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



a concertina, over this range, the pitch would break to and fro in 

 a very regular way. The corresponding reverse action would also 

 occur if the motion commenced with extension. These conditions 

 are shown in Fig. 6. Commencing at the point O, with no cm. 

 of tube-length, on the mean frequency of 825 . — •, if we shorten or 

 compress the tube to 90.5 cm., we reach P at 900 '—, near A"#. 

 The note then breaks to Q at 780 '—'. Increasing the tube-length 

 back to 95 cm., we reach R at 770 '—'. The note then breaks up- 

 wards to 6^ at 880 '—'. This humming cycle PQRS, could be repeated, 

 indefinitely with a considerable degree of precision as to pitch and 

 tube-length ; but with a more moderate degree of precision as to 

 primary current strength. Similarly, the cycle TUVW, of 10.5 cm. 

 amplitude in length, and 100 ■—' amplitude in pitch, might be re- 

 peated indefinitely. The amplitudes and areas of these humming 

 cycles vary at different breaking points. 



Purity of Humming Tone. — With the greater tube-lengths, 

 shortly before the break of pitch occurred, there was frequently 

 noted an appearance of the new tone in advance. As the breaking 

 point was approached, the old tone dwindled, while the new tone 

 strengthened. At the break, the old tone, already faint, would sud- 

 denly cease. Consequently, before breaking, both the old and new 

 tones might be recognized, forming a sort of trill, or combination 

 tone. This association of simultaneous tones had the effect of main- 

 taining the primary current strength more nearly uniform. With the 

 shorter tube-lengths, which involved a greater jump of frequency 

 at the breaks, these combination tones were rarely heard, and the old 

 note would break suddenly into the new note without any suggestion 

 of a trill. 



In some of the observations, the notes, aside from the above- 

 mentioned trilling near to the breaking points, gave acoustical evi- 

 dence of multiple tones. Occasionally, the principal tone was accom- 

 panied by an octave overtone. The octave might be either the first 

 octave below, or the first octave above, the principal tone. Such 

 overtones were comparatively faint. At other times, the superposed 

 tone, instead of being harmonic to the principal tone, appeared to 

 differ therefrom by only about one tone on the musical scale. This 

 inharmonic superposed tone was also relatively faint with respect 



