t] was
the equivalent of [G: c' e' d' e' d' c' d' e' d' e' d' e' d'],
considering the line as being middle C pitch, a fourth higher F.
This was the condition of musical notation in 1000 A.D.

To Guido d'Arezzo is ascribed its development up to some
semblance of our present system, although the claim has often
been denied. It is certain, however, that the innovations
were made at this period. In the first place Guido made the
red line _always_ stand for the pitch of F, and at a little
distance above it he added another line, this time yellow,
which was to indicate the pitch of C. Thus the signs began to
take very definite meaning as regards pitch; for, given a sign
extending from one line to the other, the reader could see
at a glance that the music progressed a fifth, from F to C,
or _vice-versa_. And now the copyists, seeing the value of
these lines in determining the pitch of the different signs,
of their own account added two more in black ink, one of which
they drew between the F and the C line, and the other above
the C line, thus [illustration]. By doing this they accurately
decided the pitch of every note, for the lowest line, being F,
the line between that and the C line must stand for A, and the
two spaces for G and B; the top line would stand for E, and the
space between it and the yellow line for D. Little by little
these copyists grew careless about making the lines in yellow,
red, and black, and sometimes drew them all in black or red,
thereby losing the distinguishing mark of the F and C lines. In
order to remedy this, Guido placed the letters F and C before
the lines representing these notes, thus [illustration]. In
this way our modern _clefs_ (_clavis_ or key) originated, for
the C clef, as it is called, gradually changed its shape to
[illustration] and [illustration], and the F clef changed to
[illustration], which is our bass clef in a rudimentary form.

Later, still another line was added to the set, thus giving
us our modern staff, and another clef, [illustration], was
added on the next to the lowest line. This, in turn, became
our present treble clef, [G:]. In the course of time the signs
themselves underwent many changes, until at last from [Podium],
etc., they became our modern signs.

Before this, however, a grave defect in the notation had to
be remedied. There was as yet no way of designating the length
of time a note was to be sustained; something definite in the
way of noting _rhythm