Prof. A. M. Mayer's Researches in Acoustics. 353 



rtesonator, by means of a perforated disk which rotated between 

 the resonator and the fork, as is shown in the accompanying figl. 



Fig. 1. 



The mean diameter of the open sectors of the disk equalled the 

 diameter of the mouth of the resonator, while the spaces of caid- 

 board between the open sectors was twice the width of these 

 openings. Thus the resonator's mouth was exposed to the 

 vibrations during an interval which equalled that during which it 

 was screened from them. A rubber tube led from the nipple of 

 the resonator to one ear, while the other ear was tightly closed 

 with a Jump of bees-wax. 



In my first experiment I firmly clamped an Ut 2 resonator, and 

 vibrated opposite its mouth an Ut 2 fork. I now placed the tube 

 in the ear, and on slowly rotating the disk I perceived a series 

 of sharply separated explosions or beats. On gradually increasing 

 the velocity of the disk these explosions gradually approached 

 each other ; and on reaching a certain frequency in their succes- 

 sion they blended into a continuous smooth sensation, similar 

 to that experienced when the disk was removed and the fork 

 vibrated gently before the resonator. I now kept the disk at the 

 velocity required just to blend the separate beats ; and I found, 

 on timing its rotations, that the resonator was sending into my 

 ear about thirty explosions or beats per second. Hence sono- 

 rous waves of Ut 2 cut into thirty parts per second, or, in other 

 words, divided into lengths of about four waves separated by the 

 same lengths of quiescence, produce the same sensation as that 

 caused by an uninterrupted flow of these sonorous waves into the 



