See in text (Text of the Poem)
Shelley sticks to a strict iambic pentameter for most of the poem, but turns to trimeter and tetrameter for several lines, including the first and third of this stanza. On one level, the shortened lines add rhythmic variety. On another level, the conspicuous space at the end of the shortened line encourages the reader to pause and reflect. After a line such as “Wandering companionless,” that pause evokes the moon’s solitude.