Mesmer's Paris practice was a theatre of therapy, and its properties explain both the crowds and the commission. Patients too numerous for individual treatment gathered around the baquet, an oaken tub filled with bottles of magnetised water bedded in glass and iron filings; jointed iron rods emerged from its lid, which patients applied to the afflicted part, and a cord looped the company together so the magnetic fluid could circulate. The room was mirrored to reflect the fluid, and Mesmer passed among the patients with his hands and an iron wand, while music played, often on the glass armonica, the instrument of rubbed glass bowls whose unearthly sustained tones he had mastered in Vienna and considered a conductor of magnetism.
Treatment aimed at the crisis: convulsions, weeping, laughter or collapse, understood as the obstruction breaking up, with a padded crisis room standing ready. It was in exactly this setting that his pupil the Marquis de Puysegur found, in 1784, a patient who did not convulse but fell instead into a lucid waking sleep, answered questions with unusual insight, and remembered nothing afterward: artificial somnambulism, the phenomenon that would outlive the fluid entirely and descend, through Braid's renaming, to hypnosis. The apparatus was abandoned; the reliable strangeness it produced in human beings proved to be the durable discovery, which is not the vindication Mesmer wanted.