2525. The different rhythms or metres are named trochaic, iambic, &c.,
according to their fundamental feet.
2526. Much of the Latin poetry (though not by any means all) was written
to be sung. The Greeks and Romans employed in their music not only
common (or 2/4) time and triple (3/8, 3/4) time, but also 5/8 time,
which last is very rarely used in modern music.
2527. The Greek and Roman metricians divided the rhythms into three
classes, according to the ratio between arsis and thesis in their
fundamental feet. These classes were:-- (_a._) the _Equal Class_ (γένος
ἴσον, _genus pār_) in which thesis and arsis are equal in duration, as
in dactylics, anapaestics, &c.; (_b._) the _Double Class_ (γένος
διπλάσιον, _genus duplex_) in which the thesis has twice the duration of
the arsis, as in trochaics, iambics, &c.; (_c._) the _Hemiolic Class_
(γένος ἡμιόλιον, _genus sēscuplex_) in which the thesis has one and a
half times the duration of the arsis, as in bacchiacs, cretics, etc.
2528. ASCENDING AND DESCENDING RHYTHMS. Rhythms in which the thesis
follows the arsis (as in iambics) are called _ascending_; those in which
it precedes the arsis (as in trochaics) are termed _descending_.