until 1650 or later.

The number of lines used in the staff has varied greatly since the time
of Guido, there having been all the way from four to fifteen at various
times and in various places, (_four_ being the standard number for a
long time). These lines (when there were quite a number in the staff)
were often divided into _groups of four_ by _red_ lines, which were not
themselves used for notes. These red lines were gradually omitted and
the staff divided into sections by a space, as in modern usage. The
number of lines in each section was changed to five (in some cases six)
for the sake of having a larger available range in each section.

The clefs at the beginning of the staffs are of course simply altered
forms of the letters F, C, and G, which were written at first by Guido
and others to make the old neume notation more definite.

The staccato sign seems not to have appeared until about the time of
Bach, the legato sign being also invented at about the same time. The
fermata was first used in imitative part-writing to show where each part
was to stop, but with the development of harmonic writing the present
practice was inaugurated. Leger lines came into use in the seventeenth
century.

Sharps and flats were invented because composers found it necessary to
use other tones than those that could be represented by the staff
degrees in their natural condition. The history of their origin and
development is somewhat complicated and cannot be given here, but it
should be noted once more that it was the need of expressing more than
could be expressed by the older symbols that called forth the newer and
more comprehensive method. The use of sharps and flats in key signatures
grew up early in the seventeenth century. In the earlier signatures it
was customary to duplicate sharps or flats on staff degrees having the
same pitch-name, thus: [Illustration] [Illustration]. (The use of the G
clef as here shown did not of course exist at that time.)

The double-sharp and double-flat became necessary when "equal
temperament" (making possible the use of the complete cycle of keys) was
adopted. This was in the time of Bach (1685-1750).

Signs of expression (relating to tempo and dynamics) date back at least
as far as the year 1000 A.D., but the modern terms used for this purpose
did not appear until some years after the invention of opera, the date
given by C.F.A. Williams in Grove's Dictionary being 1638. These words
and