92 



PROCEEDINGS OF THE AMERICAN ACADEMY 



results which are obtained. In fact, the article referred to assumes 

 that the varying pressure on the contact due to the action of the given 

 sound-waves will always have the same maximum value, ± 8. This 

 would be approximately true were the normal pressure between the 

 two electrodes alone to be varied, but the effect of the addition of 

 weights, as in the method of experiment adopted, is to increase the 



i^ 



Fig. 2. 





3 4 5 

 Fig. S. 



7 8 



mass at the same time that the normal pressure is increased, and 

 under these circumstances the effect of a sound-wave of given intensity 

 will necessarily be to give to the corresponding pressure-variation a va- 

 riable value, increasing with the added mass, and hence, with the form 

 of apparatus used, as the normal pressure is greater. The effect of this 

 will be to cause at first a gradual increase of current in the secondary, 



