nd
upon the position and nature of the reflecting surfaces and also upon
the length of time a sound persists after the vibrating body has
stopped. If it persists longer than 2-1/4 or 2-1/3 seconds the room will
not be suitable for musical performances because of the mixture of
persisting tones with following ones, this causing a blurred effect
somewhat like that obtained by playing a series of unrelated chords on
the piano while the damper-pedal is held down. The duration of the
reverberation depends upon the size and height of the room, material of
floor and walls, furniture, size of audience, etc.

6. Sound may be classified roughly into _tones_ and _noises_ although
the line of cleavage is not always sharply drawn. If I throw stones at
the side of a barn, sounds are produced, but they are caused by
irregular vibrations of an irregularly constructed surface and are
referred to as _noise_. But if I tap the head of a kettle-drum, a
regular series of vibrations is set up and the resulting sound is
referred to as _tone_. In general the material of music consists of
tones, but for special effects certain noises are also utilized (cf.
castanets, etc.).

7. Musical tones have three properties, viz.:

1. Pitch.

2. Intensity.

3. Quality (timbre).

By _pitch_ is meant the highness or lowness of tone. It depends upon
rate of vibration. If a body vibrates only 8 or 10 times per second no
tone is heard at all: but if it vibrates regularly at the rate of 16 or
18 per second a tone of very low pitch is heard. If it vibrates at the
rate of 24 the pitch is higher, at 30 higher still, at 200 yet higher,
and when a rate of about 38,000 per second has been reached the pitch is
so high that most ears cannot perceive it at all. The highest tone that
can ordinarily be heard is the E[flat] four octaves higher than the
highest E[flat] of the piano. The entire range of sound humanly audible
is therefore about eleven octaves (rates 16-38,000), but only about
_eight_ of these octaves are utilized for musical purposes. The tones of
the piano (with a range of 7-1/3 octaves) are produced by vibration
rates approximately between 27 and 4224. In the orchestra the range is
slightly more extended, the rates being from 33 to 4752.

Certain interesting facts regarding the relation between vibration-rates
and pitches have been worked out: it has been discovered for instance
that if the number of vibrations is doubled, the pitch o