pparent vibrations in what is considered as the sounding body.
We have two or three instances of this kind; one in wind instruments,
such as the flute or organ pipe; another in the discharge of a gun.

In an organ, or flute, the air, which is driven through the pipe,
strikes against the edge of the lips of the instrument in its
passage, and by being accumulated there, is condensed, and this
condensation produces waves or pulses in the air.

When a gun is discharged, a great quantity of air is produced, by the
firing of the gunpowder, which being violently propelled from the
piece, condenses the air that encompasses the space where the
expansion happens; for whatever is driven out from the space where
the expansion is made will be forcibly driven into the space all
around it. This condensation forms the first pulse, and as this, by
its elasticity, expands again, pulses of the same sort will be
produced and propagated forwards.

There is likewise another curious instance of the production of
sound, when a tube is held over a stream of inflamed hydrogen gas
issuing out of a capillary tube in a bottle.

Sounding bodies propagate their motions on all sides, directly
forwards, by successive condensations and rarefactions, so that sound
is driven in all directions, backwards and forwards, upwards and
downwards, and on every side; the pulses go on succeeding each other
like circles in disturbed water.

Sounds differ from each other both with respect to their tone and
intensity: in respect to their tone, they are distinguished into
grave and acute: in respect to their intensity, they are
distinguished into loud and low, or strong and weak. The tone of a
sound depends on the velocity with which the vibrations are
performed, for the greater the number of vibrations in a given time,
the more acute will be the tone, and on the contrary, the smaller the
number, the more grave it will be. The tone of a sound is not altered
by the distance of the ear from the sounding body; but the intensity
or strength of any sound depends on the force with which the waves of
the air strike the ear; and this force is different at different
distances; so that a sound which is very loud when we are near the
body that produces it, will be weaker if we are further from it,
though its tone will suffer no alteration; and the distance may be so
great that we cannot hear it at all. It has been demonstrated, that
the intensity of sound at different dista