=Discant=.—Another early attempt at harmonic effect was the singing of an _extemporaneous_ part or parts with the melody, called Discanting. In course of time the Discant or Organum gradually crystallized into rules, and other intervals were accepted. Strangely enough, dissonances seem to have been admitted with great freedom, and thirds and especially sixths, were avoided. The only dissonance that was _not_ allowed was the _minor second_. =The New Organum=.—In the 11th century, a method of combining sounds, called the New Organum, was developed. This kind of Organum admitted thirds and sixths. The following example will sufficiently illustrate this: [Music] =Measured Music=.—The next step in advance, and one that proved very important and far-reaching in its results on the development of music, was the invention of a notation that indicated, although not very conveniently, the _relative duration_ of sounds. Thus it became possible to express two or more parts in a permanent form. The plan of this first attempt at a notation by means of which relative duration of notes might be expressed was very complicated. Music written with these signs was called Measured Music (_Cantus Mensurabilis_). =The Record of Early Harmony=.—There are references to the manner of using voices in combination in the writings of several men associated with the Christian Church in its early days. =Censorinus=, who lived in the 3d century, makes mention of a practice of using a melody in octaves accompanied by the fifth to the lower note of the octave, which is also the fourth to the upper. =Cassiodorus=, in the 6th century, mentions various ways of accompanying the chant with consecutive fourths and fifths. In a work called “Sentences About Music,” written by =Bishop Isidore of Seville=, who lived in the 7th century, we read that “harmony is a modulation of the voice, the concordance of many sounds and their agreement.” In the 9th century we meet with the names of several writers: =Remi d’Auxerre= who defines harmony as “a consonance of voices, and their union in one group”; =Jean Scot Erigene= who recognized that the succession of chords composed of octaves, fifths and fourths is a rational one; =Odo= or =Otger=, a churchman of the south of France, whose work was the first to mark an epoch in the development of the art of music. Also another monk, the Fleming =Hucbald=, who lived in the 10th century. They defined consonance and dissonance, and appear to have been the first to give rules for the construction of Diaphony. Hucbald says in his “_Musica Enchiriadis_”: “Certain dissimilar sounds sung together make an agreeable effect, and this mingling of voices is sweet to the ear.”