348 . Prof. Riicker and Mr. Edser on the 



evident that the two ribs attached to this were not sufficient 

 to prevent a certain flapping of the projecting part, and that 

 this responded to a note of about 256 vibrations. The end of 

 the collecting pyramid was then shifted a little so that the 

 waves of sound impinged only on the more rigid part of the 

 wooden square, and the spurious effect immediately and 

 completely disappeared. 



Of the notes which caused these troubles, the lower one was 

 decidedly lower than the c' of 256; the other corresponded 

 very accurately with the e' of 320. The fact that both these 

 numbers are multiples of 64 may legitimately give rise to the 

 doubt whether the fork F can be set in motion by disturbances 

 which are multiples of its own frequency. 



Even if it be admitted that such forced vibrations would 

 be especially easy to produce, we must insist — (1) that we 

 can distinguish (as above described) between forced and 

 natural vibrations ; (2) that when the apparatus was pro- 

 perly arranged such notes could be produced by the siren 

 for lono; intervals of time without the least effect on the 

 bands ; (3) that two tuning-forks, of 256 and 320 vibrations 

 respectively, have been placed within the wooden pyramid 

 with their sounding-boxes resting on and supported by, the 

 lower side, yet no effect was produced on the bands even 

 when they were both sounding loudly at the same time ; 



(4) that one of Konig's large forks, with a frequency of 128, 

 was placed in front of the collecting cone and produced no 

 effect when sounding loudly, though the slightest tap on 

 the 64 fork caused the bands to vanish for many seconds ; 



(5) that the 320 and 384 forks produced no effect when the 

 pyramid was removed and they were held as above described 

 close to the receiving prong of the fork ; (6) and, lastly, that 

 in two out of the five experiments on the difference-tones, 

 and in all those in which the interference apparatus was used 

 to detect summation tones, the frequencies of the notes em- 

 ployed were neither multiples nor sub-multiples of 64. 



As in all the above experiments the resonator was in 

 position, they also sufficed to prove that tones of 64 vibra- 

 tions were not manufactured in it by the primary notes when 

 acting singly. 



If the objection is raised that, although neither note 

 disturbed the bands when sounded alone, the effect might be 

 due to the double disturbance produced by the two sounds, 

 we think it sufficient to answer that we have always carried 

 the two notes above the pitch at which the difference-tone 

 might be expected to affect the instrument, then lowered the 

 pitch again till the notes were too flat, and repeated this 



