A . M. Mayer — Researches in Acoustics. 9 



and then describe three other forms of apparatus used. In 

 fig. 7 is seen a perforated disk mounted on the axle of a rota- 

 tor. In front of the disk is the resonator with its nipple close 

 to the surface of the disk. A tuning-fork is opposite the 

 mouth of the resonator. On the other side of the disk, with 

 its axis in line with the axis of the nipple of the resonator, is 

 the tube which conveys the interrupted sounds to the ear. 

 The opening in this tube has the same diameter as the open- 

 ings in the revolving disk. Behind the line of this tube is 

 seen, on the end of the axle, a fly wheel of copper weighing a 

 kilogram. 



The bevelled face of the driving wheel of the rotator has 

 three grooves cut in it, in steps. Corresponding grooves are 

 cut in the pulley of the axle. 



To run a rotator of this description smoothly, without jars, 

 or vibrations, it is necessary that the cord which passes over 

 the driving wheel and pulley should be very flexible and have 

 a circular section of uniform area throughout its length. I 

 obtained such a cord by soaking a cord of porpoise leather in 

 neat's foot oil and then drawing it many times through wire- 

 drawing plates. The ends of the cord are connected by a short 

 hook and eye coupling. The driving wheel can be slid up or 

 down the standard of the rotator to adjust the tension of the 

 cord. 



The driving wheel is turned by a handle of aluminum of 

 the form shown in the figure. It is necessary to have a handle 

 of small diameter in order to turn the wheel with a uniform 

 velocity. The fingers which clasped the handle were coated 

 with plumbago dust. 



In all the experiments the driving wheel of the rotator was 

 revolved either once in a second or twice in a second. This is 

 accomplished, after some practice, in the following way. The 

 rotator, on which is mounted the disk and fly-wheel, is placed 

 near a clock giving loud beats of seconds, and the driving 

 wheel is revolved by the guidance of hand and ear The 

 results of the experiments showed that the velocities thus 

 given to the disk were sufficiently uniform, and the measures 

 of the durations of sonorous sensations sufficiently concordant , 

 and precise to obtain the data of the physiological law. 



I adopted this method of rotation in preference to mechani- 

 cal means for controlling and measuring the revolutions of the 

 disks. To determine when the interrupted sounds have 

 blended, requires, so to say, a flexible apparatus whose velocity 

 is under the immediate control of the hand and ear. This is 

 important in making the final judgment between sounds, one 

 of which appears to have too few interruptions, the other a few 

 more interruptions than are necessary to give a continuous uni- 



