338 



KENNELLY AND UPSON— HUMMING TELEPHONE. 



[July 20, 



less marked as the tube is longer, the minimum currents rising, 

 as the length increases, by about 40 mas. in 9 meters, indicating 

 steadily reduced action in the transmitter with increasing distance. 

 Since the current rose to 260 mas. when the transmitter diaphragm 

 was entirely out of action, we should expect, at this rate, to be able 

 to sustain the humming note to a total tube-length of 40 meters; 

 but no tests were actually made beyond 9 meters. 



zoo ^20 SUO 



TUBE LENGTH - CENTIMETERS. 



Fig. S. Effect of Lengthening and Shortening the Tube. 



Observation Series j. Effect of Lengthening the Tube. — Fig. 5 

 indicates the relative effects produced by lengthening, as compared 

 with shortening, the telescoping tube joining the transmitter and 

 receiver in Fig. i, using the same apparatus and connections as in 

 Figs. I, 2, 3 and 4. The heavy or continuous lines in Fig. 5 show 

 the effects of shortening the tube, or correspond to curves / in Fig. 

 2. The broken lines show the effects of lengthening the tube. It 

 will be observed that the points of maximum and minimum current 

 agree fairly well. The ascending intersections of the pitch lines 

 with the mean- frequency line of G"t 825 r~^, lie near together, and 

 approximately conform to the series 30 -|- 40;/^ cm. of tube-length. 

 The points of break in pitch do not, however, agree, and the dis- 



