represent the exact pitch, as near as may be, of this tetrachord. In early times the lyre was tuned to these four sounds, and was called the _Tetrachordon_; that is, four strings. This gracefully shaped instrument has remained to this day the symbol of music. This limited scale was extended by adding another tetrachord, which began with the last note of the first tetrachord, thus: A—B♭ C D E—F G A making a scale of seven sounds, called the scale of _Conjunct_ or _Joined Tetrachords_; also from its seven strings, the Heptachord scale. The next step was to take in the limit of the octave. The first way adopted was to raise the highest string a whole tone, thus making it the octave of the lowest; the sixth string was also raised a whole tone to make it a whole tone below the seventh. The result was a scale of seven sounds with one degree omitted, thus: A—B♭ (C) D E E—F G A The next form was: E—F G A B (C) D E It will be seen that in this scale the second tetrachord begins a whole tone above the first, instead of beginning with the final of the first. It is therefore called the scale of _Disjunct_ or _Separated Tetrachords_. The missing sound (C) is here added and the octave scale is complete. When the lyre had seven strings, the middle string, that is, the fourth, counting from either end, was called _Mese_, which means “middle”; but this word soon gained a secondary meaning which, in time, became the most important, viz.: _Keynote_. =The Lesser Perfect System=.—There was in use at the same time a scale called the _Lesser Perfect System_, which was made from the conjunct seven-note scale by adding another conjunct tetrachord below, thus: A—B♭ C D E—F G A (A) B—C D E Then A was added below the first tetrachord to make an octave with the note _Mese_. This A was the lowest sound admitted in the Greek System. It was the Romans who gave to this series of sounds the first seven letters of the alphabet, which they still retain. This octave (A to A) is also the origin of our natural minor scale. This Lesser System was the scale used in the Temple rites. It continued to be used for this purpose long after the system about to be described was invented. =The Greater Perfect System=.—This was made from the disjunct octave by adding a conjunct tetrachord below and one above, thus: E—F G A E—F G A B—C D E (A) B—C D E The A below was also added, thus making a scale two octaves in extent. In later times the disjunct tetrachord, B—C—D—E, was added at the top. This E was the highest note admitted in the Greek System; consequently, their music never exceeded the limits of two octaves and a fifth, and the sounds included in these systems were as follows: [Music: Greater Perfect System without B♭ Added Note Lesser Perfect System without B♮]