2514. SIGNS OF QUANTITY. A long syllable is indicated by -, a short one
by ⏑. A syllable which varies in quantity, being sometimes long,
sometimes short, is indicated by ⏓ or ⏒.
In the following metrical schemes, ⏓ indicates that the long is more
usual or more strictly in accordance with the rhythm than the short. The
reverse is indicated by ⏒.
2515. The UNIT OF MEASURE is the duration of a short syllable and is
called a _Time_, _Tempus_, or _Mora_. The _mora_ did not have an
absolute length, but varied with the nature of the rhythm. For greater
convenience, however, it is assumed that its length was uniform, and
equalled that of an eighth note ♪ A long syllable, being equal to two
shorts, has a length of two _morae_, which is assumed to be the same as
that of our quarter-note ♩ Hence in notation ⏑ = ♪ and - = ♩
2516. PROTRACTION. A long syllable may be prolonged (_Protraction_) so
as to have a length of three _morae_, in which case it is called a
_triseme_ (marked ⏗), or of four _morae_, when it is termed a
_tetraseme_ (marked ⏘). See 2537 and 2541.
2517. CORREPTION. A long or short syllable may be shortened so as to
occupy less than its normal time. This is called _Correption_ (Lat.
_correptiō_, _a shortening_). See 2523 and 2524.
2518. RESOLUTION AND CONTRACTION. In some kinds of verse a long syllable
may be, as it were, broken up (_Resolution_) into the equivalent two
shorts; and conversely two short syllables may in some cases be united
(_Contraction_) into the equivalent long.