[Sidenote:  Solo instruments.]

Outside the strings the instruments are treated by composers as solo instruments, a single flute, oboe, clarinet, or other wind instrument sometimes doing the same work in the development of the composition as the entire body of first violins.  As a rule, the wood-winds are used in pairs, the purpose of this being either to fill the harmony when what I may call the principal thought of the composition is consigned to a particular choir, or to strengthen a voice by permitting two instruments to play in unison.

[Sidenote:  Groupings for harmony effects.]

[Sidenote:  Wagner’s instrumental characterization.]

[Sidenote:  An instrumental language.]

Each choir, except the percussion instruments, is capable of playing in full harmony; and this effect is frequently used by composers.  In “Lohengrin,” which for that reason affords to the amateur an admirable opportunity for orchestral study, Wagner resorts to this device in some instances for the sake of dramatic characterization. Elsa, a dreamy, melancholy maiden, crushed under the weight of wrongful accusation, and sustained only by the vision of a seraphic champion sent by Heaven to espouse her cause, is accompanied on her entrance and sustained all through her scene of trial by the dulcet tones of the wood-winds, the oboe most often carrying the melody. Lohengrin’s superterrestrial character as a Knight of the Holy Grail is prefigured in the harmonies which seem to stream from the violins, and in the prelude tell of the bringing of the sacred vessel of Christ’s passion to Monsalvat; but in his chivalric character he is greeted by the militant trumpets in a strain of brilliant puissance and rhythmic energy.  Composers have studied the voices of the instruments so long and well, and have noted the kind of melodies and harmonies in which the voices are most effective, that they have formulated what might almost be called an instrumental language.  Though the effective capacity of each instrument is restricted not only by its mechanics, but also by the quality of its tones—­a melody conceived for one instrument sometimes becoming utterly inexpressive and unbeautiful by transferrence to another—­the range of effects is extended almost to infinity by means of combination, or, as a painter might say, by mixing the colors.  The art of writing effectively for instruments in combination is the art of instrumentation or orchestration, in which Berlioz and Wagner were Past Grand Masters.

[Sidenote:  Number of instruments.]

The number of instruments of each kind in an orchestra may also be said to depend measurably upon the music, or the use to which the band is to be put.  Neither in instruments nor in numbers is there absolute identity between a dramatic and a symphonic orchestra.  The apparatus of the former is generally much more varied and complex, because of the vast development of variety in dramatic expression stimulated by Wagner.