Thus we find all the leading vocal phenomena to have a physiological basis.  They are so many manifestations of the general law that feeling is a stimulus to muscular action—­a law conformed to throughout the whole economy, not of man only, but of every sensitive creature—­a law, therefore, which lies deep in the nature of animal organisation.  The expressiveness of these various modifications of voice is therefore innate.  Each of us, from babyhood upwards, has been spontaneously making them, when under the various sensations and emotions by which they are produced.  Having been conscious of each feeling at the same time that we heard ourselves make the consequent sound, we have acquired an established association of ideas between such sound and the feeling which caused it.  When the like sound is made by another, we ascribe the like feeling to him; and by a further consequence we not only ascribe to him that feeling, but have a certain degree of it aroused in ourselves:  for to become conscious of the feeling which another is experiencing, is to have that feeling awakened in our own consciousness, which is the same thing as experiencing the feeling.  Thus these various modifications of voice become not only a language through which we understand the emotions of others, but also the means of exciting our sympathy with such emotions.

Have we not here, then, adequate data for a theory of music?  These vocal peculiarities which indicate excited feeling are those which especially distinguish song from ordinary speech.  Every one of the alterations of voice which we have found to be a physiological result of pain or pleasure, is carried to its greatest extreme in vocal music.  For instance, we saw that, in virtue of the general relation between mental and muscular excitement, one characteristic of passionate utterance is loudness.  Well, its comparative loudness is one of the distinctive marks of song as contrasted with the speech of daily life; and further, the forte passages of an air are those intended to represent the climax of its emotion.  We next saw that the tones in which emotion expresses itself are, in conformity with this same law, of a more sonorous timbre than those of calm conversation.  Here, too, song displays a still higher degree of the peculiarity; for the singing tone is the most resonant we can make.  Again, it was shown that, from a like cause, mental excitement vents itself in the higher and lower notes of the register; using the middle notes but seldom.  And it scarcely needs saying that vocal music is still more distinguished by its comparative neglect of the notes in which we talk, and its habitual use of those above or below them and, moreover, that its most passionate effects are commonly produced at the two extremities of its scale, but especially the upper one.