Sound 



179 



FIG. 99. A modern dictaphone. 



Melt a piece of glass over a burner and draw it out into a 

 thread. Break off about 8 inches of this glass thread and 

 tie it firmly with cotton thread to the edge of one prong of 

 a tuning fork. Clamp the top of the tuning fork firmly above 

 the smoked drum, adjusting it so that the point of the glass 

 thread rests on the smoked paper. Turn the handle slightly 

 to see if the glass is making a mark. If it is not, ad ; 

 so that it will. Now let some one turn the cylinder quickly 

 and steadily. While it is turning, tap the tuning fork on 

 the prong which has not the glass thread fastened to it. 

 The glass point should trace a white, wavy line through 

 the smoke on the paper. If it does n>t. ktrp >n trying, 

 adjusting the apparatus until the point makes a wavy 1 



Making a record in this way is, on a large scale, al- 

 most exactly like the making of a phonograph record. 

 The smoked paper on which a tracing can easily be made 



