1 86 Common Science 



spoke you had to utter your words in exactly that pitch ; 

 that every time a car came down the street its noise 

 was like the whistle of the peanut roaster, only louder ; 

 that every step you took sounded like hitting a bell of 

 the same pitch ; that when you went to the moving- 

 picture theater the orchestra played only the one note ; 

 that when any one sang, his voice did not rise and fall ; 

 in short, that all the sounds in the world were in one 

 pitch. That is the way it would be if different kinds 

 of air vibrations did not make different kinds of notes, 

 if there were no differences in pitch. 



Pitch due to rapidity of vibration. When air vibra- 

 tions are slow, far apart, the sound is low ; when 

 they are faster, the sound is higher ; when they are 

 very quick indeed, the sound is very shrill and high. 

 In various ways, as by people talking and walking and 

 by the running of street cars and automobiles, all sorts 

 of different vibrations are started, giving us a pleasant 

 variety of high and low and medium pitches in the 

 sounds of the world around us. 



An experiment will show how pitch varies and how it 

 is regulated : 



Experiment 60. Move the slide of an adjustable tuning 

 fork well up from the end of the prongs, tap one prong 

 lightly on the desk, and listen. Move the slide somewhat 

 toward the end of the prongs, and repeat. Is a higher or a 

 lower sound produced as the slide shortens the length of the 

 prongs ? 



Whistle a low note, then a high one. Notice what you 

 do with your lips; when is the opening the smaller? Sing 

 a low note, then a high one. When are the cords in your 

 throat looser? Fill a drinking glass half full of water, and 



