Page:Popular Science Monthly Volume 12.djvu/740

This page has been validated.
720
THE POPULAR SCIENCE MONTHLY.

turned. On the surface of the cylinder is scored the same thread as on its axle. At F (shown in one-half scale in Fig. 2) is a plate of iron, A, about 1100 of an inch thick. This plate can be moved toward and from the cylinder by pushing in or pulling out the lever H G, which turns in an horizontal plane around the pin I.

PSM V12 D740 Edison talking phonograph.jpg
Fig. 1.—Edison's Talking-Phonograph.

The under side of this thin iron plate, A (Fig. 2), presses against short pieces of rubber tubing, X and X, which lie between the plate and a spring attached to E. The end of this spring carries a rounded steel point, P, which enters slightly between the threads scored on the cylinder C. The distance of this point, P, from the cylinder is regulated by a set-screw, S, against which abuts the lever, H G. Over the iron plate, A, is a disk of vulcanite, B B, with a hole in its centre. The under side of this disk nearly touches the plate A. Its upper surface is cut into a shallow, funnel-shaped cavity, leading to the opening in its centre.

To operate this machine, we first neatly coat the cylinder with a sheet of foil, made to adhere by gumming the corners; then we bring the point, P, to bear against this foil, so that, on turning the cylinder, it makes a depressed line, or furrow. The mouth is now placed close to the opening in the vulcanite disk, B B, and the metal plate is talked to while the cylinder is revolved with a uniform motion.

The plate, A, vibrates to the voice, and the point, P, indents the foil, impressing in it the varying numbers, amplitudes, and durations, of these vibrations. If the vibrations given by the voice are those causing simple sounds, and are of a uniform, regular character, then similar, regular, undulating depressions are made in the foil. If the vibrations are those causing complex and irregular sounds (like those of the voice in speaking), then, similarly, the depressions made in the foil are complex, having profiles like the curve, B, in Fig. 3. Thus the yielding and inelastic foil receives and retains the mechanical impressions of these vibrations with all their minute and subtile characteristics.

The permanent impressions of the vibrations of the voice are now