66 THE WONDERFUL CENTURY. CHAP, vm. 



known to be due to successive air-waves set up by vari- 

 ous vibrating substances; but it would seem impossible 

 by any mechanical means to reproduce these complex 

 vibrations so exactly as to cause the words of the origi- 

 nal speaker to be again heard, quite intelligibly, and 

 with all their tones and modulations, at any distant time 

 or place. Yet this has been done by means of the in- 

 strument called the phonograph, one of the many in- 

 genious inventions of the American, Edison. 



In the telephone this is effected instantaneously 

 through the medium of an electric current, which repro- 

 duces the vibrations set up by the voice of the speaker in 

 a delicate elastic diaphragm by means of another dia- 

 phragm at the end of the conducting wire, perhaps hun- 

 dreds of miles away, as already explained in Chapter 

 III. In the phonograph the whole operation is mechan- 

 ical. A diaphragm is set vibrating by the voice as in 

 the telephone, but instead of being reproduced at a dis- 

 tance by means of an electric current, it registers itself 

 permanently on a cylinder of very hard wax, as an in- 

 dented spiral line. This is effected by means of a fine 

 steel point, like a graving tool, connected by a delicate 

 lever with the centre of the diaphragm. The wax cylin- 

 der turns and travels onward at a perfectly uniform rate, 

 which can be delicately adjusted, so that the steel point, 

 if stationary, will cut in it a very fine spiral groove, uni- 

 form in depth from end to end, the turns of the groove 

 being very close to each other. But when the diaphragm 

 is set vibrating by the voice of the speaker, the steel point 

 moves rapidly up and down, and the resulting groove 

 continually varies in depth, forming a complex series of 

 undulations. If, now, the cylinder is shifted back so 



