It will be, perhaps, advisable here to close the above discussion of symmetry with a few general observations upon _harmony_. The relation of harmony is no longer one to mere quantity, but rather one to essential distinctions of _quality_, differences of tone, that is to say, which do not persist against each other in their native opposition, but as harmony or music have to be brought into concord. In music we find that the relation of the tonic to the mediant and dominant notes of the scale is no relation of bare quantity[374], but implies the presence of tones whose difference is _essentially_ a qualitative difference; which, that is to say, combine naturally in a unity, rather than continue to assert their distinguishing _timbre_ in all its glaring antithesis and contradiction. The true discord, on the contrary, requires its harmonic resolution. The same qualitative consistency is to be found in the harmony of colour, in reference to which it is likewise one of the requirements of art that it should neither manifest itself in a picture as a motley and haphazard juxtaposition of pigments, nor as a neutral surface whereon all fundamental distinction is dissolved[375], but as the artistic expression of a whole in which essential contrast is mediated through some principle of harmonious unity. Furthermore, we observe that harmony contains in itself a definite number of contrasted differences, which have naturally a particular significance of their own. Thus we find under the differentiation of colour a definite number known as the cardinal colours, which are primary derivatives of the fundamental notion of colour, and are not due to accidental composition. Harmony consists in bringing together a number of positive colours such as this classification implies, and uniting them in concordant unity. We must, that is to say, have in a picture not merely all the primary colours, yellow, blue, green, and red present, but also a harmonious scheme under which they are related; and the old masters have, without direct consciousness of the principle involved, paid express attention to this completeness of effect and arrived at artistic results which flowed out of it. And furthermore, for the very reason that we find in harmony the beginnings of a release from the bare condition of externality it is duly qualified to absorb and express a spiritual content of wider significance. We may mark an illustration of this in the way the old masters distinguished between the drapery of their principal figures and of those of less importance, painting that of the former in elementary colours of absolute purity, but only conceding to that of the rest compound varieties. The mantle of the Virgin Mary is almost always blue; blue in its assuaging sense of tranquillity is accepted as the counterfeit of the repose and tenderness of the heart. It is only rarely that we find her in a drapery of emphatic red.