove in order to impress upon the diaphragm exactly — or nearly exactly — the same vibrations which originally produced the groove. In this way the phonograph is made to repeat whatever is said to it. A new phonographic principle was in 1900 invented by Poulsen, a Danish engineer. Poulsen uses the current in a telephone circuit to magnetize a strip of steel tape which is drawn continuously between the poles of an electromagnet, the electromagnet being energized by the telephone current. The record of anything spoken into the telephone is stored in the magnetization of the steel tape. Accordingly when the steel tape is again drawn between the poles of the electromagnet, the telephone in the circuit will, owing to currents induced by the steel tape, repeat whatever was originally spoken to it. Still a third phonographic principle was in 1901 devised by Nernst; but has not been perfected. It is based upon the electrolysis produced by an electric current.