Return to Hamburg
In 1902 the family returned to Hamburg, and Warburg presented the findings of his Florentine research in a series of lectures, but at first did not take on a professorship or any other academic position. He rejected a call to a professorship at the University of Halle in 1912. He became a member of the board of the Völkerkundemuseum, with his brother Max sponsored the foundation of the "Hamburger wissenschatflichen Stiftung" (1907) and the foundation of a university in Hamburg, which succeeded in 1919, and at which he took up a professorship. At this period signs of a mental illness were present which affected his activities as a researcher and teacher.
He suffered from manic depression and symptoms of schizophrenia,[3] and was hospitalized in Ludwig Binswanger's neurological clinic in Kreuzlingen, Switzerland in 1921. There he was visited by Emil Kraepelin who did not confirm the diagnosis of schizophrenia and suggested Warburg was in a mixed manic-depressive state, a diagnosis with a more positive prognosis. Indeed, his mental conditions improved also thanks to the support of the philosopher Ernst Cassirer, who visited him in the clinic: “Warburg was highly relieved that Cassirer fully understood his plans to restart his research, that Cassirer highlighted the importance of Warburg’s ongoing scientific efforts, and felt he could contribute substantively to the art history discourse” [4] After his release from Binswanger's clinic in 1924, Warburg held occasional lectures and seminars between 1925 and 1929, which took place in a private circle or in his library.[5]
Warburg died in Hamburg of a heart attack on 26 October 1929.