THE PHONOGRAPH, OR VOICE-RECORDER. 277 



simply as an acoustical one, the idea entertained would have 

 been this that though the motions of a diaphragm receiving 

 vocal sound-waves might be generated artificially in such 

 sort as to produce the same vocal sounds, yet this could only 

 be done by first determining what particular points of the 

 diaphragm were centres of motion, so to speak, and then 

 adopting some mechanical arrangements for giving to small 

 portions of the membrane at these points the necessary 

 oscillating motions. It would not, I think, have been 

 supposed that motions communicated to the centre of the 

 diaphragm would suffice to make the whole diaphragm 

 vibrate properly in all its different parts. 



Let us briefly consider what was before known about the 

 vibrations of plates, discs, and diaphragms, when particular 

 tones were sounded in their neighbourhood ; and also what 

 (vas known respecting the requirements for vocal sounds 

 and speech as distinguished from simple tones. I need 

 hardly say that I propose only to consider these points in a 

 general, not in a special, manner. 



We must first carefully draw a distinction between the 

 vibrations of a plate or disc which is itself the source of 

 sound, and those vibrations which are excited in a plate or 

 disc by sound-waves otherwise originated. If a disc or 

 plate of given size be set in vibration by a blow or other 

 impulse it will give forth a special sound, according to the 

 place where it is struck, or it will give forth combinations of 

 the several tones which it is capable of emitting. On the 

 other hand, experiment shows that a diaphragm like that 

 used in the telephone not only the electric telephone, but 

 such common telephones as have been sold of late in large 

 quantities in toy shops, etc. will respond to any sounds 

 which are properly directed towards it, not merely repro- 

 ducing sounds of different tones, but all the peculiarities 

 which characterize vocal sounds. In the former case, the 

 size of a disc and the conditions under which it is struck 

 determine the nature of its vibrations, and the air responds 

 to the vibrations thus excited ; in the latter, the air is set 



