His works for clavier are very numerous, consisting of sonatas, concertos and solos. Eighteen of his orchestral compositions are published by Breitkopf and Härtel. Emanuel Bach’s talent as a teacher was evinced in his celebrated treatise, “On the True Art of Playing the Clavichord,” which contains the principles of all good piano playing. But his greatest services to modern music were rendered in his sonatas and symphonies, in which he not only enlarged the form, but also increased the means of expression and of instrumental effects. Emanuel Bach exercised a great influence on the clavier sonata, and first brought it into prominence. The so-called sonatas of Domenico Scarlatti were single, brilliant movements which resembled the prelude. Sebastian Bach’s sonatas for the organ, clavier and violin, etc., in three or four movements, were more or less fugal and strict. Emanuel Bach combined the solidity of the style of his father with the brilliancy and lightness of Scarlatti. Although it remained for Haydn to develop fully the principle of free thematic music, the germ of the modern style existed in the sonatas of Emanuel Bach. The habit of improvisation gave full scope to the play of his imagination, and consequently his works are characterized by a certain ease and brilliancy which distinguish him from his predecessors. He made more use than formerly of contrasted themes in the several movements of the sonata, and they were brought into relation to each other by means of free passages. His “Salon” style is distinguished for its elegance and grace, ornateness and playfulness, and well represents the polite world in which he lived. Having traced the early development of organ and clavier music, we will turn our attention, for a moment, to the growth of orchestral music to the advent of Haydn, and the so-called classical period of modern instrumental music. During the first half of the seventeenth century the instruments used in connection with the opera served a subordinate position. The accompaniments of the recitatives and arias consisted of a ground bass (_basso continuo_) for chittarone, organ, clavier, etc., which supplied the chords indicated by figures. In the opera-madrigals the orchestral accompaniment was simply a reproduction of the vocal parts, on wind and stringed instruments. In the course of time instrumental ritornelli were introduced to relieve the solo voices, and melodic phrases were given to the instruments. The first operas generally opened with a flourish of trumpets or with a madrigal played by the instruments alone; sometimes dances played by the instruments were introduced in course of the opera. The opera overture was invented subsequently, probably by Lully. It consisted, at first, of three short movements, slow, quick, slow. Scarlatti and his contemporaries adopted the overture, and changed the order of the movements to _allegro_, _adagio_, _allegro_.