Model of a Ventilator, anonymous, 1800 - 1850 demonstration model Model of a fan, working as a double bladder ball. In the large rectangular compartment, a shelf, which is mounted with hinges at half height against the short front, is moved with a lever up and down; The two halves in which the compartment are distributed through the shelf are thereby reduced and enlarged in turns. Air is let in by two square valves on the front, consisting of simple flaps with chamois leather, one upstairs and one below the hinges of the plank. By similar valves, the air is drained to a small compartment, where the air flow is led to a single output. Netherlands wood (plant material). brass (alloy). chamois (animal material)