The drinking bird is made by blowing a glass tube somewhat in the shape of a bird and joining it to a bulb, as shown. The bird is filled with a liquid which has a high vapor pressure. The bird's head is covered with fuzz to give a large evaporation area. When the head is wet, evaporation causes cooling and condensation of the fluid inside the bulb at the head. The center of gravity shifts to the head end of the bird and tips it into the beaker of water where the fuzz again becomes wet. At the same time the balance is such that the condensed fluid can flow to the bottom bulb and shift the center of gravity back. The process continues as long as there is water in the beaker.
|A few wood blocks
|Beaker with water