i9o8.] KENNELLY AND UPSON— HUMMING TELEPHONE. 341 



to the principal tone. Generally, however, no superposed tones could 

 be discerned, and the note was clear and flute-like in quality. Irregu- 

 larities in the fitting of the telescoping tube-sections, or in other 

 acoustic connections, were found to be productive of superposed 

 notes. 



Effects of Electrical Changes. 



Obscrz'aiion Scries 5. Effect of Resistance in Primary or Sec- 

 ondary Circuit. — In this test a single tube of constant length (86.5 

 cm. or 34 in.) was used. It was of pasteboard, had an internal 

 diameter of 5.1 cm. (2 in.) and weighed 113. 5 gm. This length 

 happens to be about midway between the ascending intersections of 

 pitch lines / and // in Fig. 2 measured on the mean-frequency line 

 of 825 — '. That is, the tube-length selected favored each of the lines 

 / and // nearly equally. The battery e.m.f. of 8.6 volts was the same 

 as in all the above described measurements. The same telephone 

 receiver and induction coil were also used. Substantially non-induc- 

 tive resistance was introduced, by rheostat, into either the primary, 

 or the secondary, circuit at will, leaving the connections of Fig. i 

 otherwise unchanged. 



After starting the loud humming note with no extra resistance 

 in either circuit, resistance was gradually inserted into the primary 

 circuit until the note, diminishing in amplitude, finally disappeared. 

 The extra resistance in the circuit at the extinction of the tone was 

 recorded, under the name of " extinguishing resistance." Resistance 

 was then withdrawn from the primary circuit, and, after the loud 

 note had been reestablished, was introduced gradually into the sec- 

 ondary circuit, until again the note was extinguished. The second- 

 ary extinguishing resistance was likewise recorded. The same tests 

 were repeated with the telephone receiver terminals reversed. 



It was found that both the primary and secondary extinguishing 

 resistances repeated themselves very fairly (within about 5 per cent.) 

 in successive trials. In order to obtain the best comparative results 

 in successive tests, it was found desirable to tap the transmitter 

 gently when approaching the condition of extinction. 



The pitch of the tone when enfeebled almost to extinction by 

 extra resistance, in either the primary or secondary circuit, was 

 always close to the mean frequency of 825 '—'. 



