When far away an interrupted cry Came over houses from another street, But not to call me back or say good-by (8-10)
We have another a chance to break the isolation – but, again, it fails. This voice is isolated and interrupted itself, traveling over houses to reach our speaker. Yet it's not calling for him, revealing our false hope that maybe someone cared about this poor guy.
And further still at an unearthly height, One luminary clock against the sky (11-12)
We already know that the narrator has walked past the city lights, but now we see something that is as far away and isolated as possible – the moon. These lines take the poem from a lonely and isolated night on earth to the loneliness and isolation of the sky. The moon is alone in the sky without even any stars to keep it company, at least not as we know from this poem.