An experiment will show how pitch varies and how it is regulated:
Fig. 103. When the prongs of the tuning fork are made longer or shorter, the pitch of the sound is changed.
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 strike it. Now pour half the water out, and strike the glass again. Do you get the higher sound when the column of water is shorter or when it is longer? Stretch a rubber band across your thumb and forefinger. Pick the band as you make it tighter, not making it longer, but pulling it tighter with your other fingers. Does it make a higher or a lower sound as you increase the tightness? Stretch the band from your thumb to your little finger and pick it; now put your middle finger under the band so as to divide it in halves, and pick it again. Does a short strand give a higher or lower pitch than a long strand?
A violinist tunes his violin by tightening the strings; the tighter they are and the thinner they are, the higher the note they give. Some of the strings are naturally higher than others; the highest is a smaller, finer string than the lowest. When the violinist plays, he shortens the strings by holding them down with his fingers, and the shorter he makes them the higher the note. A bass drum is much larger than a high-pitched kettledrum. The pipes of an organ are long and large for the low notes, shorter and smaller for the high ones.
In general, the longer or larger the object is that vibrates, the slower the rate of vibration and consequently the lower the pitch. But the shorter or finer the object is that vibrates, the higher the rate of vibration and the higher the pitch.
All musical instruments contain devices which can be made to vibrate,—either strings or columns of air, or other things that swing to and fro and start waves in the air. And by tightening them, or making them smaller or shorter, the pitch can be made higher; that is, the number of vibrations to each second can be increased.
Application 44. Explain why a steamboat whistle is usually of much lower pitch than is a toy whistle; why a banjo player moves his fingers toward the drum end of the banjo when he plays high notes; why the sound made by a mosquito is higher in pitch than that made by a bumblebee.
Application 45. A boy had a banjo given him for Christmas. He wanted to tune it. To make a string give a higher note, should he have tightened or loosened it? Or could he have secured the same result by moving his finger up and down the string to lengthen or shorten it?
Application 46. A man was tuning a piano for a concert. The hall was cold, yet he knew it would be warm at the time of the concert. Should he have tuned the piano to a higher pitch than he wanted it to have on the concert night, to the exact pitch, or to a lower pitch?