State of Experimental Acoustics. 293 



well as the primary notes, until the effects were most distinctly 

 obtained. Stationary nodes and loops are formed in the room 

 for all the notes present; and by taking advantage of these the 

 analysis may be much assisted. 



Curious results are undoubtedly obtained. For instance, the 

 beats of an octave slightly out of tune are almost entirely on 

 the lower note. If the notes are kept apart in the room, the 

 upper one appears quite steady; while the lower one varies 

 much in intensity, whether we listen to it with the unassisted 

 ear or with a resonator. With the assistance of a resonator 

 the much smaller variation of the upper note can be detected. 

 Ihese two phenomena are not separated by Konig, but de- 

 scribed simply as a beat. According to Helmholtz, the beat of 

 the lower note would be due to the difference-tone, that of the 

 upper note to the octave harmonic of the lower note interfering 

 with the upper one. Now it is easy to convince oneself with 

 the analyzing resonator that the latter interpretation of the 

 beat of the upper note is right : one can hear separately the 

 octave harmonic and the octave note, as well as the beat itself. 

 But the explanation of the beat of the lower note, as due to 

 the interference of the difference-tone, presents this difficultv. 

 If Ave run up the lower note by means of the siphon, the dif- 

 ference-tone should become audible. But with the arrange- 

 ments I employed no trace of difference-tone could be per- 

 ceived, even when the octave was run up to a fifth and a sen- 

 sitive resonator employed to detect the difference-tone. The 

 notes were placed far apart ; and the arrangement was, no 

 doubt, not favourable to the production of a difference-tone : 

 but then how could it be there, so as to form these strong beats 

 of the lower note, if it was not loud enough to be heard sepa- 

 rately ? I have only stated the above with the object of show- 

 ing that there is a large ground here, important in a theore- 

 tical point of view, which will repay careful working. In fact 

 the repetition and examination of the large collections of ex- 

 periments in the work of Konig above cited, with the notes of 

 such resonators as I have described, or with pure notes equally 

 powerful and manageable, is a work essential to the establish- 

 ment of the foundations of the theory of the subject. 



I have come to the conclusion that it is not practicable to 

 carry the work much further with this apparatus without a 

 much steadier wind. For this purpose it is desirable to con- 

 struct improved bellows. No existing pattern (except that of 

 Cavai le Coll) delivers a wind of any thing like the steadiness 

 desirable. I shall return to this question later. 



Although with an improved bellows hand blowing would 

 be admissible, yet it is always difficult to secure uniformity in 

 Phil. Mag. S. 5. Vol. 8. No. 49. Oct. 1879. X 



