The Science Notebook
Gilbert Sound - Chapter II

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NOTE:  This book was published around 1920 as a manual to accompany the Gilbert Sound set.  The set and manual were part of the "Boy Engineering" series, While some of the experiments and activities here may be safely done as written, some of them may be considered hazardous in today's world.  In addition, some of the information contained in this book is either outdated or inaccurate.  Therefore, this book is probably best appreciated for its historical value rather than as a source of current information and good experiments.  If you try anything here, please understand that you do so at your own risk.  See our Terms of Use.
Pages 16-24

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Chapter II
ORIGIN OF SOUND

Now we are ready for experiments and scientific research into the questions we asked in the earlier pages of this book.  What is sound?  What is it that comes from our throats when we talk?  How does it travel to our ears?

There are three things concerning sound that are necessary before there can be any sound in the proper sense of the word.  (1) Sound must begins somewhere; (2) it must travel to us; and (3) it must be heard by the ear.  First let us see where sound begins.



Take a cork hammer (see Figure 5) and lightly strike the edge of a wine glass.  It gives a strong clinking sound.  Now put your finger on the edge of the glass.  Two things should happen.  First, you feel a slight tremble or vibration on your finger  
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and, second, the sound ceases.  It should be plain to you then that the glass was vibrating and when you stopped this vibration you stopped the sound.  Now let us figure out what this vibration is.  

Special Note.  As many of the following experiments require a tuning fork to be vibrated, we will explain different methods of accomplishing this.  Each method has its advantages for certain experiments.  



1st.  Hold a tuning fork by the base and strike one of the prongs sharply against the heel of your shoe or any solid object, such as a table top.  You will not be able to hear much of a sound from the fork as you hold it in your hand, but if you bring it close to your ear or place it with the base firmly against a table top or box cover (See Figure 6) you will hear a clear, even tone.  



2nd.  Force the base of a tuning fork into a hole bored in a block of wood. Hold the block firm with the left hand and with the right, take a wood or cork hammer and strike one prong of the fork with a sharp blow.  (See Figure 7.)

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3rd.  Proceed as in the second method, except that instead of striking the fork with a hammer you take a violin bow, well resined, and draw it across the face of the tuning fork.  (See Figure 8.)  This will set the fork into violent vibration, and is  

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the method which you will find most satisfactory for a majority of your experiments.  



Experiment No. 6.  Attach a tuning fork to a block in place on a table or box and strike one of the prongs of the tuning fork with a cork hammer.  Now hold a shoe button by means of a thread (see Figure 9) against one side of the tuning fork.  The resulting action of the button will prove that the tuning fork is a vibrating body in that it is moving with a "to and fro" motion like the pendulum.  As the sound grows fainter the button does not rebound so far, because like the "to and fro" motion of the pendulum the vibrations or oscillations are growing smaller.  This proves the theory that a sound-producing body is a vibrating body.  

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Experiment No. 7. Pick up a vibrating tuning fork and place the base of it between your teeth and feel the vibration.  (See Figure 10.)  Now take the tuning fork and set it in vibration by hitting it with a cork hammer and then bring it in contact with the surface of the water.  (See Figure 11.)  To make the experiment more effective, scatter some lycopodium powder on the surface of the water.  The action of the fork will then produce beautiful waves.





Experiment No. 8.  Strike a bell with a cork hammer.  (See Figure 12.)  See if you can observe the vibration or motion of

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the bell, and notice that the sound grows less as the vibration diminishes.  We are certainly convinced by this time that sounds are produced by vibrations, and it should be conclusively proved to you that the motion which we studied in connection With the pendulum is the same kind of motion that is producing these sounds - that is, "to and fro" motion.  

HOW WE MAKE SOUNDS WITH OUR THROATS

The apparatus that nature has provided for making sounds with our throats is very simple and easily understood.

In our throats are two cords, known as the vocal cords, and when we talk air waves from the lungs throw these cords into vibration, producing the different sounds.  The wonderful part

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of the mechanism is that we can produce so many sounds with only two cords, the human throat being so constructed that the cords can be lengthened or shortened by means of muscles.  Tubes leading from these cords, in conjunction with the lips, enable us to produce almost any sound.  

VIBRATION OF AIR COLUMNS

We have discovered now that sound is produced by vibrating bodies.  You should know that it is also produced by the vibrations of columns of air contained in tubes and pipes, as in many musical instruments.  There are three classes of air instruments or mouth-piece instruments by means of which columns of air are vibrated in the instruments themselves.

1st.  We have the instruments in which the air is blown

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across the sharp edge of the opening, such as the whistle, the flute and pipe organ.  (See Figure 13.)  



2nd.  We have air instruments in which the sound is produced by blowing air past a thin tongue, known as a reed.  (See Figure 14.)  The reed opens and closes the air column.  



3rd.  There is that air instrument used in all bands, known as the cornet, where sound is produced by vibration of the lips on the mouthpiece.  (See Figure 15.)



MUSICAL FLAMES

There are probably no prettier experiments in the study of sound than those in which tones are obtained from tubes by means of a flame.



Procure of glass tube about 1/4 of an inch in diameter and 6 inches long.  Bend this tube at right angles and, by means of a staple, fasten it to a small board under a tripod covered with wire gauze.  (See Figure 16.)  Connect the bent glass tube into a gas jet and make a light,

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holding a match a over the wire gauze.  Adjust the pressure of the gas and the position of the bent glass tube until a blue flickering flame is obtained.  Now place another tube, about 2 inches in diameter and of almost any length, over the flame and you will at once here loud musical tones.  By trying tubes of different lengths, you will get many fascinating results.  

As you may have concluded already, the sounds are produced by vibrations of the air within the large glass tube.  

Go to Chapter III or To the A.C. Gilbert Collection

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