Assonance is used throughout "The Author to Her Book." The poem relies on frequent rhyming couplets, which add a sense of steadiness and regularity throughout. There is assonance within lines as well, which sometimes evoke the sense of a phrase via sound. In line 2, for example, the speaker describes her book as having stayed "by my side" after birth (the book is metaphorically transformed into a child throughout the poem). These three identical vowel sounds have the effect of clinging to the ear, as though they can't be shaken off. They represent, then, the closeness with which the author kept her book—until it was snatched from "thence" by "friends" and published abroad.
Another interesting example is in line 6, in which the speaker states that, though her book was published, no one edited it to make it better:
Made thee in raggs, halting to th’ press to trudge,
Where errors were not lessened (all may judg).
Here, similar /e/ sounds impose themselves on the poem, representing just how many supposed errors exist in the book. Later, in lines 13 and 14, the speaker describes trying to make edits/improvements to her book without much success:
I wash’d thy face, but more defects I saw,
And rubbing off a spot, still made a flaw.
These /aw/ sounds also use prominent patterning to suggest the presence of something undesired—in this case "spots" and "defects." Similar vowel sounds appear like boils or pustules on diseased skin.
In another striking example, line 15 uses assonance in its pun on human feet/metrical feet:
I stretched thy joynts to make thee even feet,
These long /e/ vowels stretch the poem's sound, evoking the image of joints being stretched and suggesting the metrical "even[ness]" that the author aspires/aspired to in her art.