the first syllable may be said to be stressed primarily for etymological reasons, the seventh primarily for syntactical or rhetorical reasons, and the third (which would not be accented in prose) for metrical reasons.
The general law of English verse is that only those syllables which bear the accent of the first class (that is, which are stressed in common speech), together with monosyllables which on occasion are stressed in common speech, shall be placed so as to receive the metrical stress; and that, if the word-stress and the metrical stress apparently conflict, the metrical stress must yield. Less generally, the rhetorical or syntactical accent in the same way takes precedence of the metrical. In both cases exceptions are of course numerous.
The following are examples of verses showing a conflict between the normal prose-accent and the normal verse-accent, where—as commonly read—the prose- (word-) accent triumphs.
The blessed damozel leaned out
From the gold bar of heaven.
(Rossetti: The Blessed Damozel.)
Love is a smoke raised with the fume of sighs;
Being purged, a fire sparkling in lover's eyes;
Being vexed, a sea nourished with lover's tears.
(Shakspere: Romeo and Juliet, I. i. 196 ff.)
Art thou so bare and full of wretchedness,
And fear'st to die? famine is in thy cheeks,
Need and oppression starveth in thine eyes.
(Shakspere: ib. V. i. 68 ff.)
Till, at his second bidding, Darkness fled,
Light shone, and order from disorder sprung.
Swift to their several quarters hasted then
The cumbrous elements—Earth, Flood, Air, Fire;
And this ethereal quintessence of Heaven
Flew upward, spirited with various forms,
That rolled orbicular, and turned to stars
Numberless, as thou seest, and how they move.