DOUBLE; two of a sort, one corresponding to the other.

Double Children, Double Cats, &c. See Monster. Double Employment, in Music, a name given by Rameau to the two different modes in which the chord of the sub-dominant may be regarded and treated, namely, as the fundamental chord of the sixth superadded, or as the chord of the great sixth, inverted from a fundamental chord of the seventh. In reality the chords carry exactly the same notes, are figured in the same manner, and are employed upon the same chord of the tone, in such a manner that frequently we cannot discern which of the two chords the author employs, except by the assistance of the subsequent chord, which resolves it, and which is different in these different cases.

To make this distinction, we must consider the diatonic progress of the two notes which form the fifth and the sixth, and which, constituting between them the interval of a second, must one or the other constitute the dissonance of the chord. Now this progress is determined by the motion of the bass. Of these two notes, then, if the superior be the dissonance, it will rise by one gradation into the subsequent chord, the lower note will keep its place, and the higher note will be a superadded sixth. If the lower be the dissonance, it will descend into the subsequent chord, the higher will remain in its place, and the chord will be that of the great sixth.

With respect to the composer, the use which he may make of the double employment is to consider the chord in its different points of view, that he may thence know how to make his entrance to it, and his exit from it; so that having, for instance, arrived at the chord of the superadded sixth, he may resolve it as a chord of the great sixth, and reciprocally.

D’Alembert has shown that one of the chief uses of the double employment is, that we may be able to carry the diatonic succession of the gamut even to an octave, without changing the mode, at least whilst we rise; for in descending we must change it. Of this gamut, and its fundamental bass, an example will be found in Rousseau’s Musical Dictionary. It is evident, according to the system of Rameau, that all the harmonic successions which result from it are in the same tone; for, in strictness, no other chords are there employed but three, namely, that of the tonic, that of the dominant, and that of the sub-dominant; which last, in the double employment, constitutes the seventh from the second note, and is employed upon the sixth.

With respect to what D’Alembert says in his Elements of Music (p. 70), and repeats in the Encyclopédie (article Double Emploi), that the chord of the seventh re fa la ut, though we should even regard it only as an inversion of fit la ut re, cannot be followed by the chord ut mi sol ut, Rousseau declares, “I cannot be of his opinion in this point.” The proof which he gives in support of this dissent is, that the dissonance ut of the first cannot be resolved in the second. And this is true, since it remains in its place; but in the chord of the seventh, re fa la ut, inverted from the chord of the superadded sixth, fa la ut re, it is not the ut, but the re, which is the dissonance; and consequently it ought to be resolved in ascending upon mi, as it really does in the subsequent chord; so that this procedure in the bass itself is forced, which, from re, cannot without an error return to ut, but ought to ascend to wtι, in order to resolve the dissonance.

D’Alembert afterwards shows that this chord re fa la ut, when preceded and followed by that of the tonic, cannot be authorized by the double employment; and this is likewise true; because, in fact, this chord, though figured with a 7, is not treated as a chord of the seventh, neither when we make our entrance to it nor our exit from it; or at least that it is not necessary to treat it as such, but simply as an inversion of the superadded sixth, of which the dissonance is the bass; in which case we ought by no means to forget that this dissonance is never prepared. Thus, though in such a transition the double employment is not in question, and though the chord of the seventh be no more than apparent, and impossible to be resolved by the rules, this does not hinder the transition from being proper and regular.
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This inversion of the chord of the sixth superadded, which transfers the dissonance to the bass, has been censured by Rameau, who, taking it for a fundamental chord, the chord of the seventh, which results from it, rather chose to make the fundamental bass descend diatonically, and resolve one seventh by another, than to unfold this seventh by an inversion. But Rousseau has dissipated this error, and many others, in some papers which long ago passed into the hands of D’Alembert when he was composing his Elements of Music. In other respects, the double employment cannot be used with too much reserve, and the greatest masters are the most temperate in putting it in practice.

Double Fichy, or Piche, in Heraldry, the denomination of a cross, when the extremity has two points; in contradistinction to fiché, where the extremity is sharpened away to one point.

Double Octave, in Music, an interval composed of fifteen notes in diatonic progression, and which, for that reason, is called a fifteenth. It is, says Rousseau, an interval composed of two octaves, called by the Greeks, disdiapason.

It deserves, however, to be remarked, that in intervals less distant and compounded, as in the third, the fifth, the simple octave, and so on, the lowest and highest extremes are included in the number from whence the interval takes its name. But, in the double octave, when termed a fifteenth, the simple number of which it is composed gives the name. This is by no means analogical, and may occasion some confusion. We should rather choose, therefore, to run any hazard which might occur from uniformly including all the terms of which the component intervals consist, and call the double octave a sixteenth, according to the general analogy.