ABSTRACT
The increasingly more advanced explanation which the subjects give of the phenomenon of communicating vessels has just shown us the importance of the formal transformations of inversion and reciprocity and of the I N R C group that they form among themselves, according to the possible combinations, for the establishment of the operational equilibrium schema. But the drawback of the experiment with communicating vessels is that the pressure intrinsic to the liquid is completely overlooked by our subjects. A detailed account of the explanation is not found until it is given in terms of acquired knowledge. In the apparatus dealt with in this chapter, two communicating vessels again appear, but one of them is provided with a piston which may be loaded with varying weights; thus, the pressure exerted on the liquid is directly proportional to the weights. (It is to be noted that the piston is propelled not by an external force but by its own weight.)
