The next group of poems is unique in Whitman's work. These poems present a mode of seeing unarguably associated with the discovery and development of photography. Poems such as "Cavalry Crossing a Ford", "Bivouac on a Mountain Side", "An Army Corps on the March", and "By the Bivouac's Fitful Flame" all vividly describe an army that is on the move during a hard day's march, at rest as the daytime fades away, the sensation of marching into combat, and the sleepless night of a soldier sitting at a fire's side, respectively. It is with this vigorous imagery that Whitman describes the evolution of the participants in this war. For example, "By the Bivouac's Fitful Flame" relentlessly describes the hollow feeling a soldier begins experience as his naïve enthusiasm for war slips away and he must now come to grips with the terror and suffering of conflict. The poet's sense of the ennobling struggle abates and now he presented with a challenge to prove his strength in the face of such terror. Much the same way that the Union must demonstrate its strength in the face of this conflict it has feared for over a decade. Whitman's imagery is interesting in how it shifts between poems. These poems have easy-rhyming rhythms that strip away his fondness of bombastic complexity and simply reports what is there (almost in the same way as a journalist). Conversely, poems in other sections have no such simple flow, instead using free verse which forces the reader to discover this higher meaning before they can even truly enjoy the poem.