Let us remember that metaphors are a form of figurative language in which one object or action is compared to something else but without the use of the world "like" or "as," which would be a simile. Often these metaphors are implied, so rather than directly stating that one thing is something else, the comparison is not directly stated. Consider the following example:
Write, for example, 'The night is starry
and the stars are blue and shiver in the distance.'
Stars obviously do not "shiver in the distance," but the speaker here is comparing the stars to people who are so cold they have turned blue, and thus are shivering.
Again, another implied metaphor that is used in this poem is the following:
The night wind revolves in the sky and sings.
The wind does not literally "sing," but Neruda here is comparing the sound of the wind flying around in the night sky to somebody singing, and we can imagine this singing to be mournful as it contributes to and develops the sad and depressing mood of the poem.