Percy Bysshe Shelley's dramatic poem "Prometheus Unbound" includes the lines:
As in the soft and sweet eclipse,
When soul meets soul on lovers' lips,
High hearts are calm, and brightest eyes are dull.
These lines clearly refer to lovers kissing under cover of darkness. The way in which Shelley describes the kiss, however, is revealing, both in terms of the poem's theme, and of his personal philosophy. Kissing is not merely a sensual act, but a meeting of two souls, a profound spiritual experience. This takes place in darkness and in secret because the lovers are not free, even though their love is the purest emotion that can be imagined.
"Prometheus Unbound" is a poem about tyranny and the fall of a tyrant. In a move which would have been unthinkable to Aeschylus, who provided Shelley with his source material, the Romantic poet has the King of the Gods fall from power, because he is tyrannical and oppressive. Shelley thought much the same about a society which disapproved of his ideas about free love. He famously wrote in his "Defence of Poetry" that "poets are the unacknowledged legislators of the world" and hoped to show the world an example of the fall of a tyrant, which might inspire a revolution in human relations. When there was no more tyranny, Shelley believed, the souls of lovers would be able to meet without restraint.