Page:The American Cyclopædia (1879) Volume XIII.djvu/473

 PHONOGRAPH 458- its upper end a point, P, made to fit into the spiral grooves of the cylinder C, and the dis- tance of which from the cylinder is regulated by the screv S, against which abuts the lever H. Before us- ing the phonograph the cylin- der is coated with a sheet of tin foil, so as to cover the spi- ral grooves on its surface. If now the point P be brought into contact with the foil and the cylinder be turned, it will make" a uniform furrow in its surface by pressing it into the spiral beneath ; but if the plate A be made to vibrate by any external force, the furrow or groove traced by the point will not be uniform, but will correspond to the vibrations of the plate. As in the telephone, sounds made in the mouthpiece F induce vi- brations in the diaphragm A. In the tele- phone these are communicated to a magnet, and through it to the wires which carry them to a distance to be reproduced by a second in- strument ; but in the phonograph they are per- manently recorded by the point P, which in- dents them in all their variations on the foil around the spiral. To work the machine, the cylinder is revolved by means of the crank D, while the words are spoken close to the open- ing of the mouthpiece F. Eve- ry sound causes its peculiar vi- bration in the air, which is re- produced in the diaphragm; and as the movements of the point P are wholly dependent on those of the diaphragm, the soft and yielding foil is marked along the line of the spiral by a series of indentations of differ- ent depths, varying with the amplitudes and durations of the vibrations, which correspond to the inflections and modulations of the speaker's voice. These indentations are really visible speech; but as they must always vary in accordance with thequal- ity and relative intensity of the voices which produce the vibra- tions, we can scarcely hope ever t<> be able to read them with the eye. But we can reproduce the sounds which caused them and which they represent. To effect this, the mouthpiece is first re- moved from the cylinder by palling back the lever H. The cylinder is then reversed by turning the crank D backward until the first part of the spiral, containing the beginning of the indentations, is again brought opposite to the point P which made them. Tho mouthpiece is now moved up to the cylin- der so that the point touches the spiral again, and is fastened in place. If the cylinder be now turned as before, so as to cause the point FIG. i. to traverse its former path, the latter will rise and fall with all the elevations and depressions made by it previously, and will reproduce in the diaphragm the precise vibrations which induced its original movements. These vibra- tions, conveyed to the ear by means of the air, excite in it the sensation of sound, and the very words spoken into the mouthpiece of the instrument are thus returned by it. As the phonograph is not yet perfected, its tones, though clear and distinct, are somewhat metallic and not very loud, and have to be re- enforced by a large funnel or cone which is FIG. 2. placed against the mouthpiece when the cylin- der is turned to reproduce sounds. The cylin-