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



the perforated disk rotating across the mouth of the resonator 

 gives rise to two secondary sounds and a resultant sound, 

 fully described in my paper of 1875 *. These sounds, from 

 their intensity in this form of experiment, mask the proper 

 sound of the fork, making the determination of the durations 

 of the sonorous sensations both difficult and uncertain. Also, 

 in these experiments the action of the interrupted sound on 

 the ear is distressing, even injurious ; for the hearing of one 

 of my ears was permanently impaired by the experiments I 

 made with this apparatus nineteen years ago. 



In the apparatus presently to be described, the fork vibrates 

 in front of the mouth of the resonator, and the interruptions 

 in the flow of sound are caused by the perforated disk re- 

 volving in front of the small opening in the nipple of the 

 resonator, as shown in fig. 7. 



Discussion of the Effects of the Relative Sizes of the Openings 

 in the Revolving Dish and of the Opening in the Tube 

 conveying the Sound to the Dish. 



First Case. Suppose that the opening of the nipple of the 

 resonator and the openings in the disk have the same dia- 

 meter. In the actual experiments these openings were 

 1 centim. in diameter. The nipple of the resonator had a 

 tube of that diameter adapted to it. 



Fig. 4. 



1.0 



•4 































































































































































J 





13 



Fig. 4 is the graphic representation of the results of com- 

 puting the varying areas of the opening of the tube of the 

 resonator, as an opening in the disk passes in front of it. 

 This diagram is to be studied in connexion with fig. 2. The 

 entire length on the axis of abscissas OX gives the space 

 A to B of fig. 2, divided into sixteen parts. The ordinates 

 of the curve give the relative areas of opening for corre- 

 sponding positions on the axis of abscissas. The ordinate 



* See a paper by Lord Rayleigh, "Acoustical Observations, III. 

 Intermittent Sounds/' Phil. Mag., April 1880, in which the author gives 

 an explanation, in mode and in measure, of the secondary soimds and of 

 the resultant sound, observed by me in these experiments. 



