The instrument, which is used to demonstrate that in communicating vessels a liquid rises to the same level in all of them, consists of a cylindrical glass recipient (diameter 14.5 cm, height 10 cm) with a brass lid on which are screwed, by means of brass rings, a central glass tube (diameter 2.2 cm, height 50 cm) which ends at the top with a glass vessel and five lateral glass tubes (diameter 1 cm, height 49.5 cm) with brass cocks.