The origin of modern harmony is wrapped in obscurity. It is believed that the Greeks knew something about chords and perhaps used a few simple ones in playing accompaniments on the lyre. But they made no extended study of them, and the early fathers, who founded their system on Greek music, had nothing to learn in this matter from the Greeks. All steps in the development of modern music have been the result of long processes of growth, and it cannot be doubted that many experiments in harmony were made before the first treatise on the subject was written. The first records of harmony are found in an old work called "Enchiridion Musicæ," and they speak of a system called Organum or Diaphony, attributed to Hucbald, a Benedictine monk of St. Armand, in Flanders, near the close of the tenth century. Hucbald appears to have studied Pythagoras's musical system, in which intervals between notes were measured according to the laws of acoustics by the number of vibrations made by each note in a second. Hucbald, finding that certain intervals had a mathematical ratio, decided that they must make concords, and he founded his system of harmony on that theory. He used the intervals of the fourth, the fifth, and the octave. The fourth is the fourth note of the major scale in ascending, the fifth the fifth note, and the octave the eighth, or the recurrence of the key-note. To make this matter clearer, let me state that modern scientists have decided that the C below the staff, in the treble clef, has 256 vibrations a minute. The next C above has 512, just double. The F of this scale, which is the fourth, has 384. This is the sum of the first C increased by one-half of itself. Consequently C and F make a scientific concord and a musical one, too. But there is hardly anything more disagreeable to the modern ear than a series of consecutive fourths. Yet Hucbald thought that such a series must be scientifically correct, and that it ought, therefore, to make good music. So he wrote such harmonies as these:-- [Music Series of Fourths: Sit glo-ri-a Do-mi-ni in sæ-cu-la.]