THE SIREN. 347 



Tour rows, let air be blown through it as steadily as 

 possible, and the handle be worked first slowly but 

 gradually more and more rapidly. At first no real 

 lote is heard, but only the whirring and whizzing 

 sound of the puffs of air rushing out of the tube ; 

 out as soon as the disc turns with a certain velocity 

 ;his sound is accompanied by a deep note. This 

 lappens when 90 or 100 puffs of air are produced in 

 me second. The notes of the largest organ-pipes are 

 produced by only thirty-two vibrations in a second, 

 out such very deep notes are only heard with difficulty ; 

 n our experiment they are overpowered by the whiz- 

 ting sound of the air, and no note is heard distinct 

 rom it, until the number of vibrations is comparatively 

 i^reat, and the note becomes high enough to be easily 

 >erceptible by the ear. In proportion to the velocity of 

 he disc the note rises, until the greatest velocity is 

 obtained which can be produced by turning the handle 

 vith the hand. If the hand is now withdrawn and the 

 iipparatus allowed to come to rest by itself, the note 

 Becomes deeper and deeper, until it is lost in the sound 

 aused by the current of air. If, during the experi- 

 ment, the velocity is maintained for some time as 

 (icarly constant as possible, the note will remain the 

 ame, or as it is expressed, its pitch or tone will remain 

 jmaltered. This experiment proves, that difference in 

 latch, that is, whether a note is low or high, depends 

 in the frequency with which the pulsations of the air 

 re produced, and that if the frequency increases the 

 ote becomes higher, if the frequency decreases the note 

 Becomes lower, or generally the pitch increases and 

 lecreases with the number of sonorous vibrations pro- 



