XEE4139837 Gas pressure: the gases are heavy. Experience of the bladder of Aristotle (384-322 BC) on the gravity of the air. He inflates a bladder with air and finds that the bladder swells weigh more than an empty bladder. Anonymous illustration from 1925. Private collection. by Anonymous; Private Collection; (add.info.: Gas pressure: the gases are heavy. Experience of the bladder of Aristotle (384-322 BC) on the gravity of the air. He inflates a bladder with air and finds that the bladder swells weigh more than an empty bladder. Anonymous illustration from 1925. Private collection.); Stefano Bianchetti; out of copyright.