 Nietzsche’s health did not measurably improve during the leave, and by 1879, he was forced to resign his professorship altogether. As a result, he was freed to write and to develop the style that suited him. He published a book almost every year thereafter. These works began with Daybreak (1881), which collected critical observations on morality and its underlying psychology, and there followed the mature works for which Nietzsche is best known: The Gay Science (1882, second expanded edition 1887), Thus Spoke Zarathustra (1883–5), Beyond Good and Evil (1886), On the Genealogy of Morality (1887), and in the last year of his productive life Twilight of the Idols (1888) and The Wagner Case (1888), along with The Antichrist and his intellectual biography, Ecce Homo, which were published only later. At the beginning of this period, Nietzsche enjoyed an intense but ultimately painful friendship with Rée and Lou Salomé, a brilliant young Russian student. The three initially planned to live together in a kind of intellectual commune, but Nietzsche and Rée both developed romantic interest in Salomé, and after Nietzsche unsuccessfully proposed marriage, Salomé and Rée departed for Berlin. Salomé later wrote an illuminating book about Nietzsche (Salomé [1894] 2001), which first proposed an influential periodization of his philosophical development.