What Leonardo da Vinci invention used a continuous bow to power a keyboard instrument?

Leonardo da Vinci’s viola organista used a continuous bowing mechanism to power a keyboard instrument.

Unlike a conventional piano, in which hammers strike strings, the viola organista was designed to produce sound by rubbing strings against a moving bow. A keyboard would control which strings touched the bow, allowing the player to select pitches while the mechanism supplied continuous friction.

Leonardo drew several related versions, and the surviving designs show belts, wheels, strings, and a keyboard working together. Because the sketches are incomplete in places, modern reconstructions differ in their mechanical solutions. Nevertheless, the central idea—keyboard selection combined with bowed-string sound—is clear.

The instrument is sometimes described as an early piano, but that is not technically correct. It belongs more naturally to the family of experimental bowed keyboard instruments. It also differs from a barrel organ, which uses a rotating cylinder to control pipes or other sound-producing mechanisms.