In November 1899, Viennese neurologist Sigmund Freud published a book called The Interpretation of Dreams. It was the beginning of a new science he called psychoanalysis, which would revolutionise our understanding of human psychology. Witness hears from Sigmund Freud himself in the only known recording of his voice - from a BBC interview in 1938.

(Photo: Austrian psychoanalyst Sigmund Freud c.1920. Credit: Hulton Archive/Getty Images)