266 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



The first test to which the apparatus was put was to obtain the 

 judgment of a person having a trained ear as to the quality of the 

 tone produced by its current in a telephone. His opinion was that 

 the tone was pure, only the fundamental being detected. The wave 

 form was then mapped. 



In planning this work it occurred to us to employ the method of 

 projection of potential whenever it was necessary to measure a P. D. 



3.o' to' io" to' iou' no- w 



Fic.hAKMf.ruRe A . Tiive Sine Cume Dotted 



it,o 



tic 1 



or E. M. F. at any instant. The opposing P. D. was obtained by the 

 fall of potential due to the passage of a direct current through a suit- 

 able resistance. As the opposing P. D. was not alternating, the 

 above mentioned contact arrangement was used in place of the ordi- 

 nary key, and its value was determined by a suitable Weston volt- 

 meter. This method of dealing with instantaneous E. M. F.'s was 

 originally suggested by Professors Foster and Maxwell, their object 



