Echo Imagery

Echoes are big in this poem. Really, if this poem is about any one thing in particular, it's about hearing the echoes of a bugle horn in a mountain valley. But as the speaker listens to those echoes, he starts to think about other kinds of echoes, as well. So, echoes aren't just cool to listen to; they're the jumping off point for all sorts of philosophical contemplation.

• Line 5: This is the first mention of the bugle, and the speaker uses apostrophe when he addresses the bugle directly, as though the bugle were actually a human who could answer. Why would he address the bugle, instead of the person who was playing it? (What? Don't you have long chats with musical instruments?) Maybe the speaker doesn't want to acknowledge that there's someone else in the valley. Or maybe he likes that he can't see the person who's playing the bugle, since it makes the bugle seem enchanted and magical.
• Line 6: The speaker again uses apostrophe to address the bugle, and then uses anaphora, or poetic repetition, when he repeats the word "blow" and says that the echoes are "dying, dying, dying." One effect of this repetition is to imitate the "echoes" that he's describing. The speaker also personifies the echoes when he says that they are "dying," since an echo can't literally "die." Only something that is actually alive can die. Maybe this is how the speaker starts thinking about his own death, and the kinds of "echoes" he'll leave behind him when he himself dies…
• Line 11: Again, the speaker uses both apostrophe when he addresses the bugle and anaphora when he repeats the same words and form. 
• Line 12: This line becomes a kind of refrain as it gets repeated at the end of each stanza—another kind of poetic "echo" to imitate the real, literal "echoes" that he's describing.
• Lines 13-14: Here, the speaker seems to be describing the ways that echoes fade away in the distance, but he personifies the echoes when he says that they "die" and "faint," since those are things that humans do. Again, these literal echoes seem to be inspiring the speaker to think about death. No wonder he gets all philosophical by the end of the poem!
• Line 15: Since echoes cannot literally "roll" anywhere, let alone "from soul to soul," this is a metaphor for how these echoes pass through all of us while we live. 
• Lines 18-19: Here's some more apostrophe as the speaker addresses the bugle directly for a final time. This is also the last repetition of the poem's refrain.