How does Walt Whitman use imagery in Leaves of Grass?

In his poem, To a Locomotive in Winter, Whitman pays tribute to the lonely locomotive as it traverses its route through the snow. The imagery of a train plowing through the snow despite the cold and likely treacherous conditions creates a sense of longing in one who dreams of travel. Whitman calls the train's smoke "vaporpennants tinged with delicate purple," perfectly describing the trail of purplish colored smoke from the burning fuel, which is further enhanced by the white snow.