Very binding indeed were these laws, and they have exercised an important, indeed, an imperishable influence upon the musical art in all the centuries that have followed. The methods of the great master-players of the cithara were in course of time resolved into forms, very simple they were and very definite. These are the laws of the tetrachord:— 1—between the two extremes of the strings of the four-stringed lyre there shall be a consonance in sound called a diatessaron. 2—between the string the highest in pitch and the string next to it lower in pitch there shall be a separation in the sounds equal to not less than one full tone. 3—between the third string (reckoning from the highest) and the fourth string there shall always be a separation in pitch equal to one hemitone. There remained therefore the neutral ground between the second and the third string—equal to a tone—but variable, according to the selection of a maximum beyond the “_not less_ than a full tone” affirmed by law 2; there might be two full tones in succession, or the upper might be increased at the expense of the lower, or on the contrary the lower might part with some of its own fulness to increase the hemitone. We should not imagine a written law at that early time ruling the craft, the oral tradition would be sufficient. Giving an account of the growth of the scale, I have put the matter in my own way, in words, that as I think, will best fix the attention of the general reader. Evidently for many centuries the orthodox Greek lyre was restricted to four strings, notwithstanding the popular adoption from time to time of an increased number of strings according to the prevalence of Asiatic influences. A time however came when authority accepted an increase to seven strings. Whether Terpander, or Archilocus, or Tyrtæus, or other poet-musicians got the innovation accepted is a question that will remain unsolved; hearsay or history favours Terpander. Terpander let it be. Olympus, who was a Phrygian, and—about 630 B.C., brought asiatic flute music into Greece,—changed this as follows, and obtained the octave on the seven strings. ╭————————^————————╮ ╭———————^—————-╮ _e_ ‿ _f_———_g_———_a_———_b_ ‿ ———_d_———_e_ * Notice particularly the interval _b_ ‿ ———_d_ as it plays an important part in the history of music. It was a flute-pipe interval, older than Terpander. Olympus was the first to introduce the disjunct form, and from _b_ to _e_ he compasses a tetrachord. Olympus was a contemporary of Terpander, and we may consider that the two scales were in favour at the same time, one as the orthodox and the other as the secular system. Pythagoras about 530 B.C., added an eighth string, and it is evident that the string he introduced was that of the missing _c_, since, as to extent, the octave already existed on the lyre.