The meter throughout William Blake's poem "The Divine Image" is iambic. Each line, in other words, is comprised entirely of iambs. An iamb is a pair of syllables in which the second syllable is stressed. In the third line of the poem, "And to these virtues of delight," there are four iambs. "And to" is the first iamb, "these virt" is the second, "ues of" is the third, and "delight" is the fourth. Because the line comprises four iambs, the meter is iambic tetrameter, where the prefix "tetra" means four.
Lines one and three in all five stanzas of the poem are written in iambic tetrameter, just like the example quoted above. Lines two and four of each stanza, however, are written in iambic trimeter, meaning that the second and fourth lines of each stanza comprise three iambs rather than four. For example, the second line of the first stanza reads, "All pray in their distress," and the fourth line of the third stanza reads, "And Peace, the human dress."
Because the final syllable in each line is stressed, the entire poem is also written in a rising meter. When a poem is written in a rising meter, this creates a rising intonation, which usually connotes an upbeat tone. A falling meter, by contrast, whereby the final syllable of each line is unstressed, usually connotes a downbeat tone.
The third line of the poem, therefore, and the third line of each stanza, is written in a rising iambic tetrameter.