d to indicate changes in value and
before long outline notes (called _empty notes_) came into use, these
being easier to make than the solid ones. The transition from square-
and diamond-shaped notes to round and oval ones also came about because
of the greater facility with which the latter could be written, and for
the same reason notes of small denomination were later "tied together"
or _stroked_. This latter usage began about 1700 A.D.

It is interesting to find that when "measured music" was finally
inaugurated there were at first but two measure-signatures, viz.--the
circle, standing for three-beat measure (the so-called _perfect
measure_) and the semi-circle (or broken circle) which indicated
two-beat measure. Occasionally three-beat measure was indicated by three
vertical strokes at the beginning of the melody, while two-beat measure
was shown by two such strokes. Upon the basis of these two varieties of
measure, primitive in conception though they may have been, has been
built nevertheless the whole system now employed, and in the last
analysis all forms of measure now in use will be found to be of either
the two-beat or the three-beat variety. The circle has disappeared
entirely as a measure-sign, but the broken circle still survives, and
from it are derived the familiar signs [common-time symbol] and
[cut-time symbol], which are sometimes erroneously referred to as being
the initial letter of our word _common_ (as used in the expression
"common time"). The transition from the older style of measure-signature
to the present one seems to have occurred during the century following
the invention of opera, _i.e._, from about 1600 to about 1700 A.D.

The rest came into use very soon after "measured music" began to be
composed and we soon find rests corresponding with the various
denominations of notes in use, viz.:

[Illustration]

The terms applied to these rests vary in different authorities, but it
will be noted that the _pausa_, _semi-pausa_, and _suspirum_ correspond
respectively to the double-whole-rest, whole-rest, and half-rest in use
at present.

The bar and double bar may be developments of the _maxima rest_ (as some
writers suggest) but are probably also derived from the practice of
drawing a line vertically through the various parts of a score to show
which notes belonged together, thus facilitating score reading. The bar
may occasionally be found as early as 1500, but was not employed
universally