This instrument consists of a glass tube which is closed from the above and results at its other end in the shape of a lamp. At this end of the tube there is a tank so that it can be adapted to a pump. We adapt the tube’s tap to the pump and remove the air from the tube. Then, we close the tank, we immerse the bottom of the tube into a basin of water and finlly, we open the tank. We are able to observe that the water of the basin stars entering forcibly into the tube due to the external atmospheric pressure and then getting slowly until it balances to a height h above the stop of the free surface of the tube’s water.