Lull’s Ars Magna was a rotating-wheel device meant to convert Muslims by demonstration

Evidence

The prolific and diversely talented Lull is perhaps best known for his Ars Magna, a treatise that describes a kind of medieval hand-operated computer. It consisted of a revolving wheel with letters on it signifying abstract principles. The rotation of its circles could be made to demonstrate the existence of God and the truths of Christian dogma and Lull seems to have hoped that a Muslim would only have to see it in operation in order to become converted. — Robert Irwin, For Lust of Knowing, 94

Categorization

• SEED: A medieval hand-cranked proof-of-God machine is a vivid image — great hook for an essay on the dream of mechanical conversion.