266 Dr. A. M. Mayer's Researches in Acoustics. 



times the diameter of the hole in the nipple of the resonator. 

 But in this form of the experiment we are again in doubt as 

 to what space should be taken as measuring the duration of 

 the uniform residual sensation. The period from the fall 

 opening of the resonator in one position to the full opening 

 in the succeeding one is equal to the time the disk takes to 

 go from G to H, which is equal to the distance D to E 

 between the centres of the openings in the disk minus the 

 diameter of the opening in the resonator, or, DE minus 

 JDE. This distance, Gr to H, evidently measures the 

 periods between maximum and maximum intensities of 

 succeeding sound-pulses ; and we have taken this distance, 

 in terms of velocity of rotation, as the measure of the 

 period of uniform residual sound-sensation, because we have 

 no certain knowledge of the relative durations of the 

 residual sensations corresponding to vibrations which pass 

 the disk with increasing intensity, from to 4, fig. 5, and 

 with decreasing intensity, from 8 to 12. 



In our experiments we measured the number of flashes of 

 sound entering the ear by knowing the number of revolutions 

 of the disk per second, and the number of holes in the disk. 

 From this knowledge we compute the time it took the disk to 

 go over D to E in fig. 6, the distance between centres of two 

 neighbouring holes ; then we reduced this time by one sixth, 

 which is the ratio of the diameter of the opening in the 

 nipple of the resonator to the distance D to E, and took this 

 reduced time as the duration of the uniform residual sensation. 

 The duration of the sonorous sensation determined in this 

 manner is evidently nearer the truth than that obtained with 

 apparatus in which the hole in the tube conveying the sound 

 to the disk and the holes in the disk have the same diameter. 



The Apparatus and Methods used to Measure the Durations 

 of Residual Sonorous Sensations. 



[A.] I shall first describe the apparatus which I found the 

 most efficient for these measures, and then describe three 

 other forms of apparatus used. 



In fig. 7 is seen a perforated disk mounted on the axle of 

 a rotator. In front of the disk is the resonator with its 

 nipple close to the surface of the disk. A tuning-fork is 

 opposite the mouth of the resonator. On the other side of 

 the disk, with its axis in line with the axis of the nipple of 

 the resonator, is the tube which conveys the interrupted 

 sounds to the ear. The opening in this tube has the same 

 diameter as the openings in the revolving disk. Behind the 

 line of this tube is seen, on the end of the axle, a fly-wheel 

 of copper weighing a kilogramme. 



