one next
to him, and the person at the end be pushed, the force will be
conveyed through all the intermediate individuals, and cause the
unsupported person at the distant end to move. So is it with the
particles of which the air is composed. The movements begun in the
drum set up by contact corresponding movements or vibrations in the
adjacent air, which ultimately reach the hearing subject's ear,
thereby affect his brain, and are accompanied by that change in
consciousness which he terms "hearing." It will be observed that these
events constitute a chain, and a break anywhere will prevent a sound
being heard; there is then, in fact, no sound.

Sounds are characterized by _pitch_, _volume_, and _quality_.

The _pitch_ is determined by the number of vibrations that reach the
ear within a certain time; the more numerous the sound-waves
(vibrations) in a second, the higher the pitch.

[Illustration: FIG. 37 (Tyndall). Meant to illustrate vibrations. The
impulse communicated by the ball pushed from the hand to all the
intervening ones causes only the last to actually move bodily.]

Animals differ a good deal as to the limits of hearing. Cats hear very
high-pitched sounds, as of mice, that human beings may not notice, and
it is likely that insects hear sounds altogether beyond the limit of
the human ear. But it is wonderful how much human beings differ among
themselves in regard to this matter. It has surprised the author to
find that many persons cannot hear the high-pitched note of certain
birds, as the wax-wing.

The lower limit, speaking generally, is for most persons 16
vibrations, and the highest 38000 vibrations a second, according to
Helmholtz, hence the entire range of the human ear would be fully 11
octaves; but the practical range of musical sounds is within 40 and
4000 vibrations a second--_i.e._, about 7 octaves--and, as is well
known, even this range is beyond the appreciation of most persons,
though as to this much depends on cultivation--attention to the
subject extending over a considerable period of time.

The _volume_, or loudness, of a sound depends on the size of the
vibrations, just as one feels a blow from a large object, other things
being equal, more than from a small one. The ear drum-head is in the
case of a large sound beaten, as it were, more powerfully. The singers
that give us bigness of sound instead of quality belabor our ears, so
to speak; they treat us as persons of mean understandin