It is a musical instrument with bellows, known as "Leonardo's Accordion". Despite some similarities with the traditional accordion, it is an instrument with a totally different timbre.
The accordion's sound, bright and vibrant, is produced by the sound of vibrating metal reeds. In the Continuous Organ, on the other hand, it is produced by the passage of air through the pipes - made of wood or, as Leonardo himself suggests, paperboard - which produce a warm, soft sound.
