licate little
instrument with which we speak, and then utter some words in a strong,
clear voice, you will doubtless feel a vibration or trembling in your
throat, just the same as I now feel in my throat while I am talking. My
effort to speak causes these little chords in my throat to vibrate, just
the same as when you pass your fingers over the chords of a harp or
violin, or when you strike the keys of a piano you make the wires
tremble and thus produce sound, so these chords in my throat tremble and
cause the air to tremble, producing what we call sound-waves. Just the
same as when you take a stone and drop it into the lake, you see the
little waves or ripples, as we call them, go out in small circles, wider
and wider, further and further, until they strike the distant shore. So
the air is made to vibrate by my effort to speak, and these little
sound-waves in the air strike against the drum of your ear, back of
which there are nerves, ever ready to convey to the brain the sensation
which we call sound,

[Illustration: "The Little Waves or Ripples."]

"Like clear circles widening round
Upon a clear blue river,
Orb after orb, the wondrous sound
Is echoed on forever."

Now, this small baking-powder box represents the ear, and the paper at
this end represents the drum of the ear, and this string represents the
nerves. This string may be prolonged for a considerable distance, and if
you were to connect the end of the string with another box of the same
sort you would then have a telephone with which you would be able to
hear quite plainly the words which are spoken by some other person at
the opposite end of the string. When I speak into this box it makes the
paper tremble, and that makes the string tremble, and if there were
another box at the far end of the line it would cause the paper on the
end of that box to tremble just the same, and that would cause the air
to tremble where that box is, and if you were to hold your ear to that
box you would be able to hear the words.

If I take this box, and instead of a string I should place the point of
a needle back of it, and a cylinder to revolve, so that the needle would
scratch the vibrations upon the cylinder, I would then have a
phonograph. I would then be able to record the words, and with another
smooth needle to go into the scratches which had been made by the sharp
needle, I would be able to reproduce the sound; or, in