136 



Lord Rayleigh. 



[June 15 y 



shown more in making the alternate drops unequal in magnitude, than 

 in projecting them into very different paths. 



Returning now to the case of a single fork screwed to the table, it 

 was found that as the pitch was lowered below 128, the double stream 

 was regularly established. The action of the tivelfth below the 

 principal note (85-g-) demands special attention, At this pitch we might 

 in general expect the first three components of a compound note to 

 influence the result. If the third component were pretty strong it 

 would determine the number of drops, and the result would be a three- 

 fold stream. In the case of a fork screwed to the table the third 

 component of the note must be extremely weak, if not altogether- 

 missing ; but the second (octave) component is fairly strong, and in 

 fact determines the number of drops (190f ). At the same time the 

 influence of the prime (85-^-) is sufficient to cause the alternate drops 

 to pursue different paths, so that a double stream is observed. 



By the addition of a 256 fork there was no difficulty in obtaining 

 the triple stream, but it was of more interest to examine whether it 

 were possible to reduce the double stream to a single one with only 

 85^- drops per second. In order to secure as strong and as pure a 

 fundamental tone as possible, I cause it to act in the most favourable 

 manner upon the jet, the air space over the water in the reservoir was 

 tuned to the note of the fork by sliding a piece of glass over the neck 

 so as partially to cover it. When the fork was held over the resonator 

 thus formed, the pressure which expels the jet was rendered variable 

 with a frequency of 85 h, and overtones were excluded as far as possible. 

 To .the unaided eye, however, the jet still appeared double, thongh on 

 more attentive examination one set of drops was seen to be decidedly 

 smaller than the other. "With the revolving disk, giving about eighty- 

 five views per second, the real state of the case was made clear. The 

 smaller drops were the spherules, and the stream was single in the 

 same sense as the streams given by pare tones of frequencies 128 and 

 256. The increased size of the spherule is of course to be attributed 

 to the greater length of the ligament, the principal drops being now 

 three times as widely spaced as when the jet is under the influence of 

 the 256 fork. 



With still graver forks screwed to the table the number of drops 

 continued to correspond to the second component of the note. The 

 double octave of the principal note (64) gave 128 drops per second, 

 and the influence of the prime was so feeble that the duplicity of the 

 stream was only just recognisable. Below 64 the observations were 

 not carried. Attempts to get a single stream of 64 drops per second 

 were unsuccessful, but it is probably quite possible to do so with 

 vibrations of greater power than I could command. 



In the case of a compound note of pitch 64 a considerable variety 

 of effects might ensue, according to the relative strengths of the 



