THE PITCH OF A NOTE 



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number of vibrations which correspond to middle C on the 

 piano, we increase the speed of the disk until the note given 

 forth by the siren agrees with middle C as sounded on the 

 piano, as nearly as the ear can judge; we then calculate the 

 number of puffs of air which took place each second at that 

 particular speed of the disk. In this way we find that middle 

 C is due to about 256 vibrations per second ; that is, a piano 



FIG. 177. A siren. 



string must vibrate 256 times per second in order for the re- 

 sultant note to be of pitch middle C. In a similar manner we 

 determine the following frequencies: 



The pitch of pianos, from the lowest bass note to the very 

 highest treble, varies from 27 to about 3500 vibrations per 

 second. No human voice, however, has so great a range of 

 tone; the highest soprano notes of women correspond to 



