"If the particles of the air be slightly disturbed from a position of stable equilibrium, every particle makes an effort to return to that position; and it can be shown that the force of restitution varies as the distance from the position of equilibrium ... a musical note is the consequence of the vibrations excited in the disturbed system, and the permanency of its musical pitch is the consequence of these vibrations being all made in the same time ... If the vibrations gradually slackened in their times, as they do in the extent of these excursions from the effect of the resistances they meet, there would be no note of sustained pitch; the sound would then be a sliding descent in pitch, and music would be impossible." - Penny Cyclopedia, Art. "Vibration." [Scientific Basis and Build of Music, page 24]
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