of cavalry, at a much greater distance than they can see
them.

For the same reason two stones being struck together under water, may
be heard at a much greater distance by an ear placed under water
likewise, than it can be heard through the air. Dr. Franklin, who
several times made this experiment, thinks that he has heard it at a
greater distance than a mile. This shows that water is better adapted
to convey sound than air.

When an elastic body is struck, that body, or some part of it, is
made to vibrate. This is evident to sense in the string of a violin
or harpsichord, for we may perceive by the eye, or feel by the hand,
the trembling of the strings, when by striking they are made to
sound. If a bell be struck by a clapper on the inside, the bell is
made to vibrate. The base, of the bell, is a circle, but it has been
found that by striking any part of this circle on the inside, that
part flies out, so that the diameter which passes through this part
of the base will be longer than the other diameter. The base, by the
stroke, is changed into an ellipse or oval, whose longer axis passes
through the part against which the clapper is struck. The elasticity
of the bell restores the figure of the base, and makes that part
which was forced out of its place, return back to its former
situation, from which the same principle throws it out again; so that
the circular figure of the bell will be again changed to an ellipse,
only now the shorter axis will pass through the part which was first
struck.

The same stroke, which makes the bell vibrate, occasions the sound,
and as the vibrations decay, the sound grows weaker. We may be
convinced by our senses that the parts of the bell are in a vibratory
motion while it sounds. If we lay the hand gently on it, we shall
easily feel this tremulous motion, and even be able to stop it, or if
small pieces of paper be put upon the bell, its vibrations will put
them in motion.

These vibrations in the sounding body will cause undulations or waves
in the air; and, as the motions of one fluid may often be illustrated
by those of another, the invisible motions of the air have been
properly enough compared to the visible waves of water produced by
throwing a stone therein. These waves spread themselves in all
directions in concentric circles, whose common centre is the spot
where the stone fell, and when they strike against a bank or other
obstacle, they return in the contrary direction