THE PHONOGRAPH* OR VOICE-RECORDER. 291 



ratus. The receiving apparatus consists of a curved tube, 

 one end of which is fitted with a mouthpiece. The other 

 end is about two inches in diameter, and is closed with a 

 disc or diaphragm of exceedingly thin metal, capable of 

 being thrust slightly outwards or vibrated upon gentle 

 pressure being applied to it from within the rube. To the 

 centre of this diaphragm (which is vertical) is fixed a small 

 blunt steel pin, which shares the vibratory motion of the 

 diaphragm. This arrangement is set on a table, and can be 

 adjusted suitably with respect to the second part of the 

 instrument the recorder. This is a brass cylinder, about 

 four inches in length and four in diameter, cut with a con- 

 tinuous V-groove from one end to the other, so that in effect 

 it represents a large screw. There are forty of these grooves 

 in the entire length of the cylinder. The cylinder turns 

 steadily, when the instrument is in operation, upon a vertical 

 axis, its face being presented to the steel point of the receiv- 

 ing apparatus. The shaft on which it turns is provided with 

 a screw-thread and works in a screwed bearing, so that as 

 the shaft is turned (by a handle) it not only turns the 

 cylinder, but steadily carries it upwards. The rate of this 

 vertical motion is such that the cylinder behaves precisely 

 as if its groove worked in a screw-bearing. Thus, if the 

 pointer be set opposite the middle of the uppermost part of 

 the continuous groove at the beginning of this turning mo- 

 tion, it will traverse the groove continuously to its lowest 

 part, which it will reach after forty turnings of the handle. 

 (More correctly, perhaps, we might say that the groove con- 

 tinuously traverses past the pointer.) Now, suppose that a 

 piece of some such substance as tinfoil is wrapped round 

 the cylinder. Then the pointer, when at rest, just touches 

 the tinfoil. But when the diaphragm is vibrating under the 

 action of aerial waves resulting from various sounds, the 

 pointer vibrates in such a way as to indent the tinfoil not 

 only to a greater pr less depth according to the play of the 

 pointer to and fro in a direction square to the face of the 

 diaphragm, but also over a range all round its mean position, 



