336 KENNELLY AND UPSON— HUMMING TELEPHONE. [July 20, 



Shortening the tube beyond this point, the pitch rises until it reaches 

 e'" of 1,300 '--', at 12.5 cm., and at a primary current strength of 

 300 mas. Here the note breaks without descending to a new low 

 note. There is silence with this connection of the receiver between 

 12.5 cm. and o cm. With the transmitter and receiver touching 

 each other, it was possible to produce almost any note between 

 620'—' and 1,300 -—', by giving suitable opening to the air at one 

 side. If, however, the outside air was shut off, and the air between 

 the transmitter and receiver diaphragms was cylindrically enclosed, 

 by bringing their faces into full opposition and contact, no note 

 could be obtained. 



If we follow pitch curve //, we find that the ascending branches 

 intersect the mean-frequency line at 50 cm. and at 10 cm. The 

 pitch 866 '—' was obtained steadily when the transmitter and receiver 

 faces were in full contact, corresponding to a " tube-length "of 

 I cm. With this connection of receiver terminals, no other note, 

 or variety of notes, could be obtained at contact. 



A telescoping tube of 9 meters (29.5 ft.) total length was used 

 in one series of measurements, and the results appear in Fig. 4. 

 They were all obtained with diminishing tube-lengths, or with com- 

 pression of the telescoping tube. The small crosses indicate dis- 

 continuities produced at the removal of sections of tube when 

 finished with. In regard to the pitch line, it will be seen that it 

 corresponds to curve / of Figs. 2 and 3. That is, it crosses the 

 mean- frequency line of 825 '— ' ascendingly at 30 -f- 40m cm. with 

 a fair degree of precision. With the shortest tube, the range in 

 pitch-frequency was from 740-—' to 1,060—', or through 320. — '. 

 At the full length of 9 meters, this range fell to 75 '— '. The ultimate 

 limit tended apparently to the mean-pitch frequency of G"# 825 — '. 

 The average note was above this pitch ; but this was probably be- 

 cause the tube was being compressed. Reference to Fig. 5 will 

 show that, when shortening the tube, the average pitch lies above 

 the mean of 825 — ' ; while in lengthening the tube, the average 

 pitch lies below. 



The primary current strength in Fig. 4 tends, in general, to 

 minima at the mean- frequency pitch of 825 r~^, and to maxima at 

 the breaks. The differences in current strength become, however, 



