102 PROCEEDINGS OF THE AMERICAN ACADEMY 



TABLE XVI. 



Electrodes. — Carbon, Copper. 



Remarks. 

 Good quality ; fluttering. 



Figures 1 to 3 show very well the characteristics of the substances 

 iron, platinum, carbon. Comparing the curves for carbon and plati- 

 num (Figs. 2, 3), it will be seen that the maximum current obtained 

 under the conditions of the experiment was about the same in both 

 cases. But the current falls off far more rapidly with platinum as 

 the pressure is further increased, thus giviDg to carbon a grpater 

 working range of pressure-variation within which it can be practically 

 used in a microphone transmitter, a fact long since recognized in 

 practice. Iron (Fig. 1) has a considerable range, but the current 

 produced is not great. 



Tables IV. to VIII., and Figures 4 to 8, illustrate the results ob- 

 tained when the electrodes were of different materials, the substance 

 of which the anvil electrode is made being the first mentioned. In the 

 experiments now particularly referred to, the two electrodes were 

 made of the customary size, the hammer small and the anvil large. 



An inspection of the curves shows that the character of the result 

 obtained under these circumstances was determined chiefly by the 

 material of the anvil rather than of the hammer electrode. This is 

 particularly well illustrated in the case of iron and carbon, as shown 

 in Figures 6 and 7. 



This difference persisted even when the hammer and anvil elec- 

 trodes were made of the same size and shape, as will be seen by an 



