4 A. 31. Mayer — Researches in Acoustics. 



duration in which the after-sensation of a sound does not per- 

 ceptibly diminish in intensity. 



In fig. 2, D and E represent openings in a screen imper- 

 vious to sound. The distance between these openings equals 

 thrice the diameter of an opening. A tube, R, having the 

 same interior diameter as the openings is supposed to convey 



Fig. 2. 



sound-vibrations against the screen, while the tube itself moves 

 from left to right with its mouth sliding along the surface of 

 the screen. In the position, A, the sound is just about to 

 traverse the opening, D, to the ear on the other side of the 

 screen. As R progresses over the opening, D, the sound 

 traverses the opening till R has reached the position F B. 

 Then, in the path of the tube from B to C no sound traverses 

 the screen. When the edge B of the tube has reached the 

 position C the sound is again just on the eve of traversing the 

 screen through the opening E. As the distance A to B equals 

 B to C, the periods during which the sound traverses the 

 screen equal those in which it does not do so. If these alter- 

 nations of sound and silence should succeed one another so 

 rapidly that the sensation of the sound is uniform in its inten- 

 sity ; it may at first sight appear that during the time that the 

 tube takes to go from B to C the after-sensation of the sound 

 has not diminished in intensity. But is B to to be taken as 

 the measure of the duration of uniform sensation % As the 

 tube, R, moves over D a sound with a varying intensity 

 traverses the opening in the screen. We cannot suppose that 

 the residual sensation caused by the stimulus of the sound 

 traversing a minute opening in the screen equals that caused 

 by the sound which traverses the screen when the circles R 

 and D coincide. In such experiments, however, we are 

 driven to take as the duration of the undiminished residual 

 sensation the time that the center of the tube, R, takes to go 

 from the center of D to the center of E. 



In this illustration I have, for simplicity and conciseness, 

 supposed the tube R to move over the openings D and E. In 

 the actual experiments D and E are two of several holes in a 

 disk, arranged in a circle, and the disk rotates while the tube 

 R is fixed. Another tube placed in the prolongation of the 

 tube R on the other side of the disk conveys the interrupted 

 sound to the ear. 



