Taking seriously the performances of mediumistic trance creativity, this chapter proposes that automatism brought back to life important questions about both the limits and possibilities of authorial agency. In 1896, a Geneva medium named Héléne Smith perceived in trance the words from an inhabitant of Mars, "michma michtmon mimini mimatchineg", that her audience dutifully transcribed. A more nuanced view of the psychological tradition, however, might suggest that Breton's automatic discourses entailed serious research into the modalities of unconscious creativity. The Magnetic Fields, written through automatic writing in six consecutive days, indeed became a turning point for the French surrealist movement, whose members increasingly resorted to writing techniques aimed at liberating inhibited forces of creativity. The text presented the trance communications of members of the group during the séances, whose regular sitters included Breton, Max Morise, Paul Éluard, Max Ernst, René Crevel, Benjamin Péret, and Robert Desnos.