The customary term for such a faculty in literature of the Romantic period is imagination.
Yet, the connotations of Walton's diction do not aspire to such a level of import,
a "day dream" implying something less substantial than a reverie, which itself signifies
a mental state much less imposing than a vision. This implicit deflation of the power
or value of the imagination will become a thematic undertone in the novel.