ry elongations or contractions (marked
_ritardando_ or _accelerando_) as may be introduced for oratorical
effects.

(2) The beats are grouped in _measures_ of uniform duration; that is,
containing equal numbers of beats.

(3) The natural _accent_ falls upon the corresponding beat, namely, the
first, of each measure; therefore it recurs regularly, at uniform
intervals of time.

(4) The _melodic contents_ of the first measure, or measures, are
copied (more or less literally) in the next measure, or measures; and
are encountered again and again in the later course of the piece, thus
insuring a fairly uniform melodic impression from which the character
and identity of the composition are derived. Turn to the 8th Song
Without Words of Mendelssohn, and observe how insistently the figure

[Illustration: first fragment of 8th Song]

and its inversion

[Illustration: second fragment of 8th Song]

run through the whole number.

(5) The specific figure of the _accompaniment_ is usually reproduced
from measure to measure (or group to group) throughout whole sections
of the piece. Observe, in the 37th Song Without Words, how constantly
the ascending figure of six tones recurs in the lower part (left hand).
Glance also at No. 30; No. 1; No. 25. Many other evidences of Unity
are invariably present in good music, so naturally and self-evidently
that they almost escape our notice. Some of these are left to the
student's discernment; others will engage our joint attention in due
time.

* * * * * *

In every one of these manifestations of unity there lies the germ of
the principle of Variety, which quickens into life with the action of
the former, always following, as offspring and consequence of the
primary unity. Thus:--

(1) The _beats_, though uniform in duration, differ from each other in
force. The first pulse in each measure (or metric group of any size)
is heavier, stronger, than the following. It--the first--is the
"impulse," and is what is called the accent. This dynamic distinction
it is that gives rise to the two fundamental classes of rhythm, the
duple and triple. In duple rhythm the accent is followed by one
unaccented or lighter beat, so that regular alternation of heavy and
light pulses prevails incessantly. In triple rhythm the accent is
followed by _two_ lighter beats, creating similarly constant, but
_irregular_ alternation of heavy and light pulses.

[Illustrati