Ventilating a mine. Hollow drum with air holes, B, at opposite sides, mounted on an axle, C, to which are fixed fans rotating inside the drum. Axle turned by water wheel through a spur gear and lantern. When axle turned, the fans rotating inside the drum would suck air in one hole and out of the opposite one, setting up a current of air. From 'De re metallica', by Agricola, pseudonym of Georg Bauer (Basle, 1556). Woodcut. Photo via Newscom