Hypnotism is the practice of hypnotizing people — the skill, the method, the whole business of guiding someone into that sleep-like focused state. In the 1800s this was a fashionable word for what looked like a new science; today it can sound a little old or theatrical next to hypnosis and hypnotherapy. People still use it for stage craft (“a show of hypnotism”) and for the general idea of the technique. Though actually, everyday talk mixes hypnotism, hypnosis, and hypnotherapy. More carefully: hypnotism is the doing; hypnosis is the state you enter; hypnotherapy is using that state to treat a problem. You can talk about the history of hypnotism without talking about a clinic at all.