e last voice
has got farther than the first or second phrase, and, moreover, the free
instrumental accompaniment is capable of furnishing a bass to a mass of
harmony otherwise incomplete.

The resources of canon, when emancipated from the principles of the
round, are considerable when the canonic form is strictly maintained,
and are inexhaustible when it is treated freely. A canon need not be in
the unison; and when it is in some other interval the imitating voice
alters the expression of the melody by transferring it to another part
of the scale. Again, the imitating voice may follow the leader at any
distance of time; and thus we have obviously a definite means of
expression in the difference of closeness with which various canonic
parts may enter, as, for instance, in the stretto of a fugue. Again, if
the answering part enters on an unaccented beat where the leader began
on the accent, there will be artistic value in the resulting difference
of rhythmic expression. This is the device known as _per arsin et
thesin_. All these devices are, in skilful hands, quite definite in
their effect upon the ear, and their expressive power is undoubtedly due
to their special canonic nature. The beauty of the pleading, rising
sequences in crossing parts that we find in the canon in the 2nd at the
opening of the _Recordare_ in Mozart's _Requiem_ is attainable by no
other technical means. The close canon in the 6th at the distance of one
minim in reversed accent in Bach's eighteenth _Goldberg_ variation owes
all its smooth harmonic expression to the fact that the two canonic
parts move in sixths which would be simultaneous but for the pause of
the minim which reverses the accents of the upper part while it creates
that chain of suspended discords which give harmonic variety to the
whole.

Two other canonic devices have important artistic value, namely,
_augmentation_ and _diminution_ (two different aspects of the same
thing) and _inversion_. In augmentation the imitating part sings twice
as slow as the leader, or sometimes still slower. This obviously should
impart a new dignity to the melody, and in diminution the expression is
generally that of an accession of liveliness.[1] Neither of these
devices, however, continues to appeal to the ear if carried on for long.
In augmentation the answering part lags so far behind the leader that
the ear cannot long follow the connexion, while a diminished answer will
obviously soon overtake th