THE PHONOGRAPH. 19 



in any part of the apparatus, no permanent impres- 

 sionability. 



In the phonograph we find impressionability 

 more or less permanent; but, while receiving im- 

 pressions, the instrument cannot give origin to 

 expressions. The one vibrating plate receives the 

 impressions, and subsequently expresses them, re- 

 tentiveness being concentrated in the tinfoil. As 

 in the telephone, so in the phonograph, an addi- 

 tional force is thrown in. While the impressions 

 are being received by the sounding-plate and 

 impressed upon the foil, it is, of course, necessary 

 that the foil be moved under the needle that 

 indents it, in order that fresh parts of the foil may 

 receive the indentations. The impressionability in 

 the arrangement may be said to be permanent, the 

 indented foil remains indented for an indefinite 

 length of time. We best know the property reten- 

 tiveness in the apparatus by the expression of the 

 sounding-plate when the cylinder is again moved 

 so as to reproduce the original sounds which came 

 to the sounding-plate. The retentiveness is indi- 

 cated by the efferent expression obtained as sound 

 on causing the foil to revolve ; the expression 

 corresponds more or less exactly to the afferent 

 sound producing the impression, although a long 

 period of time may have elapsed between receiving 

 the impression and giving out the expression. 

 Another thing to be remarked upon as essential 

 to getting expression out of the phonograph is that 

 the indented foil must be made to move the 

 sounding -plate, and mechanical force must be 



