this way by blowing across the end of any tube made of any material,
of glass, or iron, or rubber, or cane, or even the barrel of an
old-fashioned door key. The primitive Flutes found in the Egyptian
tombs and also depicted on the ancient hieroglyphics are made of reed
or cane, about 14 inches long, possessing the usual six finger-holes.
The top end is not stopped with a cork, as in the ordinary Flute, but
is thinned off to a feather edge, leaving a sharp circular ring at
right angles to the axis of the bore. By blowing across this ring a
fair but somewhat feeble Flute tone is produced.

The six holes being closed by the fingers, the ground tone of the tube
is produced. On lifting the fingers in successive order from the
bottom end, we get the seven notes of the major scale. Closing the
holes again and blowing harder, we get the scale _an octave higher_.
By blowing still harder we get an octave higher still. In other words,
we are now producing _harmonics_.

It is possible to produce from a plain tube without finger-holes or
valves, such as the French Horn, by tightening the lips and increasing
the pressure of the player's breath, the following series of harmonics:

[Illustration: Series of harmonics]

The harmonics of a pianoforte string can be easily demonstrated by the
following experiment: Depress the "loud" pedal and strike any note in
the bass a sharp blow. On listening intently, the 3d, 5th, and 8th
(the common chord) of the note struck will be heard sounding all the
way up for several octaves. In this case the other strings of the
piano act as _resonators_, enabling the harmonics to be heard.

Coming back to our Flute again and applying the knowledge we have
gained to an organ pipe, we observe:

1. That the _pitch_ of the sound depends on the length of the tube.

2. That the pitch of the sound _also_ depends on the amount of wind
pressure.

From this last will be seen how important it is that the pressure of
the wind in an organ should be steady and uniform. Otherwise the pipes
will speak a harmonic instead of the sound intended--as, indeed,
frequently happens.

When a stop is labeled "8 ft.," that means that the bottom pipe, CC is
8 feet long and the pitch will be that of the key struck. A "16-ft."
stop will sound an octave lower; a "4-ft." stop an octave higher.
These measurements refer to pipes which are open at the top and are
only correct in the case of very narrow pipes, such as the sto