Take a common tuning-fork, strike it, and hold it, (when set in
vibration,) about three or four inches from the ear, with the flat side
towards it, when the sound will be distinctly heard; let a strip of
card, somewhat longer than the flat of the tuning-fork, be interposed
at about half an inch from the fork, and the sound will be almost
entirely intercepted by it; and, if the card be alternately removed and
replaced in pretty quick succession, alternations of sound and silence
will be produced; proving that sound is by no means propagated with so
much intensity round the edge of the card, as straight forward. Indeed,
to be convinced of this fact, you have only to listen to the sound of
a carriage turning a corner from the street in which you happen to
be, into an adjoining one. Even where there is no obstacle in the
way, sounds are by no means equally audible in all directions from the
sounding body; as you may ascertain, by holding a vibrating tuning-fork
or pitch-pipe near your ear, and turning it quickly on its axis.