29 PLEASANT WAYS IN SCIENCE. 



corresponding to the play of the end of the pointer around 

 its mean position. The groove allows the pressure of the 

 pointer against the tinfoil free action. If the cylinder had 

 no groove the dead resistance of the tinfoil, thus backed up 

 by an unyielding surface, would stop the play of the pointer. 

 Under the actual conditions, the tinfoil is only kept taut 

 enough to receive the impressions, while yielding sufficiently 

 to let the play of the pointer continue unrestrained. If now 

 a person speaks into the receiving tube, and the handle of 

 the cylinder be turned, the vibrations of the pointer are im- 

 pressed upon the portion of the tinfoil lying over the hollow 

 groove, and are retained by it. They will be more or less 

 deeply marked according to the quality of the sounds 

 emitted, and according also, of course, to the strength with 

 which the speaker utters the sounds, and to the nature of 

 the modulations and inflexions of his voice. The result is 

 a message verbally imprinted upon a strip of metal. It 

 differs from the result in the case of Barlow's logograph, in 

 being virtually a record in three dimensions instead of one 

 only. The varying depth of the impressions corresponds to 

 the varying height of the curve in Barlow's diagrams ; but 

 there the resemblance ceases ; for that was the single feature 

 which Barlow's logographs could present. Edison's im- 

 printed words show, besides varying depth of impression, a 

 varying range on either side of the mean track of the pointer, 

 and also though the eye is not able to detect this effect 

 there is a varying rate of progression according as the end 

 of the pointer has been swayed towards or from the direction 

 in which, owing to the motion of the cylinder, the pointer is 

 virtually travelling. 



We may say of the record thus obtained that it is sound 

 presented in a visible form. A journalist who has written 

 on the phonograph has spoken of this record as correspond- 

 ing to the crystallization of sound. And another who, like 

 the former, has been (erroneously, but that is a detail) 

 identified with myself, has said, in like fanciful vein, that the 

 story of Baron Miinchausen hearing words which had been 



