This economical single-sentence poem manages to propose various images for the locomotive. Some of them are natural, playful, and benign, while others are threatening or overwhelming. Between these two very different representations arises an ambiguity that is one of the themes of the poem.
In one sense, this ambiguity is a question of perspective. Seen from afar, perhaps, the train is a small, toylike thing, but at close range, it is gigantic. To step around piles of mountains is to pass beyond boundaries, which is in a sense to dislocate the horizon. To peer in windows is to intrude past other kinds of boundaries, to cause private life to become public, which is to violate the border between interior and exterior realms. A star is a thing which looks tiny but which science states is in fact huge almost beyond comprehension, so that comparing the locomotive to a star is to make a thing that appeared small and yet became huge seem infinitely small again. The poem, by playing with perspective, reveals the ambiguity that is intrinsic to the seen world.
In another sense, the ambiguity is one of attitude. The beast described does much consuming—it laps, licks, feeds, and pares rocks like vegetables. “Prodigious” is only one step away from prodigality, or excessive consumption. In addition, at the end of its breathless ride, like a horse, it arrives at the stable door, inside which it will presumably be fed. Meanwhile, it is “supercilious,” or haughty, and “complain[s]” throughout its journey. The impression created by this series of images is that of a demanding, arrogant taskmaster.
Yet, ironically, the locomotive was invented to serve humanity, not to be served by humanity. So the poem, without explicitly saying so, questions the relationship between humankind and machine. This representation of the railroad as something of potential runaway power is strengthened by the references to the Boagernes, the star, and omnipotence. These images cast the locomotive in the role of a god. It resembles the disciples of Christ; its coincidence with a star associates it with the arrival of a messiah; its all-powerfulness is like God’s. Nevertheless, the train is a thing made by humans, not by God, as the many natural objects which represent it are. The problems of perspective which the poem raises call into question humankind’s ability to see accurately at all and thus to know enough to undertake such creations.
The poem exaggerates this uncertainty by expressing itself in metaphors—images which are understood to portray a subject not explicitly but by suggestion. At the same time that the poem questions the wisdom of such creations as locomotives, however, it is itself a creation. Therefore, the subtle monstrosity of the poem—its shifting, protean metaphors—comes to mirror the possible monstrosity of its subject, and the presumption of divinity on the part of the inventors of the railroad is the same presumption claimed by the poet.