256 PROCEEDINGS OF THE AMERICAN ACADEMY 



alternating currents. The needle and one pair of the quadrants were 

 connected with one terminal of the telephone, and the other pair of 

 quadrants with the remaining terminal. There was not sufficient time 

 at our disposal to obtain any series of measurements by this method, 

 but results were reached which give encouragement as to its availabil- 

 ity. It is possible that this method may prove especially useful in the 

 study of electrostatic telephones. 



The results given in the preceding pages are to be regarded only as 

 preliminary to a more extended series of measurements. But while 

 they are yet necessarily somewhat meagre, they at least show, first, 

 that an electi'o-dynamometer of a simple construction is sufficient, 

 not merely to detect, but also to measure telephone currents ; and, 

 secondly, that the strength of these currents, especially when good 

 carbon microphone transmitters are used, is far in excess of what has 

 hitherto been supposed. 



Rogers Laboratory of Physics. 



