13. Musical sounds were expressed in this manner until the year 1024, when, according to some authors, Guido Aretine, a monk of Arezzo, invented points and rhombuses. He also introduced the use of five parallel lines, upon and between which his notes were written. The seven letters which had formerly been used as notes, now became clefs. 14. Still, however, the means of determining the duration of sound belonging to each note, without consulting the quantity of syllables in the verses to be sung, were yet to be provided. This desideratum was supplied by one Franco, a German of Cologne, who lived towards the end of the eleventh century. Some, however, attribute this improvement to John de Murs. The division of one note into others of less value was invented, in the sixteenth century, by Jean Mouton, chapel-master to King Francis I. of France. 15. The knowledge of music, as a science, was preserved in Europe, after the overthrow of the Western empire, through the influence of the Church. The apostles, and Hebrew converts generally, had been accustomed to the sacred music of the Jews; and, on this account, it was easy to continue the use of the same psalms and hymns in the Christian Church. 16. Many of the Grecian and Roman melodies were also set to words adapted to Christian worship. In regard to the manner of singing, in the early days of the Church, it was sometimes in _solo_, sometimes in _alternate strains_, and at other times in _chorus_; in which the whole assembly joined, repeating what had been before sung or read. In the fourth century, with the view of securing the proper execution of this part of divine worship, _precentors_ were instituted, who were considered regular officers of the Church. 17. Pope Gregory I., surnamed the Great, distinguished himself by establishing a new singing-school, which became a model for many others, in the western division of the Church. In consequence of these schools, the singing became more artificial; and this, together with the circumstance that the hymns were in Latin, which had become obsolete, at length excluded the people from any participation in this part of the public worship. 18. Gregory also made a selection of the existing songs of the Church, and introduced a _chant_, which, through his influence, and that of his successors, was at length extended throughout Europe. It received the appellation of the _Gregorian chant_ from his name. It was also called the _choral song_, because it was sung by a choir. This chant is said to be the foundation of our present church-music. 19. Music, in distinct parts, was not known until after the introduction of the improved method of writing music, invented, as before stated, by Guido Aretine and Franco. The development of harmony, in four parts, was assisted by the _choral_; but it was more particularly advanced by musical instruments, and especially by the organ. In the fifteenth century, music began again to be treated scientifically.