KENXELLY AND UPSON— HUMMING TELEPHONE. 



351 



proximately to ascending intersections of the series 13 -|- 32fn cm. 



\'arious other modifications of receiver and receiver diaphragm 

 were tried. Loading the diaphragm with a small central mass low- 

 ered the mean humming frequency. By selecting suitable dia- 

 phragm dimensions, the mean-frequency of the hum could be varied 

 between wide limits. 



triors 

 o 



IJJ I0Z5 



az 



^im 



O <}7S 

 ISO 



sue 



230 



CO 



LU 220 



QC 



UJ 



•z. 



— 200 

 ^ ISO 



■z. 



LU 170 

 CO 



§ 160 



/so 



\ 



'■^ 



,\ 



so 90 100 110 !Z0 130 /W ISO 160 



TUBE LENGTH - CENTIMETERS. 

 FxG. 13. Discontinuous Frequencies, or Large Gaps in Curves, for Case of 



Singe-pole Receiver. 



Conclusions Directly Derivable from the Experiments. — The fol- 

 lowing more prominent conclusions are indicated by the experiments 

 themselves, independently of any theory : 



1. The mean-frequency of the humming-telephone note is deter- 

 mined solely by the receiver diaphragm, and its natural free rate 

 of vibration. 



2. The ascending intersections of the frequency zig-zag with the 

 mean-frequency line will be formed approximately at tube-lengths 

 of (f -|-w) v/n^ cm. for one connection, and of (4 + wi) v/nQ cm. 

 for the other connection, of the receiver; where v is the velocity 

 of sound in air (33,000 cm. per sec. nearly), w^ is the mean fre- 

 quency in cycles per second, and in is any positive integer, within 



