Nature of Sound.
Sound is a sensation in the nervous system resulting from vibrations of the delicate membranes in the ear (ear
drum). An analysis of sound as a sensation is beyond the scope of this text, but the cause of sound by physical vibrations
can be analyzed and measured with accuracy.
Figure 1 shows how sound results from the rapid vibration of a rigid or semirigid body. If a pencil is held
lightly against one of those vibrating bodies the physical motion can be felt by the hand. These same vibrations are
recognized by the ear as sound. The physical medium between the source of vibrations and the ear is the air which is
sufficiently dense, at atmospheric pressure, to be set in motion by the vibrating body and deliver the vibration to the
sensitive membranes of the ear.