KENNELLY AND UPSON— HUMMING TELEPHONE. 



349 



(0.015 in.), with parallel and opposite symmetrical sectors sliced 

 off, was substituted for the regular diaphragm in the test transmit- 

 ter. The primary current strength during activity was thereby in- 

 creased ; but the G"S tube-lengths remained substantially unchanged 

 at 30 -|- 40m cm. Adding loads, altering the damping-spring pres- 

 sure, or varying the other mechanical adjustments of the transmitter 

 produced either complete silence ; or else the usual G"S, at 30 -1- 

 40in cm. 



The tests showed that modifying the transmitter alters the range 

 and limits of pitch variation, as well as the primary current 

 strengths ; but does not sensibly alter the tube-lengths for mean- 

 frequency. 



/20 mo 16U ISO zoo 2Z0 su<) seo 



TUBE LENGTH - CENTIMETERS. 



Fig. 12. Comparative Frequencies and Currents with Three Different 

 Receiver Diaphragms. 



Observation Series p. Effect of Altering the Receiver. — In 

 order to determine the influence of the telephone receiver diaphragm 

 on the hum, three special receiver diaphragms were made up, each 

 of soft transformer steel, 0.355 "^i""- (0.014 in.) thick, and 5.5 cm, 

 (2.16 in.) in diameter, labeled D^, D^ and D^ respectively, D^ was 



PROG. AMF.R. PHIL. SOC, XLVII. 189 W, PRINTED OCTOBER 2, I908. 



