KENNELLY AND UPSON— HUMMING TELEPHONE. 



335 



proximately 20 cm. from, or midway between, those of the other 

 curve. 



The note frequencies and primary current strengths for tubes 

 of less than 60 cm. in length are given in Fig. 3, commencing at 

 60 cm. and shortening down to about i cm., when the receiver face 

 came into contact with the transmitter face (cone removed), and 

 so prevented closer approach. Curves / and // of Fig. 3 correspond 



W 20 30 VC» SO 60 



TUBE LENGTH - CENTIMETERS 



Fig. 3. Humming Note Frequencies and Primary Current Strengths with 



Short Tubes. 



to curves / and // of Fig. 2, respectively, and indicate the effect of 

 reversing the receiver terminals. It may be observed that follow- 

 ing the pitch line /_, the ascending branch intersects the mean fre- 

 quency line of 825 .—', at a tube-length of 30 cm., for the last time. 



