1890.] on the Physical Foundation of Music. 221 



Finding this result from the spacing out of apertures to corre- 

 spond in position and magnitude to the individual wavelets of a 

 complex train of waves, it occurred to Dr. Koenig that the phenomena 

 of beats and beat-tones might be still more fully reproduced if 

 the edge of the disk were cut away into a wave-form corresponding 

 precisely to the case of the resultant wave produced by the composi- 

 tion of two interfering waves. Accordingly, he calculated the wave- 

 forms for the cases of several intervals, and, having set out these 



Fig. 3. 



'sA _..••" j2q "•••.. ^l 



6* 



\ 



^^ 



Wave-disk giving beats and beat-tone. 

 Fig. 4. 



Wave-disk, giving beats and beat-tone. 



curves around the periphery of a brass plate, cut away the edge of 

 the plate to the form of the desired wave. Two such wave-disks, 

 looking rather like circular saws with irregular teeth, are depicted 

 in Figs. 3 and 4. These correspond to the respective intervals 8 : 15 



