Tennyson uses several figures of speech or poetic devices in this poem. One is apostrophe. Apostrophe, often introduced with "O!," is the technique of a poem directly addressing either an inanimate object or a person who is absent. In this poem, the narrator speaks to an absent beloved when he writes, "O hark, O hear!" and later "O love."
Tennyson also uses alliteration, which is beginning words that lie in close proximity to one another with the same vowel to create a sense of rhythm. He does this with the line "Blow, bugle, blow."
Tennyson employs repetition, which heightens emotional impact, repeated "Blow, bugle, blow" more than once, and repeating "dying, dying, dying."
The poem uses rhyme: the second and fourth line of each stanza rhyme, as does each stanza's final couplet. This, along with alliteration, lends a sense of rhythm to the verse
Imagery, a literary device that paints a picture, shows up in "purple glens": we can visualize these.