With regard to intervals, let any one attempt a mournful “O dear!” and a jubilant “All right!” in the major and minor thirds, and he will not remain in doubt for a moment as to which is the suitable one for each occasion. Gurney’s experiments with children resulted in the same emotional effects when the piano was very much out of tune as when it was correct,[62] and the attempt of Helmholtz to find a physical explanation signally failed. All these facts point to the independence of the musical interval. In concluding, I repeat that these two analogies are capable of fusion, as my figure of “dancing voice” implies.[63] If we try, for instance, to determine what constitutes the masculine, almost harsh, quality of Bach’s melodies, we will find on inspection that his best arias have a variety of formal qualities of which it is difficult to say whether they pertain more to movement in space or to voice expression. There is pre-eminently a fulness of accent which imparts even to the weaker notes a certain impetus (_Béreíté dích Zîón_). Moreover, his propensity to begin with two strong accents directly contiguous (_Méin gläúbiges Heize_, _In Déine Hände_), which impart to the whole a massive character from the very first, as well as the many repetitions abruptly introduced in a different pitch, and the strongly accented final syllables where again two frequently come together; all these are characteristics which tell in two directions. Here is melody governed by the laws of harmony in its forceful, clear, and irresistibly progressive movement, as well as in the expression which it gives to a purely masculine personality, full of earnest purpose and sure of himself and his aims. Only by the fusion of these two lines of association do we get at the full significance of the piece. (_b_) Productive Sound-Play An embarrassing copiousness of material greets us when we turn to the subject of sounds and tones spontaneously produced. In them too we recognise the beginnings of, or rather the introduction to, art. Adherence to facts requires our classification to distinguish between vocal and instrumental music, and we will first consider voice practice and afterward the production of acoustic effects by means of other agencies, both in their playful aspects.