Which figure of speech is used in this text?
The inmates of my cottage, all at rest,
Have left me to that solitude, which suits
Abstruser musings. . .
—Samuel Taylor Coleridge, "Frost at Midnight"

 - apostrophe
 - assonance
The text uses assonance, the repetition of a vowel sound in a series of nearby words.
The words solitude, suits, abstruser, and musings share a vowel sound.