The history of the magic lantern provides a privileged case study with which to explore the histories of projection, demonstration, illusion and the occult, and their different intersections. I focus on the role of the magic lantern in the work of the Jesuit Athanasius Kircher and the French Cartesian Abbé de Vallemont. After explaining the various meanings of the seventeenth-century concept of illusio, I propose a new solution for the long-standing problem that Kircher added the ‘wrong’ illustrations to his description of the lantern. The complex interaction between text, image and performance was crucial in Kircher's work and these ‘wrong’ figures provide us with a key to interpreting his Ars Magna. I argue that Vallemont used the magic lantern in a similar rhetorical way in a crucial phase of his argument. The magic lantern should not be understood merely as an illustrative image or an item of demonstration apparatus; rather the instrument is employed as part of a performance which is not meant simply to be entertaining. Both authors used a special form of scientific demonstration, which I will term ‘analogical demonstration’, to bolster their world view. This account opens new ways to think about the relation between instruments and the occult.

Sol fons lucis universi, vas admirabile, opus Excelsi, divinitatis thalamus, risus coeli, decor, & pulchritudo mundiA. Kircher

For one of those Gnostics, the visible universe was an illusion or, more precisely, a sophism. Mirrors and fatherhood are abominable because they multiply it and extend it.J. L. Borges