348 



DR. KCENIG's researches ON 



pose Dr.Koiuig- has constructed a siren-disk (Fig. 1), pierced with holes 

 arranged at equal distances around seven concentric circles ; but the 

 sizes of the holes are made to vary periodically from small to large. 

 In each circle are 192 equidistant holes, and the number of maxima in 

 the respective circles was 12, 16, 24, 32, 48, 64, and 96. On rotating 



^,/<7^^* ••^>\ 



^^ * •• ,.•#••0., *. • .^"v. 



.••..-.. • •.;. .;•••.■•..••, 



.• .•• ..• •..••./.. 



' • ,• . = •• ••. •. •. 



Fig. 1- 



this disk, and blowing from behind through a small tube opposite the 

 outermost circle, there are heard, if the rotation is slow, a note cor- 

 responding to the number of holes passing per second and a beat cor- 

 responding to the number of maxima per second. With more rapid 

 rotation two notes are heard — a shrill one, and another 4 octaves lower 

 in pitch, the latter being the beat-tone. On moving the pipe so that 

 wind is blown successively through each ring of apertures, there is 

 heard a shrill note, which is the same in each case, and a second note 

 (corresponding to the successive beat-tones) which rises by intervals of 

 fourths and fifths from circle to circle. 



These attempts to produce artificially the mechanism of beats were, 

 however, open to criticism ; for in them the phase of the individual 

 vibrations during one maximum is the same as that of the individual 

 vibrations in the next succeeding maximum ; whereas in the actual 

 beats produced by the interference of two tones the uhases of the indi- 



FiG. 2. 



vidual vibrations in two successive maxima differ by half a vibration, 

 as may be seen by simple inspection of the curves corresponding to a 

 series of beats. When this difference was pointed out to Dr. Koenig, 

 he constructed a new siren disk (Fig. 2), haying a similar series of 



