350 Prof. Rucker and Mr. Edser on the 



6*4 revolutions per second, the two notes corresponded to 

 51*2 and 115*2 vibrations per second, the difference-tone 

 being 64. 



The pitch was determined on different occasions by dif- 

 ferent methods. Firstly, by noting the beats between the 

 higher note and a Konig's fork adjusted to 115*2 complete 

 vibrations per second, and secondly, by watching the row of 

 eight holes through a slit carried by a fork which gave 25*5 

 vibrations per second. 



The effect was rather feebler than in the last experiment, 

 but there was absolutely no doubt as to the objective reality 

 of the difference-tone. The bands regularly disappeared 

 when the required pitch was obtained, and reappeared when 

 it was lost. 



Again the 15 and 9 rows of holes were used. The differ- 

 ence-tone is thus proportional to 6, and Konig's beat-tone to 



9x2 — 15 = 3. When the rate of revolution was 10*6 the 

 two notes were 160 and 96 respectively. In this experiment 

 the mirror-resonator which responds to 161 vibrations was 

 employed to determine the rate of the siren. The bands and 

 the spot of light were sometimes watched together : on 

 another occasion one observer who could not see the bands 

 raised his hand whenever the spot of light moved. The 

 bands invariably disappeared at the instant that this signal 

 was made. 



Experiment III. 



The next experiment was directed to determine the objective 

 reality of Konig's lower beat-tone when the interval was 

 greater than an octave. The 8 and 18 rows of holes being 

 kept open as before, the speed was increased until the lower 

 note was that of 256 vibrations. The upper note was then 

 576, and Konig's lower beat-tone was of 576 — 2x256 = 64 

 vibrations. 



We lay less stress on negative than on positive results ; 

 but we tried for a long time on two occasions to get 

 evidence of the objective character of the note, but entirely 

 failed. The pitch was determined bv the beats with a 

 256 fork. 



Experiment IY. 



We next turn to observations on the summation-tone. 

 The 8 and 10 rows of holes were opened, so that when the 

 cover made 3*55 revolutions per second the summation-tone 

 would be that of 18 x 3*5 = 64 vibrations* 



