272 Dr. A. M. Mayer's Researches in Acoustics, 



the means of obtaining a considerable range in the number of 

 interruptions of sounds per second. 



The results given by this apparatus were the same as those 

 obtained with [A], but the objection to its action is the pro- 

 duction of sounds by the apparatus itself, caused by the 

 rotation of the perforated disk. These sounds distracted the 

 attention from the phenomenon of the continuous sensation 

 produced by the interruptions of the sound from the fork, and 

 so masked it that I consider this apparatus the least efficient 

 of those I have described. 



These experiments on the blending of interrupted sounds 

 are not pleasant to make. The ear soon becomes fatigued, and 

 the perception of sound is dulled. After an experiment the 

 ear has to be rested during a considerable time before the 

 experiment can be repeated satisfactorily. Thus much time 

 is consumed, and these experiments cannot be made in a few 

 days, but weeks are required to arrive at satisfactory measures ; 

 also, considerable time is consumed in gaining mastery over 

 the apparatus. To make these experiments less tedious, 

 fatigue of the ear is to be avoided. This is done by not 

 allowing the interrupted sounds to enter the ear longer than 

 during two or three seconds ; then a rest of five to six seconds 

 is taken, while the fork is kept in action and the disk revolved 

 with the same velocity ; then another three-second period of 

 sound is given the ear. This is best done by placing the 

 rubber tube in the meatus of the ear and pinching the 

 tube between the fingers. By relieving the pressure more 

 or less we can regulate the intensity of the sound which 

 enters the ear, or we can shut the sound off. The other ear is 

 tightly closed with beeswax softened with a little turpentine. 



Within the limits of the intensities of sound used in these 

 experiments, I found no change in the duration of the sen- 

 sation with change in the intensity of the sound. It seems 

 probable that such connected changes exist. If they do exist, 

 then it would appear, from the smoothness of the curve I have 

 obtained from the experiments, that the relative mean inten- 

 sities of the sounds used did not vary sufficiently to make 

 apparent any change in the duration of the after-sensation with 

 change in the intensity of the stimulus. 



Table of Results of Experiments. — The Empirical Formula 

 ivhich gives the Relation of the Pitch of a Sound to the 

 Duration of its Residual Sensation. 



The results of the experiments made with the various 

 forms of apparatus just described are given in the following- 

 Table I. 



