The first big slide took place in a theatre in Paris in the 1790s after the Revolution. After waiting for a few minutes in total darkness with the eerie background music of a glass harmonica, the audience begins to see various shapes appear in the sky, which appear to be light and shadow patterns floating and gliding through the air. These ghosts are pale and lifelike, and can talk, shout, and cry. One of the ghosts is a bleeding nun, first coming closer and then gradually moving away. Later slides involve the ghosts of recently deceased public figures, who are said to have been summoned by the power of science. Because that's how these shows are marketed: it's an intersection between science and religion, faith and enlightenment. They're scary, but they're also hilarious.
