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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 ^ of an inch thick. This plate can be moved tow- 

 ard and from the cylinder by pushing in or pulling out the lever 

 H G, which turns in an horizontal plane around the pin I. 



Fig. 1. Edison"s Talking-Phonograph. 



The under side of this thin iron plate, A (Fig. 2), presses against 

 short pieces of rubber tubing, Xand JT, 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 regu- 

 lated by a set-screw, S, against which abuts the lever, II G. Over 

 the iron plate, A, is a disk of vulcanite, B P, 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, P P, 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, P, 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 



