We have here, then, a principle underlying all vocal phenomena; including those of vocal music, and by consequence those of music in general.  The muscles that move the chest, larynx, and vocal chords, contracting like other muscles in proportion to the intensity of the feelings; every different contraction of these muscles involving, as it does, a different adjustment of the vocal organs; every different adjustment of the vocal organs causing a change in the sound emitted;—­it follows that variations of voice are the physiological results of variations of feeling; it follows that each inflection or modulation is the natural outcome of some passing emotion or sensation; and it follows that the explanation of all kinds of vocal expression must be sought in this general relation between mental and muscular excitements.  Let us, then, see whether we cannot thus account for the chief peculiarities in the utterance of the feelings:  grouping these peculiarities under the heads of loudness, quality, or timbre, pitch, intervals, and rate of variation.

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Between the lungs and the organs of voice there is much the same relation as between the bellows of an organ and its pipes.  And as the loudness of the sound given out by an organ-pipe increases with the strength of the blast from the bellows; so, other things equal, the loudness of a vocal sound increases with the strength of the blast from the lungs.  But the expulsion of air from the lungs is effected by certain muscles of the chest and abdomen.  The force with which these muscles contract, is proportionate to the intensity of the feeling experienced.  Hence, a priori, loud sounds will be the habitual results of strong feelings.  That they are so we have daily proof.  The pain which, if moderate, can be borne silently, causes outcries if it becomes extreme.  While a slight vexation makes a child whimper, a fit of passion calls forth a howl that disturbs the neighbourhood.  When the voices in an adjacent room become unusually audible, we infer anger, or surprise, or joy.  Loudness of applause is significant of great approbation; and with uproarious mirth we associate the idea of high enjoyment.  Commencing with the silence of apathy, we find that the utterances grow louder as the sensations or emotions, whether pleasurable or painful, grow stronger.

That different qualities of voice accompany different mental states, and that under states of excitement the tones are more sonorous than usual, is another general fact admitting of a parallel explanation.  The sounds of common conversation have but little resonance; those of strong feeling have much more.  Under rising ill temper the voice acquires a metallic ring.  In accordance with her constant mood, the ordinary speech of a virago has a piercing quality quite opposite to that softness indicative of placidity.  A ringing laugh marks an especially joyous temperament.