Thus the Greeks, reduced to the resources of rhythm and melody as means of musical expression, developed these to a very high degree, in the fineness of its distinctions advanced even beyond the point which we have as yet found it necessary to reach in modern music. Their rhythm, while no doubt it had a distinct and independent existence, was primarily determined by the accent of the spoken word, the metres of poetry. Even if conceived as a musical entity, it must at all times be thought of as pertaining to the text rather than the melody. The earliest rhythm of which we have knowledge is the hexameter of the Homeric epics, and it is doubtful whether any variety in rhythmic structure was introduced until the introduction of the short iambic measures at a later period. Melody, on the other hand, while subjected to certain laws, and at first perhaps nothing more than a monotonous chant or declamation at slightly varying pitch, finally attained a variety of line and freedom of movement which rendered it capable of the most subtle shades of expression. This, we are informed, was due to a complex system of modes or scales, of _genera_ and _chroai_, which, if we understand them correctly, would credit the Greek ear with much finer distinctions of pitch than we are capable of to-day. A full discussion of this system is beyond our present purpose, and the numerous controversies concerning it, which in many respects are still unsettled, place the matter outside the pale of true history; but a brief statement of its development (in historical sequence) is necessary for the comprehension of the terms which must recur in the course of our sketch. III We have seen that the Greeks recognized the consonance of the octave. Similarly they recognized at an early period the close relationship of the interval of the perfect fifth, and its inversion, the perfect fourth. The latter became the basis of the Greek system of scales. They divided the interval into unequal smaller intervals according to three methods, or _genera_, in each case placing the larger steps at the top and the smaller at the bottom. (An equal division of the interval has, as far as we know, never been attempted and is entirely foreign to natural impulses.) The results obtained were as follows: [Illustration: THE THREE GENERA.] Of these three tetrachords (from [Greek: tetra] = four and [Greek: chordon] = string) only the first was generally accepted, the chromatic was rarely used and the enharmonic probably only by _virtuosi_, for we have the testimony of Aristoxenus that the ear accustomed itself only with difficulty to the distinction of quarter tones. By joining two diatonic tetrachords together we obtain a series of notes corresponding to the Dorian scale or mode ([Greek: harmonia])--more properly 'octave species’--which was accounted the oldest of all the modes: [Illustration: DORIAN.]