For all of Robert Louis Stevenson's achievements in fiction, most famously Treasure Island and Strange Case of Dr. Jekyll and Mr. Hyde, many of his contemporaries thought of him primarily as an essayist. His essays, known for their intellectual substance, emotional force, and stylistic vitality, were widely considered the best of their time. Despite the importance of Stevenson's nonfiction, his personal essays-80 in total-have never been printed...