10 A. M. Mayer — Researches in Acoustics. 



form sensation. It is evident that when we can at once 

 slightly increase or diminish the velocity of rotation of the 

 disk we have the means of making comparisons rapidly suc- 

 ceeding one another. A rotator driven as described forms 

 more a part of the observer than one driven and regulated by 

 mechanism. 



As there were three grooves in the driving-wheel and three 

 on the pulley on the axle, and as the driving-wheel was re- 

 volved either once or twice in a second, 18 different velocities 

 could be given to the rotating disk. 



Disks were made having numbers of holes from 5 to 19, so 

 that, with 18 velocities and the various numbers of holes in 

 the disks it was easy to select a disk driven with a known 

 velocity which gave the exact number of interrupted sounds 

 per second to blend. 



The 18 ratios of velocities of the driving-wheel and of the 

 pulley on the axle of the rotator were obtained as follows : A 

 circle of card-board, divided into 100 parts, was clamped on 

 the rotator in front of a disk. The driving-wheel was rotated 

 either once or twice in a second so that the conditions were 

 the same as in the experiments. From 10 to 100 revolutions 

 of the driving-wheel were made before the ratio was deter- 

 mined. The division to which a fixed index pointed on the 

 divided circle gave the fraction of a revolution. The whole 

 number of revolutions was given by a simple counter which 

 moved with very little friction. 



The rotating disks were made of mahogany, 5 m,n thick, with 

 disks of card-board about 2 mra thick screwed to the wooden 

 disks. The circumference of the holes in the wooden and 

 card- board disks exactly coincided. The circle of holes in the 

 disk was placed 5 cms from its border. The rotator and disks 

 were so carefully made that the nipple of the resonator was 

 only y\ mm from the surface of the revolving disk. The 

 mouth of the tube conveying the interrupted sounds to the 

 ear was about the same distance from the surface of the other 

 side of the disk. The disks were clamped on the axis of the 

 rotator between smaller flat disks of brass, not shown in the 

 figure. 



The diameter of the holes in the disk and of the interior of 

 the tube conveying the sounds to the ear was l cm . The diam- 

 eter of the openings in the nipples of the resonators was |- cm . 



The disks were made of mahogany which had been in my 

 possession for thirty years. It was well seasoned and had 

 nearly the thickness required for the disks. This wood was 

 used because it holds the form given it better than any wood 

 I have had experience with. 



