sometimes called the “polyphonic-harmonic” period, because in it the modern harmonic system was grafted upon the polyphony of Palestrina, remains to-day, from some points of view, the purest and noblest period of musical history. All the time that Bach, in the privacy of an obscure German town, was writing his wonderfully intricate and beautiful polyphonic music, the world about him, oblivious, was seeking out a quite different type of art. It is a surprising fact that Bach’s compositions were virtually unknown for fifty years after his death, and might have remained so permanently had they not been “discovered” by appreciative students, much as the receptacles of classical lore were discovered in the Renaissance after the long darkness of the Middle Ages, and made the basis of an intellectual revival. Bach’s great works, too, were full of an undying vitality; but for a long time their potency had to remain latent, because men were occupied with another order of art, a different set of problems, an alien style. Ever since the Florentine revolution, when the polyphonic texture of mediæval music was abandoned for a simple monodic or one-voiced style, in which a melody is accompanied by a series of chords, much of the musical genius of the world had been devoted to the development of eloquent single melodies, and of suitable harmonic backgrounds for them. With the systematization of harmony and the establishment of definite themes this type of art became mature. Composers discerned the possibility of building up whole movements to which interest could be given by the statement and development of one or more themes, contrasted both in character and in key. They saw that the whole could be unified by general qualities of style, by recurrence of the themes, and, above all, by being made to embody, in the long run, a single tonality, though with momentary departures from it for the sake of variety. Working out their idea, they devised a type of structure which has remained up to this day the highest and most widely useful of all musical forms. The essential features of “sonata-form,” as it is called, are, in the first place, the Exposition of two themes or subjects of discourse, contrasting both in character and in key; in the second place, the Development of these themes, the exploitation of their latent possibilities; in the third place, Restatement of them, in the central key of the movement, bringing all to a point, and completing the cycle of Statement, Argument, and Summary. Sonata-form, of which it is easy to see the naturalness and beauty, depends for its unity, not on the equal interplay of many voices, like the older polyphonic forms, but on the saliency, cumulative development, and harmonic inter-relations, of single themes. We may, therefore, call the great period of Haydn, Mozart, and Beethoven, the period in which the sonata-form attained its full maturity, the “harmonic period,” or, in view of the complete round