e substitution of trochees
for dactyls:--

_ U U | _ U | _ U U | _ U U | _ U U | _ U |
Waste are those pleasant farms, and the farmers forever departed.

_ U U | _ U | _ U U | _ U | _ U U|_ U
Scattered like dust and leaves, when the mighty blasts of October

_ U U | _ U U |_ U | _ U U | _ U U |_ U |
Seize them and whirl them aloft, and sprinkle them far o'er the ocean.

_ U U | _ U U | _ U U | _ U U | _ U U | _ U
Naught but tradition remains of the beautiful village of Grand-Pre.

It is evident that one foot can be substituted for another if the accent
is not changed. Since both the iambus and the anapest are accented on the
last syllable, they may be interchanged. The trochee and the dactyl are
both accented on the first syllable and may, therefore, be interchanged.

There are some exceptions to the general rule that in substituting one
foot for another the accented syllable must be kept in the same part of
the foot. Occasionally a poem in which the prevailing foot is iambic has a
trochee for the first foot of a line in order that it may begin with an
accented syllable. At the beginning of a line the change of accent is
scarcely noticeable.

_ U | U _ | U _ |U _ |
Over the rail my hand I trail.

_ U | U _ | U _ | U _ |
Silent the crumbling bridge we cross!

But if the reader has once fallen into the swing of iambic verse, the
substitution of a trochee will bring the accent at an unexpected place,
interrupt the smooth flow of the rhythm, and produce a harsh and jarring
effect. Such a change of accent is justified only when the sense of the
verse leads the reader to expect the changed accent, or when the emphasis
thus given to the sense of the poem more than compensates for the break in
the rhythm produced by the change of accent.

Another form of metrical variation is that in which there are too few or
too many syllables in a foot. This generally occurs at the end of a line,
but may occur at the beginning. If a syllable is added or omitted
skillfully, the rhythm will be unbroken.

When the feet are accented on the last syllable,--that is, when the verse
is iambic or anapestic,--an extra syllable may be added at the end of a
line.

U _ |U U _ |U _ | U
I stood on the bridge at midnight,

U U _ | U _ |U U _ |
As the clocks were striking the hour;