Unaccompanied vocal music, however marked may be the differences existing between its individual schools, must remain permanently subject to the  laws imposed upon it by the character of the human voice. For instrumental music no permanent legislation is possible. Every new instrument introduced into the orchestra influences, more or less, every one of its companions. Every improvement in the form, compass, quality of tone or executive powers of the instruments already in use suggests new ideas to the composer, and results in an endless variety of new combinations. To the number of such improvements there is no limit. Stringed instruments, it is true, change but little, except in the manner of the handling. The violin of today is the violin of two centuries ago. No so the wind instruments. The trumpet now in common use differs almost as much from that with which Handel and Bach were familiar as it does from the organ stop to which it lends its name. The flute as known to Haydn and Mozart could scarcely hold its own, except in the upper octave, against half a dozen violins. The tone of its modern successor is as powerful as that of the clarinet and brilliant enough to make itself heard with ease through the full orchestra; its powers of execution are almost unlimited; and better still, it can be played perfectly in tune – which the old flute could not. Improvements scarcely less important have been made in the horn, the clarinet and the oboe. The trombone has suffered comparatively little change; and the bassoon retains the form it bore when Handel wrote for it.

The most prominent characteristics of good instrumentation are:

1. Solidity of structure
2. Breath of tone
3. Boldness of contrast
4. Variety of coloring

Solidity of structure can only be obtained by careful management of the stringed instruments. If the part allotted to these be not complete in itself, it can never be completed by wind instruments. Whether written in five parts or in unison, it must sound well alone. This principle was thoroughly understood even as early as the close of the sixteenth century, when the originators of the newly invented instrumental schools bestowed as much care upon their viols as their immediate predecessors had devoted to their vocal parts.

Handel constructed many of his finest overtures upon this principle; and in common with Johann Sebastian Bach and other great composers of the eighteenth century, he delighted in its fine, bold, masculine effect. Later writers improved upon it by embellishing the stringed foundation with independent passages for wind instruments. Thus Mozart, in his overture to “Figaro” first gives the well-known subject to the violins and basses in unison, and then repeats it, note for note, with the addition of a sustained passage for the flute and oboe, which brings it out in quite a new and unexpected light.

Sometimes we find this order reversed, the subject being given to the wind, and the accompaniment to the stringed instruments.

In either case, the successful effect of the passage depends entirely upon the completeness of the stringed skeleton. A weak point in this – whether the principal subject be assigned to it or not – renders it wholly unfit to support the harmony of the wind instruments, and deprives the general structure of that firmness which it is one of the chief objects of the great master to secure.

Breadth of tone is dependent upon several conditions, not the least important of which is the necessity for writing of every instrument with a due regard to its individual peculiarities. This premised, there is little fear of thinness when the stringed parts are well arranged and strengthened where necessary by wind instruments, which may either be played in unison with them, or so disposed as to enrich the harmony in any other way best suited to the style of particular passages. It will generally be found that the most satisfactory passages are those which exhibit a judicious disposition of the harmony, a just balance between the stringed and wind instruments, and a perfect adaptation of the parts to the instruments for which they are written. These points are worth of particular attention.

Boldness of contrast is produced by so grouping together the various instruments employed as to take the greatest possible advantage of their difference of timbre. The instrumental band as now constituted naturally divides itself into certain sections, one as distinct from each other. The first and most important of these is the stringed band, which is the foundation of the whole. The second sometimes called woodwind is led by the flutes and completed by reed instruments such as the oboe, the clarinet and bassoon. The third, the brass band, is subdivided into two distinct families, one formed by the horns and trumpets to which latter the drums supply the natural bass, the other comprising of three trombones and the noisy orchestras of the present day, the tenor tuba or euphonium. The principle of subdivision is indeed frequently extended to all the great sections of the orchestra. For instance, the flutes and oboes are constantly formed into a little independent band, and contrasted with the clarinets and bassoons.

Variety of color results from the judicious blending together of several elements which we have just considered as opposed to each other in more or less violent contrast. In the instrumentation of the great masters this quality is always conspicuous in that of inferior writers never. Its presence may indeed be regarded as one of the surest possible indications of true genius which never fails to attain it in the face of any amount of difficulty.