78 PROCEEDINGS OP THE AMERICAN ACADEMY 



TABLE XII. — Continued. 



An inspection of Tables IX. to XIII. shows that the value of the 

 excursion of the hammer electrode corresjjonding to the " critical point," 

 and presumably, therefore, the excursion corresponding to any given 

 degree of excellence in the reproduction of quality, at first rises very 

 rapidly as the mass of the anvil electrode is increased, but soon reaches 

 a maximum value, which is not altered by further increase of mass. 

 The rise appears to be less rapid when both electrodes are of carbon 

 than when one or both of them are of platinum, as may be seen by a 

 comparison of the various tables, or, better still, by plotting the results 

 so as to exhibit them graphically by curves. Also, when both elec- 

 trodes are of carbon or both of platinum, the maximum and permanent 

 excursion at the critical point is considerably less than when the ham- 

 mer electrode is of platinum and the anvil of carbon, — a fact which 

 goes to explain the well known excellence of a microphone employing 

 these last materials. Further experiment is desirable, however, before 

 fully accepting this explanation. Furthermore, variations in the sur- 



