It is difficult to separate the purely musical and the purely technical causes which led to the abandonment of the polyphonic style for the monophonic in piano music, and for that reason I must state them together. The first influence was the introduction of solo singing in vocal music. We shall review the history of that when we take up opera. It is sufficient at present to say that before 1600 all vocal music written by the art composers was in the ecclesiastical polyphonic style, and that the single-voiced song with accompaniment entered vocal music at the end of the sixteenth century. The influence of this new element made itself felt in instrumental music at once. We have noticed already that in Giovanni Gabrieli's works the melody assumed a new importance, and this importance constantly increased. The second cause was the full establishment of the difference between piano and organ technic. This was chiefly due to Domenico Scarlatti (1683-1757). It was in his day that the system of equal temperament was made known, though it may be doubted whether he lived long enough after its publication in those times of slow communication to profit by it. But he certainly did profit by the high state of excellence to which the manufacture of harpsichords had advanced. And he was greatly influenced by the operatic works of his father, Alessandro, in which the simple aria was the chief element of attraction. Domenico naturally endeavored to imitate the general form and melodic fluency of the aria in his sonatas, and in doing this he developed a harpsichord style of much beauty. He introduced many technical features which are purely modern, such as the execution of runs in double notes (thirds and sixths), the rapid repetition of the same note by striking it with different fingers in succession, and running arpeggios with both hands in opposite directions. Such feats were not called for by the polyphonic music, but the new style of writing made a great use of passages built on the successive notes of the scale, and to execute these a new manner of playing had to be evolved. In evolving it the musicians discovered new feats, and these in turn took their place in the compositions of the time.