470 



NATURE 



{April II, 1878 



with a hole in its centre. The under side of this disc 

 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 coating 

 the edges with shellac varnish, 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 



Fig. I. — Edison's Talking-Phonograph. 



placed close to the opening in the vulcanite disc, 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 made. It remains to obtain from these 



impressions the aerial vibrations which made them. 

 Nothing is simpler. The plate A, with its point, P, is 

 moved away from the cylinder by pulling toward you the 

 lever, H G. Then the motion of the cylinder is reversed 

 till you have brought opposite to the point p the begin- 

 ning of the series of impressions which it has made on 

 the foil. Now bring the point up to the cylinder ; place 

 against the vulcanite plate, B B, a large cone of paper or 

 tin to re-enforce the sounds, and then steadily turn the 

 crank, D. The elevations and depressions which have 

 been made by the point, P, now pass under this point, 

 and in so doing they cause it and the thin iron plate to 

 make over again the precise vibrations which animated 

 them when they made these impressions under the action 

 of the voice. The consequence of this is, that the iron 

 plate gives out the vibrations which previously fell upon 

 it, and it talks back to you what you said to it. 



By the following method we have just obtained several 

 magnified traces on smoked glass of the contour, or pro- 

 file, of the elevations and depressions made in the foil 

 by the sonorous vibrations. On the under side of the 

 shorter arm of a delicate lever is a point, made as nearly 

 as possible like the point, P, under the thin iron plate, A. 

 Cemented to the end of the longer arm of this lever is a 

 pointed slip of thin copper-foil, which just touched the 

 vertical surface of a smoked-glass plate. The point on 

 the short arm of the lever rested in the furrow in which 

 are the depressions and elevations made in the foil on 

 the cylinder. Rotating the cylinder with a slow and 

 uniform motion, while the plate of glass was slid along, 

 the point of copper-foil scraped the lamp-black off the 

 smoked-glass plate and traced on it the magnified profile 

 of the depressions and elevations in the foil on the 

 cylinder. I say expressly elevations as well as depres- 

 sions in the foil, because, when the plate vibrates out- 

 ward,' the furrow in the foil often entirely disappears, 

 and is always lessened in its depth by this outward 

 motion of the point. One who has never made a special 

 investigation of the character of the impressions on the 

 phonograph, and forms his opinion from their appear- 

 ance to his eye, might state that they are simply dots 

 and dashes, like the marks on the filet of a Morse 

 instrument 



Another method of obtaining the profile of the impres- 

 sions on the foil is to back it with an easily-fusible sub- 

 stance, and then, cutting through the middle of the 

 furrows, we obtain a section, in which the edge of the 

 foil presents to us the form of the elevations and 

 depressions. 



The instrument has been so short a time in my posses- 

 sion, that I have not had the leisure to make on it the 

 careful and extended series of experiments which it 

 deserves. I have, however, obtained several traces, and 

 1 have especially studied the characters of the trace of 

 the sound of bat. As far as the few experiments warrant 

 an expression of opinion, it seems that the profile of the 

 impressions made on the phonograph and the contours 

 of the flames of Konig, when vibrated by the same 

 compound sound, bear a close resemblance. 



In Fig. 3 we give on line A the appearance to the eye 

 of the impressions on the foil, when the sound of a in 

 bat is sung against the iron plate of the phonograph. 

 B is the magnified profile of these impressions on the 

 smoked glass obtained as described above. C gives the 

 appearance of Konig' s flame when the same sound is 

 sung quite close to its membrane. I say expressly quite 

 close to its membrane, for the form of the trace obtained 

 from a point attached to a membrane vibrating under 

 the influence of a compound sound depends on the 

 distaiice of the source of the sound from the membrane, 

 and the same compound sound will form an infinite 

 number of different traces as we gradually increase the 

 distance of its place of origin from the membrane ; for, 

 as you increase this distance, the waves of the components 



