CHAP. vin. PHYSICAL PRINCIPLES. 67 



that the steel point is exactly where it was at starting, 

 and the cylinder is then made to revolve and move on- 

 ward at exactly the same rate as before, the up and down 

 motions of the style, due to the irregular depth of the 

 groove, set up the very same series of vibrations in the 

 diaphragm as those which cut the groove; and these 

 vibrations reproduce the voice with marvellous fidelity, 

 so that the most complex and rapid speech, or the most 

 exquisite singing, can be heard quite intelligibly, and 

 with all their modulations and expressiveness, though 

 not in exactly the same tone of voice. 



The cylinders thus produced can be preserved for 

 years, can be carried to any part of the world, and by 

 means of a duplicate of the original instrument will there 

 reproduce the words and the vocal peculiarities of the 

 speaker. Phonographs are now largely manufactured, 

 and are used for a variety of purposes. They serve for 

 the rapid dictation of correspondence, which can be re- 

 produced and copied by a clerk later on; to take down 

 discussions verbatim, with a perfection that no short- 

 hand writer can rival; the singing or the elocution of 

 celebrated performers is repeated for the gratification 

 of friends or to amuse private parties; actors, musicians, 

 and clergymen use the instrument as a means of improv- 

 ing their style ; and even the languages, songs, and folk- 

 lore of dying-out tribes are being preserved on these 

 wonderful cylinders. 



Probably there is no instrument in the world which 

 so impresses the observer with the apparent inadequacy 

 of the means to bring about so marvellous a result. At 

 the same time it renders more mysterious than ever the 

 properties and possibilities of air-waves, and the extreme 



