Final answer:
Sir Philip Sidney uses a metaphor in his sonnet sequence Astrophil and Stella, where he poetically compares Stella's dark eyes to Nature's chief work with inherently bright beams.
Step-by-step explanation:
In the lines from Sir Philip Sidney's sonnet sequence Astrophil and Stella, the literary device used is a metaphor. Sidney describes Stella's eyes as though they are a piece of Nature's work, attributing to them a bright beam-like quality despite their black color. This language is metaphoric as it compares Stella's eyes to a creation of Nature and attributes to them characteristics belonging to a celestial body.