Beyond Perrault's experiments: Repeatability, didactics and complexity

Abstract. The studies conducted in the second half of the Sixteenth Century were crucial both for the birth of the modern hydrological science and for the modern epistemology. Thanks to quantitative observations and to the new experiment–based scientific approach, the Sun was about to be fully recognized as the engine of the hydrological cycle, instead of an endogenous engine within the Earth, originally conjectured by Aristotle to explain the water supply of great rivers. In this context of great vitality and rapid cultural changes, two works were published on the origin of springs. In 1663 Gaspar Schott published the Anatomia physico–hydrostatica fontium ac fluminum (Physical–hydrostatic anatomy of springs and rivers), deeply rooted in the Aristotelian epistemology and based on the ancient humanistic and dialectical method. In this book, Schott cited some observations recently made about the capability of the water to rise within a soil column. Pierre Perrault referred to these observations as a starting point to design the experiments reported in his classical opus De l'origine des fontaines (On the origin of springs), published in 1674. With this approach Perrault places himself in the perspective of a deeply renewed epistemology: only a decade passed between the publication of Schott's opus and Perrault's one, but their perspective is radically different. At the same time, the questions posed on the hydrological cycle and on the soil hydrology, which are hardly reproducible by means of a controlled laboratory model, severely tested the modern scientific approach at its beginning. Perrault seems to be aware of such difficulties and, after discussing the results of the experiments, he moves the point of view from the scale of the laboratory model, to that of the catchment. This choice makes him a progenitor of the contemporary epistemology of complexity, which is framed both on laboratory analysis and on cases study. Thus even if Perrault's conclusions went in the direction of the ancient opinion, his work is not only seminal for hydrology, but also it helps to enlighten some intricate features of scientific revolution. Aiming at contributing to understand the importance of Perrault's opus, we will discuss his epistemological relevance through the lens of the repeatability of the experiments, of the intriguing didactic aspects which, starting from his experiments, arise for modern teaching of hydrology, and of his attitude to face the complexity of the hydrological processes.