234 PROCEEDINGS OF THE AMERICAN ACADEMY 



cases over 500 times as great as the ordinary current furnished 

 by a magneto-transmitter, with a calculated duration of current 

 of from g}^ °f a second to gi^ of a second, in no case was a com- 

 plete ellipse observed. In many cases the duration as determined 

 from the curve appeared to be substantially the same as the calcu- 

 lated amount; and when there was a prolongation of the motion it 

 was evident from the character of the curve that this was due to 

 free vibration of the diaphragm. 



From these results it would appear that the method used by us is 

 not open to the objection referred to, and that there is really no 

 material prolongation of the harmonic motion of the diaphragm of 

 the telephone after the electric undulations have ceased to actuate 

 it. Moreover, with the very weak current used in the transmission 

 of the sounds of the tuning-forks in our experiments, any such pro- 

 longation, if it existed, would of course be far less than with the 

 strong current used in testing the point immediately under consid- 

 eration. The effect of an increased rate of alternation ought to be 

 studied, but the damping effect of the magnet would be greater at 

 higher rates. 



Some other experiments were made, however, with a current 

 having 256 complete alternations per second, and of a rigorously 

 simple harmonic form; but much difficulty was experienced in 

 securing sufficiently equable driving with such means as were 

 available at the time of the experiment, so that further work in 

 this direction had to be postponed until better conditions for 

 steadiness could be secured. 



The improbability of any prolongation of the sound vibrations 

 within the ear itself has been shown by Herroun and Yeo.* 



A few experiments were made by us with a view of gaining some 

 information regarding the free vibration of the telephone diaphragm 

 after it was pulled to one side and suddenly released. For this pur- 

 pose a direct current was substituted for the alternating current 

 used in the experiments already described. The strength of the 

 current was substantially the same as before. When the circuit- 

 making wheel completed the circuit, the diaphragm was suddenly 

 drawn toward the magnet and released quickly, when the circuit 

 was broken. With a duration of current of about -giv °f a second 

 the free vibration seemed to last for about the same period. With 

 a duration of current of ^is of a second, the free vibration lasted 



* Proc. Royal Soc, Vol. L. p 318. 



