The normal order of sounds or the natural harmonic scale:
may serve as a guide to the orchestral arrangement of chords. It will be seen that the widely-spaced intervals lie in the lower part of the scale, gradually becoming closer as the upper register is approached:
The bass should rarely lie at a greater distance than an octave from the part directly above it (tenor harmony). It is necessary to make sure that the harmonic notes are not lacking in the upper parts:
The use of sixths in the upper parts, and the practice of doubling the upper note in octaves are sometimes effective methods:
When correct progression increases the distance between the top and bottom notes of the upper parts, this does not matter:
But it would be distinctly bad to fill in the second chord thus:
Hence it follows that the distribution of intermediate parts is a question of the greatest importance. Nothing is worse than writing chords, the upper and lower parts of which are separated by wide, empty intervals, especially in _forte_ passages; in _piano_ passages such distribution may be possible. Progression in contrary motion, the upper and lower parts diverging by degrees gives rise to the gradual addition of extra parts occupying the middle register:
When the voices converge, the middle parts are eliminated one by one:
It is an incontrovertible rule that the resonance of different harmonic parts must be equally balanced, but this balance will be less noticeable in short sharp chords than in those which are connected and sustained. Both these cases will be studied separately. In the first case, in order to increase the number of harmonic parts, each instrument in the string group may be provided with double notes or chords of three and four notes. In the second case, the resources are limited to double notes _unis_, or division of parts.
A. _Short chords._ Chords of three or four notes can only be executed rapidly on the strings.
_Note._ It is true that the two upper notes of a chord can be sustained and held a long time; this, however, involves complications and will be considered later.
Short chords, _arco_, only sound well when played _forte_ (_sf_), and when they can be supported by wind instruments. In the execution of double notes and chords of three and four notes on the strings, balance, perfect distribution of tone, and correct progression of parts are of minor importance. What must be considered before everything is the resonance of the chords themselves, and the degree of ease with which they can be played. Those comprising notes on the gut strings are the most powerful. Chords played on several strings are usually assigned to 1st and 2nd violins and violas, the different notes being divided between them according to ease in execution and the demands of resonance. On account of its low register the 'cello is rarely called upon to play chords on three or four strings, and is usually allotted the lowest note of the chord in company with the double bass. Chords on the latter instrument are even more uncommon, but it may supply the octave on an uncovered string.