Metrical rhythm generally involves precise arrangements of stresses or syllables into repeated patterns called feet within a line. In Modern English verse the pattern of stresses primarily differentiate feet, so rhythm based on meter in Modern English is most often founded on the pattern of stressed and unstressed syllables (alone or elided ).  In the classical languages , on the other hand, while the metrical units are similar, vowel length rather than stresses define the meter.  Old English poetry used a metrical pattern involving varied numbers of syllables but a fixed number of strong stresses in each line. 
IAGO: For when my outward action doth demonstrate
The native act and figure of my heart
In compliment extern, ’tis not long after
But I will wear my heart upon my sleeve
For daws to peck at: I am not what I am.
Leibovich, Mark. “In Turmoil of ’68, Clinton Found a New Voice.”
The New York Times . 5 September 2007.
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