ABSTRACT
Three stages may be distinguished in the explanations of the displacement of the water-level. During a first stage, the water is supposed to rise because the pebble is heavy. During a second stage, the prediction is correct: the child knows that the submerged bodies will make the water rise in proportion to their bulk. Finally, during a third stage, the correct explanation is found. To children who regard weight as always, or nearly always, proportional to volume, heavy objects are sure to be those that raise the level of the water. Thus the pebble raises the level of the water because it lies heavily at the bottom, and the wood because it lies heavily on the surface. According to the older ones, weight accounts only for the immersion of the body, and the rise of the water-level is due to the displacement of volume.
