520 Dr. 11. Koniff on the Simultaneous 



e 



primary impulses, at a sufficient number and intensity change 

 into a note. 



This may be easily demonstrated by means of a disk in 

 •which is a circle of large holes, and which is made to revolve 

 before a tuning-fork. I have used different disks with 16, 

 21, and 32 holes, 20 millims. in diameter, at various distances, 

 each disk much larger than the circle of holes, so that the 

 note, as far as possible, should only penetrate strongly to the 

 car when an opening was in front of the tuning-fork. Of 

 course any particular note will not, in any particular number 

 of intermissions, produce a note which corresponds to this 

 number of intermissions ; but it will be necessary, besides the 

 needful strength and the sufficient number of intermissions, 

 that the air-shocks which penetrate through the openings of 

 the disk shall be equal to each other; and this cannot be, for 

 instance, when the number of intermissions is greater than the 

 number of double vibrations of the note. In this case either 

 several holes pass by the same sound-wave, so that a fresh 

 part of this wave always passes through each, or, at any rate, 

 they are not equal parts of different sound-waves which the 

 openings make a way for to the ear. When, too, the number 

 of the intermissions is only a little greater than the number 

 of double vibrations of the note, similar conditions ensue, 

 and it becomes necessary that at least one entire sound- 

 wave should penetrate through the opening in order that the 

 intermission-note may be clearly perceptible. The most 

 favourable circumstance for its audibleness seems to be that in 

 which an entire series of sound-waves can penetrate through 

 each opening — that is, when the vibrations of the note are 

 considerably more in number than the intermissions. 



If a disk in which the distance of the holes from one 

 another is three times as great as their diameter (2 centims.) 

 is allowed to move with such rapidity that 128 holes pass the 

 tuning-fork in a second, the intermitting note c is heard with 

 the fork 0^ = 512 v. d. ; but it is faint, and is less prominent 

 than the two variation-notes, which equal the difference and 

 the sum of the intermitting notes and of the double vibrations of 

 the fork, and which are therefore here </ = 384 v. d. and e" ■=■ 

 640 v. d. (Tonempfind. p. 628). If, while the disk moves 

 always with the same rapidity, the forks e" , g" , seventh har- 

 monic of c, and c'" are used one after another, the intermitting 

 note increases constantly in strength and clearness. If, lastly, 

 the notes of the very powerful forks c IV and c v are allowed to 

 penetrate through the holes of the disk when the ratio between 

 the number of intermissions and that of the double vibrations 

 of the note is 1 : 16 and 1 : 32, the intermitting note is extra- 



