RECORDING SPEECH VIBRATIONS. 19 



A reproducer with free edge was then used in a gramophone. The 

 reflection on the screen showed a constantly changing figure with nodes; 

 for example, as in figure 9. The figure changed its form with every tone. 

 The dark portion was the shadow from the supporting lever and the joint 

 in the center. When a reproducer with fixed edge was used, the reflec- 

 tion showed a circle of constantly changing diameter; the changes in the 

 distribution of light over the circle were limited to concentric waves, as 

 indicated in figure 10. We can thus conclude that an important function 

 of the edge-fixation is to hinder the production of nodes. 



An attempt was made to determine the nature of the bending of the 

 diaphragm and its dependence on the edge-fixation. The arc light was 



11 12 13 



Fig. 11. — Holes in shutter and their reflection by flat diaphragm. 

 Fia. 12. — Reflection by bent diaphragm with vaseline fixation. 

 FiQ. 13.— Reflection by bent diaphragm with metal fixation. 



placed in a long box with a circular opening at one end. This opening 

 was covered by a metal plate in which equidistant concentric circular 

 series of holes were bored (figure 11). The reflection of these beams of 

 light by the diaphragm showed a similar figure. 



When a reproducer with free etlge was used, pressure on the needle 

 point moved the entire figure to one side without noticeably changing 

 it. When a reproducer with vaseline fixation was used, pressure on the 

 needle point enlarged all the circles (figure 12) ; the increase was approxi- 

 mately proportional to the diameter. A reproducer with metal fixation 

 showed little or no enlargement of the inner circle, but enlargement of the 

 others (figure 13). The other forms of fixation showed figures that lay 

 between the vasehne and the metal types. The figui-e for loose paper 

 fixation approached that for vaseUne and rubber; those for tight paper 

 and dextrine fixation approached that for metal. 



