Clearly, “free verse” can manage every tone from the pompously ceremonial to the apologetically informal. But this is not to imply that as a technique whose flowering is associated with American intellectual and emotional configurations in the mid-nineteenth century, free verse does not itself seem to generate certain specific themes, which such devices as unpredictable line-length and unadvertised rhythms seem to trigger. From the beginning of its development by Whitman, the subtle rhythmic patterns discernible in sequences of free-verse lines have been likened to sea-waves, it being widely assumed in Whitman’s time that the “natural” rather than the artificial and conventional is what governs the imperatives of art. To Whitman, the sea itself is a great free-verse poem, whose “lines” are “the liquid, billowy waves, ever rising and falling, perhaps wild with storm, always moving, always alike in their nature as rolling waves, but hardly any two exactly alike in size or measure.” In theme as well as theory, free verse has shown an affinity with the sea, inviting us to trace a thematic tradition from Whitman’s “Out of the Cradle Endlessly Rocking” all the way to A.R. Ammons’s “Corson’s Inlet,” with stops along the way at Lawrence’s “The Sea,” Robinson Jeffers’s “Night” and “November Surf,” and Marianne Moor’s “A Grave.” When we consider literary history it seems no accident that the nineteenth- and twentieth-century discovery of the sea as a useful emblem of infinity or freedom or wonder and the seashore as a venue of illumination is virtually coincident with the rise to popularity of free verse.
[From Poetic Meter & Poetic Form, by Paul Fussell]