346 Prof. Rucker and Mr. Edser on the 



blowing directly down the collecting cone, but a small 

 organ-pipe could be sounded, or a Konig's fork bowed near 

 the opening without producing the least effect if the frequency 

 of the note produced was not near 64 per second. In like 

 manner many notes of two reed wind-instruments, somewhat 

 similar in construction to the harmonium, were sounded 

 simultaneously so that the room echoed with discordant 

 sound, yet without producing the least effect on the steadiness 

 of the bands. 



On the other hand , when one of Konig's forks tuned to 64 

 vibrations was touched with the india-rubber covered handle 

 of a gimlet, or was struck with a piece of gas-tubing so lightly 

 that an observer with his ear close to the fork could not 

 detect the fundamental note, the bands instantly disappeared. 



It was therefore evident that the apparatus could respond 

 to a vibration which was quite inaudible to a person standing 

 by the resonating fork. 



When the Konig fork was weighted so as to give 63*5 

 vibrations per second, the bands appeared and disappeared at 

 regular intervals of two seconds, thus corresponding to the 

 beats between the exciting and resonating forks. The bands 

 were not disturbed when the beats exceeded 2 or 3 per second 

 unless the exciting fork was bowed very violently. In the 

 experiments with fainter tones, the resonating fork was only 

 disturbed when the frequency of the exciting note agreed very 

 exactly with its own. 



As the speed of the siren was gradually increased from 

 rest the bands always disappeared two or three times, the 

 disturbance being no doubt caused by the upper partials as 

 the vibration-frequency passed, in turn, the values 16, 21'3, 

 and 32 per second. No exact measurement was made of the 

 corresponding frequencies, as there could be no question as to 

 whether the partials were produced or as to whether the 

 apparatus could detect them. No such disappearance occurred 

 when the note was higher than C, except in the case of 

 certain spurious effects referred to below. 



All the experiments were performed several times on each 

 occasion, and on two occasions at least. The bands were 

 sometimes produced by soda-light, and watched by an ob- 

 server through a telescope. 



Sometimes the electric light was used. The bands could 

 then be projected on a screen side by side with the image 

 of the holes or cogs. In this way information as to the 

 note produced and as to the behaviour of the bands was 

 simultaneously conveyed to all who watched the experiments. 



