The most noticeable aspect of Hillman's "Air for Mercury" is its structure. Hillman divides the poem up into four separate sections, which are labeled with simple numbers, one through four. This construction is deliberate on the poet's part and works to reinforce the underlying subject of the poem, the passage of time. The number four is a potent number in poetry, especially in poems that discuss time passing, because it evokes images of the four seasons passing in nature—a powerful theme that many authors employ in their literature. Indeed, as the poem progresses, Hillman gives little clues that each section may be intended to stand for a season. Sometimes these clues are blatant, such as in the second stanza of the second section, when she notes that "A season stopped by without your / noticing." In other sections, the link to seasons is more subtle, such as in...