XLVIII
regard to the arrangements made to set the enclosed air in vib
ration we make a difference between mouth-instruments and
reed-instruments. In the former by the so-called mouth-piece
air enters not in a continuous flow (as if simply blowing into
a tube) but in an intermittent manner; in the latter air is set in
vibration by means of elastic plates, called tongues, Mouth-in
struments we have in the flute, the horn and in most pipes of
an organ; vibration by tongues is produced in the harmonium,
the clarionet, the oboe and the bassoon. Take a blade of grass
and fasten it between the thumbs of both hands and you have
a reed-instrument. On blowing into the hole or rent produced
by joining both thumbs together a sound will issue.
§ 115. If pipes are stopped, the number of vibrations are
inversely as the lengths; hence the longer a pipe of this kind the
deeper the sound. A pipe half as long as another yields a sound
which is the octave of that produced by this pipe. 256.
The note yielded by an opera pipe is always an octave higher
than the note of a closed one of the same length.
§ 116. By a reed-pipe, which in perfection surpasses any
thing constructed by art or science, the human voice is produc
ed. 257.
§ 117. There exists a curious instrument called a Chemical
Harmonicon, in which a sound is produced by a chemical pro
cess. If we hold a glass-tube, 50–100 centimeter long, above
the flame of burning hydrogen, the flame begins to tremble and
the air within the tube begins to sound. The sound changes with
the length and width of the tube. In bringing this singing or
sounding flame before a looking-glass and causing it so turn
round its own axis, we behold a circle of flames, separated from
each other by dark intervals. The sound is produced by the
vibrations of the flame and the air. The vibration of the flame
