nces from the sounding body
is inversely as the square of the distance.

Sound moves with the same velocity at all distances from the sounding
body, otherwise it would not produce the same tone at all distances.
Sounds of different tones likewise move with the same velocity. This
is evident from a peal of bells being heard in the same order in
which they are rung, whether we are near, or at a distance.

It is likewise found that sounds of the same tone but of different
intensities are propagated with the same velocity. A low sound cannot
indeed be heard so far as a loud one; but sounds, whether low or
loud, will be conveyed in an equal time to any equal distance at
which they can both be heard. The report of a cannon does not move
faster, or pass over a given space sooner, than the sound of a
musical string.

The principal cause of the decay of sound is the want of perfect
elasticity in the air: whence it happens that every subsequent
particle has not the entire motion of the preceding particle
communicated to it, as is the case with equal and perfectly elastic
bodies; consequently the further the motion is propagated, the more
will the velocity with which the particles move be diminished; the
condensation of the air will be diminished also, and consequently its
effect on the ear. That the want of perfect elasticity in the air is
the principal cause of the decay of sound, appears from this, that
sounds are perceived more distinctly when the north and easterly
winds prevail, at which time the air is dry and dense, as appears
from the hygrometer and barometer; and, of course, the air in this
state must be more elastic, for the vapours diffused through the
atmosphere, unless dilated by intense heat, diminish the spring of
the air.

That sound is not propagated to all distances instantaneously, but
requires a sensible time for its passage from one place to another,
is evident from the discharge of a gun at a distance; for the report
is not heard till some time after the flash is seen. Light moves much
more swiftly than sound; it comes from the sun in eight minutes,
which is at the rate of 74,420 leagues in a second; so that the
velocity of light may be considered as instantaneous, at any distance
on the earth; and, as sound takes up a considerable time in its
passage, the interval between the flash and the report of the gun
shows the space it passes over in a given time, which is found to be
1142 feet in a second; so