A. M. Mayer — Researches in Acoustics. 



5 



Evidently, the manner in which the tube conveying the 

 sound to the disk is opened and closed by the revolving disk 

 has to be considered in researches made with this apparatus. 

 I give two cases whose discussion has led me to modify with 

 marked efficiency the apparatus, shown in fig. 3, which was 

 used in the researches published in this Journal in 1874 and 

 1875. In that apparatus the interruptions of sound were made 

 by a perforated disk revolving in front of the mouth of a 

 resonator while the interrupted sound was conveyed to the ear 

 by a tube attached to the small opening in the nipple of the 

 resonator. 



Fig. 3. 



This mode of obtaining the interruptions of the sound is 

 objectionable because the resonator is not in tune with the 

 fork except when the former is fully opened and also because 

 the perforated disk rotating across the mouth of the resonator 

 gives rise to two secondary sounds and a resultant sound, fully 

 described in my paper of 1875.* These sounds, from their 

 intensity in this form of experiment, mask the proper sound 

 of the fork, making the determination of the durations of the 

 sonorous sensations both difficult and uncertain. Also, in 

 these experiments the action of the interrupted sound on the 

 ear is distressing ; even injurious, for the hearing of one of my 



*See a paper by Lord Rayleigh : Acoustical Observations, III, ''Intermittent 

 Sounds." Phil. Mag., April, 1880, in which the author gives an explanation, in 

 mode and in measure, of the secondary sounds and of the resultant sound, ob- 

 served by me in these experiments. 



