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



duration of the after-sensation produced by the stimulus of 

 light can be measured, as in the case of an electric flash, the 

 determination of the total duration of the after-sensation of 

 a sound appears, in the light of our present knowledge and 

 with the means of experiment at our command, to be a 

 problem very difficult to solve. 



The object of this research was not to determine the total 

 duration of the after-sensation of a sound, but to measure 

 that duration in which the after-sensation of a sound does 

 not perceptibly diminish in intensity. 



Fig. 2. 



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

 pervious to sound. The distance between the openings 

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

 the same interior diameter as the openings, is supposed to 

 convey 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 II 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 0, 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 alternations of sound and silence should 

 succeed one another so rapidly that the sensation of the 

 sound is uniform in its intensity, 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 C 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 B and D coincide. In such experi- 

 ments, however, we are driven to take as the duration of the 



