On a snowy Sunday morning in February 1808, the poet William Wordsworth was walking along Fleet Street in London. He’d just been to visit his friend, Samuel Taylor Coleridge, in his lodgings on the Strand. Coleridge was at a low ebb: stuck in an unhappy marriage, weighed down by perennial financial difficulties, mentally blocked from writing, in poor health and addicted to opium. The visit had a lowering effect on Wordsworth’s own spirits. Walking along Fleet Street, eyes downcast, “ear sleeping”, feet moving automatically, he was absorbed in sombre thoughts.