(Sunstein, 118). See also The Year Without a Summer. Sitting around a log fire at Byron's villa, the company amused themselves with German ghost stories, which prompted Byron to propose that they "each write a ghost story". Unable to think of a story, young Mary Godwin became anxious: "Have you thought of a story? I was asked each morning, and each morning I was forced to reply with a mortifying negative." During one mid-June evening, the discussions turned to the nature of the principle of life. "Perhaps a corpse would be re-animated", Mary noted; "galvanism had given token of such things". It was after midnight before they retired, and unable to sleep, she became possessed by her imagination as she beheld the grim terrors of her "waking dream", her ghost story: She began writing what she assumed would be a short story. With Percy Shelley's encouragement, she expanded this tale into her first novel, Frankenstein; or, The Modern Prometheus, published in 1818. She later described that summer in Switzerland as the moment "when I first stepped out from childhood into life". The story of the writing of Frankenstein has been fictionalised several times and formed the basis for a number of films. In September 2011, the astronomer Donald Olson, after a visit to the Lake Geneva villa the previous year, and inspecting data about the motion of the moon and stars, concluded that her waking dream took place "between 2am and 3am" 16 June 1816, several days after the initial idea by Lord Byron that they each write a ghost story. Authorship of Frankenstein While her husband Percy encouraged her writing, the extent of Percy's contribution to the novel is unknown and has been argued over by readers and critics. Mary Shelley wrote, "I certainly did not owe the suggestion of one incident, nor scarcely of one train of feeling, to my husband, and yet but for his incitement, it would never have taken the form in which it was presented to the world." She wrote that the preface to the first edition was Percy's work "as far as I can recollect." There are differences in the 1818, 1823 and 1831 editions, which have been attributed to Percy's editing. James Rieger concluded Percy's "assistance at every point in the book's manufacture was so extensive that one hardly knows whether to regard him as editor or minor collaborator", while Anne K.