ON EDISON'S TALKING-MACHINE. 



721 



made. It remains to obtain from these impressions the aerial vibra- 

 tions 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 .Pthe beginning of the series of 

 impressions which it has made on the foil. Now bring the point up 



Fio. 2. 



to the cylinder; place against the vulcanite plate, B B,& large cone 

 of paper or tin to reenforce 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 profile, 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 



TOL. XII. 46 



