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♭